Experimental and Numerical Evaluation of Direct Tension Test for Cylindrical Concrete Specimens
Directory of Open Access Journals (Sweden)
Jung J. Kim
2014-01-01
Full Text Available Concrete cracking strength can be defined as the tensile strength of concrete subjected to pure tension stress. However, as it is difficult to apply direct tension load to concrete specimens, concrete cracking is usually quantified by the modulus of rupture for flexural members. In this study, a new direct tension test setup for cylindrical specimens (101.6 mm in diameter and 203.2 mm in height similar to those used in compression test is developed. Double steel plates are used to obtain uniform stress distributions. Finite element analysis for the proposed test setup is conducted. The uniformity of the stress distribution along the cylindrical specimen is examined and compared with rectangular cross section. Fuzzy image pattern recognition method is used to assess stress uniformity along the specimen. Moreover, the probability of cracking at different locations along the specimen is evaluated using probabilistic finite element analysis. The experimental and numerical results of the cracking location showed that gravity effect on fresh concrete during setting time might affect the distribution of concrete cracking strength along the height of the structural elements.
Bune, Andris V.; Gillies, Donald C.; Lehoczky, Sandor L.
1996-01-01
A numerical model of heat transfer using combined conduction, radiation and convection in AADSF was used to evaluate temperature gradients in the vicinity of the crystal/melt interface for variety of hot and cold zone set point temperatures specifically for the growth of mercury cadmium telluride (MCT). Reverse usage of hot and cold zones was simulated to aid the choice of proper orientation of crystal/melt interface regarding residual acceleration vector without actual change of furnace location on board the orbiter. It appears that an additional booster heater will be extremely helpful to ensure desired temperature gradient when hot and cold zones are reversed. Further efforts are required to investigate advantages/disadvantages of symmetrical furnace design (i.e. with similar length of hot and cold zones).
DEFF Research Database (Denmark)
Ilic, C; Chadwick, A; Helm-Petersen, Jacob
2000-01-01
Recent studies of advanced directional analysis techniques have mainly centred on incident wave fields. In the study of coastal structures, however, partially reflective wave fields are commonly present. In the near structure field, phase locked methods can be successfully applied. In the far fie...
Direct numerical simulation of human phonation
Saurabh, Shakti; Bodony, Daniel
2016-11-01
A direct numerical simulation study of the generation and propagation of the human voice in a full-body domain is conducted. A fully compressible fluid flow model, anatomically representative vocal tract geometry, finite deformation model for vocal fold (VF) motion and a fully coupled fluid-structure interaction model are employed. The dynamics of the multi-layered VF tissue with varying stiffness are solved using a quadratic finite element code. The fluid-solid domains are coupled through a boundary-fitted interface and utilize a Poisson equation-based mesh deformation method. A new inflow boundary condition, based upon a quasi-1D formulation with constant sub-glottal volume velocity, linked to the VF movement, has been adopted. Simulations for both child and adult phonation were performed. Acoustic characteristics obtained from these simulation are consistent with expected values. A sensitivity analysis based on VF stiffness variation is undertaken and sound pressure level/fundamental frequency trends are established. An evaluation of the data against the commonly-used quasi-1D equations suggest that the latter are not sufficient to model phonation. Phonation threshold pressures are measured for several VF stiffness variations and comparisons to clinical data are carried out. Supported by the National Science Foundation (CAREER Award Number 1150439).
Direct numerical simulation of compressible isotropic turbulence
Institute of Scientific and Technical Information of China (English)
LI; Xinliang(李新亮); FU; Dexun(傅德薰); MAYanwen(马延文)
2002-01-01
Direct numerical simulation (DNS) of decaying compressible isotropic turbulence at tur-bulence Mach numbers of Mt = 0.2-0.7 and Taylor Reynolds numbers of 72 and 153 is per-formed by using the 7th order upwind-biased difference and 8th order center difference schemes.Results show that proper upwind-biased difference schemes can release the limit of "start-up"problem to Mach numbers.Compressibility effects on the statistics of turbulent flow as well as the mechanics of shockletsin compressible turbulence are also studied, and the conclusion is drawn that high Mach numberleads to more dissipation. Scaling laws in compressible turbulence are also analyzed. Evidence isobtained that scaling laws and extended self similarity (ESS) hold in the compressible turbulentflow in spite of the presence of shocklets, and compressibility has little effect on scaling exponents.
Direct numerical simulation of axisymmetric turbulence
Qu, Bo; Bos, Wouter J. T.; Naso, Aurore
2017-09-01
The dynamics of decaying, strictly axisymmetric, incompressible turbulence is investigated using direct numerical simulations. It is found that the angular momentum is a robust invariant of the system. It is further shown that long-lived coherent structures are generated by the flow. These structures can be associated with stationary solutions of the Euler equations. The structures obey relations in agreement with predictions from selective decay principles, compatible with the decay laws of the system. Two different types of decay scenarios are highlighted. The first case results in a quasi-two-dimensional flow with a dynamical behavior in the poloidal plane similar to freely decaying two-dimensional turbulence. In a second regime, the long-time dynamics is dominated by a single three-dimensional mode.
Direct numerical simulation of turbulent reacting flows
Energy Technology Data Exchange (ETDEWEB)
Chen, J.H. [Sandia National Laboratories, Livermore, CA (United States)
1993-12-01
The development of turbulent combustion models that reflect some of the most important characteristics of turbulent reacting flows requires knowledge about the behavior of key quantities in well defined combustion regimes. In turbulent flames, the coupling between the turbulence and the chemistry is so strong in certain regimes that is is very difficult to isolate the role played by one individual phenomenon. Direct numerical simulation (DNS) is an extremely useful tool to study in detail the turbulence-chemistry interactions in certain well defined regimes. Globally, non-premixed flames are controlled by two limiting cases: the fast chemistry limit, where the turbulent fluctuations. In between these two limits, finite-rate chemical effects are important and the turbulence interacts strongly with the chemical processes. This regime is important because industrial burners operate in regimes in which, locally the flame undergoes extinction, or is at least in some nonequilibrium condition. Furthermore, these nonequilibrium conditions strongly influence the production of pollutants. To quantify the finite-rate chemistry effect, direct numerical simulations are performed to study the interaction between an initially laminar non-premixed flame and a three-dimensional field of homogeneous isotropic decaying turbulence. Emphasis is placed on the dynamics of extinction and on transient effects on the fine scale mixing process. Differential molecular diffusion among species is also examined with this approach, both for nonreacting and reacting situations. To address the problem of large-scale mixing and to examine the effects of mean shear, efforts are underway to perform large eddy simulations of round three-dimensional jets.
Direct Numerical Simulation of Cell Printing
Qiao, Rui; He, Ping
2010-11-01
Structural cell printing, i.e., printing three dimensional (3D) structures of cells held in a tissue matrix, is gaining significant attention in the biomedical community. The key idea is to use desktop printer or similar devices to print cells into 3D patterns with a resolution comparable to the size of mammalian cells, similar to that in living organs. Achieving such a resolution in vitro can lead to breakthroughs in areas such as organ transplantation and understanding of cell-cell interactions in truly 3D spaces. Although the feasibility of cell printing has been demonstrated in the recent years, the printing resolution and cell viability remain to be improved. In this work, we investigate one of the unit operations in cell printing, namely, the impact of a cell-laden droplet into a pool of highly viscous liquids using direct numerical simulations. The dynamics of droplet impact (e.g., crater formation and droplet spreading and penetration) and the evolution of cell shape and internal stress are quantified in details.
Energy Technology Data Exchange (ETDEWEB)
Boughanem, H.
1998-03-24
The assumption of gradient transport for the mean reaction progress variable has a limited domain of validity in premixed turbulent combustion. The existence of two turbulent transport regimes, gradient and counter-gradient, is demonstrated in the present work using Direct Numerical Simulations (DNS) of plane flame configurations. The DNS data base describes the influence of the heat release factor, of the turbulence-to-flame velocity ratio, and of an external pressure gradient. The simulations reveal a strong correlation between the regime of turbulent transport and the turbulent flame speed and turbulent flame thickness. These effects re not well described by current turbulent combustion models. A conditional approach `fresh gases / burnt gases` is proposed to overcome these difficulties. Furthermore, he development of flame instabilities in turbulent configurations is also observed in the simulations. A criterion is derived that determines the domain of occurrence of these instabilities (Darrieus- Landau instabilities, Rayleigh- Taylor instabilities, thermo-diffusive instabilities). This criterion suggests that the domain of occurrence of flame instabilities is not limited to small Reynolds numbers. (author) 98 refs.
Efficient Numerical Evaluation of Feynman Integral
Li, Zhao; Yan, Qi-Shu; Zhao, Xiaoran
2016-01-01
Feynman loop integral is the key ingredient of high order radiation effect, which is responsible for reliable and accurate theoretical prediction. We improve the efficiency of numerical integration in sector decomposition by implementing quasi-Monte Carlo method associated with the technique of CUDA/GPU. For demonstration we present the results of several Feynman integrals up to two loops in both Euclidean and physical kinematic regions in comparison with those obtained from FIESTA3. It is shown that both planar and non-planar two-loop master integrals in physical kinematic region can be evaluated in less than half minute with $\\mathcal{O}(10^{-3})$ accuracy, which makes the direct numerical approach viable for the precise investigation on the high order effect in multi-loop processes, e.g. the next-to-leading order QCD effect in Higgs pair production via gluon fusion with finite top quark mass.
Direct numerical simulation of dynamo transition for nonhelical MHD
Energy Technology Data Exchange (ETDEWEB)
Nath, Dinesh; Verma, Mahendra K [Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016 (India); Lessinnes, Thomas; Carati, Daniele [Physique Statistique et Plasmas, Universite Libre de Bruxellers, B-1050 Bruxelles (Belgium); Sarris, Ioannis [Department of Mechanical and Industrial Engineering, University of Thessaly, Volos (Greece)
2010-02-01
Pseudospectral Direct Numerical Simulation (DNS) has been performed to simulate dynamo transition for nonhelical magnetohydrodynamics turbulence. The numerical results are compared with a recent low-dimensional model [Verma et al. [13
Numerical Analysis of Dynamic Direct Tension and Direct Compression Tests
1993-01-01
material model employed in the nonlinear analysis is a hypoelastic model based on a uniaxial stress-strain relation (Figure 18) that is generalized to...rates. Both an elastic and inelastic concrete material model were employed in all numerical analyses. The modes of failure predicted by the numerical... models ; (2) augmenting the system by adding other typical scenarios, with the ultimate goal of expanding it into a general task-oriented system/shell; and
Direct Numerical Simulation of Automobile Cavity Tones
Kurbatskii, Konstantin; Tam, Christopher K. W.
2000-01-01
The Navier Stokes equation is solved computationally by the Dispersion-Relation-Preserving (DRP) scheme for the flow and acoustic fields associated with a laminar boundary layer flow over an automobile door cavity. In this work, the flow Reynolds number is restricted to R(sub delta*) < 3400; the range of Reynolds number for which laminar flow may be maintained. This investigation focuses on two aspects of the problem, namely, the effect of boundary layer thickness on the cavity tone frequency and intensity and the effect of the size of the computation domain on the accuracy of the numerical simulation. It is found that the tone frequency decreases with an increase in boundary layer thickness. When the boundary layer is thicker than a certain critical value, depending on the flow speed, no tone is emitted by the cavity. Computationally, solutions of aeroacoustics problems are known to be sensitive to the size of the computation domain. Numerical experiments indicate that the use of a small domain could result in normal mode type acoustic oscillations in the entire computation domain leading to an increase in tone frequency and intensity. When the computation domain is expanded so that the boundaries are at least one wavelength away from the noise source, the computed tone frequency and intensity are found to be computation domain size independent.
Efficient numerical evaluation of Feynman integrals
Li, Zhao; Wang, Jian; Yan, Qi-Shu; Zhao, Xiaoran
2016-03-01
Feynman loop integrals are a key ingredient for the calculation of higher order radiation effects, and are responsible for reliable and accurate theoretical prediction. We improve the efficiency of numerical integration in sector decomposition by implementing a quasi-Monte Carlo method associated with the CUDA/GPU technique. For demonstration we present the results of several Feynman integrals up to two loops in both Euclidean and physical kinematic regions in comparison with those obtained from FIESTA3. It is shown that both planar and non-planar two-loop master integrals in the physical kinematic region can be evaluated in less than half a minute with accuracy, which makes the direct numerical approach viable for precise investigation of higher order effects in multi-loop processes, e.g. the next-to-leading order QCD effect in Higgs pair production via gluon fusion with a finite top quark mass. Supported by the Natural Science Foundation of China (11305179 11475180), Youth Innovation Promotion Association, CAS, IHEP Innovation (Y4545170Y2), State Key Lab for Electronics and Particle Detectors, Open Project Program of State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, China (Y4KF061CJ1), Cluster of Excellence Precision Physics, Fundamental Interactions and Structure of Matter (PRISMA-EXC 1098)
Evaluation of steel corrosion by numerical analysis
Kawahigashi, Tatsuo
2017-01-01
Recently, various non-destructive and numerical methods have been used and many cases of steel corrosion are examined. For example, methods of evaluating corrosion through various numerical methods and evaluating macrocell corrosion and micro-cell corrosion using measurements have been proposed. However, there are few reports on estimating of corrosion loss with distinguishing the macro-cell and micro-cell corrosion and with resembling an actuality phenomenon. In this study, for distinguishin...
Type-Directed Partial Evaluation
DEFF Research Database (Denmark)
Danvy, Olivier
1998-01-01
Type-directed partial evaluation uses a normalization function to achieve partial evaluation. These lecture notes review its background, foundations, practice, and applications. Of specific interest is the modular technique of offline and online type-directed partial evaluation in Standard ML...
Type-Directed Partial Evaluation
DEFF Research Database (Denmark)
Danvy, Olivier
1998-01-01
Type-directed partial evaluation uses a normalization function to achieve partial evaluation. These lecture notes review its background, foundations, practice, and applications. Of specific interest is the modular technique of offline and online type-directed partial evaluation in Standard ML of ...
Induction and direct resistance heating theory and numerical modeling
Lupi, Sergio; Aliferov, Aleksandr
2015-01-01
This book offers broad, detailed coverage of theoretical developments in induction and direct resistance heating and presents new material on the solution of problems in the application of such heating. The physical basis of induction and conduction heating processes is explained, and electromagnetic phenomena in direct resistance and induction heating of flat workpieces and cylindrical bodies are examined in depth. The calculation of electrical and energetic characteristics of induction and conduction heating systems is then thoroughly reviewed. The final two chapters consider analytical solutions and numerical modeling of problems in the application of induction and direct resistance heating, providing industrial engineers with the knowledge needed in order to use numerical tools in the modern design of installations. Other engineers, scientists, and technologists will find the book to be an invaluable reference that will assist in the efficient utilization of electrical energy.
Direct Numerical Simulation and Visualization of Subcooled Pool Boiling
Directory of Open Access Journals (Sweden)
Tomoaki Kunugi
2014-01-01
Full Text Available A direct numerical simulation of the boiling phenomena is one of the promising approaches in order to clarify their heat transfer characteristics and discuss the mechanism. During these decades, many DNS procedures have been developed according to the recent high performance computers and computational technologies. In this paper, the state of the art of direct numerical simulation of the pool boiling phenomena during mostly two decades is briefly summarized at first, and then the nonempirical boiling and condensation model proposed by the authors is introduced into the MARS (MultiInterface Advection and Reconstruction Solver developed by the authors. On the other hand, in order to clarify the boiling bubble behaviors under the subcooled conditions, the subcooled pool boiling experiments are also performed by using a high speed and high spatial resolution camera with a highly magnified telescope. Resulting from the numerical simulations of the subcooled pool boiling phenomena, the numerical results obtained by the MARS are validated by being compared to the experimental ones and the existing analytical solutions. The numerical results regarding the time evolution of the boiling bubble departure process under the subcooled conditions show a very good agreement with the experimental results. In conclusion, it can be said that the proposed nonempirical boiling and condensation model combined with the MARS has been validated.
Direct Numerical Simulation of a Shocked Helium Jet
Energy Technology Data Exchange (ETDEWEB)
Cloutman, L D
2002-02-01
We present direct numerical simulations of a shock tube experiment in which a cylindrical laminar jet of helium doped with biacetyl is injected into air and subjected to a weak shock wave. Computed species distributions in a planar cross section of the jet are compared to planar laser-induced fluorescence (PLIF) images produced by the experiment. The calculations are in excellent agreement with the experimental images. We find that differential diffusion of species is an important feature of this experiment.
Numerical Analysis of Lead-Bismuth-Water Direct Contact Boiling Heat Transfer
Yamada, Yumi; Takahashi, Minoru
Direct contact boiling heat transfer of sub-cooled water with lead-bismuth eutectic (Pb-Bi) was investigated for the evaluation of the performance of steam generation in direct contact of feed water with primary Pb-Bi coolant in upper plenum above the core in Pb-Bi-cooled direct contact boiling water fast reactor. An analytical two-fluid model was developed to estimate the heat transfer numerically. Numerical results were compared with experimental ones for verification of the model. The overall volumetric heat transfer coefficient was calculated from heat exchange rate in the chimney. It was confirmed that the calculated results agreed well with the experimental result.
Study of numerical errors in direct numerical simulation and large eddy simulation
Institute of Scientific and Technical Information of China (English)
YANG Xiao-long; FU Song
2008-01-01
By comparing the energy spectrum and total kinetic energy, the effects of numerical errors (which arise from aliasing and discretization errors), subgrid-scale (SGS) models, and their interactions on direct numerical simulation (DNS) and large eddy simulation (LES) are investigated. The decaying isotropic turbulence is chosen as the test case. To simulate complex geometries, both the spectral method and Pade compact difference schemes are studied. The truncated Navier-Stokes (TNS) equation model with Pade discrete filter is adopted as the SGS model. It is found that the discretization error plays a key role in DNS. Low order difference schemes may be unsuitable. However, for LES, it is found that the SGS model can represent the effect of small scales to large scales and dump the numerical errors. Therefore, reasonable results can also be obtained with a low order discretization scheme.
Norman, Michael L; So, Geoffrey C; Harkness, Robsert P
2013-01-01
We describe an extension of the {\\em Enzo} code to enable the direct numerical simulation of inhomogeneous reionization in large cosmological volumes. By direct we mean all dynamical, radiative, and chemical properties are solved self-consistently on the same mesh, as opposed to a postprocessing approach which coarse-grains the radiative transfer. We do, however, employ a simple subgrid model for star formation, which we calibrate to observations. The numerical method presented is a modification of an earlier method presented in Reynolds et al. Radiation transport is done in the grey flux-limited diffusion (FLD) approximation, which is solved by implicit time integration split off from the gas energy and ionization equations, which are solved separately. This results in a faster and more robust scheme for cosmological applications compared to the earlier method. The FLD equation is solved using the {\\em hypre} optimally scalable geometric multigrid solver from LLNL. By treating the ionizing radiation as a gri...
Direct numerical simulation of double-diffusive gravity currents
Penney, Jared; Stastna, Marek
2016-08-01
This paper presents three-dimensional direct numerical simulations of laboratory-scale double-diffusive gravity currents. Flow is governed by the incompressible Navier-Stokes equations under the Boussinesq approximation, with salinity and temperature coupled to the equations of motion using a nonlinear approximation to the UNESCO equation of state. The effects of vertical boundary conditions and current volume are examined, with focus on flow pattern development, current propagation speed, three-dimensionalization, dissipation, and stirring and mixing. It was observed that no-slip boundaries cause the gravity current head to take the standard lobe-and-cleft shape and encourage both a greater degree and an earlier onset of three-dimensionalization when compared to what occurs in the case of a free-slip boundary. Additionally, numerical simulations with no-slip boundary conditions experience greater viscous dissipation, stirring, and mixing when compared to similar configurations using free-slip conditions.
Direct numerical simulations of gas-liquid multiphase flows
Tryggvason, Grétar; Zaleski, Stéphane
2011-01-01
Accurately predicting the behaviour of multiphase flows is a problem of immense industrial and scientific interest. Modern computers can now study the dynamics in great detail and these simulations yield unprecedented insight. This book provides a comprehensive introduction to direct numerical simulations of multiphase flows for researchers and graduate students. After a brief overview of the context and history the authors review the governing equations. A particular emphasis is placed on the 'one-fluid' formulation where a single set of equations is used to describe the entire flow field and
On numerical evaluation of two-dimensional phase integrals
DEFF Research Database (Denmark)
Lessow, H.; Rusch, W.; Schjær-Jacobsen, Hans
1975-01-01
The relative advantages of several common numerical integration algorithms used in computing two-dimensional phase integrals are evaluated.......The relative advantages of several common numerical integration algorithms used in computing two-dimensional phase integrals are evaluated....
A fast direct numerical simulation method for characterising hydraulic roughness
Chung, Daniel; MacDonald, Michael; Hutchins, Nicholas; Ooi, Andrew
2015-01-01
We describe a fast direct numerical simulation (DNS) method that promises to directly characterise the hydraulic roughness of any given rough surface, from the hydraulically smooth to the fully rough regime. The method circumvents the unfavourable computational cost associated with simulating high-Reynolds-number flows by employing minimal-span channels (Jimenez & Moin 1991). Proof-of-concept simulations demonstrate that flows in minimal-span channels are sufficient for capturing the downward velocity shift, that is, the Hama roughness function, predicted by flows in full-span channels. We consider two sets of simulations, first with modelled roughness imposed by body forces, and second with explicit roughness described by roughness-conforming grids. Owing to the minimal cost, we are able to conduct DNSs with increasing roughness Reynolds numbers while maintaining a fixed blockage ratio, as is typical in full-scale applications. The present method promises a practical, fast and accurate tool for character...
Reckinger, Scott J.; Livescu, Daniel; Vasilyev, Oleg V.
2016-05-01
An investigation of compressible Rayleigh-Taylor instability (RTI) using Direct Numerical Simulations (DNS) requires efficient numerical methods, advanced boundary conditions, and consistent initialization in order to capture the wide range of scales and vortex dynamics present in the system, while reducing the computational impact associated with acoustic wave generation and the subsequent interaction with the flow. An advanced computational framework is presented that handles the challenges introduced by considering the compressive nature of RTI systems, which include sharp interfacial density gradients on strongly stratified background states, acoustic wave generation and removal at computational boundaries, and stratification dependent vorticity production. The foundation of the numerical methodology described here is the wavelet-based grid adaptivity of the Parallel Adaptive Wavelet Collocation Method (PAWCM) that maintains symmetry in single-mode RTI systems to extreme late-times. PAWCM is combined with a consistent initialization, which reduces the generation of acoustic disturbances, and effective boundary treatments, which prevent acoustic reflections. A dynamic time integration scheme that can handle highly nonlinear and potentially stiff systems, such as compressible RTI, completes the computational framework. The numerical methodology is used to simulate two-dimensional single-mode RTI to extreme late-times for a wide range of flow compressibility and variable density effects. The results show that flow compressibility acts to reduce the growth of RTI for low Atwood numbers, as predicted from linear stability analysis.
Direct Numerical Simulations of Statistically Stationary Turbulent Premixed Flames
Im, Hong G.
2016-07-15
Direct numerical simulations (DNS) of turbulent combustion have evolved tremendously in the past decades, thanks to the rapid advances in high performance computing technology. Today’s DNS is capable of incorporating detailed reaction mechanisms and transport properties of hydrocarbon fuels, with physical parameter ranges approaching laboratory scale flames, thereby allowing direct comparison and cross-validation against laser diagnostic measurements. While these developments have led to significantly improved understanding of fundamental turbulent flame characteristics, there are increasing demands to explore combustion regimes at higher levels of turbulent Reynolds (Re) and Karlovitz (Ka) numbers, with a practical interest in new combustion engines driving towards higher efficiencies and lower emissions. The article attempts to provide a brief overview of the state-of-the-art DNS of turbulent premixed flames at high Re/Ka conditions, with an emphasis on homogeneous and isotropic turbulent flow configurations. Some important qualitative findings from numerical studies are summarized, new analytical approaches to investigate intensely turbulent premixed flame dynamics are discussed, and topics for future research are suggested. © 2016 Taylor & Francis.
Directory of Open Access Journals (Sweden)
Manuel Ninaus
2017-08-01
Full Text Available There is accumulating evidence suggesting an association of numbers with physical space. However, the origin of such spatial-numerical associations (SNAs is still debated. In the present study we investigated the development of two SNAs in a cross-sectional study involving children, young and middle-aged adults as well as the elderly: (1 the SNARC (spatial-numerical association of response codes effect, reflecting a directional SNA; and (2 the numerical bisection bias in a line bisection task with numerical flankers. Results revealed a consistent SNARC effect in all age groups that continuously increased with age. In contrast, a numerical bisection bias was only observed for children and elderly participants, implying an U-shaped distribution of this bias across age groups. Additionally, individual SNARC effects and numerical bisection biases did not correlate significantly. We argue that the SNARC effect seems to be influenced by longer-lasting experiences of cultural constraints such as reading and writing direction and may thus reflect embodied representations. Contrarily, the numerical bisection bias may originate from insufficient inhibition of the semantic influence of irrelevant numerical flankers, which should be more pronounced in children and elderly people due to development and decline of cognitive control, respectively. As there is an ongoing debate on the origins of SNAs in general and the SNARC effect in particular, the present results are discussed in light of these differing accounts in an integrative approach. However, taken together, the present pattern of results suggests that different cognitive mechanisms underlie the SNARC effect and the numerical bisection bias.
Energy Technology Data Exchange (ETDEWEB)
RodrIguez-MartInez, R; Urriolagoitia-Calderon, G; Urriolagoitia-Sosa, G; Hernandez-Gomez, L H [Instituto Politecnico Nacional Seccion de Estudios de Posgrado e Investigacion (SEPI), Escuela Superior de IngenierIa Mecanica y Electrica (ESIME), Edificio 5. 2do Piso, Unidad Profesional Adolfo Lopez Mateos ' Zacatenco' Col. Lindavista, C.P. 07738, Mexico, D.F. (Mexico); Merchan-Cruz, E A; RodrIguez-Canizo, R G; Sandoval-Pineda, J M, E-mail: rrodriguezm@ipn.m, E-mail: urrio332@hotmail.co, E-mail: guiurri@hotmail.co, E-mail: luishector56@hotmail.co, E-mail: eamerchan@gmail.co, E-mail: ricname@hotmail.co, E-mail: jsandovalp@ipn.m [Instituto Politecnico Nacional Seccion de Estudios de Posgrado e Investigacion (SEPI), Escuela Superior de IngenierIa Mecanica y Electrica (ESIME). Unidad profesional, AZCAPOTZALCO, Av. de las Granjas No. 682, Col. Sta. Catarina Azcapotzalco, C.P. 02550, Mexico D.F. (Mexico)
2009-08-01
In this paper, the case of Single Edge Notch (SEN) specimens subject to opening/compressive loading was analyzed; The loads are applied in several ratios to evaluate the influence of the specimen geometry, and the Stress Intensity Factor (SIF) K{sub 1} values on the directional stability of crack propagation. The main purpose of this work is to evaluate the behaviour of the fracture propagation, when modifying the geometry of the SEN specimen and different relationships of load tension/compression are applied. Additionally, the precision of the numerical and experimental analysis is evaluated to determine its reliability when solving this type of problems. The specimens are subjected to biaxial opening/compression loading; both results (numerical and experimental) are compared in order to evaluate the condition of directional stability on crack propagation. Finally, an apparent transition point related to the length of specimens was identified, in which the behaviour of values of SIF changes for different loading ratios.
Direct numerical simulation of bluff-body-stabilized premixed flames
Arias, Paul G.
2014-01-10
To enable high fidelity simulation of combustion phenomena in realistic devices, an embedded boundary method is implemented into direct numerical simulations (DNS) of reacting flows. One of the additional numerical issues associated with reacting flows is the stable treatment of the embedded boundaries in the presence of multicomponent species and reactions. The implemented method is validated in two test con gurations: a pre-mixed hydrogen/air flame stabilized in a backward-facing step configuration, and reactive flows around a square prism. The former is of interest in practical gas turbine combustor applications in which the thermo-acoustic instabilities are a strong concern, and the latter serves as a good model problem to capture the vortex shedding behind a bluff body. In addition, a reacting flow behind the square prism serves as a model for the study of flame stabilization in a micro-channel combustor. The present study utilizes fluid-cell reconstruction methods in order to capture important flame-to-solid wall interactions that are important in confined multicomponent reacting flows. Results show that the DNS with embedded boundaries can be extended to more complex geometries without loss of accuracy and the high fidelity simulation data can be used to develop and validate turbulence and combustion models for the design of practical combustion devices.
Direct Numerical Simulation of Multiphase Flows with Unstable Interfaces
Schillaci, Eugenio; Lehmkuhl, Oriol; Antepara, Oscar; Oliva, Assensi
2016-09-01
This paper presents a numerical model that intends to simulate efficiently the surface instability that arise in multiphase flows, typically liquid-gas, both for laminar or turbulent regimes. The model is developed on the in-house computing platform TermoFluids, and operates the finite-volume, direct numerical simulation (DNS) of multiphase flows by means of a conservative level-set method for the interface-capturing. The mesh size is optimized by means of an adaptive mesh refinement (AMR) strategy, that allows the dynamic re-concentration of the mesh in the vicinity of the interfaces between fluids, in order to correctly represent the diverse structures (as ligaments and droplets) that may rise from unstable phenomena. In addition, special attention is given to the discretization of the various terms of the momentum equations, to ensure stability of the flow and correct representation of turbulent vortices. As shown, the method is capable of truthfully simulate the interface phenomena as the Kelvin-Helmholtz instability and the Plateau-Rayleigh instability, both in the case of 2-D and 3-D configurations. Therefore it is suitable for the simulation of complex phenomena such as simulation of air-blast atomization, with several important application in the field of automotive and aerospace engines. A prove is given by our preliminary study of the 3-D coaxial liquid-gas jet.
Direct numerical simulation of turbulent channel flow over porous walls
Rosti, Marco E; Cortelezzi, Luca
2014-01-01
We perform direct numerical simulations (DNS) of a turbulent channel flow over porous walls. In the fluid region the flow is governed by the incompressible Navier-Stokes equations, while in the porous layers the Volume-Averaged Navier-Stokes (VANS) equations are used, which are obtained by volume-averaging the microscopic flow field over a small volume that is larger than the typical dimensions of the pores. In this way the porous medium has a continuum description, and can be specified via global properties like permeability and porosity, without the need of a detailed knowledge of the pore microstructure. At the interface between the porous material and the fluid region, following literature momentum-transfer conditions are applied, in which an available coefficient related to the unknown structure of the interface can be used as an error estimate. To formulate the numerical problem, the velocity-vorticity formulation of the coupled Navier--Stokes and VANS equations is derived and implement into a pseudo-sp...
DIRECT NUMERICAL SIMUIATION OF BUBBLE-CLUSTER'S DYNAMIC CHARACTERISTICS
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
A Direct Numerical Simulation (DNS) for understanding the dynamic response of bubble cluster to pulses of pressure perturbations has been studied by using a front-tracking method. The results show that owing to high nonlinearity, the bubble shape and volume oscillations caused by passing by pressure wave will be transformed into an in-phase volumetric oscillation of whole bubble cluster at a particular low-frequency. The value of the frequency is independent of the pulse excitations but the characteristics of the bubble cluster such as its bubble size, bulk void fraction and its spacial distribution etc. It is believed that this study provides important information for us to understand the coupling mechanism of cavitation cloud involved in cavitation resonance, a phenomenon noticed by one of the authors more than two decades ago.
Direct numerical simulations of helical dynamo action: MHD and beyond
Directory of Open Access Journals (Sweden)
D. O. Gómez
2004-01-01
Full Text Available Magnetohydrodynamic dynamo action is often invoked to explain the existence of magnetic fields in several astronomical objects. In this work, we present direct numerical simulations of MHD helical dynamos, to study the exponential growth and saturation of magnetic fields. Simulations are made within the framework of incompressible flows and using periodic boundary conditions. The statistical properties of the flow are studied, and it is found that its helicity displays strong spatial fluctuations. Regions with large kinetic helicity are also strongly concentrated in space, forming elongated structures. In dynamo simulations using these flows, we found that the growth rate and the saturation level of magnetic energy and magnetic helicity reach an asymptotic value as the Reynolds number is increased. Finally, extensions of the MHD theory to include kinetic effects relevant in astrophysical environments are discussed.
Direct numerical simulation of pattern formation in subaqueous sediment
Kidanemariam, Aman G
2014-01-01
We present results of direct numerical simulation of incompressible fluid flow over a thick bed of mobile, spherically-shaped particles. The algorithm is based upon the immersed boundary technique for fluid-solid coupling and uses a soft-sphere model for the solid-solid contact. Two parameter points in the laminar flow regime are chosen, leading to the emergence of sediment patterns classified as `small dunes', while one case under turbulent flow conditions leads to `vortex dunes' with significant flow separation on the lee side. Wavelength, amplitude and propagation speed of the patterns extracted from the spanwise-averaged fluid-bed interface are found to be consistent with available experimental data. The particle transport rates are well represented by available empirical models for flow over a plane sediment bed in both the laminar and the turbulent regimes.
Direct numerical simulation of turbulence using GPU accelerated supercomputers
Khajeh-Saeed, Ali; Blair Perot, J.
2013-02-01
Direct numerical simulations of turbulence are optimized for up to 192 graphics processors. The results from two large GPU clusters are compared to the performance of corresponding CPU clusters. A number of important algorithm changes are necessary to access the full computational power of graphics processors and these adaptations are discussed. It is shown that the handling of subdomain communication becomes even more critical when using GPU based supercomputers. The potential for overlap of MPI communication with GPU computation is analyzed and then optimized. Detailed timings reveal that the internal calculations are now so efficient that the operations related to MPI communication are the primary scaling bottleneck at all but the very largest problem sizes that can fit on the hardware. This work gives a glimpse of the CFD performance issues will dominate many hardware platform in the near future.
Numerical Evaluations of Functionally Graded RC Slabs
Directory of Open Access Journals (Sweden)
M. Mastali
2014-01-01
Full Text Available Nowadays, using fibrous materials is used widely in strengthening applications such as cross-section enlargement and using functionally graded reinforced concrete. Functionally graded reinforced concrete is used as multireinforced concrete layers that can be reinforced by different fiber types. The objective of this research was to address the structural benefits of functionally graded concrete materials by performing analytical simulations. In order to achieve this purpose, in the first stage of this study, three functionally graded reinforced concretes by steel and polypropylene (PP were experimentally tested under flexural loading. Inverse analysis was applied to obtain the used material properties of reinforced concrete by FEMIX software. After obtaining the material properties, to assess the performance of proposed slabs, some other cases were proposed and numerically evaluated under flexural and shear loading. The results showed that increasing steel fiber in reinforced entire cross section led to achieve better shear and flexural performance while the best performance of reinforced functionally graded slabs was achieved for slab at 1% fiber content. In the second stage, nineteen reinforced functionally graded RC slabs with steel bars were simulated and assessed and some other cases were considered which were not experimentally tested.
Cascade processes in stratified media: experiment and direct numerical simulation.
Sibgatullin, Ilias; Brouzet, Christophe; Joubaud, Sylvain; Ermanyuk, Evgeny; Dauxois, Thierry
2016-04-01
Internal gravity waves may transfer substantial part of energy in oceans and astrophysical objects, influence the background stratification, and angular momentum. Internal waves can be generated by convection in astrophysical objects, by tidal motion and interaction with orography in oceans. Internal and inertial waves obey similar system of equations. Due to very particular type of dispersive relation and the way internal waves are reflected from surfaces, in confined domains the monochromatic internal waves after sequence of reflections may form closed paths, the "wave attractors" [1]. Presently, linear theory of wave attractors is quite elaborated and a principal interest of research is focused on nonlinear regimes and unstable configurations, overturning events and mixing. We have performed direct numerical simulation of wave attractors which closely reproduces experiments [2] being carried out in Ecole Normal Superior de Lyon (ENS de Lyon). Direct numerical simulation is realized with the help of spectral element approach and code nek5000. Triadic resonance is confirmed as the first instability which appears on the most energetic ray of the attractor at sufficiently large forcing. With further increase of the forcing amplitude the daughter waves also become unstable resulting in a sophisticated cascade process which was first observed experimentally. For very high forcing amplitude interaction of focused waves with the walls results in appearance of small-scale folded structures. Their interaction with principal flow is the subject of further research. 1. Maas, L. R. M. & Lam, F.-P. A., Geometric focusing of internal waves. J. Fluid Mech, 1995,. 300, 1-41 2. Scolan, H., Ermanyuk, E., Dauxois, T., 2013, Physical Review Letters, 110, 234501
Differential Diffusion Effects in Numerical Simulations on Smoke Toxicity Evaluation
Directory of Open Access Journals (Sweden)
Pan Longwei
2016-01-01
Full Text Available With the increasing frequency of fire caused by construction materials, smoke toxicity evaluation plays a key role in related fields. Numerical simulation has become a popular method to predict the toxicity of smoke. A computational study of differential diffusion effects on smoke toxicity evaluation is proposed in this study. Further, an effective Lewis number model derived from the Reynolds-averaged form of the Navier-stokes (RANS transport equations is proposed in turbulent flames. The accuracy of the study is illustrated for a polyurethane foam fire in a 1/5 scale vertical shaft. The temperature and the concentrations of smoke composition are mainly discussed. From the comparison of the calculations with the direct numerical simulations (DNS data it is observed that the temperature and mass fractions of species agree well with the DNS data when differential diffusion effects are taken into account. On the other hand, these numerical results are overestimated if differential diffusion effects are neglected. The FED values indicate that differential diffusion has a strong influence on smoke toxicity evaluation when using N-Gas model.
Direct numerical simulation of turbulence in a bent pipe
Schlatter, Philipp; Noorani, Azad
2013-11-01
A series of direct numerical simulations of turbulent flow in a bent pipe is presented. The setup employs periodic (cyclic) boundary conditions in the axial direction, leading to a nominally infinitely long pipe. The discretisation is based on the high-order spectral element method, using the code Nek5000. Four different curvatures, defined as the ratio between pipe radius and coil radius, are considered: κ = 0 (straight), 0.01 (mild curvature), 0.1 and 0.3 (strong curvature), at bulk Reynolds numbers of up to 11700 (corresponding to Reτ = 360 in the straight pipe case). The result show the turbulence-reducing effect of the curvature (similar to rotation), leading close to relaminarisation in the inner side; the outer side, however, remains fully turbulent. Prpoer orthogonal decomposition (POD) is used to extract the dominant modes, in an effort to explain low-frequency switching of sides inside the pipe. A number of additional interesting features are explored, which include sub-straight and sub-laminar drag for specific choices of curvature and Reynolds number: In particular the case with sub-laminar drag is investigated further, and our analysis shows the existence of a spanwise wave in the bent pipe, which in fact leads to lower overall pressure drop.
Bedrock incision by bedload: insights from direct numerical simulations
Aubert, Guilhem; Langlois, Vincent J.; Allemand, Pascal
2016-04-01
Bedload sediment transport is one of the main processes that contribute to bedrock incision in a river and is therefore one of the key control parameters in the evolution of mountainous landscapes. In recent years, many studies have addressed this issue through experimental setups, direct measurements in the field, or various analytical models. In this article, we present a new direct numerical approach: using the classical methods of discrete-element simulations applied to granular materials, we explicitly compute the trajectories of a number of pebbles entrained by a turbulent water stream over a rough solid surface. This method allows us to extract quantitatively the amount of energy that successive impacts of pebbles deliver to the bedrock, as a function of both the amount of sediment available and the Shields number. We show that we reproduce qualitatively the behaviour observed experimentally by Sklar and Dietrich (2001) and observe both a "tool effect" and a "cover effect". Converting the energy delivered to the bedrock into an average long-term incision rate of the river leads to predictions consistent with observations in the field. Finally, we reformulate the dependency of this incision rate with Shields number and sediment flux, and predict that the cover term should decay linearly at low sediment supply and exponentially at high sediment supply.
Design of a single-phase PTS numerical experiment for a reference Direct Numerical Simulation
Energy Technology Data Exchange (ETDEWEB)
Shams, A., E-mail: shams@nrg.eu; Damiani, G.; Rosa, D.; Komen, E.M.J.
2016-04-15
Highlights: • A numerical experiment is designed to perform DNS for a PTS scenario. • A wide range of RANS calculations are performed to design this numerical experiment. • Mesh estimation for the targeted DNS is also performed. - Abstract: The integrity assessment of the Reactor Pressure Vessel (RPV) is considered to be an important issue for lifetime extension of nuclear reactors. A severe transient that can threaten the integrity of the RPV is the existence of a Pressurized Thermal Shock (PTS) during a Loss-of-Coolant Accident (LOCA). A PTS consists of a rapid cooling of the RPV wall under pressurized conditions that may induce the criticality of existing or postulated defects inside the vessel wall. The most severe PTS event has been identified by Emergency Core Cooling (ECC) injection during a LOCA. The traditional one-dimensional system codes fail to reliably predict the complex three-dimensional thermal mixing phenomena in the downcomer occurring during the ECC injection. Hence, CFD can bring real benefits in terms of more realistic and more predictive capabilities. However, to gain trust in the application of CFD modelling for PTS, a comprehensive validation programme is necessary. In the absence of detailed experimental data for the RPV cooling during ECC injection, high fidelity Direct Numerical Simulation (DNS) databases constitute a valid alternative and can serve as a reference. The aim of this work is to design a numerical experiment aimed to generate a high quality reference DNS database for a simplified PTS scenario. This takes into account the turbulent mixing in the downcomer and the evolution of the temperature distribution for both structures and fluid during a single-phase flow PTS scenario. In spite of simplifications, such a DNS analysis represents a very demanding application. A priori, it should be demonstrated that all the relevant turbulent scales will be fully resolved, which requires a huge computational power. A wide range of
Direct Numerical Simulations of Turbulent Autoigniting Hydrogen Jets
Asaithambi, Rajapandiyan
Autoignition is an important phenomenon and a tool in the design of combustion engines. To study autoignition in a canonical form a direct numerical simulation of a turbulent autoigniting hydrogen jet in vitiated coflow conditions at a jet Reynolds number of 10,000 is performed. A detailed chemical mechanism for hydrogen-air combustion and non-unity Lewis numbers for species transport is used. Realistic inlet conditions are prescribed by obtaining the velocity eld from a fully developed turbulent pipe flow simulation. To perform this simulation a scalable modular density based method for direct numerical simulation (DNS) and large eddy simulation (LES) of compressible reacting flows is developed. The algorithm performs explicit time advancement of transport variables on structured grids. An iterative semi-implicit time advancement is developed for the chemical source terms to alleviate the chemical stiffness of detailed mechanisms. The algorithm is also extended from a Cartesian grid to a cylindrical coordinate system which introduces a singularity at the pole r = 0 where terms with a factor 1/r can be ill-defined. There are several approaches to eliminate this pole singularity and finite volume methods can bypass this issue by not storing or computing data at the pole. All methods however face a very restrictive time step when using a explicit time advancement scheme in the azimuthal direction (theta) where the cell sizes are of the order DelrDeltheta. We use a conservative finite volume based approach to remove the severe time step restriction imposed by the CFL condition by merging cells in the azimuthal direction. In addition, fluxes in the radial direction are computed with an implicit scheme to allow cells to be clustered along the jet's shear layer. This method is validated and used to perform the large scale turbulent reacting simulation. The resulting flame structure is found to be similar to a turbulent diusion flame but stabilized by autoignition at the
Direct numerical simulation of scalar transport using unstructured finite-volume schemes
Rossi, Riccardo
2009-03-01
An unstructured finite-volume method for direct and large-eddy simulations of scalar transport in complex geometries is presented and investigated. The numerical technique is based on a three-level fully implicit time advancement scheme and central spatial interpolation operators. The scalar variable at cell faces is obtained by a symmetric central interpolation scheme, which is formally first-order accurate, or by further employing a high-order correction term which leads to formal second-order accuracy irrespective of the underlying grid. In this framework, deferred-correction and slope-limiter techniques are introduced in order to avoid numerical instabilities in the resulting algebraic transport equation. The accuracy and robustness of the code are initially evaluated by means of basic numerical experiments where the flow field is assigned a priori. A direct numerical simulation of turbulent scalar transport in a channel flow is finally performed to validate the numerical technique against a numerical dataset established by a spectral method. In spite of the linear character of the scalar transport equation, the computed statistics and spectra of the scalar field are found to be significantly affected by the spectral-properties of interpolation schemes. Although the results show an improved spectral-resolution and greater spatial-accuracy for the high-order operator in the analysis of basic scalar transport problems, the low-order central scheme is found superior for high-fidelity simulations of turbulent scalar transport.
Direct numerical simulation of turbulent plane Couette flow
Lee, Moon Joo
1991-01-01
Turbulent plane Couette flow was numerically simulated at a Reynolds number (U(sub w)h/nu) of 6000, where U(sub w) is the relative wall speed and h is half the channel-height. Unlike in Poiseuille flow, where the mean shear rate changes its sign at the centerline, the sign of mean shear rate in plane Couette flow remains the same across the whole channel. This difference is expected to yield several differences between the two flows, especially in the core region. The most significant and dramatic difference observed was the existence of large-scale structures in the core region of the plane Couette flow. The large eddies are extremely long in the flow direction and fill the entire channel (i.e., their vertical extent is 2h). The large-scale structures have the largest contribution from the wavenumber (k(sub x)h,k(sub z)h) = (0, plus or minus 1.5), corresponding to a wavelength lambda(sub z)/h is approximately equal to 4. The secondary motion associated with the k(sub x)h = 0 mode consists of the large-scale vortices. The large eddies contribute about 30 percent of turbulent kinetic energy.
Inertial particles in a shearless mixing layer: direct numerical simulations
Ireland, Peter; Collins, Lance
2010-11-01
Entrainment, the drawing in of external fluid by a turbulent flow, is present in nearly all turbulent processes, from exhaust plumes to oceanic thermoclines to cumulus clouds. While the entrainment of fluid and of passive scalars in turbulent flows has been studied extensively, comparatively little research has been undertaken on inertial particle entrainment. We explore entrainment of inertial particles in a shearless mixing layer across a turbulent-non-turbulent interface (TNI) and a turbulent-turbulent interface (TTI) through direct numerical simulation (DNS). Particles are initially placed on one side of the interface and are advanced in time in decaying turbulence. Our results show that the TTI is more efficient in mixing droplets than the TNI. We also find that without the influence of gravity, over the range of Stokes numbers present in cumulus clouds, particle concentration statistics are essentially independent of the dissipation scale Stokes number. The DNS data agrees with results from experiments performed in a wind tunnel with close parametric overlap. We anticipate that a better understanding of the role of gravity and turbulence in inertial particle entrainment will lead to improved cloud evolution predictions and more accurate climate models. Sponsored by the U.S. NSF.
Direct numerical simulation of vector-controlled free jets
Energy Technology Data Exchange (ETDEWEB)
Tsujimoto, K; Ao, K; Shakouchi, T; Ando, T, E-mail: tujimoto@mach.mie-u.ac.jp [Graduate School of Engineering, Mie University, Tsu, 514-8507 (Japan)
2011-12-22
We conduct DNS (direct numerical simulation) of vector controlled free jets. The inflow velocity of jet is periodically oscillated perpendicular to the jet axis. In order to realize the high accurate computation, a discretization in space is performed with hybrid scheme in which Fourier spectral and 6th order compact scheme are adopted. From visualized instantaneous vortex structures, it is found that the flow pattern considerably changes according to the oscillating frequency, i.e., according to the increasing the frequency, wave, bifurcating and flapping modes appear in turn. In order to quantify mixing efficiency under the vector control, as the mixing measure, statistical entropy is investigated. Compared to the uncontrolled jet, the mixing efficiency is improved in order of wavy, flapping and bifurcating modes. Thus the vector control can be expected for the improvement of mixing efficiency. Further to make clear the reason for the mixing enhancement, Snapshot POD and DMD method are applied. The primary flow structures under the vector control are demonstrated.
Direct Numerical Simulation of Combustion Using Principal Component Analysis
Owoyele, Opeoluwa; Echekki, Tarek
2016-11-01
We investigate the potential of accelerating chemistry integration during the direct numerical simulation (DNS) of complex fuels based on the transport equations of representative scalars that span the desired composition space using principal component analysis (PCA). The transported principal components (PCs) offer significant potential to reduce the computational cost of DNS through a reduction in the number of transported scalars, as well as the spatial and temporal resolution requirements. The strategy is demonstrated using DNS of a premixed methane-air flame in a 2D vortical flow and is extended to the 3D geometry to further demonstrate the computational efficiency of PC transport. The PCs are derived from a priori PCA of a subset of the full thermo-chemical scalars' vector. The PCs' chemical source terms and transport properties are constructed and tabulated in terms of the PCs using artificial neural networks (ANN). Comparison of DNS based on a full thermo-chemical state and DNS based on PC transport based on 6 PCs shows excellent agreement even for species that are not included in the PCA reduction. The transported PCs reproduce some of the salient features of strongly curved and strongly strained flames. The 2D DNS results also show a significant reduction of two orders of magnitude in the computational cost of the simulations, which enables an extension of the PCA approach to 3D DNS under similar computational requirements. This work was supported by the National Science Foundation Grant DMS-1217200.
Mean-field concept and direct numerical simulations of rotating magnetoconvection and the geodynamo
Schrinner, M; Schmitt, D; Rheinhardt, M; Christensen, U R
2006-01-01
A comparison is made between mean-field models and direct numerical simulations of rotating magnetoconvection and the geodynamo. The mean-field coefficients are calculated with the fluid velocity taken from the direct numerical simulations. The magnetic fields resulting from mean-field models are then compared with the mean magnetic field from the direct numerical simulations.
Numerical GPR Imaging through Directional Antenna Systems in Complex Scenarios
Comite, Davide; Murgia, Federica; Barbara, Martina; Catapano, Ilaria; Soldovieri, Francesco; Galli, Alessandro
2017-04-01
The capability of imaging hidden targets and interfaces in non-accessible and complex scenarios is a topic of increasing interest for several practical applications, such as civil engineering, geophysics, and planetary explorations [1]. In this frame, Ground Penetrating Radar (GPR) has been proven as an efficient and reliable technique, also thanks to the development of effective imaging procedures based on linear modeling of the scattering phenomenon, which is usually considered as activated by ideal sources [1],[2]. Actually, such modeling simplifications are rarely verified in typical operative scenarios, when a number of heterogeneous targets can interact each other and with the surrounding environment, producing undesired contributions such as clutter and ghosts targets. From a physical viewpoint, these phenomena are mainly due to multipath contributions at the receiving antenna system, and different solutions have been proposed to mitigate these effects on the final image reconstruction (see, e.g., [2] and references therein). In this work we investigate on the possible improvements achievable when the directional features of the transmitting antenna system are taken into account in the imaging algorithm. Following and extending the recent investigations illustrated in [2] and [3], we consider in particular arrays of antennas, made by arbitrary types of elements, as activating the scattering phenomenon: hence, the effects of neglecting or accounting for the inherent directional radiation of the considered array are investigated as regards the accuracy of the final reconstruction of targets. Taking into account the resolution losses linked to the relevant synthetic aperture, we analyze the possibility of improving the quality of imaging, mitigating the presence of spurious contributions. By implementing a 'synthetic setup' that analyzes the scenarios under test through different electromagnetic CAD tools (mainly CST Microwave Studio and gprMax), it has been
High performance Python for direct numerical simulations of turbulent flows
Mortensen, Mikael; Langtangen, Hans Petter
2016-06-01
Direct Numerical Simulations (DNS) of the Navier Stokes equations is an invaluable research tool in fluid dynamics. Still, there are few publicly available research codes and, due to the heavy number crunching implied, available codes are usually written in low-level languages such as C/C++ or Fortran. In this paper we describe a pure scientific Python pseudo-spectral DNS code that nearly matches the performance of C++ for thousands of processors and billions of unknowns. We also describe a version optimized through Cython, that is found to match the speed of C++. The solvers are written from scratch in Python, both the mesh, the MPI domain decomposition, and the temporal integrators. The solvers have been verified and benchmarked on the Shaheen supercomputer at the KAUST supercomputing laboratory, and we are able to show very good scaling up to several thousand cores. A very important part of the implementation is the mesh decomposition (we implement both slab and pencil decompositions) and 3D parallel Fast Fourier Transforms (FFT). The mesh decomposition and FFT routines have been implemented in Python using serial FFT routines (either NumPy, pyFFTW or any other serial FFT module), NumPy array manipulations and with MPI communications handled by MPI for Python (mpi4py). We show how we are able to execute a 3D parallel FFT in Python for a slab mesh decomposition using 4 lines of compact Python code, for which the parallel performance on Shaheen is found to be slightly better than similar routines provided through the FFTW library. For a pencil mesh decomposition 7 lines of code is required to execute a transform.
Direct Numerical Simulation of Three-Dimensional Richtmyer-Meshkov Instability
Institute of Scientific and Technical Information of China (English)
FU De-Xun; MA Yan-Wen; LI Xin-Liang
2008-01-01
Direct numerical simulation(DNS)is used to study flow characteristics after interaction of a planar shock with a spherical media interface in each side of which the density is different.This interfacial instability is known as the Richtmyer-Meshkov(R-M)instability.The compressible Nayier-Stoke equations are discretized with group velocity control(GVC)modified fourth order accurate compact difference scheme.Three-dimensional numerical simulations are performed for R-M instability installed passing a shock through a spherical interface.Based on numerical results the characteristics of 3D R-M instability are analysed.The evaluation for distortion of the interface.the deformation of the incident shock wave and effects of refraction,reflection and diffraction are Dresented.The effects of the interfacial instability on produced vorticity and mixing is discussed.
Direct numerical simulation of the dynamics of sliding rough surfaces
Dang, Viet Hung; Scheibert, Julien; Bot, Alain Le
2013-01-01
The noise generated by the friction of two rough surfaces under weak contact pressure is usually called roughness noise. The underlying vibration which produces the noise stems from numerous instantaneous shocks (in the microsecond range) between surface micro-asperities. The numerical simulation of this problem using classical mechanics requires a fine discretization in both space and time. This is why the finite element method takes much CPU time. In this study, we propose an alternative numerical approach which is based on a truncated modal decomposition of the vibration, a central difference integration scheme and two algorithms for contact: The penalty algorithm and the Lagrange multiplier algorithm. Not only does it reproduce the empirical laws of vibration level versus roughness and sliding speed found experimentally but it also provides the statistical properties of local events which are not accessible by experiment. The CPU time reduction is typically a factor of 10.
Direct Numerical Simulation of Liquid Transport Through Fibrous Porous Media
Palakurthi, Nikhil Kumar
Fluid flow through fibrous media occurs in many industrial processes, including, but not limited, to fuel cell technology, drug delivery patches, sanitary products, textile reinforcement, filtration, heat exchangers, and performance fabrics. Understanding the physical processes involved in fluid flow through fibrous media is essential for their characterization as well as for the optimization and development of new products. Macroscopic porous-media equations require constitutive relations, which account for the physical processes occurring at the micro-scale, to predict liquid transport at the macro-scale. In this study, micro-scale simulations were conducted using conventional computational fluid dynamics (CFD) technique (finite-volume method) to determine the macroscopic constitutive relations. The first part of this thesis deals with the single-phase flow in fibrous media, following which multi-phase flow through fibrous media was studied. Darcy permeability is an important parameter that characterizes creeping flow through a fibrous porous medium. It has a complex dependence on the medium's properties such as fibers' in-plane and through-plane orientation, diameter, aspect ratio, curvature, and porosity. A suite of 3D virtual fibrous structures with a wide range of geometric properties were constructed, and the permeability values of the structures were calculated by solving the 3D incompressible Navier-Stokes equations. The through-plane permeability was found to be a function of only the fiber diameter, the fibers' through-plane orientation, and the porosity of the medium. The numerical results were used to extend a permeability-porosity relation, developed in literature for 3D isotropic fibrous media, to a wide range of fibers' through-plane orientations. In applications where rate of capillary penetration is important, characterization of porous media usually involves determination of either the effective pore radius from capillary penetration experiments
Optimal Taylor-Couette flow: direct numerical simulations
Mónico, Rodolfo Ostilla; Grossman, Siegfried; Verzicco, Roberto; Lohse, Detlef
2013-01-01
We numerically simulate turbulent Taylor-Couette flow for independently rotating inner and outer cylinders, focusing on the analogy with turbulent Rayleigh-B\\'enard flow. Reynolds numbers of Re_i = 8\\times10^3 and Re_o =\\pm4\\times10^3 of the inner and outer cylinders, respectively, are reached, corresponding to Taylor numbers Ta up to 10^8 . Effective scaling laws for the torque and other system responses are found. Recent experiments with the Twente turbulent Taylor-Couette (T^3C) setup at very high Reynolds numbers have vealed an optimum transport at a certain non-zero rotation rate ratio a = -{\\omega}_o/{\\omega}_i that depends on Ta. For large enough Ta in the numerically accessible range we find such an optimum at non-zero counter-rotation also in the numerics. We furthermore numerically calculate the corresponding angular velocity profiles and visualize the different flow structures for the various regimes. By writing the equations in a frame co-rotating with the outer cylinder a link is found between th...
Numerical characterization of nanopillar photonic crystal waveguides and directional couplers
DEFF Research Database (Denmark)
Chigrin, Dmitry N.; Lavrinenko, Andrei; Sotomayor Torres, Clivia M.
2005-01-01
We numerically characterize a novel type of a photonic crystal waveguide, which consists of several rows of periodically arranged dielectric cylinders. In such a nanopillar photonic crystal waveguide, light confinement is due to the total internal reflection. A nanopillar waveguide is a multimode...
A direct numerical method for quantifying regular and chaotic orbits
Energy Technology Data Exchange (ETDEWEB)
Awrejcewicz, J. E-mail: awrejcew@ck-sg.p.lodz.pl; Dzyubak, L.; Grebogi, C
2004-02-01
Both a theoretical argument and a numerical algorithm to identify periodic and chaotic orbits are presented and discussed. Reliability of the approach is verified using the Duffing oscillator through the standard computation of Lyapunov exponents. Advantages of the proposed approach are given.
Direct Numerical Simulation Sediment Transport in Horizontal Channel
Energy Technology Data Exchange (ETDEWEB)
Uhlmann, M.
2006-07-01
We numerically simulate turbulent flow in a horizontal plane channel over a bed of mobile particles. All scales of fluid motion are resolved without modeling and the phase interface is accurately represented. Our results indicate a possible scenario for the onset of erosion through collective motion induced by buffer-layer streaks. (Author) 27 refs.
The Direct Numerical Simulation of A Turbulent Channel Flow with Analyses of the Database
Institute of Scientific and Technical Information of China (English)
ChunxiaoXU; ZhaoshunZHANG
1996-01-01
The database of fully developed turbulent channel flow at low Reynolds number is set up through direct numerical simulations.The budget of dissipation-rate of turbulent kinetic energy is calculated and some existing models for the transport equation of the dissipation rate are evaluated.A new model for the turbulent production and viscous destruction terms is given.It makes a considerable improvement in the near-wall behavior,A new flow structure contributing much to high kurtosis levels in transverse velocity fluctuation in viscous sublayer is found.The common characters they possessed are described.
Parallel direct numerical simulation of three-dimensional spray formation
Chergui, Jalel; Juric, Damir; Shin, Seungwon; Kahouadji, Lyes; Matar, Omar
2015-11-01
We present numerical results for the breakup mechanism of a liquid jet surrounded by a fast coaxial flow of air with density ratio (water/air) ~ 1000 and kinematic viscosity ratio ~ 60. We use code BLUE, a three-dimensional, two-phase, high performance, parallel numerical code based on a hybrid Front-Tracking/Level Set algorithm for Lagrangian tracking of arbitrarily deformable phase interfaces and a precise treatment of surface tension forces. The parallelization of the code is based on the technique of domain decomposition where the velocity field is solved by a parallel GMRes method for the viscous terms and the pressure by a parallel multigrid/GMRes method. Communication is handled by MPI message passing procedures. The interface method is also parallelized and defines the interface both by a discontinuous density field as well as by a triangular Lagrangian mesh and allows the interface to undergo large deformations including the rupture and/or coalescence of interfaces. EPSRC Programme Grant, MEMPHIS, EP/K0039761/1.
Direct numerical simulation of solidification microstructures affected by fluid flow
Energy Technology Data Exchange (ETDEWEB)
Juric, D.
1997-12-01
The effects of fluid flow on the solidification morphology of pure materials and solute microsegregation patterns of binary alloys are studied using a computational methodology based on a front tracking/finite difference method. A general single field formulation is presented for the full coupling of phase change, fluid flow, heat and solute transport. This formulation accounts for interfacial rejection/absorption of latent heat and solute, interfacial anisotropies, discontinuities in material properties between the liquid and solid phases, shrinkage/expansion upon solidification and motion and deformation of the solid. Numerical results are presented for the two dimensional dendritic solidification of pure succinonitrile and the solidification of globulitic grains of a plutonium-gallium alloy. For both problems, comparisons are made between solidification without fluid flow and solidification within a shear flow.
Hierarchy in directed random networks: analytical and numerical results
Mones, Enys
2012-01-01
In recent years, the theory and application of complex networks has been quickly developing in a markable way due to the increasing amount of data from real systems and to the fruitful application of powerful methods used in statistical physics. Many important characteristics of social or biological systems can be described by the study of their underlying structure of interactions. Hierarchy is one of these features that can be formulated in the language of networks. In this paper we present the analytic results on the hierarchical properties of random network models with zero correlations and also investigate the effects of different type of correlations. The behavior of hierarchy is different in the absence and the presence of the giant components. We show that the hierarchical structure can be drastically different if there are one-point correlations in the network. We also show numerical results suggesting that hierarchy does not change monotonously with the correlations and there is an optimal level of ...
Three dimensional direct numerical simulation of complex jet flows
Shin, Seungwon; Kahouadji, Lyes; Juric, Damir; Chergui, Jalel; Craster, Richard; Matar, Omar
2016-11-01
We present three-dimensional simulations of two types of very challenging jet flow configurations. The first consists of a liquid jet surrounded by a faster coaxial air flow and the second consists of a global rotational motion. These computations require a high spatial resolution and are performed with a newly developed high performance parallel code, called BLUE, for the simulation of two-phase, multi-physics and multi-scale incompressible flows, tested on up to 131072 threads with excellent scalability performance. The method for the treatment of the fluid interfaces uses a hybrid Front Tracking/Level Set technique that defines the interface both by a discontinuous density field as well as by a local triangular Lagrangian mesh. Coriolis forces are taken into account and solved via an exact time-integration method that ensures numerical accuracy and stability. EPSRC UK Programme Grant EP/K003976/1.
On numerical methods for direct and inverse problems in electromagnetism
Zemanova, Viera
2009-01-01
This thesis is devoted to the study of processes in the propagation of electromagnetic fields. We do not aim at one particular problem, actually very different kinds of topics are analyzed here. We deal with direct problems as well as with inverse ones, low frequency electromagnetism is discussed and consequently the wave propagation problem in high frequency domain is studied. Study of electromagnetic materials and their behavior is of a huge interest for the technological world. Its impo...
Direct numerical simulation of incompressible multiphase flow with phase change
Lee, Moon Soo; Riaz, Amir; Aute, Vikrant
2017-09-01
Simulation of multiphase flow with phase change is challenging because of the potential for unphysical pressure oscillations, spurious velocity fields and mass flux errors across the interface. The resulting numerical errors may become critical when large density contrasts are present. To address these issues, we present a new approach for multiphase flow with phase change that features, (i) a smooth distribution of sharp velocity jumps and mass flux within a narrow region surrounding the interface, (ii) improved mass flux projection from the implicit interface onto the uniform Cartesian grid and (iii) post-advection velocity correction step to ensure accurate velocity divergence in interfacial cells. These new features are implemented in combination with a sharp treatment of the jumps in pressure and temperature gradient. A series of 1-D, 2-D, axisymmetric and 3-D problems are solved to verify the improvements afforded by the new approach. Axisymmetric film boiling results are also presented, which show good qualitative agreement with heat transfer correlations as well as experimental observations of bubble shapes.
Card, J. M.; Chen, J. H.; Day, M.; Mahalingam, S.
1994-01-01
Turbulent non-premixed stoichiometric methane-air flames modeled with reduced kinetics have been studied using the direct numerical simulation approach. The simulations include realistic chemical kinetics, and the molecular transport is modeled with constant Lewis numbers for individual species. The effect of turbulence on the internal flame structure and extinction characteristics of methane-air flames is evaluated. Consistent with earlier DNS with simple one-step chemistry, the flame is wrinkled and in some regions extinguished by the turbulence, while the turbulence is weakened in the vicinity of the flame due to a combination of dilatation and an increase in kinematic viscosity. Unlike previous results, reignition is observed in the present simulations. Lewis number effects are important in determining the local stoichiometry of the flame. The results presented in this work are preliminary but demonstrate the feasibility of incorporating reduced kinetics for the oxidation of methane with direct numerical simulations of homogeneous turbulence to evaluate the limitations of various levels of reduction in the kinetics and to address the formation of thermal and prompt NO(x).
Analysis of Multipoint Correlations in Direct Numerical Simulation
Stoevesandt, Bernhard; Shishkin, Andrei; Stresing, Robert; Wagner, Claus; Peinke, Joachim
2010-01-01
We examine the Markov properties of the three velocity components of a turbulent flow generated by a DNS simulation of the flow around an airfoil section. The spectral element code Nektar has been used to generate a well resolved flow field around an fx79w-151a airfoil profile at a Reynolds number of Re=5000 and an angle of attack of {\\alpha} = 12{\\deg}. Due to a homogeneous geometry in the spanwise direction, a Fourier expansion has been used for the third dimension of the simulation. In the...
Energy Technology Data Exchange (ETDEWEB)
Reckinger, Scott James [Montana State Univ., Bozeman, MT (United States); Livescu, Daniel [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Vasilyev, Oleg V. [Univ. of Colorado, Boulder, CO (United States)
2016-09-02
A comprehensive numerical methodology has been developed that handles the challenges introduced by considering the compressive nature of Rayleigh-Taylor instability (RTI) systems, which include sharp interfacial density gradients on strongly stratified background states, acoustic wave generation and removal at computational boundaries, and stratification-dependent vorticity production. The computational framework is used to simulate two-dimensional single-mode RTI to extreme late-times for a wide range of flow compressibility and variable density effects. The results show that flow compressibility acts to reduce the growth of RTI for low Atwood numbers, as predicted from linear stability analysis.
Numerical estimation of aircrafts' unsteady lateral-directional stability derivatives
Directory of Open Access Journals (Sweden)
Maričić N.L.
2006-01-01
Full Text Available A technique for predicting steady and oscillatory aerodynamic loads on general configuration has been developed. The prediction is based on the Doublet-Lattice Method, Slender Body Theory and Method of Images. The chord and span wise loading on lifting surfaces and longitudinal bodies (in horizontal and vertical plane load distributions are determined. The configuration may be composed of an assemblage of lifting surfaces (with control surfaces and bodies (with circular cross sections and a longitudinal variation of radius. Loadings predicted by this method are used to calculate (estimate steady and unsteady (dynamic lateral-directional stability derivatives. The short outline of the used methods is given in [1], [2], [3], [4] and [5]. Applying the described methodology software DERIV is developed. The obtained results from DERIV are compared to NASTRAN examples HA21B and HA21D from [4]. In the first example (HA21B, the jet transport wing (BAH wing is steady rolling and lateral stability derivatives are determined. In the second example (HA21D, lateral-directional stability derivatives are calculated for forward- swept-wing (FSW airplane in antisymmetric quasi-steady maneuvers. Acceptable agreement is achieved comparing the results from [4] and DERIV.
A Numerical Unitarity Formalism for Evaluating One-Loop Amplitudes
Ellis, Richard Keith; Kunszt, Z
2008-01-01
Recent progress in unitarity techniques for one-loop scattering amplitudes makes a numerical implementation of this method possible. We present a 4-dimensional unitarity method for calculating the cut-constructible part of amplitudes and implement the method in a numerical procedure. Our technique can be applied to any one-loop scattering amplitude and offers the possibility that one-loop calculations can be performed in an automatic fashion, as tree-level amplitudes are currently done. Instead of individual Feynman diagrams, the ingredients for our one-loop evaluation are tree-level amplitudes, which are often already known. To study the practicality of this method we evaluate the cut-constructible part of the 4, 5 and 6 gluon one-loop amplitudes numerically, using the analytically known 4, 5 and 6 gluon tree-level amplitudes. Comparisons with analytic answers are performed to ascertain the numerical accuracy of the method.
Pragmatics of type-directed partial evaluation
DEFF Research Database (Denmark)
1996-01-01
the user to annotate arrow types with effect information. It is achieved by delimiting and abstracting control, comparably to continuation-based specialization in direct style. It enables type-directed partial evaluation of programs with effects (e.g., a definitional lambda-interpreter for an imperative......Type-directed partial evaluation stems from the residualization of static values in dynamic contexts, given their type and the type of their free variables. Its algorithm coincides with the algorithm for coercing a subtype value into a supertype value, which itself coincides with Berger...... and Schwichtenberg's normalization algorithm for the simply typed lambda-calculus. Type-directed partial evaluation thus can be used to specialize a compiled, closed program, given its type. Since Similix, let-insertion is a cornerstone of partial evaluators for call-by-value procedural languages with computational...
Analysis of Multipoint Correlations in Direct Numerical Simulation
Stoevesandt, Bernhard; Stresing, Robert; Wagner, Claus; Peinke, Joachim
2010-01-01
We examine the Markov properties of the three velocity components of a turbulent flow generated by a DNS simulation of the flow around an airfoil section. The spectral element code Nektar has been used to generate a well resolved flow field around an fx79w-151a airfoil profile at a Reynolds number of Re=5000 and an angle of attack of {\\alpha} = 12{\\deg}. Due to a homogeneous geometry in the spanwise direction, a Fourier expansion has been used for the third dimension of the simulation. In the wake of the profile the flow field shows a von Karman street like behavior with the vortices decaying in the wake which trigger a turbulent field. Time series of the 3D flow field were extracted from the flow at different locations to analyze the stochastic features. In particular the existence of Markov properties in the flow have been shown for different cases in the surrounding of the airfoil. This is of basic interest as it indicates that fine structures of turbulence can be replaced by stochastic processes. Turbulen...
Numerical investigations on unstable direct contact condensation of cryogenic fluids
Jayachandran, K. N.; Arnab, Roy; Parthasarathi, Ghosh
2017-02-01
A typical problem of Direct Contact Condensation (DCC) occurs at the liquid oxygen (LOX) booster turbopump exit of oxidiser rich staged combustion cycle based semi-cryogenic rocket engines, where the hot gas mixture (predominantly oxygen and small amounts of combustion products) that runs the turbine mixes with LOX from the pump exit. This complex multiphase phenomena leads to the formation of solid CO2 & H2O, which is undesirable for the functioning of the main LOX turbopump. As a starting point for solving this complex problem, in this study, the hot gas mixture is taken as pure oxygen and hence, DCC of pure oxygen vapour jets in subcooled liquid oxygen is simulated using the commercial CFD package ANSYS CFX®. A two fluid model along with the thermal phase change model is employed for capturing the heat and mass transfer effects. The study mainly focuses on the subsonic DCC bubbling regime, which is reported as unstable with bubble formation, elongation, necking and collapsing effects. The heat transfer coefficients over a period of time have been computed and the various stages of bubbling have been analysed with the help of vapour volume fraction and pressure profiles. The results obtained for DCC of oxygen vapour-liquid mixtures is in qualitative agreement with the experimental results on DCC of steam-water mixtures.
Zradziński, Patryk
2015-01-01
Due to the various physical mechanisms of interaction between a worker's body and the electromagnetic field at various frequencies, the principles of numerical simulations have been discussed for three areas of worker exposure: to low frequency magnetic field, to low and intermediate frequency electric field and to radiofrequency electromagnetic field. This paper presents the identified difficulties in applying numerical simulations to evaluate physical estimators of direct and indirect effec...
Breugem, W.P.; Boersma, B.J.
2005-01-01
A direct numerical simulation (DNS) has been performed of turbulent channel flow over a three-dimensional Cartesian grid of 30×20×9 cubes in, respectively, the streamwise, spanwise, and wall-normal direction. The grid of cubes mimics a permeable wall with a porosity of 0.875. The flow field is resol
Direct numerical simulation of inertial flows in porous media
Apte, S.; Finn, J.; Wood, B. D.
2010-12-01
At modest flow rates (10 ≤ Re ≤ 300) through porous media and packed beds, fluid inertia can result in complex steady and unsteady recirculation regions, dependent on the local pore geometry. Body fitted CFD is a broadly used design and analysis tool for flows in porous media and packed bed type reactors. Unfortunately, the inherent complexities of porous media make unstructured mesh generation a difficult and time consuming step in the simulation process. To accurately capture the inertial dynamics using high-fidelity direct simulations, body fitted meshes must be high quality and sufficiently refined. We present methods to parameterize and simplify mesh generation for packed beds, with an eye toward obtaining efficient mesh independence for Reynolds numbers in the inertial and unsteady regimes. The crux of mesh generation for packed beds is dealing with sphere-sphere or sphere-wall contact points, where a geometric singularity exists. To handle the sphere-sphere and sphere-wall contact points, we use a fillet bridge model, in which every pair of contacting entities are bridged by a fillet, eliminating a small fluid region near the contact point. This results in a continuous surface mesh which does not require resizing of the spheres and can accommodate prism cells for improved boundary layer resolution. A second order accurate, parallel, incompressible flow solver [Moin and Apte, AIAA J. 2006] is used to simulate flow through three different sphere packings: a periodic simple cubic packing, a wall bounded hexagonal close packing, and a randomly packed tube. Mesh independence is assessed using several measures including Ergun pressure drop coefficients, viscous and pressure components of drag force, kinetic energy, kinetic energy dissipation and interstitial velocity profiles. The results of these test cases are used to determine the feasibility of accurate and very large scale simulations of flow through a randomly packed bed of 103 pores. Preliminary results
Memorization in Type-Directed Partial Evaluation
DEFF Research Database (Denmark)
Balat, Vincent; Danvy, Olivier
2002-01-01
We use a code generator—type-directed partial evaluation— to verify conversions between isomorphic types, or more precisely to verify that a composite function is the identity function at some complicated type. A typed functional language such as ML provides a natural support to express...... the functions and type-directed partial evaluation provides a convenient setting to obtain the normal form of their composition. However, off-the-shelf type-directed partial evaluation turns out to yield gigantic normal forms. We identify that this gigantism is due to redundancies, and that these redundancies...... originate in the handling of sums, which uses delimited continuations. We successfully eliminate these redundancies by extending type-directed partial evaluation with memoization capabilities. The result only works for pure functional programs, but it provides an unexpected use of code generation...
Memoization in Type-Directed Partial Evaluation
DEFF Research Database (Denmark)
Balat, Vincent; Danvy, Olivier
2002-01-01
We use a code generator—type-directed partial evaluation— to verify conversions between isomorphic types, or more precisely to verify that a composite function is the identity function at some complicated type. A typed functional language such as ML provides a natural support to express...... the functions and type-directed partial evaluation provides a convenient setting to obtain the normal form of their composition. However, off-the-shelf type-directed partial evaluation turns out to yield gigantic normal forms. We identify that this gigantism is due to redundancies, and that these redundancies...... originate in the handling of sums, which uses delimited continuations. We successfully eliminate these redundancies by extending type-directed partial evaluation with memoization capabilities. The result only works for pure functional programs, but it provides an unexpected use of code generation...
Direct evaluation of overlap integrals between Slater-type-orbitals
Caola, Michael J
2016-01-01
We derive direct single-stage numerical evaluation of the electronic overlap integral between arbitrary atomic orbitals (including STOs). Integration is over cartesian co-ordinates, and replaces previous sums over 'special' functions. The results, in Mathematica 10 and Maple 18, agree with the literature to 8 digits. We briefly discuss possible use in quantum chemistry, including accuracy, algorithmic suitability and operating-system machine-implementation as an intrinsic function.
Stable Numerical Evaluation of Finite Hankel Transforms and Their Application
Directory of Open Access Journals (Sweden)
Manoj P. Tripathi
2014-01-01
Full Text Available A new stable algorithm, based on hat functions for numerical evaluation of Hankel transform of order ν>-1, is proposed in this paper. The hat basis functions are used as a basis to expand a part of the integrand, rf(r, appearing in the Hankel transform integral. This leads to a very simple, efficient, and stable algorithm for the numerical evaluation of Hankel transform. The novelty of our paper is that we give error and stability analysis of the algorithm and corroborate our theoretical findings by various numerical experiments. Finally, an application of the proposed algorithm is given for solving the heat equation in an infinite cylinder with a radiation condition.
Numerical models for the evaluation of geothermal systems
Energy Technology Data Exchange (ETDEWEB)
Bodvarsson, G.S.; Pruess, K.; Lippmann, M.J.
1986-08-01
We have carried out detailed simulations of various fields in the USA (Bada, New Mexico; Heber, California); Mexico (Cerro Prieto); Iceland (Krafla); and Kenya (Olkaria). These simulation studies have illustrated the usefulness of numerical models for the overall evaluation of geothermal systems. The methodology for modeling the behavior of geothermal systems, different approaches to geothermal reservoir modeling and how they can be applied in comprehensive evaluation work are discussed.
Numerical evaluation of image parameters of ETR-1
Directory of Open Access Journals (Sweden)
Ahmed Shamim
2016-09-01
Full Text Available In this work, we developed a method to handle the image quality test-tool precisely. This test-tool is important to evaluate the quality of the medical images for pre-treatment planning phase. But the achieved images are estimated by naked eyes, which does not provide the precise result. Our main goal is to get the desired image parameters numerically. This numerical estimation overcomes the limitation of naked eye observation. Hence, it enhances the pre-treatment planning. The ETR-1 test-tool is considered here. The contrast, the low contrast details and line-pairs (lp/mm were estimated.
Numerical Evaluation of CPV Boundary Integrals with Symmetrical Quadrature Schemes
Institute of Scientific and Technical Information of China (English)
马杭; 徐凯宇
2003-01-01
Stemming from the definition of the Cauchy principal values (CPV) integrals, a newly developed symmetrical quadrature scheme was proposed in the paper for the accurate numerical evaluation of the singular boundary integrals in the sense of CPV encountered in the boundary element method. In the case of inner-element singularities, the CPV integrals could be evaluated in a straightforward way by dividing the element into the symmetrical part and the remainder(s). And in the case of end-singularities, the CPV integrals could be evaluated simply by taking a tangential distance transformation of the integrand after cutting out a symmetrical tiny zone around the singular point. In both cases, the operations are no longer necessary before the numerical implementation, which involves the dull routine work to separate out singularities from the integral kernels. Numerical examples were presented for both the two-and the three-dimensional boundary integrals in elasticity. Comparing the numerical results with those by other approaches demonstrates the feasibility and the effectiveness of the proposed scheme.
Numerical evaluation of the performance of active noise control systems
Mollo, C. G.; Bernhard, R. J.
1990-01-01
This paper presents a generalized numerical technique for evaluating the optimal performance of active noise controllers. In this technique, the indirect BEM numerical procedures are used to derive the active noise controllers for optimal control of enclosed harmonic sound fields where the strength of the noise sources or the description of the enclosure boundary may not be known. The performance prediction for a single-input single-output system is presented, together with the analysis of the stability and observability of an active noise-control system employing detectors. The numerical procedures presented can be used for the design of both the physical configuration and the electronic components of the optimal active noise controller.
A direct-numerical-simulation-based second-moment closure for turbulent magnetohydrodynamic flows
Kenjereš, S.; Hanjalić, K.; Bal, D.
2004-01-01
A magnetic field, imposed on turbulent flow of an electrically conductive fluid, is known to cause preferential damping of the velocity and its fluctuations in the direction of Lorentz force, thus leading to an increase in stress anisotropy. Based on direct numerical simulations (DNS), we have devel
Numerical evaluation of strength and deformability of fractured rocks
Institute of Scientific and Technical Information of China (English)
Majid Noorian Bidgoli; Zhihong Zhao; Lanru Jing
2013-01-01
Knowledge of the strength and deformability of fractured rocks is important for design, construction and stability evaluation of slopes, foundations and underground excavations in civil and mining engineering. However, laboratory tests of intact rock samples cannot provide information about the strength and deformation behaviors of fractured rock masses that include many fractures of varying sizes, orientations and locations. On the other hand, large-scale in situ tests of fractured rock masses are economically costly and often not practical in reality at present. Therefore, numerical modeling becomes necessary. Numerical predicting using discrete element methods (DEM) is a suitable approach for such modeling because of their advantages of explicit representations of both fractures system geometry and their constitutive behaviors of fractures, besides that of intact rock matrix. In this study, to generically determine the compressive strength of fractured rock masses, a series of numerical experiments were performed on two-dimensional discrete fracture network models based on the realistic geometrical and mechanical data of fracture systems from field mapping. We used the UDEC code and a numerical servo-controlled program for controlling the progressive compressive loading process to avoid sudden violent failure of the models. The two loading conditions applied are similar to the standard laboratory testing for intact rock samples in order to check possible differences caused by such loading conditions. Numerical results show that the strength of fractured rocks increases with the increasing confining pressure, and that deformation behavior of fractured rocks follows elasto-plastic model with a trend of strain hardening. The stresses and strains obtained from these numerical experiments were used to fit the well-known Mohr-Coulomb (M-C) and Hoek-Brown (H-B) failure criteria, represented by equivalent material properties defining these two criteria. The results show
Numerical evaluation of gas core length in free surface vortices
Cristofano, L.; Nobili, M.; Caruso, G.
2014-11-01
The formation and evolution of free surface vortices represent an important topic in many hydraulic intakes, since strong whirlpools introduce swirl flow at the intake, and could cause entrainment of floating matters and gas. In particular, gas entrainment phenomena are an important safety issue for Sodium cooled Fast Reactors, because the introduction of gas bubbles within the core causes dangerous reactivity fluctuation. In this paper, a numerical evaluation of the gas core length in free surface vortices is presented, according to two different approaches. In the first one, a prediction method, developed by the Japanese researcher Sakai and his team, has been applied. This method is based on the Burgers vortex model, and it is able to estimate the gas core length of a free surface vortex starting from two parameters calculated with single-phase CFD simulations. The two parameters are the circulation and the downward velocity gradient. The other approach consists in performing a two-phase CFD simulation of a free surface vortex, in order to numerically reproduce the gas- liquid interface deformation. Mapped convergent mesh is used to reduce numerical error and a VOF (Volume Of Fluid) method was selected to track the gas-liquid interface. Two different turbulence models have been tested and analyzed. Experimental measurements of free surface vortices gas core length have been executed, using optical methods, and numerical results have been compared with experimental measurements. The computational domain and the boundary conditions of the CFD simulations were set consistently with the experimental test conditions.
Experimental evaluation of numerical simulation of cavitating flow around hydrofoil
Energy Technology Data Exchange (ETDEWEB)
Dular, M.; Bachert, R.; Stoffel, B. [Darmstadt Univ. of Technology, Lab. for Turbomachinery and Fluid Power (Germany); Sirok, B. [Ljubljana Univ., Lab. for Water and Turbine Machines (Slovenia)
2005-08-01
Cavitation in hydraulic machines causes different problems that can be related to its unsteady nature. An experimental and numerical study of developed cavitating flow was performed. Until now simulations of cavitating flow were limited to the self developed 'in house' CFD codes. The goal of the work was to experimentally evaluate the capabilities of a commercial CFD code (Fluent) for simulation of a developed cavitating flow. Two simple hydrofoils that feature some 3D effects of cavitation were used for the experiments. A relatively new technique where PIV method combined with LIF technique was used to experimentally determine the instantaneous and average velocity and void ratio fields (cavity shapes) around the hydrofoils. Distribution of static pressure on the hydrofoil surface was determined. For the numerical simulation of cavitating flow a bubble dynamics cavitation model was used to describe the generation and evaporation of vapour phase. An unsteady RANS 3D simulation was performed. Comparison between numerical and experimental results shows good correlation. The distribution and size of vapour structures and the velocity fields agree well. The distribution of pressure on the hydrofoil surface is correctly predicted. The numerically predicted shedding frequencies are in fair agreement with the experimental data. (authors)
Numerical evaluation of tensor Feynman integrals in Euclidean kinematics
Energy Technology Data Exchange (ETDEWEB)
Gluza, J.; Kajda [Silesia Univ., Katowice (Poland). Inst. of Physics; Riemann, T.; Yundin, V. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany)
2010-10-15
For the investigation of higher order Feynman integrals, potentially with tensor structure, it is highly desirable to have numerical methods and automated tools for dedicated, but sufficiently 'simple' numerical approaches. We elaborate two algorithms for this purpose which may be applied in the Euclidean kinematical region and in d=4-2{epsilon} dimensions. One method uses Mellin-Barnes representations for the Feynman parameter representation of multi-loop Feynman integrals with arbitrary tensor rank. Our Mathematica package AMBRE has been extended for that purpose, and together with the packages MB (M. Czakon) or MBresolve (A. V. Smirnov and V. A. Smirnov) one may perform automatically a numerical evaluation of planar tensor Feynman integrals. Alternatively, one may apply sector decomposition to planar and non-planar multi-loop {epsilon}-expanded Feynman integrals with arbitrary tensor rank. We automatized the preparations of Feynman integrals for an immediate application of the package sectordecomposition (C. Bogner and S. Weinzierl) so that one has to give only a proper definition of propagators and numerators. The efficiency of the two implementations, based on Mellin-Barnes representations and sector decompositions, is compared. The computational packages are publicly available. (orig.)
A Numerical Simulation Approach for Reliability Evaluation of CFRP Composite
Liu, D. S.-C.; Jenab, K.
2013-02-01
Due to the superior mechanical properties of carbon fiber reinforced plastic (CFRP) materials, they are vastly used in industries such as aircraft manufacturers. The aircraft manufacturers are switching metal to composite structures while studying reliability (R-value) of CFRP. In this study, a numerical simulation method to determine the reliability of Multiaxial Warp Knitted (MWK) textiles used to make CFRP composites is proposed. This method analyzes the distribution of carbon fiber angle misalignments, from a chosen 0° direction, caused by the sewing process of the textile, and finds the R-value, a value between 0 and 1. The application of this method is demonstrated by an illustrative example.
,
2012-01-01
During previous numerical experiments on isotropic turbulence of surface gravity waves we observed formation of the long wave background (condensate). It was shown (Korotkevich, Phys. Rev. Lett. vol. 101 (7), 074504 (2008)), that presence of the condensate changes a spectrum of direct cascade, corresponding to the flux of energy to the small scales from pumping region (large scales). Recent experiments show that the inverse cascade spectrum is also affected by the condensate. In this case mechanism proposed as a cause for the change of direct cascade spectrum cannot work. But inverse cascade is directly influenced by the linear dispersion relation for waves, as a result direct measurement of the dispersion relation in the presence of condensate is necessary. We performed the measurement of this dispersion relation from the direct numerical experiment. The results demonstrate that in the region of inverse cascade influence of the condensate cannot be neglected.
Direct numerical simulation of turbulent flow in a channel with different types of surface roughness
Bolotnov, Igor A.
2011-11-01
Direct numerical simulation (DNS) was performed for turbulent channel flow (Reτ = 400) for two types of wall surface roughness and well as smooth walls. The roughness elements of first type were assumed to be two-dimensional, transverse square rods positioned on both walls in a non-staggered arrangement. The height of the rods corresponds to y+ = 13.6 and thus extends in the buffer layer. The second type of roughness was represented by a set of hemispherical obstacles (height of y+ = 10) located on both channel walls and arranged on a square lattice. The presented simulations are part of benchmark problems defined by thermal-hydraulics focus area of the Consortium for Advanced Simulations of Light Water Reactors (CASL). This problem simulates the effect of the presence of growing bubbles on the walls of nuclear reactor fuel rods and aimed on evaluating CFD capabilities of various codes before applying them to more advanced problems. Mean turbulent quantities were computed and compared with available analytical and experimental results. The results of this work will be used to evaluate the performance of other LES and RANS codes on this benchmark problem. Supported by Consortium for Advanced Simulation of Light Water Reactors (CASL).
Review of numerical methods for simulation of the aortic root: Present and future directions
Mohammadi, Hossein; Cartier, Raymond; Mongrain, Rosaire
2016-05-01
Heart valvular disease is still one of the main causes of mortality and morbidity in develop countries. Numerical modeling has gained considerable attention in studying hemodynamic conditions associated with valve abnormalities. Simulating the large displacement of the valve in the course of the cardiac cycle needs a well-suited numerical method to capture the natural biomechanical phenomena which happens in the valve. The paper aims to review the principal progress of the numerical approaches for studying the hemodynamic of the aortic valve. In addition, the future directions of the current approaches as well as their potential clinical applications are discussed.
Zradziński, Patryk
2015-01-01
Due to the various physical mechanisms of interaction between a worker's body and the electromagnetic field at various frequencies, the principles of numerical simulations have been discussed for three areas of worker exposure: to low frequency magnetic field, to low and intermediate frequency electric field and to radiofrequency electromagnetic field. This paper presents the identified difficulties in applying numerical simulations to evaluate physical estimators of direct and indirect effects of exposure to electromagnetic fields at various frequencies. Exposure of workers operating a plastic sealer have been taken as an example scenario of electromagnetic field exposure at the workplace for discussion of those difficulties in applying numerical simulations. The following difficulties in reliable numerical simulations of workers' exposure to the electromagnetic field have been considered: workers' body models (posture, dimensions, shape and grounding conditions), working environment models (objects most influencing electromagnetic field distribution) and an analysis of parameters for which exposure limitations are specified in international guidelines and standards.
Numerical evaluation of the tensor bispectrum in two field inflation
Raveendran, Rathul Nath
2016-01-01
We evaluate the dimensionless non-Gaussianity parameter $h_{_{\\rm NL}}$, that characterizes the amplitude of the tensor bispectrum, numerically for a class of two field inflationary models such as double inflation, hybrid inflation and aligned natural inflation. We compare the numerical results with the slow roll results which can be obtained analytically. In the context of double inflation, we also investigate the effects on $h_{_{\\rm NL}}$ due to curved trajectories in the field space. We explicitly examine the validity of the consistency relation governing the tensor bispectrum in the squeezed limit. Lastly, we discuss the contribution to $h_{_{\\rm NL}}$ due to the epoch of preheating in two field models.
Tsang, L.; Brown, R.; Kong, J. A.; Simmons, G.
1974-01-01
Two numerical methods are used to evaluate the integrals that express the em fields due to dipole antennas radiating in the presence of a stratified medium. The first method is a direct integration by means of Simpson's rule. The second method is indirect and approximates the kernel of the integral by means of the fast Fourier transform. In contrast to previous analytical methods that applied only to two-layer cases the numerical methods can be used for any arbitrary number of layers with general properties.
Numerical evaluation of tandem rotor for highly loaded transonic fan
Institute of Scientific and Technical Information of China (English)
ZHAO Bin; LIU Bao-jie
2011-01-01
Transonic tandem rotor was designed for highly loaded fan at a corrected tip speed of 381 m/s and another conventional rotor was designed as a baseline to evaluate the loading superiority of tandem rotor with three-dimensional (3-D) numerical simulation. The aft blade solidity and its impact on total loading level were studied in depth. The result indicates that tandem rotor has potential to achieve higher loading level and attain favorable aerodynamic performance in a wide range of loading coefficient 0. 55 ～ 0.68, comparing with the conventional rotor which produced a total pressure ratio of 2.0 and loading coefficient of 0. 42.
Wang, Yi
2016-07-21
Velocity of fluid flow in underground porous media is 6~12 orders of magnitudes lower than that in pipelines. If numerical errors are not carefully controlled in this kind of simulations, high distortion of the final results may occur [1-4]. To fit the high accuracy demands of fluid flow simulations in porous media, traditional finite difference methods and numerical integration methods are discussed and corresponding high-accurate methods are developed. When applied to the direct calculation of full-tensor permeability for underground flow, the high-accurate finite difference method is confirmed to have numerical error as low as 10-5% while the high-accurate numerical integration method has numerical error around 0%. Thus, the approach combining the high-accurate finite difference and numerical integration methods is a reliable way to efficiently determine the characteristics of general full-tensor permeability such as maximum and minimum permeability components, principal direction and anisotropic ratio. Copyright © Global-Science Press 2016.
Directory of Open Access Journals (Sweden)
Yadollahi Bijan
2014-01-01
Full Text Available In this study, a numerical model has been developed in AVL FIRE software to perform investigation of Direct Natural Gas Injection into the cylinder of Spark Ignition Internal Combustion Engines. In this regard two main parts have been taken into consideration, aiming to convert an MPFI gasoline engine to direct injection NG engine. In the first part of study multi-dimensional numerical simulation of transient injection process, mixing and flow field have been performed via three different validation cases in order to assure the numerical model validity of results. Adaption of such a modeling was found to be a challenging task because of required computational effort and numerical instabilities. In all cases present results were found to have excellent agreement with experimental and numerical results from literature. In the second part, using the moving mesh capability the validated model has been applied to methane Injection into the cylinder of a Direct Injection engine. Five different piston head shapes along with two injector types have been taken into consideration in investigations. A centrally mounted injector location has been adapted to all cases. The effects of injection parameters, combustion chamber geometry, injector type and engine RPM have been studied on mixing of air-fuel inside cylinder. Based on the results, suitable geometrical configuration for a NG DI Engine has been discussed.
Numerical Tracking of Limit Points for Direct Parametric Analysis in Nonlinear Rotordynamics
Xie, Lihan; Baguet, Sébastien; Prabel, Benoit; Dufour, Régis
2016-01-01
International audience; A frequency-domain approach for direct parametric analysis of limit points of nonlinear dynamical systems is presented in this paper. Instead of computing responses curves for several values of a given system parameter, the direct tracking of limit points is performed. The whole numerical procedure is based on the Harmonic Balance Method and can be decomposed in three distinct steps. Firstly, a response curve is calculated by HBM combined with a continuation technique ...
Direct numerical simulation of the very large anisotropic scales in a turbulent channel
del Alamo, Juan C
2013-01-01
Over the last decades the knowledge on the small scales of turbulent wall flows has experienced a significant advance, especially in the near-wall region where the highest production of turbulent energy and the maximum turbulence intensity occur. The development of computers has played an important role in this progress, making direct numerical simulations affordable (Kim, Moin & Moser, 1987), and offering wider observational possibilities than most laboratory experiments. The large scales have received less attention, and it has not been until recently that their significance and their real size have been widely recognized, thanks in part to the experiments by Hites (1997) and Kim & Adrian (1999), and to the compilation of experimental and numerical data by Jimenez (1998). The requirements of both a very large box and a high Reynolds number has made direct numerical simulation of the VLAS unapproachable until today. The purpose of this report is to serve as a preliminary description of a newly compil...
Direct Numerical Simulation of the Influence of Plasmas on Turbulent Flows
2006-12-31
the doctoral research of Mr. Shankar Chosh. Publications associated with this work are listed below. " Direct numerical simulation of the thermal...addition. AIAA paper 2003-3862. [4] MAKER, P., TERHUNE, R. & SAVAGE, C. 1963 Proceedings of the Third International Quantum Mechanics Conference, Paris
Direct Numerical Simulation of biomass pyrolysis and combustion with gas phase reactions
Aswasthi, A.; Kuerten, J.G.M.; Geurts, B.J.
2016-01-01
We present Direct Numerical Simulation of biomass pyrolysis and combustion in a turbulent channel flow. The model includes simplified models for biomass pyrolysis and char combustion along with a model for particle tracking. The gas phase is modelled as a mixture of reacting gas species. The gas-pa
Versluis, R.; Dorsman, R.; Thielen, L.; Roos, M.E.
2009-01-01
A new approach for performing numerical direct simulation Monte Carlo (DSMC) simulations on turbomolecular pumps in the free molecular and transitional flow regimes is described. The chosen approach is to use surfaces that move relative to the grid to model the effect of rotors and stators on a gas
Direct Numerical Simulation of structural vacillation in the transition to geostrophic turbulence
Randriamampianina, Anthony; Fruh, Wolf-Gerrit; Read, Peter L
2007-01-01
The onset of small-scale fluctuations around a steady convection pattern in a rotating baroclinic annulus filled with air is investigated using Direct Numerical Simulation. In previous laboratory experiments of baroclinic waves, such fluctuations have been associated with a flow regime termed Structural Vacillation which is regarded as the first step in the transition to fully-developed geostrophic turbulence.
Directory of Open Access Journals (Sweden)
Xingtuan Yang
2015-05-01
Full Text Available A direct numerical simulation study of the characteristics of macroscopic and microscopic rotating motions in swirling jets confined in a rectangular flow domain is carried out. The different structures of vortex cores for different swirl levels are illustrated. It is found that the vortex cores of low swirl flows are of regular cylindrical-helix patterns, whereas those of the high swirl flows are characterized by the formation of the bubble-type vortex breakdown followed by the radiant processing vortex cores. The results of mean velocity fields show the general procedures of vortex origination. Moreover, the effects of macroscopic and microscopic rotating motions with respect to the mean and fluctuation fields of the swirling flows are evaluated. The microscopic rotating effects, especially the effects with respect to the turbulent fluctuation motion, are increasingly intermittent with the increase in the swirl levels. In contrast, the maximum value of the probability density functions with respect to the macroscopic rotating effects of the fluctuation motion occurs at moderate swirl levels since the macroscopic rotating effects are attenuated by the formation of the bubble vortex breakdown with a region of stagnant fluids at supercritical swirl levels.
Energy Technology Data Exchange (ETDEWEB)
Komiwes, V.
1999-09-01
Numerical models applied to simulation of granular flow with fluid are developed. The physical model selected to describe particles flow is a discrete approach. Particle trajectories are calculated by the Newton law and collision is describe by a soft-sphere approach. The fluid flow is modelled by Navier-Stokes equations. The modelling of the momentum transfer depends on the resolution scale: for a scale of the order of the particle diameter, it is modelled by a drag-law and for a scale smaller than the particle diameter, it is directly calculated by stress tensor computation around particles. The direct model is used to find representative elementary volume and prove the local character of the Ergun's law. This application shows the numerical (mesh size), physical (Reynolds number) and computational (CPU time and memory consumptions) limitations. The drag law model and the direct model are validated with analytical and empirical solutions and compared. For the two models, the CPU time and the memory consumptions are discussed. The drag law model is applied to the simulation of gas-solid dense fluidized-beds. In the case of uniform gas distribution, the fluidized-bed simulation heights are compared to experimental data for particle of group A and B of the Geldart classification. (author)
DEFF Research Database (Denmark)
Lavrinenko, Andrei; Jacobsen, Rune Shim; Fage-Pedersen, Jacob
2005-01-01
a one-row line defect. Both the numerical and experimental methods are based on the time of flight approach for an optical pulse. An increase of the group index by approximately 45 times (from 4 to 155) has been observed when approaching the cutoff of the fundamental photonic bandgap mode. Numerical 2D...... and 3D simulations of pulse dynamics in the waveguide made by the time-domain method shows excellent agreement with measured data in most of the band. These group index values in a photonic crystal waveguide are to the best of our knowledge the largest numbers reported so far by direct tracking of pulse...
Electrokinetic Particle Transport in Micro-Nanofluidics Direct Numerical Simulation Analysis
Qian, Shizhi
2012-01-01
Numerous applications of micro-/nanofluidics are related to particle transport in micro-/nanoscale channels, and electrokinetics has proved to be one of the most promising tools to manipulate particles in micro/nanofluidics. Therefore, a comprehensive understanding of electrokinetic particle transport in micro-/nanoscale channels is crucial to the development of micro/nano-fluidic devices. Electrokinetic Particle Transport in Micro-/Nanofluidics: Direct Numerical Simulation Analysis provides a fundamental understanding of electrokinetic particle transport in micro-/nanofluidics involving elect
Thermal numerical simulator for laboratory evaluation of steamflood oil recovery
Energy Technology Data Exchange (ETDEWEB)
Sarathi, P.
1991-04-01
A thermal numerical simulator running on an IBM AT compatible personal computer is described. The simulator was designed to assist laboratory design and evaluation of steamflood oil recovery. An overview of the historical evolution of numerical thermal simulation, NIPER's approach to solving these problems with a desk top computer, the derivation of equations and a description of approaches used to solve these equations, and verification of the simulator using published data sets and sensitivity analysis are presented. The developed model is a three-phase, two-dimensional multicomponent simulator capable of being run in one or two dimensions. Mass transfer among the phases and components is dictated by pressure- and temperature-dependent vapor-liquid equilibria. Gravity and capillary pressure phenomena were included. Energy is transferred by conduction, convection, vaporization and condensation. The model employs a block centered grid system with a five-point discretization scheme. Both areal and vertical cross-sectional simulations are possible. A sequential solution technique is employed to solve the finite difference equations. The study clearly indicated the importance of heat loss, injected steam quality, and injection rate to the process. Dependence of overall recovery on oil volatility and viscosity is emphasized. The process is very sensitive to relative permeability values. Time-step sensitivity runs indicted that the current version is time-step sensitive and exhibits conditional stability. 75 refs., 19 figs., 19 tabs.
NUMERICAL SIMULATION OF AL-SI ALLOYS WITH AND WITHOUT A DIRECTIONAL SOLIDIFICATION
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Michael Roland
2014-03-01
Full Text Available Numerical simulations are presented to analyze the influence of the casting process on the resulting strength of Strontium modified Al–Si alloys. A relationship is identified between the mechanical behavior and the different 3D morphologies of the eutectic silicon of the samples obtained by the die cast procedure and the directional solidification. It is shown that the mechanical behavior of the die cast alloy is isotropic in all three directions. In contrary, for the directional solidified alloy, the mechanical strength in the direction of the temperature gradient is higher than in the transverse direction. This fact has to be taken into account when analyzing structures issued from different casting processes. The volume meshes for the simulations are generated from experimental 3D FIB/SEM data sets. The influence of several levels of coarsening of the meshes as well as the order of the Lagrange element in the finite element setup are also analyzed.
Lardeau, Sylvain; Ferrari, Simone; Rossi, Lionel
2008-12-01
Three-dimensional (3D) direct numerical simulations of a flow driven by multiscale electromagnetic forcing are performed in order to reproduce with maximum accuracy the quasi-two-dimensional (2D) flow generated by the same multiscale forcing in the laboratory. The method presented is based on a 3D description of the flow and the electromagnetic forcing. Very good agreements between our simulations and the experiments are found both on velocity and acceleration field, this last comparison being, to our knowledge, done for the first time. Such agreement requires that both experiments and simulations are carefully performed and, more importantly, that the underlying simplification to model the experiments and the multiscale electromagnetic forcing do not introduce significant errors. The results presented in this paper differ significantly from previous 2D direct numerical simulation in which a classical linear Rayleigh friction modeling term was used to mimic the effect of the wall-normal friction. Indeed, purely 2D simulations are found to underestimate the Reynolds number and, due to the dominance of nonhomogeneous bottom friction, lead to the wrong physical mechanism. For the range of conditions presented in this paper, the Reynolds number, defined by the ratio between acceleration and viscous terms, remains the order of unity, and the Hartmann number, defined by the ratio between electromagnetic force terms and viscous terms, is about 2. The main conclusion is that 3D simulations are required to model the (3D) electromagnetic forces and the wall-normal shear. Indeed, even if the flow is quasi-2D in terms of energy, a full 3D approach is required to simulate these shallow layer flows driven by multiscale electromagnetic forcing. In the range of forcing intensity investigated in this paper, these multiscale flows remain quasi-2D, with negligible energy in the wall-normal velocity component. It is also shown that the driving terms are the electromagnetic forcing and
Dividends Sharing Convertible Bonds Pricing and Numerical Evaluation
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Xu Guo
2013-01-01
Full Text Available The convertible bond is becoming one of the most important financial instruments for the company to raise capital fund since it was first issued by American New York Erie Company in 1843. In this paper, it is the first time to study the pricing problem for convertible bond whose underlying stocks pay dividends via the reflected backward stochastic differential equations. Associating the solutions of reflected BSDEs with the obstacle problems for nonlinear parabolic PDEs, we establish the pricing formulas for convertible bonds with continuous and discrete dividends by means of the viscosity solutions for some PDEs. Besides, we also derive the price of convertible bonds with higher borrowing rate which is realistic in the financial market. Then the numerical evaluations are provided by the radial basis functions method. Moreover, we discuss the influence of dividends paying as well as higher borrowing rate on the convertible bond price at last.
Numerical Analysis for Structural Safety Evaluation of Butterfly Valves
Shin, Myung-Seob; Yoon, Joon-Yong; Park, Han-Yung
2010-06-01
Butterfly valves are widely used in current industry to control the fluid flow. They are used for both on-off and throttling applications involving large flows at relatively low operating pressure especially in large size pipelines. For the industrial application of butterfly valves, it must be ensured that the valve could be used safety under the fatigue life and the deformations produced by the pressure of the fluid. In this study, we carried out the structure analysis of the body and the valve disc of the butterfly valve and the numerical simulation was performed by using ANSYS v11.0. The reliability of valve is evaluated under the investigation of the deformation, the leak test and the durability of the valve.
Evaluating the Impact of Aerosols on Numerical Weather Prediction
Freitas, Saulo; Silva, Arlindo; Benedetti, Angela; Grell, Georg; Members, Wgne; Zarzur, Mauricio
2015-04-01
The Working Group on Numerical Experimentation (WMO, http://www.wmo.int/pages/about/sec/rescrosscut/resdept_wgne.html) has organized an exercise to evaluate the impact of aerosols on NWP. This exercise will involve regional and global models currently used for weather forecast by the operational centers worldwide and aims at addressing the following questions: a) How important are aerosols for predicting the physical system (NWP, seasonal, climate) as distinct from predicting the aerosols themselves? b) How important is atmospheric model quality for air quality forecasting? c) What are the current capabilities of NWP models to simulate aerosol impacts on weather prediction? Toward this goal we have selected 3 strong or persistent events of aerosol pollution worldwide that could be fairly represented in current NWP models and that allowed for an evaluation of the aerosol impact on weather prediction. The selected events includes a strong dust storm that blew off the coast of Libya and over the Mediterranean, an extremely severe episode of air pollution in Beijing and surrounding areas, and an extreme case of biomass burning smoke in Brazil. The experimental design calls for simulations with and without explicitly accounting for aerosol feedbacks in the cloud and radiation parameterizations. In this presentation we will summarize the results of this study focusing on the evaluation of model performance in terms of its ability to faithfully simulate aerosol optical depth, and the assessment of the aerosol impact on the predictions of near surface wind, temperature, humidity, rainfall and the surface energy budget.
Jou, Jerwen
2003-01-01
In 3 experiments, subjects made comparativejudgments on a set of 2 numbers or letters, 3 numbers or letters, or 5 numbers or letters. Numeric and alphabetic serial order memories were contrasted. Three aspects of serial order memory processes were identified: computational complexity, directionality, and accessibility. Computational complexity is the number of algorithmic steps involved in identifying a target. Directional bias is measured as the speed differences in identifying serial targets of equal computational complexity in a stimulus array. Memory accessibility is measured as the numeric and alphabetic serial position effects. Subjects had a slight directional bias favoring backward ordering for single digits but no bias in 2-digit number ordering, in contrast to a strong forward directional advantage in letter ordering. The speed of number access was found to steadily and evenly decrease along the numeric scale, in contrast to a systematic pattern of variations in alphabet access along the alphabetic scale. Finally, the middle item effect (the middle item in a multi-item array is identified most slowly) found in Jou's (1997) multiple-letter comparison study was generalized to numbers.
Direct numerical simulations of an inertial wave attractor in linear and nonlinear regimes
Jouve, Laurène
2014-01-01
In a uniformly rotating fluid, inertial waves propagate along rays that are inclined to the rotation axis by an angle that depends on the wave frequency. In closed domains, multiple reflections from the boundaries may cause inertial waves to focus on to particular structures known as wave attractors. Such structures have previously been studied from a theoretical point of view, in laboratory experiments, in linear numerical calculations and in some recent numerical simulations. In the present paper, two-dimensional direct numerical simulations of an inertial wave attractor are presented. In the linear regime, we first recover the results of the linear calculations and asymptotic theory of Ogilvie (2005) who considered a prototypical problem involving the focusing of linear internal waves into a narrow beam centred on a wave attractor in a steady state. The velocity profile of the beam and its scalings with the Ekman number, as well as the asymptotic value of the dissipation rate, are found to be in agreement ...
Direct numerical simulation of turbulent liquid metal flow entering a magnetic field
Energy Technology Data Exchange (ETDEWEB)
Albets-Chico, X., E-mail: xalbets@ucy.ac.cy; Grigoriadis, D.G.E.; Votyakov, E.V.; Kassinos, S.
2013-12-15
Highlights: • Analysis of turbulence persistence of fully developed MHD pipe flow at Re{sub b} = 4000. • Turbulence decay of fully developed turbulence flow entering low, moderate and strong magnetic fields. • Analysis of the wall conductivity on the aforementioned phenomena. • Discovering and further analysis of flow instabilities of the flow entering a strong magnetic field. -- Abstract: This paper presents direct numerical simulations (DNS) of fully developed turbulent liquid-metal flow in a circular duct entering a magnetic field. The case of a magnetohydrodynamic flow leaving a strong magnetic field has been extensively studied experimentally and numerically owing to its similarity to typical flow configurations appearing in liquid metal blankets of nuclear fusion reactors. Although also relevant to the design of fusion reactor blankets, the flow entering the fringing field of a magnet remains unexplored because its high intricacy precludes any simplification of the governing equations. Indeed, the complexity of the magnetohydrodynamic–turbulence interaction can only be analysed by direct numerical simulations or experiments. With that purpose, this paper addresses the case of a fully developed turbulent flow (Re{sub τ} ≈ 520) entering low, intermediate and strong magnetic fields under electrically insulating and poorly conducting walls by means of three-dimensional direct numerical simulations. Purely hydrodynamic computations (without the effect of the magnetic field) reveal an excellent agreement against previous experimental and numerical results. Current MHD results provide a very detailed information of the turbulence decay and reveal new three-dimensional features related to liquid-metal flow entering strong increasing magnetic fields, such as flow instabilities due to the effect of the Lorentz forces within the fringing region at high Ha numbers.
Carbone, Francesco; El, Gennady
2015-01-01
We undertake a detailed comparison of the results of direct numerical simulations of the integrable soliton gas dynamics with the analytical predictions inferred from the exact solutions of the relevant kinetic equation for solitons. We use the KdV soliton gas as a simplest analytically accessible model yielding major insight into the general properties of soliton gases in integrable systems. Two model problems are considered: (i) the propagation of a `trial' soliton through a one-component `cold' soliton gas consisting of randomly distributed solitons of approximately the same amplitude; and (ii) collision of two cold soliton gases of different amplitudes (soliton gas shock tube problem) leading to the formation of an incoherend dispersive shock wave. In both cases excellent agreement is observed between the analytical predictions of the soliton gas kinetics and the direct numerical simulations. Our results confirm relevance of the kinetic equation for solitons as a quantitatively accurate model for macrosco...
Zhu, X.; Ostilla-Monico, Rodolfo; Verzicco, R.; Lohse, D.
2016-01-01
We present direct numerical simulations of Taylor–Couette flow with grooved walls at a fixed radius ratio ${\\it\\eta}=r_{i}/r_{o}=0.714$η=ri/ro=0.714 with inner cylinder Reynolds number up to $Re_{i}=3.76\\times 10^{4}$Rei=3.76×104, corresponding to Taylor number up to $Ta=2.15\\times 10^{9}$Ta=2.15×10
Direct numerical simulations of vortex rings at ReΓ = 7500
Bergdorf, Michael; Koumoutsakos, Petros; Leonard, Anthony
2007-01-01
We present direct numerical simulations of the turbulent decay of vortex rings with ReΓ = 7500. We analyse the vortex dynamics during the nonlinear stage of the instability along with the structure of the vortex wake during the turbulent stage. These simulations enable the quantification of vorticity dynamics and their correlation with structures from dye visualization and the observations of circulation decay that have been reported in related experimental works. Movies are available with th...
Pore-scale Direct Numerical Simulation of Flow and Transport in Porous Media
Pulloor Kuttanikkad, Sreejith
2009-01-01
This dissertation presents research on the pore-scale simulation of flow and transport in porous media and describes the application of a new numerical approach based on the discontinuous Galerkin (DG) finite elements to pore-scale modelling. In this approach, the partial differential equations governing the flow at the pore-scale are solved directly where the main advantage is that it does not require a body fitted grid and works on a structured partition of the domain. Furthermore this appr...
Directed polymer in random media, in two dimensions: numerical study of the aging dynamics
Barrat, A.
1997-01-01
Following a recent work by Yoshino, we study the aging dynamics of a directed polymer in random media, in 1+1 dimensions. Through temperature quench, and temperature cycling numerical experiments similar to the experiments on real spin glasses, we show that the observed behaviour is comparable to the one of a well known mean field spin glass model. The observation of various quantities (correlation function, ``clonation'' overlap function) leads to an analysis of the phase space landscape.
Numerical Evaluation of a Light-Gas Gun Facility for Impact Test
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C. Rahner
2014-01-01
Full Text Available Experimental tests which match the application conditions might be used to properly evaluate materials for specific applications. High velocity impacts can be simulated using light-gas gun facilities, which come in different types and complexities. In this work different setups for a one-stage light-gas gun facility have been numerically analyzed in order to evaluate their suitability for testing materials and composites used as armor protection. A maximal barrel length of 6 m and a maximal reservoir pressure of a standard industrial gas bottle (20 MPa were chosen as limitations. The numerical predictions show that it is not possible to accelerate the projectile directly to the desired velocity with nitrogen, helium, or hydrogen as propellant gas. When using a sabot corresponding to a higher bore diameter, the necessary velocity is achievable with helium and hydrogen gases.
Numerical and experimental direct shear tests for coarse-grained soils
Institute of Scientific and Technical Information of China (English)
Ahad Bagherzadeh-Khalkhali; Ali Asghar Mirghasemi
2009-01-01
The presence of particles larger than the permissible dimensions of conventional laboratory specimens causes difficulty in the determination of shear strength of coarse-grained soils. In this research, the influence of particle size on shear strength of coarse-grained soils was investigated by resorting to experimental tests in different scale and numerical simulations based on discrete element method (DEM). Experimental tests on such soil specimens were based on using the techniques designated as "parallel" and "scalping" to prepare gradation of samples in view of the limitation of laboratory specimen size. As a second approach, the direct shear test was numerically simulated on assemblies of elliptical particles. The behaviors of samples under experimental and numerical tests are presented and compared, indicating that the modification of sample gradation has a significant influence on the mechanical properties of coarse-grained soils. It is noted that the shear strengths of samples produced by the scalping method are higher than samples by the parallel method. The scalping method for preparing specimens for direct shear test is therefore recommended. The micromechanical behavior of assemblies under direct shear test is also discussed and the effects of stress level on sample behavior are investigated.
Wave- and Current-Supported Gravity Flows: Insights from Direct Numerical Simulations (DNS)
Ozdemir, C. E.
2016-12-01
Discoveries over the last three decades have shown that current- and wave-enhanced gravity flows (CWEGFs) are among the significant agents that carry substantial amounts of sediments across low-gradient shelves and thereby they are important elements of sediment source-to-sink. Computational fluid dynamics (CFD) complement the existing field and laboratory experiments in that it offers unprecedented details of participating physical processes. Also, since the state-of-the-art optical and acoustic sensors are limited to measure 50 kg/m3 of suspended sediment concentration, CFD becomes the only means to evaluate the physical processes when the turbid layer is highly concentrated. In this presentation, the roles of wave- and alongshore current-induced turbulent boundary layers are investigated separately on across-shelf fine sediment transport. Turbulence-resolving simulations (Direct Numerical Simulations) that utilize a simplified Eulerian-Eulerian two-phase flow model are conducted. The results show that the sediment carrying capacity of wave boundary layers far exceeds the ones carried by along-shelf currents. The results also show that across-shelf velocity in wall units obeys a logarithmic profile, u+=α ln(z+)+β . However, this logarithmic velocity profile is far apart from the log-law and parameters α and β are dependent on sediment loading and the representative settling velocity of sediments. The key parameters that characterize CWEGFs, such as drag coefficient, Cd, and their variation are also calculated and are found to be close to the ones that are observed in the field experiments. It is also found that for wave boundary layers, drag coefficient increases as the wave orbital velocity increases. Further discussion on the details of the sediment-turbulence interaction is also warranted.
Mukhadiyev, Nurzhan
2017-05-01
Combustion at extreme conditions, such as a turbulent flame at high Karlovitz and Reynolds numbers, is still a vast and an uncertain field for researchers. Direct numerical simulation of a turbulent flame is a superior tool to unravel detailed information that is not accessible to most sophisticated state-of-the-art experiments. However, the computational cost of such simulations remains a challenge even for modern supercomputers, as the physical size, the level of turbulence intensity, and chemical complexities of the problems continue to increase. As a result, there is a strong demand for computational cost reduction methods as well as in acceleration of existing methods. The main scope of this work was the development of computational and numerical tools for high-fidelity direct numerical simulations of premixed planar flames interacting with turbulence. The first part of this work was KAUST Adaptive Reacting Flow Solver (KARFS) development. KARFS is a high order compressible reacting flow solver using detailed chemical kinetics mechanism; it is capable to run on various types of heterogeneous computational architectures. In this work, it was shown that KARFS is capable of running efficiently on both CPU and GPU. The second part of this work was numerical tools for direct numerical simulations of planar premixed flames: such as linear turbulence forcing and dynamic inlet control. DNS of premixed turbulent flames conducted previously injected velocity fluctuations at an inlet. Turbulence injected at the inlet decayed significantly while reaching the flame, which created a necessity to inject higher than needed fluctuations. A solution for this issue was to maintain turbulence strength on the way to the flame using turbulence forcing. Therefore, a linear turbulence forcing was implemented into KARFS to enhance turbulence intensity. Linear turbulence forcing developed previously by other groups was corrected with net added momentum removal mechanism to prevent mean
Empirical Evaluation of Directional-Dependence Tests
Thoemmes, Felix
2015-01-01
Testing of directional dependence is a method to infer causal direction that recently has attracted some attention. Previous examples by e.g. von Eye and DeShon (2012a) and extensive simulation studies by Pornprasertmanit and Little (2012) have demonstrated that under specific assumptions, directional-dependence tests can recover the true causal…
Directory of Open Access Journals (Sweden)
M. Boumaza
2015-07-01
Full Text Available Transient convection heat transfer is of fundamental interest in many industrial and environmental situations, as well as in electronic devices and security of energy systems. Transient fluid flow problems are among the more difficult to analyze and yet are very often encountered in modern day technology. The main objective of this research project is to carry out a theoretical and numerical analysis of transient convective heat transfer in vertical flows, when the thermal field is due to different kinds of variation, in time and space of some boundary conditions, such as wall temperature or wall heat flux. This is achieved by the development of a mathematical model and its resolution by suitable numerical methods, as well as performing various sensitivity analyses. These objectives are achieved through a theoretical investigation of the effects of wall and fluid axial conduction, physical properties and heat capacity of the pipe wall on the transient downward mixed convection in a circular duct experiencing a sudden change in the applied heat flux on the outside surface of a central zone.
Direct numerical simulation methods of hypersonic flat-plate boundary layer in thermally perfect gas
Jia, WenLi; Cao, Wei
2014-01-01
High-temperature effects alter the physical and transport properties of air such as vibrational excitation in a thermally perfect gas, and this factor should be considered in order to compute the flow field correctly. Herein, for the thermally perfect gas, a simple method of direct numerical simulation on flat-plat boundary layer is put forward, using the equivalent specific heat ratio instead of constant specific heat ratio in the N-S equations and flux splitting form of a calorically perfect gas. The results calculated by the new method are consistent with that by solving the N-S equations of a thermally perfect gas directly. The mean flow has the similarity, and consistent to the corresponding Blasius solution, which confirms that satisfactory results can be obtained basing on the Blasius solution as the mean flow directly in stability analysis. The amplitude growth curve of small disturbance is introduced at the inlet by using direct numerical simulation, which is consistent with that obtained by linear stability theory. It verified that the equation established and the simulation method is correct.
Directory of Open Access Journals (Sweden)
Tobias U. Hauser
2013-06-01
Full Text Available The ability to accurately process numerical magnitudes and solve mental arithmetic is of highest importance for schooling and professional career. Although impairments in these domains in disorders such as developmental dyscalculia (DD are highly detrimental, remediation is still sparse. In recent years, transcranial brain stimulation methods such as transcranial Direct Current Stimulation (tDCS have been suggested as a treatment for various neurologic and neuropsychiatric disorders. The posterior parietal cortex (PPC is known to be crucially involved in numerical magnitude processing and mental arithmetic. In this study, we evaluated whether tDCS has a beneficial effect on numerical magnitude processing and mental arithmetic. Due to the unclear lateralization, we stimulated the left, right as well as both hemispheres simultaneously in two experiments. We found that left anodal tDCS significantly enhanced performance in a number comparison and a subtraction task, while bilateral and right anodal tDCS did not induce any improvements compared to sham. Our findings demonstrate that the left PPC is causally involved in numerical magnitude processing and mental arithmetic. Furthermore, we show that these cognitive functions can be enhanced by means of tDCS. These findings encourage to further investigate the beneficial effect of tDCS in the domain of mathematics in healthy and impaired humans.
Peeters, J.; Ribbens, B.; Dirckx, J. J. J.; Steenackers, G.
2016-07-01
Little research has examined that inaccurate estimations of directional emissivity form a major challenge during both passive and active thermographic measurements. Especially with the increasing use of complex curved shapes and the growing precision of thermal cameras, these errors limit the accuracy of the thermal measurements. In this work we developed a technique to estimate the directional emissivity using updated numerical simulations. The reradiation on concave surfaces is examined by thermal imaging of a homogeneous heated curved metal and nylon test sample. We used finite element modelling to predict the reradiation of concave structures in order to calculate the parameters of an approximating formula for the emissivity dependent on the angle to the normal vector on each element. The differences between experimental and numerical results of the steel test sample are explained using electron microscopy imaging and the validation on different materials. The results suggest that it is possible to determine the errors of thermal imaging testing of complex shapes using a numerical model.
Institute of Scientific and Technical Information of China (English)
Min Wei; Limin Wang; Jinghai Li
2013-01-01
Fully resolved simulations of particulate and aggregative fluidization systems are performed successfully with the so-called combined lattice Boltzmann method and time-driven hard-sphere model (LBM-TDHS).In this method,the discrete particle phase is described by time-driven hard-sphere model,and the governing equations of the continuous fluid phase are solved with lattice Boltzmann method.Particle-fluid coupling is implemented by immersed moving boundary method.Time averaged flow structure of the simulated results show the formation of core-annulus structure and sigmoid distribution of voidage in the axial direction,which are typical phenomena in fluidization systems.Combining the results of the simulation,the energy consumption Nst for suspending and transporting solids is calculated from the direct numerical simulation (DNS) of fluidization,and the stability criterion Nst/NT =min proposed in EMMS/bubbling model is verified numerically.Furthermore the numerical results show that the value of Nst/NT in particulate fluidization is much higher than that in aggregative fluidization,but Nst/NT =min is effective for both particulate and aggregative fluidization.
Direct numerical simulation of gravity-driven avalanches immersed in a viscous fluid
Bonometti, Thomas; Izard, Edouard; Lacaze, Laurent; OTE Team
2014-11-01
This work deals with direct numerical simulations of sediment transport at the scale of O(103) grains. A soft-sphere discrete element method is coupled to an immersed boundary method in order to compute the flow around moving and colliding grains in an incompressible Newtonian fluid. A lubrication force is added for representing fluid-particles interaction near contact. The numerical method is shown to adequately reproduce the effective coefficient of restitution measured in experiments of the normal and oblique rebound of a grain on a wall. An analytical model is proposed and highlights the importance of the grain roughness and Stokes number on the rebound phenomenon. Three-dimensional configurations of gravity-driven dense granular flows in a fluid, namely the granular avalanche on an inclined plane and the collapse of a granular column, are performed. The granular flow regimes (viscous, inertial and dry) observed in experiments are identified as a function of the grain-to-fluid density ratio and the Stokes number. In particular, the simulations provide insights on the grain and fluid velocity profiles and force balance in each regime. In the second case, results agree well with experiments and the pore pressure feedback is observed for the first time in direct numerical simulations.
Numerical Prediction of a Bi-Directional Micro Thermal Flow Sensors
Directory of Open Access Journals (Sweden)
M. Al-Amayrah
2011-09-01
Full Text Available Thermal flow sensors such as hot-wire anemometer (HWA can be used to measure the flow velocity with certain accuracy. However, HWA can measure the flow velocity without determining the flow direction. Pulsed-Wire Anemometer (PWA with 3 wires can be used to measure flow velocity and flow directions. The present study aims to develop a numerical analysis of unsteady flow around a pulsed hot-wire anemometer using three parallel wires. The pulsed wire which is called the heated wire is located in the middle and the two sensor wires are installed upstream and downstream of the pulsed wire. 2-D numerical models were built and simulated using different wires arrangements. The ratio of the separation distance between the heated wire and sensor wire (x to the diameter of the heated wire (D ratios (x/D was varied between 3.33 and 183.33. The output results are plotted as a function of Peclet number (convection time / diffusion time. It was found that as the ratio of x/D increases, the sensitivity of PWA device to the time of flight decreases. But at the same the reading of the time of flight becomes more accurate, because the effects of the diffusion and wake after the heated wire decrease. Also, a very good agreement has been obtained between the present numerical simulation and the previous experimental data.
Evaluation and directions of the photovoltaic technologies
Energy Technology Data Exchange (ETDEWEB)
Kazmerski, L.L.; Emery, K.A.; DeBlasio, R. (National Renewable Energy Lab., Golden, CO (United States))
1994-08-01
The status of, directions and expectations for photovoltaic technologies are discussed and updated, with emphasis on the performances of cells and modules used in various research and commercial solar cell approaches. Current and projected research and development directions are indicated. Special aspects of the current evolution of photovoltaics from the research laboratory to the commercial arena are discussed, including new programs directed to make this energy resource a viable electricity choice for users worldwide. (Author)
Ruban, V P
2015-01-01
The nonlinear dynamics of an obliquely oriented wave packet at sea surface is studied both analytically and numerically for various initial parameters of the packet, in connection with the problem of oceanic rogue waves. In the framework of Gaussian variational ansatz applied to the corresponding (1+2D) hyperbolic nonlinear Schr\\"odinger equation, a simplified Lagrangian system of differential equations is derived, which determines the evolution of coefficients of the real and imaginary quadratic forms appearing in the Gaussian. This model provides a semi-quantitative description for the process of nonlinear spatio-temporal focusing, which is one of the most probable mechanisms of rogue wave formation in random wave fields. The system is integrated in quadratures, which fact allows us to understand qualitative differences between the linear and nonlinear regimes of the focusing of wave packet. Comparison of the Gaussian model predictions with results of direct numerical simulation of fully nonlinear long-cres...
Wang, Peitao; Cai, Meifeng; Ren, Fenhua; Li, Changhong; Yang, Tianhong
2017-07-01
This paper develops a numerical approach to determine the mechanical behavior of discrete fractures network (DFN) models based on digital image processing technique and particle flow code (PFC2D). A series of direct shear tests of jointed rocks were numerically performed to study the effect of normal stress, friction coefficient and joint bond strength on the mechanical behavior of joint rock and evaluate the influence of micro-parameters on the shear properties of jointed rocks using the proposed approach. The complete shear stress-displacement curve of the DFN model under direct shear tests was presented to evaluate the failure processes of jointed rock. The results show that the peak and residual strength are sensitive to normal stress. A higher normal stress has a greater effect on the initiation and propagation of cracks. Additionally, an increase in the bond strength ratio results in an increase in the number of both shear and normal cracks. The friction coefficient was also found to have a significant influence on the shear strength and shear cracks. Increasing in the friction coefficient resulted in the decreasing in the initiation of normal cracks. The unique contribution of this paper is the proposed modeling technique to simulate the mechanical behavior of jointed rock mass based on particle mechanics approaches.
Direct Numerical Simulation of Insoluble Surfactant Effect on Turbulent Channel Bubbly Flows
Lu, Jiacai; Tryggvason, Gretar
2016-11-01
Direct Numerical Simulations (DNS) have been successfully used to obtain detailed data for turbulent channel bubbly flows. However, most of DNS that have been done so far remain problematic in comparing to most experiments. One of the major reasons is that real bubbly flows contain surfactants. The surfactants adhere to the interface, and produce an uneven distribution of the surfactant concentration due to the moving of bubbles and result in uneven surface tension over bubble surfaces. In this project, the effect of surfactants on the flow of many bubbles in an upward turbulent channel flow is studied by using of Direct Numerical Simulation with 3D Front-tracking method. The surfactant mass and the interfacial area are directly tracked in the method, and the surfactant mass remains conserved during the evolution. By using of different elasticity numbers in the non-linear equation of state which relates the surface tension to the surfactant concentration, the simulations show that the evolution of the turbulent channel bubbly flow are much different among the cases with contaminated bubbles and clean bubbles. Profiles of many parameters, such as streamwise velocity, shear stress and etc., are also compared at the statistically steady state for these cases. Research supported by DOE (CASL).
A Numerical Implementation of a Nonlinear Mild Slope Model for Shoaling Directional Waves
Directory of Open Access Journals (Sweden)
Justin R. Davis
2014-02-01
Full Text Available We describe the numerical implementation of a phase-resolving, nonlinear spectral model for shoaling directional waves over a mild sloping beach with straight parallel isobaths. The model accounts for non-linear, quadratic (triad wave interactions as well as shoaling and refraction. The model integrates the coupled, nonlinear hyperbolic evolution equations that describe the transformation of the complex Fourier amplitudes of the deep-water directional wave field. Because typical directional wave spectra (observed or produced by deep-water forecasting models such as WAVEWATCH III™ do not contain phase information, individual realizations are generated by associating a random phase to each Fourier mode. The approach provides a natural extension to the deep-water spectral wave models, and has the advantage of fully describing the shoaling wave stochastic process, i.e., the evolution of both the variance and higher order statistics (phase correlations, the latter related to the evolution of the wave shape. The numerical implementation (a Fortran 95/2003 code includes unidirectional (shore-perpendicular propagation as a special case. Interoperability, both with post-processing programs (e.g., MATLAB/Tecplot 360 and future model coupling (e.g., offshore wave conditions from WAVEWATCH III™, is promoted by using NetCDF-4/HD5 formatted output files. The capabilities of the model are demonstrated using a JONSWAP spectrum with a cos2s directional distribution, for shore-perpendicular and oblique propagation. The simulated wave transformation under combined shoaling, refraction and nonlinear interactions shows the expected generation of directional harmonics of the spectral peak and of infragravity (frequency <0.05 Hz waves. Current development efforts focus on analytic testing, development of additional physics modules essential for applications and validation with laboratory and field observations.
Direct Numerical Simulation of Incompressible Pipe Flow Using a B-Spline Spectral Method
Loulou, Patrick; Moser, Robert D.; Mansour, Nagi N.; Cantwell, Brian J.
1997-01-01
A numerical method based on b-spline polynomials was developed to study incompressible flows in cylindrical geometries. A b-spline method has the advantages of possessing spectral accuracy and the flexibility of standard finite element methods. Using this method it was possible to ensure regularity of the solution near the origin, i.e. smoothness and boundedness. Because b-splines have compact support, it is also possible to remove b-splines near the center to alleviate the constraint placed on the time step by an overly fine grid. Using the natural periodicity in the azimuthal direction and approximating the streamwise direction as periodic, so-called time evolving flow, greatly reduced the cost and complexity of the computations. A direct numerical simulation of pipe flow was carried out using the method described above at a Reynolds number of 5600 based on diameter and bulk velocity. General knowledge of pipe flow and the availability of experimental measurements make pipe flow the ideal test case with which to validate the numerical method. Results indicated that high flatness levels of the radial component of velocity in the near wall region are physical; regions of high radial velocity were detected and appear to be related to high speed streaks in the boundary layer. Budgets of Reynolds stress transport equations showed close similarity with those of channel flow. However contrary to channel flow, the log layer of pipe flow is not homogeneous for the present Reynolds number. A topological method based on a classification of the invariants of the velocity gradient tensor was used. Plotting iso-surfaces of the discriminant of the invariants proved to be a good method for identifying vortical eddies in the flow field.
Che, Xiao-Hua; Qiao, Wen-Xiao; Ju, Xiao-Dong; Wang, Rui-Jia
2016-03-01
We developed a novel cement evaluation logging tool, named the azimuthally acoustic bond tool (AABT), which uses a phased-arc array transmitter with azimuthal detection capability. We combined numerical simulations and field tests to verify the AABT tool. The numerical simulation results showed that the radiation direction of the subarray corresponding to the maximum amplitude of the first arrival matches the azimuth of the channeling when it is behind the casing. With larger channeling size in the circumferential direction, the amplitude difference of the casing wave at different azimuths becomes more evident. The test results showed that the AABT can accurately locate the casing collars and evaluate the cement bond quality with azimuthal resolution at the casing—cement interface, and can visualize the size, depth, and azimuth of channeling. In the case of good casing—cement bonding, the AABT can further evaluate the cement bond quality at the cement—formation interface with azimuthal resolution by using the amplitude map and the velocity of the formation wave.
Direct drive ablation front stability: numerical predictions against flame front model
Energy Technology Data Exchange (ETDEWEB)
Masse, L. [Phd Student at IRPHE St Jerome, 13 - Marseille (France)]|[CEA/DAM-Ile de France, 91 - Bruyeres Le Chatel (France); Hallo, L.; Tallot, C. [CEA/DAM-Ile de France, 91 - Bruyeres Le Chatel (France)
2000-07-01
We study the linear stability of flows resulting from constant heating of planar targets by a laser. In the coordinate system of the ablation front there is a flow from the cold to hot region, which is situated in a gravity field oriented from hot to cold region. Similar types of flow can be observed in combustion systems, which involve propagation of flame fronts. A spectral model which studies linear perturbation is directly taken from the combustion community. Here we present the results for state as well as perturbed flows. Growth rate determined from the models are compared to each other, and preliminary numerical results from FC12 simulations are shown. (authors)
Perlekar, Prasad; Pandit, Rahul
2010-01-01
We carry out a direct numerical simulation (DNS) study that reveals the effects of polymers on statistically steady, forced, homogeneous, isotropic fluid turbulence. We find clear manifestations of dissipation-reduction phenomena: On the addition of polymers to the turbulent fluid, we obtain a reduction in the energy dissipation rate, a significant modification of the fluid energy spectrum, especially in the deep-dissipation range, a suppression of small-scale intermittency, and a decrease in small-scale vorticity filaments. We also compare our results with recent experiments and earlier DNS studies of decaying fluid turbulence with polymer additives.
Testing of Subgrid—Scale Stress Models by Using Results from Direct Numerical SImulations
Institute of Scientific and Technical Information of China (English)
HongruiGONG
1998-01-01
The most commonly used dynamic subgrid models,Germano's model and dynamic kinetic energy model,and their base models-the Smagorinsky model and the kinetic energy model,were tested using results from direct numerical simulations of various turbulent flows.In germano's dynamic model,the model coefficient was treated as a constant within the test filter,This treatment is conceptually inconsistent.An iteration procedure was proposed to calculate the model coefficient and an improved correlation coefficient was found.
Institute of Scientific and Technical Information of China (English)
Zhi-yue Zhang
2002-01-01
Both numerical simulation and theoretical analysis of seawater intrusion in coastal regions are of great theoretical importance in environmental sciences. The mathematical model can be described as a coupled system of three dimensional nonlinear partial differential equations with initial-boundary value problems. In this paper, according to the actual conditions of molecular and three-dimensional characteristic of the problem,we construct the characteristic finite element alternating-direction schemes which can be divided into three continuous one-dimensional problems. By making use of tensor product algorithm, and priori estimation theory and techniques, the optimal order estimates in H1 norm are derived for the error in the approximate solution.
Evaluation of energy roof direct utilization
Energy Technology Data Exchange (ETDEWEB)
Lazzarin, R.; Rossetto, L.; Viero, L.
1984-04-01
Energy roofs are roofing systems equipped with channels which allow both solar and atmospheric energy collection. They were conceived as cold source for heat pump systems. The behavious of an energy roof in DHW direct heating was studied; this might extend energy roof utilization all year long. The estimates were performed through more reliable recently proposed correlations for wind convection heat transfer coefficients. The advantage of annual energy roof utilization in DHW direct heating is predictable.
A high-order public domain code for direct numerical simulations of turbulent combustion
Babkovskaia, N; Brandenburg, A
2010-01-01
A high-order scheme for direct numerical simulations of turbulent combustion is discussed. Its implementation in the massively parallel and publicly available Pencil Code is validated with the focus on hydrogen combustion. Ignition delay times (0D) and laminar flame velocities (1D) are calculated and compared with results from the commercially available Chemkin code. The scheme is verified to be fifth order in space. Upon doubling the resolution, a 32-fold increase in the accuracy of the flame front is demonstrated. Finally, also turbulent and spherical flame front velocities are calculated and the implementation of the non-reflecting so-called Navier-Stokes Characteristic Boundary Condition is validated in all three directions.
Direct numerical simulation of particle-fluid flows in turbulent mixing layer
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
The coherent structures of a three-dimensional temporally mixing layer and the associated dispersion patterns of particles are numerically studied using a pseudospectral method for fluid and the Lagrangian approach for tracing particles at different Stokes numbers without consideration of particle-particle interactions. The results show that the particles with Stokes number of the order of unity have the largest concentration near the outer edges of the large-scale spanwise vortex structures. The study validates the effect of the streamwise large-scale structures on the particle distribution along the spanwise and transverse directions and it enhances with the development of the three-dimensionality of the mixing layer, which results in a ‘mushroom’ shape of the particle distribution in the spanwise direction.
Directory of Open Access Journals (Sweden)
W. Kapturkiewicz
2008-12-01
Full Text Available The, developed in this study, simple model and numerical solution of diffusion growth of the solid phase under the conditions of directional solidification allow for the effect of constituent diffusion in both liquid and solid phase and assume the process run in which (like in reality the preset parameter is the velocity of sample (pulling velocity at a preset temperature gradient. The solid/liquid interface velocity is not the process parameter (like it is in numerous other solutions proposed so far but a function of this process. The effect of convection outside the diffusion layer has been included in mass balance under the assumption that in the zone of convection the mixing is complete. The above assumptions enabled solving the kinetics of growth of the solid phase (along with the diffusion field in solid and liquid phase under the conditions of diffusion well reflecting the process run starting with the initial transient state, going through the steady state period in central part of the casting, and ending in a terminal transient state. In the numerical solution obtained by the finite difference method with variable grid dimensions, the error of the mass control balance over the whole process range was 1 - 2 %.
Krygier, Michael; Grigoriev, Roman
2015-11-01
A direct transition from laminar to turbulent flow has recently been discovered experimentally in the small-gap Taylor-Couette flow with counter-rotating cylinders. The subcritical nature of this transition is a result of relatively small aspect ratio, Γ = 5 . 26 for large Γ the transition is supercritical and involves an intermediate stable state (Coughlin & Marcus, 1996) - interpenetrating spirals (IPS). We investigate this transition numerically to probe the dynamics in regimes inaccessible to experiments for a fixed Reo = - 1000 by varying Rei . The numerics reproduce all the experimentally observed features and confirm the hysteretic nature of the transition. As Rei is increased, the laminar flow transitions to turbulence, with an unstable IPS state mediating the transition, similar to the Tollmien-Schlichting waves in plane Poiseuille flow. As Rei is decreased, turbulent flow transitions to a stable, temporally chaotic IPS state. This IPS state further transitions to either laminar or turbulent flow as Rei is decreased or increased. The stable IPS state is reminiscent of the pre-turbulent chaotic states found numerically in plane Poiseuille flow (Zammert & Eckhardt, 2015), but previously never observed experimentally.
Pyszczek, R.; Mazuro, P.; Teodorczyk, A.
2016-09-01
This paper is focused on the CAI combustion control in a turbocharged 2-stroke Opposed-Piston (OP) engine. The barrel type OP engine arrangement is of particular interest for the authors because of its robust design, high mechanical efficiency and relatively easy incorporation of a Variable Compression Ratio (VCR). The other advantage of such design is that combustion chamber is formed between two moving pistons - there is no additional cylinder head to be cooled which directly results in an increased thermal efficiency. Furthermore, engine operation in a Controlled Auto-Ignition (CAI) mode at high compression ratios (CR) raises a possibility of reaching even higher efficiencies and very low emissions. In order to control CAI combustion such measures as VCR and water injection were considered for indirect ignition timing control. Numerical simulations of the scavenging and combustion processes were performed with the 3D CFD multipurpose AVL Fire solver. Numerous cases were calculated with different engine compression ratios and different amounts of directly and indirectly injected water. The influence of the VCR and water injection on the ignition timing and engine performance was determined and their application in the real engine was discussed.
Temporal, M.; Canaud, B.; Laffite, S.; Le Garrec, B. J.; Murakami, M.
2010-11-01
In the Inertial Confinement Fusion the uniformity of the irradiation still represents a crucial issue. In this context a spherical capsule directly driven by laser beams have been assessed numerically [1]. Two schemes characterized by 32 and 48 directions of irradiation [2] with associated a single laser beam or a bundle of laser beams [3] characterized by a super-Gaussian intensity profile are considered. Beam imperfections as power imbalance and pointing errors have been taken into account. It is found that the focal spot that minimizes the rms deviation depends on the beam imperfections [4]. The numerical calculations show that the uniformity of the irradiation evolves in time. The results calculated considering the illumination of a spherical target will be compared with those obtained when the irradiation is taken into account. [1] M. Temporal, B. Canaud. Eur. Phys. J. D 55 139 (2009). [2] M. Murakami, N. Sarukura, H. Azechi, M. Temporal, A.J. Schmitt, in press to Phys. Plasmas (July issue, 2010). [3] M. Temporal, B. Canaud, B. J. Le Garrec, Phys. Plasmas 17 022701 (2010). [4] M. Temporal, B. Canaud, S. Laffite, B.J. Le Garrec, M. Murakami. Phys. Plasmas 17 064504 (2010).
Direct Numerical Simulation of an Airfoil with Sand Grain Roughness on the Leading Edge
Ribeiro, Andre F. P.; Casalino, Damiano; Fares, Ehab; Choudhari, Meelan
2016-01-01
As part of a computational study of acoustic radiation due to the passage of turbulent boundary layer eddies over the trailing edge of an airfoil, the Lattice-Boltzmann method is used to perform direct numerical simulations of compressible, low Mach number flow past an NACA 0012 airfoil at zero degrees angle of attack. The chord Reynolds number of approximately 0.657 million models one of the test conditions from a previous experiment by Brooks, Pope, and Marcolini at NASA Langley Research Center. A unique feature of these simulations involves direct modeling of the sand grain roughness on the leading edge, which was used in the abovementioned experiment to trip the boundary layer to fully turbulent flow. This report documents the findings of preliminary, proof-of-concept simulations based on a narrow spanwise domain and a limited time interval. The inclusion of fully-resolved leading edge roughness in this simulation leads to significantly earlier transition than that in the absence of any roughness. The simulation data is used in conjunction with both the Ffowcs Williams-Hawkings acoustic analogy and a semi-analytical model by Roger and Moreau to predict the farfield noise. The encouraging agreement between the computed noise spectrum and that measured in the experiment indicates the potential payoff from a full-fledged numerical investigation based on the current approach. Analysis of the computed data is used to identify the required improvements to the preliminary simulations described herein.
Inflow conditions for spatial direct numerical simulation of turbulent boundary layers
Institute of Scientific and Technical Information of China (English)
2008-01-01
The inflow conditions for spatial direct numerical simulation(SDNS) of turbulent boundary layers should reflect the characteristics of upstream turbulence,which is a puzzle. In this paper a new method is suggested,in which the flow field obtained by using temporal direct numerical simulation(TDNS) for fully developed turbulent flow(only flow field for a single moment is sufficient) can be used as the inflow of SDNS with a proper transformation. The calculation results confirm that this method is feasible and effective. It is also found that,under a proper time-space transformation,all statistics of the fully developed turbulence obtained by both temporal mode and spatial mode DNS are in excellent agreement with each other,not only qualitatively,but also quantitatively. The normal-wise distributions of mean flow profile,turbulent Mach number and the root mean square(RMS) of the fluctuations of various variables,as well as the Reynolds stresses of the fully developed turbulence obtained by using SDNS,bear similarity in nature.
Energy Technology Data Exchange (ETDEWEB)
Velazquez, N.; Sauceda, D.; Beltran, R. [Instituto de Ingenieria, Universidad Autonoma de Baja California, Blvd. Benito Juarez y Calle de la Normal s/n, Mexicali, Baja California 21280 (Mexico); Garcia-Valladares, O. [Centro de Investigacion en Energia, Universidad Nacional Autonoma de Mexico, Privada Xochicalco s/n, Temixco, Morelos 62580 (Mexico)
2010-03-15
In this work a methodological analysis to design and evaluate the technical feasibility of use a Linear Fresnel Reflector Concentrator (LFRC) as generator in an advanced absorption refrigeration system (Solar-GAX cycle) has been carried out. For this purpose, a detailed one-dimensional numerical simulation of the thermal and fluid-dynamic behavior of a LFRC that solves, in a segregated manner, four subroutines: (a) fluid flow inside the receptor tube, (b) heat transfer in the receptor tube wall, (c) heat transfer in cover tube wall, and (d) solar thermal analysis in the solar concentrator has been developed. The LFRC numerical model has been validated with experimental data obtained from the technical literature; after that, a parametric study for different configurations of design has been carried out in order to obtain the highest solar concentration with the lowest thermal losses, keeping in mind both specific weather conditions and construction restrictions. The numerical result obtained demonstrates that using a LFRC as a direct generator in a Solar-GAX cycle satisfy not only the quantity and quality of the energy demanded by the advanced cooling system, it also allows to obtain higher global efficiencies of the system due to it can be operated in conditions where the maximum performance of the Solar-GAX cycle is obtained without affecting in any significant way the solar collector efficiency. (author)
Wetting of anisotropic sinusoidal surfaces—experimental and numerical study of directional spreading
Fischer, G.; Bigerelle, M.; Kubiak, K. J.; Mathia, T. G.; Khatir, Z.; Anselme, K.
2014-10-01
Directional wettability, i.e. the variation of wetting properties, depending on the surface orientation, can be achieved by anisotropic surface texturing. A new high-precision process can produce homogeneous sinusoidal surfaces (in particular, parallel grooves) at the microscale, with a nanoscale residual roughness five orders of magnitude smaller than the texture features. Static wetting experiments have shown that this pattern, even with a very small aspect ratio, can induce a strong variation of the contact angle, depending on the direction of the observation. A comparison with numerical simulations (using Surface Evolver software) shows good agreement and could be used to predict fluid-solid interaction and droplet behaviour on textured surfaces. Two primary mechanisms of directional spreading of water droplets on textured stainless steel surface have been identified. The first one is the mechanical barrier created by the textured surface peaks; this limits spreading in a perpendicular direction to the surface anisotropy. The second one is the capillary action inside of the sinusoidal grooves, which accelerates spreading along the grooves. Spreading has been shown to depend strongly on the history of wetting and internal drop dynamics.
Direct imaging of turbid media using long-time back-scattered photons, a numerical study
Energy Technology Data Exchange (ETDEWEB)
Boulanger, Joan; Liu, Fengshan [Groupe de Recherche en Ingenierie des Procedes et Systemes, Departement des Sciences Appliquees, Universite du Quebec a Chicoutimi, 555 Boulevard de l' Universite, Chicoutimi, PQ, G7H 2B1 (Canada); El Akel, Azad; Charette, Andre [Technologie de la Combustion, Institut de Technologie des Procedes Chimiques et de l' Environnement, Conseil National de Recherche du Canada, 1200 Chemin de Montreal, Ottawa, ON, K1A 0R6 (Canada)
2006-06-15
Direct imaging is a convenient way to obtain information on the interior of a semi-transparent turbid material by non-invasive probing using laser beams. The major difficulty is linked to scattering which scrambles the directional information coming from the laser beam. It is found in this paper that the long-term multiple-scattered reflected photons may provide structural information on the inside of a material, which offers an interesting alternative to using information only from un-scattered or least-scattered photons as obtained from current direct imaging set-ups for thin media. Based on some observations on a non-homogeneous three layered 1-D slab irradiated by a laser pulse, a direct probing methodology making use of the long-term back-scattered photons is illustrated to recover inclusions positions in a turbid 2-D medium. First, the numerical model is presented. Second, an extended parametrical study is conducted on 1-D homogeneous and non-homogeneous slabs with different laser pulse durations. It is found that the reflected asymptotic logarithmic slope carries information about the presence of the inclusion and that short laser pulses are not necessary since only the decaying parts of the remanent optical signature is important. Longer laser pulses allow a higher level of energy injection and signal to noise ratio. Third, those observations are used for the probing of a 2-D non-homogeneous phantom. (author)
Annenkov, Sergei; Shrira, Victor
2016-04-01
We study numerically the long-term evolution of water wave spectra without wind forcing, using three different models, aiming at understanding the role of different sets of assumptions. The first model is the classical Hasselmann kinetic equation (KE). We employ the WRT code kindly provided by G. van Vledder. Two other models are new. As the second model, we use the generalised kinetic equation (gKE), derived without the assumption of quasi-stationarity. Thus, unlike the KE, the gKE is valid in the cases when a wave spectrum is changing rapidly (e.g. at the initial stage of evolution of a narrow spectrum). However, the gKE employs the same statistical closure as the KE. The third model is based on the Zakharov integrodifferential equation for water waves and does not depend on any statistical assumptions. Since the Zakharov equation plays the role of the primitive equation of the theory of wave turbulence, we refer to this model as direct numerical simulation of spectral evolution (DNS-ZE). For initial conditions, we choose two narrow-banded spectra with the same frequency distribution (a JONSWAP spectrum with high peakedness γ = 6) and different degrees of directionality. These spectra are from the set of observations collected in a directional wave tank by Onorato et al (2009). Spectrum A is very narrow in angle (corresponding to N = 840 in the cosN directional model). Spectrum B is initially wider in angle (corresponds to N = 24). Short-term evolution of both spectra (O(102) wave periods) has been studied numerically by Xiao et al (2013) using two other approaches (broad-band modified nonlinear Schrödinger equation and direct numerical simulation based on the high-order spectral method). We use these results to verify the initial stage of our DNS-ZE simulations. However, the advantage of the DNS-ZE method is that it allows to study long-term spectral evolution (up to O(104) periods), which was previously possible only with the KE. In the short-term evolution
Directional Diffusion Regulator (DDR) for some numerical solvers of hyperbolic conservation laws
Jaisankar, S.; Sheshadri, T. S.
2013-01-01
A computational tool called "Directional Diffusion Regulator (DDR)" is proposed to bring forth real multidimensional physics into the upwind discretization in some numerical schemes of hyperbolic conservation laws. The direction based regulator when used with dimension splitting solvers, is set to moderate the excess multidimensional diffusion and hence cause genuine multidimensional upwinding like effect. The basic idea of this regulator driven method is to retain a full upwind scheme across local discontinuities, with the upwind bias decreasing smoothly to a minimum in the farthest direction. The discontinuous solutions are quantified as gradients and the regulator parameter across a typical finite volume interface or a finite difference interpolation point is formulated based on fractional local maximum gradient in any of the weak solution flow variables (say density, pressure, temperature, Mach number or even wave velocity etc.). DDR is applied to both the non-convective as well as whole unsplit dissipative flux terms of some numerical schemes, mainly of Local Lax-Friedrichs, to solve some benchmark problems describing inviscid compressible flow, shallow water dynamics and magneto-hydrodynamics. The first order solutions consistently improved depending on the extent of grid non-alignment to discontinuities, with the major influence due to regulation of non-convective diffusion. The application is also experimented on schemes such as Roe, Jameson-Schmidt-Turkel and some second order accurate methods. The consistent improvement in accuracy either at moderate or marked levels, for a variety of problems and with increasing grid size, reasonably indicate a scope for DDR as a regular tool to impart genuine multidimensional upwinding effect in a simpler framework.
Lee, David; Ge, Yi; Cha, Soyoung Stephen; Ramachandran, Narayanan; Rose, M. Franklin (Technical Monitor)
2001-01-01
Measurement of three-dimensional (3-D) three-component velocity fields is of great importance in both ground and space experiments for understanding materials processing and fluid physics. The experiments in these fields most likely inhibit the application of conventional planar probes for observing 3-D phenomena. Here, we present the investigation results of stereoscopic tracking velocimetry (STV) for measuring 3-D velocity fields, which include diagnostic technology development, experimental velocity measurement, and comparison with analytical and numerical computation. STV is advantageous in system simplicity for building compact hardware and in software efficiency for continual near-real-time monitoring. It has great freedom in illuminating and observing volumetric fields from arbitrary directions. STV is based on stereoscopic observation of particles-Seeded in a flow by CCD sensors. In the approach, part of the individual particle images that provide data points is likely to be lost or cause errors when their images overlap and crisscross each other especially under a high particle density. In order to maximize the valid recovery of data points, neural networks are implemented for these two important processes. For the step of particle overlap decomposition, the back propagation neural network is utilized because of its ability in pattern recognition with pertinent particle image feature parameters. For the step of particle tracking, the Hopfield neural network is employed to find appropriate particle tracks based on global optimization. Our investigation indicates that the neural networks are very efficient and useful for stereoscopically tracking particles. As an initial assessment of the diagnostic technology performance, laminar water jets with and without pulsation are measured. The jet tip velocity profiles are in good agreement with analytical predictions. Finally, for testing in material processing applications, a simple directional solidification
Directory of Open Access Journals (Sweden)
E. Rajabi
2014-01-01
Full Text Available In this research a direct numerical simulation (DNS of turbulent flow is performed in a geometrically standard case like plane channel flow. Pseudo spectral (PS method is used due to geometry specifications and very high accuracy achieved despite relatively few grid points. A variable time-stepping algorithm is proposed which may reduce requirement of computational cost in simulation of such wall-bounded flow. Channel flow analysis is performed with both constant and varied time-step for 128 × 65×128 grid points. The time advancement is carried out by implicit third-order backward differentiation scheme for linear terms and explicit forward Euler for nonlinear convection term. PS method is used in Cartesian coordinates with Chebychev polynomial expansion in normal direction for one non-periodic boundary condition. Also Fourier series is employed in stream-wise and span-wise directions for two periodic boundary conditions. The friction Reynolds number is about Reτ=175 based on a friction velocity and channel half width. Standard common rotational form was chosen for discritization of nonlinear convective term of Navier-Stocks equation. The comparison is made between turbulent quantities such as the turbulent statistics, Reynolds stress, wall shear velocity, standard deviation of (u and total normalized energy of instantaneous velocities in both time-discretization methods. The results show that if final decision rests on economics, the proposed variable time-stepping algorithm will be proper choice which satisfies the accuracy and reduces the computational cost.
A parallel direct numerical simulation of dust particles in a turbulent flow
Nguyen, H. V.; Yokota, R.; Stenchikov, G.; Kocurek, G.
2012-04-01
Due to their effects on radiation transport, aerosols play an important role in the global climate. Mineral dust aerosol is a predominant natural aerosol in the desert and semi-desert regions of the Middle East and North Africa (MENA). The Arabian Peninsula is one of the three predominant source regions on the planet "exporting" dust to almost the entire world. Mineral dust aerosols make up about 50% of the tropospheric aerosol mass and therefore produces a significant impact on the Earth's climate and the atmospheric environment, especially in the MENA region that is characterized by frequent dust storms and large aerosol generation. Understanding the mechanisms of dust emission, transport and deposition is therefore essential for correctly representing dust in numerical climate prediction. In this study we present results of numerical simulations of dust particles in a turbulent flow to study the interaction between dust and the atmosphere. Homogenous and passive dust particles in the boundary layers are entrained and advected under the influence of a turbulent flow. Currently no interactions between particles are included. Turbulence is resolved through direct numerical simulation using a parallel incompressible Navier-Stokes flow solver. Model output provides information on particle trajectories, turbulent transport of dust and effects of gravity on dust motion, which will be used to compare with the wind tunnel experiments at University of Texas at Austin. Results of testing of parallel efficiency and scalability is provided. Future versions of the model will include air-particle momentum exchanges, varying particle sizes and saltation effect. The results will be used for interpreting wind tunnel and field experiments and for improvement of dust generation parameterizations in meteorological models.
Investigation of the Dynamic Contact Angle Using a Direct Numerical Simulation Method.
Zhu, Guangpu; Yao, Jun; Zhang, Lei; Sun, Hai; Li, Aifen; Shams, Bilal
2016-11-15
A large amount of residual oil, which exists as isolated oil slugs, remains trapped in reservoirs after water flooding. Numerous numerical studies are performed to investigate the fundamental flow mechanism of oil slugs to improve flooding efficiency. Dynamic contact angle models are usually introduced to simulate an accurate contact angle and meniscus displacement of oil slugs under a high capillary number. Nevertheless, in the oil slug flow simulation process, it is unnecessary to introduce the dynamic contact angle model because of a negligible change in the meniscus displacement after using the dynamic contact angle model when the capillary number is small. Therefore, a critical capillary number should be introduced to judge whether the dynamic contact model should be incorporated into simulations. In this study, a direct numerical simulation method is employed to simulate the oil slug flow in a capillary tube at the pore scale. The position of the interface between water and the oil slug is determined using the phase-field method. The capacity and accuracy of the model are validated using a classical benchmark: a dynamic capillary filling process. Then, different dynamic contact angle models and the factors that affect the dynamic contact angle are analyzed. The meniscus displacements of oil slugs with a dynamic contact angle and a static contact angle (SCA) are obtained during simulations, and the relative error between them is calculated automatically. The relative error limit has been defined to be 5%, beyond which the dynamic contact angle model needs to be incorporated into the simulation to approach the realistic displacement. Thus, the desired critical capillary number can be determined. A three-dimensional universal chart of critical capillary number, which functions as static contact angle and viscosity ratio, is given to provide a guideline for oil slug simulation. Also, a fitting formula is presented for ease of use.
Direct numerical simulations of on-demand vortex generators: Mathematical formulation
Koumoutsakos, Petros
1994-01-01
The objective of the present research is the development and application of efficient adaptive numerical algorithms for the study, via direct numerical simulations, of active vortex generators. We are using innovative computational schemes to investigate flows past complex configurations undergoing arbitrary motions. Some of the questions we try to answer are: Can and how may we control the dynamics of the wake? What is the importance of body shape and motion in the active control of the flow? What is the effect of three-dimensionality in laboratory experiments? We are interested not only in coupling our results to ongoing, related experimental work, but furthermore to develop an extensive database relating the above mechanisms to the vortical wake structures with the long-range objective of developing feedback control mechanisms. This technology is very important to aircraft, ship, automotive, and other industries that require predictive capability for fluid mechanical problems. The results would have an impact in high angle of attack aerodynamics and help design ways to improve the efficiency of ships and submarines (maneuverability, vortex induced vibration, and noise).
Influence of lubrication forces in direct numerical simulations of particle-laden flows
Maitri, Rohit; Peters, Frank; Padding, Johan; Kuipers, Hans
2016-11-01
Accurate numerical representation of particle-laden flows is important for fundamental understanding and optimizing the complex processes such as proppant transport in fracking. Liquid-solid flows are fundamentally different from gas-solid flows because of lower density ratios (solid to fluid) and non-negligible lubrication forces. In this interface resolved model, fluid-solid coupling is achieved by incorporating the no-slip boundary condition implicitly at particle's surfaces by means of an efficient second order ghost-cell immersed boundary method. A fixed Eulerian grid is used for solving the Navier-Stokes equations and the particle-particle interactions are implemented using the soft sphere collision and sub-grid scale lubrication model. Due to the range of influence of lubrication force on a smaller scale than the grid size, it is important to implement the lubrication model accurately. In this work, different implementations of the lubrication model on particle dynamics are studied for various flow conditions. The effect of a particle surface roughness on lubrication force and the particle transport is also investigated. This study is aimed at developing a validated methodology to incorporate lubrication models in direct numerical simulation of particle laden flows. This research is supported from Grant 13CSER014 of the Foundation for Fundamental Research on Matter (FOM), which is part of the Netherlands Organisation for Scientific Research (NWO).
Energy Technology Data Exchange (ETDEWEB)
Lu, Tianfeng [Univ. of Connecticut, Storrs, CT (United States)
2017-02-16
The goal of the proposed research is to create computational flame diagnostics (CFLD) that are rigorous numerical algorithms for systematic detection of critical flame features, such as ignition, extinction, and premixed and non-premixed flamelets, and to understand the underlying physicochemical processes controlling limit flame phenomena, flame stabilization, turbulence-chemistry interactions and pollutant emissions etc. The goal has been accomplished through an integrated effort on mechanism reduction, direct numerical simulations (DNS) of flames at engine conditions and a variety of turbulent flames with transport fuels, computational diagnostics, turbulence modeling, and DNS data mining and data reduction. The computational diagnostics are primarily based on the chemical explosive mode analysis (CEMA) and a recently developed bifurcation analysis using datasets from first-principle simulations of 0-D reactors, 1-D laminar flames, and 2-D and 3-D DNS (collaboration with J.H. Chen and S. Som at Argonne, and C.S. Yoo at UNIST). Non-stiff reduced mechanisms for transportation fuels amenable for 3-D DNS are developed through graph-based methods and timescale analysis. The flame structures, stabilization mechanisms, local ignition and extinction etc., and the rate controlling chemical processes are unambiguously identified through CFLD. CEMA is further employed to segment complex turbulent flames based on the critical flame features, such as premixed reaction fronts, and to enable zone-adaptive turbulent combustion modeling.
Direct numerical simulation of heat transfer in a spatially developing turbulent boundary layer
Li, Dong; Luo, Kun; Fan, Jianren
2016-10-01
Direct numerical simulation has been performed to investigate heat transfer in a zero-pressure-gradient spatially developing turbulent boundary layer with realistic thermal inflow boundary conditions. The temperature is considered as a passive scalar and the molecular Prandtl number is set to be 0.71. The turbulence statistics for both the velocity and temperature fields show good agreement with previous numerical and experimental data in the literature. The present study provides a valuable database for the spatially developing turbulent thermal boundary layer over a wide range of Reynolds numbers from Reθ = 1100 to 1940. The simulation results indicate that both the peak value and peak location of the streamwise velocity fluctuation grow slightly with increasing Reynolds number, same as those of the temperature fluctuation. The relationship between the streamwise velocity and temperature fluctuations has been examined and a strong correlation is observed in the vicinity of the wall. With increasing distance from the wall, however, the degree of correlation significantly decreases. In addition, the difference between the turbulent velocity and temperature fields is also analysed by investigating the mechanisms of heat and momentum transport in boundary layer flow.
Experimentation and direct numerical simulation of self-similar convergent detonation wave
Directory of Open Access Journals (Sweden)
Bozier O.
2011-01-01
Full Text Available The propagation of self similar convergent detonation wave in TATB-based explosive composition was studied both experimentally and numerically. The device constists in a 50 mm cylinder of TATB surrounded by an HMX tube. The detonation in HMX overdrives the detonation in TATB which adapts to the propagation velocity with a convergent front at centerline. We measured a curvature of κ = −21.2 m−1 for propagation velocity of 8750 m/s, which extends the knowledge of the (Dn,κ law. A wide ranged EOS/reaction rate model inspired from previous work of Wescott et al. was calibrated to reproduce both the run-to-detonation distance and the newly extended (Dn,κ law for the 1D sligthly curved detonation theory. 2D Direct Numerical Simulations (DNS were made on fine resolved mesh grid for the experimental configuration and for various driver velocities. The simulation reproduces the experimental data both qualitatively (overall detonation structure and quantitatively (κ = −25.4 m−1.
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Ruban, V. P., E-mail: ruban@itp.ac.ru [Russian Academy of Sciences, Landau Institute for Theoretical Physics (Russian Federation)
2015-05-15
The nonlinear dynamics of an obliquely oriented wave packet on a sea surface is analyzed analytically and numerically for various initial parameters of the packet in relation to the problem of the so-called rogue waves. Within the Gaussian variational ansatz applied to the corresponding (1+2)-dimensional hyperbolic nonlinear Schrödinger equation (NLSE), a simplified Lagrangian system of differential equations is derived that describes the evolution of the coefficients of the real and imaginary quadratic forms appearing in the Gaussian. This model provides a semi-quantitative description of the process of nonlinear spatiotemporal focusing, which is one of the most probable mechanisms of rogue wave formation in random wave fields. The system of equations is integrated in quadratures, which allows one to better understand the qualitative differences between linear and nonlinear focusing regimes of a wave packet. Predictions of the Gaussian model are compared with the results of direct numerical simulation of fully nonlinear long-crested waves.
Chan, Leon; MacDonald, Michael; Chung, Daniel; Hutchins, Nicholas; Ooi, Andrew
2014-11-01
Direct Numerical Simulations (DNS) are conducted at low to medium Reynolds numbers for a turbulent pipe flow with roughness. The roughness, which is comprised of three-dimensional sinusoidal elements, causes a downward shift in the mean velocity profile known as the Hama roughness function ΔU+ . In engineering applications, ΔU+ (which is related to the coefficient of drag Cf) is an important parameter as it is used to quantify the increase in drag and the decrease in efficiency. To have a better understanding of roughness and how it affects the flow, a range of numerical studies were conducted where the roughness height h+, wavelength λ+ and Reynolds number of the flow are varied. For the range of cases simulated, it is found that the roughness average height ka+ (which is proportional to h+) is strongly correlated to the roughness function ΔU+ whereas λ+ has a weaker influence on the flow. Results from simulations of more complicated surfaces comprised of two superimposed modes of different wavelength are also presented. Analysis of the turbulence statistics convincingly supports Townsend's outer-layer hypothesis for all of the cases simulated.
Direct numerical simulation of a small Atwood number Rayleigh-Taylor instability-driven mixing layer
Mueschke, Nicholas; Schilling, Oleg; Andrews, Malcolm
2005-11-01
A direct numerical simulation (DNS) of a small Atwood number Rayleigh-Taylor mixing layer was performed using a spectral/compact-difference scheme. The initial conditions were parameterized from interfacial and velocity perturbations measured from water channel experiments at Texas A&M University. Turbulence and mixing statistics, as well as energy spectra, obtained from experimental measurements are compared with those from the DNS to validate the use of experimental measurements as computational initial conditions. The experimental and numerical data are used to examine the transitional dynamics of the mixing layer. The DNS results indicate that initial conditions including both interfacial and velocity perturbations are required to accurately simulate the flow. This research was sponsored by the U.S. DOE National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Research Grant #DE-FG03- 02NA00060. This work was also performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W- 7405-Eng-48. UCRL-ABS-214352.
Huang, Junji; Duan, Lian; Choudhari, Meelan M.
2017-01-01
The acoustic radiation from the turbulent boundary layer on the nozzle wall of a Mach 6 Ludwieg Tube is simulated using Direct Numerical Simulations (DNS), with the flow conditions falling within the operational range of the Mach 6 Hypersonic Ludwieg Tube, Braunschweig (HLB). The mean and turbulence statistics of the nozzle-wall boundary layer show good agreement with those predicted by Pate's correlation and Reynolds Averaged Navier-Stokes (RANS) computations. The rms pressure fluctuation P'(rms)/T(w) plateaus in the freestream core of the nozzle. The intensity of the freestream noise within the nozzle is approximately 20% higher than that radiated from a single at pate with a similar freestream Mach number, potentially because of the contributions to the acoustic radiation from multiple azimuthal segments of the nozzle wall.
Institute of Scientific and Technical Information of China (English)
Jun LI; Ying-wei KANG; Guang-yi CAO; Xin-jian ZHU; Heng-yong TU; Jian LI
2008-01-01
A detailed mathematical model of a direct internal reforming solid oxide fuel cell (DIR-SOFC) incorporating with simulation of chemical and physical processes in the fuel cell is presented. The model is developed based on the reforming and electrochemical reaction mechanisms, mass and energy conservation, and heat transfer. A computational fluid dynamics (CFD) method is used for solving the complicated multiple partial differential equations (PDEs) to obtain the numerical approximations.The resulting distributions of chemical species concentrations, temperature and current density in a cross-flow DIR-SOFC are given and analyzed in detail. Further, the influence between distributions of chemical species concentrations, temperature and current density during the simulation is illustrated and discussed. The heat and mass transfer, and the kinetics of reforming and electrochemical reactions have significant effects on the parameter distributions within the cell. The results show the particularchar acteristics of the DIR-SOFC among fuel cells, and can aid in stack design and control.
Direct numerical simulation of convection and dissolution at a vertical ice-seawater interface
Gayen, Bishakhdatta; Griffiths, Ross W.; Kerr, Ross C.
2015-11-01
Direct numerical simulations are performed to investigate the convection generated when a wall of ice dissolves into seawater under Antarctic ocean conditions. The ambient water temperatures are kept between - 1° C and 6° C and salinities around 35 ppm, where diffusion of salt to the ice-water interface depresses the freezing point and further enhances heat diffusion to the ice. We use three coupled interface equations, along with the Boussinesq approximation and the equation of state for seawater, to solve for interface temperature, salinity and melt rate. Fluxes of both heat and salt to the interface play a significant role in governing the rate of dissolution of ice. At the presently achievable Grashof numbers turbulence is equally produced from both buoyancy and velocity shear, which indicates the importance of shear production at geophysical scales.
Direct Numerical Simulation and Theories of Wall Turbulence with a Range of Pressure Gradients
Coleman, G. N.; Garbaruk, A.; Spalart, P. R.
2014-01-01
A new Direct Numerical Simulation (DNS) of Couette-Poiseuille flow at a higher Reynolds number is presented and compared with DNS of other wall-bounded flows. It is analyzed in terms of testing semi-theoretical proposals for universal behavior of the velocity, mixing length, or eddy viscosity in pressure gradients, and in terms of assessing the accuracy of two turbulence models. These models are used in two modes, the traditional one with only a dependence on the wall-normal coordinate y, and a newer one in which a lateral dependence on z is added. For pure Couette flow and the Couette-Poiseuille case considered here, this z-dependence allows some models to generate steady streamwise vortices, which generally improves the agreement with DNS and experiment. On the other hand, it complicates the comparison between DNS and models.
Direct numerical simulation of a heat removal configuration for fusion blankets
Energy Technology Data Exchange (ETDEWEB)
Kakarantzas, S.C.; Grecos, A.P.; Vlachos, N.S. [University of Thessaly, Volos (Greece). Department of Mechanical and Industrial Engineering; Sarris, I.E.; Knaepen, B.; Carati, D. [Universite Libre de Bruxelles, Brussels (Belgium). Physique Statistique et Plasmas
2007-11-15
A series of direct numerical simulations (DNS) are performed to study the natural convection heat transfer between concentric cylinders at several Rayleigh and Hartmann numbers. The buoyant flow is driven by the temperature difference between the inner and the outer walls, with the inner wall being at lower temperature, while an external transverse magnetic field is imposed. Both laminar and turbulent flows are observed depending on the magnitude of the Rayleigh and Hartmann numbers. The resulting flow structures of the cases studied were both laminar and turbulent. The results show the 3D nature of turbulence and the tendency of the magnetic field to form narrow Hartmann layers, 3D jets and wakes at specific azimuthal angles. Some particular features of the turbulent regime as well as the heat transfer are also investigated. The magnetic field effect on the convective heat transfer is assessed via the Nusselt number showing that conduction dominates as the Hartmann number increases. (author)
Directory of Open Access Journals (Sweden)
Xingtuan Yang
2015-01-01
Full Text Available This study investigates the anisotropic characteristics of turbulent energy dissipation rate in a rotating jet flow via direct numerical simulation. The turbulent energy dissipation tensor, including its eigenvalues in the swirling flows with different rotating velocities, is analyzed to investigate the anisotropic characteristics of turbulence and dissipation. In addition, the probability density function of the eigenvalues of turbulence dissipation tensor is presented. The isotropic subrange of PDF always exists in swirling flows relevant to small-scale vortex structure. Thus, with remarkable large-scale vortex breakdown, the isotropic subrange of PDF is reduced in strongly swirling flows, and anisotropic energy dissipation is proven to exist in the core region of the vortex breakdown. More specifically, strong anisotropic turbulence dissipation occurs concentratively in the vortex breakdown region, whereas nearly isotropic turbulence dissipation occurs dispersively in the peripheral region of the strong swirling flows.
Direct numerical simulations (DNS) of particles in spatially varying electric fields
Amah, E.; Janjua, M.; Fischer, I. S.; Singh, P.
2013-11-01
We have developed a direct numerical simulation (DNS) scheme to simulate the motion of dielectric particles suspended in a dielectric liquid in nonuniform electric fields. The motion of particles is tracked using a distributed Lagrange multiplier method (DLM) and the electric forces acting on the particles are calculated by an efficient scheme in which the Maxwell stress tensor (MST) is integrated over the surfaces of the particles to obtain the force. The code is validated by performing a convergence study and by comparing the particle trajectories in a dielectrophoretic cage with those given by the point-dipole method. We also show that the trajectories of the two or more interacting particles given by the MST method can be different from those obtained using the point-dipole method since the latter does not consider particle-particle interactions.
Wacks, Daniel H.; Chakraborty, Nilanjan; Klein, Markus; Arias, Paul G.; Im, Hong G.
2016-12-01
The distributions of flow topologies within the flames representing the corrugated flamelets, thin reaction zones, and broken reaction zone regimes of premixed turbulent combustion are investigated using direct numerical simulation data of statistically planar turbulent H2-air flames with an equivalence ratio ϕ =0.7 . It was found that the diminishing influence of dilatation rate with increasing Karlovitz number has significant influences on the statistical behaviors of the first, second, and third invariants (i.e., P ,Q , and R ) of the velocity gradient tensor. These differences are reflected in the distributions of the flow topologies within the flames considered in this analysis. This has important consequences for those topologies that make dominant contributions to the scalar-turbulence interaction and vortex-stretching terms in the scalar dissipation rate and enstrophy transport equations, respectively. Detailed physical explanations are provided for the observed regime dependences of the flow topologies and their implications on the scalar dissipation rate and enstrophy transport.
Focke, C; Kuschel, M; Sommerfeld, M
2012-01-01
Binary droplet collisions are of importance in a variety of practical applications comprising dispersed two-phase flows. The background of our research is the prediction of properties of particulate products formed in spray processes. To gain a more thorough understanding of the elementary sub-processes inside a spray, experiments and direct numerical simulations of binary droplet collisions are used. The aim of these investigations is to develop semi-analytical descriptions for the outcome of droplet collisions. Such collision models can then be employed as closure terms for scale-reduced simulations. In the present work we focus on the collision of droplets of different liquids. These kinds of collisions take place in every spray drying process when droplets with different solids contents collide in recirculation zones. A new experimental method has been developed allowing for high spatial and time resolved recordings via Laser-induced fluorescence. The results obtained with the proposed method will be comp...
Direct Numerical Simulation of Gas-Solid Two-Phase Mixing Layer
Institute of Scientific and Technical Information of China (English)
Wenchun LI; Guilin HU; Zhe ZHOU; Jianren FAN; Kefa CEN
2005-01-01
In this paper, the spatially evolving of the higher Reynolds numbers gas-solid mixing layer under compressible conditions was investigated by a new direct numerical simulation technology. A high-resolution solver was performed for the gas-phase flow-field, particles with different Stokes numbers were traced by the Lagrangian approach based on one-way coupling. The processes of the vortex rolling up and pairing in the two-dimensional mixing layer were captured precisely. The large-scale structures developed from the initial inflow are characterized by the counter-rotating vortices. The mean velocity and the fluctuation intensities profiles agree well with the experimental data. Particles with smaller Stokes numbers accumulate at the vortex centers due to the smaller aerodynamic response time; particles with moderate Stokes numbers tend to orbit around individual streamwise vortices and in the periphery of paring vortices; particles with larger Stokes numbers disperse less evenly, showing a concentration distribution in the flow field.
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
Petroleum science has made remarkable progress in organic geochemistry and in the research into the theories of petroleum origin,its transport and accumulation.In estimating the oil-gas resources of a basin.the knowledge of its evolutionary history and especially the numerical computation of fluid flow and.the history of its changes under heat is vital.The mathematical model can be described as a coupled system of nonlinear partial differentical equations with initial-boundary value problems.This thesis,from actual conditions such as the effect of fluid compressibility and the characteristic of largescal science-engineering computalion,puts forward a kind of characteristic finite difference alternating-direction scheme.Optimal order estimates in L2 norm are derived for the error in the approximate solutions.
First principle basis of the direct numerical simulation for turbulence of inert and reactive gases
Tsuge, S
1997-01-01
An open question of whether phenomenological fluid equations to be used for direct numerical simulation of turbulence are warranted on `first principles' is addressed, and the problem is posed using Klimontovich microscopic density to replace the Boltzmann function of the classical statistical mechanics. For inert monatomic gases, it is shown that all the gasdynamic equations, namely, the three conservation equations plus the Navier-Stokes stress law and the Fourier heat conduction law are retrieved as governing instantaneous quantities, without having recourse to any concepts of averaging or statistical equilibrium. For reactive gases, however, the Arrhenius reaction rate law written in terms of the fluctuating temperature is not justified, reflecting the fact that this rate law hinges crucially on these concepts.
Lieu, Binh K; Jovanović, Mihailo R
2010-01-01
This work builds on and confirms the theoretical findings of Part 1 of this paper, Moarref & Jovanovi\\'c (2010). We use direct numerical simulations of the Navier-Stokes equations to assess the efficacy of blowing and suction in the form of streamwise traveling waves for controlling the onset of turbulence in a channel flow. We highlight the effects of the modified base flow on the dynamics of velocity fluctuations and net power balance. Our simulations verify the theoretical predictions of Part 1 that the upstream traveling waves promote turbulence even when the uncontrolled flow stays laminar. On the other hand, the downstream traveling waves with parameters selected in Part 1 are capable of reducing the fluctuations' kinetic energy, thereby maintaining the laminar flow. In flows driven by a fixed pressure gradient, a positive net efficiency as large as 25 % relative to the uncontrolled turbulent flow can be achieved with downstream waves. Furthermore, we show that these waves can also relaminarize full...
Direct numerical simulation of laminar-turbulent flow over a flat plate at hypersonic flow speeds
Egorov, I. V.; Novikov, A. V.
2016-06-01
A method for direct numerical simulation of a laminar-turbulent flow around bodies at hypersonic flow speeds is proposed. The simulation is performed by solving the full three-dimensional unsteady Navier-Stokes equations. The method of calculation is oriented to application of supercomputers and is based on implicit monotonic approximation schemes and a modified Newton-Raphson method for solving nonlinear difference equations. By this method, the development of three-dimensional perturbations in the boundary layer over a flat plate and in a near-wall flow in a compression corner is studied at the Mach numbers of the free-stream of M = 5.37. In addition to pulsation characteristic, distributions of the mean coefficients of the viscous flow in the transient section of the streamlined surface are obtained, which enables one to determine the beginning of the laminar-turbulent transition and estimate the characteristics of the turbulent flow in the boundary layer.
Direct Numerical Simulation of Supersonic Turbulent Boundary Layer with Spanwise Wall Oscillation
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Weidan Ni
2016-03-01
Full Text Available Direct numerical simulations (DNS of Mach = 2.9 supersonic turbulent boundary layers with spanwise wall oscillation (SWO are conducted to investigate the turbulent heat transport mechanism and its relation with the turbulent momentum transport. The turbulent coherent structures are suppressed by SWO and the drag is reduced. Although the velocity and temperature statistics are disturbed by SWO differently, the turbulence transports of momentum and heat are simultaneously suppressed. The Reynolds analogy and the strong Reynolds analogy are also preserved in all the controlled flows, proving the consistent mechanisms of momentum transport and heat transport in the turbulent boundary layer with SWO. Despite the extra dissipation and heat induced by SWO, a net wall heat flux reduction can be achieved with the proper selected SWO parameters. The consistent mechanism of momentum and heat transports supports the application of turbulent drag reduction technologies to wall heat flux controls in high-speed vehicles.
Energy spectrum in high-resolution direct numerical simulations of turbulence
Ishihara, Takashi; Morishita, Koji; Yokokawa, Mitsuo; Uno, Atsuya; Kaneda, Yukio
2016-12-01
A study is made about the energy spectrum E (k ) of turbulence on the basis of high-resolution direct numerical simulations (DNSs) of forced incompressible turbulence in a periodic box using a Fourier spectral method with the number of grid points and the Taylor scale Reynolds number Rλ up to 12 2883 and approximately 2300, respectively. The DNS data show that there is a wave-number range (approximately 5 ×10-3 2 /3k-5 /3] =c (kL ) m , where is the mean energy dissipation rate per unit mass; L is the integral length scale; and m ≈-0.12 . The coefficient c is independent of k , but has a Rλ dependence, such as c =C Rλζ , where C ≈0.9 and ζ ≈0.14 .
Wacks, Daniel H.
2016-12-02
The distributions of flow topologies within the flames representing the corrugated flamelets, thin reaction zones, and broken reaction zone regimes of premixed turbulent combustion are investigated using direct numerical simulation data of statistically planar turbulent H-2-air flames with an equivalence ratio phi = 0.7. It was found that the diminishing influence of dilatation rate with increasing Karlovitz number has significant influences on the statistical behaviors of the first, second, and third invariants (i.e., P, Q, and R) of the velocity gradient tensor. These differences are reflected in the distributions of the flow topologies within the flames considered in this analysis. This has important consequences for those topologies that make dominant contributions to the scalar-turbulence interaction and vortex-stretching terms in the scalar dissipation rate and enstrophy transport equations, respectively. Detailed physical explanations are provided for the observed regime dependences of the flow topologies and their implications on the scalar dissipation rate and enstrophy transport.
Recursive Numerical Evaluation of the Cumulative Bivariate Normal Distribution
Meyer, Christian
2010-01-01
We propose an algorithm for evaluation of the cumulative bivariate normal distribution, building upon Marsaglia's ideas for evaluation of the cumulative univariate normal distribution. The algorithm is mathematically transparent, delivers competitive performance and can easily be extended to arbitrary precision.
Direct numerical simulations of non-premixed ethylene-air flames: Local flame extinction criterion
Lecoustre, Vivien R.
2014-11-01
Direct Numerical Simulations (DNS) of ethylene/air diffusion flame extinctions in decaying two-dimensional turbulence were performed. A Damköhler-number-based flame extinction criterion as provided by classical large activation energy asymptotic (AEA) theory is assessed for its validity in predicting flame extinction and compared to one based on Chemical Explosive Mode Analysis (CEMA) of the detailed chemistry. The DNS code solves compressible flow conservation equations using high order finite difference and explicit time integration schemes. The ethylene/air chemistry is simulated with a reduced mechanism that is generated based on the directed relation graph (DRG) based methods along with stiffness removal. The numerical configuration is an ethylene fuel strip embedded in ambient air and exposed to a prescribed decaying turbulent flow field. The emphasis of this study is on the several flame extinction events observed in contrived parametric simulations. A modified viscosity and changing pressure (MVCP) scheme was adopted in order to artificially manipulate the probability of flame extinction. Using MVCP, pressure was changed from the baseline case of 1 atm to 0.1 and 10 atm. In the high pressure MVCP case, the simulated flame is extinction-free, whereas in the low pressure MVCP case, the simulated flame features frequent extinction events and is close to global extinction. Results show that, despite its relative simplicity and provided that the global flame activation temperature is correctly calibrated, the AEA-based flame extinction criterion can accurately predict the simulated flame extinction events. It is also found that the AEA-based criterion provides predictions of flame extinction that are consistent with those provided by a CEMA-based criterion. This study supports the validity of a simple Damköhler-number-based criterion to predict flame extinction in engineering-level CFD models. © 2014 The Combustion Institute.
Numerical evaluation of spherical GJMS determinants for even dimensions
Dowker, J S
2013-01-01
The functional determinants of the GJMS scalar operators, P_{2k}, on even-dimensional spheres are computed via Barnes multiple gamma functions relying on the numerical availability of the digamma function. For the critical k=d/2 case, it is necessary to calculate the Stirling moduli. The results are presented as graphs and show a series of extrema in the effective action as k is varied in the reals. For odd dimensions these extrema occur at integer k.
Fedioun, Ivan; Lardjane, Nicolas; Gökalp, Iskender
2001-12-01
Some recent studies on the effects of truncation and aliasing errors on the large eddy simulation (LES) of turbulent flows via the concept of modified wave number are revisited. It is shown that all the results obtained for nonlinear partial differential equations projected and advanced in time in spectral space are not straightforwardly applicable to physical space calculations due to the nonequivalence by Fourier transform of spectral aliasing errors and numerical errors on a set of grid points in physical space. The consequences of spectral static aliasing errors on a set of grid points are analyzed in one dimension of space for quadratic products and their derivatives. The dynamical process that results through time stepping is illustrated on the Burgers equation. A method based on midpoint interpolation is proposed to remove in physical space the static grid point errors involved in divergence forms. It is compared to the sharp filtering technique on finer grids suggested by previous authors. Global performances resulting from combination of static aliasing errors and truncation errors are then discussed for all classical forms of the convective terms in Navier-Stokes equations. Some analytical results previously obtained on the relative magnitude of subgrid scale terms and numerical errors are confirmed with 3D realistic random fields. The physical space dynamical behavior and the stability of typical associations of numerical schemes and forms of nonlinear terms are finally evaluated on the LES of self-decaying homogeneous isotropic turbulence. It is shown that the convective form (if conservative properties are not strictly required) associated with highly resolving compact finite difference schemes provides the best compromise, which is nearly equivalent to dealiased pseudo-spectral calculations.
A testing preocedure for the evaluation of directional mesh bias
Slobbe, A.T.; Hendriks, M.A.N.; Rots, J.G.
2013-01-01
This paper presents a dedicated numerical test that enables to assess the directional mesh bias of constitutive models in a systematic way. The test makes use of periodic boundary conditions, by which strain localization can be analyzed for different mesh alignments with preservation of mesh uniform
Directory of Open Access Journals (Sweden)
Jiang Lei
2015-01-01
Full Text Available Direct numerical simulation (DNS of a round jet in crossflow based on lattice Boltzmann method (LBM is carried out on multi-GPU cluster. Data parallel SIMT (single instruction multiple thread characteristic of GPU matches the parallelism of LBM well, which leads to the high efficiency of GPU on the LBM solver. With present GPU settings (6 Nvidia Tesla K20M, the present DNS simulation can be completed in several hours. A grid system of 1.5 × 108 is adopted and largest jet Reynolds number reaches 3000. The jet-to-free-stream velocity ratio is set as 3.3. The jet is orthogonal to the mainstream flow direction. The validated code shows good agreement with experiments. Vortical structures of CRVP, shear-layer vortices and horseshoe vortices, are presented and analyzed based on velocity fields and vorticity distributions. Turbulent statistical quantities of Reynolds stress are also displayed. Coherent structures are revealed in a very fine resolution based on the second invariant of the velocity gradients.
Direct numerical simulations of type Ia supernovae flames I: The landau-darrieus instability
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Bell, J.B.; Day, M.S.; Rendleman, C.A.; Woosley, S.E.; Zingale, M.
2003-11-24
Planar flames are intrinsically unstable in open domains due to the thermal expansion across the burning front--the Landau-Darrieus instability. This instability leads to wrinkling and growth of the flame surface, and corresponding acceleration of the flame, until it is stabilized by cusp formation. We look at the Landau-Darrieus in stability for C/O thermonuclear flames at conditions relevant to the late stages of a Type Ia supernova explosion. Two-dimensional direct numerical simulations of both single-mode and multi-mode perturbations using a low Mach number hydrodynamics code are presented. We show the effect of the instability on the flame speed as a function of both the density and domain size, demonstrate the existence of the small scale cutoff to the growth of the instability, and look for the proposed breakdown of the non-linear stabilization at low densities. The effects of curvature on the flame as quantified through measurements of the growth rate and computation of the corresponding Markstein number. While accelerations of a few percent are observed, they are too small to have any direct outcome on the supernova explosion.
Numerical Aerodynamic Evaluation and Noise Investigation of a Bladeless Fan
mohammad jafari; Hossein Afshin; Bijan Farhanieh; Hamidreza bozorgasareh
2015-01-01
Bladeless fan is a novel fan type that has no observable impeller, usually used for domestic applications. Numerical investigation of a Bladeless fan via Finite Volume Method was carried out in this study. The fan was placed in center of a 4×2×2m room and 473 Eppler airfoil profile was used as cross section of the fan. Performance and noise level of the fan by solving continuity and momentum equations as well as noise equations of Broadband Noise Source (BNS) and Ffowcs Williams a...
van den Heever, S. C.; Tao, W. K.; Skofronick Jackson, G.; Tanelli, S.; L'Ecuyer, T. S.; Petersen, W. A.; Kummerow, C. D.
2015-12-01
Cloud, aerosol and precipitation processes play a fundamental role in the water and energy cycle. It is critical to accurately represent these microphysical processes in numerical models if we are to better predict cloud and precipitation properties on weather through climate timescales. Much has been learned about cloud properties and precipitation characteristics from NASA satellite missions such as TRMM, CloudSat, and more recently GPM. Furthermore, data from these missions have been successfully utilized in evaluating the microphysical schemes in cloud-resolving models (CRMs) and global models. However, there are still many uncertainties associated with these microphysics schemes. These uncertainties can be attributed, at least in part, to the fact that microphysical processes cannot be directly observed or measured, but instead have to be inferred from those cloud properties that can be measured. Evaluation of microphysical parameterizations are becoming increasingly important as enhanced computational capabilities are facilitating the use of more sophisticated schemes in CRMs, and as future global models are being run on what has traditionally been regarded as cloud-resolving scales using CRM microphysical schemes. In this talk we will demonstrate how TRMM, CloudSat and GPM data have been used to evaluate different aspects of current CRM microphysical schemes, providing examples of where these approaches have been successful. We will also highlight CRM microphysical processes that have not been well evaluated and suggest approaches for addressing such issues. Finally, we will introduce a potential NASA satellite mission, the Cloud and Precipitation Processes Mission (CAPPM), which would facilitate the development and evaluation of different microphysical-dynamical feedbacks in numerical models.
Direct numerical simulation of hydrogen turbulent lifted jet flame in a vitiated coflow
Institute of Scientific and Technical Information of China (English)
WANG ZhiHua; FAN JianRen; ZHOU JunHu; CEN KeFa
2007-01-01
The direct numerical simulation (DNS) method with 16 steps detailed chemical kinetics was applied to a lifted turbulent jet flame with H2/N2 fuel issuing into a wide hot coflow of lean combustion products, at temperature of 1045 K and low oxygen concentrations. The chemical reactions were handled by the library function of CHEMKIN which was called by the main program in every time step. Parallel computational technology based on message passing interface method (MPI) was used in the simulation. All the cases were run by 12 CPUs on a high performance computer system. Faver-averaged DNS results were obtained by long time averaging the transient profile and compared with the experimental data. The roll-up and evolution of the vortices in jet flame were well captured. The vortices in the same rotating direction attracted each other and those in different rotating directions repulsed each other. Through complex interactions between vortices, the original symmetrical vortex structure could be converted into nonsymmetrical and more complex structures by combination, distortion and splitting of the vortices. The transient profiles of H, OH and H2O mass fraction at 5.76 ms showed the flame structure in jet flame, especially the autoignition regions clearly. The lift-off height was about 9 d-11 d, in agreement with the experimental observation. At the corner point of the flame sheet indicated by OH and H profiles, the combustion was always enhanced by the flame curvature and extended resident time. The profiles of turbulence intensities show that the flames were diffused from the original two outside flame sheets into the core. The DNS results can be considered in developing more accurate and more universal turbulence models.
Direct Numerical Simulation of a Turbulent Reactive Plume on a Parallel Computer
Cook, Andrew W.; Riley, James J.
1996-12-01
A computational algorithm is described for direct numerical simulation (DNS) of a reactive plume in spatially evolving grid turbulence. The algorithm uses sixth-order compact differencing in conjunction with a fifth-order compact boundary scheme which has been developed and found to be stable. A compact filtering method is discussed as a means of stabilizing calculations where the viscous/diffusive terms are differenced in their conservative form. This approach serves as an alternative to nonconservative differencing, previously advocated as a means of damping the 2δ waves. In numerically solving the low Mach number equations the time derivative of the density field in the pressure Poisson equation was found to be the most destabilizing part of the calculation. Even-ordered finite difference approximations to this derivative were found to be more stable (allow for larger density gradients) than odd-ordered approximations. Turbulence at the inlet boundary is generated by scanning through an existing three-dimensional field of fully developed turbulence. In scanning through the inlet field, it was found that a high order interpolation, e.g., cubic-spline interpolation, is necessary in order to provide continuous velocity derivatives. Regarding pressure, a Neumann inlet condition combined with a Dirichlet outlet condition was found to work well. The chemistry follows the single-step, irreversible, global reaction: Fuel + ( r) Oxidizer → (1 + r)Product + Heat, with parameters chosen to match experimental data as far as allowed by resolution constraints. Simulation results are presented for four different cases in order to examine the effects of heat release, Damköhler number, and Arrhenius kinetics on the flow physics. Statistical data from the DNS are compared to theory and wind tunnel data and found in reasonable agreement with regard to growth of turbulent length scales, decay of turbulent kinetic energy, decay of centerline scalar concentration, decrease in
Numerical simulations of blast-impact problems using the direct simulation Monte Carlo method
Sharma, Anupam
There is an increasing need to design protective structures that can withstand or mitigate the impulsive loading due to the impact of a blast or a shock wave. A preliminary step in designing such structures is the prediction of the pressure loading on the structure. This is called the "load definition." This thesis is focused on a numerical approach to predict the load definition on arbitrary geometries for a given strength of the incident blast/shock wave. A particle approach, namely the Direct Simulation Monte Carlo (DSMC) method, is used as the numerical model. A three-dimensional, time-accurate DSMC flow solver is developed as a part of this study. Embedded surfaces, modeled as triangulations, are used to represent arbitrary-shaped structures. Several techniques to improve the computational efficiency of the algorithm of particle-structure interaction are presented. The code is designed using the Object Oriented Programming (OOP) paradigm. Domain decomposition with message passing is used to solve large problems in parallel. The solver is extensively validated against analytical results and against experiments. Two kinds of geometries, a box and an I-shaped beam are investigated for blast impact. These simulations are performed in both two- and three-dimensions. A major portion of the thesis is dedicated to studying the uncoupled fluid dynamics problem where the structure is assumed to remain stationary and intact during the simulation. A coupled, fluid-structure dynamics problem is solved in one spatial dimension using a simple, spring-mass-damper system to model the dynamics of the structure. A parametric study, by varying the mass, spring constant, and the damping coefficient, to study their effect on the loading and the displacement of the structure is also performed. Finally, the parallel performance of the solver is reported for three sample-size problems on two Beowulf clusters.
Terascale direct numerical simulations of turbulent combustion using S3D.
Energy Technology Data Exchange (ETDEWEB)
Sankaran, Ramanan; Mellor-Crummy, J.; DeVries, M.; Yoo, Chun Sang; Ma, K. L.; Podhorski, N.; Liao, W. K.; Klasky, S.; de Supinski, B.; Choudhary, A.; Hawkes, Evatt R.; Chen, Jacqueline H.; Shende, Sameer
2008-08-01
Computational science is paramount to the understanding of underlying processes in internal combustion engines of the future that will utilize non-petroleum-based alternative fuels, including carbon-neutral biofuels, and burn in new combustion regimes that will attain high efficiency while minimizing emissions of particulates and nitrogen oxides. Next-generation engines will likely operate at higher pressures, with greater amounts of dilution and utilize alternative fuels that exhibit a wide range of chemical and physical properties. Therefore, there is a significant role for high-fidelity simulations, direct numerical simulations (DNS), specifically designed to capture key turbulence-chemistry interactions in these relatively uncharted combustion regimes, and in particular, that can discriminate the effects of differences in fuel properties. In DNS, all of the relevant turbulence and flame scales are resolved numerically using high-order accurate numerical algorithms. As a consequence terascale DNS are computationally intensive, require massive amounts of computing power and generate tens of terabytes of data. Recent results from terascale DNS of turbulent flames are presented here, illustrating its role in elucidating flame stabilization mechanisms in a lifted turbulent hydrogen/air jet flame in a hot air co-flow, and the flame structure of a fuel-lean turbulent premixed jet flame. Computing at this scale requires close collaborations between computer and combustion scientists to provide optimized scaleable algorithms and software for terascale simulations, efficient collective parallel I/O, tools for volume visualization of multiscale, multivariate data and automating the combustion workflow. The enabling computer science, applied to combustion science, is also required in many other terascale physics and engineering simulations. In particular, performance monitoring is used to identify the performance of key kernels in the DNS code, S3D and especially memory
Terascale direct numerical simulations of turbulent combustion using S3D
Chen, J. H.; Choudhary, A.; de Supinski, B.; DeVries, M.; Hawkes, E. R.; Klasky, S.; Liao, W. K.; Ma, K. L.; Mellor-Crummey, J.; Podhorszki, N.; Sankaran, R.; Shende, S.; Yoo, C. S.
2009-01-01
Computational science is paramount to the understanding of underlying processes in internal combustion engines of the future that will utilize non-petroleum-based alternative fuels, including carbon-neutral biofuels, and burn in new combustion regimes that will attain high efficiency while minimizing emissions of particulates and nitrogen oxides. Next-generation engines will likely operate at higher pressures, with greater amounts of dilution and utilize alternative fuels that exhibit a wide range of chemical and physical properties. Therefore, there is a significant role for high-fidelity simulations, direct numerical simulations (DNS), specifically designed to capture key turbulence-chemistry interactions in these relatively uncharted combustion regimes, and in particular, that can discriminate the effects of differences in fuel properties. In DNS, all of the relevant turbulence and flame scales are resolved numerically using high-order accurate numerical algorithms. As a consequence terascale DNS are computationally intensive, require massive amounts of computing power and generate tens of terabytes of data. Recent results from terascale DNS of turbulent flames are presented here, illustrating its role in elucidating flame stabilization mechanisms in a lifted turbulent hydrogen/air jet flame in a hot air coflow, and the flame structure of a fuel-lean turbulent premixed jet flame. Computing at this scale requires close collaborations between computer and combustion scientists to provide optimized scaleable algorithms and software for terascale simulations, efficient collective parallel I/O, tools for volume visualization of multiscale, multivariate data and automating the combustion workflow. The enabling computer science, applied to combustion science, is also required in many other terascale physics and engineering simulations. In particular, performance monitoring is used to identify the performance of key kernels in the DNS code, S3D and especially memory
Lift capability prediction for helicopter rotor blade-numerical evaluation
Rotaru, Constantin; Cîrciu, Ionicǎ; Luculescu, Doru
2016-06-01
The main objective of this paper is to describe the key physical features for modelling the unsteady aerodynamic effects found on helicopter rotor blade operating under nominally attached flow conditions away from stall. The unsteady effects were considered as phase differences between the forcing function and the aerodynamic response, being functions of the reduced frequency, the Mach number and the mode forcing. For a helicopter rotor, the reduced frequency at any blade element can't be exactly calculated but a first order approximation for the reduced frequency gives useful information about the degree of unsteadiness. The sources of unsteady effects were decomposed into perturbations to the local angle of attack and velocity field. The numerical calculus and graphics were made in FLUENT and MAPLE soft environments. This mathematical model is applicable for aerodynamic design of wind turbine rotor blades, hybrid energy systems optimization and aeroelastic analysis.
Numerical Aerodynamic Evaluation and Noise Investigation of a Bladeless Fan
Directory of Open Access Journals (Sweden)
mohammad jafari
2015-01-01
Full Text Available Bladeless fan is a novel fan type that has no observable impeller, usually used for domestic applications. Numerical investigation of a Bladeless fan via Finite Volume Method was carried out in this study. The fan was placed in center of a 4×2×2m room and 473 Eppler airfoil profile was used as cross section of the fan. Performance and noise level of the fan by solving continuity and momentum equations as well as noise equations of Broadband Noise Source (BNS and Ffowcs Williams and Hawkings (FW-H in both steady state and unsteady conditions were studied. Flow increase ratio of the fan was captured. Furthermore, BNS method could find outlet slit of the air as the main source of the noise generation. In order to validation of aeroacousticcode results, a simulation of noise for NACA 0012 airfoil via FW-H method was compared to experimental results and good agreement was obtained.
Numerical methods for evaluating the derivatives of eigenvalues and eigenvectors
Rudisill, C. S.; Chu, Y.-Y.
1975-01-01
Two numerical methods are presented for computing the derivatives of eigenvalues and eigenvectors which do not require complete solution of the eigenvalue problem if only a few derivatives are sought. The 'iterative' method may be used to find the first derivative of one or all of the eigenvectors together with the second derivative of their eigenvalues in a self-adjoint system. If the left- and right-hand eigenvectors are known, the first derivative of the eigenvector corresponding to the largest eigenvalue and the second derivative of the largest eigenvalue may be obtained for a nonself-adjoint system. The 'algebraic' method may be used to find all orders of the derivatives, provided they exist, without requiring the left-hand eigenvectors.
Numerical evaluation of the bispectrum in multiple field inflation
Dias, Mafalda; Mulryne, David J; Seery, David
2016-01-01
We present a complete framework for numerical calculation of the power spectrum and bispectrum in canonical inflation with an arbitrary number of light or heavy fields. Our method includes all relevant effects at tree-level in the loop expansion, including (i) interference between growing and decaying modes near horizon exit; (ii) correlation and coupling between species near horizon exit and on superhorizon scales; (iii) contributions from mass terms; and (iv) all contributions from coupling to gravity. We track the evolution of each correlation function from the vacuum state through horizon exit and the superhorizon regime, with no need to match quantum and classical parts of the calculation; when integrated, our approach corresponds exactly with the tree-level Schwinger or 'in-in' formulation of quantum field theory. In this paper we give the equations necessary to evolve all two- and three-point correlation functions together with suitable initial conditions. The final formalism is suitable to compute the...
Numerical evaluation of effective unsaturated hydraulic properties for fractured rocks
Energy Technology Data Exchange (ETDEWEB)
Lu, Zhiming [Los Alamos National Laboratory; Kwicklis, Edward M [Los Alamos National Laboratory
2009-01-01
To represent a heterogeneous unsaturated fractured rock by its homogeneous equivalent, Monte Carlo simulations are used to obtain upscaled (effective) flow properties. In this study, we present a numerical procedure for upscaling the van Genuchten parameters of unsaturated fractured rocks by conducting Monte Carlo simulations of the unsaturated flow in a domain under gravity-dominated regime. The simulation domain can be chosen as the scale of block size in the field-scale modeling. The effective conductivity is computed from the steady-state flux at the lower boundary and plotted as a function of the averaging pressure head or saturation over the domain. The scatter plot is then fitted using van Genuchten model and three parameters, i.e., the saturated conductivity K{sub s}, the air-entry parameter {alpha}, the pore-size distribution parameter n, corresponding to this model are considered as the effective K{sub s}, effective {alpha}, and effective n, respectively.
Directory of Open Access Journals (Sweden)
F. P. Santos
2013-09-01
Full Text Available Direct-quadrature generalized moment based methods were analysed in terms of accuracy, computational cost and robustness for the solution of the population balance problems in the [0,∞ and [0,1] domains. The minimum condition number of the coefficient matrix of their linear system of equations was obtained by global optimization. An heuristic scaling rule from the literature was also evaluated. The results indicate that the methods based on Legendre generalized moments are the most robust for the finite domain problems, while the DQMoM formulation that solves for the abscissas and weights using the heuristic scaling rule is the best for the infinite domain problems.
Numerical Evaluation of the Bose-Ghost Propagator in Minimal Landau Gauge on the Lattice
Cucchieri, Attilio
2016-01-01
We present numerical details of the evaluation of the so-called Bose-ghost propagator in lattice minimal Landau gauge, for the SU(2) case in four Euclidean dimensions. This quantity has been proposed as a carrier of the confining force in the Gribov-Zwanziger approach and, as such, its infrared behavior could be relevant for the understanding of color confinement in Yang-Mills theories. Also, its nonzero value can be interpreted as direct evidence of BRST-symmetry breaking, which is induced when restricting the functional measure to the first Gribov region Omega. Our simulations are done for lattice volumes up to 120^4 and for physical lattice extents up to 13.5 fm. We investigate the infinite-volume and continuum limits.
Numerical evaluation of the Bose-ghost propagator in minimal Landau gauge on the lattice
Cucchieri, Attilio; Mendes, Tereza
2016-07-01
We present numerical details of the evaluation of the so-called Bose-ghost propagator in lattice minimal Landau gauge, for the SU(2) case in four Euclidean dimensions. This quantity has been proposed as a carrier of the confining force in the Gribov-Zwanziger approach and, as such, its infrared behavior could be relevant for the understanding of color confinement in Yang-Mills theories. Also, its nonzero value can be interpreted as direct evidence of Becchi-Rouet-Stora-Tyutin-symmetry breaking, which is induced when restricting the functional measure to the first Gribov region Ω . Our simulations are done for lattice volumes up to 1204 and for physical lattice extents up to 13.5 fm. We investigate the infinite-volume and continuum limits.
Scalability of Parallel Spatial Direct Numerical Simulations on Intel Hypercube and IBM SP1 and SP2
Joslin, Ronald D.; Hanebutte, Ulf R.; Zubair, Mohammad
1995-01-01
The implementation and performance of a parallel spatial direct numerical simulation (PSDNS) approach on the Intel iPSC/860 hypercube and IBM SP1 and SP2 parallel computers is documented. Spatially evolving disturbances associated with the laminar-to-turbulent transition in boundary-layer flows are computed with the PSDNS code. The feasibility of using the PSDNS to perform transition studies on these computers is examined. The results indicate that PSDNS approach can effectively be parallelized on a distributed-memory parallel machine by remapping the distributed data structure during the course of the calculation. Scalability information is provided to estimate computational costs to match the actual costs relative to changes in the number of grid points. By increasing the number of processors, slower than linear speedups are achieved with optimized (machine-dependent library) routines. This slower than linear speedup results because the computational cost is dominated by FFT routine, which yields less than ideal speedups. By using appropriate compile options and optimized library routines on the SP1, the serial code achieves 52-56 M ops on a single node of the SP1 (45 percent of theoretical peak performance). The actual performance of the PSDNS code on the SP1 is evaluated with a "real world" simulation that consists of 1.7 million grid points. One time step of this simulation is calculated on eight nodes of the SP1 in the same time as required by a Cray Y/MP supercomputer. For the same simulation, 32-nodes of the SP1 and SP2 are required to reach the performance of a Cray C-90. A 32 node SP1 (SP2) configuration is 2.9 (4.6) times faster than a Cray Y/MP for this simulation, while the hypercube is roughly 2 times slower than the Y/MP for this application. KEY WORDS: Spatial direct numerical simulations; incompressible viscous flows; spectral methods; finite differences; parallel computing.
Analytical solutions of moisture flow equations and their numerical evaluation
Energy Technology Data Exchange (ETDEWEB)
Gibbs, A.G.
1981-04-01
The role of analytical solutions of idealized moisture flow problems is discussed. Some different formulations of the moisture flow problem are reviewed. A number of different analytical solutions are summarized, including the case of idealized coupled moisture and heat flow. The evaluation of special functions which commonly arise in analytical solutions is discussed, including some pitfalls in the evaluation of expressions involving combinations of special functions. Finally, perturbation theory methods are summarized which can be used to obtain good approximate analytical solutions to problems which are too complicated to solve exactly, but which are close to an analytically solvable problem.
Numerical and experimental evaluation of performance of centrifugal seals
Indian Academy of Sciences (India)
T V SANAND; P PRADEEP KUMAR; P UNNIKRISHNAN NAIR; PAUL P GEORGE
2017-04-01
‘Centrifugal seals’ or ‘Slinger seals’ offer an attractive choice as non-contact-type sealing in fluid machinery. These seals utilize the radial pressure gradient caused by centrifugal forces in a rotating fluid ring, to create a sealing of the working fluid. Basic construction of a typical seal consists of a rotating disc inside astationary casing; one side of the disc (sealing side) is provided with a set of slots (Type-1) or vanes (Type-2) to enhance the tangential velocity of the fluid. The other side of the disk (back side) in both the configurations is exposed to high pressure liquid being sealed. Both numerical and experimental investigations of the performance of Type-1 seal (with slots) have been carried out so as to optimize the seal configuration to achieve maximum sealing capacity, with minimum power consumption. A comparison of the performance of Type-1 seal has been made with that of conventional one (Type-2) in view of economy of construction and better sealing with minimal expense of power consumption. A test rig that allows for varying the major geometrical and operating parameters was designed and tests were conducted with water as the medium. Influence of major geometric parameters like dimensions and number of slots, axial/radial clearances and major operating parameters like rotational speed, inlet pressure and sealing fluid bypass flow rate has been investigated. Apart from variouspressure, temperature, flow and torque measurements, the interface between the sealing and working fluid for the experiments was captured and recorded using a high speed camera at 26,000 frames per second. Geometrical configuration for the slots that maximizes the sealing capacity is arrived through 3D numerical simulations using commercial CFD solver ANSYS Fluent®. A good agreement is obtained with respect to experimental results. In view of economy of construction and better sealing with minimal expense of operating power, a modified version of Type-1 seal
Evaluation and purchase of confocal microscopes: Numerous factors to consider
The purchase of a confocal microscope can be a complex and difficult decision for an individual scientist, group or evaluation committee. This is true even for scientists that have used confocal technology for many years. The task of reaching the optimal decision becomes almost i...
Zhu, Xiaojue; Verzicco, Roberto; Lohse, Detlef
2015-01-01
We present direct numerical simulations of Taylor-Couette flow with grooved walls at a fixed radius ratio $\\eta=r_i/r_o=0.714$ with inner cylinder Reynolds number up to $Re_i=3.76\\times10^4$, corresponding to Taylor number up to $Ta=2.15\\times10^9$. The grooves are axisymmetric V-shaped obstacles attached to the wall with a tip angle of $90^\\circ$. Results are compared with the smooth wall case in order to investigate the effects of grooves on Taylor-Couette flow. We focus on the effective scaling laws for the torque, flow structures, and boundary layers. It is found that, when the groove height is smaller than the boundary layer thickness, the torque is the same as that of the smooth wall cases. With increasing $Ta$, the boundary layer thickness becomes smaller than the groove height. Plumes are ejected from tips of the grooves and a secondary circulation between the latter is formed. This is associated to a sharp increase of the torque and thus the effective scaling law for the torque vs. $Ta$ becomes much ...
A Novel Quantum-Behaved Bat Algorithm with Mean Best Position Directed for Numerical Optimization.
Zhu, Binglian; Zhu, Wenyong; Liu, Zijuan; Duan, Qingyan; Cao, Long
2016-01-01
This paper proposes a novel quantum-behaved bat algorithm with the direction of mean best position (QMBA). In QMBA, the position of each bat is mainly updated by the current optimal solution in the early stage of searching and in the late search it also depends on the mean best position which can enhance the convergence speed of the algorithm. During the process of searching, quantum behavior of bats is introduced which is beneficial to jump out of local optimal solution and make the quantum-behaved bats not easily fall into local optimal solution, and it has better ability to adapt complex environment. Meanwhile, QMBA makes good use of statistical information of best position which bats had experienced to generate better quality solutions. This approach not only inherits the characteristic of quick convergence, simplicity, and easy implementation of original bat algorithm, but also increases the diversity of population and improves the accuracy of solution. Twenty-four benchmark test functions are tested and compared with other variant bat algorithms for numerical optimization the simulation results show that this approach is simple and efficient and can achieve a more accurate solution.
Numerical simulation of a direct current glow discharge in atmospheric pressure helium
Yin, Zeng-Qian; Wang, Yan; Zhang, Pan-Pan; Zhang, Qi; Li, Xue-Chen
2016-12-01
Characteristics of a direct current (DC) discharge in atmospheric pressure helium are numerically investigated based on a one-dimensional fluid model. The results indicate that the discharge does not reach its steady state till it takes a period of time. Moreover, the required time increases and the current density of the steady state decreases with increasing the gap width. Through analyzing the spatial distributions of the electron density, the ion density and the electric field at different discharge moments, it is found that the DC discharge starts with a Townsend regime, then transits to a glow regime. In addition, the discharge operates in a normal glow mode or an abnormal glow one under different parameters, such as the gap width, the ballast resistors, and the secondary electron emission coefficients, judged by its voltage-current characteristics. Project supported by the National Natural Science Foundation of China (Grant Nos. 11575050 and 10805013), the Midwest Universities Comprehensive Strength Promotion Project, the Natural Science Foundation of Hebei Province, China (Grant Nos. A2016201042 and A2015201092), and the Research Foundation of Education Bureau of Hebei Province, China (Grant No. LJRC011).
Hydrodynamics of Lock-exchange Turbidity Currents down a Slope Based on Direct Numerical Simulation
Zhao, Liang; Lin, Ying-Tien; Hu, Peng; Liang, Xiaolong; He, Zhiguo
2016-01-01
Turbidity currents play a vital role in various geophysical environments. However, until now, few studies have taken into the effects of both suspended particle and slope on its evolution, which requires a precise information of the spatio-temporal flow field. Hence, this study presents high-resolution and two-dimensional direct numerical simulations (DNS) of lock-exchange turbidity currents down a slope. By analyzing front velocity, water entrainment, and energy budget, the factors that affect the driving force, thus the development of the turbidity current, are detailedly investigated. The front velocity history exhibits three distinct stages over time, i.e., a short acceleration stage, a quasi-constant stage, and a deceleration stage. The calculation of the entrainment ratio shows that the mixing due to the collapse of the dense fluid is much stronger than that due to the Kelvin-Helmholtz instabilities and turbulent billows. For a turbidity current down a slope, the entrainment volume of ambient water decr...
Pore-Network Modeling vs. Direct Numerical Simulation: a Comparative Study
Mehmani, Y.; Tchelepi, H.
2016-12-01
Pore-scale models of flow and transport fall into one of two broad categories: (a) direct numerical simulators (DNS) and (b) pore-network models (PNM). The former is more fundamental as it solves the governing equations on the "actual" pore space geometry obtained through some kind of imaging technology (e.g., µCT). Its drawback is that it is computationally very expensive. PNM, however, reduces the complex pore-space geometry into a "ball-and-stick" network representation, which makes it highly efficient. But geometric simplifications are accompanied by secondary simplifications in the flow and transport physics, which result in a loss of predictive accuracy. We perform one-to-one comparisons between PNM and DNS simulations (i.e., on the same porous media) to assess the impact of such simplifications on macroscopic single-phase transport dynamics. DNS simulations are performed using the popular OpenFOAM software, while our PNM utilizes a particle-tracking approach. The influence of order and disorder in the pore space morphology on the accuracy of PNM predictions is discussed.
Direct Numerical Simulation of a Cavity-Stabilized Ethylene/Air Premixed Flame
Chen, Jacqueline; Konduri, Aditya; Kolla, Hemanth; Rauch, Andreas; Chelliah, Harsha
2016-11-01
Cavity flame holders have been shown to be important for flame stabilization in scramjet combustors. In the present study the stabilization of a lean premixed ethylene/air flame in a rectangular cavity at thermo-chemical conditions relevant to scramjet combustors is simulated using a compressible reacting multi-block direct numerical simulation solver, S3D, incorporating a 22 species ethylene-air reduced chemical model. The fuel is premixed with air to an equivalence ratio of 0.4 and enters the computational domain at Mach numbers between 0.3 and 0.6. An auxiliary inert channel flow simulation is used to provide the turbulent velocity profile at the inlet for the reacting flow simulation. The detailed interaction between intense turbulence, nonequilibrium concentrations of radical species formed in the cavity and mixing with the premixed main stream under density variations due to heat release rate and compressibility effects is quantified. The mechanism for flame stabilization is quantified in terms of relevant non-dimensional parameters, and detailed analysis of the flame and turbulence structure will be presented. We acknowledge the sponsorship of the AFOSR-NSF Joint Effort on Turbulent Combustion Model Assumptions and the DOE Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences.
Direct numerical simulation of a low momentum round jet in channel crossflow
Energy Technology Data Exchange (ETDEWEB)
Wu, Zhao, E-mail: zhao.wu@manchester.ac.uk; Laurence, Dominique; Afgan, Imran
2017-03-15
Highlights: • Detailed flow physics of jet in crossflow with low velocity ratio, R, is analysed. • The horseshoe vortex comes from the reversed jet fluid, different from high R JICF. • CVP comes from the stretching and reorientation of the injection-flow vorticity. • Recirculation is seen at the downstream low-pressure region. • The shear layer vortices are from shed crossflow boundary layer vortices. - Abstract: Results of a direct numerical simulation of a jet in crossflow with passive scalar mixing are presented. The laminar jet issues from a circular exit into the channel crossflow with a low jet-to-crossflow velocity ratio of 1/6. The governing equations are solved by Incompact3d, an open-source code combining the high-order compact scheme and Poisson spectral solver. An internal recycling approach is used to generate the fully turbulent channel flow profile. Four main flow structures are identified: 1) a large recirculation seen immediately downstream of the jet-exit; 2) a contour-rotating vortex pair formed from the stretching and reorientation of the injection-flow vorticity; 3) a horseshoe vortex generated as a result of the stretching of the vorticity at the jet-exit windward side; 4) shear layer vortices coming from the lifted and shed crossflow boundary layer vorticity. Passive scalar profiles show the mixing are strong in the shear layer where the crossflow fluid encounters the jet fluid. The database is made available online for public access.
Direct Numerical Simulation of Hypersonic Turbulent Boundary Layer inside an Axisymmetric Nozzle
Huang, Junji; Zhang, Chao; Duan, Lian; Choudhari, Meelan M.
2017-01-01
As a first step toward a study of acoustic disturbance field within a conventional, hypersonic wind tunnel, direct numerical simulations (DNS) of a Mach 6 turbulent boundary layer on the inner wall of a straight axisymmetric nozzle are conducted and the results are compared with those for a flat plate. The DNS results for a nozzle radius to boundary-layer thickness ratio of 5:5 show that the turbulence statistics of the nozzle-wall boundary layer are nearly unaffected by the transverse curvature of the nozzle wall. Before the acoustic waves emanating from different parts of the nozzle surface can interfere with each other and undergo reflections from adjacent portions of the nozzle surface, the rms pressure fluctuation beyond the boundary layer edge increases toward the nozzle axis, apparently due to a focusing effect inside the axisymmetric configuration. Spectral analysis of pressure fluctuations at both the wall and the freestream indicates a similar distribution of energy content for both the nozzle and the flat plate, with the peak of the premultiplied frequency spectrum at a frequency of [(omega)(delta)]/U(sub infinity) approximately 6.0 inside the free stream and at [(omega)(delta)]/U(sub infinity) approximately 2.0 along the wall. The present results provide the basis for follow-on simulations involving reverberation effects inside the nozzle.
Bisetti, Fabrizio; Attili, Antonio; Pitsch, Heinz
2014-08-13
Combustion of fossil fuels is likely to continue for the near future due to the growing trends in energy consumption worldwide. The increase in efficiency and the reduction of pollutant emissions from combustion devices are pivotal to achieving meaningful levels of carbon abatement as part of the ongoing climate change efforts. Computational fluid dynamics featuring adequate combustion models will play an increasingly important role in the design of more efficient and cleaner industrial burners, internal combustion engines, and combustors for stationary power generation and aircraft propulsion. Today, turbulent combustion modelling is hindered severely by the lack of data that are accurate and sufficiently complete to assess and remedy model deficiencies effectively. In particular, the formation of pollutants is a complex, nonlinear and multi-scale process characterized by the interaction of molecular and turbulent mixing with a multitude of chemical reactions with disparate time scales. The use of direct numerical simulation (DNS) featuring a state of the art description of the underlying chemistry and physical processes has contributed greatly to combustion model development in recent years. In this paper, the analysis of the intricate evolution of soot formation in turbulent flames demonstrates how DNS databases are used to illuminate relevant physico-chemical mechanisms and to identify modelling needs.
Yu, Rixin; Lipatnikov, Andrei N.
2017-06-01
A three-dimensional (3D) direct numerical simulation (DNS) study of the propagation of a reaction wave in forced, constant-density, statistically stationary, homogeneous, isotropic turbulence is performed by solving Navier-Stokes and reaction-diffusion equations at various (from 0.5 to 10) ratios of the rms turbulent velocity U' to the laminar wave speed, various (from 2.1 to 12.5) ratios of an integral length scale of the turbulence to the laminar wave thickness, and two Zeldovich numbers Ze=6.0 and 17.1. Accordingly, the Damköhler and Karlovitz numbers are varied from 0.2 to 25.1 and from 0.4 to 36.2, respectively. Contrary to an earlier DNS study of self-propagation of an infinitely thin front in statistically the same turbulence, the bending of dependencies of the mean wave speed on U' is simulated in the case of a nonzero thickness of the local reaction wave. The bending effect is argued to be controlled by inefficiency of the smallest scale turbulent eddies in wrinkling the reaction-zone surface, because such small-scale wrinkles are rapidly smoothed out by molecular transport within the local reaction wave.
Direct numerical simulation of the motion of circular pollutant particles in Newtonian fluid
Institute of Scientific and Technical Information of China (English)
SHAO Xue-ming; LIN Jian-zhong; YU Zhao-sheng
2003-01-01
An improved implementation of distributed multiplier/fictitious domain method is presented for the direct numerical simulation of particulate flow. The key improvement is to replace a finite-element triangulation for the velocity and a "twice-coarser" triangulation for the pressure with a rectangular discretization for the velocity and pressure. For code validation, the sedimentation of a single particle in a two-dimensional channel was simulated. The results show that the simulation is independent of the mesh size as well as the time step. The comparison between experimental data and our simulation shows that our code can give a more accurate simulation on the motion of particles than previous DLM code. Our code was then applied to simulate the sedimentation of 600 particles in a rectangular box. The falling course is presented and discussed. At the same time, this simulation also demonstrates that the method presented in this paper can be used for solving the initial problems involving a lager number of particles exactly with computing durations kept at acceptable levels.
GPU accelerated flow solver for direct numerical simulation of turbulent flows
Salvadore, Francesco; Bernardini, Matteo; Botti, Michela
2013-02-01
Graphical processing units (GPUs), characterized by significant computing performance, are nowadays very appealing for the solution of computationally demanding tasks in a wide variety of scientific applications. However, to run on GPUs, existing codes need to be ported and optimized, a procedure which is not yet standardized and may require non trivial efforts, even to high-performance computing specialists. In the present paper we accurately describe the porting to CUDA (Compute Unified Device Architecture) of a finite-difference compressible Navier-Stokes solver, suitable for direct numerical simulation (DNS) of turbulent flows. Porting and validation processes are illustrated in detail, with emphasis on computational strategies and techniques that can be applied to overcome typical bottlenecks arising from the porting of common computational fluid dynamics solvers. We demonstrate that a careful optimization work is crucial to get the highest performance from GPU accelerators. The results show that the overall speedup of one NVIDIA Tesla S2070 GPU is approximately 22 compared with one AMD Opteron 2352 Barcelona chip and 11 compared with one Intel Xeon X5650 Westmere core. The potential of GPU devices in the simulation of unsteady three-dimensional turbulent flows is proved by performing a DNS of a spatially evolving compressible mixing layer.
GPU accelerated flow solver for direct numerical simulation of turbulent flows
Energy Technology Data Exchange (ETDEWEB)
Salvadore, Francesco [CASPUR – via dei Tizii 6/b, 00185 Rome (Italy); Bernardini, Matteo, E-mail: matteo.bernardini@uniroma1.it [Department of Mechanical and Aerospace Engineering, University of Rome ‘La Sapienza’ – via Eudossiana 18, 00184 Rome (Italy); Botti, Michela [CASPUR – via dei Tizii 6/b, 00185 Rome (Italy)
2013-02-15
Graphical processing units (GPUs), characterized by significant computing performance, are nowadays very appealing for the solution of computationally demanding tasks in a wide variety of scientific applications. However, to run on GPUs, existing codes need to be ported and optimized, a procedure which is not yet standardized and may require non trivial efforts, even to high-performance computing specialists. In the present paper we accurately describe the porting to CUDA (Compute Unified Device Architecture) of a finite-difference compressible Navier–Stokes solver, suitable for direct numerical simulation (DNS) of turbulent flows. Porting and validation processes are illustrated in detail, with emphasis on computational strategies and techniques that can be applied to overcome typical bottlenecks arising from the porting of common computational fluid dynamics solvers. We demonstrate that a careful optimization work is crucial to get the highest performance from GPU accelerators. The results show that the overall speedup of one NVIDIA Tesla S2070 GPU is approximately 22 compared with one AMD Opteron 2352 Barcelona chip and 11 compared with one Intel Xeon X5650 Westmere core. The potential of GPU devices in the simulation of unsteady three-dimensional turbulent flows is proved by performing a DNS of a spatially evolving compressible mixing layer.
Direct Numerical Simulation of Zero-Pressure Gradient and Sink Flow Turbulent Boundary Layers
Ramesh, O.; Patwardhan, Saurabh
2010-11-01
Direct Numerical Simulations have been performed for the zero pressure gradient (ZPG) (600 < Reθ< 900) and for the sink flow turbulent boundary layers (K = 7.71x10-7). A finite difference code on Cartesian grid was used to perform the simulations. Inflow generation method developed by Lund et al. was used to generate inflow boundary condition for the ZPG case. This method was slightly modified for the case of sink flow in view of self-similarity it possesses in the inner co-ordinates. Hence, there was no need to use empirical relations for the calculation of inlet θ or δ and rescaling in outer co-ordinates. The average statistics obtained from the simulations are in close agreement with the experimental as well as DNS data available in the literature. The intermittency distribution in the case of sink flow approaches zero inside the boundary layer (y = 0.8δ), an observation which is also confirmed by the experiments. This effect could be due to the acceleration near the boundary layer edge which suppresses the turbulent fluctuations near the boundary layer edge.
Directory of Open Access Journals (Sweden)
Hang Zhang
2014-02-01
Full Text Available The rapid development of numerical modeling techniques has led to more accurate results in modeling metal solidification processes. In this study, the cellular automaton-finite difference (CA-FD method was used to simulate the directional solidification (DS process of single crystal (SX superalloy blade samples. Experiments were carried out to validate the simulation results. Meanwhile, an intelligent model based on fuzzy control theory was built to optimize the complicate DS process. Several key parameters, such as mushy zone width and temperature difference at the cast-mold interface, were recognized as the input variables. The input variables were functioned with the multivariable fuzzy rule to get the output adjustment of withdrawal rate (v (a key technological parameter. The multivariable fuzzy rule was built, based on the structure feature of casting, such as the relationship between section area, and the delay time of the temperature change response by changing v, and the professional experience of the operator as well. Then, the fuzzy controlling model coupled with CA-FD method could be used to optimize v in real-time during the manufacturing process. The optimized process was proven to be more flexible and adaptive for a steady and stray-grain free DS process.
Direct numerical simulation of stationary lean premixed methane-air flames under intense turbulence
Energy Technology Data Exchange (ETDEWEB)
Sankaran, Ramanan [ORNL; Hawkes, Evatt R [Sandia National Laboratories (SNL); Yoo, Chun S [Sandia National Laboratories (SNL); Chen, Jacqueline H [Sandia National Laboratories (SNL); Lu, Tianfeng [Princeton University; Law, Chung K [Princeton University
2007-01-01
Direct numerical simulation of a three-dimensional spatially- developing turbulent Bunsen flame has been performed at three different turbulence intensities. The simulations are performed using a reduced methane-air chemical mechanism which is specifically tailored for the lean premixed conditions simulated here. A planar-jet turbulent Bunsen flame configuration is used in which turbulent preheated methane-air mixture at 0.7 equivalence ratio issues through a central jet and is surrounded by a hot laminar coflow of burned products. The turbulence characteristics at the jet inflow are selected such that combustion occurs in the thin reaction zones (TRZ) regime. At the lowest turbulence intensity the conditions fall on the boundary between the TRZ regime and the corrugated flamelet regime. At the highest turbulence intensity the conditions correspond to the boundary between the TRZ regime and the broken reaction zones regime. The data from the three simulations is analyzed to understand the effect of turbulent stirring on the flame structure and thickness. Statistical analysis of the data shows that the thermal preheat layer of the flame is thickened due to the action of turbulence, but the reaction zone is not significantly affected.
Institute of Scientific and Technical Information of China (English)
杨飞; 马瑞光; 吴翊; 孙昊; 纽春萍; 荣命哲
2012-01-01
This paper focuses on the numerical investigation of arc plasma behavior during arc commutation process in a medium-voltage direct current circuit breaker （DCCB） contact system. A three-dimensional magneto-hydrodynamic （MHD） model of air arc plasma in the contact system of a DCCB is developed, based on commercial software FLUENT. Coupled electromagnetic and gas dynamic interactions are considered as usual, and a thin layer of nonlinear electrical resistance elements is used to represent the voltage drop of plasma sheath and the formation of new arc root. The distributions of pressure, temperature, gas flow and current density of arc plasma in arc region are calculated. The simulation results indicate that the pressure distribution related to the contact system has a strong effect on the arc commutation process, arising from the change of electrical conductivity in the arc root region. In DCCB contact system, the pressure of arc root region will be concentrated and higher if the space above the moving contact is enclosed, which is not good for arc root commutation. However, when the region is opened, the pressure distribution would be lower and more evenly, which is favorable for the arc root commutation.
Bisetti, Fabrizio
2014-07-14
Combustion of fossil fuels is likely to continue for the near future due to the growing trends in energy consumption worldwide. The increase in efficiency and the reduction of pollutant emissions from combustion devices are pivotal to achieving meaningful levels of carbon abatement as part of the ongoing climate change efforts. Computational fluid dynamics featuring adequate combustion models will play an increasingly important role in the design of more efficient and cleaner industrial burners, internal combustion engines, and combustors for stationary power generation and aircraft propulsion. Today, turbulent combustion modelling is hindered severely by the lack of data that are accurate and sufficiently complete to assess and remedy model deficiencies effectively. In particular, the formation of pollutants is a complex, nonlinear and multi-scale process characterized by the interaction of molecular and turbulent mixing with a multitude of chemical reactions with disparate time scales. The use of direct numerical simulation (DNS) featuring a state of the art description of the underlying chemistry and physical processes has contributed greatly to combustion model development in recent years. In this paper, the analysis of the intricate evolution of soot formation in turbulent flames demonstrates how DNS databases are used to illuminate relevant physico-chemical mechanisms and to identify modelling needs. © 2014 The Author(s) Published by the Royal Society.
Assessment of tomographic PIV in wall-bounded turbulence using direct numerical simulation data
Energy Technology Data Exchange (ETDEWEB)
Silva, C.M. de; Baidya, R.; Khashehchi, M.; Marusic, I. [University of Melbourne, Department of Mechanical Engineering, Melbourne, VIC (Australia)
2012-02-15
Simulations of tomographic particle image velocimetry (Tomo-PIV) are performed using direct numerical simulation data of a channel flow at Reynolds number of Re{sub {tau}} = 934, to investigate the influence of experimental parameters such as camera position, seeding density, interrogation volume size and spatial resolution. The simulations employ camera modelling, a Mie scattering illumination model, lens distortion effects and calibration to realistically model a tomographic experiment. Results are presented for camera position and orientation in three-dimensional space, to obtain an optimal reconstruction quality. Furthermore, a quantitative analysis is performed on the accuracy of first and second order flow statistics, at various voxel sizes normalised using the viscous inner length scale. This enables the result to be used as a general reference for wall-bounded turbulent experiments. In addition, a ratio relating seeding density and the interrogation volume size is proposed to obtain an optimal reference value that remains constant. This can be used to determine the required seeding density concentration for a certain interrogation volume size. (orig.)
Utilizing Direct Numerical Simulations of Transition and Turbulence in Design Optimization
Rai, Man M.
2015-01-01
Design optimization methods that use the Reynolds-averaged Navier-Stokes equations with the associated turbulence and transition models, or other model-based forms of the governing equations, may result in aerodynamic designs with actual performance levels that are noticeably different from the expected values because of the complexity of modeling turbulence/transition accurately in certain flows. Flow phenomena such as wake-blade interaction and trailing edge vortex shedding in turbines and compressors (examples of such flows) may require a computational approach that is free of transition/turbulence models, such as direct numerical simulations (DNS), for the underlying physics to be computed accurately. Here we explore the possibility of utilizing DNS data in designing a turbine blade section. The ultimate objective is to substantially reduce differences between predicted performance metrics and those obtained in reality. The redesign of a typical low-pressure turbine blade section with the goal of reducing total pressure loss in the row is provided as an example. The basic ideas presented here are of course just as applicable elsewhere in aerodynamic shape optimization as long as the computational costs are not excessive.
Direct numerical simulation of powder electrification in a turbulent channel flow
Grosshans, Holger; Papalexandris, Miltiadis
2016-11-01
Particle electrification is often encountered in process industries. Sometimes it has useful applications, such as the control of particle trajectories through an electric field. In other situations is has negative effects. For example, during pneumatic transport it can cause particle deposition or, even worse, spark discharges and subsequent fires and explosions. Despite its frequent occurrence, due to the complexity of the underlying physical mechanisms, there are still many open questions regarding particle electrification and inconsistent theoretical predictions have been reported. The objective of our work is to gain a better understanding and physical insight of this phenomenon. To this end, we performed Direct Numerical Simulations to analyze the turbulent flow of a carrier fluid with immersed particles in a channel. Moreover, the motion of the particles was computed in a Lagrangian framework and dynamic models accounting for the particle-wall and particle-particle charge exchange were implemented. In our talk, we discuss in detail the effect of the fluid turbulence to the build-up of the electrostatic charge of the particles. Furthermore, we elaborate on the influence of the particle Stokes number and gravitational forces to the process of powder charging. Supported by the National Research Fund of Belgium (FNRS) under the GRANMIX Projet de Recherche Grant.
Direct numerical simulation of fluid-acoustic interactions in a recorder with tone holes.
Yokoyama, Hiroshi; Miki, Akira; Onitsuka, Hirofumi; Iida, Akiyoshi
2015-08-01
To clarify fluid-acoustic interactions in an actual recorder with opened and closed tone holes, flow and acoustic fields were directly numerically simulated on the basis of the compressible Navier-Stokes equations. To validate the simulation accuracy, the flow field around the windway and sound pressure above the window were measured. The predicted acoustic fields clarify changes of the positions of pressure nodes and anti-nodes in accordance with the state of the tone holes and the Mach number of the jet velocity. The fundamental mechanism of the self-sustained oscillations in a three-dimensional actual recorder is visualized by the predicted acoustic and flow fields. This result is also consistent with the relationship between the jet behaviors and pressure fluctuations based on the jet-drive model. Moreover, the effects of the fine vortices in the jet, which appear at the high Mach number of jet velocity of 0.099, on the sound are discussed. The time difference between the generation of the disturbances and the most intense deflection of the jet is identified and compared with the time delay of acoustic reflection around the window.
Large scale Direct Numerical Simulation of premixed turbulent jet flames at high Reynolds number
Attili, Antonio; Luca, Stefano; Lo Schiavo, Ermanno; Bisetti, Fabrizio; Creta, Francesco
2016-11-01
A set of direct numerical simulations of turbulent premixed jet flames at different Reynolds and Karlovitz numbers is presented. The simulations feature finite rate chemistry with 16 species and 73 reactions and up to 22 Billion grid points. The jet consists of a methane/air mixture with equivalence ratio ϕ = 0 . 7 and temperature varying between 500 and 800 K. The temperature and species concentrations in the coflow correspond to the equilibrium state of the burnt mixture. All the simulations are performed at 4 atm. The flame length, normalized by the jet width, decreases significantly as the Reynolds number increases. This is consistent with an increase of the turbulent flame speed due to the increased integral scale of turbulence. This behavior is typical of flames in the thin-reaction zone regime, which are affected by turbulent transport in the preheat layer. Fractal dimension and topology of the flame surface, statistics of temperature gradients, and flame structure are investigated and the dependence of these quantities on the Reynolds number is assessed.
Direct Numerical Simulations of Type Ia Supernovae Flames I: The Landau-Darrieus Instability
Bell, J B; Rendleman, C A; Woosley, S E; Zingale, M A
2004-01-01
Planar flames are intrinsically unstable in open domains due to the thermal expansion across the burning front--the Landau-Darrieus instability. This instability leads to wrinkling and growth of the flame surface, and corresponding acceleration of the flame, until it is stabilized by cusp formation. We look at the Landau-Darrieus instability for C/O thermonuclear flames at conditions relevant to the late stages of a Type Ia supernova explosion. Two-dimensional direct numerical simulations of both single-mode and multi-mode perturbations using a low Mach number hydrodynamics code are presented. We show the effect of the instability on the flame speed as a function of both the density and domain size, demonstrate the existence of the small scale cutoff to the growth of the instability, and look for the proposed breakdown of the non-linear stabilization at low densities. The effects of curvature on the flame as quantified through measurements of the growth rate and computation of the corresponding Markstein numb...
Direct Numerical Simulation of biomass pyrolysis and combustion with gas phase reactions
Awasthi, A.; Kuerten, J. G. M.; Geurts, B. J.
2016-09-01
We present Direct Numerical Simulation of biomass pyrolysis and combustion in a turbulent channel flow. The model includes simplified models for biomass pyrolysis and char combustion along with a model for particle tracking. The gas phase is modelled as a mixture of reacting gas species. The gas-particle interactions for mass, momentum, and energy exchange are included by two-way coupling terms. The effect of two-way coupling on the conversion time of biomass particles is found noticeable for particle volume fractions > 10-5. We also observe that at constant volume fraction the effect of two-way coupling increases as the particle size is reduced, due to the higher total heat exchange area in case of smaller particles. The inclusion of gas phase homogeneous reactions in the DNS model decreases the biomass pyrolysis time due to higher gas temperatures. In contrast, including gas phase reactions increases the combustion time of biomass due to the lower concentration of oxygen at the particle surface.
Direct numerical simulation and statistical analysis of turbulent convection in lead-bismuth
Energy Technology Data Exchange (ETDEWEB)
Otic, I.; Grotzbach, G. [Forschungszentrum Karlsruhe GmbH, Institut fuer Kern-und Energietechnik (Germany)
2003-07-01
Improved turbulent heat flux models are required to develop and analyze the reactor concept of an lead-bismuth cooled Accelerator-Driven-System. Because of specific properties of many liquid metals we have still no sensors for accurate measurements of the high frequency velocity fluctuations. So, the development of the turbulent heat transfer models which are required in our CFD (computational fluid dynamics) tools needs also data from direct numerical simulations of turbulent flows. We use new simulation results for the model problem of Rayleigh-Benard convection to show some peculiarities of the turbulent natural convection in lead-bismuth (Pr = 0.025). Simulations for this flow at sufficiently large turbulence levels became only recently feasible because this flow requires the resolution of very small velocity scales with the need for recording long-wave structures for the slow changes in the convective temperature field. The results are analyzed regarding the principle convection and heat transfer features. They are also used to perform statistical analysis to show that the currently available modeling is indeed not adequate for these fluids. Basing on the knowledge of the details of the statistical features of turbulence in this convection type and using the two-point correlation technique, a proposal for an improved statistical turbulence model is developed which is expected to account better for the peculiarities of the heat transfer in the turbulent convection in low Prandtl number fluids. (authors)
Energy Technology Data Exchange (ETDEWEB)
Wang, Guoqing; Mukherjee, Partha P.; Wang, Chao-Yang [Electrochemical Engine Center (ECEC), Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA 16802 (United States)
2007-06-30
The cathode catalyst layer (CL), due to sluggish oxygen reduction reaction and several transport losses therein, plays an important role in the overall performance of polymer electrolyte fuel cells (PEFCs). The relative volume fractions of the constituent phases, i.e. the electronic, electrolyte and void phases, of the cathode CL need to be selected appropriately in order to achieve an optimal balance between oxygen diffusion and proton conduction. In this work, the influence of electrolyte and void phase fractions of the cathode CL on the cell performance is investigated based on a pore-level description of species and charge transport through a random CL microstructure via the direct numerical simulation (DNS) model. Additionally, the effects of inlet relative humidity and net water transport from the anode on the cathode performance have been studied which indicate the interdependence between the CL composition and the cell operating conditions. The results indicate that the low humidity operation benefits the performance by enhancing the oxygen transport especially under high current densities. Finally, the DNS model predicts the volume fractions of 0.4 and 0.26 for the void and electrolyte phases, respectively, as the optimal composition of the catalyst layer for the best performance. (author)
Direct numerical simulation of broadband trailing edge noise from a NACA 0012 airfoil
Mehrabadi, Mohammad; Bodony, Daniel
2016-11-01
Commercial jet-powered aircraft produce unwanted noise at takeoff and landing when they are close to near-airport communities. Modern high-bypass-ratio turbofan engines have reduced jet exhaust noise sufficiently such that noise from the main fan is now significant. In preparation for a large-eddy simulation of the NASA/GE Source Diagnostic Test Fan, we study the broadband noise due to the turbulent flow on a NACA 0012 airfoil at zero degree angle-of-attack, a chord-based Reynolds number of 408,000 and a Mach number of 0.115 using direct numerical simulation (DNS) and wall-modeled large-eddy simulation (WMLES). The flow conditions correspond to existing experimental data. We investigate the roughness-induced transition-to-turbulence and sound generation from a DNS perspective as well as examine how these two features are captured by a wall model. Comparisons between the DNS- and WMLES-predicted noise are made and provide guidance on the use of WMLES for broadband fan noise prediction. AeroAcoustics Research Consortium.
Direct numerical simulation of turbulent combustion: fundamental insights towards predictive models
Hawkes, Evatt R.; Sankaran, Ramanan; Sutherland, James C.; Chen, Jacqueline H.
2005-01-01
The advancement of our basic understanding of turbulent combustion processes and the development of physics-based predictive tools for design and optimization of the next generation of combustion devices are strategic areas of research for the development of a secure, environmentally sound energy infrastructure. In direct numerical simulation (DNS) approaches, all scales of the reacting flow problem are resolved. However, because of the magnitude of this task, DNS of practical high Reynolds number turbulent hydrocarbon flames is out of reach of even terascale computing. For the foreseeable future, the approach to this complex multi-scale problem is to employ distinct but synergistic approaches to tackle smaller sub-ranges of the complete problem, which then require models for the small scale interactions. With full access to the spatially and temporally resolved fields, DNS can play a major role in the development of these models and in the development of fundamental understanding of the micro-physics of turbulence-chemistry interactions. Two examples, from simulations performed at terascale Office of Science computing facilities, are presented to illustrate the role of DNS in delivering new insights to advance the predictive capability of models. Results are presented from new three-dimensional DNS with detailed chemistry of turbulent non-premixed jet flames, revealing the differences between mixing of passive and reacting scalars, and determining an optimal lower dimensional representation of the full thermochemical state space.
Numerical Evaluation of Storm Surge Indices for Public Advisory Purposes
Bass, B.; Bedient, P. B.; Dawson, C.; Proft, J.
2016-12-01
After the devastating hurricane season of 2005, shortcomings with the Saffir-Simpson Hurricane Scale's (SSHS) ability to characterize a tropical cyclones potential to generate storm surge became widely apparent. As a result, several alternative surge indices were proposed to replace the SSHS, including Powell and Reinhold's Integrated Kinetic Energy (IKE) factor, Kantha's Hurricane Surge Index (HSI), and Irish and Resio's Surge Scale (SS). Of the previous, the IKE factor is the only surge index to-date that truly captures a tropical cyclones integrated intensity, size, and wind field distribution. However, since the IKE factor was proposed in 2007, an accurate assessment of this surge index has not been performed. This study provides the first quantitative evaluation of the IKEs ability to serve as a predictor of a tropical cyclones potential surge impacts as compared to other alternative surge indices. Using the tightly coupled ADvanced CIRCulation and Simulating WAves Nearshore models, the surge and wave responses of Hurricane Ike (2008) and 78 synthetic tropical cyclones were evaluated against the SSHS, IKE, HSI and SS. Results along the upper TX coast of the Gulf of Mexico demonstrate that the HSI performs best in capturing the peak surge response of a tropical cyclone, while the IKE accounting for winds greater than tropical storm intensity (IKETS) provides the most accurate estimate of a tropical cyclones regional surge impacts. These results demonstrate that the appropriate selection of a surge index ultimately depends on what information is of interest to be conveyed to the public and/or scientific community.
Numerical evaluation of acoustic power radiation and radiation efficiencies of baffled plates
Lemmen, R.L.C.; Panuszka, R.J.
1996-01-01
In this paper expressions are given for the numerical evaluation of radiation efficiencies and power radiation of baffled plates. The expressions can be used as a postprocessing tool in the Finite Element Method. Numerical results for simply supported plates are presented and compared with results o
Graham, Jonathan Pietarila; Mininni, Pablo D; Pouquet, Annick
2005-10-01
We present direct numerical simulations and Lagrangian averaged (also known as alpha model) simulations of forced and free decaying magnetohydrodynamic turbulence in two dimensions. The statistics of sign cancellations of the current at small scales is studied using both the cancellation exponent and the fractal dimension of the structures. The alpha model is found to have the same scaling behavior between positive and negative contributions as the direct numerical simulations. The alpha model is also able to reproduce the time evolution of these quantities in free decaying turbulence. At large Reynolds numbers, an independence of the cancellation exponent with the Reynolds numbers is observed.
Directory of Open Access Journals (Sweden)
S. D. Parkinson
2014-09-01
Full Text Available High-resolution direct numerical simulations (DNSs are an important tool for the detailed analysis of turbidity current dynamics. Models that resolve the vertical structure and turbulence of the flow are typically based upon the Navier–Stokes equations. Two-dimensional simulations are known to produce unrealistic cohesive vortices that are not representative of the real three-dimensional physics. The effect of this phenomena is particularly apparent in the later stages of flow propagation. The ideal solution to this problem is to run the simulation in three dimensions but this is computationally expensive. This paper presents a novel finite-element (FE DNS turbidity current model that has been built within Fluidity, an open source, general purpose, computational fluid dynamics code. The model is validated through re-creation of a lock release density current at a Grashof number of 5 × 106 in two and three dimensions. Validation of the model considers the flow energy budget, sedimentation rate, head speed, wall normal velocity profiles and the final deposit. Conservation of energy in particular is found to be a good metric for measuring model performance in capturing the range of dynamics on a range of meshes. FE models scale well over many thousands of processors and do not impose restrictions on domain shape, but they are computationally expensive. The use of adaptive mesh optimisation is shown to reduce the required element count by approximately two orders of magnitude in comparison with fixed, uniform mesh simulations. This leads to a substantial reduction in computational cost. The computational savings and flexibility afforded by adaptivity along with the flexibility of FE methods make this model well suited to simulating turbidity currents in complex domains.
Energy Technology Data Exchange (ETDEWEB)
Krisman, Alexander; Hawkes, Evatt Robert.; Talei, Mohsen; Bhagatwala, Ankit; Chen, Jacqueline H.
2016-11-11
In diesel engines, combustion is initiated by a two-staged autoignition that includes both low- and high-temperature chemistry. The location and timing of both stages of autoignition are important parameters that influence the development and stabilisation of the flame. In this study, a two-dimensional direct numerical simulation (DNS) is conducted to provide a fully resolved description of ignition at diesel engine-relevant conditions. The DNS is performed at a pressure of 40 atmospheres and at an ambient temperature of 900 K using dimethyl ether (DME) as the fuel, with a 30 species reduced chemical mechanism. At these conditions, similar to diesel fuel, DME exhibits two-stage ignition. The focus of this study is on the behaviour of the low-temperature chemistry (LTC) and the way in which it influences the high-temperature ignition. The results show that the LTC develops as a “spotty” first-stage autoignition in lean regions which transitions to a diffusively supported cool-flame and then propagates up the local mixture fraction gradient towards richer regions. The cool-flame speed is much faster than can be attributed to spatial gradients in first-stage ignition delay time in homogeneous reactors. The cool-flame causes a shortening of the second-stage ignition delay times compared to a homogeneous reactor and the shortening becomes more pronounced at richer mixtures. Multiple high-temperature ignition kernels are observed over a range of rich mixtures that are much richer than the homogeneous most reactive mixture and most kernels form much earlier than suggested by the homogeneous ignition delay time of the corresponding local mixture. Altogether, the results suggest that LTC can strongly influence both the timing and location in composition space of the high-temperature ignition.
Parkinson, S. D.; Hill, J.; Piggott, M. D.; Allison, P. A.
2014-09-01
High-resolution direct numerical simulations (DNSs) are an important tool for the detailed analysis of turbidity current dynamics. Models that resolve the vertical structure and turbulence of the flow are typically based upon the Navier-Stokes equations. Two-dimensional simulations are known to produce unrealistic cohesive vortices that are not representative of the real three-dimensional physics. The effect of this phenomena is particularly apparent in the later stages of flow propagation. The ideal solution to this problem is to run the simulation in three dimensions but this is computationally expensive. This paper presents a novel finite-element (FE) DNS turbidity current model that has been built within Fluidity, an open source, general purpose, computational fluid dynamics code. The model is validated through re-creation of a lock release density current at a Grashof number of 5 × 106 in two and three dimensions. Validation of the model considers the flow energy budget, sedimentation rate, head speed, wall normal velocity profiles and the final deposit. Conservation of energy in particular is found to be a good metric for measuring model performance in capturing the range of dynamics on a range of meshes. FE models scale well over many thousands of processors and do not impose restrictions on domain shape, but they are computationally expensive. The use of adaptive mesh optimisation is shown to reduce the required element count by approximately two orders of magnitude in comparison with fixed, uniform mesh simulations. This leads to a substantial reduction in computational cost. The computational savings and flexibility afforded by adaptivity along with the flexibility of FE methods make this model well suited to simulating turbidity currents in complex domains.
Direct Numerical Simulation of Evaporative Cooling at the Lateral Boundary of Shallow Cumulus Clouds
Heus, T.; Abma, D.; Mellado, J.
2012-12-01
This study investigates the dynamics of a narrow region of subsiding air at the lateral boundary of cumulus clouds, focusing on the role of evaporative cooling. Previous observational and large-eddy simulations showed the relevance of this subsiding shell in cloud dynamics, but have also showed that the size of this shell is well below what large-eddy simulations can resolve. Therefore, we have performed direct numerical simulations of an idealized subsiding shell to investigate accurately the complete turbulent field. The system develops a self-similar, Reynolds number independent flow which allows for the determination of explicit scaling laws relating the characteristic length, time and velocity scales of the shell. In particular, it is found that the shell width grows quadratically in time, and linearly with decreasing height. The magnitude of these growth rates confirm the importance of the subsiding shell because of the relatively fast development of entrainment-determining scales: for typical thermodynamic conditions in cumulus clouds, a velocity of the order of 1~m~s-1 and a thickness of the order of 10 meters are established in about 2 minutes. This fits well within the typical cloud life time, suggesting that our idealization is an adequate framework for the analysis of relevant aspects in the subsiding shell associated with buoyancy reversal. It also indicates that the scaling laws derived here can be used to estimate the potential strength of a subsiding shell and the mean lateral entrainment associated with it, provided an estimate of the local thermodynamical state of the cloud boundary. It is shown that the dominant parameter of this system is the saturation buoyancy, whereas the effect of the saturation mixing fraction is minor.uoyancy field in the subsiding shell. Blue colors are low values, red colors are high values.
Directory of Open Access Journals (Sweden)
S. D. Parkinson
2014-05-01
Full Text Available High resolution direct numerical simulations (DNS are an important tool for the detailed analysis of turbidity current dynamics. Models that resolve the vertical structure and turbulence of the flow are typically based upon the Navier–Stokes equations. Two-dimensional simulations are known to produce unrealistic cohesive vortices that are not representative of the real three-dimensional physics. The effect of this phenomena is particularly apparent in the later stages of flow propagation. The ideal solution to this problem is to run the simulation in three dimensions but this is computationally expensive. This paper presents a novel finite-element (FE DNS turbidity current model that has been built within Fluidity, an open source, general purpose, computational fluid dynamics code. The model is validated through re-creation of a lock release density current at a Grashof number of 5 × 106 in two, and three-dimensions. Validation of the model considers the flow energy budget, sedimentation rate, head speed, wall normal velocity profiles and the final deposit. Conservation of energy in particular is found to be a good metric for measuring mesh performance in capturing the range of dynamics. FE models scale well over many thousands of processors and do not impose restrictions on domain shape, but they are computationally expensive. Use of discontinuous discretisations and adaptive unstructured meshing technologies, which reduce the required element count by approximately two orders of magnitude, results in high resolution DNS models of turbidity currents at a fraction of the cost of traditional FE models. The benefits of this technique will enable simulation of turbidity currents in complex and large domains where DNS modelling was previously unachievable.
Mukkavilli, S. K.; Kay, M. J.; Taylor, R.; Prasad, A. A.; Troccoli, A.
2014-12-01
The Australian Solar Energy Forecasting System (ASEFS) project requires forecasting timeframes which range from nowcasting to long-term forecasts (minutes to two years). As concentrating solar power (CSP) plant operators are one of the key stakeholders in the national energy market, research and development enhancements for direct normal irradiance (DNI) forecasts is a major subtask. This project involves comparing different radiative scheme codes to improve day ahead DNI forecasts on the national supercomputing infrastructure running mesoscale simulations on NOAA's Weather Research & Forecast (WRF) model. ASEFS also requires aerosol data fusion for improving accurate representation of spatio-temporally variable atmospheric aerosols to reduce DNI bias error in clear sky conditions over southern Queensland & New South Wales where solar power is vulnerable to uncertainities from frequent aerosol radiative events such as bush fires and desert dust. Initial results from thirteen years of Bureau of Meteorology's (BOM) deseasonalised DNI and MODIS NASA-Terra aerosol optical depth (AOD) anomalies demonstrated strong negative correlations in north and southeast Australia along with strong variability in AOD (~0.03-0.05). Radiative transfer schemes, DNI and AOD anomaly correlations will be discussed for the population and transmission grid centric regions where current and planned CSP plants dispatch electricity to capture peak prices in the market. Aerosol and solar irradiance datasets include satellite and ground based assimilations from the national BOM, regional aerosol researchers and agencies. The presentation will provide an overview of this ASEFS project task on WRF and results to date. The overall goal of this ASEFS subtask is to develop a hybrid numerical weather prediction (NWP) and statistical/machine learning multi-model ensemble strategy that meets future operational requirements of CSP plant operators.
Temporal slow-growth formulation for direct numerical simulation of compressible wall-bounded flows
Topalian, Victor; Oliver, Todd A.; Ulerich, Rhys; Moser, Robert D.
2017-08-01
A slow-growth formulation for DNS of wall-bounded turbulent flow is developed and demonstrated to enable extension of slow-growth modeling concepts to wall-bounded flows with complex physics. As in previous slow-growth approaches, the formulation assumes scale separation between the fast scales of turbulence and the slow evolution of statistics such as the mean flow. This separation enables the development of approaches where the fast scales of turbulence are directly simulated while the forcing provided by the slow evolution is modeled. The resulting model admits periodic boundary conditions in the streamwise direction, which avoids the need for extremely long domains and complex inflow conditions that typically accompany spatially developing simulations. Further, it enables the use of efficient Fourier numerics. Unlike previous approaches [Guarini, Moser, Shariff, and Wray, J. Fluid Mech. 414, 1 (2000), 10.1017/S0022112000008466; Maeder, Adams, and Kleiser, J. Fluid Mech. 429, 187 (2001), 10.1017/S0022112000002718; Spalart, J. Fluid Mech. 187, 61 (1988), 10.1017/S0022112088000345], the present approach is based on a temporally evolving boundary layer and is specifically tailored to give results for calibration and validation of Reynolds-averaged Navier-Stokes (RANS) turbulence models. The use of a temporal homogenization simplifies the modeling, enabling straightforward extension to flows with complicating features, including cold and blowing walls. To generate data useful for calibration and validation of RANS models, special care is taken to ensure that the mean slow-growth forcing is closed in terms of the mean and other quantities that appear in standard RANS models, ensuring that there is no confounding between typical RANS closures and additional closures required for the slow-growth problem. The performance of the method is demonstrated on two problems: an essentially incompressible, zero-pressure-gradient boundary layer and a transonic boundary layer over
DEFF Research Database (Denmark)
Jacobsen, Rune Shim; Lavrinenko, Andrei; Frandsen, Lars Hagedorn
2005-01-01
We report on time-of-flight experimental measurements and numerical calculations of the group-index dispersion in a photonic crystal waveguide realized in silicon-on-insulator material. Experimentally group indices higher than 230 has been observed. Numerical 2D and 3D time-domain simulations show...
[Numerical evaluation of soil quality under different conservation tillage patterns].
Wu, Yu-Hong; Tian, Xiao-Hong; Chi, Wen-Bo; Nan, Xiong-Xiong; Yan, Xiao-Li; Zhu, Rui-Xiang; Tong, Yan-An
2010-06-01
A 9-year field experiment was conducted on the Guanzhong Plain of Shaanxi Province to study the effects of subsoiling, rotary tillage, straw return, no-till seeding, and traditional tillage on the soil physical and chemical properties and the grain yield in a winter wheat-summer maize rotation system, and a comprehensive evaluation was made on the soil quality under these tillage patterns by the method of principal components analysis (PCA). Comparing with traditional tillage, all the conservation tillage patterns improved soil fertility quality and soil physical properties. Under conservative tillage, the activities of soil urease and alkaline phosphatase increased significantly, soil quality index increased by 19.8%-44.0%, and the grain yield of winter wheat and summer maize (expect that under no till seeding with straw covering) increased by 13%-28% and 3%-12%, respectively. Subsoiling every other year, straw-chopping combined with rotary tillage, and straw-mulching combined with subsoiling not only increased crop yield, but also improved soil quality. Based on the economic and ecological benefits, the practices of subsoiling and straw return should be promoted.
NASA Numerical and Experimental Evaluation of UTRC Low Emissions Injector
Hicks, Yolanda R.; Tedder, Sarah A.; Anderson, Robert C.; Iannetti, Anthony C.; Smith, Lance L.; Dai, Zhongtao
2014-01-01
Computational and experimental analyses of a PICS-Pilot-In-Can-Swirler technology injector, developed by United Technologies Research Center (UTRC) are presented. NASA has defined technology targets for near term (called "N+1", circa 2015), midterm ("N+2", circa 2020) and far term ("N+3", circa 2030) that specify realistic emissions and fuel efficiency goals for commercial aircraft. This injector has potential for application in an engine to meet the Pratt & Whitney N+3 supersonic cycle goals, or the subsonic N+2 engine cycle goals. Experimental methods were employed to investigate supersonic cruise points as well as select points of the subsonic cycle engine; cruise, approach, and idle with a slightly elevated inlet pressure. Experiments at NASA employed gas analysis and a suite of laser-based measurement techniques to characterize the combustor flow downstream from the PICS dump plane. Optical diagnostics employed for this work included Planar Laser-Induced Fluorescence of fuel for injector spray pattern and Spontaneous Raman Spectroscopy for relative species concentration of fuel and CO2. The work reported here used unheated (liquid) Jet-A fuel for all fuel circuits and cycle conditions. The initial tests performed by UTRC used vaporized Jet-A to simulate the expected supersonic cruise condition, which anticipated using fuel as a heat sink. Using the National Combustion Code a PICS-based combustor was modeled with liquid fuel at the supersonic cruise condition. All CFD models used a cubic non-linear k-epsilon turbulence wall functions model, and a semi-detailed Jet-A kinetic mechanism based on a surrogate fuel mixture. Two initial spray droplet size distribution and spray cone conditions were used: (1) an initial condition (Lefebvre) with an assumed Rosin-Rammler distribution, and 7 degree Solid Spray Cone; and (2) the Boundary Layer Stripping (BLS) primary atomization model giving the spray size distribution and directional properties. Contour and line plots
The Second Futamura Projection for Type-Directed Partial Evaluation
DEFF Research Database (Denmark)
Grobauer, Bernd; Yang, Zhe
2001-01-01
The second Futamura projection describes the automatic generation of non-trivial generating extensions by applying a partial evaluator to itself. We derive an ML implementation of the second Futamura projection for Type-Directed Partial Evaluation (TDPE). Due to the differences between `traditional......', syntax-directed partial evaluation and TDPE, this derivation involves several conceptual and technical steps. These include a suitable formulation of the second Futamura projection and techniques for using TDPE to specialize type-indexed programs. In the context of the second Futamura projection, we also...
Direct numerical simulations and modeling of a spatially-evolving turbulent wake
Cimbala, John M.
1994-01-01
Understanding of turbulent free shear flows (wakes, jets, and mixing layers) is important, not only for scientific interest, but also because of their appearance in numerous practical applications. Turbulent wakes, in particular, have recently received increased attention by researchers at NASA Langley. The turbulent wake generated by a two-dimensional airfoil has been selected as the test-case for detailed high-resolution particle image velocimetry (PIV) experiments. This same wake has also been chosen to enhance NASA's turbulence modeling efforts. Over the past year, the author has completed several wake computations, while visiting NASA through the 1993 and 1994 ASEE summer programs, and also while on sabbatical leave during the 1993-94 academic year. These calculations have included two-equation (K-omega and K-epsilon) models, algebraic stress models (ASM), full Reynolds stress closure models, and direct numerical simulations (DNS). Recently, there has been mutually beneficial collaboration of the experimental and computational efforts. In fact, these projects have been chosen for joint presentation at the NASA Turbulence Peer Review, scheduled for September 1994. DNS calculations are presently underway for a turbulent wake at Re(sub theta) = 1000 and at a Mach number of 0.20. (Theta is the momentum thickness, which remains constant in the wake of a two dimensional body.) These calculations utilize a compressible DNS code written by M. M. Rai of NASA Ames, and modified for the wake by J. Cimbala. The code employs fifth-order accurate upwind-biased finite differencing for the convective terms, fourth-order accurate central differencing for the viscous terms, and an iterative-implicit time-integration scheme. The computational domain for these calculations starts at x/theta = 10, and extends to x/theta = 610. Fully developed turbulent wake profiles, obtained from experimental data from several wake generators, are supplied at the computational inlet, along with
Directory of Open Access Journals (Sweden)
Zhengrong Zhang
2012-01-01
Full Text Available Numerical manifold method was applied to directly solve Navier-Stokes (N-S equations for incompressible viscous flow in this paper, and numerical manifold schemes for N-S equations coupled velocity and pressure were derived based on Galerkin weighted residuals method as well. Mixed cover with linear polynomial function for velocity and constant function for pressure was employed in finite element cover system. As an application, mixed cover 4-node rectangular manifold element has been used to simulate the incompressible viscous flow around a square cylinder in a channel. Numerical tests illustrate that NMM is an effective and high-order accurate numerical method for incompressible viscous flow N-S equations.
Givi, Peyman; Madnia, Cyrus K.; Steinberger, C. J.; Frankel, S. H.
1992-01-01
The principal objective is to extend the boundaries within which large eddy simulations (LES) and direct numerical simulations (DNS) can be applied in computational analyses of high speed reacting flows. A summary of work accomplished during the last six months is presented.
Direct numerical simulation of Taylor-Couette flow subjected to a radial temperature gradient
Energy Technology Data Exchange (ETDEWEB)
Teng, Hao; Liu, Nansheng, E-mail: lns@ustc.edu.cn; Lu, Xiyun [Department of Modern Mechanics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Khomami, Bamin, E-mail: bkhomami@utk.edu [Department of Chemical and Biomolecular Engineering, The University of Tennessee, Knoxville, Tennessee 37996 (United States)
2015-12-15
Direct numerical simulations have been performed to study the Taylor-Couette (TC) flow between two rotating, coaxial cylinders in the presence of a radial temperature gradient. Specifically, the influence of the buoyant force and the outer cylinder rotation on the turbulent TC flow system with the radius ratio η = 0.912 was examined. For the co-rotating TC flows with Re{sub i} (inner cylinder) =1000 and Re{sub o} (outer cylinder) =100, a transition pathway to highly turbulent flows is realized by increasing σ, a parameter signifying the ratio of buoyant to inertial force. This nonlinear flow transition involves four intriguing states that emerge in sequence as chaotic wavy vortex flow for σ = 0, wavy interpenetrating spiral flows for σ = 0.02 and 0.05, intermittent turbulent spirals for σ = 0.1 and 0.2, and turbulent spirals for σ = 0.4. Overall, the fluid motion changes from a centrifugally driven flow regime characterized by large-scale wavy Taylor vortices (TVs) to a buoyancy-dominated flow regime characterized by small-scale turbulent vortices. Commensurate changes in turbulence statistics and heat transfer are seen as a result of the weakening of large-scale TV circulations and enhancement of turbulent motions. Additionally, the influence of variation of the outer cylinder rotation, −500 < Re{sub o} < 500 in presence of buoyancy (σ = 0.1) with Re{sub i} = 1000, has been considered. Specifically, it is demonstrated that this variation strongly influences the azimuthal and axial mean flows with a weaker influence on the fluctuating fluid motions. Of special interest, here are the turbulent dynamics near the outer wall where a marked decrease of turbulence intensity and a sign inversion of the Reynolds stress R{sub rz} are observed for the strongly counter-rotating regimes (Re{sub o} = − 300 and −500). To this end, it has been shown that the underlying flow physics for this drastic modification are associated with the modification of the correlation
Energy Technology Data Exchange (ETDEWEB)
Pedler, William H. (Radon Abatement Systems, Inc., Golden, CO); Jepsen, Richard Alan (Sandia National Laboratories, Carlsbad, NM)
2003-08-01
The requirement to accurately measure subsurface groundwater flow at contaminated sites, as part of a time and cost effective remediation program, has spawned a variety of flow evaluation technologies. Validation of the accuracy and knowledge regarding the limitations of these technologies are critical for data quality and application confidence. Leading the way in the effort to validate and better understand these methodologies, the US Army Environmental Center has funded a multi-year program to compare and evaluate all viable horizontal flow measurement technologies. This multi-year program has included a field comparison phase, an application of selected methods as part of an integrated site characterization program phase, and most recently, a laboratory and numerical simulator phase. As part of this most recent phase, numerical modeling predictions and laboratory measurements were made in a simulated fracture borehole set-up within a controlled flow simulator. The scanning colloidal borescope flowmeter (SCBFM) and advanced hydrophysical logging (NxHpL{trademark}) tool were used to measure velocities and flow rate in a simulated fractured borehole in the flow simulator. Particle tracking and mass flux measurements were observed and recorded under a range of flow conditions in the simulator. Numerical models were developed to aid in the design of the flow simulator and predict the flow conditions inside the borehole. Results demonstrated that the flow simulator allowed for predictable, easily controlled, and stable flow rates both inside and outside the well. The measurement tools agreed well with each other over a wide range of flow conditions. The model results demonstrate that the Scanning Colloidal Borescope did not interfere with the flow in the borehole in any of the tests. The model is capable of predicting flow conditions and agreed well with the measurements and observations in the flow simulator and borehole. Both laboratory and model results showed a
Direct Numerical Simulations of Local and Global Torque in Taylor-Couette Flow up to Re=30.000
Brauckmann, Hannes
2015-01-01
The torque in turbulent Taylor-Couette flows for shear Reynolds numbers Re_S up to 3x10^4 at various mean rotations is studied by means of direct numerical simulations for a radius ratio of \\eta=0.71. Convergence of simulations is tested using three criteria of which the agreement of dissipation values estimated from the torque and from the volume dissipation rate turns out to be most demanding. We evaluate the influence of Taylor vortex heights on the torque for a stationary outer cylinder and select a value of the aspect ratio of \\Gamma=2, close to the torque maximum. The connection between the torque and the transverse current J^\\omega of azimuthal motion which can be computed from the velocity field enables us to investigate the local transport resulting in the torque. The typical spatial distribution of the individual convective and viscous contributions to the local current is analysed for a turbulent flow case. To characterise the turbulent statistics of the transport, PDF's of local current fluctuatio...
Directory of Open Access Journals (Sweden)
Yong Cheng
2014-01-01
Full Text Available The transient response of the VLFS subjected to arbitrary external load is systematically investigated by a direct time domain modal expansion method, in which the BEM solutions based on time domain Kelvin sources are used for hydrodynamic forces. In the analysis, the time domain free-surface Green functions with sufficient accuracy are rapidly evaluated in finite water depth by the interpolation-tabulation method, and the boundary integral equation with a quarter VLFS model is established taking advantage of symmetry of flow field and structure. The validity of the present method is verified by comparing with the time histories of vertical displacements of the VLFS during a mass drop and airplane landing and takeoff in still water conditions, respectively. Then the developed numerical scheme is used in wave conditions to study the combined action taking into account the mass drop/airplane landing/takeoff loads as well as incident wave action. It is found that the elevation of structural waves due to mass drop load can be significantly changed near the impact region, while the vertical motion of runway in wave conditions is dominant as compared with that only generated by airplane.
Ruith, Michael Rudolf
Vortex breakdown of nominally axisymmetric, swirling incompressible jets and wakes issuing into a semi-infinite domain is studied by means of direct numerical simulations, as well as local and global linear stability analyses. From the point of view of specifying conditions at the open boundaries, this class of flows is particularly challenging due to its ability to support traveling waves. Several boundary conditions, ranging from free-slip and various homogeneous Neumann conditions to radiation conditions, are implemented in a staggered grid, finite difference algorithm that solves the unsteady Navier-Stokes equations in cylindrical coordinates by means of a fractional step method. Their advantages and shortcomings are evaluated in detail, and the question of the proper implementation of intermediate step boundary conditions is addressed. The data obtained from a large variety of test simulations points to the radiation condition as the most suitable lateral and outflow boundary condition for both high and low entrainment jets and wakes. A two-parameterc low entrainment velocity profile for which the steady, axisymmetric breakdown is well studied is selected for further investigation. Hence, issues regarding the role of three-dimensionality and unsteadiness with respect to the existence, mode selection, and internal structure of vortex breakdown can be addressed in terms of the two governing parameters and the Reynolds number. Low Reynolds numbers are found to yield flow fields lacking breakdown bubbles or helical breakdown modes even for high swirl. In contrast, highly swirling flows at large Reynolds numbers exhibit bubble, helical or double helical breakdown modes, where the axisymmetric mode is promoted by a jet-like axial velocity profile, while a wake-like profile renders the flow helically unstable and ultimately yields non-axisymmetric breakdown modes. It is shown that a transition from super- to subcritical flow, accurately predicts the parameter
Global evaluation of ammonia bi-directional exchange
Zhu, L; D. Henze; J. Bash; G.-R. Jeong; Cady-Pereira, K.; Shephard, M; Luo, M; F. Paulot; Capps, S.
2015-01-01
Bi-directional air–surface exchange of ammonia (NH3) has been neglected in many air quality models. In this study, we implement the bi-directional exchange of NH3 in the GEOS-Chem global chemical transport model. We also introduce an updated diurnal variability scheme for NH3 livestock emissions and evaluate the recently developed MASAGE_NH3 bottom up inventory. While updated diurnal variability improves comparison of modeled-to-hourly in situ measurements i...
Numerical Simulation of Transit-Time Ultrasonic Flowmeters by a Direct Approach.
Luca, Adrian; Marchiano, Regis; Chassaing, Jean-Camille
2016-06-01
This paper deals with the development of a computational code for the numerical simulation of wave propagation through domains with a complex geometry consisting in both solids and moving fluids. The emphasis is on the numerical simulation of ultrasonic flowmeters (UFMs) by modeling the wave propagation in solids with the equations of linear elasticity (ELE) and in fluids with the linearized Euler equations (LEEs). This approach requires high performance computing because of the high number of degrees of freedom and the long propagation distances. Therefore, the numerical method should be chosen with care. In order to minimize the numerical dissipation which may occur in this kind of configuration, the numerical method employed here is the nodal discontinuous Galerkin (DG) method. Also, this method is well suited for parallel computing. To speed up the code, almost all the computational stages have been implemented to run on graphical processing unit (GPU) by using the compute unified device architecture (CUDA) programming model from NVIDIA. This approach has been validated and then used for the two-dimensional simulation of gas UFMs. The large contrast of acoustic impedance characteristic to gas UFMs makes their simulation a real challenge.
Energy Technology Data Exchange (ETDEWEB)
Albets-Chico, X., E-mail: xalbets@ucy.ac.c [Computational Science Laboratory - UCY-CompSci, Department of Mechanical and Manufacturing Engineering, University of Cyprus, 75 Kallipoleos, Nicosia 1678 (Cyprus); Votyakov, E.V.; Radhakrishnan, H. [Computational Science Laboratory - UCY-CompSci, Department of Mechanical and Manufacturing Engineering, University of Cyprus, 75 Kallipoleos, Nicosia 1678 (Cyprus); Kassinos, S., E-mail: kassinos@ucy.ac.c [Computational Science Laboratory - UCY-CompSci, Department of Mechanical and Manufacturing Engineering, University of Cyprus, 75 Kallipoleos, Nicosia 1678 (Cyprus)
2011-01-15
We investigate the effects of the consistency of strong fringing decreasing magnetic fields on numerical simulations of classical experimental data. Studies about fringing magnetic fields have attracted the attention of the fusion community in relation to the design of the liquid-metal flow blankets for fusion nuclear reactors. One-dimensional fitting functions neglecting magnetic field consistency have been adopted in previous numerical studies. Thanks to complete three-dimensional numerical simulations, the effect of the physical consistency of the magnetic field on fluid flow can now be assessed. We present a technique for generating discretely consistent magnetic fields based on classical one-dimensional fittings. With this method, key magnetic field features, such as the bending of the magnetic lines, are accurately reproduced and, therefore, the validity of the technique is established. Consistent and inconsistent magnetic fields have been tested under very strong decreasing magnetic fields with insulating and conducting walls using direct numerical simulations. The results show a moderate, but systematic, improvement of the predictions with respect to the experiments. As an example, the repeated under-prediction of the peak transverse pressure gradient, observed in the results of asymptotic methods and of direct numerical simulations, is explained by the historically neglected consistency of the fringing magnetic field.
Direct Numerical Simulation of Interaction Between Wave and Porous Breakwater Based on N-S Equation
Institute of Scientific and Technical Information of China (English)
WANG Deng-ting
2012-01-01
In this paper,a numerical model is established.A modified N-S equation is used as a control equation for the wave field and porous flow area.The control equations are discreted and solved by the finite difference method.The free surface is tracked by the VOF method.The pressure field and velocity field of the whole flow area are solved by the reiterative iteration method.Finally,compared with the physical model test results of wave flume,the numerical model established in the present study is validated.
Laboratory investigation and direct numerical simulation of wind effect on steep surface waves
Troitskaya, Yuliya; Sergeev, Daniil; Druzhinin, Oleg; Ermakova, Olga
2015-04-01
particles 20 μm in diameter were injected into the airflow. The images of the illuminated particles were photographed with a digital CCD video camera at a rate of 1000 frames per second. For the each given parameters of wind and waves, a statistical ensemble of 30 movies with duration from 200 to 600 ms was obtained. Individual flow realizations manifested the typical features of flow separation, while the average vector velocity fields obtained by the phase averaging of the individual vector fields were smooth and slightly asymmetrical, with the minimum of the horizontal velocity near the water surface shifted to the leeward side of the wave profile, but do not demonstrate the features of flow separation. The wave-induced pressure perturbations, averaged over the turbulent fluctuations, were retrieved from the measured velocity fields, using the Reynolds equations. It ensures sufficient accuracy for study of the dependence of the wave increment on the wave amplitude. The dependences of the wave growth rate on the wave steepness are weakly decreasing, serving as indirect proof of the non-separated character of flow over waves. Also direct numerical simulation of the airflow over finite amplitude periodic surface wave was performed. In the experiments the primitive 3-dimensional fluid mechanics equations were solved in the airflow over curved water boundary for the following parameters: the Reynolds number Re=15000, the wave steepness ka=0-0.2, the parameter c/u*=0-10 (where u* is the friction velocity and c is the wave celerity). Similar to the physical experiment the instant realizations of the velocity field demonstrate flow separation at the crests of the waves, but the ensemble averaged velocity fields had typical structures similar to those excising in shear flows near critical levels, where the phase velocity of the disturbance coincides with the flow velocity. The wind growth rate determined by the ensemble averaged wave-induced pressure component in phase of the
Li, Jianying; Li, Haiyan; Fok, Alex S L; Watts, David C
2012-09-01
The aim of this study was to numerically evaluate the effects of filler contents and resin properties on the material properties of dental composites utilizing realistic 3D micromechanical finite element models. 3D micromechanical finite element models of dental composites containing irregular fillers with non-uniform sizes were created based on a large-scale, surrogate mixture fabricated from irregularly shaped stones and casting resin. The surrogate mixture was first scanned with a micro-CT scanner, and the images reassembled to produce a 3D finite element model. Different filler fractions were achieved by adjusting the matrix volume while keeping the fillers unchanged. Polymerization shrinkage, Young's modulus, Poisson's ratio and viscosity of the model composites were predicted using the finite element models, and their dependence on the filler fraction and material properties of the resin matrix were considered. Comparison of the numerical predictions with available experimental data and analytical models from the literature was performed. Increased filler fraction resulted in lower material shrinkage, higher Young's modulus, lower Poisson's ratio and higher viscosity in the composite. Predicted shrinkage and Young's modulus agreed well with the experimental data and analytical predictions. The McGee-McCullough model best fit the shrinkage and Young's modulus predicted by the finite element method. However, a new parameter, used as the exponent of the filler fraction, had to be introduced to the McGee-McCullough model to better match the predicted viscosity and Poisson's ratio with those from the finite element analysis. Realistic micro-structural finite element models were successfully applied to study the effects of filler fraction and matrix properties on a wide range of mechanical properties of dental composites with irregular fillers. The results can be used to direct the design of such materials to achieve the desired mechanical properties. Published by
Evaluation of Hydrodynmic Coefficients of Ships Oscillating in A Numerical Wave Tank
Institute of Scientific and Technical Information of China (English)
ZHU Ren-chuan; MIAO Guo-ping; GUO Hai-qiang; YU Jian-wei
2009-01-01
A technique for the evaluation of the hydrodynamic coefficients of ships is outlined for ship oscillating in a numerical wave tank,which is established on Computational Fluid Dynamics (CFD) theories.The numerical simulation of ship sections and bodies forced oscillating in the tank are carried out.The added mass and damping coefficients are obtained by the decomposition of the computational results,which agree well with the corresponding ones of potential theories.
Numerically Stable Evaluation of Moments of Random Gram Matrices With Applications
Elkhalil, Khalil
2017-07-31
This paper focuses on the computation of the positive moments of one-side correlated random Gram matrices. Closed-form expressions for the moments can be obtained easily, but numerical evaluation thereof is prone to numerical stability, especially in high-dimensional settings. This letter provides a numerically stable method that efficiently computes the positive moments in closed-form. The developed expressions are more accurate and can lead to higher accuracy levels when fed to moment based-approaches. As an application, we show how the obtained moments can be used to approximate the marginal distribution of the eigenvalues of random Gram matrices.
A Direct Numerical Reconstruction Algorithm for the 3D Calderón Problem
DEFF Research Database (Denmark)
Delbary, Fabrice; Hansen, Per Christian; Knudsen, Kim
2011-01-01
In three dimensions Calderón's problem was addressed and solved in theory in the 1980s in a series of papers, but only recently the numerical implementation of the algorithm was initiated. The main ingredients in the solution of the problem are complex geometrical optics solutions to the conducti...
IR DirectFET Extreme Environments Evaluation Final Report
Burmeister, Martin; Mottiwala, Amin
2008-01-01
In 2007, International Rectifier (IR) introduced a new version of its DirectFET metal oxide semiconductor field effect transistor (MOSFET) packaging. The new version (referred to as 'Version 2') enhances device moisture resistance, makes surface mount (SMT) assembly of these devices to printed wiring boards (PWBs) more repeatable, and subsequent assembly inspection simpler. In the present study, the National Aeronautics Space Administration (NASA) Jet Propulsion Laboratory (JPL), in collaboration with Stellar Microelectronics (Stellar), continued an evaluation of the DirectFET that they started together in 2006. The present study focused on comparing the two versions of the DirectFET and examining the suitability of the DirectFET devices for space applications. This study evaluated both versions of two DirectFET packaged devices that had both been shown in the 2006 study to have the best electrical and thermal properties: the IRF6635 and IRF6644. The present study evaluated (1) the relative electrical and thermal performance of both versions of each device, (2) the performance through high reliability testing, and (3) the performance of these devices in combination with a range of alternate solder alloys in the extreme thermal environments of deep space....
46 Evaluating Foreign Direct Investment and Africa's Development ...
African Journals Online (AJOL)
Evaluating Foreign Direct Investment and Africa's. Development. Nicholas ... trade was “economic, not racial; it had to do not with the colour of the labourer but ... transition from this trade relation to that of development through colonization. ... This explains the dominance of rich states over ..... The invisible hand of the market ...
A Unifying Approach to Goal-Directed Evaluation
DEFF Research Database (Denmark)
Danvy, Olivier; Rhiger, Morten; Grobauer, Bernd
2001-01-01
semantics coincides with Gudeman’s continuation semantics of Icon. We then compile Icon programs by specializing their interpreter (i.e., by using the first Futamura projection), using type-directed partial evaluation. Through various back ends, including a run-time code generator, we generate ML code, C...
Evaluating Direct Marketing Campaigns: recent findings and future research topics
J-J. Jonker (Jedid-Jah); Ph.H.B.F. Franses (Philip Hans); N. Piersma (Nanda)
2002-01-01
textabstractThis paper contains a survey of the recent literature on the evaluation of direct marketing campaigns. We give an outline of the various stages included in such a campaign. Next, we review the statistical methods most frequently used and we review the general findings from using these me
Evaluating Direct Marketing Campaigns: recent findings and future research topics
Jonker, Jedid-Jah; Franses, Philip Hans; Piersma, Nanda
2002-01-01
textabstractThis paper contains a survey of the recent literature on the evaluation of direct marketing campaigns. We give an outline of the various stages included in such a campaign. Next, we review the statistical methods most frequently used and we review the general findings from using these methods.
Correction to the crack extension direction in numerical modelling of mixed mode crack paths
DEFF Research Database (Denmark)
Lucht, Tore; Aliabadi, M.H.
2007-01-01
In order to avoid introduction of an error when a local crack-growth criterion is used in an incremental crack growth formulation, each straight crack extension would have to be infinitesimal or have its direction corrected. In this paper a new procedure to correct the crack extension direction i...
A Unifying Approach to Goal-Directed Evaluation
DEFF Research Database (Denmark)
Danvy, Olivier; Rhiger, Morten; Grobauer, Bernd
2001-01-01
Goal-directed evaluation, as embodied in Icon and Snobol, is built on the notions of backtracking and of generating successive results, and therefore it has always been something of a challenge to specify and implement. In this article, we address this challenge using computational monads...... and partial evaluation. We consider a subset of Icon and we specify it with a monadic semantics and a list monad. We then consider a spectrum of monads that also fit the bill, and we relate them to each other. For example, we derive a continuation monad as a Church encoding of the list monad. The resulting...... semantics coincides with Gudeman’s continuation semantics of Icon. We then compile Icon programs by specializing their interpreter (i.e., by using the first Futamura projection), using type-directed partial evaluation. Through various back ends, including a run-time code generator, we generate ML code, C...
Direct Numerical Simulation of the Rayleigh-Taylor Instability with the Spectral Element Method
Institute of Scientific and Technical Information of China (English)
ZHANG Xu; TAN Duo-Wang
2009-01-01
A novel method is proposed to simulate Rayleigh-Taylor instabilities using a specially-developed unsteady threedimensional high-order spectral element method code.The numerical model used consists of Navier-Stokes equations and a transport-diffusive equation.The code is first validated with the results of linear stability perturbation theory.Then several characteristics of the Rayleigh-Taylor instabjJjties are studied using this three-dimensional unsteady code,inducling instantaneous turbulent structures and statistical turbulent mixing heights under different initial wave numbers.These results indicate that turbulent structures ofRayleigh-Taylor instabilities are strongly dependent on the initial conditions.The results also suggest that a high-order numerical method should provide the capability of sir.ulating small scale fluctuations of Rayleigh-Taylor instabilities of turbulent flows.
Direct Numerical Simulation of Electrokinetic Instability and Transition to Chaotic Motion
Demekhin, E A; Shelistov, V S
2013-01-01
A new type of instability - electrokinetic instability - and an unusual transition to chaotic motion near a charge-selective surface was studied by numerical integration of the Nernst-Planck-Poisson-Stokes system and a weakly nonlinear analysis near the threshold of instability. Two kinds of initial conditions were considered: (a) white noise initial conditions to mimic "room disturbances" and subsequent natural evolution of the solution; (b) an artificial monochromatic ion distribution with a fixed wave number to simulate regular wave patterns. The results were studied from the viewpoint of hydrodynamic stability and bifurcation theory. The threshold of electroconvective movement was found by the linear spectral stability theory, the results of which were confirmed by numerical simulation of the entire system. The following regimes, which replace each other as the potential drop between the selective surfaces increases, were obtained: one-dimensional steady solution; two-dimensional steady electroconvective ...
de Groh, Henry C., III; Yao, Minwu
1994-01-01
A numerical and experimental study of the growth of succinonitrile (SCN) using a horizontal Bridginan furnace and transparent glass ampoule was conducted. Two experiments were considered: one in which the temperature profile was fixed relative to the ampoule (no-growth case); and a second in which the thermal profile was translated at a constant rate (steady growth case). Measured temperature profiles on the outer surface of the ampoule were used as thermal boundary conditions for the modelling. The apparent heat capacity formulation combined with the variable viscositymeth was used to model the phase change in SeN. Both 2-D and 3-D models were studied and numerical solutions obtained using the commercial finite element code, FIDAP1. Comparison of the numerical results to experimental data showed excellent agreement. The complex 3-D shallow-cavity flow in the melt, differences between 2-D and 3-D models, effects of natural convection on the thermal gradient and shape of the solid/liquid interface, and the sensitivity of simulations to specific assumptions, are also discussed.
Energy Technology Data Exchange (ETDEWEB)
Murakami, Satoshi [Customer System Co. Ltd. (Japan); Muramatsu, Toshiharu [Japan Nuclear Cycle Development Inst., Oarai, Ibaraki (Japan). Oarai Engineering Center
2002-05-01
Numerical analyses for turbulence thermal mixing, the aim of which is to evaluate relationship between hydrodynamics and temperature distribution of an arched-vortex, were carried out using the direct numerical simulation code DINUS-3. From the analyses, the following results have been obtained: (1) Transportation period of the arched-vortex and distance between the arched-vortices were kept constant in isothermal and non-isothermal conditions. (2) The transportation period of arched-vortex was decreased with increasing Reynolds number under the condition of the constant flow velocity ratio between both coolant pipes. (3) One of the main reasons for this behavior was considered that the motion of the cold fluid flowing out of the branch pipe was restricted by the difference of fluid density between the branch and the main pipes. The amplitudes of the cross flow velocity fluctuation in the leg region of the arched-vortex were larger than those under isothermal condition. (4) It was confirmed that the arched-vortex consists of two kinds of vortexes, i.e., a longitudinal vortex generated by a shear motion at the top of the arched-vortex, and a horizontal vortex by shedding motion at both sides of the branch jet flow. (author)
Ryabinkin, Ilya G; Nagesh, Jayashree; Izmaylov, Artur F
2015-11-05
We have developed a numerical differentiation scheme that eliminates evaluation of overlap determinants in calculating the time-derivative nonadiabatic couplings (TDNACs). Evaluation of these determinants was the bottleneck in previous implementations of mixed quantum-classical methods using numerical differentiation of electronic wave functions in the Slater determinant representation. The central idea of our approach is, first, to reduce the analytic time derivatives of Slater determinants to time derivatives of molecular orbitals and then to apply a finite-difference formula. Benchmark calculations prove the efficiency of the proposed scheme showing impressive several-order-of-magnitude speedups of the TDNAC calculation step for midsize molecules.
Direct numerical simulation of electrokinetic instability and transition to chaotic motion
Energy Technology Data Exchange (ETDEWEB)
Demekhin, E. A., E-mail: edemekhi@gmail.com [Laboratory of Micro- and Nanofluidics, Moscow State University, Moscow 119192 (Russian Federation); Department of Computation Mathematics and Computer Science, Kuban State University, Krasnodar 350040 (Russian Federation); Institute of Mechanics, Moscow State University, Moscow 117192 (Russian Federation); Nikitin, N. V. [Institute of Mechanics, Moscow State University, Moscow 117192 (Russian Federation); Shelistov, V. S. [Institute of Mechanics, Moscow State University, Moscow 117192 (Russian Federation); Scientific Research Department, Kuban State University, Krasnodar 350040 (Russian Federation)
2013-12-15
A new type of instability—electrokinetic instability—and an unusual transition to chaotic motion near a charge-selective surface (semiselective electric membrane, electrode, or system of micro-/nanochannels) was studied by the numerical integration of the Nernst-Planck-Poisson-Stokes system and a weakly nonlinear analysis near the threshold of instability. A special finite-difference method was used for the space discretization along with a semi-implicit 31/3 -step Runge-Kutta scheme for the integration in time. Two kinds of initial conditions were considered: (a) white-noise initial conditions to mimic “room disturbances” and subsequent natural evolution of the solution, and (b) an artificial monochromatic ion distribution with a fixed wave number to simulate regular wave patterns. The results were studied from the viewpoint of hydrodynamic stability and bifurcation theory. The threshold of electroconvective movement was found by the linear spectral stability theory, the results of which were confirmed by numerical simulation of the entire system. Our weakly nonlinear analysis and numerical integration of the entire system predict possibility of both kinds of bifurcations at the critical point, supercritical and subcritical, depending on the system parameters. The following regimes, which replace each other as the potential drop between the selective surfaces increases, were obtained: one-dimensional steady solution, two-dimensional steady electroconvective vortices (stationary point in a proper phase space), unsteady vortices aperiodically changing their parameters (homoclinic contour), periodic motion (limit cycle), and chaotic motion. The transition to chaotic motion does not include Hopf bifurcation. The numerical resolution of the thin concentration polarization layer showed spike-like charge profiles along the surface, which could be, depending on the regime, either steady or aperiodically coalescent. The numerical investigation confirmed the
NUMERICAL SIMULATION OF SEA SURFACE DIRECTIONAL WAVE SPECTRA UNDER TYPHOON WIND FORCING
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
Numercial simulation of sea surface directional wave spectra under typhoon wind forcing in the South China Sea (SCS) was carreid out using the WAVEWATCH-III wave model. The simulation was run for 210 h until the Typhoon Damrey (2005) approached Vietnam. The simulated data were compared with buoy observations, which were obtained in the northwest sea area of Hainan Island. The results show that the significant wave height, wave direction, wave length and frequency spetra agree well with buoy observations. The spatial characteristics of the signifciant wave height, mean wave period, mean wave length, wave age and directional spectra depend on the relative position from the typhoon center. Also, the misalignment between local wind and wave directions were investigated.
Numerical Evaluation of Seepage Monitoring in Embankment Dams Utilizing Temperature Method
Directory of Open Access Journals (Sweden)
Mohammad Amin Kalantari
2016-06-01
provides a useful measure to recognize seepage in primary state. There are various methods based on temperature measurement and analysis in embankment dams that are assessed in this paper. For this purpose, the methods including lag-time, amplitude, numerical, and optical fiber sensors methods are evaluated and compared relevantly, for the sake of recognition of the most recent and preferable method. A system based on optical fiber sensors is known as the most recent, powerful and economized method in monitoring of hydraulic structures. This paper provides the Parametric Models methods and numerical model such as McCormack Explicit scheme and Pressman Implicit scheme using Hec-Ras to simulate dam break furthermore it used to predict breach outflow hydrographs .Unsteady flow modeling is often used in dam breach analysis due to the need to obtain more detailed or accurate results. The breach parameters will directly and substantially affect the estimate of the flows. Due to this illustrate the failure time is very low, as a result the negative surge occurs, However De St. Venant differential equations are not valid in the neighborhood of the surge. In order to evaluate the effective of negative wave on the outflow hydrograph.
Global evaluation of ammonia bi-directional exchange
Directory of Open Access Journals (Sweden)
L. Zhu
2015-02-01
Full Text Available Bi-directional air–surface exchange of ammonia (NH3 has been neglected in many air quality models. In this study, we implement the bi-directional exchange of NH3 in the GEOS-Chem global chemical transport model. We also introduce an updated diurnal variability scheme for NH3 livestock emissions and evaluate the recently developed MASAGE_NH3 bottom up inventory. While updated diurnal variability improves comparison of modeled-to-hourly in situ measurements in the Southeastern US, NH3 concentrations decrease throughout the globe, up to 17 ppb in India and Southeastern China, with corresponding decreases in aerosol nitrate by up to 7 μg m−3. The ammonium (NH4+ soil pool in the bi-directional exchange model largely extends the NH3 lifetime in the atmosphere. Including bi-directional exchange generally increases NH3 gross emissions (7.1% and surface concentrations (up to 3.9 ppb throughout the globe in July, except in India and Southeastern China. In April and October, it decreases NH3 gross emissions in the Northern Hemisphere (e.g., 43.6% in April in China and increases NH3 gross emissions in the Southern Hemisphere. Bi-directional exchange does not largely impact NH4+ wet deposition overall. While bi-directional exchange is fundamentally a better representation of NH3 emissions from fertilizers, emissions from primary sources are still underestimated and thus significant model biases remain when compared to in situ measurements in the US. The adjoint of bi-directional exchange has also been developed for the GEOS-Chem model and is used to investigate the sensitivity of NH3 concentrations with respect to soil pH and fertilizer application rate. This study thus lays the groundwork for future inverse modeling studies to more directly constrain these physical processes rather than tuning bulk uni-directional NH3 emissions.
Global evaluation of ammonia bi-directional exchange
Zhu, L.; Henze, D.; Bash, J.; Jeong, G.-R.; Cady-Pereira, K.; Shephard, M.; Luo, M.; Paulot, F.; Capps, S.
2015-02-01
Bi-directional air-surface exchange of ammonia (NH3) has been neglected in many air quality models. In this study, we implement the bi-directional exchange of NH3 in the GEOS-Chem global chemical transport model. We also introduce an updated diurnal variability scheme for NH3 livestock emissions and evaluate the recently developed MASAGE_NH3 bottom up inventory. While updated diurnal variability improves comparison of modeled-to-hourly in situ measurements in the Southeastern US, NH3 concentrations decrease throughout the globe, up to 17 ppb in India and Southeastern China, with corresponding decreases in aerosol nitrate by up to 7 μg m-3. The ammonium (NH4+) soil pool in the bi-directional exchange model largely extends the NH3 lifetime in the atmosphere. Including bi-directional exchange generally increases NH3 gross emissions (7.1%) and surface concentrations (up to 3.9 ppb) throughout the globe in July, except in India and Southeastern China. In April and October, it decreases NH3 gross emissions in the Northern Hemisphere (e.g., 43.6% in April in China) and increases NH3 gross emissions in the Southern Hemisphere. Bi-directional exchange does not largely impact NH4+ wet deposition overall. While bi-directional exchange is fundamentally a better representation of NH3 emissions from fertilizers, emissions from primary sources are still underestimated and thus significant model biases remain when compared to in situ measurements in the US. The adjoint of bi-directional exchange has also been developed for the GEOS-Chem model and is used to investigate the sensitivity of NH3 concentrations with respect to soil pH and fertilizer application rate. This study thus lays the groundwork for future inverse modeling studies to more directly constrain these physical processes rather than tuning bulk uni-directional NH3 emissions.
Direct numerical simulation of rotating fluid flow in a closed cylinder
DEFF Research Database (Denmark)
Sørensen, Jens Nørkær; Christensen, Erik Adler
1995-01-01
, is validated against experimental visualizations of both transient and stable periodic flows. The complexity of the flow problem is illuminated numerically by injecting flow tracers into the flow domain and following their evolution in time. The vortex dynamics appears as stretching, folding and squeezing...... to three multiple solutions for the same Reynolds number, and to contain four discernible branches. The transition to strange attractor behavior was identified as a nontrivial Ruelle-Takens transition through a transient torus. The various solution branches of the rotating flow problem are illustrated...
Institute of Scientific and Technical Information of China (English)
Che Xiao-Hua; Qiao Wen-Xiao; Ju Xiao-Dong; Wang Rui-Jia
2016-01-01
We developed a novel cement evaluation logging tool, named the azimuthally acoustic bond tool (AABT), which uses a phased-arc array transmitter with azimuthal detection capability. We combined numerical simulations andfi eld tests to verify the AABT tool. The numerical simulation results showed that the radiation direction of the subarray corresponding to the maximum amplitude of the first arrival matches the azimuth of the channeling when it is behind the casing. With larger channeling size in the circumferential direction, the amplitude difference of the casing wave at different azimuths becomes more evident. The test results showed that the AABT can accurately locate the casing collars and evaluate the cement bond quality with azimuthal resolution at the casing–cement interface, and can visualize the size, depth, and azimuth of channeling. In the case of good casing–cement bonding, the AABT can further evaluate the cement bond quality at the cement–formation interface with azimuthal resolution by using the amplitude map and the velocity of the formation wave.
Institute of Scientific and Technical Information of China (English)
Elisabetta Santi; M.G. Cimoroni
2002-01-01
In this paper, product formulas based on projector-splines for the numerical evaluation of 2-D CPV integrals are proposed. Convergence results are proved, numerical examples and comparisons are given.
Stelian, Carmen; Duffar, Thierry; Nicoara, Irina
2003-07-01
The effect of Bridgman furnace configuration on the temperature field, melt convection and the solute distribution in the resulting crystal are experimentally and numerically analyzed for the semiconductor diluted alloy solidification. The governing equations of the heat and mass transfer are solved by using the finite element method with help of the commercial software FIDAP ®. Two different solidification experiments of Ga 1- xIn xSb ( x=0.01 and 0.04) are simulated in order to compare the numerical results for thermal, velocity and solute fields. The central objective of the work is to give the conditions for which a more uniform distribution of the solute in the crystal can be obtained. It is found that crystals obtained in conditions of a strong convective regime in the vicinity of the solid-liquid interface are more homogeneous radially and on a significant length than the crystals for which solidification occurred in a quasi-diffusive regime. The results, in terms of axial and radial segregation, are compared to experimental chemical analysis.
Direct numerical simulation of fluid-particle mass, momentum, and heat tranfers in reactive systems.
Hammouti, Abdelkader; Wachs, Anthony
2015-11-01
Many industrial processes like coal combustion, catalytic cracking, gas phase polymerization reactors and more recently biomass gasification and chemical looping involve two-phase reactive flows in which the continuous phase is a fluid and the dispersed phase consists of rigid particles. Improving both the design and the operating conditions of these processes represents a major scientific and industrial challenge in a context of markedly rising energy cost and sustainable development. Thus, it is above all important to better understand the coupling of hydrodynamic, chemical and thermal phenomena in those flows in order to be able to predict them reliably. The aim of our work is to build up a multi-scale modelling approach of reactive particulate flows and at first to focus on the development of a microscopic-scale including heat and mass transfers and chemical reactions for the prediction of particle-laden flows in dense and dilute regimes. A first step is the upgrading and the validation of our numerical tools via analytical solutions or empirical correlations when it is feasible. These couplings are implemented in a massively parallel numerical code that already enable to take a step towards the enhanced design of semi-industrial processes.
Song, Bo; Wen, Peng; Ahfock, Tony; Li, Yan
2016-01-01
This study constructed a series of high-resolution realistic human-head models with brain tumors, and numerically investigated the influence of brain tumor's location and grade on the current distributions, under different electrode montages during tDCS. The threshold area and the peak current density were also derived and analyzed in the region of interest. The simulation result showed that it is safe to apply tDCS on the patients with brain tumors to treat their neuropsychiatric conditions and cancer pain caused by the tumor; although considerable changes of the current distributions are induced by the presence of a brain tumor. In addition, several observations on the global and local influences of tumor grade and possible edema have been made as well. These findings should be helpful for researchers and clinical doctors to treat patients with brain tumors. This study is also the first numerical study to fill in the gap of tDCS applications on the patients with brain tumors.
A Unifying Approach to Goal-Directed Evaluation
DEFF Research Database (Denmark)
Danvy, Olivier; Grobauer, Bernd; Rhiger, Morten
2001-01-01
Goal-directed evaluation, as embodied in Icon and Snobol, is built on the notions of backtracking and of generating successive results, and therefore it has always been something of a challenge to specify and implement. In this article, we address this challenge using computational monads...... and partial evaluation. We consider a subset of Icon and we specify it with a monadic semantics and a list monad. We then consider a spectrum of monads that also fit the bill, and we relate them to each other. For example, we derive a continuation monad as a Church encoding of the list monad. The resulting...
A Unifying Approach to Goal-Directed Evaluation
DEFF Research Database (Denmark)
Danvy, Olivier; Grobauer, Bernd; Rhiger, Morten
2001-01-01
Goal-directed evaluation, as embodied in Icon and Snobol, is built on the notions of backtracking and of generating successive results, and therefore it has always been something of a challenge to specify and implement. In this article, we address this challenge using computational monads...... and partial evaluation.We consider a subset of Icon and we specify it with a monadic semantics and a list monad. We then consider a spectrum of monads that also fit the bill, and we relate them to each other. For example, we derive a continuation monad as a Church encoding of the list monad. The resulting...
Experimental Study and Numerical Simulation of Directionally Solidified Turbine Blade Casting
Institute of Scientific and Technical Information of China (English)
Jing YU; Qingyan XU; Baicheng LIU; Jiarong LI; Hailong YUAN; Haipeng JIN
2008-01-01
The directional solidification process of turbine blade sample castings was investigated in the work. Variable withdrawal rates were used in one withdrawal process and compared with the other using uniform rate. A mathematical model for heat radiation transfer and microstructure simulation of directional solidification process was developed based on CA-FD method. The temperature distribution and microstructure were simulated and compared with the experimental results. The stray grains were predicted and compared with the experimental results. The uneven temperature distribution of platform was the main reason of the formation of stray grains.
The numeric evaluation of the magnetic field produced by a rotor with alternating poles
Directory of Open Access Journals (Sweden)
Greconici Marian
2005-01-01
Full Text Available The magnetic field produced by a rotor with alternating magnetic poles in a magnetic fluid hydrostatic bearing is numerically evaluated. There has been used a 3D program based on the finite element method (3D-FEM.
A Framework for Evaluating Regional-Scale Numerical Photochemical Modeling Systems
This paper discusses the need for critically evaluating regional-scale (~ 200-2000 km) three dimensional numerical photochemical air quality modeling systems to establish a model's credibility in simulating the spatio-temporal features embedded in the observations. Because of li...
Vesicoureteric reflux: Evaluation by bladder volume graded direct radionuclide cystogram
Agrawal Vikesh; Rangarajan Venkatesh; Kamath Tejaswini; Borwankar S
2009-01-01
Aim : Evaluation of vesicoureteric reflux (VUR) in children by bladder volume graded direct radionuclide cystogram (BVG DRC). This technique allows detection of VUR at different bladder volume grades. Materials and Methods : In this prospective study, 33 patients (66 renal units) with suspected vesicoureteric reflux were subjected to a voiding cystourethrogram (VCUG) and BVG DRC. The patients were assessed further with radioisotope renal scans for renal cortical scars. Results : Twenty-two...
Direct numerical simulation of three-dimensional coherent structure in plane mixing layer
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
The three-dimensional temporally evolving plane mixing layer is sinulated by directly solying the Navier-Stokes equations using pseudo-spectral method. The process of loss of stability, and the formation paring, and development of vortex are presented. The simulated result shows that the evolving characteristics of coherent structure are important mechanism of growing and entrainment of mixing layer.
Modesti, Davide
2016-01-01
We develop a semi-implicit algorithm for time-accurate simulation of the compressible Navier-Stokes equations, with special reference to wall-bounded flows. The method is based on linearization of the partial convective fluxes associated with acoustic waves, in such a way to suppress, or at least mitigate the acoustic time step limitation. Together with replacement of the total energy equation with the entropy transport equation, this approach avoids the inversion of block-banded matrices involved in classical methods, which is replaced by less demanding inversion of standard banded matrices. The method is extended to deal with implicit integration of viscous terms and to multiple space dimensions through approximate factorization, and used as a building block of third-order Runge-Kutta time stepping scheme. Numerical experiments are carried out for isotropic turbulence, plane channel flow, and flow in a square duct. All available data support higher computational efficiency than existing methods, and saving ...
Liu, Xinghua; Xian, Richang; Yu, Peng; Pei, Ying; Lv, Xuebin; Sun, Xuefeng; Wang, Tao; Ning, Shangyuan; Wang, Shikun
2017-05-01
In order to explore the characteristics of electron in DC negative corona discharge, microcosmic process of negative corona discharge in air is simulated in this paper. The numerical computation is established with a bar-plate electrode configuration with an inter-electrode gap of 3.3 mm, the negative DC voltage applied to the bar is 5.0 kV, the pressure in air discharge is fixed at 1.0 atm, and the gas temperature is assumed to be a constant (300 K). By solution the system of electron conservation equation, the electron mean energy conservation, the heavy species multi-component diffusion transport equation, and the Poisson’s equation, characteristics of electrons (electron mean energy, electron density, and generation and dissipation performances of electrons) at 6 representative time points during a pulse are obtained and then discussed emphatically.
Estimation of turbulent diffusivity with direct numerical simulation of stellar convection
Hotta, H; Yokoyama, T
2012-01-01
We investigate the value of horizontal turbulent diffusivity {\\eta} by numerical calculation of thermal convection. In this study, we introduce a new method whereby the turbulent diffusivity is estimated by monitoring the time devel- opment of the passive scalar, which is initially distributed in a given Gaussian function with a spatial scale d0. Our conclusions are as follows: (1) Assuming the relation {\\eta} = Lcvrms/3 where vrms is the RMS velocity, the characteristic length Lc is restricted by the shortest one among the pressure (density) scale height and the region depth. (2) The value of turbulent diffusivity becomes greater with the larger initial distribution scale d0. (3) The approximation of turbulent diffusion holds better when the ratio of the initial distribution scale d0 to the characteristic length Lc is larger.
Energy Technology Data Exchange (ETDEWEB)
Ceuca, Sabin Cristian [Gesellschaft fuer Anlagen- und Reaktorsicherheit (GRS) gGmbH, Garching (Germany); Laurinavicius, Darius [Lithuanian Energy Institute, Kaunas (Lithuania)
2016-11-15
The complex direct contact condensation phenomenon is investigated in horizontal flow channels both experimentally and numerically with special emphasis on its implications on safety assessment studies. Under certain conditions direct contact condensation can act as the driving force for the water hammer phenomenon with potentially local devastating results, thus posing a threat to the integrity of the affected NPP components. New experimental results of in-depth analysis of the direct contact condensation phenomena obtained in Kaunas at the Lithuanian Energy Institute will be presented. The German system code ATHLET employing for the calculation of the heat transfer coefficient a mechanistic model accounting for two different eddy length scales, combined with the interfacial area transport equation will be assessed against condensation induced water hammer experimental data from the integral thermal-hydraulic experimental facility PMK-2, located at the KFKI Atomic Energy Research Institute in Budapest Hungary.
Shen, M.; Touchard, F.; Bezine, G.; Brillaud, J.
2010-06-01
The work is to predict fracture behaviour of bio-composites from the tensile properties of its components. In this work, we have realized a direct numerical simulation of fracture behaviour for random short spruce fibers reinforced composites. For calculations, wood fibers have been considered as linear elastic bodies, polypropylene matrix as an elastic-plastic material. Then, numerical results have been compared with experimental results that have been obtained by digital image correlation. This comparison indicates that random fiber FE model of random short spruce fibers reinforced composites can be able to fairly reflect the influence of random fibers microstructure in the composite on its fracture behavior. The calculation of both random fiber and homogeneous FE model and their comparison with experiments show that the average values of J-integral in a region in the front of the crack tip from both numerical FE models are in good agreement with the average J value of DIC experiment in the same region when the numerical and experimental CT specimens of the short spruce fiber reinforced composite are subjected to the same extension at their loading point.
Directory of Open Access Journals (Sweden)
Brillaud J.
2010-06-01
Full Text Available The work is to predict fracture behaviour of bio-composites from the tensile properties of its components. In this work, we have realized a direct numerical simulation of fracture behaviour for random short spruce fibers reinforced composites. For calculations, wood fibers have been considered as linear elastic bodies, polypropylene matrix as an elastic-plastic material. Then, numerical results have been compared with experimental results that have been obtained by digital image correlation. This comparison indicates that random fiber FE model of random short spruce fibers reinforced composites can be able to fairly reflect the influence of random fibers microstructure in the composite on its fracture behavior. The calculation of both random fiber and homogeneous FE model and their comparison with experiments show that the average values of J-integral in a region in the front of the crack tip from both numerical FE models are in good agreement with the average J value of DIC experiment in the same region when the numerical and experimental CT specimens of the short spruce fiber reinforced composite are subjected to the same extension at their loading point.
Nonlinear mechanics of thin-walled structures asymptotics, direct approach and numerical analysis
Vetyukov, Yury
2014-01-01
This book presents a hybrid approach to the mechanics of thin bodies. Classical theories of rods, plates and shells with constrained shear are based on asymptotic splitting of the equations and boundary conditions of three-dimensional elasticity. The asymptotic solutions become accurate as the thickness decreases, and the three-dimensional fields of stresses and displacements can be determined. The analysis includes practically important effects of electromechanical coupling and material inhomogeneity. The extension to the geometrically nonlinear range uses the direct approach based on the principle of virtual work. Vibrations and buckling of pre-stressed structures are studied with the help of linearized incremental formulations, and direct tensor calculus rounds out the list of analytical techniques used throughout the book. A novel theory of thin-walled rods of open profile is subsequently developed from the models of rods and shells, and traditionally applied equations are proven to be asymptotically exa...
Direct numerical reconstruction of conductivities in three dimensions using scattering transforms
DEFF Research Database (Denmark)
Bikowski, Jutta; Knudsen, Kim; Mueller, Jennifer L
2011-01-01
A direct three-dimensional EIT reconstruction algorithm based on complex geometrical optics solutions and a nonlinear scattering transform is presented and implemented for spherically symmetric conductivity distributions. The scattering transform is computed both with a Born approximation and fro...... the forward problem for purposes of comparison. Reconstructions are computed for several test problems. A connection to Calderón's linear reconstruction algorithm is established, and reconstructions using both methods are compared....
Quanren Zeng; Zhenhai Xu; Yankang Tian; Yi Qin
2016-01-01
The development speed and application range of the additive manufacturing (AM) processes, such as selective laser melting (SLM), laser metal deposition (LMD) or laser-engineering net shaping (LENS), are ever-increasing in modern advanced manufacturing field for rapid manufacturing, tooling repair or surface enhancement of the critical metal components. LMD is based on a kind of directed energy deposition (DED) technology which ejects a strand of metal powders into a moving molten pool caused ...
2016-02-26
massive direct numerical simulations ( DNS ), detailed molecular dynamics simulations and novel laser based experimental approaches were developed to explore...TERMS Aerothermodynamics and Nonequillibrium, Hypersonic and Gas-surface Interaction 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT UU 18...multidisciplinary nature of the scientific problem, a combination of state-of-the-art massive direct numerical simulations ( DNS ), detailed molecular dynamics
Numerical modeling and validation of wave heights and directionality in the ice using WAVEWATCH III
Ardhuin, Fabrice; Dumont, Dany; Accensi, Mickael; Sevigny, Caroline; Boutin, Guillaume; Rogers, Erick
2016-04-01
The poorly understood attenuation of waves, the key dynamic effect that defines the width of the Marginal Ice Zone, has been attributed to the combined effect of wave scattering and wave dissipation. Because scattering and dissipation have very different effects on the directional distribution of wave energy, it is possible to better understand the balance between scattering and dissipation by an analysis of the width of the directional wave spectrum. We have thus introduced dissipation and scattering terms in the spectral wave model WAVEWATCH III, and an estimation of the maximum ice floe size. Academic and realistic simulations show that the energy level and directional spreading far into the Arctic pack ice (Wadhams and Doble 2009) can be well explained by dissipative processes without the need for scattering. The same is true of observed swells in the Southern Ocean (Ardhuin et al. 2015). However, the dissipation level required to explain the observed wave height goes from 2 in the southern ocean to 12 times the viscous dissipation under a smooth ice plate. This and other data suggest that broken ice causes less dissipation than a continuous ice cover, possibly due to the dissipation by creep inside the ice when it is not broken and bends. Work is under way to parameterize that effect using the estimated maximum ice floe size.
Madavan, Nateri K.
1995-01-01
The work in this report was conducted at NASA Ames Research Center during the period from August 1993 to January 1995 deals with the direct numerical simulation of transitional and turbulent flow at low Mach numbers using high-order-accurate finite-difference techniques. A computation of transition to turbulence of the spatially-evolving boundary layer on a heated flat plate in the presence of relatively high freestream turbulence was performed. The geometry and flow conditions were chosen to match earlier experiments. The development of the momentum and thermal boundary layers was documented. Velocity and temperature profiles, as well as distributions of skin friction, surface heat transfer rate, Reynolds shear stress, and turbulent heat flux were shown to compare well with experiment. The numerical method used here can be applied to complex geometries in a straightforward manner.
Institute of Scientific and Technical Information of China (English)
Zhang Hong-Na; Li Feng-Chen; Cao Yang; Kunugi Tomoaki; Yu Bo
2013-01-01
In this paper,we present a direct numerical simulation (DNS) of elastic turbulence of viscoelastic fluid at vanishingly low Reynolds number (Re =1) in a three-dimensional straight channel flow for the first time,using the Giesekus constitutive model for the fluid.In order to generate and maintain the turbulent fluid motion in the straight channel,a sinusoidal force term is added to the momentum equation,and then the elastic turbulence is numerically realized with an initialized chaotic velocity field and a stretched conformation field.Statistical and structural characteristics of the elastic turbulence therein are analyzed based on the detailed information obtained from the DNS.The fluid mixing enhancement effect of elastic turbulence is also demonstrated for the potential applications of this phenomenon.
Energy Technology Data Exchange (ETDEWEB)
Rincon, Jose; Almao, Nastia [Universidad del Zulia, Lab. de Simulacion Computacional, Zulia (Venezuela); Gonzalez, Eduardo [Universidad del Zulia, Inst. de Investigaciones de la Facultad de Arquitectura, Zulia (Venezuela)
2001-07-01
The thermal performance of a solar passive cooling system (SPCS) under a hot and humid climate is experimentally and numerically evaluated. The experimental data were obtained from two full scale cells, with identical walls, but different roof configurations. One cell has a highly-insulated roof and the other has an SPCS incorporated consisting of a thermal mass (water), which is cooled by evaporation and long wave nocturnal radiation. The study was conducted taking into account the local climatic conditions of Maracaibo, a tropical city located in Venezuela. The numerical evaluation was accomplished using the computational code 'EVITA' which is based on the finite volume approach with high order bounded treatment of the convective terms. A PISO-like solution algorithm is used to solve the transient form of the continuity, momentum and energy equations. It has been demonstrated experimentally and numerically that under a hot and humid climate, it is possible to keep the indoor temperature below the outdoor temperature, using a passive cooling technique of a roof pond. The numerical results obtained using the model have demonstrated that the computational code used is a suitable cost-efficient alternative for the thermal performance evaluation of SPCS. (Author)
Numerical evaluation of virtual corrections to multi-jet production in massless QCD
DEFF Research Database (Denmark)
Badger, S.; Yundin, V.; Biedermann, B.
2013-01-01
.7.4. Classification: 11.5. External routines: QCDLoop (http://qcdloop.fnal.gov/), qd (http://crd.lbl.gov/dhbailey/mpdist/), both included in the distribution file. Nature of problem:. Evaluation of virtual corrections for multi-jet production in massless QCD. Solution method:. Purely numerical approach based on tree......We present a C++ library for the numerical evaluation of one-loop virtual corrections to multi-jet production in massless QCD. The pure gluon primitive amplitudes are evaluated using NGluon (Badger et al., (2011) [62]). A generalized unitarity reduction algorithm is used to construct arbitrary...... amplitudes obtained via Berends-Giele recursion combined with unitarity method. Restrictions:. Full colour and helicity summed corrections only up to 5 final state jets. Running time:. Full colour and helicity summed 2 ¿ 4 channels take around 0.5-8 s per point depending on the number of fermion lines...
Energy Technology Data Exchange (ETDEWEB)
Marxen, Olaf, E-mail: olaf.marxen@vki.ac.be [Center for Turbulence Research, Building 500, Stanford University, Stanford, CA 94305-3035 (United States); Aeronautics and Aerospace Department, von Karman Institute for Fluid Dynamics, Chaussée de Waterloo, 72, 1640 Rhode-St-Genèse (Belgium); Magin, Thierry E. [Aeronautics and Aerospace Department, von Karman Institute for Fluid Dynamics, Chaussée de Waterloo, 72, 1640 Rhode-St-Genèse (Belgium); Shaqfeh, Eric S.G.; Iaccarino, Gianluca [Center for Turbulence Research, Building 500, Stanford University, Stanford, CA 94305-3035 (United States)
2013-12-15
A new numerical method is presented here that allows to consider chemically reacting gases during the direct numerical simulation of a hypersonic fluid flow. The method comprises the direct coupling of a solver for the fluid mechanical model and a library providing the physio-chemical model. The numerical method for the fluid mechanical model integrates the compressible Navier–Stokes equations using an explicit time advancement scheme and high-order finite differences. This Navier–Stokes code can be applied to the investigation of laminar-turbulent transition and boundary-layer instability. The numerical method for the physio-chemical model provides thermodynamic and transport properties for different gases as well as chemical production rates, while here we exclusively consider a five species air mixture. The new method is verified for a number of test cases at Mach 10, including the one-dimensional high-temperature flow downstream of a normal shock, a hypersonic chemical reacting boundary layer in local thermodynamic equilibrium and a hypersonic reacting boundary layer with finite-rate chemistry. We are able to confirm that the diffusion flux plays an important role for a high-temperature boundary layer in local thermodynamic equilibrium. Moreover, we demonstrate that the flow for a case previously considered as a benchmark for the investigation of non-equilibrium chemistry can be regarded as frozen. Finally, the new method is applied to investigate the effect of finite-rate chemistry on boundary layer instability by considering the downstream evolution of a small-amplitude wave and comparing results with those obtained for a frozen gas as well as a gas in local thermodynamic equilibrium.
Direct numerical simulation of a compressible multiphase flow through the fast Eulerian approach
Cerminara, Matteo; Ongaro, Tomaso Esposti; Salvetti, Maria Vittoria
2014-01-01
Our work is motivated by the analysis of ash plume dynamics, arising in the study of volcanic eruptions. Such phenomena are characterized by large Reynolds number (exceeding $10^7$) and a large number of polydispersed particles~[1]. Thus, the choice of the methodology to be used is straightforward: we need LES of a multiphase gas-particles flow. Since the simulation of the behavior of a large number of dispersed particles is very difficult with Lagrangian methods, we model the particles as a continuum, Eulerian fluid (dust), by using reduced models involving two fluids, as proposed in Ref.~[2,3,4]. Moreover, we need a robust numerical scheme to simultaneously treat compressibility, buoyancy effects and turbulent dispersal dynamics. We analyze the turbulence properties of such models in a homogeneous and isotropic setting, with the aim of formulating a LES model. In particular, we examine the development of freely decaying homogeneous and isotropic turbulence in subsonic regime (the r.m.s. Mach number either 0...
Mixa, T.; Fritts, D. C.; Laughman, B.; Wang, L.; Kantha, L. H.
2015-12-01
Multiple observations provide compelling evidence that gravity wave dissipation events often occur in multi-scale environments having highly-structured wind and stability profiles extending from the stable boundary layer into the mesosphere and lower thermosphere. Such events tend to be highly localized and thus yield local energy and momentum deposition and efficient secondary gravity wave generation expected to have strong influences at higher altitudes [e.g., Fritts et al., 2013; Baumgarten and Fritts, 2014]. Lidars, radars, and airglow imagers typically cannot achieve the spatial resolution needed to fully quantify these small-scale instability dynamics. Hence, we employ high-resolution modeling to explore these dynamics in representative environments. Specifically, we describe numerical studies of gravity wave packets impinging on a sheet of high stratification and shear and the resulting instabilities and impacts on the gravity wave amplitude and momentum flux for various flow and gravity wave parameters. References: Baumgarten, Gerd, and David C. Fritts (2014). Quantifying Kelvin-Helmholtz instability dynamics observed in noctilucent clouds: 1. Methods and observations. Journal of Geophysical Research: Atmospheres, 119.15, 9324-9337. Fritts, D. C., Wang, L., & Werne, J. A. (2013). Gravity wave-fine structure interactions. Part I: Influences of fine structure form and orientation on flow evolution and instability. Journal of the Atmospheric Sciences, 70(12), 3710-3734.
Catalina, Adrian V.; Sen, S.; Rose, M. Franklin (Technical Monitor)
2001-01-01
The evolution of cellular solid/liquid interfaces from an initially unstable planar front was studied by means of a two-dimensional computer simulation. The developed numerical model makes use of an interface tracking procedure and has the capability to describe the dynamics of the interface morphology based on local changes of the thermodynamic conditions. The fundamental physics of this formulation was validated against experimental microgravity results and the predictions of the analytical linear stability theory. The performed simulations revealed that in certain conditions, based on a competitive growth mechanism, an interface could become unstable to random perturbations of infinitesimal amplitude even at wavelengths smaller than the neutral wavelength, lambda(sub c), predicted by the linear stability theory. Furthermore, two main stages of spacing selection have been identified. In the first stage, at low perturbations amplitude, the selection mechanism is driven by the maximum growth rate of instabilities while in the second stage the selection is influenced by nonlinear phenomena caused by the interactions between the neighboring cells. Comparison of these predictions with other existing theories of pattern formation and experimental results will be discussed.
Directory of Open Access Journals (Sweden)
Kun Zhou
2013-01-01
Full Text Available The concentration and orientation of suspended fibers in a mixing layer are investigated numerically. Two cases (diffusive and nondiffusive are investigated for the fiber concentration distribution. The fine structures of the instantaneous distributions under these two cases are very different due to molecular diffusion. Sharp front of concentration is observed in the nondiffusive case. However, there is no obvious difference in the mean concentration between the two cases. With regard to the orientation, a fiber may rotate periodically or approach an asymptotic orientation, which is determined by a determinant defined with the stain rate. The symmetric part of the strain rate tends to make a fiber align to an asymptotic orientation, while the antisymmetric part drives a fiber to rotate. When a fluid parcel passes through a region with relatively high shear rate, fibers carried by the fluid parcel are most likely to rotate incessantly. On the other hand, in the region of relatively high extension rate, fibers tend to align to some asymptotic orientation. Generally, fibers tend to align with the shear plane. This fact has significant implications in predicting the rheological properties of fiber suspension flows.
Campbell, Bryce; Hendrickson, Kelli; Liu, Yuming; Subramani, Hariprasad
2014-11-01
For gas-liquid flows through pipes and channels, a flow regime (referred to as slug flow) may occur when waves form at the interface of a stratified flow and grow until they bridge the pipe diameter trapping large elongated gas bubbles within the liquid. Slug formation is often accompanied by strong nonlinear wave-wave interactions, wave breaking, and gas entrainment. This work numerically investigates the fully nonlinear interfacial evolution of a two-phase density/viscosity stratified flow through a horizontal channel. A Navier-Stokes flow solver coupled with a conservative volume-of-fluid algorithm is use to carry out high resolution three-dimensional simulations of a turbulent gas flowing over laminar (or turbulent) liquid layers. The analysis of such flows over a range of gas and liquid Reynolds numbers permits the characterization of the interfacial stresses and turbulent flow statistics allowing for the development of physics-based models that approximate the coupled interfacial-turbulent interactions and supplement the heuristic models built into existing industrial slug simulators.
Numerical modeling of a Jet Ignition Direct Injection (JIDI) LPG engine
albert boretti
2016-01-01
The paper presents indirectly validated simulations of the operation of a LPG engine fitted with Direct Injection (DI) and Jet Ignition (JI). It is demonstrated that the engine may have diesel like efficiencies and load control by quantity of fuel injected. As the liquid propane quickly evaporates after injection in the main chamber, the main chamber mixture may be much closer to stoichiometry than a diesel for a better specific power at low engine speeds. This design also works at the high ...
Sharma, Anupam; Long, Lyle N.
2004-10-01
A particle approach using the Direct Simulation Monte Carlo (DSMC) method is used to solve the problem of blast impact with structures. A novel approach to model the solid boundary condition for particle methods is presented. The solver is validated against an analytical solution of the Riemann shocktube problem and against experiments on interaction of a planar shock with a square cavity. Blast impact simulations are performed for two model shapes, a box and an I-shaped beam, assuming that the solid body does not deform. The solver uses domain decomposition technique to run in parallel. The parallel performance of the solver on two Beowulf clusters is also presented.
Yang, Xiaofan; Scheibe, Timothy D.; Richmond, Marshall C.; Perkins, William A.; Vogt, Sarah J.; Codd, Sarah L.; Seymour, Joseph D.; McKinley, Matthew I.
2013-04-01
A significant body of current research is aimed at developing methods for numerical simulation of flow and transport in porous media that explicitly resolve complex pore and solid geometries, and at utilizing such models to study the relationships between fundamental pore-scale processes and macroscopic manifestations at larger (i.e., Darcy) scales. A number of different numerical methods for pore-scale simulation have been developed, and have been extensively tested and validated for simplified geometries. However, validation of pore-scale simulations of fluid velocity for complex, three-dimensional (3D) pore geometries that are representative of natural porous media is challenging due to our limited ability to measure pore-scale velocity in such systems. Recent advances in magnetic resonance imaging (MRI) offer the opportunity to measure not only the pore geometry, but also local fluid velocities under steady-state flow conditions in 3D and with high spatial resolution. In this paper, we present a 3D velocity field measured at sub-pore resolution (tens of micrometers) over a centimeter-scale 3D domain using MRI methods. We have utilized the measured pore geometry to perform 3D simulations of Navier-Stokes flow over the same domain using direct numerical simulation techniques. We present a comparison of the numerical simulation results with the measured velocity field. It is shown that the numerical results match the observed velocity patterns well overall except for a variance and small systematic scaling which can be attributed to the known experimental uncertainty in the MRI measurements. The comparisons presented here provide strong validation of the pore-scale simulation methods and new insights for interpretation of uncertainty in MRI measurements of pore-scale velocity. This study also provides a potential benchmark for future comparison of other pore-scale simulation methods. 2012 Elsevier Science.
Numerical simulation on directional solidification of Al-Ni-Co alloy based on FEM
Directory of Open Access Journals (Sweden)
Yang Zhili
2010-02-01
Full Text Available The ratio, of the temperature gradient at the solidification front to the solidification rate of solid-liquid interface, plays a large part in columnar grain growth. The transient temperature fields of directional solidification of Al-Ni-Co alloy were studied by employing a finite element method. The temperature gradient at the solidification front and the solidification rate were analyzed for molten steels pouring at different temperatures. The results show that with different initial pouring temperatures, the individual ratio of the temperature gradient at solidification front to the solidification rate soars up in the initial stage of solidification, then varies within 2,000-6,000 ℃·s·cm-2, and finally goes down rapidly and even tend to be closed to each other when the solidification thickness reaches 5-6 cm. The simulation result is consistent with the practical production which can provide an available reference for process optimization of directional solidified Al-Ni-Co alloy.
DIRECT NUMERICAL SIMULATION OF TURBULENT HEAT TRANSFER IN A WALL-NORMAL ROTATING CHANNEL FLOW
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
Direct Nmerical Simulation (DNS) of turbulent heat transfer in a wall-normal rotating channel flow has been carried out for the rotation number Nτ from 0 to 0.1, the Reynolds number 194 based on the friction velocity of non-rotating case and the half-height of the channel, and the Prandtl number 1. The objective of this study is to reveal the effects of rotation on the characteristics of turbulent flow and heat transfer. Based on the present calculated results, two typical rotation regimes are identified. When 0＜Nτ＜0.06, turbulence and thermal statistics correlated with the spanwise velocity fluctuation are enhanced since the shear rate of spanwise mean flow induced by Coriolis force increases; however, the other statistics are suppressed. When Nτ＞0.06, turbulence and thermal statistics are suppressed significantly because the Coriolis force effect plays as a dominated role in the rotating flow. Remarkable change of the direction of near-wall streak structures based on the velocity and temperature fluctuations is identified.
Directory of Open Access Journals (Sweden)
Xue Xiang
2010-08-01
Full Text Available The boundary heat flow has important significance for the microstructures of directional solidified binary alloy. Interface evolution of the directional solidified microstructure with different boundary heat flow was discussed. In this study, only one interface was allowed to have heat flow, and Neumann boundary conditions were imposed at the other three interfaces. From the calculated results, it was found that different boundary heat flows will result in different microstructures. When the boundary heat flow equals to 20 W·cm-2, the growth of longitudinal side branches is accelerated and the growth of transverse side branches is restrained, and meanwhile, there is dendritic remelting in the calculation domain. When the boundary heat flow equals to 40 W·cm-2, the growths of the transverse and longitudinal side branches compete with each other, and when the boundary heat flow equals to 100-200 W·cm-2, the growth of transverse side branches dominates absolutely. The temperature field of dendritic growth was analyzed and the relation between boundary heat flow and temperature field was also investigated.
Institute of Scientific and Technical Information of China (English)
Xue Xiang; Tang Jinjun
2010-01-01
The boundary heat flow has important significance for the microstructures of directional solidified binary alloy. Interface evolution of the directional solidified microstructure with different boundary heat flow was discussed. In this study, only one interface was allowed to have heat flow, and Neumann boundary conditions were imposed at the other three interfaces. From the calculated results, it was found that different boundary heat flows will result in different microstructures. When the boundary heat flow equals to 20 W-cm-2, the growth of longitudinal side branches is accelerated and the growth of transverse side branches is restrained, and meanwhile, there is dendritic remelting in the calculation domain. When the boundary heat flow equals to 40 W-cm-2, the growths of the transverse and longitudinal side branches compete with each other, and when the boundary heat flow equals to 100-200 W-cm-2, the growth of transverse side branches dominates absolutely. The temperature field of dendritic growth was analyzed and the relation between boundary heat flow and temperature field was also investigated.
Topalian, Victor; Oliver, Todd; Ulerich, Rhys; Moser, Robert
2013-11-01
A DNS of a compressible, reacting boundary layer flow at Reθ ~ 430 was performed using a temporal slow-growth homogenization, for a multispecies flow model of air at supersonic regime. The overall scenario parameters are related to those of the flow over an ablating surface of a space capsule upon Earth's atmospheric re-entry. The simulation algorithm features Fourier spatial discretization in the streamwise and spanwise directions, B-splines in the wall normal direction, and is marched semi-implicitly in time using the SMR91 scheme. Flow statistics will be presented for relevant flow quantities, in particular those related with RANS modeling. Since analogous slow growth computations can be performed using RANS to predict the flow mean profiles, the use of data gathered from this type of simulation as a vehicle for the calibration and uncertainty quantification of RANS models will be discussed. This work is supported by the Department of Energy [National Nuclear Security Administration] under Award Number [DE-FC52-08NA28615].
Criteria for clinical translucency evaluation of direct esthetic restorative materials
2016-01-01
The purpose of this review was to suggest practical criteria for the clinical translucency evaluation of direct esthetic restorative materials, and to review the translucency with these criteria. For the evaluation of reported translucency values, measuring instrument and method, specimen thickness, background color, and illumination should be scrutinized. Translucency parameter (TP) of 15 to 19 could be regarded as the translucency of 1 mm thick human enamel. Visual perceptibility threshold for translucency difference in contrast ratio (ΔCR) of 0.07 could be transformed into ΔTP value of 2. Translucency differences between direct and indirect resin composites were perceivable (ΔTP > 2). Universal and corresponding flowable resin composites did not show perceivable translucency differences in most products. Translucency differed significantly by the product within each shade group, and by the shade group within each product. Translucency of human enamel and perceptibility threshold for translucency difference may be used as criteria for the clinical evaluation of translucency of esthetic restorative materials. PMID:27508156
Criteria for clinical translucency evaluation of direct esthetic restorative materials.
Lee, Yong-Keun
2016-08-01
The purpose of this review was to suggest practical criteria for the clinical translucency evaluation of direct esthetic restorative materials, and to review the translucency with these criteria. For the evaluation of reported translucency values, measuring instrument and method, specimen thickness, background color, and illumination should be scrutinized. Translucency parameter (TP) of 15 to 19 could be regarded as the translucency of 1 mm thick human enamel. Visual perceptibility threshold for translucency difference in contrast ratio (ΔCR) of 0.07 could be transformed into ΔTP value of 2. Translucency differences between direct and indirect resin composites were perceivable (ΔTP > 2). Universal and corresponding flowable resin composites did not show perceivable translucency differences in most products. Translucency differed significantly by the product within each shade group, and by the shade group within each product. Translucency of human enamel and perceptibility threshold for translucency difference may be used as criteria for the clinical evaluation of translucency of esthetic restorative materials.
Arrighi, Chiara; Campo, Lorenzo
2017-04-01
In last years, the concern about the economical and lives loss due to urban floods has grown hand in hand with the numerical skills in simulating such events. The large amount of computational power needed in order to address the problem (simulating a flood in a complex terrain such as a medium-large city) is only one of the issues. Among them it is possible to consider the general lack of exhaustive observations during the event (exact extension, dynamic, water level reached in different parts of the involved area), needed for calibration and validation of the model, the need of considering the sewers effects, and the availability of a correct and precise description of the geometry of the problem. In large cities the topographic surveys are in general available with a number of points, but a complete hydraulic simulation needs a detailed description of the terrain on the whole computational domain. LIDAR surveys can achieve this goal, providing a comprehensive description of the terrain, although they often lack precision. In this work an optimal merging of these two sources of geometrical information, measured elevation points and LIDAR survey, is proposed, by taking into account the error variance of both. The procedure is applied to a flood-prone city over an area of 35 square km approximately starting with a DTM from LIDAR with a spatial resolution of 1 m, and 13000 measured points. The spatial pattern of the error (LIDAR vs points) is analysed, and the merging method is tested with a series of Jackknife procedures that take into account different densities of the available points. A discussion of the results is provided.
Statistics for long irregular wave run-up on a plane beach from direct numerical simulations
Didenkulova, Ira; Senichev, Dmitry; Dutykh, Denys
2017-04-01
Very often for global and transoceanic events, due to the initial wave transformation, refraction, diffraction and multiple reflections from coastal topography and underwater bathymetry, the tsunami approaches the beach as a very long wave train, which can be considered as an irregular wave field. The prediction of possible flooding and properties of the water flow on the coast in this case should be done statistically taking into account the formation of extreme (rogue) tsunami wave on a beach. When it comes to tsunami run-up on a beach, the most used mathematical model is the nonlinear shallow water model. For a beach of constant slope, the nonlinear shallow water equations have rigorous analytical solution, which substantially simplifies the mathematical formulation. In (Didenkulova et al. 2011) we used this solution to study statistical characteristics of the vertical displacement of the moving shoreline and its horizontal velocity. The influence of the wave nonlinearity was approached by considering modifications of probability distribution of the moving shoreline and its horizontal velocity for waves of different amplitudes. It was shown that wave nonlinearity did not affect the probability distribution of the velocity of the moving shoreline, while the vertical displacement of the moving shoreline was affected substantially demonstrating the longer duration of coastal floods with an increase in the wave nonlinearity. However, this analysis did not take into account the actual transformation of irregular wave field offshore to oscillations of the moving shoreline on a slopping beach. In this study we would like to cover this gap by means of extensive numerical simulations. The modeling is performed in the framework of nonlinear shallow water equations, which are solved using a modern shock-capturing finite volume method. Although the shallow water model does not pursue the wave breaking and bore formation in a general sense (including the water surface
Numerical and experimental investigation of direct solar crop dryer for farmers
Kareem, M. W.; Habib, Khairul; Sulaiman, S. A.
2015-07-01
This article presents a theoretical and experimental investigation on effects of weather on direct solar crop drying technique. The SIMULINK tool was employed to analyze the energy balance equations of the transient system model. A prototype of the drying system was made and data were collected between the months of June and July in Perak, Malaysia. The contribution of intense sunny days was encouraging despite the wet season, and the wind velocity was dynamic during the period of investigation. However, high percentage of relative humidity was observed. This constitutes a hindrance to efficient drying process. The reported studies were silent on the effect of thick atmospheric moisture content on drying rate of agricultural products in tropic climate. This finding has revealed the mean values of insolation, wind speed, moisturized air, system performance efficiency and chili microscopy image morphology. The predicted and measured results were compared with good agreement.
Numerical modeling of a Jet Ignition Direct Injection (JIDI LPG engine
Directory of Open Access Journals (Sweden)
albert boretti
2016-12-01
Full Text Available The paper presents indirectly validated simulations of the operation of a LPG engine fitted with Direct Injection (DI and Jet Ignition (JI. It is demonstrated that the engine may have diesel like efficiencies and load control by quantity of fuel injected. As the liquid propane quickly evaporates after injection in the main chamber, the main chamber mixture may be much closer to stoichiometry than a diesel for a better specific power at low engine speeds. This design also works at the high engine speeds impossible for the diesel, as combustion within the main chamber is controlled by the turbulent mixing rather than the vaporization and diffusion processes of the injected fuel of the diesel.
Numerical simulation of direct methanol fuel cells using lattice Boltzmann method
Energy Technology Data Exchange (ETDEWEB)
Delavar, Mojtaba Aghajani; Farhadi, Mousa; Sedighi, Kurosh [Faculty of Mechanical Engineering, Babol University of Technology, Babol, P.O. Box 484 (Iran)
2010-09-15
In this study Lattice Boltzmann Method (LBM) as an alternative of conventional computational fluid dynamics method is used to simulate Direct Methanol Fuel Cell (DMFC). A two dimensional lattice Boltzmann model with 9 velocities, D2Q9, is used to solve the problem. The computational domain includes all seven parts of DMFC: anode channel, catalyst and diffusion layers, membrane and cathode channel, catalyst and diffusion layers. The model has been used to predict the flow pattern and concentration fields of different species in both clear and porous channels to investigate cell performance. The results have been compared well with results in literature for flow in porous and clear channels and cell polarization curves of the DMFC at different flow speeds and feed methanol concentrations. (author)
Generalization Evaluation of Machine Learning Numerical Observers for Image Quality Assessment.
Kalayeh, Mahdi M; Marin, Thibault; Brankov, Jovan G
2013-06-01
In this paper, we present two new numerical observers (NO) based on machine learning for image quality assessment. The proposed NOs aim to predict human observer performance in a cardiac perfusion-defect detection task for single-photon emission computed tomography (SPECT) images. Human observer (HumO) studies are now considered to be the gold standard for task-based evaluation of medical images. However such studies are impractical for use in early stages of development for imaging devices and algorithms, because they require extensive involvement of trained human observers who must evaluate a large number of images. To address this problem, numerical observers (also called model observers) have been developed as a surrogate for human observers. The channelized Hotelling observer (CHO), with or without internal noise model, is currently the most widely used NO of this kind. In our previous work we argued that development of a NO model to predict human observers' performance can be viewed as a machine learning (or system identification) problem. This consideration led us to develop a channelized support vector machine (CSVM) observer, a kernel-based regression model that greatly outperformed the popular and widely used CHO. This was especially evident when the numerical observers were evaluated in terms of generalization performance. To evaluate generalization we used a typical situation for the practical use of a numerical observer: after optimizing the NO (which for a CHO might consist of adjusting the internal noise model) based upon a broad set of reconstructed images, we tested it on a broad (but different) set of images obtained by a different reconstruction method. In this manuscript we aim to evaluate two new regression models that achieve accuracy higher than the CHO and comparable to our earlier CSVM method, while dramatically reducing model complexity and computation time. The new models are defined in a Bayesian machine-learning framework: a channelized
Direct Numerical Simulation of Interfacial Flows: Implicit Sharp-Interface Method (I-SIM)
Energy Technology Data Exchange (ETDEWEB)
Robert Nourgaliev; Theo Theofanous; HyeongKae Park; Vincent Mousseau; Dana Knoll
2008-01-01
In recent work (Nourgaliev, Liou, Theofanous, JCP in press) we demonstrated that numerical simulations of interfacial flows in the presence of strong shear must be cast in dynamically sharp terms (sharp interface treatment or SIM), and that moreover they must meet stringent resolution requirements (i.e., resolving the critical layer). The present work is an outgrowth of that work aiming to overcome consequent limitations on the temporal treatment, which become still more severe in the presence of phase change. The key is to avoid operator splitting between interface motion, fluid convection, viscous/heat diffusion and reactions; instead treating all these non-linear operators fully-coupled within a Newton iteration scheme. To this end, the SIM’s cut-cell meshing is combined with the high-orderaccurate implicit Runge-Kutta and the “recovery” Discontinuous Galerkin methods along with a Jacobian-free, Krylov subspace iteration algorithm and its physics-based preconditioning. In particular, the interfacial geometry (i.e., marker’s positions and volumes of cut cells) is a part of the Newton-Krylov solution vector, so that the interface dynamics and fluid motions are fully-(non-linearly)-coupled. We show that our method is: (a) robust (L-stable) and efficient, allowing to step over stability time steps at will while maintaining high-(up to the 5th)-order temporal accuracy; (b) fully conservative, even near multimaterial contacts, without any adverse consequences (pressure/velocity oscillations); and (c) highorder-accurate in spatial discretization (demonstrated here up to the 12th-order for smoothin-the-bulk-fluid flows), capturing interfacial jumps sharply, within one cell. Performance is illustrated with a variety of test problems, including low-Mach-number “manufactured” solutions, shock dynamics/tracking with slow dynamic time scales, and multi-fluid, highspeed shock-tube problems. We briefly discuss preconditioning, and we introduce two physics
Feedback-Based Coverage Directed Test Generation: An Industrial Evaluation
Ioannides, Charalambos; Barrett, Geoff; Eder, Kerstin
Although there are quite a few approaches to Coverage Directed test Generation aided by Machine Learning which have been applied successfully to small and medium size digital designs, it is not clear how they would scale on more elaborate industrial-level designs. This paper evaluates one of these techniques, called MicroGP, on a fully fledged industrial design. The results indicate relative success evidenced by a good level of code coverage achieved with reasonably compact tests when compared to traditional test generation approaches. However, there is scope for improvement especially with respect to the diversity of the tests evolved.
Energy evaluation of the compaction process of directly compressible isomalt.
Muzíková, Jitka; Pavlasová, Veronika
2011-02-01
The paper compares the compressibility of two directly compressible isomalts, galenIQ 720 and galenIQ721, using the energy evaluation of the compaction process by means of the force--displacement profiles. It evaluates the energies for friction, energies accumulated by the tablet, energy of decompression, energy of compaction and plasticity in pure dry binders, in dry binders with lubricants (0.5 and 1% of magnesium stearate and sodium stearyl fumarate) and further in the tableting materials containing the model ingredients acetylsalicylic acid and ascorbic acid. The results of the study have revealed that lower values of the energy for friction and compaction with the identical compression force are found by the substance galenIQ 720, which is therefore better compressible than the substance galenIQ 721.
Type Directed Partial Evaluation for Level-1 Shift and Reset
Directory of Open Access Journals (Sweden)
Danko Ilik
2013-09-01
Full Text Available We present an implementation in the Coq proof assistant of type directed partial evaluation (TDPE algorithms for call-by-name and call-by-value versions of shift and reset delimited control operators, and in presence of strong sum types. We prove that the algorithm transforms well-typed programs to ones in normal form. These normal forms can not always be arrived at using the so far known equational theories. The typing system does not allow answer-type modification for function types and allows delimiters to be set on at most one atomic type. The semantic domain for evaluation is expressed in Constructive Type Theory as a dependently typed monadic structure combining Kripke models and continuation passing style translations.
Fang, Wen-Zhen; Zhang, Hu; Chen, Li; Tao, Wen-Quan
2015-01-01
In this paper, a multiple-relaxation-time lattice Boltzmann model with an off-diagonal collision matrix was adopted to predict the effective thermal conductivities of the anisotropic heterogeneous materials whose components are also anisotropic. The half lattice division scheme was adopted to deal with the internal boundaries to guarantee the heat flux continuity at the interfaces. Accuracy of the model was confirmed by comparisons with benchmark results and existing simulation data. The present method was then adopted to numerically predict the transverse and longitudinal effective thermal conductivities of three-dimensional (3D) four-directional braided composites. Some corresponding experiments based on the Hot Disk method were conducted to measure their transverse and longitudinal effective thermal conductivities. The predicted data fit the experiment data well. Influences of fiber volume fractions and interior braiding angles on the effective thermal conductivities of 3D four-directional braided composit...
Abbott, B. P.; Abbott, R.; Abbott, T. D.; Abernathy, M. R.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Addesso, P.; Adhikari, R. X.; Adya, V. B.; Affeldt, C.; Agathos, M.; Agatsuma, K.; Aggarwal, N.; Aguiar, O. D.; Aiello, L.; Ain, A.; Ajith, P.; Allen, B.; Allocca, A.; Altin, P. A.; Anderson, S. B.; Anderson, W. G.; Arai, K.; Araya, M. C.; Arceneaux, C. C.; Areeda, J. S.; Arnaud, N.; Arun, K. G.; Ascenzi, S.; Ashton, G.; Ast, M.; Aston, S. M.; Astone, P.; Aufmuth, P.; Aulbert, C.; Babak, S.; Bacon, P.; Bader, M. K. M.; Baker, P. T.; Baldaccini, F.; Ballardin, G.; Ballmer, S. W.; Barayoga, J. C.; Barclay, S. E.; Barish, B. C.; Barker, D.; Barone, F.; Barr, B.; Barsotti, L.; Barsuglia, M.; Barta, D.; Bartlett, J.; Bartos, I.; Bassiri, R.; Basti, A.; Batch, J. C.; Baune, C.; Bavigadda, V.; Bazzan, M.; Bejger, M.; Bell, A. S.; Berger, B. K.; Bergmann, G.; Berry, C. P. L.; Bersanetti, D.; Bertolini, A.; Betzwieser, J.; Bhagwat, S.; Bhandare, R.; Bilenko, I. A.; Billingsley, G.; Birch, J.; Birney, R.; Biscans, S.; Bisht, A.; Bitossi, M.; Biwer, C.; Bizouard, M. A.; Blackburn, J. K.; Blair, C. D.; Blair, D. G.; Blair, R. M.; Bloemen, S.; Bock, O.; Boer, M.; Bogaert, G.; Bogan, C.; Bohe, A.; Bond, C.; Bondu, F.; Bonnand, R.; Boom, B. A.; Bork, R.; Boschi, V.; Bose, S.; Bouffanais, Y.; Bozzi, A.; Bradaschia, C.; Brady, P. R.; Braginsky, V. B.; Branchesi, M.; Brau, J. E.; Briant, T.; Brillet, A.; Brinkmann, M.; Brisson, V.; Brockill, P.; Broida, J. E.; Brooks, A. F.; Brown, D. A.; Brown, D. D.; Brown, N. M.; Brunett, S.; Buchanan, C. C.; Buikema, A.; Bulik, T.; Bulten, H. J.; Buonanno, A.; Buskulic, D.; Buy, C.; Byer, R. L.; Cabero, M.; Cadonati, L.; Cagnoli, G.; Cahillane, C.; Calderón Bustillo, J.; Callister, T.; Calloni, E.; Camp, J. B.; Cannon, K. C.; Cao, J.; Capano, C. D.; Capocasa, E.; Carbognani, F.; Caride, S.; Casanueva Diaz, J.; Casentini, C.; Caudill, S.; Cavaglià, M.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cepeda, C. B.; Cerboni Baiardi, L.; Cerretani, G.; Cesarini, E.; Chamberlin, S. J.; Chan, M.; Chao, S.; Charlton, P.; Chassande-Mottin, E.; Cheeseboro, B. D.; Chen, H. Y.; Chen, Y.; Cheng, C.; Chincarini, A.; Chiummo, A.; Cho, H. S.; Cho, M.; Chow, J. H.; Christensen, N.; Chu, Q.; Chua, S.; Chung, S.; Ciani, G.; Clara, F.; Clark, J. A.; Cleva, F.; Coccia, E.; Cohadon, P.-F.; Colla, A.; Collette, C. G.; Cominsky, L.; Constancio, M.; Conte, A.; Conti, L.; Cook, D.; Corbitt, T. R.; Cornish, N.; Corsi, A.; Cortese, S.; Costa, C. A.; Coughlin, M. W.; Coughlin, S. B.; Coulon, J.-P.; Countryman, S. T.; Couvares, P.; Cowan, E. E.; Coward, D. M.; Cowart, M. J.; Coyne, D. C.; Coyne, R.; Craig, K.; Creighton, J. D. E.; Cripe, J.; Crowder, S. G.; Cumming, A.; Cunningham, L.; Cuoco, E.; Dal Canton, T.; Danilishin, S. L.; D'Antonio, S.; Danzmann, K.; Darman, N. S.; Dasgupta, A.; Da Silva Costa, C. F.; Dattilo, V.; Dave, I.; Davier, M.; Davies, G. S.; Daw, E. J.; Day, R.; De, S.; DeBra, D.; Debreczeni, G.; Degallaix, J.; De Laurentis, M.; Deléglise, S.; Del Pozzo, W.; Denker, T.; Dent, T.; Dergachev, V.; De Rosa, R.; DeRosa, R. T.; DeSalvo, R.; Devine, R. C.; Dhurandhar, S.; Díaz, M. C.; Di Fiore, L.; Di Giovanni, M.; Di Girolamo, T.; Di Lieto, A.; Di Pace, S.; Di Palma, I.; Di Virgilio, A.; Dolique, V.; Donovan, F.; Dooley, K. L.; Doravari, S.; Douglas, R.; Downes, T. P.; Drago, M.; Drever, R. W. P.; Driggers, J. C.; Ducrot, M.; Dwyer, S. E.; Edo, T. B.; Edwards, M. C.; Effler, A.; Eggenstein, H.-B.; Ehrens, P.; Eichholz, J.; Eikenberry, S. S.; Engels, W.; Essick, R. C.; Etzel, T.; Evans, M.; Evans, T. M.; Everett, R.; Factourovich, M.; Fafone, V.; Fair, H.; Fan, X.; Fang, Q.; Farinon, S.; Farr, B.; Farr, W. M.; Favata, M.; Fays, M.; Fehrmann, H.; Fejer, M. M.; Fenyvesi, E.; Ferrante, I.; Ferreira, E. C.; Ferrini, F.; Fidecaro, F.; Fiori, I.; Fiorucci, D.; Fisher, R. P.; Flaminio, R.; Fletcher, M.; Fournier, J.-D.; Frasca, S.; Frasconi, F.; Frei, Z.; Freise, A.; Frey, R.; Frey, V.; Fritschel, P.; Frolov, V. V.; Fulda, P.; Fyffe, M.; Gabbard, H. A. G.; Gair, J. R.; Gammaitoni, L.; Gaonkar, S. G.; Garufi, F.; Gaur, G.; Gehrels, N.; Gemme, G.; Geng, P.; Genin, E.; Gennai, A.; George, J.; Gergely, L.; Germain, V.; Ghosh, Abhirup; Ghosh, Archisman; Ghosh, S.; Giaime, J. A.; Giardina, K. D.; Giazotto, A.; Gill, K.; Glaefke, A.; Goetz, E.; Goetz, R.; Gondan, L.; González, G.; Gonzalez Castro, J. M.; Gopakumar, A.; Gordon, N. A.; Gorodetsky, M. L.; Gossan, S. E.; Gosselin, M.; Gouaty, R.; Grado, A.; Graef, C.; Graff, P. B.; Granata, M.; Grant, A.; Gras, S.; Gray, C.; Greco, G.; Green, A. C.; Groot, P.; Grote, H.; Grunewald, S.; Guidi, G. M.; Guo, X.; Gupta, A.; Gupta, M. K.; Gushwa, K. E.; Gustafson, E. K.; Gustafson, R.; Hacker, J. J.; Hall, B. R.; Hall, E. D.; Hammond, G.; Haney, M.; Hanke, M. M.; Hanks, J.
2016-09-01
We compare GW150914 directly to simulations of coalescing binary black holes in full general relativity, including several performed specifically to reproduce this event. Our calculations go beyond existing semianalytic models, because for all simulations—including sources with two independent, precessing spins—we perform comparisons which account for all the spin-weighted quadrupolar modes, and separately which account for all the quadrupolar and octopolar modes. Consistent with the posterior distributions reported by Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016)] (at the 90% credible level), we find the data are compatible with a wide range of nonprecessing and precessing simulations. Follow-up simulations performed using previously estimated binary parameters most resemble the data, even when all quadrupolar and octopolar modes are included. Comparisons including only the quadrupolar modes constrain the total redshifted mass Mz∈[64 M⊙-82 M⊙] , mass ratio 1 /q =m2/m1∈[0.6 ,1 ], and effective aligned spin χeff∈[-0.3 ,0.2 ], where χeff=(S1/m1+S2/m2).L ^/M . Including both quadrupolar and octopolar modes, we find the mass ratio is even more tightly constrained. Even accounting for precession, simulations with extreme mass ratios and effective spins are highly inconsistent with the data, at any mass. Several nonprecessing and precessing simulations with similar mass ratio and χeff are consistent with the data. Though correlated, the components' spins (both in magnitude and directions) are not significantly constrained by the data: the data is consistent with simulations with component spin magnitudes a1 ,2 up to at least 0.8, with random orientations. Further detailed follow-up calculations are needed to determine if the data contain a weak imprint from transverse (precessing) spins. For nonprecessing binaries, interpolating between simulations, we reconstruct a posterior distribution consistent with previous results. The final black hole
Tomar, P.; Pandey, R. K.; Nath, Y.
2013-11-01
The objective of this article is to investigate numerically frictional stress in the contact zone at the die/billet interface in the direct extrusion of aluminum alloys considering starved lubricated conditions. In the modeling, both the inlet and work zones have been investigated by coupled solution of the governing equations. The influences of the billet material's strain hardening and its heating due to the plastic deformation are accounted for in the numerical computation. The frictional shear stress at the die/billet interface is computed using three different lubricating oils. Numerical results have been presented herein for the various operating parameters viz. starvation factor ( ψ = 0.2-0.6), lubricants' viscosities ( η 0 = 0.05 Pa s-0.2 Pa s), semi die angle ( β = 10°-20°), and material parameter ( G = 0.56-2.25). It has been observed that the frictional stress increases with an increase in the severity of the lubricant's starvation for the given values of semi-die angle, extrusion speed, and material parameter.
Zhang, Hong-Na; Li, Feng-Chen; Li, Xiao-Bin; Li, Dong-Yang; Cai, Wei-Hua; Yu, Bo
2016-09-01
Direct numerical simulations (DNSs) of purely elastic turbulence in rectilinear shear flows in a three-dimensional (3D) parallel plate channel were carried out, by which numerical databases were established. Based on the numerical databases, the present paper analyzed the structural and statistical characteristics of the elastic turbulence including flow patterns, the wall effect on the turbulent kinetic energy spectrum, and the local relationship between the flow motion and the microstructures’ behavior. Moreover, to address the underlying physical mechanism of elastic turbulence, its generation was presented in terms of the global energy budget. The results showed that the flow structures in elastic turbulence were 3D with spatial scales on the order of the geometrical characteristic length, and vortex tubes were more likely to be embedded in the regions where the polymers were strongly stretched. In addition, the patterns of microstructures’ elongation behave like a filament. From the results of the turbulent kinetic energy budget, it was found that the continuous energy releasing from the polymers into the main flow was the main source of the generation and maintenance of the elastic turbulent status. Project supported by the National Natural Science Foundation of China (Grant Nos. 51276046 and 51506037), the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant No. 51421063), the China Postdoctoral Science Foundation (Grant No. 2016M591526), the Heilongjiang Postdoctoral Fund, China (Grant No. LBH-Z15063), and the China Postdoctoral International Exchange Program.
Directory of Open Access Journals (Sweden)
Sergiu Ciprian Catinas
2015-07-01
Full Text Available A detailed theoretical and practical investigation of the reinforced concrete elements is due to recent techniques and method that are implemented in the construction market. More over a theoretical study is a demand for a better and faster approach nowadays due to rapid development of the calculus technique. The paper above will present a study for implementing in a static calculus the direct stiffness matrix method in order capable to address phenomena related to different stages of loading, rapid change of cross section area and physical properties. The method is a demand due to the fact that in our days the FEM (Finite Element Method is the only alternative to such a calculus and FEM are considered as expensive methods from the time and calculus resources point of view. The main goal in such a method is to create the moment-curvature diagram in the cross section that is analyzed. The paper above will express some of the most important techniques and new ideas as well in order to create the moment curvature graphic in the cross sections considered.
Institute of Scientific and Technical Information of China (English)
Liu Xing-Hua; He Wei; Yang Fan; Wang Hong-Yu; Liao Rui-Jin; Xiao Han-Guang
2012-01-01
Air corona discharge is one of the critical problems associated with high-voltage equipment.Investigating the corona mechanism plays a key role in enhancing the electrical insulation performance.An improved self-consistent multi-component two-dimensional plasma hybrid model is presented for the simulation of a direct current atmospheric pressure corona discharge in air.The model is based on plasma hydrodynamic and chemical models,and includes 12 species and 26 reactions.In addition,the photoionization effect is introduced into the model.The simulation on a bar-plate electrode configuration with an inter-electrode gap of 5.0 mm is carried out.The discharge voltage-current characteristics and the current density distribution predicted by the hybrid model agree with the experimental measurements.In addition,the dynamics of volume charged species generation,discharge current waveform,current density distribution at an electrode,charge density,electron temperature,and electric field variations are investigated in detail based on the model.The results indicate that the model can contribute valuable insights into the physics of an air plasma discharge.
Numerical studies of spray breakup in a gasoline direct injection (GDI engine
Directory of Open Access Journals (Sweden)
Jafarmadar Samad
2011-01-01
Full Text Available The objective of this study is to investigate Spray Breakup process of sprays injected from single and two-hole nozzles for gasoline direct Injection (GDI engines by using three dimensional CFD code. Spray characteristics were examined for spray tip penetration and other characteristics including: the vapor phase concentration distribution and droplet spatial distribution, which were acquired using the computational fluid dynamics (CFD simulation. Results showed that as the hole-axis-angle (γ of the two-hole nozzle decreased, the droplet coalescence increased and vapor mass decreased. The spray with cone angle (θ0 5 deg for single hole nozzle has the longest spray tip penetration and the spray with the γ of 30 deg and spray cone angle θ0=30 deg for two hole nozzles had the shortest one. Also, when the spray cone angle (θ0 and hole-axis-angle (γ increased from 5 to 30 deg, the Sauter mean diameter (SMD decreased for both single-hole and two-hole nozzles used in this study. For a single-hole nozzle, when spray cone angle increased from 5 to 30 deg, the vaporization rate very much because of low level of coalescence. The result of model for tip penetration is good agreement with the corresponding experimental data in the literatures.
Abbott, B P; Abbott, T D; Abernathy, M R; Acernese, F; Ackley, K; Adams, C; Adams, T; Addesso, P; Adhikari, R X; Adya, V B; Affeldt, C; Agathos, M; Agatsuma, K; Aggarwal, N; Aguiar, O D; Aiello, L; Ain, A; Ajith, P; Allen, B; Allocca, A; Altin, P A; Anderson, S B; Anderson, W G; Arai, K; Araya, M C; Arceneaux, C C; Areeda, J S; Arnaud, N; Arun, K G; Ascenzi, S; Ashton, G; Ast, M; Aston, S M; Astone, P; Aufmuth, P; Aulbert, C; Babak, S; Bacon, P; Bader, M K M; Baker, P T; Baldaccini, F; Ballardin, G; Ballmer, S W; Barayoga, J C; Barclay, S E; Barish, B C; Barker, D; Barone, F; Barr, B; Barsotti, L; Barsuglia, M; Barta, D; Bartlett, J; Bartos, I; Bassiri, R; Basti, A; Batch, J C; Baune, C; Bavigadda, V; Bazzan, M; Bejger, M; Bell, A S; Berger, B K; Bergmann, G; Berry, C P L; Bersanetti, D; Bertolini, A; Betzwieser, J; Bhagwat, S; Bhandare, R; Bilenko, I A; Billingsley, G; Birch, J; Birney, R; Biscans, S; Bisht, A; Bitossi, M; Biwer, C; Bizouard, M A; Blackburn, J K; Blair, C D; Blair, D G; Blair, R M; Bloemen, S; Bock, O; Boer, M; Bogaert, G; Bogan, C; Bohe, A; Bond, C; Bondu, F; Bonnand, R; Boom, B A; Bork, R; Boschi, V; Bose, S; Bouffanais, Y; Bozzi, A; Bradaschia, C; Brady, P R; Braginsky, V B; Branchesi, M; Brau, J E; Briant, T; Brillet, A; Brinkmann, M; Brisson, V; Brockill, P; Broida, J E; Brooks, A F; Brown, D A; Brown, D D; Brown, N M; Brunett, S; Buchanan, C C; Buikema, A; Bulik, T; Bulten, H J; Buonanno, A; Buskulic, D; Buy, C; Byer, R L; Cabero, M; Cadonati, L; Cagnoli, G; Cahillane, C; Bustillo, J Calder'on; Callister, T; Calloni, E; Camp, J B; Cannon, K C; Cao, J; Capano, C D; Capocasa, E; Carbognani, F; Caride, S; Diaz, J Casanueva; Casentini, C; Caudill, S; Cavagli`a, M; Cavalier, F; Cavalieri, R; Cella, G; Cepeda, C B; Baiardi, L Cerboni; Cerretani, G; Cesarini, E; Chan, M; Chao, S; Charlton, P; Chassande-Mottin, E; Cheeseboro, B D; Chen, H Y; Chen, Y; Cheng, C; Chincarini, A; Chiummo, A; Cho, H S; Cho, M; Chow, J H; Christensen, N; Chu, Q; Chua, S; Chung, S; Ciani, G; Clara, F; Clark, J A; Cleva, F; Coccia, E; Cohadon, P -F; Colla, A; Collette, C G; Cominsky, L; Constancio, M; Conte, A; Conti, L; Cook, D; Corbitt, T R; Cornish, N; Corsi, A; Cortese, S; Costa, C A; Coughlin, M W; Coughlin, S B; Coulon, J -P; Countryman, S T; Couvares, P; Cowan, E E; Coward, D M; Cowart, M J; Coyne, D C; Coyne, R; Craig, K; Creighton, J D E; Cripe, J; Crowder, S G; Cumming, A; Cunningham, L; Cuoco, E; Canton, T Dal; Danilishin, S L; D'Antonio, S; Danzmann, K; Darman, N S; Dasgupta, A; Costa, C F Da Silva; Dattilo, V; Dave, I; Davier, M; Davies, G S; Daw, E J; Day, R; De, S; DeBra, D; Debreczeni, G; Degallaix, J; De Laurentis, M; Del'eglise, S; Del Pozzo, W; Denker, T; Dent, T; Dergachev, V; De Rosa, R; DeRosa, R T; DeSalvo, R; Devine, R C; Dhurandhar, S; D'iaz, M C; Di Fiore, L; Di Giovanni, M; Di Girolamo, T; Di Lieto, A; Di Pace, S; Di Palma, I; Di Virgilio, A; Dolique, V; Donovan, F; Dooley, K L; Doravari, S; Douglas, R; Downes, T P; Drago, M; Drever, R W P; Driggers, J C; Ducrot, M; Dwyer, S E; Edo, T B; Edwards, M C; Effler, A; Eggenstein, H -B; Ehrens, P; Eichholz, J; Eikenberry, S S; Engels, W; Essick, R C; Etzel, T; Evans, M; Evans, T M; Everett, R; Factourovich, M; Fafone, V; Fair, H; Fairhurst, S; Fan, X; Fang, Q; Farinon, S; Farr, B; Farr, W M; Favata, M; Fays, M; Fehrmann, H; Fejer, M M; Fenyvesi, E; Ferrante, I; Ferreira, E C; Ferrini, F; Fidecaro, F; Fiori, I; Fiorucci, D; Fisher, R P; Flaminio, R; Fletcher, M; Fournier, J -D; Frasca, S; Frasconi, F; Frei, Z; Freise, A; Frey, R; Frey, V; Fritschel, P; Frolov, V V; Fulda, P; Fyffe, M; Gabbard, H A G; Gair, J R; Gammaitoni, L; Gaonkar, S G; Garufi, F; Gaur, G; Gehrels, N; Gemme, G; Geng, P; Genin, E; Gennai, A; George, J; Gergely, L; Germain, V; Ghosh, Abhirup; Ghosh, Archisman; Ghosh, S; Giaime, J A; Giardina, K D; Giazotto, A; Gill, K; Glaefke, A; Goetz, E; Goetz, R; Gondan, L; Gonz'alez, G; Castro, J M Gonzalez; Gopakumar, A; Gordon, N A; Gorodetsky, M L; Gossan, S E; Gosselin, M; Gouaty, R; Grado, A; Graef, C; Graff, P B; Granata, M; Grant, A; Gras, S; Gray, C; Greco, G; Green, A C; Groot, P; Grote, H; Grunewald, S; Guidi, G M; Guo, X; Gupta, A; Gupta, M K; Gushwa, K E; Gustafson, E K; Gustafson, R; Hacker, J J; Hall, B R; Hall, E D; Hammond, G; Haney, M; Hanke, M M; Hanks, J; Hanna, C; Hanson, J; Hardwick, T; Harms, J; Harry, G M; Harry, I W; Hart, M J; Hartman, M T; Haster, C -J; Haughian, K; Heidmann, A; Heintze, M C; Heitmann, H; Hello, P; Hemming, G; Hendry, M; Heng, I S; Hennig, J; Henry, J; Heptonstall, A W; Heurs, M; Hild, S; Hoak, D; Hofman, D; Holt, K; Holz, D E; Hopkins, P; Hough, J; Houston, E A; Howell, E J; Hu, Y M; Huang, S; Huerta, E A; Huet, D; Hughey, B; Huttner, S H; Huynh-Dinh, T; Indik, N; Ingram, D R; Inta, R; Isa, H N; Isac, J -M; Isi, M; Isogai, T; Iyer, B R; Izumi, K; Jacqmin, T; Jang, H; Jani, K; Jaranowski, P; Jawahar, S; Jian, L; Jim'enez-Forteza, F; Johnson, W W; Jones, D I; Jones, R; Jonker, R J G; Ju, L; K, Haris; Kalaghatgi, C V; Kalogera, V; Kandhasamy, S; Kang, G; Kanner, J B; Kapadia, S J; Karki, S; Karvinen, K S; Kasprzack, M; Katsavounidis, E; Katzman, W; Kaufer, S; Kaur, T; Kawabe, K; K'ef'elian, F; Kehl, M S; Keitel, D; Kelley, D B; Kells, W; Kennedy, R; Key, J S; Khalili, F Y; Khan, I; Khan, Z; Khazanov, E A; Kijbunchoo, N; Kim, Chi-Woong; Kim, Chunglee; Kim, J; Kim, K; Kim, N; Kim, W; Kim, Y -M; Kimbrell, S J; King, E J; King, P J; Kissel, J S; Klein, B; Kleybolte, L; Klimenko, S; Koehlenbeck, S M; Koley, S; Kondrashov, V; Kontos, A; Korobko, M; Korth, W Z; Kowalska, I; Kozak, D B; Kringel, V; Krishnan, B; Kr'olak, A; Krueger, C; Kuehn, G; Kumar, P; Kumar, R; Kuo, L; Kutynia, A; Lackey, B D; Landry, M; Lange, J; Lantz, B; Lasky, P D; Laxen, M; Lazzarini, A; Lazzaro, C; Leaci, P; Leavey, S; Lebigot, E O; Lee, C H; Lee, H K; Lee, H M; Lee, K; Lenon, A; Leonardi, M; Leong, J R; Leroy, N; Letendre, N; Levin, Y; Lewis, J B; Li, T G F; Libson, A; Littenberg, T B; Lockerbie, N A; Lombardi, A L; Lord, J E; Lorenzini, M; Loriette, V; Lormand, M; Losurdo, G; Lough, J D; L"uck, H; Lundgren, A P; Lynch, R; Ma, Y; Machenschalk, B; MacInnis, M; Macleod, D M; Magaña-Sandoval, F; Zertuche, L Magaña; Magee, R M; Majorana, E; Maksimovic, I; Malvezzi, V; Man, N; Mandic, V; Mangano, V; Mansell, G L; Manske, M; Mantovani, M; Marchesoni, F; Marion, F; M'arka, S; M'arka, Z; Markosyan, A S; Maros, E; Martelli, F; Martellini, L; Martin, I W; Martynov, D V; Marx, J N; Mason, K; Masserot, A; Massinger, T J; Masso-Reid, M; Mastrogiovanni, S; Matichard, F; Matone, L; Mavalvala, N; Mazumder, N; McCarthy, R; McClelland, D E; McCormick, S; McGuire, S C; McIntyre, G; McIver, J; McManus, D J; McRae, T; McWilliams, S T; Meacher, D; Meadors, G D; Meidam, J; Melatos, A; Mendell, G; Mercer, R A; Merilh, E L; Merzougui, M; Meshkov, S; Messenger, C; Messick, C; Metzdorff, R; Meyers, P M; Mezzani, F; Miao, H; Michel, C; Middleton, H; Mikhailov, E E; Milano, L; Miller, A L; Miller, A; Miller, B B; Miller, J; Millhouse, M; Minenkov, Y; Ming, J; Mirshekari, S; Mishra, C; Mitra, S; Mitrofanov, V P; Mitselmakher, G; Mittleman, R; Moggi, A; Mohan, M; Mohapatra, S R P; Montani, M; Moore, B C; Moore, C J; Moraru, D; Moreno, G; Morriss, S R; Mossavi, K; Mours, B; Mow-Lowry, C M; Mueller, G; Muir, A W; Mukherjee, Arunava; Mukherjee, D; Mukherjee, S; Mukund, N; Mullavey, A; Munch, J; Murphy, D J; Murray, P G; Mytidis, A; Nardecchia, I; Naticchioni, L; Nayak, R K; Nedkova, K; Nelemans, G; Nelson, T J N; Neri, M; Neunzert, A; Newton, G; Nguyen, T T; Nielsen, A B; Nissanke, S; Nitz, A; Nocera, F; Nolting, D; Normandin, M E N; Nuttall, L K; Oberling, J; Ochsner, E; O'Dell, J; Oelker, E; Ogin, G H; Oh, J J; Oh, S H; Ohme, F; Oliver, M; Oppermann, P; Oram, Richard J; O'Reilly, B; O'Shaughnessy, R; Ottaway, D J; Overmier, H; Owen, B J; Pai, A; Pai, S A; Palamos, J R; Palashov, O; Palomba, C; Pal-Singh, A; Pan, H; Pankow, C; Pant, B C; Paoletti, F; Paoli, A; Papa, M A; Paris, H R; Parker, W; Pascucci, D; Pasqualetti, A; Passaquieti, R; Passuello, D; Patricelli, B; Patrick, Z; Pearlstone, B L; Pedraza, M; Pedurand, R; Pekowsky, L; Pele, A; Penn, S; Perreca, A; Perri, L M; Phelps, M; Piccinni, O J; Pichot, M; Piergiovanni, F; Pierro, V; Pillant, G; Pinard, L; Pinto, I M; Pitkin, M; Poe, M; Poggiani, R; Popolizio, P; Post, A; Powell, J; Prasad, J; Predoi, V; Prestegard, T; Price, L R; Prijatelj, M; Principe, M; Privitera, S; Prix, R; Prodi, G A; Prokhorov, L; Puncken, O; Punturo, M; Puppo, P; P"urrer, M; Qi, H; Qin, J; Qiu, S; Quetschke, V; Quintero, E A; Quitzow-James, R; Raab, F J; Rabeling, D S; Radkins, H; Raffai, P; Raja, S; Rajan, C; Rakhmanov, M; Rapagnani, P; Raymond, V; Razzano, M; Re, V; Read, J; Reed, C M; Regimbau, T; Rei, L; Reid, S; Reitze, D H; Rew, H; Reyes, S D; Ricci, F; Riles, K; Rizzo, M; Robertson, N A; Robie, R; Robinet, F; Rocchi, A; Rolland, L; Rollins, J G; Roma, V J; Romano, J D; Romano, R; Romanov, G; Romie, J H; Rosi'nska, D; Rowan, S; R"udiger, A; Ruggi, P; Ryan, K; Sachdev, S; Sadecki, T; Sadeghian, L; Sakellariadou, M; Salconi, L; Saleem, M; Salemi, F; Samajdar, A; Sammut, L; Sanchez, E J; Sandberg, V; Sandeen, B; Sanders, J R; Sassolas, B; Sathyaprakash, B S; Saulson, P R; Sauter, O E S; Savage, R L; Sawadsky, A; Schale, P; Schilling, R; Schmidt, J; Schmidt, P; Schnabel, R; Schofield, R M S; Sch"onbeck, A; Schreiber, E; Schuette, D; Schutz, B F; Scott, J; Scott, S M; Sellers, D; Sengupta, A S; Sentenac, D; Sequino, V; Sergeev, A; Setyawati, Y; Shaddock, D A; Shaffer, T; Shahriar, M S; Shaltev, M; Shapiro, B; Shawhan, P; Sheperd, A; Shoemaker, D H; Siellez, K; Siemens, X; Sieniawska, M; Sigg, D; Silva, A D; Singer, A; Singer, L P; Singh, A; Singh, R; Singhal, A; Sintes, A M; Slagmolen, B J J; Smith, J R; Smith, N D; Smith, R J E; Son, E J; Sorazu, B; Sorrentino, F; Souradeep, T; Srivastava, A K; Staley, A; Steinke, M; Steinlechner, J; Steinlechner, S; Steinmeyer, D; Stephens, B C; Stone, R; Strain, K A; Straniero, N; Stratta, G; Strauss, N A; Strigin, S; Sturani, R; Stuver, A L; Summerscales, T Z; Sun, L; Sunil, S; Sutton, P J; Swinkels, B L; Szczepa'nczyk, M J; Tacca, M; Talukder, D; Tanner, D B; T'apai, M; Tarabrin, S P; Taracchini, A; Taylor, R; Theeg, T; Thirugnanasambandam, M P; Thomas, E G; Thomas, M; Thomas, P; Thorne, K A; Thrane, E; Tiwari, S; Tiwari, V; Tokmakov, K V; Toland, K; Tomlinson, C; Tonelli, M; Tornasi, Z; Torres, C V; Torrie, C I; T"oyr"a, D; Travasso, F; Traylor, G; Trifir`o, D; Tringali, M C; Trozzo, L; Tse, M; Turconi, M; Tuyenbayev, D; Ugolini, D; Unnikrishnan, C S; Urban, A L; Usman, S A; Vahlbruch, H; Vajente, G; Valdes, G; van Bakel, N; van Beuzekom, M; Brand, J F J van den; Broeck, C Van Den; Vander-Hyde, D C; van der Schaaf, L; van Heijningen, J V; van Veggel, A A; Vardaro, M; Vass, S; Vas'uth, M; Vaulin, R; Vecchio, A; Vedovato, G; Veitch, J; Veitch, P J; Venkateswara, K; Verkindt, D; Vetrano, F; Vicer'e, A; Vinciguerra, S; Vine, D J; Vinet, J -Y; Vitale, S; Vo, T; Vocca, H; Vorvick, C; Voss, D V; Vousden, W D; Vyatchanin, S P; Wade, A R; Wade, L E; Wade, M; Walker, M; Wallace, L; Walsh, S; Wang, G; Wang, H; Wang, M; Wang, X; Wang, Y; Ward, R L; Warner, J; Was, M; Weaver, B; Wei, L -W; Weinert, M; Weinstein, A J; Weiss, R; Wen, L; Wessels, P; Westphal, T; Wette, K; Whelan, J T; Whiting, B F; Williams, R D; Williamson, A R; Willis, J L; Willke, B; Wimmer, M H; Winkler, W; Wipf, C C; Wittel, H; Woan, G; Woehler, J; Worden, J; Wright, J L; Wu, D S; Wu, G; Yablon, J; Yam, W; Yamamoto, H; Yancey, C C; Yu, H; Yvert, M; zny, A Zadro; Zangrando, L; Zanolin, M; Zendri, J -P; Zevin, M; Zhang, L; Zhang, M; Zhang, Y; Zhao, C; Zhou, M; Zhou, Z; Zhu, X J; Zucker, M E; Zuraw, S E; Zweizig, J; Boyle, M; Campanelli, M; Chu, T; Clark, M; Fauchon-Jones, E; Fong, H; Hannam, M; Healy, J; Hemberger, D; Hinder, I; Husa, S; Kalaghati, C; Khan, S; Kidder, L E; Kinsey, M; Laguna, P; London, L T; Lousto, C O; Lovelace, G; Ossokine, S; Pannarale, F; Pfeiffer, H P; Scheel, M; Shoemaker, D M; Szilagyi, B; Teukolsky, S; Vinuales, A Vano; Zlochower, Y
2016-01-01
We compare GW150914 directly to simulations of coalescing binary black holes in full general relativity, accounting for all the spin-weighted quadrupolar modes, and separately accounting for all the quadrupolar and octopolar modes. Consistent with the posterior distributions reported in LVC_PE[1] (at 90% confidence), we find the data are compatible with a wide range of nonprecessing and precessing simulations. Followup simulations performed using previously-estimated binary parameters most resemble the data. Comparisons including only the quadrupolar modes constrain the total redshifted mass Mz \\in [64 - 82M_\\odot], mass ratio q = m2/m1 \\in [0.6,1], and effective aligned spin \\chi_eff \\in [-0.3, 0.2], where \\chi_{eff} = (S1/m1 + S2/m2) \\cdot\\hat{L} /M. Including both quadrupolar and octopolar modes, we find the mass ratio is even more tightly constrained. Simulations with extreme mass ratios and effective spins are highly inconsistent with the data, at any mass. Several nonprecessing and precessing simulation...
Institute of Scientific and Technical Information of China (English)
CHEN Chang-ping; LI Yu-cheng; ZHAO Yun-peng; DONG Guo-hai; GUI Fu-kun
2009-01-01
In this paper,the numerical model of the net cage with the grid mooring system in waves is set up by the lumped mass method and rigid kinematics theory,and then the motion equations of floating system,net system,mooring system,and floaters are solved by the Runge-Kutta fifth-order method.For the verification of the numerical model,a series of physical model tests have been carried out.According to the comparisons between the simulated and experimental results,it can be found that the simulated and experimental results agree well in each condition.Then,the effects of submerged depth of grid and direction of incident wave propagation on hydrodynamic behaviors of the net cage are analyzed.According to the simulated results,it can be found that with the increase of submerged depth of grid,the forces acting on mooring lines and bridle lines increase,while the forces on grid lines decrease;the horizontal motion amplitudes of floating collar decrease obviously,while the vertical motion amplitudes of floating collar change little.When the direction of incident wave propagation changes,forces on mooting lines and motion of net cage also change accordingly.When the propagation direction of incident wave changes from 0° to 45°,forces on the main ropes and bridle ropes increase,while the forces on the grid ropes decrease.With the increasing propagation direction of incident wave,the horizontal amplitude of the forces collar decreases,while the vertical amplitude of the floating collar has little variation.
Numerical assessment of the mechanical stability in vertical, directional and horizontal wellbores
Institute of Scientific and Technical Information of China (English)
Kamran Goshtasbi; Ayub Elyasi; Ali Naeimipour
2013-01-01
In this research the stability of wellbore is evaluated in seven different stress regimes and diverse orien-tations using FLAC3D software. The normalized yielded zone area (NYZA, i.e., the ratio of surrounding yielded cross-sectional area to initial area of wellbore) is determined for different mud pressures as well as diverse orientations of wellbore. By means of MATLAB software the best curve is fitted to the recorded points and then the optimized mud pressure is calculated using these plots. The optimized orientation is selected considering these data. Finally the mud pressure resulted from this method was compared with the mud pressure obtained from the Mogi-Coulomb criterion and then with the fields data. The minimum allowable mud pressure obtained from the NYZA criterion is close to actual data and the value obtained from the Mogi-Coulomb criterion. Hence, the NYZA is considered to be an appropriate criterion for well-bore stability analysis.
Waveform propagation in black hole spacetimes evaluating the quality of numerical solutions
Rezzolla, L; Baumgarte, T W; Cook, G B; Scheel, M A; Shapiro, S L; Teukolsky, S A
1998-01-01
We compute the propagation and scattering of linear gravitational waves off a Schwarzschild black hole using a numerical code which solves a generalization of the Zerilli equation to a three dimensional cartesian coordinate system. Since the solution to this problem is well understood it represents a very good testbed for evaluating our ability to perform three dimensional computations of gravitational waves in spacetimes in which a black hole event horizon is present.
Vinous M. Hameed, Bashar Muslem Essa
2015-01-01
Experimental and numerical investigation has been performed in this work to evaluate the performance for triangular finned tube heat exchanger. Experimental work included designing and manufacturing of shaped triangular fins from copper material of (10mm) length, (10mm) height, (1mm) thickness, (22 mm) distance between every two fins shaped and (15mm) pitch between each two of fins which are install on the straight copper tube of (2m) length having (20mm) inner diameter and (22mm) outer diame...
Algorithm for direct numerical simulation of emulsion flow through a granular material
Zinchenko, Alexander Z.; Davis, Robert H.
2008-08-01
A multipole-accelerated 3D boundary-integral algorithm capable of modelling an emulsion flow through a granular material by direct multiparticle-multidrop simulations in a periodic box is developed and tested. The particles form a random arrangement at high volume fraction rigidly held in space (including the case of an equilibrium packing in mechanical contact). Deformable drops (with non-deformed diameter comparable with the particle size) squeeze between the particles under a specified average pressure gradient. The algorithm includes recent boundary-integral desingularization tools especially important for drop-solid and drop-drop interactions, the Hebeker representation for solid particle contributions, and unstructured surface triangulations with fixed topology. Multipole acceleration, with two levels of mesh node decomposition (entire drop/solid surfaces and "patches"), is a significant improvement over schemes used in previous, purely multidrop simulations; it remains efficient at very high resolutions ( 104- 105 triangular elements per surface) and has no lower limitation on the number of particles or drops. Such resolutions are necessary in the problem to alleviate lubrication difficulties, especially for near-critical squeezing conditions, as well as using ˜104 time steps and an iterative solution at each step, both for contrast and matching viscosities. Examples are shown for squeezing of 25-40 drops through an array of 9-14 solids, with the total volume fraction of 70% for particles and drops. The flow rates for the drop and continuous phases are calculated. Extensive convergence testing with respect to program parameters (triangulation, multipole truncation, etc.) is made.
Direct numerical simulations of homogeneous isotropic turbulence in a dense gas
Giauque, A.; Corre, C.; Menghetti, M.
2017-03-01
A study of turbulence in BZT dense gas flows is performed using DNS. It is shown that for a large but realistic intensity, the turbulence in dense gas flows behaves in a highly compressible manner when the average thermodynamic state lies within the inversion region in which the gas fundamental derivative is negative. A close similarity is observed in the evolution of the kinetic energy when the initial turbulent Mach number and the Taylor Reynolds number are matched regardless of the Equation of State (EoS) considered. A large turbulent Mach number is yet more easily attained in dense gas flows lying in the inversion region because of the low speed of sound associated with it. In this case the turbulence shows a highly compressible evolution with periodic exchanges between the internal and kinetic energies. In order to assess the capabilities of currently available Large Eddy Simulation (LES) subgrid-scale models, a-posteriori tests are performed using the dynamic Smagorinsky model. Coherently with the hypothesis it relies on, the model perfectly captures the evolution of the kinetic energy when the turbulent Mach number is low enough. When using the perfect gas EoS at a higher turbulent Mach number the agreement is reasonable. Yet, when the average thermodynamic state lies within the inversion region and when using the thermal and caloric Martin&Hou EoS, the model is not able to capture the correct evolution of the kinetic energy. The results presented in this study call for a specific research effort directed towards the assessment and possibly the development of advanced subgrid-scale models for LES of turbulent dense gas flows.
Evaluation of bone surrogates for indirect and direct ballistic fractures.
Bir, Cynthia; Andrecovich, Chris; DeMaio, Marlene; Dougherty, Paul J
2016-04-01
The mechanism of injury for fractures to long bones has been studied for both direct ballistic loading as well as indirect. However, the majority of these studies have been conducted on both post-mortem human subjects (PMHS) and animal surrogates which have constraints in terms of storage, preparation and testing. The identification of a validated bone surrogate for use in forensic, medical and engineering testing would provide the ability to investigate ballistic loading without these constraints. Two specific bone surrogates, Sawbones and Synbone, were evaluated in comparison to PMHS for both direct and indirect ballistic loading. For the direct loading, the mean velocity to produce fracture was 121 ± 19 m/s for the PMHS, which was statistically different from the Sawbones (140 ± 7 m/s) and Synbone (146 ± 3 m/s). The average distance to fracture in the indirect loading was .70 cm for the PMHS. The Synbone had a statistically similar average distance to fracture (.61 cm, p=0.54) however the Sawbones average distance to fracture was statistically different (.41 cm, pballistic testing was not identified and future work is warranted.
Giannaros, Theodore M.; Melas, Dimitrios; Matzarakis, Andreas
2015-02-01
The evaluation of thermal bioclimate can be conducted employing either observational or modeling techniques. The advantage of the numerical modeling approach lies in that it can be applied in areas where there is lack of observational data, providing a detailed insight on the prevailing thermal bioclimatic conditions. However, this approach should be exploited carefully since model simulations can be frequently biased. The aim of this paper is to examine the suitability of a mesoscale atmospheric model in terms of evaluating thermal bioclimate. For this, the numerical weather prediction Weather Research and Forecasting (WRF) model and the radiation RayMan model are employed for simulating thermal bioclimatic conditions in Greece during a 1-year time period. The physiologically equivalent temperature (PET) is selected as an index for evaluating thermal bioclimate, while synoptic weather station data are exploited for verifying model performance. The results of the present study shed light on the strengths and weaknesses of the numerical modeling approach. Overall, it is shown that model simulations can provide a useful alternative tool for studying thermal bioclimate. Specifically for Greece, the WRF/RayMan modeling system was found to perform adequately well in reproducing the spatial and temporal variations of PET.
Direct numerical simulation of particulate flows with an overset grid method
Koblitz, A. R.; Lovett, S.; Nikiforakis, N.; Henshaw, W. D.
2017-08-01
We evaluate an efficient overset grid method for two-dimensional and three-dimensional particulate flows for small numbers of particles at finite Reynolds number. The rigid particles are discretised using moving overset grids overlaid on a Cartesian background grid. This allows for strongly-enforced boundary conditions and local grid refinement at particle surfaces, thereby accurately capturing the viscous boundary layer at modest computational cost. The incompressible Navier-Stokes equations are solved with a fractional-step scheme which is second-order-accurate in space and time, while the fluid-solid coupling is achieved with a partitioned approach including multiple sub-iterations to increase stability for light, rigid bodies. Through a series of benchmark studies we demonstrate the accuracy and efficiency of this approach compared to other boundary conformal and static grid methods in the literature. In particular, we find that fully resolving boundary layers at particle surfaces is crucial to obtain accurate solutions to many common test cases. With our approach we are able to compute accurate solutions using as little as one third the number of grid points as uniform grid computations in the literature. A detailed convergence study shows a 13-fold decrease in CPU time over a uniform grid test case whilst maintaining comparable solution accuracy.
Sekimoto, Atsushi; Jiménez, Javier
2016-01-01
Statistically stationary and homogeneous shear turbulence (SS-HST) is investigated by means of a new direct numerical simulation, spectral in the two horizontal directions and compact-finite-differences in the direction of the shear. No remeshing is used to impose the shear-periodic boundary condition. The influence of the geometry of the computational box is explored. Since HST has no characteristic outer length scale and tends to fill the computational domain, long-term simulations of HST are `minimal' in the sense of containing on average only a few large-scale structures. It is found that the main limit is the spanwise box width, $L_z$, which sets the length and velocity scales of the turbulence, and that the two other box dimensions should be sufficiently large $(L_x\\gtrsim 2L_z$, $L_y \\gtrsim L_z$) to prevent other directions to be constrained as well. It is also found that very long boxes, $L_x \\gtrsim 2 L_y$, couple with the passing period of the shear-periodic boundary condition, and develop strong u...
Srinivasan, M.; Karuppasamy, P.; Ramasamy, P.; Barua, A. K.
2016-07-01
Numerical modelling has emerged as a powerful tool for the development and optimization of directional solidification process for mass production of multicrystalline silicon. A transient global heat transfer model is performed to investigate the effect of bottom grooved furnace upon the directional solidification (DS) process of multi-crystalline silicon (mc-Si). The temperature distribution, von Mises stress, residual stress and dislocation density rate in multi-crystalline silicon ingots grown by modified directional solidification method have been investigated for five growth stages using finite volume method at the critical Prandtl number, Pr = 0.01. This paper discusses bottom groove furnace instead of seed crystal DS method. It achieves an advanced understanding of the thermal and mechanical behaviour in grown multi-crystalline ingot by bottom grooved directional solidification method. The von Mises stress and dislocation density were reduced while using the bottom grooved furnace. This work was carried out in the different grooves of radius 30 mm, 60 mm and 90 mm of the heat exchanger block of the DS furnace. In this paper, the results are presented for 60 mm radius groove only because it has got better results compared to the other grooves. Also, the computational results of bottom grooved DS method show better performance compared the conventional DS method for stress and dislocation density in grown ingot. [Figure not available: see fulltext.
Sondergaard, R.; Cantwell, B.; Mansour, N.
1997-01-01
Direct numerical simulations have been used to examine the effect of the initial disturbance field on the development of three-dimensionality and the transition to turbulence in the incompressible plane wake. The simulations were performed using a new numerical method for solving the time-dependent, three-dimensional, incompressible Navier-Stokes equations in flows with one infinite and two periodic directions. The method uses standard Fast Fourier Transforms and is applicable to cases where the vorticity field is compact in the infinite direction. Initial disturbances fields examined were combinations of two-dimensional waves and symmetric pairs of 60 deg oblique waves at the fundamental, subharmonic, and sub-subharmonic wavelengths. The results of these simulations indicate that the presence of 60 deg disturbances at the subharmonic streamwise wavelength results in the development of strong coherent three-dimensional structures. The resulting strong three-dimensional rate-of-strain triggers the growth of intense fine scale motions. Wakes initiated with 60 deg disturbances at the fundamental streamwise wavelength develop weak coherent streamwise structures, and do not develop significant fine scale motions, even at high Reynolds numbers. The wakes which develop strong three-dimensional structures exhibit growth rates on par with experimentally observed turbulent plane wakes. Wakes which develop only weak three-dimensional structures exhibit significantly lower late time growth rates. Preliminary studies of wakes initiated with an oblique fundamental and a two-dimensional subharmonic, which develop asymmetric coherent oblique structures at the subharmonic wavelength, indicate that significant fine scale motions only develop if the resulting oblique structures are above an angle of approximately 45 deg.
A Mutual-Evaluation Genetic Algorithm for Numerical and Routing Optimization
Directory of Open Access Journals (Sweden)
Chih-Hao Lin
2013-01-01
Full Text Available Many real-world problems can be formulated as numerical optimization with certain objective functions. However, these objective functions often contain numerous local optima, which could trap an algorithm from moving toward the desired global solution. To improve the search efficiency of traditional genetic algorithms, this paper presents a mutual-evaluation genetic algorithm (MEGA. A novel mutual-evaluation approach is employed so that the merit of selected genes in a chromosome can be determined by comparing the fitness changes before and after interchanging with those in the mating chromosome. According to the determined genome merit, a therapy crossover can generate effective schemata to explore the solution space efficiently. The computational experiments for twelve numerical problems show that the MEGA can find near optimal solutions in all test benchmarks and achieve solutions with higher accuracy than those obtained by eight existing algorithms. This study also uses the MEGA to find optimal flow-allocation strategies for multipath-routing problems. Experiments on quality-of-service routing scenarios show that the MEGA can deal with these constrained routing problems effectively and efficiently. Therefore, the MEGA not only can reduce the effort of function analysis but also can deal with a wide spectrum of real-world problems.
Kuruoǧlu, Zeki C.
2016-11-01
Direct numerical solution of the coordinate-space integral-equation version of the two-particle Lippmann-Schwinger (LS) equation is considered without invoking the traditional partial-wave decomposition. The singular kernel of the three-dimensional LS equation in coordinate space is regularized by a subtraction technique. The resulting nonsingular integral equation is then solved via the Nystrom method employing a direct-product quadrature rule for three variables. To reduce the computational burden of discretizing three variables, advantage is taken of the fact that, for central potentials, the azimuthal angle can be integrated out, leaving a two-variable reduced integral equation. A regularization method for the kernel of the two-variable integral equation is derived from the treatment of the singularity in the three-dimensional equation. A quadrature rule constructed as the direct product of single-variable quadrature rules for radial distance and polar angle is used to discretize the two-variable integral equation. These two- and three-variable methods are tested on the Hartree potential. The results show that the Nystrom method for the coordinate-space LS equation compares favorably in terms of its ease of implementation and effectiveness with the Nystrom method for the momentum-space version of the LS equation.
Qian, Ying-Jing; Yang, Xiao-Dong; Zhai, Guan-Qiao; Zhang, Wei
2017-08-01
Innovated by the nonlinear modes concept in the vibrational dynamics, the vertical periodic orbits around the triangular libration points are revisited for the Circular Restricted Three-body Problem. The ζ -component motion is treated as the dominant motion and the ξ and η -component motions are treated as the slave motions. The slave motions are in nature related to the dominant motion through the approximate nonlinear polynomial expansions with respect to the ζ -position and ζ -velocity during the one of the periodic orbital motions. By employing the relations among the three directions, the three-dimensional system can be transferred into one-dimensional problem. Then the approximate three-dimensional vertical periodic solution can be analytically obtained by solving the dominant motion only on ζ -direction. To demonstrate the effectiveness of the proposed method, an accuracy study was carried out to validate the polynomial expansion (PE) method. As one of the applications, the invariant nonlinear relations in polynomial expansion form are used as constraints to obtain numerical solutions by differential correction. The nonlinear relations among the directions provide an alternative point of view to explore the overall dynamics of periodic orbits around libration points with general rules.
Numerical evaluation of two-center integrals over Slater type orbitals
Kurt, S. A.; Yükçü, N.
2016-03-01
Slater Type Orbitals (STOs) which one of the types of exponential type orbitals (ETOs) are used usually as basis functions in the multicenter molecular integrals to better understand physical and chemical properties of matter. In this work, we develop algorithms for two-center overlap and two-center two-electron hybrid and Coulomb integrals which are calculated with help of translation method for STOs and some auxiliary functions by V. Magnasco's group. We use Mathematica programming language to produce algorithms for these calculations. Numerical results for some quantum numbers are presented in the tables. Consequently, we compare our obtained numerical results with the other known literature results and other details of evaluation method are discussed.
Lee, Chany; Jung, Young-Jin; Lee, Sang Jun; Im, Chang-Hwan
2017-02-01
Since there is no way to measure electric current generated by transcranial direct current stimulation (tDCS) inside the human head through in vivo experiments, numerical analysis based on the finite element method has been widely used to estimate the electric field inside the head. In 2013, we released a MATLAB toolbox named COMETS, which has been used by a number of groups and has helped researchers to gain insight into the electric field distribution during stimulation. The aim of this study was to develop an advanced MATLAB toolbox, named COMETS2, for the numerical analysis of the electric field generated by tDCS. COMETS2 can generate any sizes of rectangular pad electrodes on any positions on the scalp surface. To reduce the large computational burden when repeatedly testing multiple electrode locations and sizes, a new technique to decompose the global stiffness matrix was proposed. As examples of potential applications, we observed the effects of sizes and displacements of electrodes on the results of electric field analysis. The proposed mesh decomposition method significantly enhanced the overall computational efficiency. We implemented an automatic electrode modeler for the first time, and proposed a new technique to enhance the computational efficiency. In this paper, an efficient toolbox for tDCS analysis is introduced (freely available at http://www.cometstool.com). It is expected that COMETS2 will be a useful toolbox for researchers who want to benefit from the numerical analysis of electric fields generated by tDCS. Copyright © 2016. Published by Elsevier B.V.
Numerical evaluation of Auger recombination coefficients in relaxed and strained germanium
Dominici, Stefano; Wen, Hanqing; Bertazzi, Francesco; Goano, Michele; Bellotti, Enrico
2016-05-01
The potential applications of germanium and its alloys in infrared silicon-based photonics have led to a renewed interest in their optical properties. In this letter, we report on the numerical determination of Auger coefficients at T = 300 K for relaxed and biaxially strained germanium. We use a Green's function based model that takes into account all relevant direct and phonon-assisted processes and perform calculations up to a strain level corresponding to the transition from indirect to direct energy gap. We have considered excess carrier concentrations ranging from 1016 cm-3 to 5 × 1019 cm-3. For use in device level simulations, we also provide fitting formulas for the calculated electron and hole Auger coefficients as functions of carrier density.
Kidanemariam, Aman G
2014-01-01
A numerical method based upon the immersed boundary technique for the fluid-solid coupling and on a soft-sphere approach for solid-solid contact is used to perform direct numerical simulation of the flow-induced motion of a thick bed of spherical particles in a horizontal plane channel. The collision model features a normal force component with a spring and a damper, as well as a damping tangential component, limited by a Coulomb friction law. The standard test case of a single particle colliding perpendicularly with a horizontal wall in a viscous fluid is simulated over a broad range of Stokes numbers, yielding values of the effective restitution coefficient in close agreement with experimental data. The case of bedload particle transport by laminar channel flow is simulated for 24 different parameter values covering a broad range of the Shields number. Comparison of the present results with reference data from the experiment of Aussillous et al. (J. Fluid Mech. 2013) yields excellent agreement. It is confir...
Institute of Scientific and Technical Information of China (English)
LEE; ChunHian
2010-01-01
Direct numerical simulation (DNS) of incompressible magnetohydrodynamic (MHD) turbulent channel flow has been performed under the low magnetic Reynolds number assumption.The velocity-electric field and electric-electric field correlations were studied in the present work for different magnetic field orientations.The Kenjeres-Hanjalic (K-H) model was validated with the DNS data in a term by term manner.The numerical results showed that the K-H model makes good predictions for most components of the velocity-electric field correlations.The mechanisms of turbulence suppression were also analyzed for different magnetic field orientations utilizing the DNS data and the K-H model.The results revealed that the dissipative MHD source term is responsible for the turbulence suppression for the case of streamwise and spanwise magnetic orientation,while the Lorentz force which speeds up the near-wall fluid and decreases the production term is responsible for the turbulence suppression for the case of the wall normal magnetic orientation.
Energy Technology Data Exchange (ETDEWEB)
Nourgaliev R.; Knoll D.; Mousseau V.; Berry R.
2007-04-01
The state-of-the-art for Direct Numerical Simulation (DNS) of boiling multiphase flows is reviewed, focussing on potential of available computational techniques, the level of current success for their applications to model several basic flow regimes (film, pool-nucleate and wall-nucleate boiling -- FB, PNB and WNB, respectively). Then, we discuss multiphysics and multiscale nature of practical boiling flows in LWR reactors, requiring high-fidelity treatment of interfacial dynamics, phase-change, hydrodynamics, compressibility, heat transfer, and non-equilibrium thermodynamics and chemistry of liquid/vapor and fluid/solid-wall interfaces. Finally, we outline the framework for the {\\sf Fervent} code, being developed at INL for DNS of reactor-relevant boiling multiphase flows, with the purpose of gaining insight into the physics of multiphase flow regimes, and generating a basis for effective-field modeling in terms of its formulation and closure laws.
Liu, Nan-Suey; Shih, Tsan-Hsing; Wey, C. Thomas
2011-01-01
A series of numerical simulations of Jet-A spray reacting flow in a single-element lean direct injection (LDI) combustor have been conducted by using the National Combustion Code (NCC). The simulations have been carried out using the time filtered Navier-Stokes (TFNS) approach ranging from the steady Reynolds-averaged Navier-Stokes (RANS), unsteady RANS (URANS), to the dynamic flow structure simulation (DFS). The sub-grid model employed for turbulent mixing and combustion includes the well-mixed model, the linear eddy mixing (LEM) model, and the filtered mass density function (FDF/PDF) model. The starting condition of the injected liquid spray is specified via empirical droplet size correlation, and a five-species single-step global reduced mechanism is employed for fuel chemistry. All the calculations use the same grid whose resolution is of the RANS type. Comparisons of results from various models are presented.
Characterization and evaluation of isomalt performance in direct compression.
Ndindayino, F; Henrist, D; Kiekens, F; Vervaet, C; Remon, J P
1999-10-28
Isomalt is a sugar substitute with a wide range of potential pharmaceutical applications as a result of its physicochemical properties. Four grades of this material were evaluated for their physical characteristics. Only Palatinit(R) C and F exhibited potential characteristics for direct compression. As expected, the products required lubrification for tabletting. A level of 1% lubricant gave the best performance for Palatinit(R) C, the most compressible grade as shown by compaction profiles generated using a single-punch machine. However, its flow behaviour had to be improved by including 0.5% Aerosil(R) 200 as shown by tablet weight uniformity data. Further evaluation by Heckel analysis showed that isomalt exhibited plastic behaviour and underwent elastic recovery primary in the die. Its dilution potential was examined using powdered paracetamol. Acceptable tablets were produced up to 30% drug dilution, but the tensile strength values were reduced, disintegration time and friability increased as expected. Drug dissolution profiles showed a decreasing dissolution rate with the increase of compression force and drug concentration, but considerable improvement was noted when a disintegrant was included. The physical characteristics of the tablets were relatively stable after half a year storage at different humidities as a result of the low hygroscopicity of isomalt.
Numerical evaluation of cavitation void ratio significance on hydrofoil dynamic response
Liu, Xin; Wang, Zhengwei; Escaler, Xavier; Zhou, Lingjiu
2015-12-01
The added mass effects on a NACA0009 hydrofoil under cavitation conditions determined in a cavitation tunnel have been numerically simulated using finite element method (FEM). Based on the validated model, the effects of averaged properties of the cavity considered as a two-phase mixture have been evaluated. The results indicate that the void ratio of the cavity plays an increasing role on the frequency reduction ratio and on the mode shape as the mode number increases. Moreover, the sound speed shows a more important role than the average cavity density.
Precise numerical evaluation of the two loop sunrise graph Master Integrals in the equal mass case
Pozzorini, Stefano
2006-01-01
We present a double precision routine in Fortran for the precise and fast numerical evaluation of the two Master Integrals (MIs) of the equal mass two-loop sunrise graph for arbitrary momentum transfer in d=2 and d=4 dimensions. The routine implements the accelerated power series expansions obtained by solving the corresponding differential equations for the MIs at their singular points. With a maximum of 22 terms for the worst case expansion a relative precision of better than a part in 10^{15} is achieved for arbitrary real values of the momentum transfer.
Directory of Open Access Journals (Sweden)
Vinous M. Hameed, Bashar Muslem Essa
2015-01-01
Full Text Available Experimental and numerical investigation has been performed in this work to evaluate the performance for triangular finned tube heat exchanger. Experimental work included designing and manufacturing of shaped triangular fins from copper material of (10mm length, (10mm height, (1mm thickness, (22 mm distance between every two fins shaped and (15mm pitch between each two of fins which are install on the straight copper tube of (2m length having (20mm inner diameter and (22mm outer diameter. The inner tube is inserted inside the Perspex tube of (54mm inner diameter and (60mm outer diameter. Cold Air and hot water are used as working fluids in the shell side and tube side, respectively. Air at various mass flow rates (0.001875 to 0.003133 kg/sec flows through annuli and water at Reynold's numbers ranging from (10376.9 to 23348.03 flows through the inner tube. Performance of (smooth and finned tube heat exchanger was investigated experimentally. Experimental results showed that the enhancement of heat dissipation for triangular finned tube is (3.252 to4.502 times than that of smooth tube respectively. Numerical simulation has been carried out on present heat exchanger to analyze flow field and heat transfer using COMSOL computational fluid dynamic (CFD package model. The comparison between experimental work and numerical results showed good agreement.
NUMERICAL EVALUATION OF TWO-FLUID MIXING IN A SWIRL MICRO-MIXER
Institute of Scientific and Technical Information of China (English)
JIN Si-yu; LIU Ying-zheng; WANG Wei-zhe; CAO Zhao-min; KOYAMA Hide S.
2006-01-01
A collaborative investigation of two-fluid mixing in a swirl micro-mixer was carried out by the Shanghai Jiao Tong University and the Tokyo Denki University. Pure water and a mixture of glycerol and water were separately injected into branch channels and they were subsequently mixed in the central chamber. The two-fluid flow pattern was numerically modeled, in which the dependence of the mixture viscosity and density on the mass fraction of glycerol in the mixing fluid was carefully taken into consideration. The mixing performance of the two fluids was evaluated by varying the Reynolds numbers and the mass fractions of glycerol in water. The mixing process was extensively analyzed using streamline maps and contour plotting distributions of pressure and glycerol concentration. The numerical results show that the acceptable uniformity of mixing at Re = 0.1 is primarily attributed to the time-consuming molecular diffusion, whereas the cost-effective mixing at Re ＞ 500 was obtained because of the generation of the swirling flow. The increasing mass fraction of glycerol in water was found to attenuate the mixing performance. The preliminary microscopic visualization of the two-fluid mixing at Re=1300 demonstrated the consistence with the numerical results.
A posttreatment evaluation of direct bonding in orthodontics.
Zachrisson, B J
1977-02-01
A long-term evaluation was made of results achieved in direct bonding of metal attachments with a chemically polymerized composite material. A total of 705 attachments were bonded to different teeth, including premolars and molars, in forty-six children. Slim bracket bases, small quantities of adhesive paste, and trimming of the excess material were used to improve esthetics and to benefit in respect of gingival condition. The same person bonded all brackets and performed the orthodontic treatment by a friction-free edgewise light-wire technique. Mean treatment time was 17 months. The clinical appearance before, during, and after treatment is shown in Figs. 3 to 5. The failure rates for the whole treatment period were 4 to 10 per cent for central and lateral incisors, canines, and first premolars in both dental arches. The second premolars, which were often in various stages of eruption at the time of bonding, and the molars had higher failure rates (Table I). An evident individual variation was noted, as a few children had a high number of loose brackets. Clinical and scanning electron microscopic studies of tooth surfaces following removal of the brackets demonstrated normal surface appearance when plain-cut tungsten carbide burs rotated at low speed were used to remove remnants of adhesive that could not easily be scraped off. Precoating etched enamel with sealant, in combination with daily fluoride mouth rinses and good oral hygiene, virtually eliminated the caries problem, but regular inspection for interproximal cavities was needed. There were no signs of enamel damage or discoloration for periods of up to 12 months subsequent to bracket removal. Further details of the technical operative procedure, failure analysis, bracket type and design, gingival health, and other aspects of direct bonding were also discussed.
Directory of Open Access Journals (Sweden)
Yu Ji
2016-01-01
Full Text Available The present article analyzes the dissipation characteristics of the direct contact condensation (DCC phenomenon that occurs when steam is injected into a water tank at a subsonic speed using a new modeling approach for the entropy generation over the calculation domain. The developed entropy assessment model is based on the local equilibrium hypothesis of non-equilibrium thermodynamics. The fluid flow and heat transfer processes are investigated numerically. To describe the condensation and evaporation process at the vapor-liquid interface, a phase change model originated from the kinetic theory of gas is implemented with the mixture model for multiphase flow in the computational fluid dynamics (CFD code ANSYS-FLUENT. The CFD predictions agree well with the published works, which indicates the phase change model combined with the mixture model is a promising way to simulate the DCC phenomenon. In addition, three clear stages as initial stage, developing stage and oscillatory stage are discriminated from both the thermal-hydraulic results and the entropy generation information. During different stages, different proportion of the entropy generation rate owing to heat transfer, viscous direct dissipation, turbulent dissipation and inner phase change in total entropy generation rate is estimated, which is favorable to deeper understanding the irreversibility of DCC phenomenon, designing and optimizing the equipment involved in the process.
Wu, Yu-liang; Jiang, Ze-yi; Zhang, Xin-xin; Wang, Peng; She, Xue-feng
2013-07-01
A mathematical model was established to describe the direct reduction of pellets in a rotary hearth furnace (RHF). In the model, heat transfer, mass transfer, and gas-solid chemical reactions were taken into account. The behaviors of iron metallization and dezincification were analyzed by the numerical method, which was validated by experimental data of the direct reduction of pellets in a Si-Mo furnace. The simulation results show that if the production targets of iron metallization and dezincification are up to 80% and 90%, respectively, the furnace temperature for high-temperature sections must be set higher than 1300°C. Moreover, an undersupply of secondary air by 20% will lead to a decline in iron metallization rate of discharged pellets by 10% and a decrease in dezincing rate by 13%. In addition, if the residence time of pellets in the furnace is over 20 min, its further extension will hardly lead to an obvious increase in production indexes under the same furnace temperature curve.
Energy Technology Data Exchange (ETDEWEB)
Pecha, M. Brennan; Garcia-Perez, Manuel; Foust, Thomas D.; Ciesielski, Peter N.
2017-01-03
Direct numerical simulation of convective heat transfer from hot gas to isolated biomass particle models with realistic morphology and explicit microstructure was performed over a range of conditions with laminar flow of hot gas (500 degrees C). Steady-state results demonstrated that convective interfacial heat transfer is dependent on the wood species. The computed heat transfer coefficients were shown to vary between the pine and aspen models by nearly 20%. These differences are attributed to the species-specific variations in the exterior surface morphology of the biomass particles. We also quantify variations in heat transfer experienced by the particle when positioned in different orientations with respect to the direction of fluid flow. These results are compared to previously reported heat transfer coefficient correlations in the range of 0.1 < Pr < 1.5 and 10 < Re < 500. Comparison of these simulation results to correlations commonly used in the literature (Gunn, Ranz-Marshall, and Bird-Stewart-Lightfoot) shows that the Ranz-Marshall (sphere) correlation gave the closest h values to our steady-state simulations for both wood species, though no existing correlation was within 20% of both species at all conditions studied. In general, this work exemplifies the fact that all biomass feedstocks are not created equal, and that their species-specific characteristics must be appreciated in order to facilitate accurate simulations of conversion processes.
Models for Numerical Evaluation of Variable Speed Different Wind Generator Systems
DEFF Research Database (Denmark)
Li, Hui; Chen, Zhe; Polinder, H.
2007-01-01
of different wind generator systems, the other presents the optimization results and evaluation of variable speed wind generator systems. In this report, firstly, it gives an overview of various wind generator topologies, including their advantages and disadvantages, market status and developing trends. Next......, the analytical models include the wind turbine power characteristics; the single/threestage gearbox and the power electronic converter for possible wind turbine concepts are described. Finally, the electromagnetic design models of the investigated generator topologies are presented, including the squirrel cage...... induction generator (SCIG), the doubly-fed induction generator (DFIG), the electrically excited synchronous generator (EESG) and permanent magnet synchronous generator (PMSG). Numerical evaluation with optimized design and comparison of variable speed wind generator systems by using the presented models...
Vesicoureteric reflux: Evaluation by bladder volume graded direct radionuclide cystogram
Directory of Open Access Journals (Sweden)
Agrawal Vikesh
2009-01-01
Full Text Available Aim : Evaluation of vesicoureteric reflux (VUR in children by bladder volume graded direct radionuclide cystogram (BVG DRC. This technique allows detection of VUR at different bladder volume grades. Materials and Methods : In this prospective study, 33 patients (66 renal units with suspected vesicoureteric reflux were subjected to a voiding cystourethrogram (VCUG and BVG DRC. The patients were assessed further with radioisotope renal scans for renal cortical scars. Results : Twenty-two patients and 36 renal units were found to have VUR in either of the reflux studies. A VCUG was able to detect 20 units (55.50% and a BVG DRC was able to detect 35 units (97.2%. A VCUG had a test accuracy of 77.8% and a BVG DRC had a test accuracy of 98.6%. There was a positive correlation between bladder volume grades and scarring on a DMSA scan. Conclusions : Like a conventional DRC, BVG DRC is a sensitive and an accurate test. It gives additional information on the reflux phenomenon with respect to bladder filling. The bladder volume graded technique is better than conventional DRC for grading of VUR.
Numerical test and evaluating method of impact trend of rock-coal system
Institute of Scientific and Technical Information of China (English)
JIANG Jin-quan; CHENG Jia-guo; QU Hua; DONG Jian-jun
2008-01-01
The impact trend of rock-coal system was studied by the method of accumulat-ing and releasing of deformation energy and interaction of rock-coal system. The system model of roof-coal-floor was established. Based on the RFPA software, rock fracture process analysis system, the numerical test of deformation, fracture and energy transmis-sion of nonlinear and nonhomogeneous rock-coal system, and the numerical test and evaluating method of impact trend of rock-coal system were achieved. When the same coal seam was in different roof and floor conditions, the fracture process of rock-coal sys-tem can be classified as gradual, sudden and delayed fracture three kinds, and their im-pact trend can be classified as void, intense and medium correspondingly. The rock-coal system's impact trend is evaluated by the system impact index μ and burst expanding forms. The criteria μ are μ＜1.0, 1.0≤μ＜1.5 and μ≥1.5 when the impact trend is void, in-tense or medium, which are tested and verified by the No.2 and No.4 coal seams in Sun-cun mine.
Directory of Open Access Journals (Sweden)
HIDERALDO L. V. SANTOS
2013-08-01
Full Text Available Usually, electrical machines have a metallic cylinder made up of a compacted stack of thin metal plates (referred as laminated core assembled with an interference fit on the shaft. The laminated structure is required to improve the electrical performance of the machine and, besides adding inertia, also enhances the stiffness of the system. Inadequate characterization of this element may lead to errors when assessing the dynamic behavior of the rotor. The aim of this work was therefore to evaluate three beam models used to represent the laminated core of rotating electrical machines. The following finite element beam models are analyzed: (i an “equivalent diameter model”, (ii an “unbranched model” and (iii a “branched model”. To validate the numerical models, experiments are performed with nine different electrical rotors so that the first non-rotating natural frequencies and corresponding vibration modes in a free-free support condition are obtained experimentally. The models are evaluated by comparing the natural frequencies and corresponding vibration mode shapes obtained experimentally with those obtained numerically. Finally, a critical discussion of the behavior of the beam models studied is presented. The results show that for the majority of the rotors tested, the “branched model” is the most suitable
He, Yuan-Yao; Wu, Han-Qing; Meng, Zi Yang; Lu, Zhong-Yi
2016-05-01
The aim of this series of two papers is to discuss topological invariants for interacting topological insulators (TIs). In the first paper (I), we provide a paradigm of efficient numerical evaluation scheme for topological invariants, in which we demystify the procedures and techniques employed in calculating Z2 invariant and spin Chern number via zero-frequency single-particle Green's function in quantum Monte Carlo (QMC) simulations. Here we introduce an interpolation process to overcome the ubiquitous finite-size effect, so that the calculated spin Chern number shows ideally quantized values. We also show that making use of symmetry properties of the underlying systems can greatly reduce the computational effort. To demonstrate the effectiveness of our numerical evaluation scheme, especially the interpolation process, for calculating topological invariants, we apply it on two independent two-dimensional models of interacting topological insulators. In the subsequent paper (II), we apply the scheme developed here to wider classes of models of interacting topological insulators, for which certain limitation of constructing topological invariant via single-particle Green's functions will be presented.
Experimental and numerical evaluation of drug release from nanofiber mats to brain tissue.
Nakielski, Paweł; Kowalczyk, Tomasz; Zembrzycki, Krzysztof; Kowalewski, Tomasz A
2015-02-01
Drug delivery systems based on nanofibrous mats appear to be a promising healing practice for preventing brain neurodegeneration after surgery. One of the problems encountered during planning and constructing optimal delivery system based on nanofibrous mats is the estimation of parameters crucial for predicting drug release dynamics. This study describes our experimental setup allowing for spatial and temporary evaluation of drug release from nanofibrous polymers to obtain data necessary to validate appropriate numerical models. We applied laser light sheet method to illuminate released fluorescent drug analog and CCD camera for imaging selected cross-section of the investigated volume. Transparent hydrogel was used as a brain tissue phantom. The proposed setup allows for continuous observation of drug analog (fluorescent dye) diffusion for time span of several weeks. Images captured at selected time intervals were processed to determine concentration profiles and drug release kinetics. We used presented method to evaluate drug release from several polymers to validate numerical model used for optimizing nanofiber system for neuroprotective dressing.
1983-09-01
Industry Australian Atomic Energy Commission, Director CSIROj Materials Science Division, Library Trans-Australia Airlines, Library Qantas Airways ...designed to evaluate the reliability functions that result from the application of reliability analysis to the fatigue of aircraft structures, in particular...Messages 60+ A.4. Program Assembly 608 DISTRIBUTION DOCUMENT CONTROL DATA II 1. INTRODUCTION The application of reliability analysis to the fatigue
Ultra-fast evaluation of protein energies directly from sequence.
Directory of Open Access Journals (Sweden)
Gevorg Grigoryan
2006-06-01
Full Text Available The structure, function, stability, and many other properties of a protein in a fixed environment are fully specified by its sequence, but in a manner that is difficult to discern. We present a general approach for rapidly mapping sequences directly to their energies on a pre-specified rigid backbone, an important sub-problem in computational protein design and in some methods for protein structure prediction. The cluster expansion (CE method that we employ can, in principle, be extended to model any computable or measurable protein property directly as a function of sequence. Here we show how CE can be applied to the problem of computational protein design, and use it to derive excellent approximations of physical potentials. The approach provides several attractive advantages. First, following a one-time derivation of a CE expansion, the amount of time necessary to evaluate the energy of a sequence adopting a specified backbone conformation is reduced by a factor of 10(7 compared to standard full-atom methods for the same task. Second, the agreement between two full-atom methods that we tested and their CE sequence-based expressions is very high (root mean square deviation 1.1-4.7 kcal/mol, R2 = 0.7-1.0. Third, the functional form of the CE energy expression is such that individual terms of the expansion have clear physical interpretations. We derived expressions for the energies of three classic protein design targets-a coiled coil, a zinc finger, and a WW domain-as functions of sequence, and examined the most significant terms. Single-residue and residue-pair interactions are sufficient to accurately capture the energetics of the dimeric coiled coil, whereas higher-order contributions are important for the two more globular folds. For the task of designing novel zinc-finger sequences, a CE-derived energy function provides significantly better solutions than a standard design protocol, in comparable computation time. Given these advantages
Remy, Samuel; Benedetti, Angela; Jones, Luke; Razinger, Miha; Haiden, Thomas
2014-05-01
The WMO-sponsored Working Group on Numerical Experimentation (WGNE) set up a project aimed at understanding the importance of aerosols for numerical weather prediction (NWP). Three cases are being investigated by several NWP centres with aerosol capabilities: a severe dust case that affected Southern Europe in April 2012, a biomass burning case in South America in September 2012, and an extreme pollution event in Beijing (China) which took place in January 2013. At ECMWF these cases are being studied using the MACC-II system with radiatively interactive aerosols. Some preliminary results related to the dust and the fire event will be presented here. A preliminary verification of the impact of the aerosol-radiation direct interaction on surface meteorological parameters such as 2m Temperature and surface winds over the region of interest will be presented. Aerosol optical depth (AOD) verification using AERONET data will also be discussed. For the biomass burning case, the impact of using injection heights estimated by a Plume Rise Model (PRM) for the biomass burning emissions will be presented.
Numerical evaluation of turbulence models for dense to dilute gas-solid flows in vertical conveyor
Institute of Scientific and Technical Information of China (English)
Salar Azizi; Dariush Mowla; Goodarz Ahmadi
2012-01-01
A two-fluid model (TFM) of multiphase flows based on the kinetic theory and small frictional limit boundary condition of granular flow was used to study the behavior of dense to dilute gas-solid flows in vertical pneumatic conveyor.An axisymmetric 2-dimensional,vertical pipe with 5.6 m length and 0.01 m internal diameter was chosen as the computation domain,same to that used for experimentation in the literature.The chosen particles are spherical,of diameter 1.91 mm and density 2500 kg/m3.Turbulence interaction between the gas and particle phases was investigated by Simonin's and Ahmadi's models and their numerical results were validated for dilute to dense conveying of particles.Flow regimes transition and pressure drop were predicted.Voidage and velocity profiles of each phase were calculated in radial direction at different lengths of the conveying pipe.It was found that the voidage has a minimum,and gas and solid velocities have maximum values along the center line of the conveying pipe and pressure drop has a minimum value in transition from dense slugging to dilute stable flow regime.Slug length and pressure fluctuation reduction were predicted with increasing gas velocity,too.It is shown that solid phase turbulence plays a significant role in numerical prediction of hydrodynamics of conveyor and the capability of particles turbulence models depends on tuning parameters of slip-wall boundary condition.
DESIGN AND EVALUATION OF LOW COST DIRECTLY COMPRESSIBLE EXCIPIENTS - II
Directory of Open Access Journals (Sweden)
Swamy P. V.
2010-12-01
Full Text Available The aim of the present study was to develop dispersible / mouth dissolving tablets (orodispersible tablets using piroxicam as a model drug for improving patient compliance, employing low cost directly compressible co-processed granular excipients developed in our laboratory, based on various sugars/polyols such as mannitol, maltodextrin and dicalcium phosphate dihydrate along with a native food grade corn starch. The designed tablet formulations were evaluated for hardness, friability, weight variation, in vitro dispersion time, wetting time, water absorption ratio, drug content, in-vitro dissolution rate (in pH 6.8 phosphate buffer, short-term stability and drug-excipient interaction (IR spectroscopy. Among the designed piroxicam tablets, one formulation prepared with the granular excipient containing 25% w/w corn starch and 75% w/w dicalcium phosphate dihydrate using starch paste for granulation, without super disintegrant addition was found to be promising dispersible tablet formulation (in vitro dispersion time of 17.66 s and wetting time 8.4 s. Another tablet formulation prepared with the granular excipient containing mannitol and food grade corn starch (50:50 ratio and granulated with starch paste, along with 2% w/w crospovidone as superdisintegrant emerged as promising orodispersible tablet formulation (in vitro dispersion time 17.66 s and wetting time 14.3 s. Short-term stability studies of promising formulations (over a period of 3 months indicated that there are no significant changes in drug content and in vitro dispersion time (p<0.05. IR-spectroscopic studies indicated that there are no drug–excipient interactions.
Evaluation of microelectrode materials for direct-current electrocorticography.
Li, Chunyan; Narayan, Raj K; Wu, Pei-Ming; Rajan, Neena; Wu, Zhizhen; Mehan, Neal; Golanov, Eugene V; Ahn, Chong H; Hartings, Jed A
2016-02-01
Direct-current electrocorticography (DC-ECoG) allows a more complete characterization of brain states and pathologies than traditional alternating-current recordings (AC-ECoG). However, reliable recording of DC signals is challenging because of electrode polarization-induced potential drift, particularly at low frequencies and for more conducting materials. Further challenges arise as electrode size decreases, since impedance is increased and the potential drift is augmented. While microelectrodes have been investigated for AC-ECoG recordings, little work has addressed microelectrode properties for DC-signal recording. In this paper, we investigated several common microelectrode materials used in biomedical application for DC-ECoG. Five of the most common materials including gold (Au), silver/silver chloride (Ag/AgCl), platinum (Pt), Iridium oxide (IrOx), and platinum-iridium oxide (Pt/IrOx) were investigated for electrode diameters of 300 μm. The critical characteristics such as polarization impedance, AC current-induced polarization, long-term stability and low-frequency noise were studied in vitro (0.9% saline). The two most promising materials, Pt and Pt/lrOx were further investigated in vivo by recording waves of spreading depolarization, one of the most important applications for DC-ECoG in clinical and basic science research. Our experimental results indicate that IrOx-based microelectrodes, particularly with composite layers of nanostructures, are excellent in all of the common evaluation characteristics both in vitro and in vivo and are most suitable for multimodal monitoring applications. Pt electrodes suffer high current-induced polarization, but have acceptable long-term stability suitable for DC-ECoG. Major significance. The results of this study provide quantitative data on the electrical properties of microelectrodes with commonly-used materials and will be valuable for development of neural recordings inclusive of low frequencies.
Evaluation of microelectrode materials for direct-current electrocorticography
Li, Chunyan; Narayan, Raj K.; Wu, Pei-Ming; Rajan, Neena; Wu, Zhizhen; Mehan, Neal; Golanov, Eugene V.; Ahn, Chong H.; Hartings, Jed A.
2016-02-01
Objective. Direct-current electrocorticography (DC-ECoG) allows a more complete characterization of brain states and pathologies than traditional alternating-current recordings (AC-ECoG). However, reliable recording of DC signals is challenging because of electrode polarization-induced potential drift, particularly at low frequencies and for more conducting materials. Further challenges arise as electrode size decreases, since impedance is increased and the potential drift is augmented. While microelectrodes have been investigated for AC-ECoG recordings, little work has addressed microelectrode properties for DC-signal recording. In this paper, we investigated several common microelectrode materials used in biomedical application for DC-ECoG. Approach. Five of the most common materials including gold (Au), silver/silver chloride (Ag/AgCl), platinum (Pt), Iridium oxide (IrOx), and platinum-iridium oxide (Pt/IrOx) were investigated for electrode diameters of 300 μm. The critical characteristics such as polarization impedance, AC current-induced polarization, long-term stability and low-frequency noise were studied in vitro (0.9% saline). The two most promising materials, Pt and Pt/lrOx were further investigated in vivo by recording waves of spreading depolarization, one of the most important applications for DC-ECoG in clinical and basic science research. Main results. Our experimental results indicate that IrOx-based microelectrodes, particularly with composite layers of nanostructures, are excellent in all of the common evaluation characteristics both in vitro and in vivo and are most suitable for multimodal monitoring applications. Pt electrodes suffer high current-induced polarization, but have acceptable long-term stability suitable for DC-ECoG. Major significance. The results of this study provide quantitative data on the electrical properties of microelectrodes with commonly-used materials and will be valuable for development of neural recordings inclusive of
Truong, Cao Dung; Trinh, M. Tuan; Dang, Hoai Bac; Nguyen, Van Tho
2017-02-01
We propose a polarization insensitive two-mode division (de)multiplexer based on a silicon-on-insulator platform operating with a broadband, low insertion and scattering loss, and small crosstalk. By using an asymmetric directional coupler, two-mode (de)multiplexing functions for both polarization TE and TM states can be realized by the numerical simulation. Simulated results using a three dimensional beam propagation method (3D-BPM) incorporated with an effective index method (EIM) show high performance of the device with an operation efficiency above 81.2% (i.e., insertion loss is less than 0.9 dB) in the range of ±5 nm around the central wavelength of 1550 nm. Fabrication tolerances also have proved suitability to current manufacture technologies for the planar waveguides. Besides a low scattering loss of the sidewall roughness and a little influence of dispersion, a small footprint can bring the device to applications of high bitrate and compact on-chip silicon photonic integrated circuits.
Bishop, Joseph E.; Emery, John M.; Battaile, Corbett C.; Littlewood, David J.; Baines, Andrew J.
2016-05-01
Two fundamental approximations in macroscale solid-mechanics modeling are (1) the assumption of scale separation in homogenization theory and (2) the use of a macroscopic plasticity material model that represents, in a mean sense, the multitude of inelastic processes occurring at the microscale. With the goal of quantifying the errors induced by these approximations on engineering quantities of interest, we perform a set of direct numerical simulations (DNS) in which polycrystalline microstructures are embedded throughout a macroscale structure. The largest simulations model over 50,000 grains. The microstructure is idealized using a randomly close-packed Voronoi tessellation in which each polyhedral Voronoi cell represents a grain. An face centered cubic crystal-plasticity model is used to model the mechanical response of each grain. The overall grain structure is equiaxed, and each grain is randomly oriented with no overall texture. The detailed results from the DNS simulations are compared to results obtained from conventional macroscale simulations that use homogeneous isotropic plasticity models. The macroscale plasticity models are calibrated using a representative volume element of the idealized microstructure. Ultimately, we envision that DNS modeling will be used to gain new insights into the mechanics of material deformation and failure.
Drost, Kevin; Apte, Sourabh
2010-11-01
Direct numerical simulations are performed to investigate the effect of a movable leading edge on the unsteady flow at high angles of attack over a flat, thin airfoil at Reynolds number of 14700 based on the chord length. The leading edge of the airfoil is hinged at one-third chord length allowing dynamic variations in the effective angle of attack through specified oscillations (or flapping). A fictitious-domain based finite volume approach [(Apte et al. (JCP 2009)] is used to compute the flow over an airfoil with a flapping leading edge on a fixed background mesh. Cases were run at 20 degrees angle of attack to study the drag and lift characteristics with sinusoidal flapping of the leading edge about the hinge over a range of reduced frequencies (k=πf c/U∞ = 0.57- 5.7). It is shown that high-frequency low amplitude actuation of the leading edge significantly alters the leading edge boundary-layer and vortex shedding and increases the mean lift- to-drag ratio. The concept of an actuated leading-edge flap has potential for development of control techniques to stabilize and maneuver low-Reynolds number micro-air vehicles in response to unsteady perturbations.
Rosenberg, D; Marino, R; Mininni, P D
2014-01-01
We report results on rotating stratified turbulence in the absence of forcing, with large-scale isotropic initial conditions, using direct numerical simulations computed on grids of up to 4096^3 points. The Reynolds and Froude numbers are respectively equal to Re=5.4 x 10^4 and Fr=0.0242. The ratio of the Brunt-V\\"ais\\"al\\"a to the inertial wave frequency, N/f, is taken to be equal to 4.95, a choice appropriate to model the dynamics of the southern abyssal ocean at mid latitudes. This gives a global buoyancy Reynolds number R_B=ReFr^2=32, a value sufficient for some isotropy to be recovered in the small scales beyond the Ozmidov scale, but still moderate enough that the intermediate scales where waves are prevalent are well resolved. We concentrate on the large-scale dynamics, for which we find a spectrum compatible with the Bolgiano-Obukhov scaling, and confirm that the Froude number based on a typical vertical length scale is of order unity, with strong gradients in the vertical. Two characteristic scales e...
Becus, Georges A.; Chan, Alistair K.
1993-01-01
Three neural network processing approaches in a direct numerical optimization model reduction scheme are proposed and investigated. Large structural systems, such as large space structures, offer new challenges to both structural dynamicists and control engineers. One such challenge is that of dimensionality. Indeed these distributed parameter systems can be modeled either by infinite dimensional mathematical models (typically partial differential equations) or by high dimensional discrete models (typically finite element models) often exhibiting thousands of vibrational modes usually closely spaced and with little, if any, damping. Clearly, some form of model reduction is in order, especially for the control engineer who can actively control but a few of the modes using system identification based on a limited number of sensors. Inasmuch as the amount of 'control spillover' (in which the control inputs excite the neglected dynamics) and/or 'observation spillover' (where neglected dynamics affect system identification) is to a large extent determined by the choice of particular reduced model (RM), the way in which this model reduction is carried out is often critical.
Directory of Open Access Journals (Sweden)
Wenkai Xu
2014-01-01
Full Text Available A direct numerical simulation (DNS was carried out to study twin swirling jets which are issued from two parallel nozzles at a Reynolds number of Re = 5000 and three swirl levels of S = 0.68, 1.08, and 1.42, respectively. The basic structures of vortex-vortex interaction and temporal evolution are illustrated. The characteristics of axial variation of turbulent fluctuation velocities, in both the near and far field, in comparison to a single swirling jet, are shown to explore the effects of vortex-vortex interaction on turbulence modifications. Moreover, the second order turbulent fluctuations are also shown, by which the modification of turbulence associated with the coherent or correlated turbulent fluctuation and turbulent kinetic energy transport characteristics are clearly indicated. It is found that the twin swirling flow has a fairly strong localized vortex-vortex interaction between a pair of inversely rotated vortices. The location and strength of interaction depend on swirl level greatly. The modification of vortex takes place by transforming large-scale vortices into complex small ones, whereas the modulation of turbulent kinetic energy is continuously augmented by strong vortex modification.
Robbins, Joshua; Voth, Thomas
2011-06-01
Material response to dynamic loading is often dominated by microstructure such as grain topology, porosity, inclusions, and defects; however, many models rely on assumptions of homogeneity. We use the probabilistic finite element method (WK Liu, IJNME, 1986) to introduce local uncertainty to account for material heterogeneity. The PFEM uses statistical information about the local material response (i.e., its expectation, coefficient of variation, and autocorrelation) drawn from knowledge of the microstructure, single crystal behavior, and direct numerical simulation (DNS) to determine the expectation and covariance of the system response (velocity, strain, stress, etc). This approach is compared to resolved grain-scale simulations of the equivalent system. The microstructures used for the DNS are produced using Monte Carlo simulations of grain growth, and a sufficient number of realizations are computed to ensure a meaningful comparison. Finally, comments are made regarding the suitability of one-dimensional PFEM for modeling material heterogeneity. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Directory of Open Access Journals (Sweden)
J. A. Ruiz-Arias
2014-01-01
Full Text Available Broadband short-wave (SW surface direct and diffuse irradiances are not typically within the set of output variables produced by numerical weather prediction (NWP models. However, they are being more and more demanded in solar energy applications. A detailed representation of the aerosol optical properties is important to achieve an accurate assessment of these direct and diffuse irradiances. Nonetheless, NWP models typically oversimplify its representation or even neglect its effect. In this work, a flexible method to account for the SW aerosol optical properties in the computation of broadband SW surface direct and diffuse irradiances is presented. It only requires aerosol optical depth at 0.55 μm and the type of predominant aerosol. The rest of parameters needed to consider spectral aerosol extinction, namely, Angström exponent, aerosol single-scattering albedo and aerosol asymmetry factor, are parameterized. The parameterization has been tested in the RRTMG SW scheme of the Weather Research and Forecasting (WRF NWP model. However, it can be adapted to any other SW radiative transfer band model. It has been verified against a control experiment along five radiometric stations in the contiguous US. The control experiment consisted of a clear-sky evaluation of the RRTMG solar radiation estimates obtained in WRF when RRTMG is driven with ground-observed aerosol optical properties. Overall, the verification has shown very satisfactory results for both broadband SW surface direct and diffuse irradiances. It has proven effective to significantly reduce the prediction error and constraint the seasonal bias in clear-sky conditions to within the typical observational error in well-maintained radiometers.
Evaluation of the GlideScope Direct: A New Video Laryngoscope for Teaching Direct Laryngoscopy
Directory of Open Access Journals (Sweden)
Darwin Viernes
2012-01-01
Full Text Available Background. Teaching direct laryngoscopy is limited by the inability of the instructor to simultaneously view the airway with the laryngoscopist. Our primary aim is to report our initial use of the GlideScope Direct, a video-enabled, Macintosh laryngoscope intended primarily as a training tool in direct laryngoscopy. Methods. The GlideScope Direct was made available to anyone who planned on performing direct laryngoscopy as the primary technique for intubation. Novices were those who had performed <30 intubations. Results. The GlideScope Direct was used 123 times as primarily a direct laryngoscope while the instructor viewed the intubation on the monitor. It was highly successful as a direct laryngoscope (93% success. Salvage by indirect laryngoscopy occurred in 7/9 remaining patients without changing equipment. Novices performed 28 intubations (overall success rate of 79%. In 6 patients, the instructor took over and successfully intubated the patient. Instructors used the video images to guide the operator in 16 (57% of those patients. Seven different instructors supervised the 28 novices, all of who subjectively felt advantaged by having the laryngoscopic view available. Conclusions. The GlideScope Direct functions similarly to a Macintosh laryngoscope and provides the instructor subjective reassurance, while providing the ability to guide the trainee laryngoscopist.
SEQUESTRATION OF METALS IN ACTIVE CAP MATERIALS: A LABORATORY AND NUMERICAL EVALUATION
Energy Technology Data Exchange (ETDEWEB)
Dixon, K.; Knox, A.
2012-02-13
Active capping involves the use of capping materials that react with sediment contaminants to reduce their toxicity or bioavailability. Although several amendments have been proposed for use in active capping systems, little is known about their long-term ability to sequester metals. Recent research has shown that the active amendment apatite has potential application for metals contaminated sediments. The focus of this study was to evaluate the effectiveness of apatite in the sequestration of metal contaminants through the use of short-term laboratory column studies in conjunction with predictive, numerical modeling. A breakthrough column study was conducted using North Carolina apatite as the active amendment. Under saturated conditions, a spike solution containing elemental As, Cd, Co, Se, Pb, Zn, and a non-reactive tracer was injected into the column. A sand column was tested under similar conditions as a control. Effluent water samples were periodically collected from each column for chemical analysis. Relative to the non-reactive tracer, the breakthrough of each metal was substantially delayed by the apatite. Furthermore, breakthrough of each metal was substantially delayed by the apatite compared to the sand column. Finally, a simple 1-D, numerical model was created to qualitatively predict the long-term performance of apatite based on the findings from the column study. The results of the modeling showed that apatite could delay the breakthrough of some metals for hundreds of years under typical groundwater flow velocities.
Dritselis, Chris D.
2017-04-01
In the first part of this study (Dritselis 2016 Fluid Dyn. Res. 48 015507), the Reynolds stress budgets were evaluated through point-particle direct numerical simulations (pp-DNSs) for the particle-laden turbulent flow in a vertical channel with two- and four-way coupling effects. Here several turbulence models are assessed by direct comparison of the particle contribution terms to the budgets, the dissipation rate, the pressure-strain rate, and the transport rate with the model expressions using the pp-DNS data. It is found that the models of the particle sources to the equations of fluid turbulent kinetic energy and dissipation rate cannot represent correctly the physics of the complex interaction between turbulence and particles. A relatively poor performance of the pressure-strain term models is revealed in the particulate flows, while the algebraic models for the dissipation rate of the fluid turbulence kinetic energy and the transport rate terms can adequately reproduce the main trends due to the presence of particles. Further work is generally needed to improve the models in order to account properly for the momentum exchange between the two phases and the effects of particle inertia, gravity and inter-particle collisions.
Evaluating Self-directed Learning Skills in SALC Modules
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Junko Noguchi
2014-06-01
Full Text Available This article is one of the last contributions to the column which followed the self-directed learning curriculum renewal project being conducted at Kanda University of International Studies in Japan. Junko Noguchi unpacks the complicated issue of assessing self-directed learning.
Full 3-D numerical modeling of borehole electric image logging and the evaluation model of fracture
Institute of Scientific and Technical Information of China (English)
2008-01-01
A full 3-D finite element method numerical modeling program is written based on the principle and technical specification of borehole electric image well logging tool. The response of well logging is computed in the formation media model with a single fracture. The effect of changing fracture aperture and resistivity ratio to the logging response is discussed. The identification ability for two parallel fractures is also present. A quantitative evaluation formula of fracture aperture from borehole electric image logging data is set up. A case study of the model well is done to verify the accuracy of the for-mula. The result indicates that the formula is more accurate than the foreign one.
Evaluation of a new parallel numerical parameter optimization algorithm for a dynamical system
Duran, Ahmet; Tuncel, Mehmet
2016-10-01
It is important to have a scalable parallel numerical parameter optimization algorithm for a dynamical system used in financial applications where time limitation is crucial. We use Message Passing Interface parallel programming and present such a new parallel algorithm for parameter estimation. For example, we apply the algorithm to the asset flow differential equations that have been developed and analyzed since 1989 (see [3-6] and references contained therein). We achieved speed-up for some time series to run up to 512 cores (see [10]). Unlike [10], we consider more extensive financial market situations, for example, in presence of low volatility, high volatility and stock market price at a discount/premium to its net asset value with varying magnitude, in this work. Moreover, we evaluated the convergence of the model parameter vector, the nonlinear least squares error and maximum improvement factor to quantify the success of the optimization process depending on the number of initial parameter vectors.
Numerical evaluation of the radiation from unbaffled, finite plates using the FFT
Williams, E. G.
1983-01-01
An iteration technique is described which numerically evaluates the acoustic pressure and velocity on and near unbaffled, finite, thin plates vibrating in air. The technique is based on Rayleigh's integral formula and its inverse. These formulas are written in their angular spectrum form so that the fast Fourier transform (FFT) algorithm may be used to evaluate them. As an example of the technique the pressure on the surface of a vibrating, unbaffled disk is computed and shown to be in excellent agreement with the exact solution using oblate spheroidal functions. Furthermore, the computed velocity field outside the disk shows the well-known singularity at the rim of the disk. The radiated fields from unbaffled flat sources of any geometry with prescribed surface velocity may be evaluated using this technique. The use of the FFT to perform the integrations in Rayleigh's formulas provides a great savings in computation time compared with standard integration algorithms, especially when an array processor can be used to implement the FFT.
Numerical simulation and fracture evaluation method of dual laterolog in organic shale
Tan, Maojin; Wang, Peng; Li, Jun; Liu, Qiong; Yang, Qinshan
2014-01-01
Fracture identification and parameter evaluation are important for logging interpretation of organic shale, especially fracture evaluation from conventional logs in case the imaging log is not available. It is helpful to study dual laterolog responses of the fractured shale reservoir. First, a physical model is set up according to the property of organic shale, and three-dimensional finite element method (FEM) based on the principle of dual laterolog is introduced and applied to simulate dual laterolog responses in various shale models, which can help identify the fractures in shale formations. Then, through a number of numerical simulations of dual laterolog for various shale models with different base rock resistivities and fracture openings, the corresponding equations of various cases are constructed respectively, and the fracture porosity can be calculated consequently. Finally, we apply this methodology proposed above to a case study of organic shale, and the fracture porosity and fracture opening are calculated. The results are consistent with the fracture parameters processed from Full borehole Micro-resistivity Imaging (FMI). It indicates that the method is applicable for fracture evaluation of organic shale.
Bianco, Vincenzo; Borreani, Walter; Lomonaco, Guglielmo
2017-06-01
The present paper reports a numerical investigation of a forced convection water flow within a two-dimensional ribbed channel. A uniform heat flux is applied on the external walls. The flow regime is turbulent and Reynolds numbers are in the range 10·103÷100·103. Square and chamfered rib shapes with different arrangements are analyzed in terms of various dimensionless heights and pitches of elements. The investigation is accomplished by using a CFD code and its aim consists in finding of arrangements to obtain a high Performance Evaluation Criterion (PEC). Results are presented in terms of temperature and velocity fields, profiles of average Nusselt number, average heat transfer coefficients and required pumping power. Heat transfer enhancement increases with the ribs presence, but it is accompanied by an increasing pumping power. In particular, the best performances in terms of Nusselt are shown for p/e = 4 and 12 for both the square and chamfered cases. The heat transfer improves as Reynolds number raises, but a substantial increase of pumping power is also observed. The utilization of chamfered ribs allows to increase the PEC, especially at low Re. The maximum PEC is equal to 1.3 and it is obtained for Re = 104 and p/e = 4.
Evaluation of the GlideScope Direct: A New Video Laryngoscope for Teaching Direct Laryngoscopy.
Viernes, Darwin; Goldman, Allan J; Galgon, Richard E; Joffe, Aaron M
2012-01-01
Background. Teaching direct laryngoscopy is limited by the inability of the instructor to simultaneously view the airway with the laryngoscopist. Our primary aim is to report our initial use of the GlideScope Direct, a video-enabled, Macintosh laryngoscope intended primarily as a training tool in direct laryngoscopy. Methods. The GlideScope Direct was made available to anyone who planned on performing direct laryngoscopy as the primary technique for intubation. Novices were those who had performed laryngoscope while the instructor viewed the intubation on the monitor. It was highly successful as a direct laryngoscope (93% success). Salvage by indirect laryngoscopy occurred in 7/9 remaining patients without changing equipment. Novices performed 28 intubations (overall success rate of 79%). In 6 patients, the instructor took over and successfully intubated the patient. Instructors used the video images to guide the operator in 16 (57%) of those patients. Seven different instructors supervised the 28 novices, all of who subjectively felt advantaged by having the laryngoscopic view available. Conclusions. The GlideScope Direct functions similarly to a Macintosh laryngoscope and provides the instructor subjective reassurance, while providing the ability to guide the trainee laryngoscopist.
Ostoich, Christopher Mark
due to a dome-induced horseshoe vortex scouring the panel's surface. Comparisons with reduced-order models of heat transfer indicate that they perform with varying levels of accuracy around some portions of the geometry while completely failing to predict significant heat loads in re- gions where the dome-influenced flow impacts the ceramic panel. Cumulative effects of flow-thermal coupling at later simulation times on the reduction of panel drag and surface heat transfer are quantified. The second fluid-structure study investigates the interaction between a thin metallic panel and a Mach 2.25 turbulent boundary layer with an ini- tial momentum thickness Reynolds number of 1200. A transient, non-linear, large deformation, 3D finite element solver is developed to compute the dynamic response of the panel. The solver is coupled at the fluid-structure interface with the compressible Navier-Stokes solver, the latter of which is used for a direct numerical simulation of the turbulent boundary layer. In this approach, no simplifying assumptions regarding the structural solution or turbulence modeling are made in order to get detailed solution data. It is found that the thin panel state evolves into a flutter type response char- acterized by high-amplitude, high-frequency oscillations into the flow. The oscillating panel disturbs the supersonic flow by introducing compression waves, modifying the turbulence, and generating fluctuations in the power exiting the top of the flow domain. The work in this thesis serves as a step forward in structural response prediction in high-speed flows. The results demonstrate the ability of high- fidelity numerical approaches to serve as a guide for reduced-order model improvement and as well as provide accurate and detailed solution data in scenarios where experimental approaches are difficult or impossible.
Castellanza, Riccardo; Lollino, Piernicola; Oryem Ciantia, Matteo; di Prisco, Claudio; Crosta, Giovanni; Frigerio, Gabriele
2013-04-01
Soft and highly porous rocks such as tuffs and calcarenites are very common rocks. Due to their porous calcareous structure they are quite prone to water induced weathering mechanisms. Onshore and inland natural underground cavities are evident signs of these phenomena and of the effects in terms of failure. These materials have been largely employed in the past as building and ornamental stones and as sites to excavate underground cavities for different uses. The world famous Unesco site of "Sassi di Matera", the underground cavities in Canosa di Puglia and Gravina di Puglia , or the calcarenite cliff and natural caves of Polignano a Mare are the most representative cases. Nowadays, many of these are deteriorating because of weathering due to humidity, water infiltration, environmental pollution, and direct exposure to marine aerosols and meteoric water precipitations. In all these cases, a careful assessment of the safety of the built environment and a conscious identification of the safety measures cannot be separated from the analysis of the interaction between the cavities and the overlying buildings, and of the evolution and spatial distribution of the weathering processes. This contribute summarizes the authors' experience on the subject and suggests a methodological approach to quantitatively assess the stability of underground cavities. Starting from experimental evidences at micro and macroscale, the main debonding mechanisms have been taken into account in numerical models. The time-evolution scenarios of the weathering processes is introduced in three-dimensional numerical modelling. The intention is to provide a potentially useful tool for risk assessment in similar complex geomechanical situations.
Evaluation of Competence of Medical Students in Performing Direct ...
African Journals Online (AJOL)
which they underwent a didactic lecture on direct ophthalmoscopy and ... exam. Exclusion criteria. Medical students who failed to meet 75% attendance as ... the Y instructor believes students are motivated to learn willingly without close ...
Directory of Open Access Journals (Sweden)
D. L. Shrestha
2013-05-01
Full Text Available The quality of precipitation forecasts from four Numerical Weather Prediction (NWP models is evaluated over the Ovens catchment in Southeast Australia. Precipitation forecasts are compared with observed precipitation at point and catchment scales and at different temporal resolutions. The four models evaluated are the Australian Community Climate Earth-System Simulator (ACCESS including ACCESS-G with a 80 km resolution, ACCESS-R 37.5 km, ACCESS-A 12 km, and ACCESS-VT 5 km. The skill of the NWP precipitation forecasts varies considerably between rain gauging stations. In general, high spatial resolution (ACCESS-A and ACCESS-VT and regional (ACCESS-R NWP models overestimate precipitation in dry, low elevation areas and underestimate in wet, high elevation areas. The global model (ACCESS-G consistently underestimates the precipitation at all stations and the bias increases with station elevation. The skill varies with forecast lead time and, in general, it decreases with the increasing lead time. When evaluated at finer spatial and temporal resolution (e.g. 5 km, hourly, the precipitation forecasts appear to have very little skill. There is moderate skill at short lead times when the forecasts are averaged up to daily and/or catchment scale. The precipitation forecasts fail to produce a diurnal cycle shown in observed precipitation. Significant sampling uncertainty in the skill scores suggests that more data are required to get a reliable evaluation of the forecasts. The non-smooth decay of skill with forecast lead time can be attributed to diurnal cycle in the observation and sampling uncertainty. Future work is planned to assess the benefits of using the NWP rainfall forecasts for short-term streamflow forecasting. Our findings here suggest that it is necessary to remove the systematic biases in rainfall forecasts, particularly those from low resolution models, before the rainfall forecasts can be used for streamflow forecasting.
Reinink, Shawn K.; Yaras, Metin I.
2015-06-01
Forced-convection heat transfer in a heated working fluid at a thermodynamic state near its pseudocritical point is poorly predicted by correlations calibrated with data at subcritical temperatures and pressures. This is suggested to be primarily due to the influence of large wall-normal thermophysical property gradients that develop in proximity of the pseudocritical point on the concentration of coherent turbulence structures near the wall. The physical mechanisms dominating this influence remain poorly understood. In the present study, direct numerical simulation is used to study the development of coherent vortical structures within a turbulent spot under the influence of large wall-normal property gradients. A turbulent spot rather than a fully turbulent boundary layer is used for the study, for the coherent structures of turbulence in a spot tend to be in a more organized state which may allow for more effective identification of cause-and-effect relationships. Large wall-normal gradients in thermophysical properties are created by heating the working fluid which is near the pseudocritical thermodynamic state. It is found that during improved heat transfer, wall-normal gradients in density accelerate the growth of the Kelvin-Helmholtz instability mechanism in the shear layer enveloping low-speed streaks, causing it to roll up into hairpin vortices at a faster rate. It is suggested that this occurs by the baroclinic vorticity generation mechanism which accelerates the streamwise grouping of vorticity during shear layer roll-up. The increased roll-up frequency leads to reduced streamwise spacing between hairpin vortices in wave packets. The density gradients also promote the sinuous instability mode in low-speed streaks. The resulting oscillations in the streaks in the streamwise-spanwise plane lead to locally reduced spanwise spacing between hairpin vortices forming over adjacent low-speed streaks. The reduction in streamwise and spanwise spacing between
Energy Technology Data Exchange (ETDEWEB)
Molins, Sergi [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Earth Sciences Division; Trebotich, David [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Computational Research Division; Steefel, Carl I. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Earth Sciences Division; Shen, Chaopeng [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Computational Research Division
2012-03-30
The scale-dependence of geochemical reaction rates hinders their use in continuum scale models intended for the interpretation and prediction of chemical fate and transport in subsurface environments such as those considered for geologic sequestration of CO_{2}. Processes that take place at the pore scale, especially those involving mass transport limitations to reactive surfaces, may contribute to the discrepancy commonly observed between laboratory-determined and continuum-scale or field rates. In this study we investigate the dependence of mineral dissolution rates on the pore structure of the porous media by means of pore scale modeling of flow and multicomponent reactive transport. The pore scale model is composed of high-performance simulation tools and algorithms for incompressible flow and conservative transport combined with a general-purpose multicomponent geochemical reaction code. The model performs direct numerical simulation of reactive transport based on an operator-splitting approach to coupling transport and reactions. The approach is validated with a Poiseuille flow single-pore experiment and verified with an equivalent 1-D continuum-scale model of a capillary tube packed with calcite spheres. Using the case of calcite dissolution as an example, the high-resolution model is used to demonstrate that nonuniformity in the flow field at the pore scale has the effect of decreasing the overall reactivity of the system, even when systems with identical reactive surface area are considered. In conclusion, the effect becomes more pronounced as the heterogeneity of the reactive grain packing increases, particularly where the flow slows sufficiently such that the solution approaches equilibrium locally and the average rate becomes transport-limited.
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Malapaka, Shiva Kumar; Mueller, Wolf-Christian [Max-Planck Institute for Plasma Physics, Boltzmannstrasse 2, D-85748 Garching bei Muenchen (Germany)
2013-09-01
Statistical properties of the Sun's photospheric turbulent magnetic field, especially those of the active regions (ARs), have been studied using the line-of-sight data from magnetograms taken by the Solar and Heliospheric Observatory and several other instruments. This includes structure functions and their exponents, flatness curves, and correlation functions. In these works, the dependence of structure function exponents ({zeta}{sub p}) of the order of the structure functions (p) was modeled using a non-intermittent K41 model. It is now well known that the ARs are highly turbulent and are associated with strong intermittent events. In this paper, we compare some of the observations from Abramenko et al. with the log-Poisson model used for modeling intermittent MHD turbulent flows. Next, we analyze the structure function data obtained from the direct numerical simulations (DNS) of homogeneous, incompressible 3D-MHD turbulence in three cases: sustained by forcing, freely decaying, and a flow initially driven and later allowed to decay (case 3). The respective DNS replicate the properties seen in the plots of {zeta}{sub p} against p of ARs. We also reproduce the trends and changes observed in intermittency in flatness and correlation functions of ARs. It is suggested from this analysis that an AR in the onset phase of a flare can be treated as a forced 3D-MHD turbulent system in its simplest form and that the flaring stage is representative of decaying 3D-MHD turbulence. It is also inferred that significant changes in intermittency from the initial onset phase of a flare to its final peak flaring phase are related to the time taken by the system to reach the initial onset phase.
Luong, Minhbau
2013-10-01
The effects of fuel composition, thermal stratification, and turbulence on the ignition of lean homogeneous primary reference fuel (PRF)/air mixtures under the conditions of constant volume and elevated pressure are investigated by direct numerical simulations (DNSs) with a new 116-species reduced kinetic mechanism. Two-dimensional DNSs were performed in a fixed volume with a two-dimensional isotropic velocity spectrum and temperature fluctuations superimposed on the initial scalar fields with different fuel compositions to elucidate the influence of variations in the initial temperature fluctuation and turbulence intensity on the ignition of three different lean PRF/air mixtures. In general, it was found that the mean heat release rate increases slowly and the overall combustion occurs fast with increasing thermal stratification regardless of the fuel composition under elevated pressure and temperature conditions. In addition, the effect of the fuel composition on the ignition characteristics of PRF/air mixtures was found to vanish with increasing thermal stratification. Chemical explosive mode (CEM), displacement speed, and Damköhler number analyses revealed that the high degree of thermal stratification induces deflagration rather than spontaneous ignition at the reaction fronts, rendering the mean heat release rate more distributed over time subsequent to thermal runaway occurring at the highest temperature regions in the domain. These analyses also revealed that the vanishing of the fuel effect under the high degree of thermal stratification is caused by the nearly identical propagation characteristics of deflagrations of different PRF/air mixtures. It was also found that high intensity and short-timescale turbulence can effectively homogenize mixtures such that the overall ignition is apt to occur by spontaneous ignition. These results suggest that large thermal stratification leads to smooth operation of homogeneous charge compression-ignition (HCCI
Okong'o, Nora; Leboissetier, Anthony; Bellan, Josette
2008-10-01
Results are compared from direct numerical simulation (DNS) and large eddy simulation (LES) of a temporal mixing layer laden with evaporating drops to assess the ability of LES to reproduce detailed characteristics of DNS. The LES used computational drops, each of which represented eight physical drops, and a reduced flow field resolution using a grid spacing four times larger than that of the DNS. The LES also used models for the filtered source terms, which express the coupling of the drops with the flow, and for the unresolved subgrid-scale (SGS) fluxes of species mass, momentum, and enthalpy. The LESs were conducted using one of three different SGS-flux models: dynamic-coefficient gradient (GRD), dynamic-coefficient Smagorinsky (SMD), and constant-coefficient scale similarity (SSC). The comparison of the LES with the filtered-and-coarsened (FC) DNS considered detailed aspects of the flow that are of interest in ignition or full combustion. All LESs captured the largest-scale vortex, the global amount of vapor emanating from the drops, and the overall size distribution of the drops. All LESs tended to underpredict the global amount of irreversible entropy production (dissipation). The SMD model was found unable to capture either the global or local vorticity variation and had minimal small-scale activity in dynamic and thermodynamic variables compared to the FC-DNS. The SMD model was also deficient in predicting the spatial distribution of drops and of the dissipation. In contrast, the GRD and SSC models did mimic the small-scale activity of the FC-DNS and the spatial distribution of drops and of the dissipation. Therefore, the GRD and SSC models are recommended, while the SMD model seems inappropriate for combustion or other problems where the local activity must be predicted.
Directory of Open Access Journals (Sweden)
Ghofrane Sekrani
2016-11-01
Full Text Available In the present paper, laminar forced convection nanofluid flows in a uniformly heated horizontal tube were revisited by direct numerical simulations. Single and two-phase models were employed with constant and temperature-dependent properties. Comparisons with experimental data showed that the mixture model performs better than the single-phase model in the all cases studied. Temperature-dependent fluid properties also resulted in a better prediction of the thermal field. Particular attention was paid to the grid arrangement. The two-phase model was used then confidently to investigate the influence of the nanoparticle size on the heat and fluid flow with a particular emphasis on the sedimentation process. Four nanoparticle diameters were considered: 10, 42, 100 and 200 nm for both copper-water and alumina/water nanofluids. For the largest diameter d n p = 200 nm, the Cu nanoparticles were more sedimented by around 80%, while the A l 2 O 3 nanoparticles sedimented only by 2 . 5 %. Besides, it was found that increasing the Reynolds number improved the heat transfer rate, while it decreased the friction factor allowing the nanoparticles to stay more dispersed in the base fluid. The effect of nanoparticle type on the heat transfer coefficient was also investigated for six different water-based nanofluids. Results showed that the Cu-water nanofluid achieved the highest heat transfer coefficient, followed by C, A l 2 O 3 , C u O , T i O 2 , and S i O 2 , respectively. All results were presented and discussed for four different values of the concentration in nanoparticles, namely φ = 0 , 0 . 6 % , 1 % and 1 . 6 % . Empirical correlations for the friction coefficient and the average Nusselt number were also provided summarizing all the presented results.
Energy Technology Data Exchange (ETDEWEB)
Kwon, Kyung [Tuskegee Univ., Tuskegee, AL (United States); Fan, Liang-Shih [The Ohio State Univ., Columbus, OH (United States); Zhou, Qiang [The Ohio State Univ., Columbus, OH (United States); Yang, Hui [The Ohio State Univ., Columbus, OH (United States)
2014-09-30
A new and efficient direct numerical method with second-order convergence accuracy was developed for fully resolved simulations of incompressible viscous flows laden with rigid particles. The method combines the state-of-the-art immersed boundary method (IBM), the multi-direct forcing method, and the lattice Boltzmann method (LBM). First, the multi-direct forcing method is adopted in the improved IBM to better approximate the no-slip/no-penetration (ns/np) condition on the surface of particles. Second, a slight retraction of the Lagrangian grid from the surface towards the interior of particles with a fraction of the Eulerian grid spacing helps increase the convergence accuracy of the method. An over-relaxation technique in the procedure of multi-direct forcing method and the classical fourth order Runge-Kutta scheme in the coupled fluid-particle interaction were applied. The use of the classical fourth order Runge-Kutta scheme helps the overall IB-LBM achieve the second order accuracy and provides more accurate predictions of the translational and rotational motion of particles. The preexistent code with the first-order convergence rate is updated so that the updated new code can resolve the translational and rotational motion of particles with the second-order convergence rate. The updated code has been validated with several benchmark applications. The efficiency of IBM and thus the efficiency of IB-LBM were improved by reducing the number of the Lagragian markers on particles by using a new formula for the number of Lagrangian markers on particle surfaces. The immersed boundary-lattice Boltzmann method (IBLBM) has been shown to predict correctly the angular velocity of a particle. Prior to examining drag force exerted on a cluster of particles, the updated IB-LBM code along with the new formula for the number of Lagrangian markers has been further validated by solving several theoretical problems. Moreover, the unsteadiness of the drag force is examined when a
Numerical evaluation of weld overlay applied to a pressurized water reactor nozzle mock-up
Energy Technology Data Exchange (ETDEWEB)
Rabello, Emerson G.; Silva, Luiz L.; Gomes, Paulo T.V., E-mail: egr@cdtn.b, E-mail: silvall@cdtn.b, E-mail: gomespt@cdtn.b [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil). Servico de Integridade Estrutural
2011-07-01
The primary water stress corrosion cracking (PWSCC) is a major mechanism of failure in the primary circuit of PWR type nuclear power plants. The PWSCC is associated with the presence of corrosive environment, the susceptibility to corrosion cracking of the materials involved and the tensile stresses presence. Residual stresses generated during dissimilar materials welding can contribute to PWSCC. An alternative to the PWSCC mitigation is the application of external weld layers in the regions of greatest susceptibility to corrosion cracking. This process, called Weld Overlay (WOL), has been widely used in regions of dissimilar weld (low alloy steel and stainless steel with nickel alloy addition) of nozzles and pipes on the primary circuit in order to promote internal compressive stresses on the wall of these components. This paper presents the steps required to the numerical stress evaluation (by finite element method) during the dissimilar materials welding as well as application of Weld Overlay process in a nozzle mock-up. Thus, one can evaluate the effectiveness of the application of weld overlay process to internal compressive stress generation on the wall nozzle. (author)
Numerical evaluation of seismic response of shallow foundation on loose silt and silty sand
Indian Academy of Sciences (India)
Ali Asgari; Aliakbar Golshani; Mohsen Bagheri
2014-03-01
This study includes the results of a set of numerical simulations carried out for sands containing plastic/non-plastic fines, and silts with relative densities of approximately 30−40% under different surchargeson the shallow foundation using FLAC 2D. Each model was subjected to three ground motion events, obtained by scaling the amplitude of the El Centro (1940), Kobe (1995) and Kocaeli (1999) earthquakes. Dynamic behaviour of loose deposits underlying shallow foundations is evaluated through fully coupled nonlinear effective stress dynamic analyses. Effects of nonlinear soil structure interaction (SSI) were also considered by using interface elements. This parametric study evaluates the effects of soil type, structure weight, liquefiable soil layer thickness, event parameters (e.g., moment magnitude of earthquake (), peak ground acceleration PGA, PGV/PGA ratio and the duration of strong motion (5−95)and their interactions on the seismic responses. Investigation on the effects of these parameters and their complex interactions can be a valuable tool to gain new insights for improved seismic design and construction.
Direct Integration: Training Software Developers to Conduct Usability Evaluations
DEFF Research Database (Denmark)
Skov, Mikael B.; Stage, Jan
2008-01-01
is based on an empirical study where 36 teams with a total of 234 first-year university students on software development and design educations were trained in a simple approach for user-based website usability testing that was taught in a 40 hour course. This approach supported them in planning, conducting......Many improvements of the interplay between usability evaluation and software development rely either on better methods for conducting usability evaluations or on better formats for presenting evaluation results in ways that are useful for software designers and developers. Both approaches involve...... a complete division of work between developers and evaluators, which is an undesirable complexity for many software development projects. This paper takes a different approach by exploring to what extent software developers and designers can be trained to carry out their own usability evaluations. The paper...
Direct Integration: Training Software Developers to Conduct Usability Evaluations
DEFF Research Database (Denmark)
Skov, Mikael B.; Stage, Jan
2008-01-01
Many improvements of the interplay between usability evaluation and software development rely either on better methods for conducting usability evaluations or on better formats for presenting evaluation results in ways that are useful for software designers and developers. Both approaches involve...... is based on an empirical study where 36 teams with a total of 234 first-year university students on software development and design educations were trained in a simple approach for user-based website usability testing that was taught in a 40 hour course. This approach supported them in planning, conducting......, and interpreting the results of a usability evaluation of an interactive website. They gained good competence in conducting the evaluation, defining task assignments and producing a usability report, while they were less successful in acquiring skills for identifying and describing usability problems....
DEFF Research Database (Denmark)
Sigurdsson, Haftor Örn; Kær, Søren Knudsen
2011-01-01
Numerical and experimental study is performed to evaluate the reactant by-pass flow in a catalytic plate reactor with a coated wire mesh catalyst for steam reforming of methane for hydrogen generation. By-pass of unconverted methane is evaluated under different wire mesh catalyst width to reactor...
Huq, Sadiq; De Roo, Frederik; Foken, Thomas; Mauder, Matthias
2017-06-01
The Campbell CSAT3 sonic anemometer is one of the most popular instruments for turbulence measurements in basic micrometeorological research and ecological applications. While measurement uncertainty has been characterized by field experiments and wind-tunnel studies in the past, there are conflicting estimates, which motivated us to conduct a numerical experiment using large-eddy simulation to evaluate the probe-induced flow distortion of the CSAT3 anemometer under controlled conditions, and with exact knowledge of the undisturbed flow. As opposed to wind-tunnel studies, we imposed oscillations in both the vertical and horizontal velocity components at the distinct frequencies and amplitudes found in typical turbulence spectra in the surface layer. The resulting flow-distortion errors for the standard deviations of the vertical velocity component range from 3 to 7%, and from 1 to 3% for the horizontal velocity component, depending on the azimuth angle. The magnitude of these errors is almost independent of the frequency of wind speed fluctuations, provided the amplitude is typical for surface-layer turbulence. A comparison of the corrections for transducer shadowing proposed by both Kaimal et al. (Proc Dyn Flow Conf, 551-565, 1978) and Horst et al. (Boundary-Layer Meteorol 155:371-395, 2015) show that both methods compensate for a larger part of the observed error, but do not sufficiently account for the azimuth dependency. Further numerical simulations could be conducted in the future to characterize the flow distortion induced by other existing types of sonic anemometers for the purposes of optimizing their geometry.
Direct Shear Tests with Evaluation of Variable Shearing Area
Directory of Open Access Journals (Sweden)
Šarūnas Skuodis
2014-12-01
Full Text Available Investigations of soil shear strength properties for Baltic Sea shore sand along Klaipėda city are presented. Investigated sand angle of internal friction (φ and cohesion (c is determined via two different direct shear tests procedures. First procedure is standard and ordinary in geotechnical practice, when direct shear test is provided using constant shearing area A0. Second test procedure is different because shearing area according to horizontal displacement each test second is recalculated. This recalculated shearing area author’s call corrected shearing area A. Obtained normal and tangential stresses’ difference via two different testing procedures was 10%.
Tani, Kotaro; Kurihara, Osamu; Kim, Eunjoo; Sakai, Kazuo; Akashi, Makoto
2016-09-01
After the Fukushima Daiichi Nuclear Power Station accident, the National Institute of Radiological Sciences examined seven heavily exposed emergency workers and performed internal dose estimations. The largest dose contributor was found to be (131)I, which was detected by thyroid monitor with an HPGe detector. Different energy peaks from (131)I were simultaneously identified in the pulse-height spectra of the two subjects with the highest doses regardless of late measurements. A closer look at the spectra indicated that the count ratio of the two peak areas at 80.2 and 365 keV differed somewhat between the individual workers, suggesting a difference in attenuation in the overlaying soft tissue and in the thyroid itself. In this study, the relationship between the count ratio (80.2/365 keV) and the thickness of soft tissue overlying the thyroid was investigated by means of numerical simulations performed using the Japanese Male (JM) phantom varying the thickness of the overlaying tissue. From the measured count ratios, it was possible to estimate that the overlaying tissue was thinner for Worker 1 (difference from the JM phantom: -0.34±1.29 cm) and thicker for Worker 2 (diff.: 2.5±1.2 cm). The thyroid (131)I contents evaluated taking into account the individual thicknesses were 4.3 kBq for Worker 1 and 8.4 kBq for Worker 2, resulting in a significant increase for Worker 2 compared with the content based on the default counting efficiency at 365 keV of the original JM phantom. However, the results have large uncertainty factors of 1.4 for Worker 1 and 1.3 for Worker 2 and should be carefully considered together with other factors influencing the attenuation.
Evaluation of the successive approximations method for acoustic streaming numerical simulations.
Catarino, S O; Minas, G; Miranda, J M
2016-05-01
This work evaluates the successive approximations method commonly used to predict acoustic streaming by comparing it with a direct method. The successive approximations method solves both the acoustic wave propagation and acoustic streaming by solving the first and second order Navier-Stokes equations, ignoring the first order convective effects. This method was applied to acoustic streaming in a 2D domain and the results were compared with results from the direct simulation of the Navier-Stokes equations. The velocity results showed qualitative agreement between both methods, which indicates that the successive approximations method can describe the formation of flows with recirculation. However, a large quantitative deviation was observed between the two methods. Further analysis showed that the successive approximation method solution is sensitive to the initial flow field. The direct method showed that the instantaneous flow field changes significantly due to reflections and wave interference. It was also found that convective effects contribute significantly to the wave propagation pattern. These effects must be taken into account when solving the acoustic streaming problems, since it affects the global flow. By adequately calculating the initial condition for first order step, the acoustic streaming prediction by the successive approximations method can be improved significantly.
Evaluation of health information outreach: theory, practice, and future direction*
Whitney, Wanda; Dutcher, Gale A.; Keselman, Alla
2013-01-01
Objective: Convincing evidence of the effectiveness of health information outreach projects is essential to ensure their continuity. This paper reviews the current state of health information outreach evaluation, characterizes strengths and weaknesses in projects' ability to measure their impact, and assesses enablers of and barriers to projects' success. It also relates the projects' characteristics to evaluation practices. The paper then makes recommendations for strengthening evaluation. Methods: Upon conducting a literature search, the authors identified thirty-three articles describing consumer health information outreach programs, published between 2000 and 2010. We then analyzed the outreach projects with respect to their goals and characteristics, evaluation methods and measures, and reported outcomes. Results: The results uncovered great variation in the quality of evaluation methods, outcome measures, and reporting. Outcome measures did not always match project objectives; few quantitative measures employed pretests or reported statistical significance; and institutional change was not measured in a structured way. While papers reported successful outcomes, greater rigor in measuring and documenting outcomes would be helpful. Conclusion: Planning outcome evaluation carefully and conducting research into mediators between health information and behavior will strengthen the ability to identify best practices and develop a theoretical framework and practical guidance for health information outreach. PMID:23646029
SaiToh, Akira
2013-01-01
The time-dependent matrix-product-state (TDMPS) simulation method has been used for numerically simulating quantum computing for a decade. We introduce our C++ library ZKCM_QC developed for multiprecision TDMPS simulations of quantum circuits. Besides its practical usability, the library is useful for evaluation of the method itself. With the library, we can capture two types of numerical errors in the TDMPS simulations: one due to rounding errors caused by the shortage in mantissa portions of floating-point numbers; the other due to truncations of nonnegligible Schmidt coefficients and their corresponding Schmidt vectors. We numerically analyze these errors in TDMPS simulations of quantum algorithms.
Cantonese versus Canadian Evaluation of Directive and Non-Directive Therapy.
Waxer, Peter H.
1989-01-01
Examined differences between Canadian and Cantonese university students who read transcripts of Carl Rogers and Albert Ellis counseling sessions and rated these counselors on directiveness, forcefulness, repetitiveness, sensitivity, politeness, and willingness to see either Ellis or Rogers. Found Canadians more willing to see Rogers than Chinese…
Druzhinin, Oleg A.; Troitskaya, Yuliya I.; Zilitinkevich, Sergej S.
2016-04-01
The detailed knowledge of the interaction of wind with surface water waves is necessary for correct parameterization of turbulent exchange at the air-sea interface in prognostic models. At sufficiently strong winds, sea-spray-generated droplets interfere with the wind-waves interaction. The results of field experiments and laboratory measurements (Andreas et al., JGR 2010) show that mass fraction of air-borne spume water droplets increases with the wind speed and their impact on the carrier air-flow may become significant. Phenomenological models of droplet-laden marine atmospheric boundary layer (Kudryavtsev & Makin, Bound.-Layer Met. 2011) predict that droplets significantly increase the wind velocity and suppress the turbulent air stress. The results of direct numerical simulation (DNS) of a turbulent particle-laden Couette flow over a flat surface show that inertial particles may significantly reduce the carrier flow vertical momentum flux (Richter & Sullivan, GRL 2013). The results also show that in the range of droplet sizes typically found near the air-sea interface, particle inertial effects are significant and dominate any particle-induced stratification effects. However, so far there has been no attempt to perform DNS of a droplet-laden air-flow over waved water surface. In this report, we present results of DNS of droplet-laden, turbulent Couette air-flow over waved water surface. The carrier, turbulent Couette-flow configuration in DNS is similar to that used in previous numerical studies (Sullivan et al., JFM 2000, Shen et al., JFM 2010, Druzhinin et al., JGR 2012). Discrete droplets are considered as non-deformable solid spheres and tracked in a Lagrangian framework, and their impact on the carrier flow is modeled with the use of a point-force approximation. The droplets parameters in DNS are matched to the typical known spume-droplets parameters in laboratory and field experiments. The DNS results show that both gravitational settling of droplets and
Farahmand, Parisa
In oil and gas industry, soil particles, crude oil, natural gas, particle-laden liquids, and seawater can carry various highly aggressive elements, which accelerate the material degradation of component surfaces by combination of slurry erosion, corrosion, and wear mechanisms. This material degradation results into the loss of mechanical properties such as strength, ductility, and impact strength; leading to detachment, delamination, cracking, and ultimately premature failure of components. Since the failure of high valued equipment needs considerable cost and time to be repaired or replaced, minimizing the tribological failure of equipment under aggressive environment has been gaining increased interest. It is widely recognized that effective management of degradation mechanisms will contribute towards the optimization of maintenance, monitoring, and inspection costs. The hardfacing techniques have been widely used to enhance the resistance of surfaces against degradation mechanisms. Applying a surface coating improves wear and corrosion resistance and ensures reliability and long-term performance of coated parts. A protective layer or barrier on the components avoids the direct mechanical and chemical contacts of tool surfaces with process media and will reduce the material loss and ultimately its failure. Laser cladding as an advanced hardfacing technique has been widely used for industrial applications in order to develop a protective coating with desired material properties. During the laser cladding, coating material is fused into the base material by means of a laser beam in order to rebuild a damaged part's surface or to enhance its surface function. In the hardfacing techniques such as atmospheric plasma spraying (APS), high velocity oxygen-fuel (HVOF), and laser cladding, mixing of coating materials with underneath surface has to be minimized in order to utilize the properties of the coating material most effectively. In this regard, laser cladding offers
Evaluation of Directed Diffusion Protocol for Mobile Sensor Networks
Directory of Open Access Journals (Sweden)
K.E.Kannammal
2010-06-01
Full Text Available Recent technological advances have enabled distributed information gathering from a given region by deploying a large number of networked tiny microsensors which are low power devices equipped withprogrammable computing, multiple sensing and communication capability thus forms Wireless Sensor networks. Directed Diffusion is a data centric routing protocol in Wireless Sensor Networks (WSN. It is a reactive protocol which creates routes based on needs. Sensed data’s are stored in attribute value pairs. A Sink request data by sendinginterests. The interest messages are flooding through the network and are added to each node’s interest cache. The data that match the interests are sent towards the sink. However, there is very little research addressing the impact of mobility on this class of routing protocols. In this paper, we address the behavior of a Directed Diffusion routing under different scenarios.
Performance Evaluation of Direction of Arrival Estimation Using Matlab
Sai Suhas Balabadrapatruni
2012-01-01
This paper presents the performance analysis of directions of arrival estimation techniques, Subspace and the Non-Subspace methods. In this paper, exploring the Eigen-analysis category of high resolution and super resolution algorithms, presentation of description, comparison and the performance and resolution analyses of these algorithms are made. Sensitivity to various perturbations and the effect of parameters related to the design of the sensor array itself such as the number ...
Operation control of fluids pumping in curved pipes during annular flow: a numerical evaluation
Directory of Open Access Journals (Sweden)
T Andrade
2016-10-01
Full Text Available To generate projects which provide significant volume recovery from heavy oils reservoirs and improve existing projects, is important to develop new production and transport technologies, especially in the scenario of offshore fields. The core-flow technique is one of new technologies used in heavy oil transportation. This core-flow pattern is characterized by a water pellicle that is formed close or adjacent to the inner wall of the pipe, functioning as a lubricant. The oil flows in the center of the pipe causing a reduction in longitudinal pressure drop. In this sense, this work presents a numerical study of heavy oil annular flow (core-flow assisted by computational tool ANSYS CFX® Release 12.0. It was used a three-dimensional, transient and isothermal mathematical model considered by the mixture and turbulence - models to address the water-heavy oil two-phase flow, assuming laminar flow for oil phase and turbulent flow for water phase. Results of the pressure, velocity and volume fraction distributions of the phases and the pressure drop for different operation conditions are presented and evaluated. It was observed that the oil core flowing eccentrically in the pipe and stops of the water flux considerably increases the pressure drop in the pipe after the restart of the pump.
A numerical study on the performance evaluation of ventilation systems for indoor radon reduction
Energy Technology Data Exchange (ETDEWEB)
Lee, Ji Eun; Park, Hoon Chae; Choi, Hang Seok; Cho, Seung Yeon; Jeong, Tae Young; Roh, Sung Cheoul [Yonsei University, Wonju (Korea, Republic of)
2016-03-15
Numerical simulations were conducted using computational fluid dynamics to evaluate the effect of ventilation conditions on radon ({sup 222}Rn) reduction performance in a residential building. The results indicate that at the same ventilation rate, a mechanical ventilation system is more effective in reducing indoor radon than a natural ventilation system. For the same ventilation type, the indoor radon concentration decreases as the ventilation rate increases. When the air change per hour (ACH) was 1, the indoor radon concentration was maintained at less than 100 Bq/m{sup 3}. However, when the ACH was lowered to 0.01, the average indoor radon concentration in several rooms exceeded 148 Bq/ m{sup 3}. The angle of the inflow air was found to affect the indoor air stream and consequently the distribution of the radon concentration. Even when the ACH was 1, the radon concentrations of some areas were higher than 100 Bq/m{sup 3} for inflow air angles of 5 .deg. and 175 .deg.
Numerical evaluation of E-fields induced by body motion near high-field MRI scanner.
Crozier, S; Liu, F
2004-01-01
In modern magnetic resonance imaging (MRI), both patients and radiologists are exposed to strong, nonuniform static magnetic fields inside or outside of the scanner, in which the body movement may be able to induce electric currents in tissues which could be possibly harmful. This paper presents theoretical investigations into the spatial distribution of induced E-fields in the human model when moving at various positions around the magnet. The numerical calculations are based on an efficient, quasistatic, finite-difference scheme and an anatomically realistic, full-body, male model. 3D field profiles from an actively-shielded 4 T magnet system are used and the body model projected through the field profile with normalized velocity. The simulation shows that it is possible to induce E-fields/currents near the level of physiological significance under some circumstances and provides insight into the spatial characteristics of the induced fields. The results are easy to extrapolate to very high field strengths for the safety evaluation at a variety of field strengths and motion velocities.
Yoshida, Hiroyuki; Takase, Kazuyuki
Thermal-hydraulic design of the current boiling water reactor (BWR) is performed with the subchannel analysis codes which incorporated the correlations based on empirical results including actual-size tests. Then, for the Innovative Water Reactor for Flexible Fuel Cycle (FLWR) core, an actual size test of an embodiment of its design is required to confirm or modify such correlations. In this situation, development of a method that enables the thermal-hydraulic design of nuclear reactors without these actual size tests is desired, because these tests take a long time and entail great cost. For this reason, we developed an advanced thermal-hydraulic design method for FLWRs using innovative two-phase flow simulation technology. In this study, a detailed Two-Phase Flow simulation code using advanced Interface Tracking method: TPFIT is developed to calculate the detailed information of the two-phase flow. In this paper, firstly, we tried to verify the TPFIT code by comparing it with the existing 2-channel air-water mixing experimental results. Secondary, the TPFIT code was applied to simulation of steam-water two-phase flow in a model of two subchannels of a current BWRs and FLWRs rod bundle. The fluid mixing was observed at a gap between the subchannels. The existing two-phase flow correlation for fluid mixing is evaluated using detailed numerical simulation data. This data indicates that pressure difference between fluid channels is responsible for the fluid mixing, and thus the effects of the time average pressure difference and fluctuations must be incorporated in the two-phase flow correlation for fluid mixing. When inlet quality ratio of subchannels is relatively large, it is understood that evaluation precision of the existing two-phase flow correlations for fluid mixing are relatively low.
Charles, Winsbert Curt
Seismic protective techniques utilizing specialized energy dissipation devices within the lateral resisting frames have been successfully used to limit inelastic deformation in reinforced concrete buildings by increasing damping and/or altering the stiffness of these structures. However, there is a need to investigate and develop systems with self-centering capabilities; systems that are able to assist in returning a structure to its original position after an earthquake. In this project, the efficacy of a shape memory alloy (SMA) based device, as a structural recentering device is evaluated through numerical analysis using the OpenSees framework. OpenSees is a software framework for simulating the seismic response of structural and geotechnical systems. OpenSees has been developed as the computational platform for research in performance-based earthquake engineering at the Pacific Earthquake Engineering Research Center (PEER). A non-ductile reinforced concrete building, which is modelled using OpenSees and verified with available experimental data is used for the analysis in this study. The model is fitted with Tension/Compression (TC) SMA devices. The performance of the SMA recentering device is evaluated for a set of near-field and far-field ground motions. Critical performance measures of the analysis include residual displacements, interstory drift and acceleration (horizontal and vertical) for different types of ground motions. The results show that the TC device's performance is unaffected by the type of ground motion. The analysis also shows that the inclusion of the device in the lateral force resisting system of the building resulted in a 50% decrease in peak horizontal displacement, and inter-story drift elimination of residual deformations, acceleration was increased up to 110%.
Moving beyond traditional null hypothesis testing: evaluating expectations directly
van de Schoot, R.; Hoijtink, H.J.A.; Romeijn, J.W.
2011-01-01
This mini-review illustrates that testing the traditional null hypothesis is not always the appropriate strategy. Half in jest, we discuss Aristotle's scientific investigations into the shape of the earth in the context of evaluating the traditional null hypothesis. We conclude that Aristotle was ac
New Directions in Open Classroom Evaluation: Situational Tasks.
Rentfrow, Robert K.
The material reported here was developed as part of a systematic effort to develop techniques to evaluate the effectiveness of a nationally implemented early childhood program. The Classroom Attitude Observation Schedule technique has been implemented in a number of school districts as a means of assessing program implementation of the Tucson…
Ryabinkin, Ilya G; Izmaylov, Artur F
2015-01-01
We have developed a numerical differentiation scheme which eliminates evaluation of overlap determinants in calculating the time-derivative non-adiabatic couplings (TDNACs). Evaluation of these determinants was a bottleneck in previous implementations of mixed quantum-classical methods using numerical differentiation of electronic wave functions in the Slater-determinant representation. The central idea of our approach is, first, to reduce the analytic time derivatives of Slater determinants to time derivatives of molecular orbitals, and then to apply a finite-difference formula. Benchmark calculations prove the efficiency of the proposed scheme showing impressive several-order-of-magnitude speedups of the TDNAC calculation step for midsize molecules.
pySecDec: a toolbox for the numerical evaluation of multi-scale integrals arXiv
Borowka, S.; Jahn, S.; Jones, S.P.; Kerner, M.; Schlenk, J.; Zirke, T.
We present pySecDec, a new version of the program SecDec, which performs the factorisation of dimensionally regulated poles in parametric integrals, and the subsequent numerical evaluation of the finite coefficients. The algebraic part of the program is now written in the form of python modules, which allow a very flexible usage. The optimization of the C++ code, generated using FORM, is improved, leading to a faster numerical convergence. The new version also creates a library of the integrand functions, such that it can be linked to user-specific codes for the evaluation of matrix elements in a way similar to analytic integral libraries.
Institute of Scientific and Technical Information of China (English)
Hong Jin; Teng Shao
2014-01-01
The wind environment around residential building groups is increasingly concerned, while the dwelling groups as the elementary unit of planning design, its quality of surrounding wind environment will directly affect people’ s life. This study based on the climatic conditions of severe cold regions, selects four dwellings groups with different openings scale and position as the research objects, and then simulates and analyzes the wind speed distribution characteristics of each pattern. Meanwhile, it extracts the wind speed values of one hundred points of each pattern and applies the coefficient of uniformity method to the ecological evaluation. It has been found that grouping pattern of buildings has a dramatic effect on the resulting airflow behavior. Configurations that contain a T⁃shaped central space with small opened side can effectively prevent and contain airflow in the site offer. The interactive influence between layout of dwelling groups and wind environment are explored, so as to provide basis for the planning design of dwelling groups.
Numerical evaluation of the Kalina cycle for concentrating solar power plants
DEFF Research Database (Denmark)
Modi, Anish
of using a Kalina cycle is evaluated with a thermoeconomic optimization with a turbine inlet temperature of 500 C for a central receiver solar power plant with direct vapour generation, and 370 C for a parabolic trough solar power plant with Therminol VP-1 as the solar field heat transfer fluid. No thermal......Concentrating solar power plants use a number of reflecting mirrors to focus and convert the incident solar energy to heat, and a power cycle to convert this heat into electricity. One of the key challenges currently faced by the solar industry is the high cost of electricity production....... These costs may be driven down by developing more cost-effective plant components and improving the system designs. This thesis focuses on the power cycle aspect of the concentrating solar power plants by studying the use a Kalina cycle with ammonia-water mixtures as the cycle working fluid. The potential...
Borehole Radar Evaluation Program: Antenna designs for optimal directionality
Castle, J. G.; Morris, H. E.
1991-05-01
The thrust of this progress report deals with the significant advances we have made in the past few months toward optimal radiating efficiency and optimal directionality from antenna arrays that fit inside a 5.5 in.-OD tool. The reasons spawning this development effort on antennas are the many uses for underground radar systems that can be built around such high-performance antennas. Targets of interest include large man-made voids, natural voids in strata, fractures zones in hard rock, edges and internal faults in salts domes and glaciers, etc. Recent progress includes observation of the radiation patterns of several dipole arrays which we designed to fit within a 5.5-inch OD borehole tool and to radiate efficiently at wavelengths in the band from 0.4 meter to 2 meters with optimal directionality. Front-to-back ratios of 15 dB are consistently observed in the horizontal plane of these arrays. These antennas are observed to radiate with high efficiencies, less than 1 dB loss, into air at 1.3 meter wavelength.
Borehole Radar Evaluation Program: Antenna designs for optimal directionality
Energy Technology Data Exchange (ETDEWEB)
Castle, J.G.; Morris, H.E.
1991-05-01
The thrust of this progress report deals with the significant advances we have made in the past few months toward optimal radiating efficiency and optimal directionality from antenna arrays that fit inside a 5.5 in.-OD tool. The reasons spawning this development effort on antennas are the many uses for underground radar systems that can be built around such high-performance antennas. Targets of interest include large man-made voids, natural voids in strata, fractures zones in hard rock, edges and internal faults in salts domes and glaciers, etc. Recent progress includes observation of the radiation patterns of several dipole arrays which we designed to fit within a 5.5-inch OD borehole tool and to radiate efficiently at wavelengths in the band from 0.4 meter to 2 meters with optimal directionality. Front-to-back ratios of 15 dB are consistently observed in the horizontal plane of these arrays. These antennas are observed to radiate with high efficiencies, less than 1 dB loss, into air at 1.3 meter wavelength. 18 figs.
Energy Technology Data Exchange (ETDEWEB)
Dritselis, Chris D, E-mail: dritseli@mie.uth.gr [Mechanical Engineering Department, University of Thessaly, Pedion Areos, 38334 Volos (Greece)
2016-02-15
The budgets of the Reynolds stress and streamwise enstrophy are evaluated through direct numerical simulations for the turbulent particle-laden flow in a vertical channel with momentum exchange between the two phases. The influence of the dispersed particles on the budgets is examined through a comparison of the particle-free and the particle-laden cases at the same Reynolds number of Re{sub b} = 5600 based on the bulk fluid velocity and the distance between the channel walls. Results are obtained for particle ensembles with four response times in simulations with and without streamwise gravity and inter-particle collisions at average mass (volume) fractions of 0.2 (2.7 × 10{sup −5}) and 0.5 (6.8 × 10{sup −5}). The particle feedback force on the flow of the carrier phase is modeled by a point-force approximation (PSIC-method). It is shown that all the terms in the budgets of the Reynolds stress components are decreased in the presence of particles. The level of reduction depends on the particle response time and it is higher under the effects of gravity and inter-particle collisions. A considerable reduction in all the terms of the streamwise enstrophy budget is also observed. In particular, all production mechanisms, and mainly vortex stretching, are inhibited in the particulate flows and thus the production of streamwise vorticity is significantly damped. A further insight into the direct particle effects on the fluid turbulence is provided by analyzing in detail the fluid–fluid, fluid–particle and particle–particle correlations, and the spectra of the fluid–particle energy exchange rate. The present results indicate that the turbulence production, dissipation and pressure–strain term are generally large quantities, but their summation is relatively small and comparable to the fluid–particle direct energy exchange rate. Consequently, the particle contribution can potentially increase or decrease the fluctuating fluid velocities and eventually
Evaluating the use of high-resolution numerical weather forecast for debris flow prediction.
Nikolopoulos, Efthymios I.; Bartsotas, Nikolaos S.; Borga, Marco; Kallos, George
2015-04-01
The sudden occurrence combined with the high destructive power of debris flows pose a significant threat to human life and infrastructures. Therefore, developing early warning procedures for the mitigation of debris flows risk is of great economical and societal importance. Given that rainfall is the predominant factor controlling debris flow triggering, it is indisputable that development of effective debris flows warning procedures requires accurate knowledge of the properties (e.g. duration, intensity) of the triggering rainfall. Moreover, efficient and timely response of emergency operations depends highly on the lead-time provided by the warning systems. Currently, the majority of early warning systems for debris flows are based on nowcasting procedures. While the latter may be successful in predicting the hazard, they provide warnings with a relatively short lead-time (~6h). Increasing the lead-time is necessary in order to improve the pre-incident operations and communication of the emergency, thus coupling warning systems with weather forecasting is essential for advancing early warning procedures. In this work we evaluate the potential of using high-resolution (1km) rainfall fields forecasted with a state-of-the-art numerical weather prediction model (RAMS/ICLAMS), in order to predict the occurrence of debris flows. Analysis is focused over the Upper Adige region, Northeast Italy, an area where debris flows are frequent. Seven storm events that generated a large number (>80) of debris flows during the period 2007-2012 are analyzed. Radar-based rainfall estimates, available from the operational C-band radar located at Mt Macaion, are used as the reference to evaluate the forecasted rainfall fields. Evaluation is mainly focused on assessing the error in forecasted rainfall properties (magnitude, duration) and the correlation in space and time with the reference field. Results show that the forecasted rainfall fields captured very well the magnitude and
Evaluation of the influence mode on the CVC GaN HEMT using numerical modeling
Parnes, Ya M.; Tikhomirov, V. G.; Petrov, V. A.; Gudkov, A. G.; Marzhanovskiy, I. N.; Kukhareva, E. S.; Vyuginov, V. N.; Volkov, V. V.; Zybin, A. A.
2016-08-01
Done numerically simulated the effects of certain modes of operation on the CVC of field microwave transistors on the basis of heterostructures AlGaN / GaN (HEMT). The results of these studies suggest the possibility of quite efficient use of numerical simulation for the development of HEMT microwave transistors allowing for the real instrument designs.
Evaluation of bleeding in patients receiving direct oral anticoagulants.
Hellenbart, Erika L; Faulkenberg, Kathleen D; Finks, Shannon W
2017-01-01
Direct oral anticoagulants (DOACs) are recognized by evidence-based treatment guidelines as the first-line option for the treatment of venous thromboembolism and prevention of stroke and systemic embolism in nonvalvular atrial fibrillation. As use of these anticoagulants has become favored over the past several years, reported bleeding-related adverse drug events with these agents has increased. In randomized clinical trials, all DOACs have a reduced risk for intracranial hemorrhage, while major and other bleeding results have varied among the agents compared to vitamin K antagonists. We have reviewed the bleeding incidence and severity from randomized and real-world data in patients receiving DOACs in an effort to provide the clinician with a critical review of bleeding and offer practical considerations for avoiding adverse events with these anticoagulants.
Numerical Surrogates for Human Observers in Myocardial Motion Evaluation From SPECT Images.
Marin, Thibault; Kalayeh, Mahdi M; Parages, Felipe M; Brankov, Jovan G
2014-01-01
In medical imaging, the gold standard for image-quality assessment is a task-based approach in which one evaluates human observer performance for a given diagnostic task (e.g., detection of a myocardial perfusion or motion defect). To facilitate practical task-based image-quality assessment, model observers are needed as approximate surrogates for human observers. In cardiac-gated SPECT imaging, diagnosis relies on evaluation of the myocardial motion as well as perfusion. Model observers for the perfusion-defect detection task have been studied previously, but little effort has been devoted toward development of a model observer for cardiac-motion defect detection. In this work, we describe two model observers for predicting human observer performance in detection of cardiac-motion defects. Both proposed methods rely on motion features extracted using previously reported deformable mesh model for myocardium motion estimation. The first method is based on a Hotelling linear discriminant that is similar in concept to that used commonly for perfusion-defect detection. In the second method, based on relevance vector machines (RVM) for regression, we compute average human observer performance by first directly predicting individual human observer scores, and then using multi reader receiver operating characteristic analysis. Our results suggest that the proposed RVM model observer can predict human observer performance accurately, while the new Hotelling motion-defect detector is somewhat less effective.
Evaluation of the Direct View Storage Display for Signal Analysis
1976-03-01
evaluation as completed was on NUNIX [1]/ which is an NPS oriainated version of the original Bell Laos UNIX [11] operating system. Due to the nature of a...March 197b. 5. Bell Laboratories* P rpgr amm i nq i n C an w . Kernighan , 197a. - A Tutorial* Br i - 6. Lewin* Morton H., An Introduction to Computer...Ref e rence Manua 1 * Dennis M . January 197a. Ritchie* 79 11. Ritchie* D.E. and Thompson, K . , " The Unix Timesharing Svstpw " , Communications of the
Olivares-Rivas, Wilmer; Colmenares, Pedro J; López, Floralba
2013-08-21
We derive expressions for the transverse diffusion coefficient D(z) and the average persistence time τ(z; L) within a layer of width L, for particles of a non-homogeneous fluid enclosed in a planar nanopore. The method allows the direct evaluation of these position-dependent dynamical quantities from the equilibrium local particle density profile. We use results for the density and persistence time profiles from the virtual layer molecular dynamics method to numerically assess the significance of the Smoluchowski approximation.
Evaluation of CSSR with Direct TCH Assignment in Cellular Networks
Directory of Open Access Journals (Sweden)
Paula Aninyie
2014-08-01
Full Text Available Global System for Mobile communication (GSM operators make use of Key Performance Indicators (KPIs to appreciate the network performance and evaluate the Quality of Service (QoS regarding end user perceived quality. KPIs are therefore becoming increasingly important in the context of network rollouts as well as within mature network optimization cycles. The performance of the mobile network is measured based on several counters describing the most important events over a measurement period. The KPIs are derived with the help of these counters using different formulations. Call Setup Success Rate (CSSR is one of the most important KPIs used by all mobile operators. In Ouagadougou, Burkina-Faso, most of the active workers and remote area farmers rely largely on mobile communication services; the GPRS as data services remain highly competitive with GSM voice services. This paper presents a comparative evaluation of theoretically estimated CSSR to measured CSSR data on a real network with regard to GPRS services. The measured data was obtained from the Nokia Siemens Network (NSN statistical tool. The results obtained showed significant improvements in areas where sharp drops in CSSR values were recorded for the measured CSSR. Significantly high R square values of close to 1 representing a high predictive ability from the regression analysis of the estimated CSSR were also recorded. It was concluded that the implementation of the CSSR formulation be extended to CSSR measurements to ensure increased subscriber satisfaction.
Wu, Mingliang; Yang, Fei; Rong, Mingzhe; Wu, Yi; Qi, Yang; Cui, Yufei; Liu, Zirui; Guo, Anxiang
2016-04-01
This paper focuses on the numerical investigation of arc characteristics in an air direct current circuit breaker (air DCCB). Using magneto-hydrodynamics (MHD) theory, 3D laminar model and turbulence model are constructed and calculated. The standard k-epsilon model is utilized to consider the turbulence effect in the arc chamber of the DCCB. Several important phenomena are found: the arc column in the turbulence-model case is more extensive, moves much more slowly than the counterpart in the laminar-model case, and shows stagnation at the entrance of the chamber, unlike in the laminar-model case. Moreover, the arc voltage in the turbulence-model case is much lower than in the laminar-model case. However, the results in the turbulence-model case show a much better agreement with the results of the breaking experiments under DC condition than in the laminar-model case, which is contradictory to the previous conclusions from the arc researches of both the low-voltage circuit breaker and the sulfur hexafluoride (SF6) nozzle. First, in the previous air-arc research of the low-voltage circuit breaker, it is assumed that the air plasma inside the chamber is in the state of laminar, and the laminar-model application gives quite satisfactory results compared with the experiments, while in this paper, the laminar-model application works badly. Second, the turbulence-model application in the arc research of the SF6-nozzle performs much better and gives higher arc voltage than the laminar-model application does, whereas in this paper, the turbulence-model application predicts lower arc voltage than the laminar-model application does. Based on the analysis of simulation results in detail, the mechanism of the above phenomena is revealed. The transport coefficients are strongly changed by turbulence, which will enhance the arc diffusion and make the arc volume much larger. Consequently, the arc appearance and the distribution of Lorentz force in the turbulence-model case
Numerical Evaluation of Parameter Correlation in the Hartmann-Tran Line Profile
Adkins, Erin M.; Reed, Zachary; Hodges, Joseph T.
2017-06-01
The partially correlated quadratic, speed-dependent hard-collision profile (pCqSDHCP), for simplicity referred to as the Hartmann-Tran profile (HTP), has been recommended as a generalized lineshape for high resolution spectroscopy. The HTP parameterizes complex collisional effects such as Dicke narrowing, speed dependent narrowing, and correlations between velocity-changing and dephasing collisions, while also simplifying to simpler profiles that are widely used, such as the Voigt profile. As advanced lineshape profiles are adopted by more researchers, it is important to understand the limitations that data quality has on the ability to retrieve physically meaningful parameters using sophisticated lineshapes that are fit to spectra of finite signal-to-noise ratio. In this work, spectra were simulated using the HITRAN Application Programming Interface (HAPI) across a full range of line parameters. Simulated spectra were evaluated to quantify the precision with which fitted lineshape parameters can be determined at a given signal-to-noise ratio, focusing on the numerical correlation between the retrieved Dicke narrowing frequency and the velocity-changing and dephasing collisions correlation parameter. Tran, H., N. Ngo, and J.-M. Hartmann, Journal of Quantitative Spectroscopy and Radiative Transfer 2013. 129: p. 89-100. Tennyson, et al., Pure Appl. Chem. 2014, 86: p. 1931-1943. Kochanov, R.V., et al., Journal of Quantitative Spectroscopy and Radiative Transfer 2016. 177: p. 15-30. Tran, H., N. Ngo, and J.-M. Hartmann, Journal of Quantitative Spectroscopy and Radiative Transfer 2013. 129: p. 199-203.
Directory of Open Access Journals (Sweden)
Shim S.M.
2012-01-01
Full Text Available The performance of the CO2 absorber column using mono-ethanolamine (MEA solution as chemical solvent are predicted by a One-Dimensional (1-D rate based model in the present study. 1-D Mass and heat balance equations of vapor and liquid phase are coupled with interfacial mass transfer model and vapor-liquid equilibrium model. The two-film theory is used to estimate the mass transfer between the vapor and liquid film. Chemical reactions in MEA-CO2-H2O system are considered to predict the equilibrium pressure of CO2 in the MEA solution. The mathematical and reaction kinetics models used in this work are calculated by using in-house code. The numerical results are validated in the comparison of simulation results with experimental and simulation data given in the literature. The performance of CO2 absorber column is evaluated by the 1-D rate based model using various reaction rate coefficients suggested by various researchers. When the rate of liquid to gas mass flow rate is about 8.3, 6.6, 4.5 and 3.1, the error of CO2 loading and the CO2 removal efficiency using the reaction rate coefficients of Aboudheir et al. is within about 4.9 % and 5.2 %, respectively. Therefore, the reaction rate coefficient suggested by Aboudheir et al. among the various reaction rate coefficients used in this study is appropriate to predict the performance of CO2 absorber column using MEA solution. [Acknowledgement. This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF, funded by the Ministry of Education, Science and Technology (2011-0017220].
Evaluating theories of bird song learning: implications for future directions.
Margoliash, D
2002-12-01
Studies of birdsong learning have stimulated extensive hypotheses at all levels of behavioral and physiological organization. This hypothesis building is valuable for the field and is consistent with the remarkable range of issues that can be rigorously addressed in this system. The traditional instructional (template) theory of song learning has been challenged on multiple fronts, especially at a behavioral level by evidence consistent with selectional hypotheses. In this review I highlight the caveats associated with these theories to better define the limits of our knowledge and identify important experiments for the future. The sites and representational forms of the various conceptual entities posited by the template theory are unknown. The distinction between instruction and selection in vocal learning is not well established at a mechanistic level. There is as yet insufficient neurophysiological data to choose between competing mechanisms of error-driven learning and reinforcement learning. Both may obtain for vocal learning. The possible role of sleep in acoustic or procedural memory consolidation, while supported by some physiological observations, does not yet have support in the behavioral literature. The remarkable expansion of knowledge in the past 20 years and the recent development of new technologies for physiological and behavioral experiments should permit direct tests of these theories in the coming decade.
Design and performance evaluation of direct routing mobile IP
Jang, Jongwook; Jang, SeongHo; Kim, Kilyeun; Lee, Jung-Tae
2001-07-01
Mobility support on the network layer is of special importance, as the network layer holds together the huge Internet with common protocol IP. Although based on possibility different wireless or wired technologies, all nodes of the network should be able to communicate. Therefore, mobile IP (an extension of the classical IP) has been designed which enables mobility in the Internet without changing existing wired systems. However, mobile IP leaves some points unsolved. Especially, if it comes to security, efficient of the packet flow that is called triangular routing. Especially triangular routing can cause unnecessary overhead for the network. Furthermore latency can increase dramatically. This is particularly unfortunate if two communicating hosts are separated by transatlantic links. In order to this problem, many methods like IPv6 and ROMIP are proposed. But these methods have limitation. In other words, they have not compatibility because of needing modification or original IP scheme. Especially ROMIP is very complex and the overhead of control message and processing are serious. The problem of inconsistency of Binding caches may occur tool. We therefore propose and analyze the DRMIP (Direct Routing Mobile IP) which do not modify IP source needed in the sender, is compatible with IP and Mobile IP.
Grieco, F.; Capra, L.; Groppelli, G.; Norini, G.
2007-05-01
The present study concerns the numerical modeling of debris avalanches on the Nevado de Toluca Volcano (Mexico) using TITAN2D simulation software, and its application to create hazard maps. Nevado de Toluca is an andesitic to dacitic stratovolcano of Late Pliocene-Holocene age, located in central México near to the cities of Toluca and México City; its past activity has endangered an area with more than 25 million inhabitants today. The present work is based upon the data collected during extensive field work finalized to the realization of the geological map of Nevado de Toluca at 1:25,000 scale. The activity of the volcano has developed from 2.6 Ma until 10.5 ka with both effusive and explosive events; the Nevado de Toluca has presented long phases of inactivity characterized by erosion and emplacement of debris flow and debris avalanche deposits on its flanks. The largest epiclastic events in the history of the volcano are wide debris flows and debris avalanches, occurred between 1 Ma and 50 ka, during a prolonged hiatus in eruptive activity. Other minor events happened mainly during the most recent volcanic activity (less than 50 ka), characterized by magmatic and tectonic-induced instability of the summit dome complex. According to the most recent tectonic analysis, the active transtensive kinematics of the E-W Tenango Fault System had a strong influence on the preferential directions of the last three documented lateral collapses, which generated the Arroyo Grande and Zaguàn debris avalanche deposits towards E and Nopal debris avalanche deposit towards W. The analysis of the data collected during the field work permitted to create a detailed GIS database of the spatial and temporal distribution of debris avalanche deposits on the volcano. Flow models, that have been performed with the software TITAN2D, developed by GMFG at Buffalo, were entirely based upon the information stored in the geological database. The modeling software is built upon equations
Kamiya, Tetsu; Toyama, Yoshio; Michiwaki, Yukihiro; Kikuchi, Takahiro
2013-01-01
The aim of the present study was to evaluate the possibility of numerical simulation of the swallowing process using a moving particle simulation (MPS) method, which defined the food bolus as a number of particles in a fluid, a solid, and an elastic body. In order to verify the accuracy of the simulation results, a simple water bolus falling model was solved using the three-dimensional (3D) MPS method. We also examined the simplified swallowing simulation using a two-dimensional (2D) MPS method to confirm the interactions between the liquid, solid, elastic bolus, and organ structure. In a comparison of the 3D MPS simulation and experiments, the falling time of the water bolus and the configuration of the interface between the liquid and air corresponded exactly to the experimental measurements and the visualization images. The results showed that the accuracy of the 3D MPS simulation was qualitatively high for the simple falling model. Based on the results of the simplified swallowing simulation using the 2D MPS method, each bolus, defined as a liquid, solid, and elastic body, exhibited different behavior when the organs were transformed forcedly. This confirmed that the MPS method could be used for coupled simulations of the fluid, the solid, the elastic body, and the organ structures. The results suggested that the MPS method could be used to develop a numerical simulator of the swallowing process.
Kalmykov, M Yu
2004-01-01
Generalized log-sine functions appear in higher order epsilon-expansion of different Feynman diagrams. We present an algorithm for numerical evaluation of these functions of real argument. This algorithm is implemented as C++ library with arbitrary-precision arithmetics for integer 0 1. Some new relations and representations for the generalized log-sine functions are given.
Performance evaluation and improvement directions for an Indian electric utility
Energy Technology Data Exchange (ETDEWEB)
Yadav, Vinod Kumar, E-mail: vinod@gbu.ac.in [Electrical Engineering Department, Gautam Buddha University, Greater Noida 201310 (India); Padhy, N.P.; Gupta, H.O. [Electrical Engineering Department, Indian Institute of Technology, Roorkee 247667 (India)
2011-11-15
This study evaluates the performance of 29 Electricity Distribution Divisions (EDDs) of an Indian state - Uttarakhand - deploying Input oriented Data Envelopment Analysis (DEA). The results indicate that the performance of several EDDs is sub-optimal, suggesting the potential for cost reductions and possible reduction in employees number. In the DEA method more than one unit are identified as efficient. Therefore, this study suggests a method for ranking the efficient units by their importance as benchmarks for the inefficient units through benchmark share measure. The bigger the benchmark share, the more important an efficient division is in benchmarking for inefficient ones. Result reveals that plain area divisions are relatively efficient and have higher potential to influence the performance of inefficient EDDs. This study is envisaged to be instrumental to policy makers and managers to increase the operational efficiency of inefficient EDDs and thereby increase the competitiveness in the face of restructuring and liberalization of Indian electricity sector. - Highlights: > Plain area divisions are more effective in integrating resources than hilly divisions. > For prevalent inefficiency two models are developed to varying environmental conditions. > Benchmark share identifies the variable that is influential in increasing the efficiency. > Savings in terms of reduction in O and M cost and number of Employees. > Findings of research work redefine the view point of the utility planners.
EVALUATION OF THREE-DIMENSIONAL NUMERICAL MODEL FOR SALINE INTRUSION AND PURGING IN SEWAGE OUTFALLS
Institute of Scientific and Technical Information of China (English)
WU Wei; YAN Zhong-min
2007-01-01
Saline intrusion into sewage outfalls will greatly decrease the efficiency of the structures. The numerical model for this flow has been limited to one- and two-dimensional ones. In this article, a three-dimensional numerical model for saline intrusion and purging in sewage outfalls was developed. The flow was modeled in three dimensions under turbulent conditions with the RNG turbulence model. The numerical results provided quantitative evidence of the fundamental flow mechanisms that took place during saline intrusion and purging. The comparisons of the results with that of two-dimensional model and that of experiments indicate that the three-dimensional numerical model developed in this article is more effective in predicting the internal flow in outfalls.
Evaluation of combined direct-push methods used for aquifer model generation.
Köber, Ralf; Hornbruch, Götz; Leven, Carsten; Tischer, Lars; Grossmann, Jochen; Dietrich, Peter; Weiss, Holger; Dahmke, Andreas
2009-01-01
Most established methods to characterize aquifer structure and hydraulic conductivities of hydrostratigraphical units are not capable of delivering sufficient information in the spatial resolution that is desired for sophisticated numerical contaminant transport modeling and adapted remediation design. With hydraulic investigation methods based on the direct-push (DP) technology such as DP slug tests, DP injection logging, and the hydraulic profiling tool, it is possible to rapidly delineate hydrogeological structures and estimate their hydraulic conductivity in shallow unconsolidated aquifers without the need for wells. A combined application of these tools was used for the investigation of a contaminated German refinery site and for the setup of hydraulic aquifer models. The quality of DP investigation and the models was evaluated by comparisons of tracer transport simulations using these models and measured breakthroughs of two natural gradient tracer tests. Model scenarios considering the information of all tools together showed good reproduction of the measured breakthroughs, indicating the suitability of the approach and a minor impact of potential technical limitations. Using the DP slug tests alone yielded significantly higher deviations for the determined hydraulic conductivities compared to considering two or three of the tools. Realistic aquifer models developed on basis of such combined DP investigation approaches can help optimize remediation concepts or identify flow regimes for aquifers with a complex structure.
Evaluating next-generation sequencing for direct clinical diagnostics in diarrhoeal disease.
Joensen, K G; Engsbro, A L Ø; Lukjancenko, O; Kaas, R S; Lund, O; Westh, H; Aarestrup, F M
2017-03-11
The accurate microbiological diagnosis of diarrhoea involves numerous laboratory tests and, often, the pathogen is not identified in time to guide clinical management. With next-generation sequencing (NGS) becoming cheaper, it has huge potential in routine diagnostics. The aim of this study was to evaluate the potential of NGS-based diagnostics through direct sequencing of faecal samples. Fifty-eight clinical faecal samples were obtained from patients with diarrhoea as part of the routine diagnostics at Hvidovre University Hospital, Denmark. Ten samples from healthy individuals were also included. DNA was extracted from faecal samples and sequenced on the Illumina MiSeq system. Species distribution was determined with MGmapper and NGS-based diagnostic prediction was performed based on the relative abundance of pathogenic bacteria and Giardia and detection of pathogen-specific virulence genes. NGS-based diagnostic results were compared to conventional findings for 55 of the diarrhoeal samples; 38 conventionally positive for bacterial pathogens, two positive for Giardia, four positive for virus and 11 conventionally negative. The NGS-based approach enabled detection of the same bacterial pathogens as the classical approach in 34 of the 38 conventionally positive bacterial samples and predicted the responsible pathogens in five of the 11 conventionally negative samples. Overall, the NGS-based approach enabled pathogen detection comparable to conventional diagnostics and the approach has potential to be extended for the detection of all pathogens. At present, however, this approach is too expensive and time-consuming for routine diagnostics.
Andersson, A.
2005-08-01
The ability to predict surface defects in outer panels is of vital importance in the automotive industry, especially for brands in the premium car segment. Today, measures to prevent these defects can not be taken until a test part has been manufactured, which requires a great deal of time and expense. The decision as to whether a certain surface is of acceptable quality or not is based on subjective evaluation. It is quite possible to detect a defect by measurement, but it is not possible to correlate measured defects and the subjective evaluation. If all results could be based on the same criteria, it would be possible to compare a surface by both FE simulations, experiments and subjective evaluation with the same result. In order to find a solution concerning the prediction of surface defects, a laboratory tool was manufactured and analysed both experimentally and numerically. The tool represents the area around a fuel filler lid and the aim was to recreate surface defects, so-called "teddy bear ears". A major problem with the evaluation of such defects is that the panels are evaluated manually and to a great extent subjectivity is involved in the classification and judgement of the defects. In this study the same computer software was used for the evaluation of both the experimental and the numerical results. In this software the surface defects were indicated by a change in the curvature of the panel. The results showed good agreement between numerical and experimental results. Furthermore, the evaluation software gave a good indication of the appearance of the surface defects compared to an analysis done in existing tools for surface quality measurements. Since the agreement between numerical and experimental results was good, this indicates that these tools can be used for an early verification of surface defects in outer panels.
Energy Technology Data Exchange (ETDEWEB)
Andrea Prosperetti
2006-03-24
The report briefly describes the activities carried out in the course of the project. A first line of research was the development of systematic closure relations for averaged equations for disperse multiphase flow. A second line was the development of efficient numerical methods for the simulation of Navier-Stokes flows with many suspended particles. The report also lists the 21 journal articles in which this work is more fully decsribed.
2014-12-06
SECURITY CLASSIFICATION OF: The research employed stable boundary layer measurements using the DataHawk UAV and high-resolution direct numerical...simulations ( DNS ) to examine the interactions and instabilities occurring in multi-scale flows that drive intermittent turbulence events in the stable...atmosphere. Both measurements and the DNS revealed the occurrence and persistence of sheet-and-layer structures in the temperature and velocity fields that
Numerical prediction of slamming loads
DEFF Research Database (Denmark)
Seng, Sopheak; Jensen, Jørgen J; Pedersen, Preben T
2012-01-01
. The pressure distribution as well as the total force is then determined by integration over a pseudo-three-dimensional presentation of the hull geometry.In this paper the evaluation of the slamming load is taken one step further by performing direct three-dimensional, fully non-linear numerical calculations...... in a realistic wave environment.Both the global and the local slamming loads are assessed numerically using a finite-volume formulation with the free surface captured by a volume-of-fluid technique. This numerical procedure is justified by comprehensive validation studies where numerically evaluated slamming...... pressures are compared with experimentally measured results.To obtain an insight into the three-dimensional flow effects the next step is to apply the validated numerical procedure to evaluate and compare the accuracy and performance of the traditionally used two-dimensional formulations by a comparison...
Ballarini, E; Bauer, S; Eberhardt, C; Beyer, C
2012-06-01
Transverse dispersion represents an important mixing process for transport of contaminants in groundwater and constitutes an essential prerequisite for geochemical and biodegradation reactions. Within this context, this work describes the detailed numerical simulation of highly controlled laboratory experiments using uranine, bromide and oxygen depleted water as conservative tracers for the quantification of transverse mixing in porous media. Synthetic numerical experiments reproducing an existing laboratory experimental set-up of quasi two-dimensional flow through tank were performed to assess the applicability of an analytical solution of the 2D advection-dispersion equation for the estimation of transverse dispersivity as fitting parameter. The fitted dispersivities were compared to the "true" values introduced in the numerical simulations and the associated error could be precisely estimated. A sensitivity analysis was performed on the experimental set-up in order to evaluate the sensitivities of the measurements taken at the tank experiment on the individual hydraulic and transport parameters. From the results, an improved experimental set-up as well as a numerical evaluation procedure could be developed, which allow for a precise and reliable determination of dispersivities. The improved tank set-up was used for new laboratory experiments, performed at advective velocities of 4.9 m d(-1) and 10.5 m d(-1). Numerical evaluation of these experiments yielded a unique and reliable parameter set, which closely fits the measured tracer concentration data. For the porous medium with a grain size of 0.25-0.30 mm, the fitted longitudinal and transverse dispersivities were 3.49×10(-4) m and 1.48×10(-5) m, respectively. The procedures developed in this paper for the synthetic and rigorous design and evaluation of the experiments can be generalized and transferred to comparable applications.
Evaluation of a transfinite element numerical solution method for nonlinear heat transfer problems
Cerro, J. A.; Scotti, S. J.
1991-01-01
Laplace transform techniques have been widely used to solve linear, transient field problems. A transform-based algorithm enables calculation of the response at selected times of interest without the need for stepping in time as required by conventional time integration schemes. The elimination of time stepping can substantially reduce computer time when transform techniques are implemented in a numerical finite element program. The coupling of transform techniques with spatial discretization techniques such as the finite element method has resulted in what are known as transfinite element methods. Recently attempts have been made to extend the transfinite element method to solve nonlinear, transient field problems. This paper examines the theoretical basis and numerical implementation of one such algorithm, applied to nonlinear heat transfer problems. The problem is linearized and solved by requiring a numerical iteration at selected times of interest. While shown to be acceptable for weakly nonlinear problems, this algorithm is ineffective as a general nonlinear solution method.
Hughes, R. D.; Charng, T.
1983-01-01
A computerized model was developed for analyzing the temperature distribution of a two dimensional body which is located at or near the soil surface and is partially exposed to solar radiation. The body may have one or more interior cavities containing air or another fluid. The methodology which evolved is also applicable to a general class of thermal analyses involving a body surrounded by a semi-infinite medium exposed to surface radiation energy. The theoretical analysis, numerical procedure, and a sample case are discussed.
DEFF Research Database (Denmark)
Yang, Zhiwen; Liu, Shuxue; Bingham, Harry B.
2013-01-01
of regular waves, and the re-reflection control on the wave paddle is also not included. In order to validate the solution methodology further, a series of nonlinear, periodic waves based on stream function theory are generated in a physical wave tank using a piston-type wavemaker. These experiments show......A full second-order theory for coupling numerical and physical wave tanks is presented. The ad hoc unified wave generation approach developed by Zhang et al. [Zhang, H., Schäffer, H.A., Jakobsen, K.P., 2007. Deterministic combination of numerical and physical coastal wave models. Coast. Eng. 54...... nonlinear wave generation in the physical wave tank based on target numerical solutions. The performance and efficiency of the new model is first evaluated theoretically based on second order Stokes waves. Due to the complexity of the problem, the proposed method has been truncated at 2D and the treatment...
A novel state-space based method for direct numerical simulation of particle-laden turbulent flows
Ranjan, Reetesh; Pantano, Carlos
2012-11-01
We present a novel state-space-based numerical method for transport of the particle density function, which can be used to investigate particle-laden turbulent flows. Here, the problem can be stated purely in a deterministic Eulerian framework. The method is coupled to an incompressible three-dimensional flow solver. We consider a dilute suspension where the volume fraction and mass loading of the particles in the flow are low enough so that the approximation of one-way coupling remains valid. The particle transport equation is derived from the governing equation of the particle dynamics described in a Lagrangian frame, by treating position and velocity of the particle as state-space variables. Application and features of this method will be demonstrated by simulating a particle-laden decaying isotropic turbulent flow. It is well known that even in an isotropic turbulent flow, the distribution of particles is not uniform. For example, heavier-than-fluid particles tend to accumulate in regions of low vorticity and high strain rate. This lead to large regions in the flow where particles remain sparsely distributed. The new approach can capture the statistics of the particle in such sparsely distributed regions in an accurate manner compared to other numerical methods.
Evaluate shock capturing capability with the numerical methods in OpenFOAM
Directory of Open Access Journals (Sweden)
Khodadadi Azadboni Reza
2013-01-01
Full Text Available Simulations for both multiphase flows and supersonic single phased flows are well known, however the combination is a less investigated area of research, as the two basic approaches of CFD, the pressure and the density based approach, each describe one of the phases in a better way than the other one. In this paper, we systematically investigate the solver quality of the open source CFD code OpenFOAM in handling transonic flow phenomena that typically occur inside the breaking chamber of high voltage circuit breakers, during contact separation. The solver quality is then compared with that of chosen commercial CFD tools. The main advantage of OpenFOAM is that, contrary to most of the commercial simulation tools, it is license fee free and allows access to the source code. This means that complicated multi physics phenomena inside the arcing chamber can be directly modeled into the code by users, which opens an opportunity to remove limitations of commercial CFD tools. Particularly, the shock capturing capability of OpenFOAM will be evaluated for the transonic internal flow which typically occurs in high voltage circuit breakers. Overall, Open-FOAM shows acceptable shock capturing capabilities in the performed verification and validation studies, with the solver quality comparable to some of the tested commercial CFD tools. There is still room for further solver quality improvements in OpenFOAM by implementing better shock capturing schemes such as a density-based flux-difference-splitting scheme or by writing better physical modeling of the shock/boundary layer interaction into the open architecture of OpenFOAM.
Numerical Simulation of Multi-track and Multi-layer Temperature Field on Laser Direct Metal Shaping
Institute of Scientific and Technical Information of China (English)
LONG Risheng; LIU Weijun
2006-01-01
To improve the mechanical properties of the parts fabricated by Laser Direct Metal Shaping (LDMS), it is of great significance to understand the distribution regularities of transient temperature field during LDMS process. Based on the "element birth and death" technique of finite element method, a three-dimensional multi-track and multi-layer model for the transient temperature field analysis of LDMS is developed by ANSYS Parametric Design Language (APDL) for the first time. In the fabricated model, X-direction parallel reciprocating scanning paths is introduced. Using the same process parameters, the simulation results show good agreement with the microstructure features of samples which fabricated by LDMS.
Sapounas, A.; Nikita-Martzopoulou, Ch.; Bartzanas, T.; Kittas, C.
2008-01-01
An experimental greenhouse equipped with fan and pad evaporative cooling is analysed using two different models. The first one consists of a numerical simulation approach applying a commercial CFD code. The main aspects of evaporative cooling systems, in terms of heat and mass transfer and both the
Concept and evaluation of bay health：the role of numerical model in the Yueqing Bay, China
Institute of Scientific and Technical Information of China (English)
ZHOU Dacheng; SUN Zhilin; HUANG Yu; HUANG Saihua; LI Li
2016-01-01
To better evaluate the three-dimensional bay health and predict the dynamic bay health conditions, a concept of numerical bay health was introduced and a method of numerical bay health evaluation (NBHE) was developed. To support the NBHE method, a numerical bay health index (NBHI) system was constructed, which assess the natural and socio-economic effects on the entire bay. Five index groups are combined to formulate the NBHI, including geometry, hydrodynamics and sediment dynamics, bio-ecology, water quality and socio-economy. Each group has different number of indices selected and weighted using AHP method according to their importance. Data were mainly synthesized from a variety of numerical models together with monitoring programs, which provide superior to other approaches in discriminating data integrity and predicting data in future. The NBHE method using NBHI system was applied in the Yueqing Bay during spring tide in April 2007. According to the NBHE results, Sta. A, at the surface level of the estuarine mouth, has a healthy geometry condition, sub-healthy hydrodynamic and sediment dynamic condition, and unhealthy water quality and bio-ecology conditions. The integrated healthy score at Sta. A indicates its sub-healthy condition.
Hey, Tobias; Bajraktari, Niada; Davidsson, Åsa; Vogel, Jörg; Madsen, Henrik Tækker; Hélix-Nielsen, Claus; Jansen, Jes la Cour; Jönsson, Karin
2017-02-22
Municipal wastewater treatment commonly involves mechanical, biological and chemical treatment steps to protect humans and the environment from adverse effects. Membrane technology has gained increasing attention as an alternative to conventional wastewater treatment due to increased urbanization. Among the available membrane technologies, microfiltration and forward osmosis have been selected for this study due to their specific characteristics, such as compactness and efficient removal of particles. In this study, two treatment concepts were evaluated with regard to their specific electricity, energy and area demands. Both concepts would fulfil the Swedish discharge demands for small and medium-sized wastewater treatment plants at full scale: 1) direct microfiltration and 2) direct forward osmosis with seawater as the draw solution. The framework of this study is based on a combination of data obtained from bench- and pilot-scale experiments applying direct microfiltration and forward osmosis, respectively. Additionally, available complementary data from a Swedish full-scale wastewater treatment plant and the literature were used to evaluate the concepts in depth. The results of this study indicate that both concepts are net positive with respect to electricity and energy, as more biogas can be produced compared to conventional wastewater treatment. Furthermore, the specific area demand is significantly reduced. This study demonstrates that municipal wastewater could be treated in a more energy- and area-efficient manner with techniques that are already commercially available and with future membrane technology.
Directory of Open Access Journals (Sweden)
Dinsenmeyer Rémi
2014-01-01
Full Text Available Numerical simulations using CFD are conducted on a boiling two-phase flow in order to study the changes in flow patterns during evaporation. A model for heat and mass transfer at the tube inner wall and at the liquid-gas interface is presented. Transport of two custom scalars is solved: one stands for the enthalpy fields in the flow, the other represents a new dispersed vapor phase in the liquid. A correlation is used to model heat and mass transfer at the tube inner wall. The dispersed phase is created at the surface in the liquid and flows up to the liquid-vapor interface. There, it is transformed into actual vapor phase. The multiphase VOF model is validated for the creation of slugs in an horizontal tube for an adiabatic flow. Results are presented for a subcooled boiling flow in a bend.
Farhaoui, Asma; Kahouadji, Lyes; Chergui, Jalel; Juric, Damir; Shin, Seungwon; Craster, Richard; Matar, Omar
2016-11-01
We carry out three-dimensional numerical simulations of co/counter current Gas-Liquid annular flows using the parallel code, BLUE, based on a projection method for the resolution of the Navier-Stokes equations and a hybrid Front-Tracking/Level-Set method for the interface advection. Gas-Liquid annular flows and falling films in a pipe are present in a broad range of industrial processes. This configuration consists of an important multiphase flow regime where the liquid occupies the area adjacent to the internal circumference of the pipe and the gas flows in the pipe core. Experimentally, four distinctive flow regimes were identified ('dual-wave', 'thick ripple', 'disturbance wave' and 'regular wave' regimes), that we attempt to simulate. In order to visualize these different regimes, various liquid (water) and gas (air) flow-rates are investigated. EPSRC UK Programme Grant EP/K003976/1.
Peiseniece, Līga
2011-01-01
The goal of the dissertation „Methods of Human Resource Management Evaluation and Directions for Their Improvement in Large Enterprises of Latvia” is to establish new methods for efficiency evaluation of human resource management to improve processes of human resource management in large enterprises of Latvia. The first chapter covers the nature and methods of evaluation of human resource management. The necessity of evaluation of human resource management has been based ...
Desjouy, Cyril; Ollivier, Sébastien; Marsden, Olivier; Karzova, Maria; Blanc-Benon, Philippe
2016-02-01
The local interactions occurring between incident and reflected shock waves in the vicinity of rigid surfaces are investigated. Both regular and irregular — also called von Neumann — regimes of reflection are studied, via experimental and numerical simulations. Shock waves are produced experimentally with a 20 kV electrical spark source which allows the generation of spherically diverging acoustic shocks. The behaviour of the resulting weak acoustic shocks near rigid boundaries is visualized with a Schlieren optical technique which allows the spatial structure of the shocks to be studied. In particular, the evolution of the Mach stem forming above a flat surface is examined, and its height is observed to be directly linked to the angle of incidence and the pressure amplitude of the incident shock. The propagation of an acoustic shock between two parallel rigid boundaries is also studied. It is shown that the strong interactions between the Mach stems emerging from the two boundaries can lead to a drastic modification of the morphology of the acoustic field in the waveguide. Experimental results are compared to numerical results obtained from high-order finite-difference based simulations of the 2D Navier-Stokes equations. The good agreement between the experimental distribution of the acoustic field and numerical results suggests that numerical simulations are promising as a predictive tool to study nonlinear acoustic propagation of acoustic waves in complex geometrical configurations with rigid boundaries.
CSIR Research Space (South Africa)
Dorasamy, Kribashnee
2016-12-01
Full Text Available ) Advances in Visual Computing. ISVC 2016. Lecture Notes in Computer Science, vol 10073. Evaluating the Change of Directional Patterns for Fingerprints with Missing Singular Points Under Rotation Kribashnee Dorasamy Leandra Webb-Ray Jules...
Zhao, Qing; Bo, Yong; Lei, Mingda; Liu, Shuzhang; Liu, Ying; Liu, Jianwei; Zhao, Yizhe
2016-11-01
Numerical study of electromagnetic (EM) wave transmission through the magnetized plasma layer is presented in this paper. The plasma parameters are derived from computational fluid dynamics simulation of the flow field around a blunt body flying at supersonic speed and serve as the background plasma condition in the numerical modeling for EM wave transmission. The EM wave is generated by our newly designed coaxial feed GPS patch antenna. The external magnetic field is applied and assumed to vary linearly as a function of wall distance. The effects of the external applied magnetic field and the plasma parameters on wave transmission are studied, and the results show that EM wave propagation in the non-uniformly magnetized plasma is a matter of impedance matching, and the EM wave transmission can be adjusted only when the proper strength of the magnetic field is applied.
Numerical evaluation of renewal equations: applications to risk theory and financial models
Usábel Rodrigo, Miguel Arturo
1997-01-01
The so-called Renewal Theory is a frequently used methodology in applied mathematics. Renewal Theory is mainly focussed on solving a Volterra integral equation of the second kind known as Renewal Integral EquationAn interesting problem arises when choosing the appropriate numerical tool in order to approximate the solution of the former integral. The decision will be based on the degree of knowledge of function F(x) and some properties of (u). Three methods based in classical methodologies (s...
Stress analysis and damage evaluation of flawed composite laminates by hybrid-numerical methods
Yang, Yii-Ching
1992-01-01
Structural components in flight vehicles is often inherited flaws, such as microcracks, voids, holes, and delamination. These defects will degrade structures the same as that due to damages in service, such as impact, corrosion, and erosion. It is very important to know how a structural component can be useful and survive after these flaws and damages. To understand the behavior and limitation of these structural components researchers usually do experimental tests or theoretical analyses on structures with simulated flaws. However, neither approach has been completely successful. As Durelli states that 'Seldom does one method give a complete solution, with the most efficiency'. Examples of this principle is seen in photomechanics which additional strain-gage testing can only average stresses at locations of high concentration. On the other hand, theoretical analyses including numerical analyses are implemented with simplified assumptions which may not reflect actual boundary conditions. Hybrid-Numerical methods which combine photomechanics and numerical analysis have been used to correct this inefficiency since 1950's. But its application is limited until 1970's when modern computer codes became available. In recent years, researchers have enhanced the data obtained from photoelasticity, laser speckle, holography and moire' interferometry for input of finite element analysis on metals. Nevertheless, there is only few of literature being done on composite laminates. Therefore, this research is dedicated to this highly anisotropic material.