China and the TPP: A Numerical Simulation Assessment of the Effects Involved
Chunding Li; John Whalley
2012-01-01
The Trans-Pacific Partnership (TPP) is a new negotiation on cross border liberalization of goods and service flows going beyond WTO disciplines and focused on issues such as regulation and border controls. Though the US, Australia and other pacific countries are included, China is notable for its exclusion from the process thus far. This paper uses numerical simulation methods to assess the potential effects of a TPP agreement on China and the other participating countries. We use a numerical...
Improvement of numerical simulation methods on safety assessment of the spent fuel storage facility
International Nuclear Information System (INIS)
Improvement of numerical simulation methods on safety assessment of the spent fuel storage facility is one of main objectives of JNES activities. For the thermal and structural analyses, the radiative heat transfer analysis code S-FOKS has been developed to reduce computing time and to avoid using large memory area. In order to simulate the specular reflection, a new model (called 'model-2') is planned to install to S-FOKS code. The theoretical values with the specular reflection in simple geometry were lead to verify S-FOKS model-2. (author)
DEFF Research Database (Denmark)
Christiansen, Thomas; Dahl, Kristian Vinter; Somers, Marcel A. J.
2008-01-01
The present paper addresses the experimental assessment of the concentration dependent nitrogen diffusion coefficient in stress free expanded austenite foils from thermogravimetry, the numerical simulation of nitrogen concentration depth profiles on growth of expanded austenite into stainless ste...
Confidence in Numerical Simulations
Energy Technology Data Exchange (ETDEWEB)
Hemez, Francois M. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2015-02-23
This PowerPoint presentation offers a high-level discussion of uncertainty, confidence and credibility in scientific Modeling and Simulation (M&S). It begins by briefly evoking M&S trends in computational physics and engineering. The first thrust of the discussion is to emphasize that the role of M&S in decision-making is either to support reasoning by similarity or to “forecast,” that is, make predictions about the future or extrapolate to settings or environments that cannot be tested experimentally. The second thrust is to explain that M&S-aided decision-making is an exercise in uncertainty management. The three broad classes of uncertainty in computational physics and engineering are variability and randomness, numerical uncertainty and model-form uncertainty. The last part of the discussion addresses how scientists “think.” This thought process parallels the scientific method where by a hypothesis is formulated, often accompanied by simplifying assumptions, then, physical experiments and numerical simulations are performed to confirm or reject the hypothesis. “Confidence” derives, not just from the levels of training and experience of analysts, but also from the rigor with which these assessments are performed, documented and peer-reviewed.
Confidence in Numerical Simulations
International Nuclear Information System (INIS)
This PowerPoint presentation offers a high-level discussion of uncertainty, confidence and credibility in scientific Modeling and Simulation (M&S). It begins by briefly evoking M&S trends in computational physics and engineering. The first thrust of the discussion is to emphasize that the role of M&S in decision-making is either to support reasoning by similarity or to ''forecast,'' that is, make predictions about the future or extrapolate to settings or environments that cannot be tested experimentally. The second thrust is to explain that M&S-aided decision-making is an exercise in uncertainty management. The three broad classes of uncertainty in computational physics and engineering are variability and randomness, numerical uncertainty and model-form uncertainty. The last part of the discussion addresses how scientists ''think.'' This thought process parallels the scientific method where by a hypothesis is formulated, often accompanied by simplifying assumptions, then, physical experiments and numerical simulations are performed to confirm or reject the hypothesis. ''Confidence'' derives, not just from the levels of training and experience of analysts, but also from the rigor with which these assessments are performed, documented and peer-reviewed.
Infiltration in layered loessial deposits: Revised numerical simulations and recharge assessment
Dafny, Elad; Šimůnek, Jirka
2016-07-01
The objective of this study is to assess recharge rates and their timing under layered loessial deposits at the edge of arid zones. Particularly, this study is focused on the case of the coastal plain of Israel and Gaza. First, results of a large-scale field infiltration test were used to calibrate the van Genuchten parameters of hydraulic properties of the loessial sediments using HYDRUS (2D/3D). Second, optimized soil hydraulic parameters were used by HYDRUS-1D to simulate the water balance of the sandy-loess sediments during a 25-year period (1990-2015) for three environmental conditions: bare soil, and soil with both sparse and dense natural vegetation. The best inverse parameter optimization run fitted the infiltration test data with the RMSE of 0.27 d (with respect to a moisture front arrival) and R2 of 96%. The calibrated model indicates that hydraulic conductivities of the two soil horizons, namely sandy loam and sandy clay loam, are 81 cm/d and 17.5 cm/d, respectively. These values are significantly lower than those previously reported, based on numerical simulations, for the same site. HYDRUS-1D simulation of natural recharge under bare soil resulted in recharge estimates (to the aquifer) in the range of 21-93 mm/yr, with an average recharge of 63 mm/yr. Annual precipitation in the same period varied between 100 and 300 mm/yr, with an average of 185 mm/yr. For semi-stabilized dunes, with 26% of the soil surface covered by local shrub (Artemisia monosperma), the mean annual recharge was 28 mm. For the stabilized landscape, with as much as 50% vegetation coverage, it was only 2-3 mm/yr. In other words, loessial sediments can either be a source of significant recharge, or of no recharge at all, depending on the degree of vegetative cover. Additionally, the time lag between specific rainy seasons and corresponding recharge events at a depth of 22 m, increased from 2.5 to 5 years, and to about 20 years, respectively, with an increasing vegetative cover. For
NUMERICAL FLOW AND TRANSPORT SIMULATIONS SUPPORTING THE SALTSTONE FACILITY PERFORMANCE ASSESSMENT
Energy Technology Data Exchange (ETDEWEB)
Flach, G.
2009-02-28
The Saltstone Disposal Facility Performance Assessment (PA) is being revised to incorporate requirements of Section 3116 of the Ronald W. Reagan National Defense Authorization Act for Fiscal Year 2005 (NDAA), and updated data and understanding of vault performance since the 1992 PA (Cook and Fowler 1992) and related Special Analyses. A hybrid approach was chosen for modeling contaminant transport from vaults and future disposal cells to exposure points. A higher resolution, largely deterministic, analysis is performed on a best-estimate Base Case scenario using the PORFLOW numerical analysis code. a few additional sensitivity cases are simulated to examine alternative scenarios and parameter settings. Stochastic analysis is performed on a simpler representation of the SDF system using the GoldSim code to estimate uncertainty and sensitivity about the Base Case. This report describes development of PORFLOW models supporting the SDF PA, and presents sample results to illustrate model behaviors and define impacts relative to key facility performance objectives. The SDF PA document, when issued, should be consulted for a comprehensive presentation of results.
Assessment of the State-Of-The-Art of Numerical Simulation of Enhanced Geothermal Systems
International Nuclear Information System (INIS)
The reservoir features of importance in the operation of enhanced geothermal systems are described first (Section 2). The report then reviews existing reservoir simulators developed for application to HDR reservoirs (Section 3), hydrothermal systems (Section 4), and nuclear waste isolation (Section 5), highlighting capabilities relevant to the evaluation and assessment of EGS. The report focuses on simulators that include some representation of flow in fractures, only mentioning other simulators, such as general-purpose programs or groundwater models (Section 6). Following these detailed descriptions, the report summarizes and comments on the simulators (Section 7), and recommends a course of action for further development (Section 8). The references are included in Section 9. Appendix A contains contractual information, including a description of the original and revised scope of work for this study. Appendix B presents comments on the draft report from DOE reviewer(s) and the replies of the authors to those comments. [DJE-2005
Assessment of the State-Of-The-Art of Numerical Simulation of Enhanced Geothermal Systems
Energy Technology Data Exchange (ETDEWEB)
None
1999-11-01
The reservoir features of importance in the operation of enhanced geothermal systems are described first (Section 2). The report then reviews existing reservoir simulators developed for application to HDR reservoirs (Section 3), hydrothermal systems (Section 4), and nuclear waste isolation (Section 5), highlighting capabilities relevant to the evaluation and assessment of EGS. The report focuses on simulators that include some representation of flow in fractures, only mentioning other simulators, such as general-purpose programs or groundwater models (Section 6). Following these detailed descriptions, the report summarizes and comments on the simulators (Section 7), and recommends a course of action for further development (Section 8). The references are included in Section 9. Appendix A contains contractual information, including a description of the original and revised scope of work for this study. Appendix B presents comments on the draft report from DOE reviewer(s) and the replies of the authors to those comments. [DJE-2005
Leonelli, Cristina; Veronesi, Paolo; Grisoni, Fabio
2007-01-01
Industrial-scale filter dryers, equipped with one or more microwave input ports, have been modelled with the aim of detecting existing criticalities, proposing possible solutions and optimizing the overall system efficiency and treatment homogeneity. Three different loading conditions have been simulated, namely the empty applicator, the applicator partially loaded by both a high-loss and low loss load whose dielectric properties correspond to the one measured on real products. Modeling results allowed for the implementation of improvements to the original design such as the insertion of a wave guide transition and a properly designed pressure window, modification of the microwave inlet's position and orientation, alteration of the nozzles' geometry and distribution, and changing of the cleaning metallic torus dimensions and position. Experimental testing on representative loads, as well as in production sites, allowed for the confirmation of the validity of the implemented improvements, thus showing how numerical simulation can assist the designer in removing critical features and improving equipment performances when moving from conventional heating to hybrid microwave-assisted processing. PMID:18350999
Energy Technology Data Exchange (ETDEWEB)
Neeraj Gupta
2008-03-31
A series of numerical simulations of carbon dioxide (CO{sub 2}) injection were conducted as part of a program to assess the potential for geologic sequestration in deep geologic reservoirs (the Rose Run and Copper Ridge formations), at the American Electric Power (AEP) Mountaineer Power Plant outside of New Haven, West Virginia. The simulations were executed using the H{sub 2}O-CO{sub 2}-NaCl operational mode of the Subsurface Transport Over Multiple Phases (STOMP) simulator (White and Oostrom, 2006). The objective of the Rose Run formation modeling was to predict CO{sub 2} injection rates using data from the core analysis conducted on the samples. A systematic screening procedure was applied to the Ohio River Valley CO{sub 2} storage site utilizing the Features, Elements, and Processes (FEP) database for geological storage of CO{sub 2} (Savage et al., 2004). The objective of the screening was to identify potential risk categories for the long-term geological storage of CO{sub 2} at the Mountaineer Power Plant in New Haven, West Virginia. Over 130 FEPs in seven main classes were assessed for the project based on site characterization information gathered in a geological background study, testing in a deep well drilled on the site, and general site conditions. In evaluating the database, it was apparent that many of the items were not applicable to the Mountaineer site based its geologic framework and environmental setting. Nine FEPs were identified for further consideration for the site. These FEPs generally fell into categories related to variations in subsurface geology, well completion materials, and the behavior of CO{sub 2} in the subsurface. Results from the screening were used to provide guidance on injection system design, developing a monitoring program, performing reservoir simulations, and other risk assessment efforts. Initial work indicates that the significant FEPs may be accounted for by focusing the storage program on these potential issues. The
International Nuclear Information System (INIS)
Certification process of PWR fuel requires irradiation experiments in test reactors in order to guarantee safety of facilities, workers and environment. In these tests, the fuel is submitted to stress conditions prior to its real usage in a commercial reactor. Post-irradiation examination of burned fuel is conducted in hot-cells. Dose assessment during fuel transportation and manipulation in hot-cells is required. This work simulated commercial (below 6 wt% enriched) PWR spent fuel fission products using ORIGEN-ARP code. Different scenarios, varying fuel burn-up and pool decay storage time, were simulated. The simulation results were used to determine the maximum amount of spent fuel allowed to be transported and manipulated inside a hot-cell. GEANT4, an open source Monte Carlo toolkit simulation package used to track particles, was used to assess radiation doses given to workers and environment. A commercial B(U) type Agnes - La Calhene transportation cask with storage capacity limited to three mini rods was considered. Fission products were classified according to three categories: short-lived radionuclides (half-life around months), medium-lived radionuclides (half-life around tenths of years) and long-lived radionuclides (half-life of hundreds of years and beyond). Short lived radionuclides are left to decay inside the reactor's pool while long-lived radionuclides present no real radioprotection concern, since they emit mainly alpha particles and have low activities compared with medium-lived radionuclides. In this work, activities around 1000 TBq were found. Considering current radioprotection limits, doses were numerically calculated using an anthropomorphic human phantom simulating an average person. (author)
Numerical simulation of dusty plasmas
Energy Technology Data Exchange (ETDEWEB)
Winske, D.
1995-09-01
The numerical simulation of physical processes in dusty plasmas is reviewed, with emphasis on recent results and unresolved issues. Three areas of research are discussed: grain charging, weak dust-plasma interactions, and strong dust-plasma interactions. For each area, we review the basic concepts that are tested by simulations, present some appropriate examples, and examine numerical issues associated with extending present work.
Numerical simulation and impact assessment of a groundwater pollution based on MODFLOW
International Nuclear Information System (INIS)
Based on MODFLOW, SRTM3 DEM data and GIS tool, a saturated-zone groundwater flow and radionuclide transport numerical model in a research area had been developed to evaluate the migration trend and environmental impact. The results showed that 3H transporting with the groundwater had a fast velocity and a pulse concentration which can not reduce to acceptable level within short times. that may cause groundwater pollution in downstream region. However, 90Sr was transported slowly with the groundwater, and may only cause a pollution area of about 200 m around the source. (authors)
Performance assessment of a small wind turbine with crossflow runner by numerical simulations
Energy Technology Data Exchange (ETDEWEB)
Dragomirescu, A. [University Politehnica of Bucharest, Department of Hydraulics, Hydraulic Machinery and Environmental Engineering, Splaiul Independentei 313, 060042 Bucharest (Romania)
2011-03-15
Most of the classical wind turbines are not able to start at wind speeds as low as 2-3 m/s. Other turbines, like Savonius, have a low maximum efficiency, which renders them useless in poor wind conditions. Therefore, new turbine designs are required to harvest wind power even when the wind speed is low. A wind turbine having a crossflow runner, similar to the Banki water turbine, is studied numerically in this work in order to estimate its performance. The results obtained suggest that this turbine has a considerable high starting torque and its maximum power coefficient is comparable to those of horizontal axis wind turbines. Based on the results obtained, some improvements of the design are proposed in order to further increase turbine performance. (author)
Combining Narrative and Numerical Simulation
DEFF Research Database (Denmark)
Hansen, Mette Sanne; Ladeby, Klaes Rohde; Rasmussen, Lauge Baungaard; Jacobsen, Peter
Strategic simulation is the combination of narrative and numerical simulation and can be used as a tool to support strategic decision making by providing different scenarios in combination with computer modelling. The core of the combined simulation approach (CSA) is to make it possible for...... decision making in operations and production management by providing new insights into modelling and simulation based on the combined narrative and numerical simulation approach as a tool for strategy making. The research question asks, “How can the CSA be applied in a practical context to support strategy...
Numerical simulation of welding
DEFF Research Database (Denmark)
Hansen, Jan Langkjær; Thorborg, Jesper
, good predictions of the thermal field are obtained. This has been verified with experiments. The significance of the right fitting of the model to the topical welding process must be emphasized. With a mechanical model in ABAQUS based on a thermal model as described, distributions of both transient...... welding process. Various circumstances are process dependent and require not only knowledge of the process in practice butalso a thorough experience with the numerical modelling of the problem....
Directory of Open Access Journals (Sweden)
Yan Zhenzhen
2016-01-01
Full Text Available In order to obtain the Required Safety Egress Time (RSET accurately, traditional engineering calculation method of evacuation time has been optimized in this paper. Several principles and fact situations were used to optimize the method, such as detecting principle of the fire detecting system, reaction characteristics of staff being in urgent situation, evacuating queuing theory, building structure and the plugging at the porthole. Taking a three-storey KTV as an example, two methods are used to illustrate the reliability and scientific reasonability of the calculation result. The result is deduced by comparing the error (less than 2% at an allowable range between two results. One result is calculated by a modified method of engineering calculation method, and the other one is given based on a Steering model of Pathfinder evacuation simulation software. The optimized RSET has a good feasibility and Accuracy.
International Nuclear Information System (INIS)
Using protons for the treatment of ocular melanoma (especially of posterior pole tumours), the radiation quality of the beam must be precisely assessed to preserve the vision and to minimise the damage to healthy tissue. The radiation quality of a therapeutic proton beam at the Centre Antoine Lacassagne in Nice (France) was measured using microdosimetric techniques, i.e. a miniaturised version of a tissue-equivalent proportional counter. Measurements were performed in a 1-μm site at different depths in a Lucite phantom. Experimental data showed a significant increase in the beam quality at the distal edge of the spread-out Bragg peak (SOBP). In this paper, the numerical simulation of the experimental setup is done with the FLUKA Monte Carlo radiation transport code. The calculated microdosimetric spectra are compared with the measured ones at different depths in tissue for a monoenergetic proton beam (E=62 MeV) and for a modulated SOBP. Numerically and experimentally predicted relative biological effectiveness values are in good agreement. The calculated frequency-averaged and dose-averaged lineal energy mean values are consistent with measured data. (authors)
Numerical simulation of laser resonators
International Nuclear Information System (INIS)
We developed numerical simulation packages for laser resonators on the bases of a pair of integral equations. Two numerical schemes, a matrix formalism and an iterative method, were programmed for finding numeric solutions to the pair of integral equations. The iterative method was tried by Fox and Li, but it was not applicable for high Fresnel numbers since the numerical errors involved propagate and accumulate uncontrollably. In this paper, we implement the matrix method to extend the computational limit further. A great number of case studies are carried out with various configurations of stable and unstable r;esonators to compute diffraction losses, phase shifts, intensity distributions and phases of the radiation fields on mirrors. Our results presented in this paper show not only a good agreement with the results previously obtained by Fox and Li, but also the legitimacy of our numerical procedures for high Fresnel numbers.
Monte Carlo simulation and numerical integration
Geweke, John F.
1995-01-01
This is a survey of simulation methods in economics, with a specific focus on integration problems. It describes acceptance methods, importance sampling procedures, and Markov chain Monte Carlo methods for simulation from univariate and multivariate distributions and their application to the approximation of integrals. The exposition gives emphasis to combinations of different approaches and assessment of the accuracy of numerical approximations to integrals and expectations. The survey illus...
Numerical simulation of electrochemical desalination
Hlushkou, D.; Knust, K. N.; Crooks, R. M.; Tallarek, U.
2016-05-01
We present an effective numerical approach to simulate electrochemically mediated desalination of seawater. This new membraneless, energy efficient desalination method relies on the oxidation of chloride ions, which generates an ion depletion zone and local electric field gradient near the junction of a microchannel branch to redirect sea salt into the brine stream, consequently producing desalted water. The proposed numerical model is based on resolution of the 3D coupled Navier–Stokes, Nernst–Planck, and Poisson equations at non-uniform spatial grids. The model is implemented as a parallel code and can be employed to simulate mass–charge transport coupled with surface or volume reactions in 3D systems showing an arbitrarily complex geometrical configuration.
Numerical simulations in quantum chromodynamics
International Nuclear Information System (INIS)
One of the most outstanding challenges in physics today is to explain quantitatively the observed properties of protons, neutrons etc. generically called hadrons. A significant part of this challenge is also to explain so called Quark Confinement. Though there is very strong evidence that the correct theoretical description is provided by the so called Quantum Chromodynamics (QCD), it is an extremely difficult theory to solve by traditional analytical techniques. Great strides have been made over the last couple of decades in numerical simulations of this theory which require the fastest available supercomputers. In this paper I shall briefly describe QCD and also describe its numerical simulations and their complexity. I shall briefly describe the most recent results obtained on the Teraflop Linux cluster KABRU at IMSc. (author)
Numerical simulations of strong Turbulence
Czech Academy of Sciences Publication Activity Database
Jásenský, Václav; Trávníček, Pavel; Váňa, Ondřej
Prague : Faculty of mathematics and physics, Charles University, 2001 - (Šafránková, J.), s. 378-380 [10th Annual Conference of Doctoral Students. Prague (CZ), 12.06.2001-15.06.2001] R&D Projects: GA ČR GA205/01/1064 Institutional research plan: CEZ:AV0Z3042911 Keywords : Strong Turbulence * Zakharov Equations * Numeric Simulations Solitons Subject RIV: BE - Theoretical Physics
Numerical Simulation of Flame Propagation
Uddholm, Per
2008-01-01
The effects of the temperature and length, of the preheat zone, on the deflagration to detonation transition are investigated through numerical simulation. The Navier-Stokes equations, with a reaction term, are solved in one dimension. The time integration is a one-dimensional adaptation of an existing two-dimensional finite volume method code. An iterative scheme, based on an overlap integral, is developed for the determination of the deflagration to detonation transition. The code is tested...
Ferrara, P; Ciofini, M; Esposito, L; Hostaša, J; Labate, L; Lapucci, A; Pirri, A; Toci, G; Vannini, M; Gizzi, L A
2014-03-10
We present a study of Yb:YAG active media slabs, based on a ceramic layered structure with different doping levels. We developed a procedure allowing 3D numerical analysis of the slab optical properties as a consequence of the thermal load induced by the pump process. The simulations are compared with a set of experimental results in order to validate the procedure. These structured ceramics appear promising in appropriate geometrical configurations, and thus are intended to be applied in the construction of High Energy Diode Pumped Solid State Laser (DPSSL) systems working in high repetition-rate pulsed regimes. PMID:24663877
International Nuclear Information System (INIS)
The numerical simulation of the heating process of steel slabs in a walking beam reheating furnace is reported using two different models. In one model, the turbulent reactive flow in the furnace is simulated together with the heat conduction in the slabs. The calculations are performed using a commercial code and a user-defined function is used to simulate the periodic movement of the slabs by the walking beams in the furnace. Unsteady calculations are performed until a periodic transient solution is achieved. In the second model, the furnace is divided into a small number of zones and the average temperature and chemical composition are prescribed in every zone based on the results of the first model. The unsteady heating process of the slabs is modeled using the same software and accounting for radiative transfer in the furnace and heat conduction in the slabs. The results of the first model are taken as a benchmark for the second one. It is shown that the first model predicts radiative heat fluxes and temperatures of the slabs that are consistent with previous work. The two models yield volume average temperatures of the slabs leaving the furnace that differ by less than 3%, provided that accurate values of the temperature of the gases and walls are used. The second model is computationally more economical, requiring only about 5% of the computational time of the first one. - Highlights: • The heating process of steel slabs in a reheating furnace is numerically simulated. • Unsteady calculations accounting for the periodic movement of the slabs are reported. • We compare two models differing on how the thermochemical composition is obtained. • The models predict mean slab temperatures at the exit that differ by less than 3%. • The computational time of the fastest model is only about 5% of the slowest one
Directory of Open Access Journals (Sweden)
Lei Zhang
2010-01-01
Full Text Available The importance of wind observations has been recognized for many years. However, wind observations—especially three-dimensional global wind measurements—are very limited. A satellite-based Doppler Wind Lidar (DWL is proposed to measure three-dimensional wind profiles using remote sensing techniques. Assimilating these observations into a mesoscale model is expected to improve the performance of the numerical weather prediction (NWP models. In order to examine the potential impact of the DWL three-dimensional wind profile observations on the numerical simulation and prediction of tropical cyclones, a set of observing simulation system experiments (OSSEs is performed using the advanced research version of the Weather Research and Forecasting (WRF model and its three-dimensional variational (3DVAR data assimilation system. Results indicate that assimilating the DWL wind observations into the mesoscale numerical model has significant potential for improving tropical cyclone track and intensity forecasts.
AGN feedback in numerical simulations
Ciotti, L
2009-01-01
The passively evolving stellar population in elliptical galaxies (Es) provides a continuous source of fuel for accretion on the central supermassive black hole (SMBH), which is 1) extended over the entire galaxy life (but declining with cosmic time), 2) linearly proportional to the stellar mass of the host spheroid, 3) summing up to a total gas mass that is >100 times larger than the currently observed SMBH masses, 4) available independently of merging events. The main results of numerical simulations of Es with central SMBH, in which a physically based implementation of radiative and mechanical feedback effects is considered, are presented.
Plasma modelling and numerical simulation
International Nuclear Information System (INIS)
Plasma modelling is an exciting subject in which virtually all physical disciplines are represented. Plasma models combine the electromagnetic, statistical and fluid dynamical theories that have their roots in the 19th century with the modern insights concerning the structure of matter that were developed throughout the 20th century. The present cluster issue consists of 20 invited contributions, which are representative of the state of the art in plasma modelling and numerical simulation. These contributions provide an in-depth discussion of the major theories and modelling and simulation strategies, and their applications to contemporary plasma-based technologies. In this editorial review, we introduce and complement those papers by providing a bird's eye perspective on plasma modelling and discussing the historical context in which it has surfaced. (editorial review)
Numerical Simulation for Space Charge Effect Calculation
International Nuclear Information System (INIS)
Numerical simulation of space charge effect, analysis of three dimensional uniformly charged zero emittance ellipsoidal bunch as well as comparative analysis of numerical and analytical results are presented. (author)
Numerical Simulation of a Hypersonic Air Intake
Soumyajit Saha; Debasis Chakraborty
2015-01-01
Numerical simulations were carried out to study the unsteady flow in an intake of hypersonic air-breathing vehicle. Unsteady RANS simulations were performed to examine started flow of the intake when cowl surface is parallel to the ramp surface. Though started, the flow was unsteady due to flow separation bubbles inside intake. Intake with larger cowl opening at which intake unstarted was also simulated. Simulations indicated unstarted flow, with large pressure oscillations. The numerically s...
Rocket Engine Numerical Simulator (RENS)
Davidian, Kenneth O.
1997-01-01
Work is being done at three universities to help today's NASA engineers use the knowledge and experience of their Apolloera predecessors in designing liquid rocket engines. Ground-breaking work is being done in important subject areas to create a prototype of the most important functions for the Rocket Engine Numerical Simulator (RENS). The goal of RENS is to develop an interactive, realtime application that engineers can utilize for comprehensive preliminary propulsion system design functions. RENS will employ computer science and artificial intelligence research in knowledge acquisition, computer code parallelization and objectification, expert system architecture design, and object-oriented programming. In 1995, a 3year grant from the NASA Lewis Research Center was awarded to Dr. Douglas Moreman and Dr. John Dyer of Southern University at Baton Rouge, Louisiana, to begin acquiring knowledge in liquid rocket propulsion systems. Resources of the University of West Florida in Pensacola were enlisted to begin the process of enlisting knowledge from senior NASA engineers who are recognized experts in liquid rocket engine propulsion systems. Dr. John Coffey of the University of West Florida is utilizing his expertise in interviewing and concept mapping techniques to encode, classify, and integrate information obtained through personal interviews. The expertise extracted from the NASA engineers has been put into concept maps with supporting textual, audio, graphic, and video material. A fundamental concept map was delivered by the end of the first year of work and the development of maps containing increasing amounts of information is continuing. Find out more information about this work at the Southern University/University of West Florida. In 1996, the Southern University/University of West Florida team conducted a 4day group interview with a panel of five experts to discuss failures of the RL10 rocket engine in conjunction with the Centaur launch vehicle. The
Numerical simulation of drifting sand
Alhajraf, Salem
2000-01-01
Two-phase flows are involved in many industrial and natural flow phenomena varying from as specific as the transport of crude oil in pipelines to as general as the dispersion of pollutants in the atmosphere. Numerical modelling based on Computational Fluid Dynamics (CFD), has attracted the attention of scientists and engineers from a wide range of backgrounds over recent decades during which these models have been extensively developed, analysed and applied to many practical...
Numerical simulation of conservation laws
Chang, Sin-Chung; To, Wai-Ming
1992-01-01
A new numerical framework for solving conservation laws is being developed. This new approach differs substantially from the well established methods, i.e., finite difference, finite volume, finite element and spectral methods, in both concept and methodology. The key features of the current scheme include: (1) direct discretization of the integral forms of conservation laws, (2) treating space and time on the same footing, (3) flux conservation in space and time, and (4) unified treatment of the convection and diffusion fluxes. The model equation considered in the initial study is the standard one dimensional unsteady constant-coefficient convection-diffusion equation. In a stability study, it is shown that the principal and spurious amplification factors of the current scheme, respectively, are structurally similar to those of the leapfrog/DuFort-Frankel scheme. As a result, the current scheme has no numerical diffusion in the special case of pure convection and is unconditionally stable in the special case of pure diffusion. Assuming smooth initial data, it will be shown theoretically and numerically that, by using an easily determined optimal time step, the accuracy of the current scheme may reach a level which is several orders of magnitude higher than that of the MacCormack scheme, with virtually identical operation count.
NUMERICAL SIMULATION OF CASTING'S MOLD FILLING PROCESS
Institute of Scientific and Technical Information of China (English)
J.X. Zhou; R.X. Liu; L.L. Chen; D.M. Liao; H.S. Wei
2005-01-01
Numerical simulation of casting's mold filling process is the main and the most important aspect of the foundry CAE technology. But it is time-consuming; it may take dozens of hours or several days. While with the development of computer hardware, numerical simulation of casting' s mold filling process has made rapid progress. The simulation results, therefore, have become more and more practical. This study tries to find some clues of the computational time of mold filling process. Firstly, this paper introduces mathematic model and the basic route of numerical simulation of casting's mold filling process. Then the computational time of mold filling process has been carefully studied, and some new and useful results have been gained from the study of the computational time. Finally, this paper has given some real applications of numerical simulation of casting's mold filling process.
Numerical methods in simulation of resistance welding
DEFF Research Database (Denmark)
Nielsen, Chris Valentin; Martins, Paulo A.F.; Zhang, Wenqi;
2015-01-01
Finite element simulation of resistance welding requires coupling betweenmechanical, thermal and electrical models. This paper presents the numerical models and theircouplings that are utilized in the computer program SORPAS. A mechanical model based onthe irreducible flow formulation is utilized....... From a resistance welding point of view, the most essential coupling between the above mentioned models is the heat generation by electrical current due to Joule heating. The interaction between multiple objects is anothercritical feature of the numerical simulation of resistance welding because it...... influences thecontact area and the distribution of contact pressure. The numerical simulation of resistancewelding is illustrated by a spot welding example that includes subsequent tensile shear testing...
Numerical Simulations of HH 555
Kajdic, Primoz
2007-01-01
We present 3D gasdynamic simulations of the Herbig Haro object HH 555. HH 555 is a bipolar jet emerging from the tip of an elephant trunk entering the Pelican Nebula from the adjacent molecular cloud. Both beams of HH 555 are curved away from the center of the H II region. This indicates that they are being deflected by a side-wind probably coming from a star located inside the nebula or by the expansion of the nebula itself. HH 555 is most likely an irradiated jet emerging from a highly embedded protostar, which has not yet been detected. In our simulations we vary the incident photon flux, which in one of our models is equal to the flux coming from a star 1 pc away emitting 5x10^48 ionizing (i. e., with energies above the H Lyman limit) photons per second. An external, plane-parallel flow (a ``side-wind'') is coming from the same direction as the photoionizing flux. We have made four simulations, decreasing the photon flux by a factor of 10 in each simulation. We discuss the properties of the flow and we co...
Numerical simulation of hydraulic transients
International Nuclear Information System (INIS)
A numerical method suitable for the analysis of hydraulic transients in one-dimensional pipelines as well as some applications of the method are presented in this thesis. In the present method one-dimensional flow equations are solved in a characteristic form using a finite difference technique. A non-equilibrium two-phase flow model is used, which makes it possible to analyze the effect of vaporization. The motion of the pipe-wall, which is important in some types of hydraulic transients, can be taken into account approximately. The main application of the method has been the piping of nuclear reactors
Design and numerical simulation of novel DBRs
Institute of Scientific and Technical Information of China (English)
Wei Su (苏伟); Jingchang Zhong (钟景昌); Wenli Liu (刘文莉); Yan-Kuin Su (苏炎坤); Shoou-Jinn Chang (张守进); Hsin-Chieh Yu (龙信介); Liangwen Ji (姬梁文); Lin Li (李林); Yingjie Zhao (赵英杰)
2003-01-01
In this paper, a numerical simulation of the traditional graded distributed Bragg reflector (DBR) and a design of the novel DBR with short period superlattices (SPSs DBR) used by vertical cavity surface emitting laser (VCSEL) are reported. First, the optical characteristic matrix of the graded DBRs is derived using the theories of thin film optics. Second, its reflective spectrum is numerical simulated and it is found that the simulative results are similar with the experimental data. The difference of the cavity mode position between the experimental and simulative data is discussed. Finally, based on the simulative results of graded DBR, a novel DBR with 4.5-pair GaAs/AlAs SPSs is designed, and its reflective spectrum is numerical simulated and analyzed.
Energy Technology Data Exchange (ETDEWEB)
Scheider, I.
2001-07-01
This thesis introduces a concept for fracture mechanical assessment of structures with heterogenuous material properties like weldments. It is based on the cohesive zone model for numerical crack propagation analysis. With that model the failure of examined structures due to fracture can be determined. One part of the thesis contains the extension of the capabilities of the cohesive zone model regarding modelling threedimensional problems, shear fracture and unloading. In a second part new methods are developed for determination of elastic-plastic and fracture mechanical material properties, resp., which are based on optical determination of the specimen deformation. The whole concept has been used successfully for the numerical simulation of small laser welded specimens. (orig.) [German] In der vorliegenden Arbeit wird ein Konzept vorgestellt, mit dem es moeglich ist, Bauteile mit heterogenen Materialeigenschaften, wie z.B. Schweissverbindungen, bruchmechanisch zu bewerten. Es basiert auf einem Modell zur numerischen Rissfortschrittsimulation, dem Kohaesivzonenmodell, um das Versagen des zu untersuchenden Bauteils infolge von Bruch zu bestimmen. Ein Teil der Arbeit umfasst die Weiterentwicklung des Kohaesivzonenmodells zur Vorhersage des Bauteilversagens in Bezug auf die Behandlung dreidimensionaler Probleme, Scherbuch und Entlastung. In einem zweiten Teil werden Methoden zur Bestimmung sowohl der elastischplastischen als auch der bruchmechanischen Materialparameter entwickelt, die zum grossen Teil auf optischen Auswertungsmethoden der Deformationen beruhen. Das geschlossene Konzept wird erfolgreich auf lasergeschweisste Kleinproben angewendet. (orig.)
Numerical simulation of hydrogen combustion
International Nuclear Information System (INIS)
The aim of this paper is to present a combustion model of hydrogen developed using the Star-cd fluid mechanics code. The model involves a detailed reaction process (11 elementary reactions and 4 intermediate elements) and a procedure is developed to solve the set of fully coupled reactions. Then, a preliminary study allowed to determine ignition conditions needed to numerically trigger a detonation phenomenon. The detonation phenomenon is computed on a first test case and the comparison with literature and another code shows a good agreement (temperature, pressure and velocity of the reaction front). The validation process is still in progress by comparison with other available results. Furthermore, combustion calculations including the prior hydrogen diffusion process can be foreseen. (author)
Visualization of numerically simulated aerodynamic flow fields
International Nuclear Information System (INIS)
The focus of this paper is to describe the development and the application of an interactive integrated software to visualize numerically simulated aerodynamic flow fields so as to enable the practitioner of computational fluid dynamics to diagnose the numerical simulation and to elucidate essential flow physics from the simulation. The input to the software is the numerical database crunched by a supercomputer and typically consists of flow variables and computational grid geometry. This flow visualization system (FVS), written in C language is targetted at the Personal IRIS Workstations. In order to demonstrate the various visualization modules, the paper also describes the application of this software to visualize two- and three-dimensional flow fields past aerodynamic configurations which have been numerically simulated on the NEC-SXIA Supercomputer. 6 refs
Numerical tools for atomistic simulations.
Energy Technology Data Exchange (ETDEWEB)
Fang, H. (Mississippi State University); Gullett, Philip Michael; Slepoy, Alexander (Sandia National Laboratories, Albuquerque, NM); Horstemeyer, Mark F. (Mississippi State University); Baskes, Michael I. (Los Alamos National Laboratory, Los Alamos, NM); Wagner, Gregory John; Li, Mo (Materials Science and Engineering, Atlanta, GA)
2004-01-01
The final report for a Laboratory Directed Research and Development project entitled 'Parallel Atomistic Computing for Failure Analysis of Micromachines' is presented. In this project, atomistic algorithms for parallel computers were developed to assist in quantification of microstructure-property relations related to weapon micro-components. With these and other serial computing tools, we are performing atomistic simulations of various sizes, geometries, materials, and boundary conditions. These tools provide the capability to handle the different size-scale effects required to predict failure. Nonlocal continuum models have been proposed to address this problem; however, they are phenomenological in nature and are difficult to validate for micro-scale components. Our goal is to separately quantify damage nucleation, growth, and coalescence mechanisms to provide a basis for macro-scale continuum models that will be used for micromachine design. Because micro-component experiments are difficult, a systematic computational study that employs Monte Carlo methods, molecular statics, and molecular dynamics (EAM and MEAM) simulations to compute continuum quantities will provide mechanism-property relations associated with the following parameters: specimen size, number of grains, crystal orientation, strain rates, temperature, defect nearest neighbor distance, void/crack size, chemical state, and stress state. This study will quantify sizescale effects from nanometers to microns in terms of damage progression and thus potentially allow for optimized micro-machine designs that are more reliable and have higher fidelity in terms of strength. In order to accomplish this task, several atomistic methods needed to be developed and evaluated to cover the range of defects, strain rates, temperatures, and sizes that a material may see in micro-machines. Therefore we are providing a complete set of tools for large scale atomistic simulations that include pre
Numerical Simulations of Thermographic Responses in Composites
Winfree, William P.; Cramer, K. Elliot; Zalameda, Joseph N.; Howell, Patricia A.
2015-01-01
Numerical simulations of thermographic responses in composite materials have been a useful for evaluating and optimizing thermographic analysis techniques. Numerical solutions are particularly beneficial for thermographic techniques, since the fabrication of specimens with realistic flaws is difficult. Simulations are presented with different ply layups that incorporated the anisotropic thermal properties that exist in each ply. The results are compared to analytical series solutions and thermal measurements on composites with flat bottom holes and delaminations.
Numerical simulation of mechatronic sensors and actuators
Kaltenbacher, Manfred
2007-01-01
Focuses on the physical modeling of mechatronic sensors and actuators and their precise numerical simulation using the Finite Element Method (FEM). This book discusses the physical modeling as well as numerical computation. It also gives a comprehensive introduction to finite elements, including their computer implementation.
Anomalous fermion number violation and numerical simulations
International Nuclear Information System (INIS)
After discussing the problem of lattice regularization of chiral gauge theories, a simple model for anomalous fermion number violation is formulated which can be numerically studied with present day technique. Exploratory results of numerical simulations of a two-dimensional U(1) Higgs model are presented. (orig.)
Numerical simulations of the reditron
Kwan, Thomas J. T.; Davis, Harold A.
1988-04-01
The reflected-electrons discrimination microwave generator (reditron) is a high-power, narrow-band, and single-mode microwave generation that makes exclusive use of the oscillatory character of the virtual-cathode of a relativistic electron beam. The complex, nonlinear character of the virtual-cathode device necessitates particle-in-cell plasma simulation techniques. Investigations indicate two sources of the radiation: (1) the trapped electrons reflexing between the real and virtual cathodes, and (2) the oscillation of the virtual cathode. In the conventional design, the two mechanisms coexist and interfere with each other destructively, causing degradation of the efficiency of microwave generation. The authors have investigated a configuration with a slotted, thick anode and an external magnetic field, which effectively eliminates the reflexing electrons. Two-dimensional particle-in-cell simulations showed that such a configuration exploits the oscillation of the virtual cathode exclusively, and it generates single-mode, narrowbandwidth, and high-power microwave radiation with a potential efficiency over 10 percent. It was found that further optimization could be achieved by the use of a density (current) modulated electron beam at appropriate frequencies.
Numerical simulation of autoigniting flames
Asaithambi, Rajapandiyan; Mahesh, Krishnan
2012-11-01
Autoignition is highly sensitive to temperature and mixing. A density based method for DNS/LES of compressible chemically reacting flows is proposed with an explicit predictor step for advection and diffusion terms, and a semi-implicit corrector step for stiff chemical source terms. This segregated approach permits independent modification of the Navier-Stokes solver and the time integration algorithm for the chemical source term. The algorithm solves the total chemical and sensible energy equation and heat capacities of species are obtained from thermodynamic tables. Chemical mechanisms in the Chemkin format is parsed and source terms are automatically linearized allowing the ability to simulate multiple fuels with minimal effort. Validation of the algorithm is presented and results from autoigniting non-premixed flames in vitiated coflow with different fuels are discussed.
Directory of Open Access Journals (Sweden)
Patryk Zradziński
2013-12-01
Full Text Available Background: The assessment of electromagnetic field distribution near radiophones and their use warranted an analysis of thermal exposure hazards and related health effects, based on i.e. numerical calculations of specific energy absorption rate (SAR. Materials and Methods: The investigation concerned radiophones of conventional and trunked communication systems. Electromagnetic hazards assessment involved numerical simulations of SAR inside users' models (male and female for 5 radiophones locations - near the ear, arm, chest, hip and face. Results: Maximum SAR (10 g values depend on radiophone type, output power and locations. Near the chest, hip and face they are 6-, 2- and 2-fold higher than for location near the ear. SAR (10 g may exceed Directive 2013/35/EU limits at maximum (4 W output power of conventional radiophones, and the distance between antenna and worker's body shorter than 5 cm. SAR (10 g values near trunked radiophones do not exceed 35% of the Directive limits. The Polish safety and health regulations in particular cases of radiophones use and local exposure may not guarantee the compliance with Directive 2013/35/EU requirements, i.e. SAR (10 g may locally exceed exposure limit values (ELVs during exposure to electromagnetic fields of hazardous, and even intermediate zones. Conclusions: It was demonstrated that exposure of trunked radiophones users does not exceed the limits laid down in the Polish safety and health regulations and Directive 2013/35/EU, however, in particular scenarios of the conventional radiophones use overexposure can be observed. The results showed that in exposure to electromagnetic field emitted by sources located near workers' body there is a need for more detailed analysis of the compliance of Polish safety and health regulations with Directive 2013/35/EU requirements. Med Pr 2013;64(6:817–827
Numerical Simulation of Nanostructure Growth
Hwang, Helen H.; Bose, Deepak; Govindan, T. R.; Meyyappan, M.
2004-01-01
Nanoscale structures, such as nanowires and carbon nanotubes (CNTs), are often grown in gaseous or plasma environments. Successful growth of these structures is defined by achieving a specified crystallinity or chirality, size or diameter, alignment, etc., which in turn depend on gas mixture ratios. pressure, flow rate, substrate temperature, and other operating conditions. To date, there has not been a rigorous growth model that addresses the specific concerns of crystalline nanowire growth, while demonstrating the correct trends of the processing conditions on growth rates. Most crystal growth models are based on the Burton, Cabrera, and Frank (BCF) method, where adatoms are incorporated into a growing crystal at surface steps or spirals. When the supersaturation of the vapor is high, islands nucleate to form steps, and these steps subsequently spread (grow). The overall bulk growth rate is determined by solving for the evolving motion of the steps. Our approach is to use a phase field model to simulate the growth of finite sized nanowire crystals, linking the free energy equation with the diffusion equation of the adatoms. The phase field method solves for an order parameter that defines the evolving steps in a concentration field. This eliminates the need for explicit front tracking/location, or complicated shadowing routines, both of which can be computationally expensive, particularly in higher dimensions. We will present results demonstrating the effect of process conditions, such as substrate temperature, vapor supersaturation, etc. on the evolving morphologies and overall growth rates of the nanostructures.
Numerical simulation of LIGO input optics
None, Shivanand; Jamal, Nafis; Yoshida, Sanichiro
2005-11-01
Numerical analysis has been carried out to understand the performance of the Input Optics used in the first generation of LIGO (Laser Interferometer Gravitational-wave Observatory) detector. The input optics is a subsystem consisting of a mode cleaner and mode-matching telescope, where all the optics are suspended and installed in vacuum. Using the end-to-end package (LIGO programming language), computer codes have been made to simulate the input optics. Giving realistic seismic noise to the suspension point of the optics and using the length sensing/alignment sensing control for the mode cleaner, the performance of the input optics has been simulated under various scenarios such as with an order of magnitude higher seismic noise than the normal level, and with/without the alignment sensing control feedback from the arm cavity to the mode-matching telescope. The results are assessed in terms of the beam pointing fluctuation of the laser beam going into the arm cavities, and its influence on the optical coupling to the arm cavities and the noise level at the gravitational wave port signal.
Boundary acquisition for setup of numerical simulation
Energy Technology Data Exchange (ETDEWEB)
Diegert, C. [Sandia National Lab., Albuquerque, NM (United States)
1997-12-31
The author presents a work flow diagram that includes a path that begins with taking experimental measurements, and ends with obtaining insight from results produced by numerical simulation. Two examples illustrate this path: (1) Three-dimensional imaging measurement at micron scale, using X-ray tomography, provides information on the boundaries of irregularly-shaped alumina oxide particles held in an epoxy matrix. A subsequent numerical simulation predicts the electrical field concentrations that would occur in the observed particle configurations. (2) Three-dimensional imaging measurement at meter scale, again using X-ray tomography, provides information on the boundaries fossilized bone fragments in a Parasaurolophus crest recently discovered in New Mexico. A subsequent numerical simulation predicts acoustic response of the elaborate internal structure of nasal passageways defined by the fossil record. The author must both add value, and must change the format of the three-dimensional imaging measurements before the define the geometric boundary initial conditions for the automatic mesh generation, and subsequent numerical simulation. The author applies a variety of filters and statistical classification algorithms to estimate the extents of the structures relevant to the subsequent numerical simulation, and capture these extents as faceted geometries. The author will describe the particular combination of manual and automatic methods used in the above two examples.
Numerical simulation of sand jet in water
Energy Technology Data Exchange (ETDEWEB)
Azimi, A.H.; Zhu, D.; Rajaratnam, N. [Alberta Univ., Edmonton, AB (Canada). Dept. of Civil and Environmental Engineering
2008-07-01
A numerical simulation of sand jet in water was presented. The study involved a two-phase flow using two-phase turbulent jets. A literature review was also presented, including an experiment on particle laden air jet using laser doppler velocimetry (LDV); experiments on the effect of particle size and concentration on solid-gas jets; an experimental study of solid-liquid jets using particle image velocimetry (PIV) technique where mean velocity and fluctuations were measured; and an experimental study on solid-liquid jets using the laser doppler anemometry (LDA) technique measuring both water axial and radial velocities. Other literature review results included a photographic study of sand jets in water; a comparison of many two-phase turbulent flow; and direct numerical simulation and large-eddy simulation to study the effect of particle in gas jet flow. The mathematical model and experimental setup were also included in the presentation along with simulation results for sand jets, concentration, and kinetic energy. The presentation concluded with some proposed future studies including numerical simulation of slurry jets in water and numerical simulation of slurry jets in MFT. tabs., figs.
Numerical Simulation of Underwater Explosion Loads
Institute of Scientific and Technical Information of China (English)
XIN Chunliang; XU Gengguang; LIU Kezhong
2008-01-01
Numerical simulation of TNT underwater explosion was carried out with AUTODYN software.Influences of artificial viscosity and mesh density on simulation results were discussed.Detonation waves in explosive and shock wave in water during early time of explosion are high frequency waves.Fine meshes (less than 1 mm) in explosive and water nearby,and small linear viscosity coefficients and quadratic viscosity coefficients (0.02 and 0.1 respectively,1/10 of default values) are needed in numerical simulation model.According to these rules,numerical computing pressure profiles can match well with those calculated by Zamyshlyayev empirical formula.Otherwise peak pressure would be smeared off and upstream relative errors would be cumulated downstream to make downstream peak pressure lower.
DIRECT NUMERICAL SIMULATIONS OF MULTIPHASE FLOWS
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Direct numerical simulations have recently emerged as a viable tool to study finite Reynolds number multiphase flows. The approach parallels direct numerical simulations of turbulent flows, but the unsteady motion of a deformable phase boundary adds considerable complexity.Here, a front tracking method that has been used to study several multiphase flow problems is described. The Navier-Stokes equations are solved by a finite difference/front tracking technique that allows the inclusion of fully deformable interfaces and surface tension, in addition to inertial and viscous effects. A parallel version of the method makes it possible to use large grids and resolve flows containing a few hundred bubbles.``
Numerically simulating the sandwich plate system structures
Feng, Guo-Qing; Li, Gang; Liu, Zhi-Hui; Niu, Huai-Lei; Li, Chen-Feng
2010-09-01
Sandwich plate systems (SPS) are advanced materials that have begun to receive extensive attention in naval architecture and ocean engineering. At present, according to the rules of classification societies, a mixture of shell and solid elements are required to simulate an SPS. Based on the principle of stiffness decomposition, a new numerical simulation method for shell elements was proposed. In accordance with the principle of stiffness decomposition, the total stiffness can be decomposed into the bending stiffness and shear stiffness. Displacement and stress response related to bending stiffness was calculated with the laminated shell element. Displacement and stress response due to shear was calculated by use of a computational code write by FORTRAN language. Then the total displacement and stress response for the SPS was obtained by adding together these two parts of total displacement and stress. Finally, a rectangular SPS plate and a double-bottom structure were used for a simulation. The results show that the deflection simulated by the elements proposed in the paper is larger than the same simulated by solid elements and the analytical solution according to Hoff theory and approximate to the same simulated by the mixture of shell-solid elements, and the stress simulated by the elements proposed in the paper is approximate to the other simulating methods. So compared with calculations based on a mixture of shell and solid elements, the numerical simulation method given in the paper is more efficient and easier to do.
Correcting Numerical Simulations for Known Expectations
Myerscough, K.W.
2015-01-01
Predictions of the future climate require long-time simulation of a chaotic dynamical system. This poses a challenge for numerical simulations, as these do not necessarily capture the correct long-term behaviour of chaotic systems. This problem is exacerbated by the wide range of length scales present in atmospheric and oceanic dynamics. The modeling choices for small scale processes have a large impact on long term statistics of the scales of interest. This thesis studies the dynamics of two...
Numerical simulation of radial compressor stage
Luňáček O.; Syka T.
2013-01-01
Article describes numerical simulations of air flow in radial compressor stage in NUMECA CFD software. In simulations geometry variants with and without seals are used. During tasks evaluating was observed seals influence on flow field and performance parameters of compressor stage. Also is described CFDresults comparison with results from design software based on experimental measurements and monitoring of influence of seals construction on compressor stage efficiency.
Spectral Methods in Numerical Plasma Simulation
DEFF Research Database (Denmark)
Coutsias, E.A.; Hansen, F.R.; Huld, T.;
1989-01-01
An introduction is given to the use of spectral methods in numerical plasma simulation. As examples of the use of spectral methods, solutions to the two-dimensional Euler equations in both a simple, doubly periodic region, and on an annulus will be shown. In the first case, the solution is expanded...
Numerical simulations of compact object binaries
Pfeiffer, Harald P.
2012-01-01
Coalescing compact object binaries consisting of black holes and/or Neutron stars are a prime target for ground-based gravitational wave detectors. This article reviews the status of numerical simulations of these systems, with an emphasis on recent progress.
Numerical Simulations of a Vibrating Elasticum
DEFF Research Database (Denmark)
Sinclair, Robert
1999-01-01
Two robust numerical algorithms for simulating the dynamics of a clamped, massless, incompressibleelasticum with a unit point mass at the free end are presented, along with some first results concerning various modes of oscillation, and further data with some relevance to the question of whether ...
Database application platform for earthquake numerical simulation
Institute of Scientific and Technical Information of China (English)
LUO Yan; ZHENG Yue-jun; CHEN Lian-wang; LU Yuan-zhong; HUANG Zhong-xian
2006-01-01
@@ Introduction In recent years, all kinds of observation networks of seismology have been established, which have been continuously producing numerous digital information. In addition, there are many study results about 3D velocity structure model and tectonic model of crust (Huang and Zhao, 2006; Huang et al, 2003; Li and Mooney, 1998),which are valuable for studying the inner structure of the earth and earthquake preparation process. It is badly needed to combine the observed data, experimental study and theoretical analyses results by the way of numerical simulation and develop a database and a corresponding application platform to be used by numerical simulation,and is also a significant way to promote earthquake prediction.
Fluid Dynamics Theory, Computation, and Numerical Simulation
Pozrikidis, Constantine
2009-01-01
Fluid Dynamics: Theory, Computation, and Numerical Simulation is the only available book that extends the classical field of fluid dynamics into the realm of scientific computing in a way that is both comprehensive and accessible to the beginner. The theory of fluid dynamics, and the implementation of solution procedures into numerical algorithms, are discussed hand-in-hand and with reference to computer programming. This book is an accessible introduction to theoretical and computational fluid dynamics (CFD), written from a modern perspective that unifies theory and numerical practice. There are several additions and subject expansions in the Second Edition of Fluid Dynamics, including new Matlab and FORTRAN codes. Two distinguishing features of the discourse are: solution procedures and algorithms are developed immediately after problem formulations are presented, and numerical methods are introduced on a need-to-know basis and in increasing order of difficulty. Matlab codes are presented and discussed for ...
Fluid dynamics theory, computation, and numerical simulation
Pozrikidis, C
2001-01-01
Fluid Dynamics Theory, Computation, and Numerical Simulation is the only available book that extends the classical field of fluid dynamics into the realm of scientific computing in a way that is both comprehensive and accessible to the beginner The theory of fluid dynamics, and the implementation of solution procedures into numerical algorithms, are discussed hand-in-hand and with reference to computer programming This book is an accessible introduction to theoretical and computational fluid dynamics (CFD), written from a modern perspective that unifies theory and numerical practice There are several additions and subject expansions in the Second Edition of Fluid Dynamics, including new Matlab and FORTRAN codes Two distinguishing features of the discourse are solution procedures and algorithms are developed immediately after problem formulations are presented, and numerical methods are introduced on a need-to-know basis and in increasing order of difficulty Matlab codes are presented and discussed for a broad...
Numerical Simulation of Asynchronous Simulated Moving Bed Chromatography
Institute of Scientific and Technical Information of China (English)
卢建刚
2004-01-01
Asynchronous simulated moving bed chromatography (ASMBC), known also as the "VARICOL" process, is more efficient and flexible than the well-known and traditional simulated moving bed chromatography (SMBC). A detailed model of ASMBC, taking account of non-linear competitive isotherms, mass transfer parameters, and complex port switching schedule parameters, was developed to simulate the complex dynamics of ASMBC.The simulated performance is in close agreement with the experimental data of chiral separation reported in the literature. The simulation results show that ASMBC can achieve the performance similar to SMBC with fewer columns and can achieve better performance than SMBC with the same total column number. All design and operation parameters can be chosen correctly by numerical simulation. This detailed ASMBC model and the numerical technique are useful for design, operation, optimization and scale-up of ASMBC.
The direct numerical simulation of pipe flow
Institute of Scientific and Technical Information of China (English)
LIU Zheng-gang; DU Guang-sheng; SHAO Zhu-feng
2013-01-01
The conservative difference scheme and the third-order Runge-Kutta scheme in combination with the the Crank-Nicholson scheme are used to directly simulate the flow field in a pipe with the Reynolds number of 2 600.The flow field,including the velocity distribution and the turbulence intensity,is obtained by the direct numerical simulation.From the calculated results,the ratio of the linear average velocity along the ultrasonic propagation path to the profile average velocity on the pipe cross-section is also obtained in an ultrasonic flow meter.It is concluded that the direct numerical simulation method can be used to study the ratio of the profile-linear average velocity at low Reynolds number conditions in the transition region and to improve the measurement accuracy of the ultrasonic flow meter.
Numerical simulation of groundwater flow on MPPs
Energy Technology Data Exchange (ETDEWEB)
Ashby, S.; Falgout, R.; Tompson, A. [Lawrence Livermore National Lab., CA (United States); Fogwell, T. [International Technology Corp., Martinez, CA (United States)
1994-03-01
Mathematical models are often used to aid in the design and management of engineered remediation procedures. This paper discusses the numerical simulation of groundwater flow in three-dimensional heterogeneous porous media. A portable and scalable code called PARFLOW is being developed for massively parallel computers to enable the detailed modeling of large sites. This code uses a turning bands algorithm to generate a statistically accurate subsurface realization, and preconditioned conjugate gradients to solve the linear system that yields the flow velocity field. Preliminary numerical results for the LLNL site are presented.
Numerical simulation of groundwater flow on MPPs
International Nuclear Information System (INIS)
Mathematical models are often used to aid in the design and management of engineered remediation procedures. This paper discusses the numerical simulation of groundwater flow in three-dimensional heterogeneous porous media. A portable and scalable code called PARFLOW is being developed for massively parallel computers to enable the detailed modeling of large sites. This code uses a turning bands algorithm to generate a statistically accurate subsurface realization, and preconditioned conjugate gradients to solve the linear system that yields the flow velocity field. Preliminary numerical results for the LLNL site are presented
International Nuclear Information System (INIS)
Highlights: • DNS database of propagating turbulent premixed flames for a range of Lewis numbers. • A-priori analysis of 7 different algebraic LES sub-grid scalar flux models. • Gradient closure does neither capture the quantitative nor the qualitative trend. • Models based on a BML like expression tend to over-predict counter-gradient transport. • Models using a tensor diffusivity perform relatively better than alternative models. - Abstract: The statistical behaviours of sub-grid flux of reaction progress variable has been assessed for premixed turbulent flames with global Lewis number Le (=thermal diffusivity/mass diffusivity) ranging from 0.34 to 1.2 using a Direct Numerical Simulation (DNS) database of freely propagating statistically planar flames. It is known that the sub-grid scalar flux shows counter-gradient transport when the velocity jump across the flame due to heat release overcomes the effects of turbulent velocity fluctuation. The results show that the sub-grid scalar flux components exhibit counter-gradient transport for all cases considered here. The extent of counter-gradient transport increases with increasing filter width Δ and decreasing value of Le. This is due to the fact that flames with Le ≪ 1 (e.g. Le = 0.34) exhibit thermo-diffusive instabilities, which in turn increases the extent of counter-gradient transport. The effects of heat release and flame normal acceleration weaken with increasing Le. Several established algebraic models have been assessed in comparison to the sub-grid scalar flux components extracted from explicitly filtered DNS data in terms of their correlation coefficients at the vector level and their mean variation conditional on the Favre-filtered progress variable. The gradient transport closure does neither capture the quantitative nor the qualitative behaviour of the different sub-grid scalar flux components for all filter widths in all cases considered here. Models which account for local flame normal
Numerical simulation of centrifugal casting of pipes
International Nuclear Information System (INIS)
A numerical simulation model for the horizontal centrifugal pipe casting process was developed with the commercial simulation package Flow3D. It considers - additionally to mass, energy and momentum conservation equations and free surface tracking - the fast radial and slower horizontal movement of the mold. The iron inflow is not steady state but time dependent. Of special importance is the friction between the liquid and the mold in connection with the viscosity and turbulence of the iron. Experiments with the mold at controlled revolution speeds were carried out using a high-speed camera. From these experiments friction coefficients for the description of the interaction between mold and melt were obtained. With the simulation model, the influence of typical process parameters (e.g. melts inflow, mold movement, melt temperature, cooling media) on the wall thickness of the pipes can be studied. The comparison to results of pipes from production shows a good agreement between simulation and reality.
Numerical simulation of centrifugal casting of pipes
Kaschnitz, E.
2012-07-01
A numerical simulation model for the horizontal centrifugal pipe casting process was developed with the commercial simulation package Flow3D. It considers - additionally to mass, energy and momentum conservation equations and free surface tracking - the fast radial and slower horizontal movement of the mold. The iron inflow is not steady state but time dependent. Of special importance is the friction between the liquid and the mold in connection with the viscosity and turbulence of the iron. Experiments with the mold at controlled revolution speeds were carried out using a high-speed camera. From these experiments friction coefficients for the description of the interaction between mold and melt were obtained. With the simulation model, the influence of typical process parameters (e.g. melts inflow, mold movement, melt temperature, cooling media) on the wall thickness of the pipes can be studied. The comparison to results of pipes from production shows a good agreement between simulation and reality.
Numerical simulation of biped locomotion robot
International Nuclear Information System (INIS)
The Human Acts Simulation Program (HASP) has been performed since 1987 at JAERI. In this program, a human-shaped robot reads and understands instructions written in natural languages such as Japanese, planning and producing a required sequence of actions, approach to a device or an instrument recognizing its entity and does the ordered work for plant maintenance. All of these processes are simulated by logical and numerical computations. The major aim of the HASP is to develop fundamental technologies for design of intelligent robots. This report will describe the simulation methods and results of a human-shaped robot motions. The simulation methods of robot's arms and robot's start and stop motions have been newly developed based on the steady walking model with fixed arms developed by M. Vukobratovic. The influence of arm motions to the stable walking and the continuous connection from start to steady walking, etc. will be discussed. (author)
Large scale numerical simulation for superfluid turbulence
International Nuclear Information System (INIS)
Large scale numerical simulation of quantum turbulence is performed by using 3-D time-dependent Gross-Pitaevskii equation. The energy spectrum obeying Kolmogorov law and large scale self-similar structure of quantum vortex tangle are found in a fully developed dumped turbulent state. We confirm that inertial range of the energy spectrum becomes large as the system size of the simulation becomes large that is consistent with the result of the normal fluid turbulence. On the other hand, bottleneck effect near coherent length prevents the inertial range from extending to smaller scale. (author)
Numerical simulation of gaseous ionization detectors
International Nuclear Information System (INIS)
Here, various approaches adopted to numerically simulate the detailed device physics of gaseous ionization detectors. Related experimental efforts will also be mentioned. Mathematical formulations, algorithms and simulation frameworks will be touched upon, in general. In particular, focus on several physics issues that author have addressed in recent times, such as, a) effects of non-uniformities and imperfections on device response, b) estimation of gain, spatial, temporal and energy resolutions, c) effects of electronic heating on device performance, and d) estimation of ion backflow in Micromegas - (single and double mesh) and GEM - (single and layered) based detectors
Contributions to reinforced concrete structures numerical simulations
International Nuclear Information System (INIS)
In order to be able to carry out simulations of reinforced concrete structures, it is necessary to know two aspects: the behaviour laws have to reflect the complex behaviour of concrete and a numerical environment has to be developed in order to avoid to the user difficulties due to the softening nature of the behaviour. This work deals with these two subjects. After an accurate estimation of two behaviour models (micro-plan and mesoscopic models), two damage models (the first one using a scalar variable, the other one a tensorial damage of the 2 order) are proposed. These two models belong to the framework of generalized standard materials, which renders their numerical integration easy and efficient. A method of load control is developed in order to make easier the convergence of the calculations. At last, simulations of industrial structures illustrate the efficiency of the method. (O.M.)
Numerical Simulation of Piston Ring Lubrication
DEFF Research Database (Denmark)
Felter, Christian Lotz
2006-01-01
and the angle between the normals of the solid and the free surface. The numerical model is compared with the results from an analytical solution of Reynolds equation for a fixed incline slider bearing. Then results from a more compli- cated simulation of piston ring lubrication is given and discussed.......This paper describes a numerical method that can be used to model the lubrication of piston rings. Classical lubrication theory is based on the Reynolds equation which is ap- plicable to confined geometries and open geometries where the flooding conditions are known. Lubrication of piston rings...... extended to include also the oil film outside the piston rings. The numerical model consists of a 2D free surface code that solves the time dependent compressible Navier-Stokes equations. The equations are cast in Lagrangian form and discretized by a meshfree moving least squares method using the primitive...
Numerical Simulation on CCOS Controllable Variable
Institute of Scientific and Technical Information of China (English)
CHENG Hao-bo; FENG Zhi-jing
2003-01-01
On the basis of Preston hypothesis,the motion relationship between tool and workpiece upon the tool's motion in planar model is analyzed.The effect on computer controlled optical surfacing (CCOS) caused by controllable variable is simulated except for the dwelling time,thus,some reference on theory is provided to optimize the former numerical control (NC) model,and fast manufacturing of large departure aspherics is realized.
Numerical simulation of spherical plasma focus diode
International Nuclear Information System (INIS)
A self-magnetically insulated, three-dimensionally-focused ion-beam diode, spherical plasma focus diode (SPFD), is studied by numerical simulation using a two-dimensional, electromagnetic, relativistic particle-in-cell computer code. The calculated results of the diode impedance, the ion-current efficiency, and the focusing characteristics of the ion beam are presented. These results, except the data of the ion-beam current, are in good agreement with the experimental results. (author)
Numerical simulation of galvanized rebars pullout
Hélder Pereira; Cunha, Vitor M. C. F.; Sena-Cruz, José
2015-01-01
The usage of rebars in construction is the most common method for reinforcing plain concrete and thus bridging the tensile stresses along the concrete crack surfaces. Usually design codes for modelling the bond behaviour of rebars and concrete suggest a local bond stress – slip relationship that comprises distinct reinforcement mechanisms, such as adhesion, friction and mechanical anchorage. In this work, numerical simulations of pullout tests were performed using the finite element method fr...
Numerical simulation of cardiovascular baroreflex control
Czech Academy of Sciences Publication Activity Database
Převorovská, Světlana; Maršík, František
Vol. 3. Praha : UTAM AV ČR, 2000 - (Náprstek, J.; Minster, J.), s. 91-96 ISBN 80-86246-06-X. [International conference Engineering mechanics 2000. Svratka (CZ), 15.05.2000-18.05.2000] R&D Projects: GA ČR GA106/98/1373; GA AV ČR KSK1076602 Keywords : numerical simulation * baroreflex control * cardiovascular system Subject RIV: BO - Biophysics
Numerical Simulation of the Atmospheric Boundary Layer
Czech Academy of Sciences Publication Activity Database
Bauer, Petr
Praha : Česká technika - nakladatelství ČVUT, 2006 - (Ambrož, P.; Masáková, Z.), s. 11-18 [Doktorandské dny 2006. Katedra matematiky FJFI ČVUT, Praha (CZ), 10.11.2006-24.11.2006] Institutional research plan: CEZ:AV0Z20760514 Keywords : atmospheric boundary layer * numerical simulation * finite element method Subject RIV: DI - Air Pollution ; Quality
Numerical Simulations of Boundary-Driven Dynamos
White, K.; Brummell, N.; Glatzmaier, G. A.
2012-12-01
An important topic of physics research is how magnetic fields are generated and maintained in the many astrophysical bodies where they are ubiquitously observed. Of particular interest, are reversals of magnetic fields of planets and stars, especially those of the Earth and the Sun. In an attempt to provide intuition on this problem, numerous physical dynamo experiments have been performed in different configurations. Recently, a tremendous breakthrough was made in the Von Karman sodium (VKS) experiments in France when the most realistic laboratory fluid dynamo to date was produced by driving an unconstrained flow in a cylinder of liquid sodium (Monchaux et al, 2007, PRL). One of the curiosities of the VKS experiment however is the effect of the composition of the impellers that drive the flow. Steel blades failed to produce a dynamo, but soft iron impellers, which have much higher magnetic permeability, succeeded. The role of the magnetic properties of the boundaries in boundary-driven dynamos is therefore clearly of interest. Kinematic and laminar numerical dynamo simulations (Giesecke et al, 2010, PRL & Gissinger et al, 2008 EPL) have shed some light but turbulent, nonlinear simulations are necessary. Roberts, Glatzmaier & Clune 2010 created a simplified model of the VKS setup by using three-dimensional numerical simulations in a spherical geometry with differential zonal motions of the boundary replacing the driving impellers of the VKS experiment. We have extended these numerical simulations further towards a more complete understanding of such boundary-forced dynamos. In particular, we have examined the effect of the magnetic boundary conditions - changes in the wall thickness, the magnetic permeability, and the electrical conductivity - on the mechanisms responsible for dynamo generation. Enhanced permeability, conductivity and wall thickness all help dynamo action to different degrees. We are further extending our investigations to asymmetric forcing to
Efficient Numerical Inversion for Financial Simulations
Derflinger, Gerhard; Hörmann, Wolfgang; Leydold, Josef; Sak, Halis
2009-01-01
Generating samples from generalized hyperbolic distributions and non-central chi-square distributions by inversion has become an important task for the simulation of recent models in finance in the framework of (quasi-) Monte Carlo. However, their distribution functions are quite expensive to evaluate and thus numerical methods like root finding algorithms are extremely slow. In this paper we demonstrate how our new method based on Newton interpolation and Gauss-Lobatto quadrature can be util...
Numerical Simulations of Hyperfine Transitions of Antihydrogen
Kolbinger, B; Diermaier, M; Lehner, S; Malbrunot, C; Massiczek, O; Sauerzopf, C; Simon, M C; Widmann, E
2015-01-01
One of the ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons) collaboration's goals is the measurement of the ground state hyperfine transition frequency in antihydrogen, the antimatter counterpart of one of the best known systems in physics. This high precision experiment yields a sensitive test of the fundamental symmetry of CPT. Numerical simulations of hyperfine transitions of antihydrogen atoms have been performed providing information on the required antihydrogen events and the achievable precision.
Numerical simulations of hyperfine transitions of antihydrogen
International Nuclear Information System (INIS)
One of the ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons) collaboration’s goals is the measurement of the ground state hyperfine transition frequency in antihydrogen, the antimatter counterpart of one of the best known systems in physics. This high precision experiment yields a sensitive test of the fundamental symmetry of CPT. Numerical simulations of hyperfine transitions of antihydrogen atoms have been performed providing information on the required antihydrogen events and the achievable precision
Numerical simulations of hyperfine transitions of antihydrogen
Energy Technology Data Exchange (ETDEWEB)
Kolbinger, B., E-mail: bernadette.kolbinger@oeaw.ac.at; Capon, A.; Diermaier, M.; Lehner, S. [Stefan Meyer Institute for Subatomic Physics, Austrian Academy of Sciences (Austria); Malbrunot, C. [CERN (Switzerland); Massiczek, O.; Sauerzopf, C.; Simon, M. C.; Widmann, E. [Stefan Meyer Institute for Subatomic Physics, Austrian Academy of Sciences (Austria)
2015-08-15
One of the ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons) collaboration’s goals is the measurement of the ground state hyperfine transition frequency in antihydrogen, the antimatter counterpart of one of the best known systems in physics. This high precision experiment yields a sensitive test of the fundamental symmetry of CPT. Numerical simulations of hyperfine transitions of antihydrogen atoms have been performed providing information on the required antihydrogen events and the achievable precision.
Theoretical issues in Numerical Relativity simulations
Alic, Daniela Delia
2009-01-01
In this thesis we address several analytical and numerical problems related with the general relativistic study of black hole space-times and boson stars. We have developed a new centered finite volume method based on the flux splitting approach. The techniques for dealing with the singularity, steep gradients and apparent horizon location, are studied in the context of a single Schwarzschild black hole, in both spherically symmetric and full 3D simulations. We present an extended study of ga...
Numerical simulation of electrostatic waves in plasmas
International Nuclear Information System (INIS)
In this paper the propagation of electrostatic waves in plasmas and the non-linear interactions, which occur in the case of large wave amplitudes, are studied using a new numerical method for plasma simulation. This mathematical description is based on the Vlasov-model. Changes in the distribution-function are taken into account and thus plasma kinetic effects can be treated. (orig./HT)
Advanced numerical techniques in core simulations
International Nuclear Information System (INIS)
The whole core simulations are one of the most CPU intensive calculations in reactor physics design and analyses. For a designer it is imperative to perform these calculations with good accuracy and in least time possible to try out various options. It is important for the code developers to use techniques involving minimum approximations and to use most recent numerical methods applied in tandem with huge computing power available today. In the presented paper, some of these methods are discussed. (author)
Numerical schemes for large eddy simulation
International Nuclear Information System (INIS)
This thesis is devoted to the simulation of incompressible or low Mach turbulent flows, for nuclear safety applications. In particular, we focus on the development and analysis of performing numerical schemes for the Large Eddy Simulation technique. These schemes are based on fractional step methods of pressure correction type and on nonconforming low degree finite elements. Two requirements seems essential to build such schemes, namely a control of kinetic energy and the accuracy for convection dominated flows. Concerning the time marching algorithm, we propose a Crank-Nicolson like scheme for which we prove a kinetic energy control. This scheme has the advantage to be numerically low dissipative (numerical dissipation residual is second order in time). Concerning the low accuracy of the Rannacher-Turek discretization, two approaches are investigated in this work. The first one consists in building a penalized scheme constraining the velocity degrees of freedom tangent to the faces to be written as a linear combination of the normal ones. The second approach relies on the enrichment of the pressure approximation discrete space. Finally, various numerical tests are presented in both two and three dimensions and for general meshes, to illustrate the capacity of the schemes and compare theoretical and experimental results. (author)
Numerical simulation of nuclear pebble bed configurations
Energy Technology Data Exchange (ETDEWEB)
Shams, A., E-mail: shams@nrg.eu [Nuclear Research and Consultancy Group (NRG), Petten (Netherlands); Roelofs, F., E-mail: roelofs@nrg.eu [Nuclear Research and Consultancy Group (NRG), Petten (Netherlands); Komen, E.M.J., E-mail: komen@nrg.eu [Nuclear Research and Consultancy Group (NRG), Petten (Netherlands); Baglietto, E., E-mail: emiliob@MIT.EDU [Massachusetts Institute of Technology (MIT) (United States)
2015-08-15
Highlights: • Numerical simulations of a single face cubic centred pebble bed are performed. • Wide range of turbulence modelling techniques are used to perform these calculations. • The methods include 1-DNS, 1-LES, 3-Hybrid (RANS/LES) and 3-RANS models, respectively. • The obtained results are extensively compared to provide guidelines for such flow regimes. • These guidelines are used to perform reference LES for a limited sized random pebble bed. - Abstract: High Temperature Reactors (HTRs) are being considered all over the world. An HTR uses helium gas as a coolant, while the moderator function is taken up by graphite. The fuel is embedded in the graphite moderator. A particular inherent safety advantage of HTR designs is that the graphite can withstand very high temperatures, that the fuel inside will stay inside the graphite pebble and cannot escape to the surroundings even in the event of loss of cooling. Generally, the core can be designed using a graphite pebble bed. Some experimental and demonstration reactors have been operated using a pebble bed design. The test reactors have shown safe and efficient operation, however questions have been raised about possible occurrence of local hot spots in the pebble bed which may affect the pebble integrity. Analysis of the fuel integrity requires detailed evaluation of local heat transport phenomena in a pebble bed, and since such phenomena cannot easily be modelled experimentally, numerical simulations are a useful tool. As a part of a European project, named Thermal Hydraulics of Innovative Nuclear Systems (THINS), a benchmarking quasi-direct numerical simulation (q-DNS) of a well-defined pebble bed configuration has been performed. This q-DNS will serve as a reference database in order to evaluate the prediction capabilities of different turbulence modelling approaches. A wide range of numerical simulations based on different available turbulence modelling approaches are performed and compared with
Numerical simulation of nuclear pebble bed configurations
International Nuclear Information System (INIS)
Highlights: • Numerical simulations of a single face cubic centred pebble bed are performed. • Wide range of turbulence modelling techniques are used to perform these calculations. • The methods include 1-DNS, 1-LES, 3-Hybrid (RANS/LES) and 3-RANS models, respectively. • The obtained results are extensively compared to provide guidelines for such flow regimes. • These guidelines are used to perform reference LES for a limited sized random pebble bed. - Abstract: High Temperature Reactors (HTRs) are being considered all over the world. An HTR uses helium gas as a coolant, while the moderator function is taken up by graphite. The fuel is embedded in the graphite moderator. A particular inherent safety advantage of HTR designs is that the graphite can withstand very high temperatures, that the fuel inside will stay inside the graphite pebble and cannot escape to the surroundings even in the event of loss of cooling. Generally, the core can be designed using a graphite pebble bed. Some experimental and demonstration reactors have been operated using a pebble bed design. The test reactors have shown safe and efficient operation, however questions have been raised about possible occurrence of local hot spots in the pebble bed which may affect the pebble integrity. Analysis of the fuel integrity requires detailed evaluation of local heat transport phenomena in a pebble bed, and since such phenomena cannot easily be modelled experimentally, numerical simulations are a useful tool. As a part of a European project, named Thermal Hydraulics of Innovative Nuclear Systems (THINS), a benchmarking quasi-direct numerical simulation (q-DNS) of a well-defined pebble bed configuration has been performed. This q-DNS will serve as a reference database in order to evaluate the prediction capabilities of different turbulence modelling approaches. A wide range of numerical simulations based on different available turbulence modelling approaches are performed and compared with
Advanced numerical simulations of selected metallurgical units
Directory of Open Access Journals (Sweden)
G. Kokot
2012-12-01
Full Text Available Purpose: of this paper is to present numerical simulations of large structures in metallurgical industry. Some examples of finite element analysis are presented. The calculations were performed for the determining the stress effort of the metallurgical units mainly blast furnace, throath’s gas pipelines, hot blast stoves, etc. during the working conditions and for the repairing purpose.Design/methodology/approach: The way of conducting simulations and analysis were the finite element method connected with the optimization process.Findings: Performing the numerical analysis the changes in the structures design were applied what extremely influenced on the state effort and the durability of considered structures.Research limitations/implications: Development of the presented approach solving the coupled field and CFD problems, the application of the parallel computing and domain decomposition methods in the large structure simulations.Practical implications: Presented results shows the possibility of application the advanced computational methods in the computer aided engineering processes of designing and analysing the large structure as the metallurgical units are. It can dramatically influence on the recognizing of the effort stets and helps in the monitoring, overhauls and redesigning process. Those methods gives the global very precise information which cannot be obtain in other ways (analytical solutions, experimental methods.Originality/value: The paper present the original research results comes from the complex numerical simulations of the main metallurgical units in the blast furnace train. The original value of the paper is the introduction of the advanced finite element simulation in the field of iron steel industry structures design and developing.
NUMERICAL MODEL APPLICATION IN ROWING SIMULATOR DESIGN
Directory of Open Access Journals (Sweden)
Petr Chmátal
2016-04-01
Full Text Available The aim of the research was to carry out a hydraulic design of rowing/sculling and paddling simulator. Nowadays there are two main approaches in the simulator design. The first one includes a static water with no artificial movement and counts on specially cut oars to provide the same resistance in the water. The second approach, on the other hand uses pumps or similar devices to force the water to circulate but both of the designs share many problems. Such problems are affecting already built facilities and can be summarized as unrealistic feeling, unwanted turbulent flow and bad velocity profile. Therefore, the goal was to design a new rowing simulator that would provide nature-like conditions for the racers and provide an unmatched experience. In order to accomplish this challenge, it was decided to use in-depth numerical modeling to solve the hydraulic problems. The general measures for the design were taken in accordance with space availability of the simulator ́s housing. The entire research was coordinated with other stages of the construction using BIM. The detailed geometry was designed using a numerical model in Ansys Fluent and parametric auto-optimization tools which led to minimum negative hydraulic phenomena and decreased investment and operational costs due to the decreased hydraulic losses in the system.
Mathematical models and numerical simulation in electromagnetism
Bermúdez, Alfredo; Salgado, Pilar
2014-01-01
The book represents a basic support for a master course in electromagnetism oriented to numerical simulation. The main goal of the book is that the reader knows the boundary-value problems of partial differential equations that should be solved in order to perform computer simulation of electromagnetic processes. Moreover it includes a part devoted to electric circuit theory based on ordinary differential equations. The book is mainly oriented to electric engineering applications, going from the general to the specific, namely, from the full Maxwell’s equations to the particular cases of electrostatics, direct current, magnetostatics and eddy currents models. Apart from standard exercises related to analytical calculus, the book includes some others oriented to real-life applications solved with MaxFEM free simulation software.
Numerical Simulation of a Seaway with Breaking
Dommermuth, Douglas; O'Shea, Thomas; Brucker, Kyle; Wyatt, Donald
2012-11-01
The focus of this presentation is to describe the recent efforts to simulate a fully non-linear seaway with breaking by using a high-order spectral (HOS) solution of the free-surface boundary value problem to drive a three-dimensional Volume of Fluid (VOF) solution. Historically, the two main types of simulations to simulate free-surface flows are the boundary integral equations method (BIEM) and high-order spectral (HOS) methods. BIEM calculations fail at the point at which the surface impacts upon itself, if not sooner, and HOS methods can only simulate a single valued free-surface. Both also employ a single-phase approximation in which the effects of the air on the water are neglected. Due to these limitations they are unable to simulate breaking waves and air entrainment. The Volume of Fluid (VOF) method on the other hand is suitable for modeling breaking waves and air entrainment. However it is computationally intractable to generate a realistic non-linear sea-state. Here, we use the HOS solution to quickly drive, or nudge, the VOF solution into a non-linear state. The computational strategies, mathematical formulation, and numerical implementation will be discussed. The results of the VOF simulation of a seaway with breaking will also be presented, and compared to the single phase, single valued HOS results.
Numerical simulation of the fouling process
Energy Technology Data Exchange (ETDEWEB)
Brahim, Fahmi; Augustin, Wolfgang; Bohnet, Matthias [Institut fuer Chemische und Termische Verfahrenstechnik, Technische Universitaet Braunschweig, Langer Kamp 7, 38106, Braunschweig (Germany)
2003-03-01
Fouling of heat transfer surfaces causes serious technical and economic problems in industry. The goal of this work is to simulate the aforementioned fouling process using the CFD code FLUENT. The obtained numerical results assist in designing and running heat exchangers.Based on models for the calculation of deposition and removal mass rates [S. Krause, Internat. Chem. Engrg. 33 (1993)], the crystallization fouling of calcium sulfate on flat heat transfer surfaces was simulated. The induction period, which occurs with almost all fouling processes, was therefore not considered.The simulation of real crystal growth requires a continuous variation of the geometric flow model and therefore considerable computational effort. For that reason fictitious crystal growth was simulated instead. This numerical simplification enabled an unsteady simulation to be obtained, of the fouling process and a realistic description of the temporal modification of both the flow and temperature field due to the continuous crystal growth.Based on experimental results of Hirsch [M. Bohnet et al., in: T.R. Bott et al. (Eds.), Understanding Heat Exchanger Fouling and its Mitigation, United Engineering Foundation and Begell House, New York, 1997, pp. 201-208], a model was developed which enables the calculation of the density of the fouling layer not only as a function of the local position within the fouling layer, but also as a function of the time-dependent total thickness of the fouling layer. In addition a model was developed, that enables a realistic distribution of the heat flux along the heat transfer surface during the simulation. Both models provide a more exact description of the complicated fouling process.Results of the numerical simulation are the prediction of the fouling resistance as a function of time and the calculation of the temperature distribution within the fouling layer. In view of the complexity of the fouling process during the incrustation of heat transfer surfaces
Direct numerical simulation of the Leidenfrost Effect
Rueda Villegas, Lucia; Tanguy, Sébastien
2012-11-01
We present direct numerical simulations of the impact of a single droplet on a heated flat surface in the Leidenfrost regime. To that end, we solve the Navier-Stokes equations, the energy equation, and the species mass fraction equation. The Level Set method is used to track the liquid-gas interface motion and the Ghost Fluid Method is implemented to treat the jump conditions. To get rid of the temporal stability condition due to viscosity, an implicit temporal discretization is used. Some specific numerical methods have been developed to deal with droplet vaporization interface jump conditions. Since the vapor layer is very thin compared to the droplet size, a non-uniform structured grid strongly refined near the wall is used to capture the droplet bounce. We present numerical simulations that enable us to study accurately the bouncing dynamics by analyzing the momentum balance during the droplet bounce. Moreover, we determine from such computation the ratio of the droplet heat transfer flux by comparing the energy used for the phase change (latent heat) to the energy used for droplet heating (specific heat). We then compare the shape of the droplet during the impact with some experimental results.
Numerical simulation of lower hybrid wave propagation
International Nuclear Information System (INIS)
Concerning the LHRH (Lower Hybrid Resonance Heating) in a tokamak, a numerical simulation is made of the propagation of a lower hybrid wave. By solving the system of two-fluid equations and Poisson's equation, ray trajectories of the lower hybrid waves are traced. The cases of cold plasma approximation, linear approximation and nonlinear two-fluid model are examined. The effect of density fluctuation due to the presence of a drift wave on the conical ray trajectories is also studied. Only the preliminary results are presented in this report. (auth.)
Tornado structure interaction: a numerical simulation
International Nuclear Information System (INIS)
The effects of tornadoes on buildings are examined to determine the wind forces on structures. The American National Standards Institute (ANSI) has developed guidelines for building code requirements for the minimum wind loads a building must be designed to withstand. The conservatism or nonconservatism on the ANSI approach is evaluated by simulating tornado-structure interaction numerically with a two-dimensional fluid dynamics computer code and a vortex model. Only external pressures are considered. The computer calculations yield the following percentages of the ANSI design pressures: rigid frame, 50 to 90%; individual wall panels, 75 to 200%; and wall corners, 50 to 75%
Numerical Simulations of Thermionic Electron Guns
Czech Academy of Sciences Publication Activity Database
Jánský, Pavel; Lencová, Bohumila; Zlámal, J.
Brno: Institute of Scientific Instruments AS CR, v.v.i, 2008 - (Mika, F.), s. 51-52 ISBN 978-80-254-0905-3. [International Seminar on Recent Trends in Charged Particle Optics and Surface Physics Instrumentation /11./. Skalský dvůr (CZ), 14.07.2008-18.07.2008] R&D Projects: GA AV ČR IAA100650805 Institutional research plan: CEZ:AV0Z20650511 Keywords : electron emission * electron gun * space charge * numerical simulations Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering
Numerical considerations in simulating the global magnetosphere
Directory of Open Access Journals (Sweden)
A. J. Ridley
2010-08-01
Full Text Available Magnetohydrodynamic (MHD models of the global magnetosphere are very good research tools for investigating the topology and dynamics of the near-Earth space environment. While these models have obvious limitations in regions that are not well described by the MHD equations, they can typically be used (or are used to investigate the majority of magnetosphere. Often, a secondary consideration is overlooked by researchers when utilizing global models – the effects of solving the MHD equations on a grid, instead of analytically. Any discretization unavoidably introduces numerical artifacts that affect the solution to various degrees. This paper investigates some of the consequences of the numerical schemes and grids that are used to solve the MHD equations in the global magnetosphere. Specifically, the University of Michigan's MHD code is used to investigate the role of grid resolution, numerical schemes, limiters, inner magnetospheric density boundary conditions, and the artificial lowering of the speed of light on the strength of the ionospheric cross polar cap potential and the build up of the ring current in the inner magnetosphere. It is concluded that even with a very good solver and the highest affordable grid resolution, the inner magnetosphere is not grid converged. Artificially reducing the speed of light reduces the numerical diffusion that helps to achieve better agreement with data. It is further concluded that many numerical effects work nonlinearly to complicate the interpretation of the physics within the magnetosphere, and so simulation results should be scrutinized very carefully before a physical interpretation of the results is made. Our conclusions are not limited to the Michigan MHD code, but apply to all MHD models due to the limitations of computational resources.
The numerical simulation of accelerator components
International Nuclear Information System (INIS)
The techniques of the numerical simulation of plasmas can be readily applied to problems in accelerator physics. Because the problems usually involve a single component ''plasma,'' and times that are at most, a few plasma oscillation periods, it is frequently possible to make very good simulations with relatively modest computation resources. We will discuss the methods and illustrate them with several examples. One of the more powerful techniques of understanding the motion of charged particles is to view computer-generated motion pictures. We will show several little movie strips to illustrate the discussions. The examples will be drawn from the application areas of Heavy Ion Fusion, electron-positron linear colliders and injectors for free-electron lasers. 13 refs., 10 figs., 2 tabs
Numerical Simulation of Level Magnetic Field
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
According to Maxwell electromagnetic field theory and magnetic vector potential integral equation, a mathematical model of LMF (Level Magnetic Field) for EMBR (Electromagnetic brake) was proposed, and the reliable software for LMF calculation was developed. The distribution of magnetic flux density given by numerical simulation shows that the magnetic flux density is greater in the magnet and magnetic leakage is observed in the gap. The magnetic flux density is uniform in horizontal plane and a peak is observed in vertical plane. Furthermore, the effects of electromagnetic and structural parameters on magnetic flux density were discussed. The relationship between magnetic flux, electromagnetic parameters and structural parameters is obtained by dimensional analysis, simulation experiment and least square method.
Highly focused supersonic microjets: numerical simulations
Peters, Ivo R; Oudalov, Nikolai; Sun, Chao; Prosperetti, Andrea; Lohse, Detlef; van der Meer, Devaraj
2012-01-01
By focusing a laser pulse inside a capillary partially filled with liquid, a vapour bubble is created which emits a pressure wave. This pressure wave travels through the liquid and creates a fast, focused axisymmetric microjet when it is reflected at the meniscus. We numerically investigate the formation of this microjet using axisymmetric boundary-integral simulations, where we model the pressure wave as a pressure pulse applied on the bubble. We find a good agreement between the simulations and experimental results in terms of the time evolution of the jet and on all parameters that can be compared directly. We present a simple analytical model that accurately predicts the velocity of the jet after the pressure pulse and its maximum velocity.
Numerical simulations of disc-planet interactions
Paardekooper, Richard P Nelson Sijme-Jan
2009-01-01
The gravitational interaction between a protoplanetary disc and planetary sized bodies that form within it leads to the exchange of angular momentum, resulting in migration of the planets and possible gap formation in the disc for more massive planets. In this article, we review the basic theory of disc-planet interactions, and discuss the results of recent numerical simulations of planets embedded in protoplanetary discs. We consider the migration of low mass planets and recent developments in our understanding of so-called type I migration when a fuller treatment of the disc thermodynamics is included. We discuss the runaway migration of intermediate mass planets (so-called type III migration), and the migration of giant planets (type II migration) and the associated gap formation in the disc. The availability of high performance computing facilities has enabled global simulations of magnetised, turbulent discs to be computed, and we discuss recent results for both low and high mass planets embedded in such...
Numerical simulation of attosecond nanoplasmonic streaking
Energy Technology Data Exchange (ETDEWEB)
Skopalova, E; Lei, D Y; Witting, T; Arrell, C; Frank, F; Sonnefraud, Y; Maier, S A; Tisch, J W G; Marangos, J P, E-mail: e.skopalova07@imperial.ac.uk [Blackett Laboratory, Department of Physics, Imperial College London, London SW7 2AZ (United Kingdom)
2011-08-15
The characterization of the temporal profile of plasmonic fields is important both from the fundamental point of view and for potential applications in ultrafast nanoplasmonics. It has been proposed by Stockman et al (2007 Nat. Photonics 1 539) that the plasmonic electric field can be directly measured by the attosecond streaking technique; however, streaking from nanoplasmonic fields differs from streaking in the gas phase because of the field localization on the nanoscale. To understand streaking in this new regime, we have performed numerical simulations of attosecond streaking from fields localized in nanoantennas. In this paper, we present simulated streaked spectra for realistic experimental conditions and discuss the plasmonic field reconstruction from these spectra. We show that under certain circumstances when spatial averaging is included, a robust electric field reconstruction is possible.
Numerical simulation of a sour gas flare
International Nuclear Information System (INIS)
Due to the limited amount of information in the literature on sour gas flares and the cost of conducting wind tunnel and field experiments on sour flares, this presentation presented a modelling project that predicted the effect of operating conditions on flare performance and emissions. The objectives of the project were to adapt an existing numerical model suitable for flare simulation, incorporate sulfur chemistry, and run simulations for a range of conditions typical of sour flares in Alberta. The study involved the use of modelling expertise at the University of Utah, and employed large eddy simulation (LES) methods to model open flames. The existing model included the prediction of turbulent flow field; hydrocarbon reaction chemistry; soot formation; and radiation heat transfer. The presentation addressed the unique features of the model and discussed whether LES could predict the flow field. Other topics that were presented included the results from a University of Utah comparison; challenges of the LES model; an example of a run time issue; predicting the impact of operating conditions; and the results of simulations. Last, several next steps were identified and preliminary results were provided. Future work will focus on reducing computation time and increasing information reporting. figs
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.
Direct Numerical Simulations of Transient Dispersion
Porter, M.; Valdes-Parada, F.; Wood, B.
2008-12-01
Transient dispersion is important in many engineering applications, including transport in porous media. A common theoretical approach involves upscaling the micro-scale mass balance equations for convection- diffusion to macro-scale equations that contain effective medium quantities. However, there are a number of assumptions implicit in the various upscaling methods. For example, results obtained from volume averaging are often dependent on a given set of length and time scale constraints. Additionally, a number of the classical models for dispersion do not fully capture the early-time dispersive behavior of the solute for a general set of initial conditions. In this work, we present direct numerical simulations of micro-scale transient mass balance equations for convection-diffusion in both capillary tubes and porous media. Special attention is paid to analysis of the influence of a new time- decaying coefficient that filters the effects of the initial conditions. The direct numerical simulations were compared to results obtained from solving the closure problem associated with volume averaging. These comparisons provide a quantitative measure of the significance of (1) the assumptions implicit in the volume averaging method and (2) the importance of the early-time dispersive behavior of the solute due to various initial conditions.
Numerical simulation in tunneling - recent developments
International Nuclear Information System (INIS)
The paper presents recent findings of the Austrian joint research initiative 'Numerical Simulation in Tunneling'. The five year initiative, which was supported by the Austrian research fund, was started in 1997 with the main aim of developing and improving methods for the computer analysis of tunnels. The Problem areas that were looked at were: data acquisition and generation of input data, modeling strategies, visualization, material behavior and effects of water and air pressure. Only some topics are discussed here, others are presented in the mini-symposium Computational Methods in Tunneling. The topics that will be presented are: automatic acquisition of geological data (research performed at the institutes of rock mechanics and tunneling and the Institute for computer graphics and vision): a new system was developed that allows to create digital 3-D images of the tunnel face that can be interpreted by a geologist on a computer graphics work station. Some preliminary interpretation may be made by the software so that the work by the geologist is reduced. The interpreted data is used to generate the Input for numerical simulation models. Modeling strategies at the tunnel site (research performed at Institute of rock mechanics and tunneling): the feasibility of using three-dimensional modeling on site in order to interpret observation and measurements or to decide necessary support measures due to the occurrence of unforeseen geological features was investigated. The conclusion is, that if approached in an intelligent way three-dimensional modeling is feasible at the tunnel site and brings advantages. Visualization (research performed at the institute for structural analysis): numerical models of ten create a large amount of data, whose interpretation is difficult without advanced visualization techniques. The prototype of an advanced 3-D visualization system using virtual reality and a head-mounted display is presented. Refs. 2 (author)
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.
Numerical Simulation of DC Coronal Heating
Dahlburg, Russell B.; Einaudi, G.; Taylor, Brian D.; Ugarte-Urra, Ignacio; Warren, Harry; Rappazzo, A. F.; Velli, Marco
2016-05-01
Recent research on observational signatures of turbulent heating of a coronal loop will be discussed. The evolution of the loop is is studied by means of numerical simulations of the fully compressible three-dimensional magnetohydrodynamic equations using the HYPERION code. HYPERION calculates the full energy cycle involving footpoint convection, magnetic reconnection, nonlinear thermal conduction and optically thin radiation. The footpoints of the loop magnetic field are convected by random photospheric motions. As a consequence the magnetic field in the loop is energized and develops turbulent nonlinear dynamics characterized by the continuous formation and dissipation of field-aligned current sheets: energy is deposited at small scales where heating occurs. Dissipation is non-uniformly distributed so that only a fraction of thecoronal mass and volume gets heated at any time. Temperature and density are highly structured at scales which, in the solar corona, remain observationally unresolved: the plasma of the simulated loop is multi thermal, where highly dynamical hotter and cooler plasma strands are scattered throughout the loop at sub-observational scales. Typical simulated coronal loops are 50000 km length and have axial magnetic field intensities ranging from 0.01 to 0.04 Tesla. To connect these simulations to observations the computed number densities and temperatures are used to synthesize the intensities expected in emission lines typically observed with the Extreme ultraviolet Imaging Spectrometer (EIS) on Hinode. These intensities are then employed to compute differential emission measure distributions, which are found to be very similar to those derived from observations of solar active regions.
Numerical simulations of convectively excited gravity waves
International Nuclear Information System (INIS)
Magneto-convection and gravity waves are numerically simulated with a nonlinear, three-dimensional, time-dependent model of a stratified, rotating, spherical fluid shell heated from below. A Solar-like reference state is specified while global velocity, magnetic field, and thermodynamic perturbations are computed from the anelastic magnetohydrodynamic equations. Convective overshooting from the upper (superadiabatic) part of the shell excites gravity waves in the lower (subadiabatic) part. Due to differential rotation and Coriolis forces, convective cell patterns propagate eastward with a latitudinally dependent phase velocity. The structure of the excited wave motions in the stable region is more time-dependent than that of the convective motions above. The magnetic field tends to be concentrated over giant-cell downdrafts in the convective zone but is affected very little by the wave motion in the stable region
Numerical simulations of coupled problems in engineering
2014-01-01
This book presents and discusses mathematical models, numerical methods and computational techniques used for solving coupled problems in science and engineering. It takes a step forward in the formulation and solution of real-life problems with a multidisciplinary vision, accounting for all of the complex couplings involved in the physical description. Simulation of multifaceted physics problems is a common task in applied research and industry. Often a suitable solver is built by connecting together several single-aspect solvers into a network. In this book, research in various fields was selected for consideration: adaptive methodology for multi-physics solvers, multi-physics phenomena and coupled-field solutions, leading to computationally intensive structural analysis. The strategies which are used to keep these problems computationally affordable are of special interest, and make this an essential book.
Numerical Simulation of Cyclic Thermodynamic Processes
DEFF Research Database (Denmark)
Andersen, Stig Kildegård
2006-01-01
engine, 2) optimal regenerator designs which takes into account the effects of the regenerator matrix temperature oscillations, 3) transverse asymmetry in the temperature profile of a regenerator in a pulse tube cooler, and 4) the appendix gap losses in a Stirling engine.......This thesis is on numerical simulation of cyclic thermodynamic processes. A modelling approach and a method for finding periodic steady state solutions are described. Examples of applications are given in the form of four research papers. Stirling machines and pulse tube coolers are introduced and...... oscillating, compressible flow in one space dimension is presented. The implementation produces models where all the equations, which are on a form that should be understandable to someone with a background in engineering thermodynamics, can be accessed and modified individually. The implementation was...
The Beam Break-Up Numerical Simulator
Energy Technology Data Exchange (ETDEWEB)
Travish, G.A.
1989-11-01
Beam Break-Up (BBU) is a severe constraint in accelerator design, limiting beam current and quality. The control of BBU has become the focus of much research in the design of the next generation collider, recirculating and linear induction accelerators and advanced accelerators. Determining the effect on BBU of modifications to cavities, the focusing elements or the beam is frequently beyond the ability of current analytic models. A computer code was written to address this problem. The Beam Break-Up Numerical Simulator (BBUNS) was designed to numerically solve for beam break-up (BBU) due to an arbitrary transverse wakefield. BBUNS was developed to be as user friendly as possible on the Cray computer series. The user is able to control all aspects of input and output by using a single command file. In addition, the wakefield is specified by the user and read in as a table. The program can model energy variations along and within the beam, focusing magnetic field profiles can be specified, and the graphical output can be tailored. In this note we discuss BBUNS, its structure and application. Included are detailed instructions, examples and a sample session of BBUNS. This program is available for distribution. 50 refs., 18 figs., 5 tabs.
The Beam Break-Up Numerical Simulator
International Nuclear Information System (INIS)
Beam Break-Up (BBU) is a severe constraint in accelerator design, limiting beam current and quality. The control of BBU has become the focus of much research in the design of the next generation collider, recirculating and linear induction accelerators and advanced accelerators. Determining the effect on BBU of modifications to cavities, the focusing elements or the beam is frequently beyond the ability of current analytic models. A computer code was written to address this problem. The Beam Break-Up Numerical Simulator (BBUNS) was designed to numerically solve for beam break-up (BBU) due to an arbitrary transverse wakefield. BBUNS was developed to be as user friendly as possible on the Cray computer series. The user is able to control all aspects of input and output by using a single command file. In addition, the wakefield is specified by the user and read in as a table. The program can model energy variations along and within the beam, focusing magnetic field profiles can be specified, and the graphical output can be tailored. In this note we discuss BBUNS, its structure and application. Included are detailed instructions, examples and a sample session of BBUNS. This program is available for distribution. 50 refs., 18 figs., 5 tabs
Numerical simulations of capillary barrier field tests
Energy Technology Data Exchange (ETDEWEB)
Morris, C.E. [Univ. of Wollongong (Australia); Stormont, J.C. [Univ. of New Mexico, Albuquerque, NM (United States)
1997-12-31
Numerical simulations of two capillary barrier systems tested in the field were conducted to determine if an unsaturated flow model could accurately represent the observed results. The field data was collected from two 7-m long, 1.2-m thick capillary barriers built on a 10% grade that were being tested to investigate their ability to laterally divert water downslope. One system had a homogeneous fine layer, while the fine soil of the second barrier was layered to increase its ability to laterally divert infiltrating moisture. The barriers were subjected first to constant infiltration while minimizing evaporative losses and then were exposed to ambient conditions. The continuous infiltration period of the field tests for the two barrier systems was modelled to determine the ability of an existing code to accurately represent capillary barrier behavior embodied in these two designs. Differences between the field test and the model data were found, but in general the simulations appeared to adequately reproduce the response of the test systems. Accounting for moisture retention hysteresis in the layered system will potentially lead to more accurate modelling results and is likely to be important when developing reasonable predictions of capillary barrier behavior.
Numerical simulation of turbulence over tensegrity fabric
Luo, Haoxiang; Bewley, Thomas
2003-11-01
In this research we aim to reduce turbulent skin friction by designing and optimizing tensegrity fabrics. Such fabrics form a new class of compliant surfaces consisting of a weave of both members under tension and members under compression. Boundary conditions on the flow are handled with a time-dependent coordinate transformation. We first note that, when designing the numerical algorithm for approximating the Navier-Stokes equation in the flow domain (with moving boundaries), special care (intrinsic differentiation of a contravariant vector) is needed to handle the temporal differentiation of the momentum term when using a contravariant formulation. A Cartesian-based formulation may also be used, and has proven to be more tractable in the 3D setting. The spectral DNS flow code is coupled with a tensegrity simulation code to compute the flow/structure interaction; recent simulation results will be presented. A complex-step derivative (CSD) technique may then be used to optimize the response characteristics of the tensegrity structure in order to minimize the drag at the flow/structure interface; this strategy will also be discussed.
Numerical simulations of capillary barrier field tests
International Nuclear Information System (INIS)
Numerical simulations of two capillary barrier systems tested in the field were conducted to determine if an unsaturated flow model could accurately represent the observed results. The field data was collected from two 7-m long, 1.2-m thick capillary barriers built on a 10% grade that were being tested to investigate their ability to laterally divert water downslope. One system had a homogeneous fine layer, while the fine soil of the second barrier was layered to increase its ability to laterally divert infiltrating moisture. The barriers were subjected first to constant infiltration while minimizing evaporative losses and then were exposed to ambient conditions. The continuous infiltration period of the field tests for the two barrier systems was modelled to determine the ability of an existing code to accurately represent capillary barrier behavior embodied in these two designs. Differences between the field test and the model data were found, but in general the simulations appeared to adequately reproduce the response of the test systems. Accounting for moisture retention hysteresis in the layered system will potentially lead to more accurate modelling results and is likely to be important when developing reasonable predictions of capillary barrier behavior
基于数值模拟的某垃圾填埋场渗漏性评价%Based on numerical simulation of a landfill leakage assessment
Institute of Scientific and Technical Information of China (English)
杨泽; 杜泽; 陈正林
2015-01-01
基于对云南某拟建垃圾填埋场稳定渗流场的数值模拟，对该填埋场进行渗漏性评价，发现填埋场内渗滤液整体向垃圾坝方向运移，在分级堆积体每一级坡脚处运移方向发生突变，且会有部分渗滤液进入全风化岩层，导致地下水污染。针对所得结论，提出一定建议，以期为该垃圾填埋场的建设提供一定的参考。%Based on seepage numerical simulation of a proposed landfil in Yunnan, evaluating the leakage. We find that landfil percolate integraly migrate in the direction of refuse dam, and changing at the toe of slope in every platform. In addition, part of the percolate wil permeate into the seriously weathered sand rock stratum, leading to polute the underground water. Aiming at the conclusions, we give some suggestions, expecting to providing some references for the construction of the landfil.
Numerical simulation of "An American Haboob"
Directory of Open Access Journals (Sweden)
A. Vukovic
2013-10-01
Full Text Available A dust storm of fearful proportions hit Phoenix in the early evening hours of 5 July 2011. This storm, an American haboob, was predicted hours in advance because numerical, land-atmosphere modeling, computing power and remote sensing of dust events have improved greatly over the past decade. High resolution numerical models are required for accurate simulation of the small-scales of the haboob process, with high velocity surface winds produced by strong convection and severe downbursts. Dust productive areas in this region consist mainly of agricultural fields, with soil surfaces disturbed by plowing and tracks of land in the high Sonoran desert laid barren by ongoing draught. Model simulation of the 5 July 2011 dust storm uses the coupled atmospheric-dust model NMME-DREAM with 3.5 km horizontal resolution. A mask of the potentially dust productive regions is obtained from the land cover and the Normalized Difference Vegetation Index (NDVI data from the Moderate Resolution Imaging Spectroradiometer (MODIS. Model results are compared with radar and other satellite-based images and surface meteorological and PM10 observations. The atmospheric model successfully hindcasted the position of the front in space and time, with about 1 h late arrival in Phoenix. The dust model predicted the rapid uptake of dust and high values of dust concentration in the ensuing storm. South of Phoenix, over the closest source regions (~ 25 km, the model PM10 surface dust concentration reached ~ 2500 μg m−3, but underestimated the values measured by the PM10stations within the city. Model results are also validated by the MODIS aerosol optical depth (AOD, employing deep blue (DB algorithms for aerosol loadings. Model validation included Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO, equipped with the lidar instrument, to disclose the vertical structure of dust aerosols as well as aerosol subtypes. Promising results encourage further
Numerical Simulations of Saturn's Polar Cyclones
Brueshaber, Shawn R.; Sayanagi, Kunio M.
2014-11-01
Shawn R. Brueshaber, Department of Mechanical Engineering, Western Michigan UniversityKunio M. Sayanagi, Atmospheric and Planetary Sciences, Hampton UniversityCassini mission to Saturn has revealed evidences of a warm core cyclone centered on each of the poles of the planet. The morphology of the clouds in these cyclones resembles that of a terrestrial hurricane. The formation and maintenance mechanisms of these large polar cyclones are yet to be explained. Scott (2011, Astrophys. Geophys. Fluid Dyn) proposed that cyclonic vortices beta-drifting poleward can result in a polar cyclone, and demonstrated that beta-drifting cyclonic vortices can indeed cause accumulation of cyclonic vorticity at the pole using a 1-layer quasi-geostrophic model.The objectives of our project is to test Scott's hypothesis using a 1.5-layer shallow-water model and many-layer primitive equations model. We use the Explicit Planetary Isentropic Coordinate (EPIC) model (Dowling et al. 1998, 2004, Icarus) to perform direct numerical simulations of Saturn's polar atmosphere. To date, our project has focused on modifying the model to construct a polar rectangular model grid in order to avoid the problem of polar singularity associated with the conventional latitude-longitude grids employed in many general circulation models. We present our preliminary simulations, which show beta-drifting cyclones cause a poleward flux of cyclonic vorticity, which is consistent with Scott's results.Our study is partially supported by NASA Outer Planets Research Grant NNX12AR38G and NSF Astronomy and Astrophysics Grant 1212216 to KMS.
Numerical simulation of magma chamber dynamics.
Longo, Antonella; Papale, Paolo; Montagna, Chiara Paola; Vassalli, Melissa; Giudice, Salvatore; Cassioli, Andrea
2010-05-01
Magma chambers are characterized by periodic arrivals of deep magma batches that give origin to complex patterns of magma convection and mixing, and modify the distribution of physical quantities inside the chamber. We simulate the transient, 2D, multi-component homogeneous dynamics in geometrically complex dyke+chamber systems, by means of GALES, a finite element parallel C++ code solving mass, momentum and energy equations for multi-component homogeneous gas-liquid (± crystals) mixtures in compressible-to-incompressible flow conditions. Code validation analysis includes several cases from the classical engineering literature, corresponding to a variety of subsonic to supersonic gas-liquid flow regimes (see http://www.pi.ingv.it/~longo/gales/gales.html). The model allows specification of the composition of the different magmas in the domain, in terms of ten major oxides plus the two volatile species H2O and CO2. Gas-liquid thermodynamics are modeled by using the compositional dependent, non-ideal model in Papale et al. (Chem.. Geol., 2006). Magma properties are defined in terms of local pressure, temperature, and composition including volatiles. Several applications are performed within domains characterized by the presence of one or more magma chambers and one or more dykes, with different geometries and characteristic size from hundreds of m to several km. In most simulations an initial compositional interface is placed at the top of a feeding dyke, or at larger depth, with the deeper magma having a lower density as a consequence of larger volatile content. The numerical results show complex patterns of magma refilling in the chamber, with alternating phases of magma ingression and magma sinking from the chamber into the feeding dyke. Intense mixing takes place in feeding dykes, so that the new magma entering the chamber is always a mixture of the deep and the initially resident magma. Buoyant plume rise occurs through the formation of complex convective
Numerical simulation methods of fires in nuclear power plants
International Nuclear Information System (INIS)
Fire is a significant hazard to the safety of nuclear power plants (NPP). Fire may be serious accident as such, but even small fire at a critical point in a NPP may cause an accident much more serious than fire itself. According to risk assessments a fire may be an initial cause or a contributing factor in a large part of reactor accidents. At the Fire Technology and the the Nuclear Engineering Laboratory of the Technical Research Centre of Finland (VTT) fire safety research for NPPs has been carried out in a large extent since 1985. During years 1988-92 a project Advanced Numerical Modelling in Nuclear Power Plants (PALOME) was carried out. In the project the level of numerical modelling for fire research in Finland was improved by acquiring, preparing for use and developing numerical fire simulation programs. Large scale test data of the German experimental program (PHDR Sicherheitsprogramm in Kernforschungscentral Karlsruhe) has been as reference. The large scale tests were simulated by numerical codes and results were compared to calculations carried out by others. Scientific interaction with outstanding foreign laboratories and scientists has been an important part of the project. This report describes the work of PALOME-project carried out at the Fire Technology Laboratory only. A report on the work at the Nuclear Engineering Laboratory will be published separatively. (au)
Proton decay: Numerical simulations confront grand unification
International Nuclear Information System (INIS)
The Grand Unified Theories of the electromagnetic, weak and strong interactions constitute a far reaching attempt to synthesize our knowledge of theoretical particle physics into a consistent and compelling whole. Unfortunately, many quantitative predictions of such unified theories are sensitive to the analytically intractible effects of the strong subnuclear theory (Quantum Chromodynamics or QCD). The consequence is that even ambitious experimental programs exploring weak and super-weak interaction effects often fail to give definitive theoretical tests. This paper describes large-scale calculations on a supercomputer which can help to overcome this gap between theoretical predictions and experimental results. Our focus here is on proton decay, though the methods described are useful for many weak processes. The basic algorithms for the numerical simulation of QCD are well known. We will discuss the advantages and challenges of applying these methods to weak transitions. The algorithms require a very large data base with regular data flow and are natural candidates for vectorization. Also, 32-bit floating point arithmetic is adequate. Thus they are most naturally approached using a supercomputer alone or in combination with a dedicated special purpose processor. (orig.)
Transonic aeroelastic numerical simulation in aeronautical engineering
International Nuclear Information System (INIS)
An LU-SGS (lower-upper symmetric Gauss-Seidel) subiteration scheme is constructed for time-marching of the fluid equations. The HLLEW (Harten-Lax-van Leer-Einfeldt-Wada) scheme is used for the spatial discretization. The same subiteration formulation is applied directly to the structural equations of motion in generalized coordinates. Through subiteration between the fluid and structural equations, a fully implicit aeroelastic solver is obtained for the numerical simulation of fluid/structure interaction. To improve the ability for application to complex configurations, a multiblock grid is used for the flow field calculation and Transfinite Interpolation (TFI) is employed for the adaptive moving grid deformation. The infinite plate spline (IPS) and the principal of virtual work are utilized for the data transformation between the fluid and structure. The developed code was first validated through the comparison of experimental and computational results for the AGARD 445.6 standard aeroelastic wing. Then the flutter character of a tail wing with control surface was analyzed. Finally, flutter boundaries of a complex aircraft configuration were predicted. (author)
Numerical simulation of noninvasive blood pressure measurement.
Hayashi, Satoru; Hayase, Toshiyuki; Shirai, Atsushi; Maruyama, Masaru
2006-10-01
In this paper, a simulation model based on the partially pressurized collapsible tube model for reproducing noninvasive blood pressure measurement is presented. The model consists of a collapsible tube, which models the pressurized part of the artery, rigid pipes connected to the collapsible tube, which model proximal and distal region far from the pressurized part, and the Windkessel model, which represents the capacitance and the resistance of the distal part of the circulation. The blood flow is simplified to a one-dimensional system. Collapse and expansion of the tube is represented by the change in the cross-sectional area of the tube considering the force balance acting on the tube membrane in the direction normal to the tube axis. They are solved using the Runge-Kutta method. This simple model can easily reproduce the oscillation of inner fluid and corresponding tube collapse typical for the Korotkoff sounds generated by the cuff pressure. The numerical result is compared with the experiment and shows good agreement. PMID:16995754
Numerical simulation of ball-racket impact
Yu, Yingpang
The collision of a ball with a tennis racket is usually modeled in terms of rigid body dynamics or an elastic system involving only a few springs. In this paper, we study the impact between a tennis ball and racket, by modeling the tennis ball in two different yaws. One method models the tennis ball as a Hertz elastic body and the other one models the ball by a more accurate finite element analysis. In the first model, we assume that the elastic properties of the ball obeys Hertz's law. In the finite element model, we consider the tennis ball as a shell witch is a elastic system constructed out of many isotropic small linear flat, elements, witch have both elastic and damping properties. The damping in each way is approximated as viscous term. In both methods, we study the static condition of deformation against a rigid surface before applying these models to dynamical processes. We compare these two methods and eventually determine how the racket parameters effect the performance of the racket, using numerical simulations. Comparison with experiment are show to confirm the general conclusion of the model.
Direct numerical simulation of active fiber composite
Kim, Seung J.; Hwang, Joon S.; Paik, Seung H.
2003-08-01
Active Fiber Composites (AFC) possess desirable characteristics for smart structure applications. One major advantage of AFC is the ability to create anisotropic laminate layers useful in applications requiring off-axis or twisting motions. AFC is naturally composed of two different constituents: piezoelectric fiber and matrix. Therefore, homogenization method, which is utilized in the analysis of laminated composite material, has been used to characterize the material properties. Using this approach, the global behaviors of the structures are predicted in an averaged sense. However, this approach has intrinsic limitations in describing the local behaviors in the level of the constituents. Actually, the failure analysis of AFC requires the knowledge of the local behaviors. Therefore, microscopic approach is necessary to predict the behaviors of AFC. In this work, a microscopic approach for the analysis of AFC was performed. Piezoelectric fiber and matrix were modeled separately and finite element method using three-dimensional solid elements was utilized. Because fine mesh is essential, high performance computing technology was applied to the solution of the immense degree-of-freedom problem. This approach is called Direct Numerical Simulation (DNS) of structure. Through the DNS of AFC, local stress distribution around the interface of fiber and matrix was analyzed.
Numerical simulations of shocks encountering clumpy regions
Alūzas, R; Hartquist, T W; Falle, S A E G; Langton, R
2012-01-01
We present numerical simulations of the adiabatic interaction of a shock with a clumpy region containing many individual clouds. Our work incorporates a sub-grid turbulence model which for the first time makes this investigation feasible. We vary the Mach number of the shock, the density contrast of the clouds, and the ratio of total cloud mass to inter-cloud mass within the clumpy region. Cloud material becomes incorporated into the flow. This "mass-loading" reduces the Mach number of the shock, and leads to the formation of a dense shell. In cases in which the mass-loading is sufficient the flow slows enough that the shock degenerates into a wave. The interaction evolves through up to four stages: initially the shock decelerates; then its speed is nearly constant; next the shock accelerates as it leaves the clumpy region; finally it moves at a constant speed close to its initial speed. Turbulence is generated in the post-shock flow as the shock sweeps through the clumpy region. Clouds exposed to turbulence ...
Numerical simulations of a restarting jet
International Nuclear Information System (INIS)
The first self-consistent two-dimensional numerical simulation of an axisymmetric intermittent jet is presented. It is found that if the jet parameters at the jet nozzle do not vary widely from one duty cycle to the next, the restarted jet will always be overdense if the original jet is underdense relative to the quiescent intergalactic medium. Although the working surface advance speed of the restarted jet is greater than that of the original jet, the Mach number of the advance speed is less. Because the advance speed Mach number of the new working surface is relatively low, the bow shock excited by the new jet is weak regardless of the strength of the original bow shock in the quiescent ambient medium. Because the bow shock and terminal Mach disk must have comparable strengths, the brightness contrast of emission features associated with the shock should be roughly the same. Without the momentum flux of the jet, the hot spot expands in a time short compared with the duty cycle. 27 refs
Direct numerical simulations of aeolian sand ripples.
Durán, Orencio; Claudin, Philippe; Andreotti, Bruno
2014-11-01
Aeolian sand beds exhibit regular patterns of ripples resulting from the interaction between topography and sediment transport. Their characteristics have been so far related to reptation transport caused by the impacts on the ground of grains entrained by the wind into saltation. By means of direct numerical simulations of grains interacting with a wind flow, we show that the instability turns out to be driven by resonant grain trajectories, whose length is close to a ripple wavelength and whose splash leads to a mass displacement toward the ripple crests. The pattern selection results from a compromise between this destabilizing mechanism and a diffusive downslope transport which stabilizes small wavelengths. The initial wavelength is set by the ratio of the sediment flux and the erosion/deposition rate, a ratio which increases linearly with the wind velocity. We show that this scaling law, in agreement with experiments, originates from an interfacial layer separating the saltation zone from the static sand bed, where momentum transfers are dominated by midair collisions. Finally, we provide quantitative support for the use of the propagation of these ripples as a proxy for remote measurements of sediment transport. PMID:25331873
ITER TF coil double pancake assembly: Laser welding numerical simulation
International Nuclear Information System (INIS)
In the frame of the ITER coils production, one crucial point is the cover plate welding to complete a coil layer, the so called double pancake (DP). The scope of the activity here described is the assessment of the deformation induced by this laser welding through a FE numerical simulation, in order to find the welding sequence that minimize the global distortion. At this concern, the Local-Global approach technique has been adopted using Abaqus Code, in order to be able to compare several long welding paths in acceptable CPU time increasing analysis speed and model definition easiness in spite of partial loss in the results accuracy. The numerical methodology has been tuned and assessed on experimental data from a welding sample in which a 2.5 mm deep welding has been performed and the deformation induced by 1 and 2 mm deep welds (the ones that will be used in the complete DP) has been extrapolated. These local strains have then been applied on the global models reproducing the middle and side DP, and their deformation has been computed. The rather good fitting between the experimental and numerical results is very promising, and a complete asses of the procedure could be performed in the frame of an experimental-numerical research campaign.
Direct numerical simulation of turbulent aerosol coagulation
Reade, Walter Caswell
There are numerous systems-including both industrial applications and natural occurring phenomena-in which the collision/coagulation rates of aerosols are of significant interest. Two examples are the production of fine powders (such as titanium dioxide) and the formation of rain drops in the atmosphere. During the last decade, it has become apparent that dense aerosol particles behave much differently in a turbulent fluid than has been previously assumed. Particles with a response time on the order of the small-scale fluid time scale tend to collect in regions of low vorticity. The result is a particle concentration field that can be highly non-uniform. Sundaram and Collins (1997) recently demonstrated the effect that turbulence can have on the particle collision rate of a monodisperse system. The collision rates of finite-inertia particles can be as much as two orders of magnitude greater than particles that precisely follow the fluid streamlines. Sundaram and Collins derived a general collision expression that explicitly accounted for the two phenomena that affect the collision rate-changes in the particle concentration field and changes in the particle relative velocities. The result of Sundaram and Collins has generated further interest in the turbulent-aerosol problem. This thesis shows that, in addition to changing the rate that an aerosol size distribution might form, turbulence has the potential of dramatically changing the shape of the distribution. This result is demonstrated using direct numerical simulation of a turbulent-aerosol system over a wide range of particle parameters, and a moderate range of turbulence levels. Results show that particles with a small (but finite) initial inertia have the greatest potential of forming broad size distributions. The shape of the resulting size distribution is also affected by the initial size of the particles. Observations are explained using the statistics identified by Sundaram and Collins (1997). A major
Restoration of cloud contaminated ocean color images using numerical simulation
Yang, Xuefei; Mao, Zhihua; Chen, Jianyu; Huang, Haiqing
2015-10-01
It is very hard to access cloud-free remote sensing data, especially for the ocean color images. A cloud removal approach from ocean color satellite images based on numerical modeling is introduced. The approach removes cloud-contaminated portions and then reconstructs the missing data utilizing model simulated values. The basic idea is to create the relationship between cloud-free patches and cloud-contaminated patches under the assumption that both of them are influenced by the same marine hydrodynamic conditions. Firstly, we find cloud-free GOCI (the Geostationary Ocean Color Imager) retrieved suspended sediment concentrations (SSC) in the East China Sea before and after the time of cloudy images, which are set as initial field and validation data for numerical model, respectively. Secondly, a sediment transport model based on COHERENS, a coupled hydrodynamic-ecological ocean model for regional and shelf seas, is configured. The comparison between simulated results and validation images show that the sediment transport model can be used to simulate actual sediment distribution and transport in the East China Sea. Then, the simulated SSCs corresponding to the cloudy portions are used to remove the cloud and replace the missing values. Finally, the accuracy assessments of the results are carried out by visual and statistical analysis. The experimental results demonstrate that the proposed method can effectively remove cloud from GOCI images and reconstruct the missing data, which is a new way to enhance the effectiveness and availability of ocean color data, and is of great practical significance.
Numerical simulation and experiment study of vircator
International Nuclear Information System (INIS)
A 2 1/2 dimensional, fully electromagnetic, relativistic CIC particle simulation code has been developed to simulate the virtual cathode oscillations and the HPM generations. Solid electron beams are used both in the simulations and the experiments. The microwave radiations whose average power is of the order of GW have been observed. The simulations are in agreement with the experiments
Numerical simulation of 3D breaking waves
Fraunie, Philippe; Golay, Frederic
2015-04-01
Numerical methods dealing with two phase flows basically can be classified in two ways : the "interface tracking" methods when the two phases are resolved separately including boundary conditions fixed at the interface and the "interface capturing" methods when a single flow is considered with variable density. Physical and numerical properties of the two approaches are discussed, based on some numerical experiments performed concerning 3D breaking waves. Acknowledgements : This research was supported by the Modtercom program of Region PACA.
glsim: A general library for numerical simulation
Grigera, Tomas S
2011-01-01
We describe glsim, a C++ library designed to provide routines to perform basic housekeeping tasks common to a very wide range of simulation programs, such as reading simulation parameters or reading and writing self-describing binary files with simulation data. The design also provides a framework to add features to the library while preserving its structure and interfaces.
Model validation for the numerical simulation of the Double Punch Test
Pros Parés, Alba; Díez, Pedro; Molins i Borrell, Climent
2008-01-01
The Double Punch test, an indirect traction test, is simulated numerically considering two different models (the nonlocal Mazars damage model and an heuristic crack model with joint elements). The test was designed to measure indirectly the tensile strength of concrete, hence, through these two numerical models, we are able to assess the tensile strength numerically. Experimental results present scattering when assessing the tensile strength, therefore, other tests are needed to set all...
Numerical simulation of pressure pulsations in Francis turbines
Magnoli, M. V.; Schilling, R.
2012-11-01
In the last decades, hydraulic turbines have experienced the increase of their power density and the extension of their operating range, leading the fluid and mechanical dynamic effects to become significantly more pronounced. The understanding of the transient fluid flow and of the associated unsteady effects is essential for the reduction of the pressure pulsation level and improvement of the machine dynamic behaviour. In this study, the instationary fluid flow through the complete turbine was numerically calculated for an existing Francis machine with high specific speed. The hybrid turbulence models DES (detached eddy simulation) and SAS (scale adaptive simulation) allowed the accurate simulation of complex dynamic flow effects, such as the rotor-stator-interaction and the draft tube instabilities. Different operating conditions, as full load, part load, higher part load and deep part load, were successfully simulated and showed very tight agreement with the experimental results from the model tests. The transient pressure field history, obtained from the CFD (computational fluid dynamics) simulation and stored for each time step, was used as input for the full instationary FEA (finite element analysis) of turbine components. The assessment of the machine dynamic motion also offered the possibility to contribute to the understanding of the pressure pulsation effects and to further increase the turbine stability. This research project was developed at the Institute of Fluid Mechanics of the TU München.
Probing Strong Field Gravity Through Numerical Simulations
Choptuik, Matthew W; Pretorius, Frans
2015-01-01
This article is an overview of the contributions numerical relativity has made to our understanding of strong field gravity, to be published in the book "General Relativity and Gravitation: A Centennial Perspective", commemorating the 100th anniversary of general relativity.
Numerical Simulation of Rotating Vertical Bridgman Growth
S. Nouri; P. Spiterri; Ghezal, A.
2016-01-01
The present work is proposed a numerical parametric study of heat and mass transfer in a rotating vertical cylinder during the solidification of a binary metallic alloy. The aim of this paper is to present an enthalpy formulation based on the fixed grid methodology for the numerical solution of convective-diffusion during the phase change in the case of the steady crucible rotation. The extended Darcy model including the time derivative and Coriolis terms was applied as momentum equation. It...
Modular numerical tool for gas turbine simulation
Sampedro Casis, Rodrigo
2015-01-01
In this work a free tool for the simulation of turboprops was implemented, capable of simulating the various components of a jet engine, separately or in conjunction, with different degrees of thermodynamic modelling or complexity, in order to simulate an entire jet engine. The main characteristics of this software includes its compatibility, open code and GNU license, non-existing in today's market. Furthermore, the tool was designed with a greater flexibility and a more adapted work environ...
Numerical Simulation Of Cutting Of Gear Teeth
Oswald, Fred B.; Huston, Ronald L.; Mavriplis, Dimitrios
1994-01-01
Shapes of gear teeth produced by gear cutters of specified shape simulated computationally, according to approach based on principles of differential geometry. Results of computer simulation displayed as computer graphics and/or used in analyses of design, manufacturing, and performance of gears. Applicable to both standard and non-standard gear-tooth forms. Accelerates and facilitates analysis of alternative designs of gears and cutters. Simulation extended to study generation of surfaces other than gears. Applied to cams, bearings, and surfaces of arbitrary rolling elements as well as to gears. Possible to develop analogous procedures for simulating manufacture of skin surfaces like automobile fenders, airfoils, and ship hulls.
Woolfenden, Linda R.; Koczot, Kathryn M.
2001-01-01
The Rialto?Colton Basin, in western San Bernardino County, California, was chosen for storage of imported water because of the good quality of native ground water, the known storage capacity for additional ground-water storage in the basin, and the availability of imported water. To supplement native ground-water resources and offset overdraft conditions in the basin during dry periods, artificial-recharge operations during wet periods in the Rialto?Colton Basin were begun in 1982 to store surplus imported water. Local water purveyors recognized that determining the movement and ultimate disposition of the artificially recharged imported water would require a better understanding of the ground-water flow system. In this study, a finite-difference model was used to simulate ground-water flow in the Rialto?Colton Basin to gain a better understanding of the ground-water flow system and to evaluate the hydraulic effects of artificial recharge of imported water. The ground-water basin was simulated as four horizontal layers representing the river- channel deposits and the upper, middle, and lower water-bearing units. Several flow barriers bordering and internal to the Rialto?Colton Basin influence the direction of ground-water flow. Ground water may flow relatively unrestricted in the shallow parts of the flow system; however, the faults generally become more restrictive at depth. A particle-tracking model was used to simulate advective transport of imported water within the ground-water flow system and to evaluate three artificial-recharge alternatives. The ground-water flow model was calibrated to transient conditions for 1945?96. Initial conditions for the transient-state simulation were established by using 1945 recharge and discharge rates, and assuming no change in storage in the basin. Average hydrologic conditions for 1945?96 were used for the predictive simulations (1997?2027). Ground-water-level measurements made during 1945 were used for comparison with the
Schwichtenberg, Fabian; Callies, Ulrich; Groll, Nikolaus; Maßmann, Silvia
2016-06-01
Oil dispersed in the water column remains sheltered from wind forcing, so that an altered drift path is a key consequence of using chemical dispersants. In this study, ensemble simulations were conducted based on 7 years of simulated atmospheric and marine conditions, evaluating 2,190 hypothetical spills from each of 636 cells of a regular grid covering the inner German Bight (SE North Sea). Each simulation compares two idealized setups assuming either undispersed or fully dispersed oil. Differences are summarized in a spatial map of probabilities that chemical dispersant applications would help prevent oil pollution from entering intertidal coastal areas of the Wadden Sea. High probabilities of success overlap strongly with coastal regions between 10 m and 20 m water depth, where the use of chemical dispersants for oil spill response is a particularly contentious topic. The present study prepares the ground for a more detailed net environmental benefit analysis (NEBA) accounting also for toxic effects.
Numerical simulation of tyre/road noise
Schutte, Jan Henk
2011-01-01
In modern society, traffic noise has become an important issue for mental health. A significant contributor to this noise pollution is exterior tyre/road noise, which is caused by the interaction between tyre and road surface and. In order to reduce tyre/road noise at the source, accurate numerical
Numerical simulation of the hepatic circulation
Van Der Plaats, A; 'tHart, NA; Verkerke, GJ; Leuvenink, HGD; Verdonck, P; Ploeg, RJ; Rakhorst, G
2004-01-01
Availability of donor livers and the relatively short preservation time limit the success of liver transplantation. The use of hypothermic machine perfusion could pave the way for expansion of the donor pool. To better define optimal settings of such a device, the feasibility of using a numerical si
Numerical simulation of AM1 microstructure
Rougier Luc; Jacot Alain; Gandin Charles-André; Napoli Paolo Di; Ponsen Damien; Jaquet Virginie
2014-01-01
A modelling approach is developed for the description of microstructure formation in the industrial AM1 Ni-base superalloy. Solidification and homogenization simulations are first carried out using a microsegregation model, before using the local compositions as an input for precipitation calculations, in order to characterize the influence of segregation on precipitation. First, the precipitation model was validated by comparing simulated and measured evolutions of the average precipitate ra...
A numerical simulation of a contrail
Energy Technology Data Exchange (ETDEWEB)
Levkov, L.; Boin, M.; Meinert, D. [GKSS-Forschungszentrum Geesthacht GmbH, Geesthacht (Germany)
1997-12-31
The formation of a contrail from an aircraft flying near the tropopause is simulated using a three-dimensional mesoscale atmospheric model including a very complex scheme of parameterized cloud microphysical processes. The model predicted ice concentrations are in very good agreement with data measured during the International Cirrus Experiment (ICE), 1989. Sensitivity simulations were run to determine humidity forcing on the life time of contrails. (author) 4 refs.
Numerical simulation of pump-intake vortices
Rudolf Pavel; Klas Roman
2015-01-01
Pump pre-swirl or uneven flow distribution in front of the pump can induce pump-intake vortices. These phenomena result in blockage of the impeller suction space, deterioration of efficiency, drop of head curve and earlier onset of cavitation. Real problematic case, where head curve drop was documented, is simulated using commercial CFD software. Computational simulation was carried out for three flow rates, which correspond to three operating regimes of the vertical pump. The domain consists...
Numerical simulations of a propeller wake impacting
Energy Technology Data Exchange (ETDEWEB)
Hi, M.; Veitch, B.; Bose, N. [Memorial Univ. of Newfoundland, Faculty of Engineering and Applied Science, St. John' s, Newfoundland (Canada)]. E-mail: moqinhe@engr.mun.ca; Bruce, C.; Liu, P. [National Research Council Canada, Inst. for Ocean Technology, St. John' s, Newfoundland (Canada)
2005-07-01
This paper introduces a newly developed Wake Impingement Model (WIM) that aims to simulate of the dynamic loads induced by a three dimensional, unsteady, and strong vortical propeller wake. Simulations of loads on an ice class, tractor type podded propeller in straight ahead motion are presented consisting of mean loads on the propeller and side force on the pod and strut. The side force fluctuations for three different advance coefficients have also been predicted. These simulations were carried out by using a panel code, PROPELLA, with or without WIM. Simulated results were compared with and without WIM and with experimental data. The comparison of the propeller open water characteristics of two simulated results shown there is almost no difference between predictions with and without WIM. It was found by comparing with experimental data that the simulations of the side force on the pod and strut with WIM successfully captured the fluctuation which was dominated by the component at the blade passing frequency, although this was at a reduced level compared with the measurements. (author)
Fastening elements in concrete structures - numerical simulations
Ozbolt, Josko; Eligehausen, Rolf
1993-01-01
Anchoring elements such as headed and expansion studs and grouted or undercut anchors, are often used for local transfer of loads into concrete members. In order to better understand the failure mechanism, a large number of experiments have been carried out in the past. However, due to the complicated three-dimensional load transfer a very few or no numerical studies have been performed for a number of different fastening situations i.e. influence of the embedment depth, crack-width inftuence...
Numerical simulation of hemorrhage in human injury
Chong, Kwitae; Jiang, Chenfanfu; Santhanam, Anand; Benharash, Peyman; Teran, Joseph; Eldredge, Jeff
2015-11-01
Smoothed Particle Hydrodynamics (SPH) is adapted to simulate hemorrhage in the injured human body. As a Lagrangian fluid simulation, SPH uses fluid particles as computational elements and thus mass conservation is trivially satisfied. In order to ensure anatomical fidelity, a three-dimensional reconstruction of a portion of the human body -here, demonstrated on the lower leg- is sampled as skin, bone and internal tissue particles from the CT scan image of an actual patient. The injured geometry is then generated by simulation of ballistic projectiles passing through the anatomical model with the Material Point Method (MPM) and injured vessel segments are identified. From each such injured segment, SPH is used to simulate bleeding, with inflow boundary condition obtained from a coupled 1-d vascular tree model. Blood particles interact with impermeable bone and skin particles through the Navier-Stokes equations and with permeable internal tissue particles through the Brinkman equations. The SPH results are rendered in post-processing for improved visual fidelity. The overall simulation strategy is demonstrated on several injury scenarios in the lower leg.
Numerical simulation of AM1 microstructure
Directory of Open Access Journals (Sweden)
Rougier Luc
2014-01-01
Full Text Available A modelling approach is developed for the description of microstructure formation in the industrial AM1 Ni-base superalloy. Solidification and homogenization simulations are first carried out using a microsegregation model, before using the local compositions as an input for precipitation calculations, in order to characterize the influence of segregation on precipitation. First, the precipitation model was validated by comparing simulated and measured evolutions of the average precipitate radius during isothermal heat treatments at 1100 ∘C and 1210 ∘C. The chained microsegregation and precipitation simulations indicate that the global sequences of precipitation events remains are qualitatively the same at the different locations in the microstructure, but the growth and dissolution kinetics are strongly influenced by the local compositions. Local supersaturations have a larger effect on the average radius of the precipitates than certain stages of the precipitation heat treatment.
A numerical simulation of auroral ionospheric electrodynamics
Mallinckrodt, A. J.
1985-01-01
A computer simulation of auroral ionospheric electrodynamics in the altitude range 80 to 250 km has been developed. The routine will either simulate typical electron precipitation profiles or accept observed data. Using a model background ionosphere, ion production rates are calculated from which equilibrium electron densities and the Hall and Pedersen conductivities may be determined. With the specification of suitable boundary conditions, the entire three-dimensional current system and electric field may be calculated within the simulation region. The results of the application of the routine to a typical inverted-V precipitation profile are demonstrated. The routine is used to explore the observed anticorrelation between electric field magnitude and peak energy in the precipitating electron spectrum of an auroral arc.
Numerical simulation of neutron penumbral imaging
International Nuclear Information System (INIS)
Penumbral imaging has high sensitivity, which will be the main technical method of neutron imaging in inertial confinement fusion (ICF) experiments. Based on the requirement of neutron penumbral imaging, two-dimensional image of neutrons transport in the coded aperture is simulated by Monte Carlo method, with the biased sampling skill and surface-flux replaced by volume-flux skill. The source image is obtained by reconstruction program. According to the simulation result, the 5 cm thick W bulk is selected as the shielding material and the optimized aperture outer radius is 1 cm. (authors)
Pseudo-reconnection in MHD numerical simulation
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
A class of pseudo-reconnections caused by a shifted mesh in magnetohydrodynamics (MHD) simulations is reported. In terms of this mesh system, some non-physical results may be obtained in certain circumstances, e.g. magnetic reconnection occurs without resistivity. After comparison, another kind of mesh is strongly recommended.
A numerical simulation of ablation controlled arcs
Energy Technology Data Exchange (ETDEWEB)
Godin, D.; Trepanier, J.Y. [Ecole Polytechnique, Dept. of Mechanical Engineering, Montreal, PQ (Canada); Eby, S.D. [Ecole Polytechnique, Centre de Recherche en Calcul Applique, Montreal, PQ (Canada); Robin-Jouan, P. [GEC-Alsthom T and D, Villeurbanne, (France)
1998-09-01
An approach to model the ablation phenomenon of ablation controlled arcs using computational fluid dynamics was presented. Ablation controlled arcs are found in high voltage electrical equipment such as fuses and circuit-breakers. A qualitative prediction of the ablation level is critical from an industrial point of view because deliberate use of ablation is made to increase the pressure in a circuit-breaker chamber to allow for an efficient extinction when the current returns to zero. The numerical model was validated by comparing results of published experimental data. 7 refs., 10 figs.
Numerical simulations at CEBAF using PARMELA
Liu, H.
1993-12-01
PARMELA has been used at CEBAF for numerical modeling of the nuclear physics injector chopping system, a possible FEL laser gun injector, and the rf steering and focusing effects of the standard CEBAF SRF cavities. These applications call for the code to input field data consistently from SUPERFISH, POISSON, and MAFIA, to properly treat a focusing solenoidal lens having an actual field profile either individually or together with its adjacent rf cavity, to deal with the space charge forces, to model the longitudinal phase space matching required for bunching electrons using a phase-compressor chicane, etc. In this paper, we describe in detail these issues of general interest.
Numerical analysis and geotechnical assessment of mine scale model
Institute of Scientific and Technical Information of China (English)
Khanal Manoj; Adhikary Deepak; Balusu Rao
2012-01-01
Various numerical methods are available to model,simulate,analyse and interpret the results; however a major task is to select a reliable and intended tool to perform a realistic assessment of any problem.For a model to be a representative of the realistic mining scenario,a verified tool must be chosen to perform an assessment of mine roof support requirement and address the geotechnical risks associated with longwall mining.The dependable tools provide a safe working environment,increased production,efficient management of resources and reduce environmental impacts of mining.Although various methods,for example,analytical,experimental and empirical are being adopted in mining,in recent days numerical tools are becoming popular due to the advancement in computer hardware and numerical methods.Empirical rules based on past experiences do provide a general guide,however due to the heterogeneous nature of mine geology (i.e.,none of the mine sites are identical),numerical simulations of mine site specific conditions would lend better insights into some underlying issues.The paper highlights the use of a continuum mechanics based tool in coal mining with a mine scale model.The continuum modelling can provide close to accurate stress fields and deformation.The paper describes the use of existing mine data to calibrate and validate the model parameters,which then are used to assess geotechnical issues related with installing a new high capacity longwall mine at the mine site.A variety of parameters,for example,chock convergences,caveability of overlying sandstones,abutment and vertical stresses have been estimated.
Direct numerical simulation of flow past cactus--shaped cylinders
Babu, Pradeep; Mahesh, Krishnan
2006-11-01
The Saguaro cacti are tall, have short root systems and can withstand high wind velocities (Bulk 1984, Talley et al. 2002). Their trunks are essentially cylindrical with V--shaped longitudinal cavities. The size and number of cavities on the Saguaro cacti vary so that they have a near--constant fraction cavity depth (l/D ratio of about 0.07, Geller & Nobel 1984). Direct numerical simulations is used to assess the aerodynamic effect of the grooves on the cactus. DNS is performed for cactus shaped cylinders with l/d ratio's of 0.07 and 0.105, and smooth cylinders (l/d=0) at the same Reynolds number. Presence of the V--shaped cavities is found to decrease the drag on the cylindrical trunk as well as affect the fluctuating lift forces. The talk will quantify these differences, and discuss the physical mechanisms by which V--shaped cavities on the surface influence the flow.
Holistic simulation of geotechnical installation processes numerical and physical modelling
2015-01-01
The book provides suitable methods for the simulations of boundary value problems of geotechnical installation processes with reliable prediction for the deformation behavior of structures in static or dynamic interaction with the soil. It summarizes the basic research of a research group from scientists dealing with constitutive relations of soils and their implementations as well as contact element formulations in FE-codes. Numerical and physical experiments are presented providing benchmarks for future developments in this field. Boundary value problems have been formulated and solved with the developed tools in order to show the effectivity of the methods. Parametric studies of geotechnical installation processes in order to identify the governing parameters for the optimization of the process are given in such a way that the findings can be recommended to practice for further use. For many design engineers in practice the assessment of the serviceability of nearby structures due to geotechnical installat...
Numerical simulation of avascular tumor growth
Energy Technology Data Exchange (ETDEWEB)
Slezak, D Fernandez; Suarez, C; Soba, A; Risk, M; Marshall, G [Laboratorio de Sistemas Complejos, Departamento de Computacion, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires (C1428EGA) Buenos Aires (Argentina)
2007-11-15
A mathematical and numerical model for the description of different aspects of microtumor development is presented. The model is based in the solution of a system of partial differential equations describing an avascular tumor growth. A detailed second-order numeric algorithm for solving this system is described. Parameters are swiped to cover a range of feasible physiological values. While previous published works used a single set of parameters values, here we present a wide range of feasible solutions for tumor growth, covering a more realistic scenario. The model is validated by experimental data obtained with a multicellular spheroid model, a specific type of in vitro biological model which is at present considered to be optimum for the study of complex aspects of avascular microtumor physiology. Moreover, a dynamical analysis and local behaviour of the system is presented, showing chaotic situations for particular sets of parameter values at some fixed points. Further biological experiments related to those specific points may give potentially interesting results.
Numerical Simulation of Rotating Vertical Bridgman Growth
Directory of Open Access Journals (Sweden)
S. Nouri
2016-01-01
Full Text Available The present work is proposed a numerical parametric study of heat and mass transfer in a rotating vertical cylinder during the solidification of a binary metallic alloy. The aim of this paper is to present an enthalpy formulation based on the fixed grid methodology for the numerical solution of convective-diffusion during the phase change in the case of the steady crucible rotation. The extended Darcy model including the time derivative and Coriolis terms was applied as momentum equation. It was found that the buoyancy driven flow and solute distribution can be affected significantly by the rotating cylinder. The problem is governed by the Navier-Stokes equations coupled with the conservation laws of energy and solute. The resulting system was discretized by the control volume method and solved by the SIMPLER algorithm proposed by Patankar. A computer code was developed and validated by comparison with previous studies. It can be observed that the forced convection introduced by rotation, dramatically changes the flow and solute distribution at the interface (liquid-mushy zone. The effect of Reynolds number on the Nusselt number, flow and solute distribution is presented and discussed.
Radiative Transfer in 3D Numerical Simulations
Stein, R; Stein, Robert; Nordlund, Aake
2002-01-01
We simulate convection near the solar surface, where the continuum optical depth is of order unity. Hence, to determine the radiative heating and cooling in the energy conservation equation, we must solve the radiative transfer equation (instead of using the diffusion or optically thin cooling approximations). A method efficient enough to calculate the radiation for thousands of time steps is needed. We assume LTE and a non-gray opacity grouped into 4 bins according to strength. We perform a formal solution of the Feautrier equation along a vertical and four straight, slanted, rays (at four azimuthal angles which are rotated 15 deg. every time step). We present details of our method. We also give some results: comparing simulated and observed line profiles for the Sun, showing the importance of 3D transfer for the structure of the mean atmosphere and the eigenfrequencies of p-modes, illustrating Stokes profiles for micropores, and analyzing the effect of radiation on p-mode asymmetries.
Numerical simulation of jet flow using LES
Czech Academy of Sciences Publication Activity Database
Louda, Petr; Kozel, K.; Příhoda, Jaromír
Praha : Ústav termomechaniky AV ČR v. v. i., 2009 - (Jonáš, P.; Uruba, V.), s. 1-6 ISBN 978-80-87012-21-5. [Colloquium Fluid Dynamics 2009. Praha (CZ), 21.10.2009-23.10.2009] R&D Projects: GA ČR GA103/09/0977 Institutional research plan: CEZ:AV0Z20760514 Keywords : turbulence modelling * large eddy simulation * plane free jet Subject RIV: BK - Fluid Dynamics
Numerical Simulation of Magnetic Pulse Welding
Beyer, Eckhard; Brenner, Berndt; Göbel, Gunther; Körner, Julia
2012-01-01
The increasing demand for the use of lightweight materials and part designs, especially in the automotive industry, is a driving factor for the development of new joining techniques. One of the main challenges is joining of dissimilar materials. Magnetic pulse welding (MPW), a high-velocity, cold forming technique is a possible solution, as it is known for its ability to join dissimilar metals. To determine the potential of this technology for a certain application, simulation ...
Numerical simulations of square arrayed rod bundles
International Nuclear Information System (INIS)
Highlights: ► CFD simulations with square arrayed rod bundles. ► Mesh dependency and turbulence model study by comparison with experiments. ► Gibson and Launder Reynolds stress model shows good agreement with experiments. ► Effect of pitch to diameter ratio and Reynolds number is correctly captured. - Abstract: Computational fluid dynamics (CFD) simulations were performed with square arrayed rod bundles featuring pitch to diameter (P/D) ratio of 1.194 and 1.326 in order to find an optimal mesh and turbulence model for simulations with more complex geometries in the future. With the tighter lattice a mesh sensitivity and turbulence model study were accomplished and the post processed turbulence quantities, velocity field and wall shear stress were compared with experimental data ( Developed single phase turbulent flow through a square-pitch rod cluster. Nuclear Engineering and Design 60, 365–379.). The comparisons show that Reynolds-Averaged Navier–Stokes method with the Reynolds stress model of Gibson and Launder in conjunction with an appropriate mesh can provide reasonable agreement with the experiment for this lattice. For pure bundle simulations the body fitted structured meshes are suggested, since slightly better agreement can be captured considering all quantities with the same number of cells. Based on the drawn conclusions the procession was repeated for P/D = 1.326, where, due to lack of experiment, just the correct tendencies of the turbulence quantities and velocity field were established. The results show Reynolds number independency correctly and the increase of P/D issues in more similar flow to axisymmetric pipe flow.
Numerical Simulations of Europa Hydrothermal Plumes
Goodman, J. C.; Lenferink, E.
2009-12-01
The liquid water interiors of Europa and other icy moons of the outer solar system are likely to be driven by geothermal heating from the sea floor, leading to the development of buoyant hydrothermal plumes. These plumes potentially control icy surface geomorphology, and are of interest to astrobiologists. We have performed a series of simulations of these plumes using the MITGCM. We assume in this experiment that Europa's ocean is deep (of order 100 km) and unstratified, and that plume buoyancy is controlled by temperature, not composition. A series of experiments was performed to explore a limited region of parameter space, with ocean depth H ranging from 50 to 100 km deep, source heat flux Q between 1 and 10 GW, and values of the Coriolis parameter f between 30% and 90% of the Europa average value. As predicted by earlier work, the plumes in our simulations form narrow cylindrical chimneys (a few km across) under the influence of the Coriolis effect. These plumes broaden over time until they become baroclinically unstable, breaking up into cone-shaped eddies when they become 20-35 km in diameter; the shed eddies are of a similar size. Large-scale currents in the region of the plume range between 1.5 and 5 cm/s; temperature anomalies in the plume far from the seafloor are tiny, varying between 30 and 160 microkelvin. Variations in plume size, shape, speed, and temperature are in excellent agreement with previous laboratory tank experiments, and in rough agreement with theoretical predictions. Plume dynamics and geometry are controlled by a "natural Rossby number" which depends strongly on depth H and Coriolis parameter f, but only weakly on source heat flux Q. However, some specific theoretical predictions are not borne out by these simulations. The time elapsed between startup of the source and the beginning of eddy-shedding is much less variable than predicted; also, the plume temperature varies with ocean depth H when our theory says it should not. Both of
Numerical Simulation of Rocket Exhaust Interaction with Lunar Soil
Liever, Peter; Tosh, Abhijit; Curtis, Jennifer
2012-01-01
This technology development originated from the need to assess the debris threat resulting from soil material erosion induced by landing spacecraft rocket plume impingement on extraterrestrial planetary surfaces. The impact of soil debris was observed to be highly detrimental during NASA s Apollo lunar missions and will pose a threat for any future landings on the Moon, Mars, and other exploration targets. The innovation developed under this program provides a simulation tool that combines modeling of the diverse disciplines of rocket plume impingement gas dynamics, granular soil material liberation, and soil debris particle kinetics into one unified simulation system. The Unified Flow Solver (UFS) developed by CFDRC enabled the efficient, seamless simulation of mixed continuum and rarefied rocket plume flow utilizing a novel direct numerical simulation technique of the Boltzmann gas dynamics equation. The characteristics of the soil granular material response and modeling of the erosion and liberation processes were enabled through novel first principle-based granular mechanics models developed by the University of Florida specifically for the highly irregularly shaped and cohesive lunar regolith material. These tools were integrated into a unique simulation system that accounts for all relevant physics aspects: (1) Modeling of spacecraft rocket plume impingement flow under lunar vacuum environment resulting in a mixed continuum and rarefied flow; (2) Modeling of lunar soil characteristics to capture soil-specific effects of particle size and shape composition, soil layer cohesion and granular flow physics; and (3) Accurate tracking of soil-borne debris particles beginning with aerodynamically driven motion inside the plume to purely ballistic motion in lunar far field conditions. In the earlier project phase of this innovation, the capabilities of the UFS for mixed continuum and rarefied flow situations were validated and demonstrated for lunar lander rocket
Dimensionless numerical model for simulation of active magnetic regenerator refrigerator
Energy Technology Data Exchange (ETDEWEB)
Sarlah, A.; Poredos, A. [Faculty of Mechanical Engineering, University of Ljubljana, Askerceva 6, SI-1000 Ljubljana (Slovenia)
2010-09-15
In order to obtain a better reliability, consistency and accuracy of results obtained with a numerical simulation of an AMRR (active magnetic regenerator refrigerator), a dimensionless numerical model was developed, which can equally be used for determination of regenerator's heat transfer coefficient and simulation of passive heat regenerators or AMRR operation. Regenerator's heat transfer coefficient {alpha}{sub f}, is a crucial input parameter in the simulation of AMRR operation and has a primal effect on the outcome of a solution. This paper deals with a derived dimensionless model and discusses errors involved when using different models for heat transfer coefficient and AMRR operation simulation. (author)
Partial Differential Equations Modeling and Numerical Simulation
Glowinski, Roland
2008-01-01
This book is dedicated to Olivier Pironneau. For more than 250 years partial differential equations have been clearly the most important tool available to mankind in order to understand a large variety of phenomena, natural at first and then those originating from human activity and technological development. Mechanics, physics and their engineering applications were the first to benefit from the impact of partial differential equations on modeling and design, but a little less than a century ago the Schrödinger equation was the key opening the door to the application of partial differential equations to quantum chemistry, for small atomic and molecular systems at first, but then for systems of fast growing complexity. Mathematical modeling methods based on partial differential equations form an important part of contemporary science and are widely used in engineering and scientific applications. In this book several experts in this field present their latest results and discuss trends in the numerical analy...
Coherent Structures in Numerically Simulated Plasma Turbulence
DEFF Research Database (Denmark)
Kofoed-Hansen, O.; Pécseli, H.L.; Trulsen, J.
1989-01-01
Low level electrostatic ion acoustic turbulence generated by the ion-ion beam instability was investigated numerically. The fluctuations in potential were investigated by a conditional statistical analysis revealing propagating coherent structures having the form of negative potential wells which...... correspond to ion phase space vortices. The results demonstrate the importance of clump formation in ion phase space for the dynamics of the turbulence. The statistical analysis gives results in terms of averages over a conditionally selected subensemble. Because of the intermittent character of the...... turbulence it proved possible to devise a method, which permits recognition of essentially all coherent structures. With most of the structures recovered we are able to estimate their distributions of amplitude, width and velocity. A statistical evidence for interaction, i.e., binding, of phase space...
Numerical simulation of distributed parameter processes
Colosi, Tiberiu; Unguresan, Mihaela-Ligia; Muresan, Vlad
2013-01-01
The present monograph defines, interprets and uses the matrix of partial derivatives of the state vector with applications for the study of some common categories of engineering. The book covers broad categories of processes that are formed by systems of partial derivative equations (PDEs), including systems of ordinary differential equations (ODEs). The work includes numerous applications specific to Systems Theory based on Mpdx, such as parallel, serial as well as feed-back connections for the processes defined by PDEs. For similar, more complex processes based on Mpdx with PDEs and ODEs as components, we have developed control schemes with PID effects for the propagation phenomena, in continuous media (spaces) or discontinuous ones (chemistry, power system, thermo-energetic) or in electro-mechanics (railway – traction) and so on. The monograph has a purely engineering focus and is intended for a target audience working in extremely diverse fields of application (propagation phenomena, diffusion, hydrodyn...
NUMERICAL SIMULATION OF SEDIMENT RELEASE FROM RESERVOIRS
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
For the computation of the sediment quantity released from reservoirs, a vertical two-dimensional hydrodynamic model is combined with a sediment transport model. The hydrodynamic model is based on the equations of mass and momentum conservation along with a k - ε model for closure of the Reynolds stresses. The sediment transport model is based on the convection-diffusion equation of sediment concentration and the sediment continuity equation. Both the hydrodynamic and sediment transport models are developed in a boundary-fitted curvilinear co-ordinate system. Comparison of the predicted mean velocity field with laboratory results indicates that the present model captures most experimental trends with reasonable accuracy. Also good agreement is found in comparison of the sediment transport results for the numerical model and the experimental model.
Dynamics of a compound vesicle: numerical simulations
Veerapaneni, Shravan; Young, Yuan-Nan; Vlahovska, Petia; Blawzdziewicz, Jerzy
2010-11-01
Vesicles (self-enclosing lipid membranes) in simple linear flows are known to exhibit rich dynamics such as tank-treading, tumbling, trembling (swinging), and vacillating breathing. Recently, vesicles have been used as a multi-functional platform for drug-delivery. In this work, the dynamics of simplified models for such compound vesicles is investigated numerically using a state-of-the-art boundary-integral code that has been validated with high accuracy and efficiency. Results show that for a vesicle enclosing a rigid particle in a simple shear flow, transition from tank-treading to tumbling is possible even in the absence of viscosity mismatch in the interior and exterior fluids. We will discuss the shape transformations, multiple particle interactions and the flow properties. Comparison with results from analytical modeling gives insights to the underlying physics for such novel dynamics.
Numerical simulation of vircator with the feedback
International Nuclear Information System (INIS)
By means of a 2,5-dimensional PIC-code the processes of dynamics of a relativistic electron beam in vircator, forming of two joined cylinders of different radiuses in the presence of a feedback across the field was modeled numerically. Modeling has shown that at model selected options the virtual cathode is formed at and around of step change of radius of a side surface of vircator. It is revealed that feedback introduction across the field gives the chance to change time of formation of the virtual cathode, and also its position in space by means of feedback factor changing. With increase in value of a feedback factor in a spectrum of oscillations of electric field the amplitude of high-frequency components increases that finally, can lead to breakdown of an electron bunch.
The Lexington Benchmarks for Numerical Simulations of Nebulae
Ferland, G; Contini, M; Harrington, J; Kallman, T; Netzer, H; Péquignot, D; Raymond, J; Rubin, R; Shields, G; Sutherland, R; Viegas, S
2016-01-01
We present the results of a meeting on numerical simulations of ionized nebulae held at the University of Kentucky in conjunction with the celebration of the 70th birthdays of Profs. Donald Osterbrock and Michael Seaton.
Numerical simulation of an axial blood pump.
Chua, Leok Poh; Su, Boyang; Lim, Tau Meng; Zhou, Tongming
2007-07-01
The axial blood pump with a magnetically suspended impeller is superior to other artificial blood pumps because of its small size. In this article, the distributions of velocity, path line, pressure, and shear stress in the straightener, the rotor, and the diffuser of the axial blood pump, as well as the gap zone were obtained using the commercial software, Fluent (version 6.2). The main focus was on the flow field of the blood pump. The numerical results showed that the axial blood pump could produce 5.14 L/min of blood at 100 mm Hg through the outlet when rotating at 11,000 rpm. However, there was a leakage flow of 1.06 L/min in the gap between the rotor cylinder and the pump housing, and thus the overall flow rate the impeller could generate was 6.2 L/min. The numerical results showed that 75% of the scalar shear stresses (SSs) were less than 250 Pa, and 10% were higher than 500 Pa within the whole pump. The high SS region appeared around the blade tip where a large variation of velocity direction and magnitude was found, which might be due to the steep angle variation at the blade tip. Because the exposure time of the blood cell at the high SS region within the pump was relatively short, it might not cause serious damage to the blood cells, but the improvement of blade profile should be considered in the future design of the axial pump. PMID:17584481
Numerical simulation tests with light dynamical quarks
International Nuclear Information System (INIS)
Two generate flavours of quarks are simulated with small masses down to about one fifth of the strange quark mass by using the two-step multi-boson (TSMB) algorithm. The lattice size is 83 . 16 with lattice spacing about a ≅ 0.27 fm which is not far from the Nt = 4 thermodynamical cross-over line. Autocorrelations of different physical quantities are estimated as a function of the quark mass. The eigenvalue spectra of the Wilson-Dirac operator are investigated. (orig.)
Numerical simulations of Klein-Gordon solitary-wave interactions
International Nuclear Information System (INIS)
Solitons of a non-linear Klein-Gordon equation are studied numerically using a cubic B-spline finite-element method. Test results indicate that, when solitary waves interact, the final state obtained depends on their relative velocity.The simulations confirm existing observations and produce new results. The numerical algorithm developed is efficient with an undemanding stability criterion
Numerical simulations of cardiovascular diseases and global matter transport
Simakov, S S; Evdokimov, A V; Kholodov, Y A
2007-01-01
Numerical model of the peripheral circulation and dynamical model of the large vessels and the heart are discussed in this paper. They combined together into the global model of blood circulation. Some results of numerical simulations concerning matter transport through the human organism and heart diseases are represented in the end.
Numerical simulation of ventilation in blinding heading
Institute of Scientific and Technical Information of China (English)
CHANG De-qiang; LIU Jing-xian; CHEN Bao-zhi
2008-01-01
The way of ventilation in all its forms and characteristics in the blinding heading was studied.On the basis of computational fluid dynamics (CFD) the turbulence model of restrained ventilation in blinding heading was set up,and the calculation boundary conditions were analyzed.According to the practice application the three-dimensional flow field of ventilation in blinding heading was simulated by the computational fluid dynamics software.The characteristics of the ventilation flow field such as the temperature field zone and the flow filed zone and the rule of the flow velocity were obtained.The ventilation in blinding heading under certain circumstances was calculated and simulated for optimization.The optimal ventilation form and related parameters under given condition were obtained.The rule of the ventilation in blinding heading was theoretical analyzed,which provided reference for the research on the process of mass transfer,the rule of hazardous substances transportation and ventilation efficiency,provided a new method for the study of reasonable and effective ventilation in blinding heading.
Numerical Simulations of the Mechanics of Vitrectomy
Young, Ethan; Eldredge, Jeff; Hubschman, Jean-Pierre
2015-11-01
Vitreous is the clear, gel-like substance that fills the cavity between the lens and retina in the eye. Treating certain eye abnormalities requires removing this substance using a minimally-invasive device called a vitreous cutter. Understanding the behavior of this viscoelastic biofluid during surgeries is essential to improving the effectiveness of the procedure. In this study, three-dimensional computational models of vitreous cutters are investigated using an immersed boundary method paired with a viscoelastic constitutive model. The solver uses a fractional-step method to satisfy continuity and traction boundary conditions to simulate the applied suction. The current work extends previous efforts to accurately model the rheological parameters measured by Sharif-Kashani et al. using the Giesekus constitutive equation [Retina, 2013]. The simulations were used to quantify both the average and time-varying flow rate through the device. Values for flow rate are compared with experimental results from Hubschman et al. [Retina, 2009]. Flow features associated with the cutting dynamics are of particular interest, as is the geometry of the cutter itself. These operational and design changes are a target for improving cutter efficacy while minimizing potential tissue damage.
Numerical simulation of ventilation in blinding heading
Institute of Scientific and Technical Information of China (English)
CHANG De-qiang; LIU Jing-xian; CHEN Bao-zhi
2008-01-01
The way of ventilation in all its forms and characteristics in the blinding heading was studied. On the basis of computational fluid dynamics (CFD) the turbulence model of restrained ventilation in blinding heading was set up, and the calculation boundary condi-tions were analyzed. According to the practice application the three-dimensional flow field of ventilation in blinding heading was simulated by the computational fluid dynamics soft-ware. The characteristics of the ventilation flow field such as the temperature field zone and the flow filed zone and the rule of the flow velocity were obtained. The ventilation in blinding heading under certain circumstances was calculated and simulated for optimiza-tion. The optimal ventilation form and related parameters under given condition were ob-tained. The rule of the ventilation in blinding heading was theoretical analyzed, which pro-vided reference for the research on the process of mass transfer, the rule of hazardous substances transportation and ventilation efficiency, provided a new method for the study of reasonable and effective ventilation in blinding heading.
Gravity Currents with Convective Mixing: High-resolution Numerical Simulations
Voskov, D.; Elenius, M. T.; Tchelepi, H.
2014-12-01
Due to challenges in performing direct numerical simulations for gravity currents with convective mixing, different attempts have been made to simplify the problem. In this work, the full problem is investigated with direct numerical simulations. Our simulations employ a recently developed capability in our General Purpose Research Simulator (AD-GPRS). The compositional approach is based on K-values and a linear density model. A shared-memory parallel implementation allows for high resolution simulations in a reasonable time frame. Our results indicate that it is important to consider the reduction in the dissolution rate after the fingers begin to interact with the bottom of the aquifer. Another important observation suggests considering a reduction in the dissolution rate where the plume thickness increases in time. In addition to the large-scale simulations, we performed convective-mixing simulations in relatively small domains to support the analysis of large-scale plume migration and CO2 trapping.
Mottyll, Stephan; Skoda, Romuald
2016-07-01
As a contribution to a better understanding of cavitation erosion mechanisms, a compressible inviscid finite volume flow solver with barotropic homogeneous liquid-vapor mixture cavitation model is applied to ultrasonic horn set-ups with and without stationary specimen, that exhibit attached cavitation at the horn tip. Void collapses and shock waves, which are closely related to cavitation erosion, are resolved. The computational results are compared to hydrophone, shadowgraphy and erosion test data. At the horn tip, vapor volume and topology, subharmonic oscillation frequency as well as the amplitude of propagating pressure waves are in good agreement with experimental data. For the evaluation of flow aggressiveness and the assessment of erosion sensitive wall zones, statistical analyses of wall loads and of the multiplicity of distinct collapses in wall-adjacent flow regions are applied to the horn tip and the stationary specimen. An a posteriori projection of load collectives, i.e. cumulative collapse rate vs. collapse pressure, onto a reference grid eliminates the grid dependency effectively for attached cavitation at the horn tip, whereas a significant grid dependency remains at the stationary specimen. The load collectives show an exponential decrease towards higher collapse pressures. Erosion sensitive wall zones are well predicted for both, horn tip and stationary specimen, and load profiles are in good qualitative agreement with measured topography profiles of eroded duplex stainless steel samples after long-term runs. For the considered amplitude and gap width according to ASTM G32-10 standard, the analysis of load collectives reveals that the distinctive erosive ring shape at the horn tip can be attributed to frequent breakdown and re-development of a small portion of the tip-attached cavity. This partial breakdown of the attached cavity repeats at each driving cycle and is associated with relatively moderate collapse peak pressures, whereas the
Numerical Simulations of a Flux Rope Ejection
Indian Academy of Sciences (India)
P. Pagano; D. H. Mackay; S. Poedts
2015-03-01
Coronal mass ejections (CMEs) are the most violent phenomena observed on the Sun. One of the most successful models to explain CMEs is the flux rope ejection model, where a magnetic flux rope is expelled from the solar corona after a long phase along which the flux rope stays in equilibrium while magnetic energy is being accumulated. However, still many questions are outstanding on the detailed mechanism of the ejection and observations continuously provide new data to interpret and put in the context. Currently, extreme ultraviolet (EUV) images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) are providing new insights into the early phase of CME evolution. In particular, observations show the ejection of magnetic flux ropes from the solar corona and how they evolve into CMEs. However, these observations are difficult to interpret in terms of basic physical mechanisms and quantities, thus, we need to compare equivalent quantities to test and improve our models. In our work, we intend to bridge the gap between models and observations with our model of flux rope ejection where we consistently describe the full life span of a flux rope from its formation to ejection. This is done by coupling the global non-linear force-free model (GNLFFF) built to describe the slow low- formation phase, with a full MHD simulation run with the software MPI-AMRVAC, suitable to describe the fast MHD evolution of the flux rope ejection that happens in a heterogeneous regime. We also explore the parameter space to identify the conditions upon which the ejection is favoured (gravity stratification and magnetic field intensity) and we produce synthesised AIA observations (171 Å and 211 Å). To carry this out, we run 3D MHD simulation in spherical coordinates where we include the role of thermal conduction and radiative losses, both of which are important for determining the temperature distribution of the solar corona during a CME. Our model of flux
Numerical simulation of supersonic gap flow.
Directory of Open Access Journals (Sweden)
Xu Jing
Full Text Available Various gaps in the surface of the supersonic aircraft have a significant effect on airflows. In order to predict the effects of attack angle, Mach number and width-to-depth ratio of gap on the local aerodynamic heating environment of supersonic flow, two-dimensional compressible Navier-Stokes equations are solved by the finite volume method, where convective flux of space term adopts the Roe format, and discretization of time term is achieved by 5-step Runge-Kutta algorithm. The numerical results reveal that the heat flux ratio is U-shaped distribution on the gap wall and maximum at the windward corner of the gap. The heat flux ratio decreases as the gap depth and Mach number increase, however, it increases as the attack angle increases. In addition, it is important to find that chamfer in the windward corner can effectively reduce gap effect coefficient. The study will be helpful for the design of the thermal protection system in reentry vehicles.
Numerical simulation of permafrost depth at Olkiluoto
International Nuclear Information System (INIS)
This study provides a numerical estimation of the development of permafrost and frozen ground at Olkiluoto, where an underground repository for spent nuclear fuel is being designed at a depth of 420 metres. Calculations are carried out in 1-D for a 10 000 metres deep subsurface model using Olkiluoto's site-specific data. The time histories of ground level temperatures, ice sheet thickness, shoreline migration and vegetation covers effects are considered for two climate scenarios, Weichselian-R and Emissions-M. The model also includes the effects of decay heat from the spent fuel. Results are presented for the next 125 000 years for the Weichselian-R scenario and 200 000 years for the Emissions-M scenario. This study shows that in both Weichselian-R and Emissions-M scenarios the depth of the permafrost and frozen ground stays well above the repository level. The maximum permafrost depth is about 170 metres in the Weichselian-R scenario and 80 metres in the Emissions-M scenario. The depth of frozen ground is from a few metres to some twenty metres shallower than the permafrost depth, except during the glacial periods with warm-based ice-sheets when the subglacial permafrost remains completely unfrozen due to high water pressures induced by the ice load. (orig.)
Numerical simulations on the magnetopause current layer
International Nuclear Information System (INIS)
One-dimensional particle simulations are carried out in order to study the current layer between a plasma and magnetic field such as seen at the magnetopause boundary layer. When a subsonic solar wind plasma flow impinges upon a vacuum dipole magnetic field, the width of the current layer is found much smaller than the ion gyroradius and is close to theoretically predicted geometric mean of the ion and electron gyroradii. The width remains essentially the same when the magnetic field is filled with a thermal plasma whose density is smaller than the incoming solar wind density. The width, therefore, remains much smaller than the ion gyroradius. It is found that a similar sharp current layer develops in a plasma confined in a magnetic field such as seen in laboratory and space plasmas. 15 refs., 11 figs
AGN feedback in elliptical galaxies: numerical simulations
Ciotti, L
2011-01-01
The importance of feedback (radiative and mechanical) from massive black holes at the centers of elliptical galaxies is not in doubt, given the well established relation among black hole mass and galaxy optical luminosity. Here, with the aid of high-resolution hydrodynamical simulations, we discuss how this feedback affects the hot ISM of isolated elliptical galaxies of different mass. The cooling and heating functions include photoionization plus Compton heating, the radiative transport equations are solved, and the mechanical feedback due to the nuclear wind is also described on a physical basis; star formation is considered. In the medium-high mass galaxies the resulting evolution is highly unsteady. At early times major accretion episodes caused by cooling flows in the recycled gas produced by stellar evolution trigger AGN flaring: relaxation instabilities occur so that duty cycles are small enough to account for the very small fraction of massive ellipticals observed to be in the QSO-phase, when the accr...
Numerical simulation of aeolian sand ripples
International Nuclear Information System (INIS)
With a new horizontal saltation displacement vector, a model is implemented to simulate the initiation and evolution of aeolian sand ripples. In the model, saltation distance considers the effects of surface height and slope. A linear stability analysis is also carried out for formation of sand ripples. The results show that, the model can be able to successfully reproduce sand ripples which can increase in scale by merging of small ripples. The linear stability analysis indicates that sand ripples appear when the relaxation rate parameter is below a threshold value and wind strength parameter is larger than a critical value. The results also verified that the formation of sand ripples is a self-organization process
Numerical simulation of strong proton rings
International Nuclear Information System (INIS)
Recent calculations suggest the possibility of achieving a Lawson breakeven condition by the magnetic compression of proton rings to field reversal. A physical model and computer code RING developed to study equilibria of strong proton rings and their behavior under an adiabatic increase in the external magnetic field are described. Ring ion motion is followed using a volume-weighted finite-size particle-in-cell method. Because of the very short electron time scale, the electrons are simulated by a simple fluid model using Ohm's law. Quasineutrality, current neutralization in the r-z plane, cylindrical symmetry and a magneto-static model are assumed. Preliminary results indicate that (a) equilibria tend to be intermediate between the long layer and bicycle tire cases; and (b) compression past field reversal on the axis is possible within the framework of this model. Some aspects of the formation and injection of proton rings have also been studied with this code. (author)
Numerical simulation of synthesis gas incineration
Kazakov, A. V.; Khaustov, S. A.; Tabakaev, R. B.; Belousova, Y. A.
2016-04-01
The authors have analysed the expediency of the suggested low-grade fuels application method. Thermal processing of solid raw materials in the gaseous fuel, called synthesis gas, is investigated. The technical challenges concerning the applicability of the existing gas equipment developed and extensively tested exclusively for natural gas were considered. For this purpose computer simulation of three-dimensional syngas-incinerating flame dynamics was performed by means of the ANSYS Multiphysics engineering software. The subjects of studying were: a three-dimensional aerodynamic flame structure, heat-release and temperature fields, a set of combustion properties: a flare range and the concentration distribution of burnout reagents. The obtained results were presented in the form of a time-averaged pathlines with color indexing. The obtained results can be used for qualitative and quantitative evaluation of complex multicomponent gas incineration singularities.
Batman-cracks. Observations and numerical simulations
Selvadurai, A. P. S.; Busschen, A. Ten; Ernst, L. J.
1991-05-01
To ensure mechanical strength of fiber reinforced plastics (FRP), good adhesion between fibers and the matrix is considered to be an essential requirement. An efficient test of fiber-matrix interface characterization is the fragmentation test which provides information about the interface slip mechanism. This test consists of the longitudinal loading of a single fiber which is embedded in a matrix specimen. At critical loads the fiber experiences fragmentation. This fragmentation will terminate depending upon the shear-slip strength of the fiber-matrix adhesion, which is inversely proportional to average fragment lengths. Depending upon interface strength characteristics either bond or slip matrix fracture can occur at the onset of fiber fracture. Certain particular features of matrix fracture are observed at the locations of fiber fracture in situations where there is sufficient interface bond strength. These refer to the development of fractures with a complex surface topography. The experimental procedure involved in the fragmentation tests is discussed and the boundary element technique to examine the development of multiple matrix fractures at the fiber fracture locations is examined. The mechanics of matrix fracture is examined. When bond integrity is maintained, a fiber fracture results in a matrix fracture. The matrix fracture topography in a fragmentation test is complex; however, simplified conoidal fracture patterns can be used to investigate the crack extension phenomena. Via a mixed-mode fracture criterion, the generation of a conoidal fracture pattern in the matrix is investigated. The numerical results compare favorably with observed experimental data derived from tests conducted on fragmentation test specimens consisting of a single glass fiber which is embedded in a polyester matrix.
Numerical simulation of Glacial Isostatic Adjustment
Miglio, E.
2015-12-01
In the Earth's crust, stress can be subdivided into tectonic background stress, overburden pressure, and pore-fluid pressure. The superposition of the first two and the variation of the third part are key factors in controlling movement along faults. Furthermore, stresses due to sedimentation and erosion contribute to the total stress field. In deglaciated regions, an additional stress must be considered: the rebound stress, which is related to rebounding of the crust and mantle after deglaciation. During the growth of a continental ice sheet, the lithosphere under the iceload is deformed and the removal of the ice load during deglaciation initiates a rebound process. The uplift is well known in formerly glaciated areas, e.g.North America and Scandinavia, and in currently deglaciating areas, e.g.Alaska, Antarctica, and Greenland. The whole process of subsiding and uplifting during the growth and melting of an iceload and all related phenomena is known as glacial isostatic adjustment. During the process of glaciation, the surface of the lithosphere is depressed underneath the ice load and compressional flexural stresses are induced in the upper lithosphere, whereas the bottom of the lithosphere experiences extensional flexural stresses; an additional vertical stress due to the ice load is present and it decreases to zero during deglaciation. During rebound, flexural stresses relax slowly. These stresses are able to change the original stress directions and regime.In this work we aim to study the effect of the GIA process in the context of petroleum engineering. The main aspect we will focus on is the mathematical and numerical modeling of the GIA including thermal effects. We plan also to include a preliminary study of the effect of the glacial erosion. All these phenomena are of paramount importance in petroleum engineering: for example some reservoir have been depleted due to tilting caused by both GIA, erosion and thermal effects.
Numerical Simulation of Pulse Shortening in RBWOs
Institute of Scientific and Technical Information of China (English)
GONG Yu-bin; ZHANG Zhang; WANG Wen-xiang; MENG Fan-bao; FAN Zhi-kai; HUANG Min-zhi
2005-01-01
Pulse shortening hinders improvement of microwave output energy for high power microwave tubes. So far, it is also an unresolved problem in the field of high power microwave devices. In this paper, relativistic backward wave tube (RBWO) is treated as an example to study the pulse shortening phenomena. The influences of gas existing in the tube and explosive emission in inner surface of RBWO are all investigated by means of the particle-in-cell method. Through the simulation results, it can be predicted that the background gas in the tube is one but not the most important factor resulting in pulse shortening, in order to broaden the pulse width of gas-filled RBWO, the pressure of the filled gas must be controlled in a proper value. The explosive emission in the surface of slow wave structure due to intense electric field is one of the most important factors causing pulse shortening in high power microwave tube.Some methods to overcome this find of explosive emission are also given.
Numerical simulation of flow past circular duct
Directory of Open Access Journals (Sweden)
Ze-gao YIN
2010-06-01
Full Text Available On the basis of Fluent software, Renormalization Group (RNGk-ε turbulent model and Volume of Fluid (VOF method are employed to simulate the flow past circular duct to obtain and analyze the hydraulic parameters. According to various upper and bottom gap-ratios, the force on duct is calculated. Firstly, when bottom gap-ratio is 0, drag force coefficient, lift force coefficient and composite force reach the maximum respectively and azimuth reaches the minimum. Secondly, with the increase of bottom gap-ratio from 0 to 1, drag force coefficient and composite force decrease sharply, lift force coefficient decreases a little, but azimuth increases dramatically. Thirdly, with the continuous increase of bottom gap-ratio from 1, drag force coefficient, lift force coefficient, composite force and azimuth vary little. So, bottom gap-ratio is the key factor influencing the force on circular duct. When bottom gap-ratio is less than 1, upper gap-ratio has the remarkable influence on the circular duct force. When bottom gap-ratio is greater than 1, the varation of upper gap-ratio has a little influence on the circular duct force.
Numerical simulations for terrestrial planets formation
Directory of Open Access Journals (Sweden)
Ji J.
2011-07-01
Full Text Available We investigate the formation of terrestrial planets in the late stage of planetary formation using two-planet model. At that time, the protostar has formed for about 3 Myr and the gas disk has dissipated. In the model, the perturbations from Jupiter and Saturn are considered. We also consider variations of the mass of outer planet, and the initial eccentricities and inclinations of embryos and planetesimals. Our results show that, terrestrial planets are formed in 50 Myr, and the accretion rate is about 60%–80%. In each simulation, 3–4 terrestrial planets are formed inside “Jupiter” with masses of 0.15–3.6 M⊕. In the 0.5–4 AU, when the eccentricities of planetesimals are excited, planetesimals are able to accrete material from wide radial direction. The plenty of water material of the terrestrial planet in the Habitable Zone may be transferred from the farther places by this mechanism. Accretion may also happen a few times between two giant planets only if the outer planet has a moderate mass and the small terrestrial planet could survive at some resonances over time scale of 108 yr.
Numerical simulation of flow past circular duct
Institute of Scientific and Technical Information of China (English)
Ze-gao YIN; Xian-wei Cao; Hong-da SHI; Jian MA
2010-01-01
The Renormalization Group(RNG)k-ε turbulence model and Volume of Fluid(VOF)method were employed to simulate the flow past a circular duct in order to obtain and analyze hydraulic parameters.According to various upper and bottom gap ratios,the force on the duct was calculated.When the bottom gap ratio is 0,the drag force coefficient,lift force coefficient,and composite force reach their maximum values,and the azimuth reaches its minimum.With an increase of the bottom gap ratio from 0 to 1,the drag force coefficient and composite force decrease sharply,and the lift force coefficient does not decreases so much,but the azimuth increases dramatically.With a continuous increase of the bottom gap ratio from 1 upward,the drag force coefficient,lift force coefficient,composite force,and azimuth vary little.Thus,the bottom gap ratio is the key factor influencing the force on the circular duct.When the bottom gap ratio is less than 1,the upper gap ratio has a remarkable influence on the force of the circular duct.When the bottom gap ratio is greater than 1,the variation of the upper gap ratio has little influence on the force of the circular duct.
Numerical simulation of fundamental trapped sausage modes
Cécere, M; Reula, O
2011-01-01
Context: We integrate the 2D MHD ideal equations of a straight slab to simulate observational results associated with fundamental sausage trapped modes. Aims: Starting from a non-equilibrium state with a dense chromospheric layer, we analyse the evolution of the internal plasma dynamics of magnetic loops, subject to line-tying boundary conditions, and with the coronal parameters described in Asai et al. (2001) and Melnikov et al. (2002) to investigate the onset and damping of sausage modes. Methods: To integrate the equations we used a high resolution shock-capturing (HRSC) method specially designed to deal appropriately with flow discontinuities. Results: Due to non-linearities and inhomogeneities, pure modes are difficult to sustain and always occur coupled among them so as to satisfy, e.g., the line-tying constraint. We found that, in one case, the resonant coupling of the sausage fundamental mode with a slow one results in a non-dissipative damping of the former. Conclusions: In scenarios of thick and den...
NUMERICAL SIMULATION OF ICE ACCRETION ON AIRFOIL
Directory of Open Access Journals (Sweden)
Nicusor ALEXANDRESCU
2009-09-01
Full Text Available This work consists in the simulation of the ice accretion in the leading edge of aerodynamic profiles and our proposed model encompasses: geometry generation, calculation of the potential flow around the body, boundary layer thickness computation, water droplet trajectory computation, heat and mass balances and the consequent modification of the geometry by the ice growth. The flow calculation is realized with panel methods, using only segments defined over the body contour. The viscous effects are considered using the Karman-Pohlhausen method for the laminar boundary layer. The local heat transfer coefficient is obtained by applying the Smith-Spalding method for the thermal boundary layer. The ice accretion limits and the collection efficiency are determined by computing water droplet trajectories impinging the surface. The heat transfer process is analyzed with an energy and a mass balance in each segment defining the body. Finally, the geometry is modified by the addition of the computed ice thickness to the respective panel. The process by repeating all the steps. The model validation is done using a selection of problems with experimental solution, CIRA (the CESAR project. Hereinafter, results are obtained for different aerodynamic profiles, angles of attack and meteorological parameters
Numerical simulation of subcooled flow boiling
Park, Won Cheol
Sub-cooled flow boiling in a U-bend has been examined using numerical methods. An Eulerian/Eulerian mathematical description was used with a multiphase computational algorithm to predict several types of flows and to examine sub-cooled flow boiling. As a prelude to the study of sub-cooled boiling and two-phase flows, single-phase laminar and turbulent flows in a U-bend were investigated. Air-water bubbly up flow in a vertical straight duct followed by a U-bend with heat transfer was analyzed. In such a flow, as the flow develops through the U-bend the bubbles move from center and outer wall toward inner wall. After half way through the U-bend, the fluids do not have sufficient time for complete reorganization in the presence of centrifugal forces and the pressure gradients. After the U-bend, the bubbles finally reach the original distribution in about forty diameters. The heat transfer in the U-bend was also calculated and as expected heat transfer rate on the outer wall is higher than on the inner wall. For air-water bubbly two-phase flow, Nusselt numbers in the U-bend can be as high as 400 percent of the value in the straight duct on one of the walls. The method of partitioned wall heat flux was used to study sub-cooled flow boiling. For sub-cooled flow boiling in a U-bend, axial and lateral velocity distributions as well as quality and void fraction variations were analyzed. Computed axial and lateral variations of void fraction compare favorably with existing experimental data. As expected, the pressure drop for bubbly flow through the U-bend is larger than for single-phase flow by as much as fifty percent. Computed pressure drop for flow with phase change falls between the predictions of two different correlations in the literature, and thus seems reasonable. Predictions of heat transfer and void fraction under sub-cooled flow boiling using two-fluid models need better quantitative knowledge related to the mechanisms associated with bubble growth and
Numerical simulation of photoexcited polaron states in water
Energy Technology Data Exchange (ETDEWEB)
Zemlyanaya, E. V., E-mail: elena@jinr.ru; Volokhova, A. V.; Amirkhanov, I. V.; Puzynin, I. V.; Puzynina, T. P.; Rikhvitskiy, V. S. [Laboratory of Information Technologies, Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Lakhno, V. D. [Institute of Mathematical Problems of Biology, Russian Academy of Science, Pushchino 142290 (Russian Federation); Atanasova, P. Kh. [Faculty of Mathematics and Informatics, Paisii Hilendarski University of Plovdiv 4003 (Bulgaria)
2015-10-28
We consider the dynamic polaron model of the hydrated electron state on the basis of a system of three nonlinear partial differential equations with appropriate initial and boundary conditions. A parallel numerical algorithm for the numerical solution of this system has been developed. Its effectiveness has been tested on a few multi-processor systems. A numerical simulation of the polaron states formation in water under the action of the ultraviolet range laser irradiation has been performed. The numerical results are shown to be in a reasonable agreement with experimental data and theoretical predictions.
Three-Dimensional Numerical Simulation to Mud Turbine for LWD
Yao, Xiaojiang; Dong, Jingxin; Shang, Jie; Zhang, Guanqi
Hydraulic performance analysis was discussed for a type of turbine on generator used for LWD. The simulation models were built by CFD analysis software FINE/Turbo, and full three-dimensional numerical simulation was carried out for impeller group. The hydraulic parameter such as power, speed and pressure drop, were calculated in two kinds of medium water and mud. Experiment was built in water environment. The error of numerical simulation was less than 6%, verified by experiment. Based on this rationalization proposals would be given to choice appropriate impellers, and the rationalization of methods would be explored.
Feasibility study for a numerical aerodynamic simulation facility. Volume 1
Lincoln, N. R.; Bergman, R. O.; Bonstrom, D. B.; Brinkman, T. W.; Chiu, S. H. J.; Green, S. S.; Hansen, S. D.; Klein, D. L.; Krohn, H. E.; Prow, R. P.
1979-01-01
A Numerical Aerodynamic Simulation Facility (NASF) was designed for the simulation of fluid flow around three-dimensional bodies, both in wind tunnel environments and in free space. The application of numerical simulation to this field of endeavor promised to yield economies in aerodynamic and aircraft body designs. A model for a NASF/FMP (Flow Model Processor) ensemble using a possible approach to meeting NASF goals is presented. The computer hardware and software are presented, along with the entire design and performance analysis and evaluation.
Numerical Simulation of Barotropic Tides around Taiwan
Directory of Open Access Journals (Sweden)
Chih-Kai Hu
2010-01-01
Full Text Available A _ 2-D barotropic tide model was used to examine the characteristics of barotropic tides and to improve the accuracy of predicting tidal sea levels and currents in the seas around Taiwan. The form ratio suggests that tides are predominantly semidiurnal in the northern reaches of the Taiwan Strait and mixed of diurnal and semidiurnal elsewhere around Taiwan. When the dominant M2 wave enters the Strait from the north, its amplitude is magnified to ~2 m in the middle, and then decreases rapidly toward the south end of the Strait. The predominance of diurnal tides along the southwest to the south coast of Taiwan is attributed to the quasi-resonance of diurnal waves in the South China Sea. The tidal range is small and tidal currents are weak off the east coast of Taiwan. Barotropic tidal energy is mostly dissipated on the shallow banks of the southwestern Strait. Results summarized from sensitivity tests on the bottom drag coefficient (CD and horizontal eddy viscosity (AM indicate that CD = 0.0015 - 0.00175 and AM = 150 m2 s-1 lead to the best model-data fit when compared to the observed tidal sea levels at ten reference tide-gauge stations around Taiwan. The averaged root-mean-squared (RMS differences of the simulated tidal sea level for the six principal constituents of O1, P1, K1, N2, M2, and S2 are significantly reduced to 1.3, 0.7, 2.0, 1.6, 5.1, and 3.1 cm, respectively, compared to that calculated from a _ resolution global tide harmonic constant database, NAO.99b (Matsumoto et al. 2000. The averaged RMS differences of barotropic tidal currents (U, V for O1, K1, M2, and S2 are (0.92, 1.64, (1.17, 0.61, (3.88, 2.37, and (1.52, 1.20 cm s-1. A database of tidal sea levels and current harmonic constants, TWTIDE08, for Q1, O1, P1, K1, J1, OO1, 2N2, _ N2, _ M2, L2, T2, S2, and K2 is established with this study.
The numerical simulation of the impact phenomena in nail penetration
International Nuclear Information System (INIS)
Powder actuated fastening is a quick and cost efficient method to fasten building materials together. In this method, a nail is placed in a hand-held tool and driven by a flying piston into hard construction materials such as steel and concrete. The piston is propelled by the explosive force of a powder cartridge. Numerical simulations are used to help engineers design better powder actuated tools and fastenings. These simulations require the numerical treatment of stress wave propagation, large strain, strain-rate material behaviour and sliding contact and impact. In this paper, the numerical contact algorithm implemented in an explicit dynamic finite element program used to simulate nail penetrations is described. The results of several example simulations are presented. ((orig.))
Numerical simulation of turbulent flow in a cyclonic separator
Bogdanov, Dmitry; Poniaev, Sergey
2014-12-01
Numerical simulation of a turbulent flow of air with dispersed particles through a cyclonic separator is presented. Because of a high streamline curvature in the separator it is difficult to simulate the flow by using the conventional turbulent models. In this work the curvature correction term was included into the k - ω - SST turbulence model implemented in the OpenFOAM® software. Experimental data and results of numerical simulation by the commercial ANSYS Fluent® solver for a turbulent flow in a U-duct were used to validate the model. The numerical simulation of the flow in the cyclonic separator demonstrates that the implemented turbulence model successfully predicts the cyclonic separator efficiency.
Numerical relativity simulations in the era of the Einstein Telescope
Hannam, Mark; Hawke, Ian
2009-01-01
Numerical-relativity (NR) simulations of compact binaries are expected to be an invaluable tool in gravitational-wave (GW) astronomy. The sensitivity of future detectors such as the Einstein Telescope (ET) will place much higher demands on NR simulations than first- and second-generation ground-based detectors. We discuss the issues facing compact-object simulations over the next decade, with an emphasis on estimating where the accuracy and parameter space coverage will be sufficient for ET a...
Numerical Simulation of Carbon Dioxide Injection in the Western Section of the Farnsworth Unit
Energy Technology Data Exchange (ETDEWEB)
White, Mark D.; McPherson, Brian J.; Grigg, Reid B.; Ampomah, William; Appold, Martin S.
2014-05-05
Numerical simulation is an invaluable analytical tool for scientists and engineers in making predictions about of the fate of carbon dioxide injected into deep geologic formations for long-term storage. Current numerical simulators for assessing storage in deep saline formations have capabilities for modeling strongly coupled processes involving multifluid flow, heat transfer, chemistry, and rock mechanics in geologic media. Except for moderate pressure conditions, numerical simulators for deep saline formations only require the tracking of two immiscible phases and a limited number of phase components, beyond those comprising the geochemical reactive system. The requirements for numerically simulating the utilization and storage of carbon dioxide in partially depleted petroleum reservoirs are more numerous than those for deep saline formations. The minimum number of immiscible phases increases to three, the number of phase components may easily increase fourfold, and the coupled processes of heat transfer, geochemistry, and geomechanics remain. Public and scientific confidence in the ability of numerical simulators used for carbon dioxide sequestration in deep saline formations has advanced via a natural progression of the simulators being proven against benchmark problems, code comparisons, laboratory-scale experiments, pilot-scale injections, and commercial-scale injections. This paper describes a new numerical simulator for the scientific investigation of carbon dioxide utilization and storage in partially depleted petroleum reservoirs, with an emphasis on its unique features for scientific investigations; and documents the numerical simulation of the utilization of carbon dioxide for enhanced oil recovery in the western section of the Farnsworth Unit and represents an early stage in the progression of numerical simulators for carbon utilization and storage in depleted oil reservoirs.
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
This paper presents new weighting functions in grid generation and new discretizing scheme of momentum equations in numerical simulation of river flow. By using the new weighting functions, the curvilinear grid could be concentrated as desired near the assigned points or lines in physical plane. By using the new discretizing scheme, the difficulties caused by movable boundary and dry riverbed can be overcome. As an application, the flow in the Wuhan Section of Yangtze River is simulated. The computational results are in good agreement with the measured results. The new method is applicable to the numerical simulation of 2-D river flow with irregular region and moveable boundary.
Numerical simulations of plasma brush behavior in hybrid armatures
Hawke, R. S.; Pincosy, P. A.
1993-01-01
Hybrid armatures used to accelerate projectiles in railguns are often the consequence of using a solid armature or in some cases the preferred armature type. Although hybrid armatures are often used, their design has been empirical and their performance sporadic. As a first step towards understanding hybrid design and performance, we have begun a combined numerical simulation and experimental verification effort. This paper will describe numerical simulations performed with a quasi 1-D MHD code (CONFUSE) which has been applied to simulate the behavior of plasma brushes used in hybrid armatures. The simulations have provided estimates of the plasma brush length, resistive voltage drop and temperatures corresponding to a range of; 1) brush gap size, 2) fuse thickness, and 3) magnetic pressure. The results of these simulations is presented and discussed.
Numerical simulations of plasma brush behavior in hybrid armatures
Energy Technology Data Exchange (ETDEWEB)
Hawke, R.S.; Pincosy, P.A.
1992-04-01
Hybrid armatures used to accelerate projectiles in railguns are often the consequence of using a solid armature or in some cases the preferred armature type. Although hybrid armatures are often used, their design has been empirical and their performance sporadic. As a first step towards understanding hybrid design and performance, we have begun a combined numerical simulation and experimental verification effort This paper will describe numerical simulations performed with liquid 1-D MHD code (CONFUSE) which has been applied to simulate the behavior of plasma brushes used in hybrid armatures. The simulations have provided estimates of the plasma brush length, resistive voltage drop and temperatures corresponding to a range of; (1) brush gap size, (2) fuse thickness, and (3) magnetic pressure. The results of these simulations will be presented and discussed.
Numerical simulations of bubbly flows using an averaged equations' model
International Nuclear Information System (INIS)
The paper discusses a numerical method for solving a two phase flow model based on the interpenetrating continua hypothesis. The model incorporates terms to account for the effects of virtual mass force, different pressures for the two phases and the viscous dissipation. Our numerical scheme extends the incremental projection scheme for the incompressible Navier-Stokes equation toward the multiphase flows. An optimal stability is obtained by slightly modifying the Galerkin formulation. The stabilized Galerkin technique we used is based on a two-level hierarchical decomposition of the approximation space. Numerical simulations of the three-dimensional bubbly flows in a periodic domain are presented. These simulations are compared with experiments. The stability of this flow with respect to 3D perturbations is studied numerically and a discussion of the results is presented. (author)
Calibration of a pebble bed configuration for direct numerical simulation
International Nuclear Information System (INIS)
The appearance of hot spots in the pebble bed cores of High Temperature Reactors (HTR) may affect the integrity of the pebbles. A good prediction of the flow and heat transport in such a pebble bed core is a challenge for available turbulence models. Such models need to be validated in order to gain trust in the simulation of these types of flow configurations. Direct Numerical Simulation (DNS) can serve as a reference for validation, however, it poses restrictions in terms of flow parameters and numerical tools corresponding to the available computational resources. In the present study, a wide range of numerical simulations has been performed in order to calibrate a pebble bed configuration for DNS which may serve as reference for validation. (author)
Numerical simulations of hydraulic transients in hydropower plant Jajce II
Škifić, Jerko; Radošević, Adrijana; Brajković, Đani; Družeta, Siniša; Čavrak, Marko
2013-01-01
Hydraulic transients in hydropower plant Jajce II (Bosnia and Herzegovina) were simulated with 1D unsteady pipe flow model. High accuracy of the model was accomplished with the use of non-conservative formulation of an unsteady pipe flow model incorporating a modified instantaneous acceleration-based unsteady friction model and second order flux limited numerical scheme. In order to apply the model, complex dual surge tank geometry needed to be represented with a unified surge tank. The numer...
On Numerical Simulation of Flow Through Oil Filters
Iliev, O.; Laptev, V.
2003-01-01
This paper concerns numerical simulation of flow through oil filters. Oil filters consist of filter housing (filter box), and a porous filtering medium, which completely separates the inlet from the outlet. We discuss mathematical models, describing coupled flows in the pure liquid subregions and in the porous filter media, as well as interface conditions between them. Further, we reformulate the problem in fictitious regions method manner, and discuss peculiarities of the numerical algorithm...
Numerical simulation of a synthetic jet with OpenFoam
Liu, Qiong; Kazakidi, Asimina; Medeiros, Marcello A. F.; Theofilis, Vassilios
2013-01-01
Numerical simulations of flow surrounding a synthetic jet actuating device are presented. By modifying a dynamic mesh technique available in OpenFoam-a well-documented open-source solver for fluid dynamics, detailed computations of the sinusoidal motion of the synthetic jet diaphragm were possible. Numerical solutions were obtained by solving the two dimensional incompressible viscous N-S equations, with the use of a second order implicit time marching scheme and a central finite volume metho...
Numerical simulation of the rheological behavior of fresh concrete
Shyshko, Sergiy
2014-01-01
This thesis reports recent numerical investigation of the rheological behavior of fresh concrete using the Distinct Element Method (DEM). Some relevant questions of the concrete rheology e.g. the influence of the concrete composition on the rheological behavior of the fresh concrete, the experimental determination of the Bingham rheological constants as well as the use of these constants in the numerical simulation were discussed thoroughly. An important topic of the performed investigation w...
Numerical Simulations of Unsteady Shock Reflection Processes by a Ramp
Aso, Shigeru; Hayashi, Masanori; Takano, Masanori
1990-01-01
Numerical simulations of unsteady shock reflections by a ramp have been conducted. The two-dimensional Euler equations are solved numerically by a TVD scheme proposed by Harten with modified flux approach and resolution enhancement by artificial compression. The calculations have been carried out for regular reflections, single Mach reflections, complex Mach reflections and double Mach reflections under the conditions of shock Mach number from 1.34 to 3.10 and ramp angles from 35 to 48 degree...
Numerical simulation of the countercurrent flow in a gas centrifuge
Energy Technology Data Exchange (ETDEWEB)
Cloutman, L.D.; Gentry, R.A.
1983-03-01
We present a finite difference method for the numerical simulation of the axisymmetric countercurrent flow in a gas centrifuge. A time-marching technique is used to relax an arbitrary initial condition to the desired steady-state solution. All boundary layers can be resolved, and nonlinear effects may be included. Numerical examples are presented. We conclude that this technique is capable of predicting accurately the performance of a wide variety of machines under all operating conditions of interest.
Numerical Simulation of Two-dimensional Nonlinear Sloshing Problems
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
Numerical simulation of a two-dimensional nonlinearsloshing problem is preceded by the finite element method. Two theories are used. One is fully nonlinear theory; the other is time domain second order theory. A liquid sloshing in a rectangular container subjected to a horizontal excitation is simulated using these two theories. Numerical results are obtained and comparisons are made. It is found that a good agreement is obtained for the case of small amplitude oscillation. For the situation of large amplitude excitation, although the differences between using the two theories are obvious the second order solution can still exhibit typical nonlinear features of nonlinear wave.
Numerical Simulations of a Possible Hypercomputational Quantum Algorithm
Sicard, A; Vélez, M; Sicard, Andr\\'es; Ospina, Juan; V\\'elez, Mario
2005-01-01
The hypercomputers compute functions or numbers, or more generally solve problems or carry out tasks, that cannot be computed or solved by a Turing machine. Several numerical simulations of a possible hypercomputational algorithm based on quantum computations previously constructed by the authors are presented. The hypercomputability of our algorithm is based on the fact that this algorithm could solve a classically non-computable decision problem, Hilbert's tenth problem. The numerical simulations were realized for three types of Diophantine equations: with and without solutions in non-negative integers, and without solutions by way of various traditional mathematical packages.
NUMERICAL SIMULATION FOR FORMED PROJECTILE OF DEPLETED URANIUM ALLOY
Institute of Scientific and Technical Information of China (English)
宋顺成; 高平; 才鸿年
2003-01-01
The numerical simulation for forming projectile of depleted uranium alloy with the SPH ( Smooth Particle Hydrodynamic ) algorithm was presented. In the computations the artificial pressures of detonation were used, i. e. , the spatial distribution and time distribution were given artificially. To describe the deformed behaviors of the depleted uranium alloy under high pressure and high strain rate, the Johnson-Cook model of materials was introduced. From the numerical simulation the formed projectile velocity,projectile geometry and the minimum of the height of detonation are obtained.
Modeling and Numerical Simulation of Solid Rocket Motors Internal Ballistics
CAVALLINI, ENRICO
2010-01-01
In the design and development of solid propellant rocket motors, the use of numerical tools able to simulate, predict and reconstruct the behavior of a given motor in all its operative conditions is particularly important in order to decrease all the planning times and costs. This work is devoted to present an approach to the numerical simulation of SRM internal ballistic during the entire combustion time (ignition transient, quasi steady state and tail-off) by means of a Q1D unsteady nume...
Numerical Simulation of the Submarine Pipeline under Wave Action
Directory of Open Access Journals (Sweden)
Zhi-Yong Zhang
2013-06-01
Full Text Available A two-dimensional viscous numerical wave flume is established in this study. The Navier-Stokes equations are discretized by Finite Difference Method (FDM. The turbulence is considered by using the standard k-ε turbulence model. Volume of Fluid (VOF method is adopted to capture the free surface of water wave. A virtual inclined porous structure is devised to absorb the wave energy near the end of computational domain. The numerical wave flume was validated by the comparisons with analytical result. Based on the numerical wave flume, the wave field around submarine pipeline was simulated and the numerical results were compared with experimental data. The comparison results show that the present numerical model works well. The maximum horizontal wave force and vertical wave force increase with the wave height.
Numerical simulation of tethered DNA in shear flow
Energy Technology Data Exchange (ETDEWEB)
Litvinov, S; Hu, X Y; Adams, N A [Institute of Aerodynamics, Technische Universitaet Muenchen, D-85747 Garching (Germany)
2011-05-11
The behavior of tethered DNA in shear flow is investigated numerically by the smoothed dissipative particle dynamics (SDPD) method. Unlike numerical methods used in previous studies, SDPD models the solvent explicitly, takes into account the fully coupled hydrodynamic interactions and is free of the numerical artifact of wall sticking. Based on numerical simulations the static and dynamic properties of a tethered DNA is studied both qualitatively and quantitatively. The observed properties are in general agreement with previous experimental, numerical and theoretical work. Furthermore, the cyclic-motion phenomenon is studied by power spectrum density and cross-correlation function analysis, which suggest that there is only a very weak coherent motion of tethered DNA for a characteristic timescale larger than the relaxation time. Cyclic motion is more likely relevant as an isolated event than a typical mode of DNA motion.
Processing biobased polymers using plasticizers: Numerical simulations versus experiments
Desplentere, Frederik; Cardon, Ludwig; Six, Wim; Erkoç, Mustafa
2016-03-01
In polymer processing, the use of biobased products shows lots of possibilities. Considering biobased materials, biodegradability is in most cases the most important issue. Next to this, bio based materials aimed at durable applications, are gaining interest. Within this research, the influence of plasticizers on the processing of the bio based material is investigated. This work is done for an extrusion grade of PLA, Natureworks PLA 2003D. Extrusion through a slit die equipped with pressure sensors is used to compare the experimental pressure values to numerical simulation results. Additional experimental data (temperature and pressure data along the extrusion screw and die are recorded) is generated on a dr. Collin Lab extruder producing a 25mm diameter tube. All these experimental data is used to indicate the appropriate functioning of the numerical simulation tool Virtual Extrusion Laboratory 6.7 for the simulation of both the industrial available extrusion grade PLA and the compound in which 15% of plasticizer is added. Adding the applied plasticizer, resulted in a 40% lower pressure drop over the extrusion die. The combination of different experiments allowed to fit the numerical simulation results closely to the experimental values. Based on this experience, it is shown that numerical simulations also can be used for modified bio based materials if appropriate material and process data are taken into account.
Numerical simulation of airfoil trailing edge serration noise
DEFF Research Database (Denmark)
Zhu, Wei Jun; Shen, Wen Zhong
In the present work, numerical simulations are carried out for a low noise airfoil with and without serrated Trailing Edge. The Ffowcs Williams-Hawkings acoustic analogy is implemented into the in-house incompressible flow solver EllipSys3D. The instantaneous hydrodynamic pressure and velocity...... field are obtained using Large Eddy Simulation. To obtain the time history data of sound pressure, the flow quantities are integrated around the airfoil surface through the FW-H approach. The extended length of the serration is about 16.7% of the airfoil chord and the geometric angle of the serration is...... 28 degrees. The chord based Reynolds number is around 1.5x106. Simulations are compared with existing wind tunnel experiments at various angles of attack. Even though the airfoil under investigation is already optimized for low noise emission, numerical simulations and wind tunnel experiments show...
NUMERICAL PREDICTION OF SUBMARINE HYDRODYNAMIC COEFFICIENTS USING CFD SIMULATION
Institute of Scientific and Technical Information of China (English)
PAN Yu-cun; ZHANG Huai-xin; ZHOU Qi-dou
2012-01-01
The submarine Hydrodynamic coefficients are predicted by numerical simulations.Steady and unsteady Reynolds Averaged Navier-Stokes (RANS) simulations are carried out to numerically simulate the oblique towing experiment and the Planar Motion Mechanism (PMM) experiment performed on the SUBOFF submarine model.The dynamic mesh method is adopted to simulate the maneuvering motions of pure heaving,pure swaying,pure pitching and pure yawing.The hydrodynamic forces and moments acting on the maneuvering submarine are obtained.Consequently,by analyzing these results,the hydrodynamic coefficients of the submarine maneuvering motions can be determined.The computational results are verified by comparison with experimental data,which show that this method can be used to estimate the hydrodynamic derivatives of a fully appended submarine.
Numerical Simulations of the Digital Microfluidic Manipulation of Single Microparticles.
Lan, Chuanjin; Pal, Souvik; Li, Zhen; Ma, Yanbao
2015-09-01
Single-cell analysis techniques have been developed as a valuable bioanalytical tool for elucidating cellular heterogeneity at genomic, proteomic, and cellular levels. Cell manipulation is an indispensable process for single-cell analysis. Digital microfluidics (DMF) is an important platform for conducting cell manipulation and single-cell analysis in a high-throughput fashion. However, the manipulation of single cells in DMF has not been quantitatively studied so far. In this article, we investigate the interaction of a single microparticle with a liquid droplet on a flat substrate using numerical simulations. The droplet is driven by capillary force generated from the wettability gradient of the substrate. Considering the Brownian motion of microparticles, we utilize many-body dissipative particle dynamics (MDPD), an off-lattice mesoscopic simulation technique, in this numerical study. The manipulation processes (including pickup, transport, and drop-off) of a single microparticle with a liquid droplet are simulated. Parametric studies are conducted to investigate the effects on the manipulation processes from the droplet size, wettability gradient, wetting properties of the microparticle, and particle-substrate friction coefficients. The numerical results show that the pickup, transport, and drop-off processes can be precisely controlled by these parameters. On the basis of the numerical results, a trap-free delivery of a hydrophobic microparticle to a destination on the substrate is demonstrated in the numerical simulations. The numerical results not only provide a fundamental understanding of interactions among the microparticle, the droplet, and the substrate but also demonstrate a new technique for the trap-free immobilization of single hydrophobic microparticles in the DMF design. Finally, our numerical method also provides a powerful design and optimization tool for the manipulation of microparticles in DMF systems. PMID:26241832
3-D MHD Numerical Simulations of Cloud-Wind Interactions
Gregori, G.; Miniati, Francesco; Ryu, Dongsu; Jones, T. W.
2000-01-01
We present results from three-dimensional (3-D) numerical simulations investigating the magnetohydrodynamics of cloud-wind interactions. The initial cloud is spherical while the magnetic field is uniform and transverse to the cloud motion. A simplified analytical model that describes the magnetic energy evolution in front of the cloud is developed and compared with simulation results. In addition, it is found the interaction of the cloud with a magnetized interstellar medium (ISM) results in ...
Dynamic Analysis and CFD Numerical Simulation on Backpressure Filling System
Jing Qian; Lu, J. P.; Hui, S L; Ma, Y J; D. Y. Li
2015-01-01
A backpressure filling system is a kind of air type filling system which could be applied to power type, fine or coarse grain, or mixtures with fine and coarse components. The working principle of backpressure filling system was discussed based on fundamental hydromechanics. The research limit values of backpressure were achieved via mechanical analysis. Comparing with the exit velocity of material by theoretical analysis and numerical simulation, the CFD simulation model was confirmed and it...
Numerical Simulation of slug flow in a micro-channel
Carlson, Andreas
2007-01-01
Multiphase dynamics and characteristics of slug flow in micro channels are investigated computationally by means of advanced numerical simulation methods. Although, due to its importance in many engineering and biomedical applications, the topic has been studied previously, methods for robust and accurate simulation of slug flow remain elusive. Evaluation of current state-of-the-art Computational Multi Fluid Dynamics (CMFD) technology depicts deficiency with advanced computational methods (Vo...
Numerical Simulation of the Double Slit Interference with Ultracold Atoms
Gondran, Michel; Gondran, Alexandre
2007-01-01
We present a numerical simulation of the double slit interference experiment realized by F. Shimizu, K. Shimizu and H. Takuma with ultracold atoms. We show how the Feynman path integral method enables the calculation of the time-dependent wave function. Because the evolution of the probability density of the wave packet just after it exits the slits raises the issue of the interpreting the wave/particle dualism, we also simulate trajectories in the de Broglie-Bohm interpretation.
APPLICATION OF NUMERICAL SIMULATION TO STUDY ON THERMAL CONDUCTION
Institute of Scientific and Technical Information of China (English)
C. Zhu; Z. Xu; D.E. Wu
2004-01-01
In this paper, using computer simulation and mathematic experiment method to solve the simplified one dimensional thermal conduction equation and to obtain the temperature distribution in a metal bar when its one end was heated. According to principle of hot expansion, a holograph of temperature distribution in the bar by laser holotechnique was taken. The results of numerical simulation and experiments are in good agreement and a new method for study on thermal conduction by laser holo-technique was found.
Numerical simulation of deformation and figure quality of precise mirror
Vit, Tomáš; Melich, Radek; Sandri, Paolo
2015-01-01
The presented paper shows results and a comparison of FEM numerical simulations and optical tests of the assembly of a precise Zerodur mirror with a mounting structure for space applications. It also shows how the curing of adhesive film can impact the optical surface, especially as regards deformations. Finally, the paper shows the results of the figure quality analysis, which are based on data from FEM simulation of optical surface deformations.
Numerical simulations and modeling for stochastic biological systems with jumps
Zou, Xiaoling; Wang, Ke
2014-05-01
This paper gives a numerical method to simulate sample paths for stochastic differential equations (SDEs) driven by Poisson random measures. It provides us a new approach to simulate systems with jumps from a different angle. The driving Poisson random measures are assumed to be generated by stationary Poisson point processes instead of Lévy processes. Methods provided in this paper can be used to simulate SDEs with Lévy noise approximately. The simulation is divided into two parts: the part of jumping integration is based on definition without approximation while the continuous part is based on some classical approaches. Biological explanations for stochastic integrations with jumps are motivated by several numerical simulations. How to model biological systems with jumps is showed in this paper. Moreover, method of choosing integrands and stationary Poisson point processes in jumping integrations for biological models are obtained. In addition, results are illustrated through some examples and numerical simulations. For some examples, earthquake is chose as a jumping source which causes jumps on the size of biological population.
FEM and FVM compound numerical simulation of aluminum extrusion processes
Institute of Scientific and Technical Information of China (English)
周飞; 苏丹; 彭颖红; 阮雪榆
2003-01-01
The finite element method (FEM) and the finite volume method (FVM) numerical simulation methods have been widely used in forging industries to improve the quality of products and reduce the costs. Because of very concentrative large deformation during the aluminum extrusion processes, it is very difficult to simulate the whole forming process only by using either FEM or FVM. In order to solve this problem, an FEM and FVM compound simulation method was proposed. The theoretical equations of the compound simulation method were given and the key techniques were studied. Then, the configuration of the compound simulation system was established. The tube extrusion process was simulated successfully so as to prove the validity of this approach for aluminum extrusion processes.
Numerical simulation of piezoelectric effect of bone under ultrasound irradiation
Hosokawa, Atsushi
2015-07-01
The piezoelectric effect of bone under ultrasound irradiation was numerically simulated using an elastic finite-difference time-domain method with piezoelectric constitutive equations (PE-FDTD method). First, to demonstrate the validity of the PE-FDTD method, the ultrasound propagation in piezoelectric ceramics was simulated and then compared with the experimental results. The simulated and experimental waveforms propagating through the ceramics were in good agreement. Next, the piezoelectric effect of human cortical bone on the ultrasound propagation was investigated by PE-FDTD simulation. The simulated result showed that the difference between the waveforms propagating through the bone without and with piezoelectricity was negligible. Finally, the spatial distributions of the electric fields in a human femur induced by ultrasound irradiation were simulated. The electric fields were changed by a bone fracture, which depended on piezoelectric anisotropy. In conclusion, the PE-FDTD method is considered to be useful for investigating the piezoelectric effect of bone.
Numerical simulation and experimental study of thrust air bearings with multiple orifices
CHARKI, Abderafi; DIOP, Khadim; CHAMPMARTIN, Stéphane; AMBARI, Abdelhak
2013-01-01
The objective of this paper is to provide a numerical simulation and an experimental study in order to assess stiffness and damping characteristics of thrust air bearings with multiple orifices. Finite element modeling is used to solve the non-linear Reynolds equation while taking into account the movement equation for the bearing. The numerical results obtained show that performance characteristics are related to bearing design type. An experimental investigation allows us to analyze the beh...
Clinical learning & assessment in simulated & virtual worlds
Harper, Mick; WILLIAMS Andy
2012-01-01
•To provide an overview of current simulation modalities available •To provide an understanding of the underpinning educational theory for learning & assessment in simulated & VR environments •To outline current research into learning & assessment through simulation
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.
Large eddy simulations and direct numerical simulations of high speed turbulent reacting flows
Givi, P.; Frankel, S. H.; Adumitroaie, V.; Sabini, G.; Madnia, C. K.
1993-01-01
The primary objective of this research is to extend current capabilities of Large Eddy Simulations (LES) and Direct Numerical Simulations (DNS) for the computational analyses of high speed reacting flows. Our efforts in the first two years of this research have been concentrated on a priori investigations of single-point Probability Density Function (PDF) methods for providing subgrid closures in reacting turbulent flows. In the efforts initiated in the third year, our primary focus has been on performing actual LES by means of PDF methods. The approach is based on assumed PDF methods and we have performed extensive analysis of turbulent reacting flows by means of LES. This includes simulations of both three-dimensional (3D) isotropic compressible flows and two-dimensional reacting planar mixing layers. In addition to these LES analyses, some work is in progress to assess the extent of validity of our assumed PDF methods. This assessment is done by making detailed companions with recent laboratory data in predicting the rate of reactant conversion in parallel reacting shear flows. This report provides a summary of our achievements for the first six months of the third year of this program.
NUMERICAL SIMULATION OF TURBULENT FREE SURFACE FLOW OVER OBSTRUCTION
Institute of Scientific and Technical Information of China (English)
LU Lin; LI Yu-cheng; TENG Bin; CHEN Bing
2008-01-01
A two-dimensional hybrid numerical model, FEM-LES-VOF, for free surface flows is proposed in this study, which is a combination of three-step Taylor-Galerkin finite element method, large eddy simulation with the Smagorinsky sub-grid model and Computational Lagrangian-Eulerian Advection Remap Volume of Fluid (CLEAR-VOF) method. The present FEM-LES-VOF model allows the fluid flows involving violent free surface and turbulence subject to complex boundary configuration to be simulated in a straightforward manner with unstructured grids in the context of finite element method. Numerical simulation of a benchmark problem of dam breaking is conducted to verify the present model. Comparisons with experimental data show that the proposed model works well and is capable of producing reliable predictions for free surface flows. Using the FEM-LES-VOF model, the free surface flow over a semi-circular obstruction is investigated. The simulation results are compared with available experimental and numerical results. Good performance of the FEM-LES-VOF model is demonstrated again. Moreover, the numerical studies show that the turbulence plays an important role in the evolution of free surface when the reflected wave propagates upstream during the fluid flow passing the submerged obstacle.
Numerical simulation of two phase flows in heat exchangers
International Nuclear Information System (INIS)
The report presents globally the works done by the author in the thermohydraulic applied to nuclear reactors flows. It presents the studies done to the numerical simulation of the two phase flows in the steam generators and a finite element method to compute these flows. (author)
Numerical model of human cardiovascular system-Korotkoff's sound simulation
Czech Academy of Sciences Publication Activity Database
Maršík, František; Převorovská, Světlana; Štembera, Vítězslav
Graz, Rakousko: Departments of Mathematics and Physiology University of Graz, 2003 - (Kappel, F.; Batzel, J.; Fink, M.; Schneditz, D.). s. 24 [Workshop on Cardiovascular, Respiratory and Metabolic Control Modeling. 11.06.2003-14.06.2003, Graz] Institutional research plan: CEZ:AV0Z2076919 Keywords : cardiovascular system * Korotkoff's sound * numerical simulation Subject RIV: ED - Physiology
Numerical simulation of the gas driven fracture propagation
International Nuclear Information System (INIS)
The process of the gas driven fracture propagation has been studied. The mathematical model of this physical process has been proposed. The numerical algorithm has been developed and the mathematical simulation of the process of the gas driven fracture propagation has been performed
Seasonal cycle of Martian climate : Experimental data and numerical simulation
Rodin, A. V.; Willson, R. J.
2006-01-01
The most adequate theoretical method of investigating the present-day Martian climate is numerical simulation based on a model of general circulation of the atmosphere. First and foremost, such models encounter the greatest difficulties in description of aerosols and clouds, which in turn essentiall
Direct Numerical Simulation Sediment Transport in Horizontal Channel
International Nuclear Information System (INIS)
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
Detonation wave problems : modeling, numerical simulations and linear stability
Carvalho, Filipe; Soares, A. J.
2012-01-01
Traveling waves arising in detonation physics are described by the reactive Euler equations obtained in the fluid dynamical limit of the Boltzmann equation for a binary reactive mixture. The hydrodynamic linear stability of the detonation wave solution is investigated with a normal mode analysis. Numerical simulations are performed for both the detonation wave solution and its linear stability.
Structure and stationarity of quasi-perpendicular shocks: Numerical simulations
Czech Academy of Sciences Publication Activity Database
Hellinger, Petr
2003-01-01
Roč. 51, - (2003), s. 649-657. ISSN 0032-0633 R&D Projects: GA ČR GP205/01/P079 Institutional research plan: CEZ:AV0Z3042911 Keywords : collisionless shocks * numerical simulations * quasi -perpendicular shocks * stationarity Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 1.375, year: 2003
Numerical simulation of inverse problems using LTSN method
International Nuclear Information System (INIS)
This work shows the feasibility of application of the LTSN method to solve the following inverse problems in transport theory: the determination of the incident flux knowing the scalar flux at the domain and parameter identification (cross sections). Numerical simulations are reported. (author). 8 refs, 2 tabs
Decoupled numerical simulation of a solid fuel fired retort boiler
International Nuclear Information System (INIS)
The paper deals with numerical simulation of the retort boiler fired with solid fuel. Such constructions are very popular for heating systems and their development is mostly based on the designer experience. The simulations have been done in ANSYS/Fluent package and involved two numerical models. The former deals with a fixed-bed combustion of the solid fuel and free-board gas combustion. Solid fuel combustion is based on the coal kinetic parameters. This model encompasses chemical reactions, radiative heat transfer and turbulence. Coal properties have been defined with user defined functions. The latter model describes flow of water inside a water jacked that surrounds the combustion chamber and flue gas ducts. The novelty of the proposed approach is separating of the combustion simulation from the water flow. Such approach allows for reducing the number of degrees of freedom and thus lowering the necessary numerical effort. Decoupling combustion from water flow requires defining interface boundary condition. As this boundary condition is unknown it is adjusted iteratively. The results of the numerical simulation have been successfully validated against measurement data. - Highlights: • New decoupled modelling of small scale boiler is proposed. • Fixed-bed combustion model based on kinetic parameters is introduced. • Decoupling reduced the complexity of the model and computational time. • Simple and computationally inexpensive coupling algorithm is proposed. • Model is successfully validated against measurements
Numerical Simulation and Cold Modeling experiments on Centrifugal Casting
Keerthiprasad, Kestur Sadashivaiah; Murali, Mysore Seetharam; Mukunda, Pudukottah Gopaliengar; Majumdar, Sekhar
2011-02-01
In a centrifugal casting process, the fluid flow eventually determines the quality and characteristics of the final product. It is difficult to study the fluid behavior here because of the opaque nature of melt and mold. In the current investigation, numerical simulations of the flow field and visualization experiments on cold models have been carried out for a centrifugal casting system using horizontal molds and fluids of different viscosities to study the effect of different process variables on the flow pattern. The effects of the thickness of the cylindrical fluid annulus formed inside the mold and the effects of fluid viscosity, diameter, and rotational speed of the mold on the hollow fluid cylinder formation process have been investigated. The numerical simulation results are compared with corresponding data obtained from the cold modeling experiments. The influence of rotational speed in a real-life centrifugal casting system has also been studied using an aluminum-silicon alloy. Cylinders of different thicknesses are cast at different rotational speeds, and the flow patterns observed visually in the actual castings are found to be similar to those recorded in the corresponding cold modeling experiments. Reasonable agreement is observed between the results of numerical simulation and the results of cold modeling experiments with different fluids. The visualization study on the hollow cylinders produced in an actual centrifugal casting process also confirm the conclusions arrived at from the cold modeling experiments and numerical simulation in a qualitative sense.
Numerical simulations of time-resolved quantum electronics
International Nuclear Information System (INIS)
Numerical simulation has become a major tool in quantum electronics both for fundamental and applied purposes. While for a long time those simulations focused on stationary properties (e.g. DC currents), the recent experimental trend toward GHz frequencies and beyond has triggered a new interest for handling time-dependent perturbations. As the experimental frequencies get higher, it becomes possible to conceive experiments which are both time-resolved and fast enough to probe the internal quantum dynamics of the system. This paper discusses the technical aspects–mathematical and numerical–associated with the numerical simulations of such a setup in the time domain (i.e. beyond the single-frequency AC limit). After a short review of the state of the art, we develop a theoretical framework for the calculation of time-resolved observables in a general multiterminal system subject to an arbitrary time-dependent perturbation (oscillating electrostatic gates, voltage pulses, time-varying magnetic fields, etc.) The approach is mathematically equivalent to (i) the time-dependent scattering formalism, (ii) the time-resolved non-equilibrium Green’s function (NEGF) formalism and (iii) the partition-free approach. The central object of our theory is a wave function that obeys a simple Schrödinger equation with an additional source term that accounts for the electrons injected from the electrodes. The time-resolved observables (current, density, etc.) and the (inelastic) scattering matrix are simply expressed in terms of this wave function. We use our approach to develop a numerical technique for simulating time-resolved quantum transport. We find that the use of this wave function is advantageous for numerical simulations resulting in a speed up of many orders of magnitude with respect to the direct integration of NEGF equations. Our technique allows one to simulate realistic situations beyond simple models, a subject that was until now beyond the simulation
Working mechanism and numerical simulation of assembly coastal building techniques
Institute of Scientific and Technical Information of China (English)
陈育民; 刘汉龙; 陈泽
2008-01-01
A new coastal technique, named as assembly coastal building, was introduced. The main concept of the technique was the assembling components which could be combined and locked together to form a large caisson. The assembly coastal building technique was used in a sea access road in Zhuanghai 4X1 well, Dagang Oilfield. The design plans and in-situ tests in the sea access road project were introduced in detail. According to the Zhuanghai project, the numerical simulation method of assembly coastal building technique was proposed. 2D numerical simulations were performed in FLAC to analyze the displacement and stability of the technique in the construction process and post-construction period. The settlement calculated is close to the in-situ results, which proves that the proposed numerical method is reasonable. Results show that the assembly coastal building technique has large safety factor under the gravity loading and wave loadings.
Mathematical modeling and numerical simulation of Czochralski Crystal Growth
Energy Technology Data Exchange (ETDEWEB)
Jaervinen, J.; Nieminen, R. [Center for Scientific Computing, Espoo (Finland)
1996-12-31
A detailed mathematical model and numerical simulation tools based on the SUPG Finite Element Method for the Czochralski crystal growth has been developed. In this presentation the mathematical modeling and numerical simulation of the melt flow and the temperature distribution in a rotationally symmetric crystal growth environment is investigated. The temperature distribution and the position of the free boundary between the solid and liquid phases are solved by using the Enthalpy method. Heat inside of the Czochralski furnace is transferred by radiation, conduction and convection. The melt flow is governed by the incompressible Navier-Stokes equations coupled with the enthalpy equation. The melt flow is numerically demonstrated and the temperature distribution in the whole Czochralski furnace. (author)
D. Nunn
1993-01-01
This paper presents a highly efficient and stable algorithm for the numerical simulation of collision free plasma. This algorithm has been successfully used to numerically model non linear electron cyclotron resonance in VLF band radio waves in space, and has produced good simulations of radio emissions such as ‘dawn chorus’ and ‘triggered VLF emissions’. The algorithm fills the phase box with simulation particles which represent phase space trajectories. Particle trajectories are followed fo...
Numerical Simulation on Freezing Process of Saturated Granlar Soil
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The relation between ice pressure and load as a criterion of segregated ice initiation is introduced into the rigid ice model to simulate frost heave in saturated and granular soil. The calculated results show that unfrozen water content, thermal conductivity and hydraulic conductivity change greatly in frozen fringe. In numerical simulations, the influence of load, hydraulic conductivity and property of soil containing water on the process of soil freezing are analyzed, and the simulation curves such as cumulative heave,the change of depth of frozen and the distributions of water content are similar to the observations reported elsewhere.
Numerical simulation of a possible counterexample to cosmic censorship
International Nuclear Information System (INIS)
A numerical simulation is presented here of the evolution of initial data of the kind that was conjectured by Hertog, Horowitz, and Maeda to be a violation of cosmic censorship. Those initial data are essentially a thick domain wall connecting two regions of anti-de Sitter space. The initial data have a free parameter that is the initial size of the wall. The simulation shows no violation of cosmic censorship, but rather the formation of a small black hole. The simulation described here is for a moderate wall size and leaves open the possibility that cosmic censorship might be violated for larger walls
Numerical Simulations of Equiaxed Dendrite Growth Using Phase Field Method
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
Phase field method offers the prospect of being able to perform realistic numerical experiments on dendrite growthin a metallic system. In this paper, the equiaxed dendrite evolution during the solidification of a pure material wasnumerically simulated using the phase field model. The equiaxed dendrite growth in a two-dimensional square domainof undercooled melt (nickel) with four-fold anisotropy was simulated. The phase field model equations was solvedusing the explicit finite difference method on a uniform mesh. The formation of various equiaxed dendrite patternswas shown by a series of simulations, and the effect of anisotropy on equiaxed dendrite morphology was investigated.
Numerical Simulation System for Casting Process in Concurrent Engineering
Institute of Scientific and Technical Information of China (English)
无
1999-01-01
According to the implementing principle and application background of the Concurrent Engineering (CE) project, studies on the integration of numerical simulation system for casting process with CE, simulation of turbulent phenomena in filling process of casting by Algebraic Stress Model (ASM), computation efficiency of filling process and quantitative prediction of shrinkage cavity and porosity under feeding condition of several risers are discussed. After the simulation of casting process of typical magnesium-based alloy casting with complicated structure, remarkable success in assuring the quality is also presented.
Simulation of Fully Nonlinear 3-D Numerical Wave Tank
Institute of Scientific and Technical Information of China (English)
张晓兔; 滕斌; 宁德志
2004-01-01
A fully nonlinear numerical wave tank (NWT) has been simulated by use of a three-dimensional higher order boundary element method (HOBEM) in the time domain. Within the frame of potential flow and the adoption of simply Rankine source, the resulting boundary integral equation is repeatedly solved at each time step and the fully nonlinear free surface boundary conditions are integrated with time to update its position and boundary values. A smooth technique is also adopted in order to eliminate the possible saw-tooth numerical instabilities. The incident wave at the uptank is given as theoretical wave in this paper. The outgoing waves are absorbed inside a damping zone by spatially varying artificial damping on the free surface at the wave tank end. The numerical results show that the NWT developed by these approaches has a high accuracy and good numerical stability.
A Numerical Formulation for Simulating Free-Surface Hydrodynamics
O'Shea, Thomas T; Dommermuth, Douglas G; Wyatt, Donald C
2014-01-01
Cartesian-grid methods in combination with immersed-body and volume-of-fluid methods are ideally suited for simulating breaking waves around ships. A surface panelization of the ship hull is used as input to impose body-boundary conditions on a three-dimensional cartesian grid. The volume-of-fluid portion of the numerical algorithm is used to capture the free-surface interface, including the breaking of waves. The numerical scheme is implemented on a parallel computer. Recent improvements to the numerical scheme are discussed, including implementation of a new multigrid procedure and conversion to MPI communication. Numerical predictions are compared to laboratory measurements of a towed transom-stern model.
Numerical simulations for impact damage detection in composites using vibrothermography
International Nuclear Information System (INIS)
Composite materials are widely used in many engineering applications due to their high strength-to-weight ratios. However, it is well known that composites are susceptible to impact damage. Detection of impact damage is an important issue in maintenance of composite structures. Various non-destructive image-based techniques have been developed for damage detection in composite materials. These include vibrothermography that detects surface temperature changes due to heating associated with frictional energy dissipation by damage. In the present paper numerical simulations are used to investigate heat generation in a composite plate with impact damage in order to support damage detection analysis with vibrothermography. Explicit finite elements are used to model ultrasonic wave propagation in the damaged plate. Simulated delamination and cracks induce frictional heating in the plate. Coupled thermo-mechanical simulations are performed in high frequencies using commercial LS-Dyna finite element code. Very good qualitative agreement between measurements and simulations has been obtained. The area of increased temperature corresponds very well with the damaged area in both experiments and simulations. Numerical model has to be further refined in order to quantitatively match the experiments. The main issues of concern are frictional and thermal properties of composites. The final goal of these research efforts is to predict damage detection sensitivity of vibrothermography in real engineering applications based on numerical models.
Numerical simulation of manual operation at MID stand control room
International Nuclear Information System (INIS)
Since 2000 at INR Pitesti a package of software products devoted to numerical simulation of manual operations at fueling machine control room was developed. So far, specified, designed, worked out and implemented was the PUPITRU code. The following issues were solved: graphical aspects of specific computer - human operator interface; functional and graphical simulation of the whole associated equipment of the control desk components; implementation of the main notation as used in the automated schemes of the control desk in view of the fast identification of the switches, lamps, instrumentation, etc.; implementation within PUPITRU code of the entire data base used in the frame of MID tests; implementation of a number of about 1000 numerical simulation equations describing specific operational MID testing situations
Extended Scaling Laws in Numerical Simulations of MHD Turbulence
Mason, Joanne; Cattaneo, Fausto; Boldyrev, Stanislav
2011-01-01
Magnetised turbulence is ubiquitous in astrophysical systems, where it notoriously spans a broad range of spatial scales. Phenomenological theories of MHD turbulence describe the self-similar dynamics of turbulent fluctuations in the inertial range of scales. Numerical simulations serve to guide and test these theories. However, the computational power that is currently available restricts the simulations to Reynolds numbers that are significantly smaller than those in astrophysical settings. In order to increase computational efficiency and, therefore, probe a larger range of scales, one often takes into account the fundamental anisotropy of field-guided MHD turbulence, with gradients being much slower in the field-parallel direction. The simulations are then optimised by employing the reduced MHD equations and relaxing the field-parallel numerical resolution. In this work we explore a different possibility. We propose that there exist certain quantities that are remarkably stable with respect to the Reynold...
Dynamic Analysis and CFD Numerical Simulation on Backpressure Filling System
Directory of Open Access Journals (Sweden)
Jing Qian
2015-01-01
Full Text Available A backpressure filling system is a kind of air type filling system which could be applied to power type, fine or coarse grain, or mixtures with fine and coarse components. The working principle of backpressure filling system was discussed based on fundamental hydromechanics. The research limit values of backpressure were achieved via mechanical analysis. Comparing with the exit velocity of material by theoretical analysis and numerical simulation, the CFD simulation model was confirmed and its related parameters were determined. The CFD numerical simulation shows the relationship between production capacity of packaging machine and backpressure, and the results matched actual operation of the equipment well. Combining with the demand of device capacity, the range of backpressure could be controlled at 8 kPa~11 kPa.
NUMERICAL SIMULATION OF SKIMMING FLOW OVER MILD STEPPED CHANNEL
Institute of Scientific and Technical Information of China (English)
DONG Zhi-yong; LEE Joseph Hun-wei
2006-01-01
Numerical simulation of stepped channel flow was conducted using turbulence models based on the VOF technique. Stepped channel flow is a complicated air-water two-phase flow with free surface, which can be divided into three flow regimes: skimming flow, nappe flow and transition flow. The characteristics of skimming flow over mild stepped channel was investigated, including friction factors, air concentration profiles velocity field, clear-water and bulked depths, static pressure, etc. Smooth channel flow was also simulated to compare the hydraulic characteristics of the stepped channel flow with the smooth one. Comparisons between the computed and the measured were made. Furthermore, comparison of the computed air concentration with Straub and Anderson's data was also performed. The Fluent 6.1 software was employed to conduct this numerical simulation work.
Numerical simulation of small scale soft impact tests
Energy Technology Data Exchange (ETDEWEB)
Varpasuo, Pentti [Fortum Nuclear Services Ltd. P.O. Box 10, 00048 Fortum (Finland)
2008-07-01
This paper describes the small scale soft missile impact tests. The purpose of the test program is to provide data for the calibration of the numerical simulation models for impact simulation. In the experiments, both dry and fluid filled missiles are used. The tests with fluid filled missiles investigate the release speed and the droplet size of the fluid release. This data is important in quantifying the fire hazard of flammable liquid after the release. The spray release velocity and droplet size are also input data for analytical and numerical simulation of the liquid spread in the impact. The behaviour of the impact target is the second investigative goal of the test program. The response of reinforced and pre-stressed concrete walls is studied with the aid of displacement and strain monitoring. (authors)
Numerical simulation of small scale soft impact tests
International Nuclear Information System (INIS)
This paper describes the small scale soft missile impact tests. The purpose of the test program is to provide data for the calibration of the numerical simulation models for impact simulation. In the experiments, both dry and fluid filled missiles are used. The tests with fluid filled missiles investigate the release speed and the droplet size of the fluid release. This data is important in quantifying the fire hazard of flammable liquid after the release. The spray release velocity and droplet size are also input data for analytical and numerical simulation of the liquid spread in the impact. The behaviour of the impact target is the second investigative goal of the test program. The response of reinforced and pre-stressed concrete walls is studied with the aid of displacement and strain monitoring. (authors)
International Nuclear Information System (INIS)
Numerical simulation of the transport of neutron and gamma has been used for measurement instrument design for decades. Improvement of the simulation codes combined with an increase in computer capability has led to the possibility of numerical calibration of instruments or interpretation of field measurements. This technique has become common practice in the nuclear industry and is being introduced in Safeguards. Typical examples are total neutron or coincidence neutron counters where availability of representative reference material may be difficult. In such cases, the main objectives for using numerical simulation are savings in manpower, money and time. The use of simulation for the direct interpretation of measurements is also an important issue. In some cases, like assay of nuclear material holdup in large and complex equipment, experimental calibration might be practically impossible and numerical calibration the only way to achieve quantitative results. In any case, the main issue is the validation of the simulation model, which remains based on reference materials. The point here is that reference materials do not have to be physically similar to assayed objects and therefore have larger availability and lower costs. In the future, advanced use of simulation could lead to a different approach of NDA referred to as finger printing. At present the concept of finger printing is limited to follow-up of NDA signatures and the demonstration that no change occurred. Simulation could help predicting the initial fingerprint and also its normal evolution due to decay. With prediction capability the concept of finger printing could be extended. One of the applications of this concept could be the verification of spent fuel casks by neutron measurements. Results of spent fuel individual verification could be used to verify input data used for the simulation of casks in order to predict neutron flux outside of the cask. In the field of gamma spectrometry, present use
Numerical simulation of thermal behavior during laser metal deposition shaping
Institute of Scientific and Technical Information of China (English)
LONG Ri-sheng; LIU Wei-jun; XING Fei; WANG Hua-bing
2008-01-01
Based on the element life and death theory of finite element analysis (FEA),a three-dimensional multi-track and multi-layer model for laser metal deposition shaping (LMDS) was developed with ANSYS parametric design language (APDL),and detailed numerical simulations of temperature and thermal stress were conducted.Among those simulations,long-edge parallel reciprocating scanning method was introduced.The distribution regularities of temperature,temperature gradient,Von Mise's effective stress,X-directional,Y-directional and Z-directional thermal stresses were studied.LMDS experiments were carried out with nickel-based superalloy using the same process parameters as those in simulation.The measured temperatures of molten pool are in accordance with the simulated results.The crack engendering and developing regularities of samples show good agreement with the simulation results.
Higher entropy conservation and numerical stability of compressible turbulence simulations
International Nuclear Information System (INIS)
We present a numerical formulation for the treatment of nonlinear instabilities in shock-free compressible turbulence simulations. The formulation is high order and contains no artificial dissipation. Numerical stability is enhanced through semi-discrete satisfaction of global conservation properties stemming from the second law of thermodynamics and the entropy equation. The numerical implementation is achieved using a conservative skew-symmetric splitting of the nonlinear terms. The robustness of the method is demonstrated by performing unresolved numerical simulations and large eddy simulations of compressible isotropic turbulence at a very high Reynolds number. Results show the scheme is capable of capturing the statistical equilibrium of low Mach number compressible turbulent fluctuations at infinite Reynolds number. Comparisons with the entropy splitting technique [J. Comput. Phys. 162 (2000) 33; J. Comput. Phys. 178 (2002) 307], staggered method [J. Comput. Phys. 191(2) (2003) 392], and skew-symmetric like schemes [J. Comput. Phys. 161 (2000) 114] confirm the superiority of the current approach. We also discuss a flaw in the skew-symmetric splitting implemented in the literature. Very good results are obtained based on the proper splitting
Numerical Simulation of Snow Drifting Disaster on Embankment Project
Directory of Open Access Journals (Sweden)
Shouyun Liang
2010-01-01
Full Text Available Snow drifting is a typical natural disaster, and an increasing importance has been attached to its theory research and field observation for the sake of cold region engineering. Numerical simulation, as an efficient method of studying snow drifting, promises to be widely applied in this field. In this paper, the finite element method is used to simulate the wind velocity field. Selected upwind, downwind and middle part of a road as key comparison points, a quantitative analysis constructed of the influence of subgrade width, height and slope ratio on the wind velocity of embankment. The results showed that, under certain circumstances, the velocity of snow drifting demonstrated different function types of increase with the height and slope ratio of subgrade enhancing, and the influence of the height is greater than the slop ratio of subgrade, while the velocity of wind decreases with the width of subgrade increasing; the numerical values approximately agreed with the field observed results, but the numerical simulation is more sensitive to various forms of embankment. The numerical results can offer references for engineering construction when the region in which wind velocity is slower than the threshold velocity as snowpack area.
Comparative Laboratory and Numerical Simulations of Shearing Granular Fault Gouge
Morgan, J. K.; Marone, C.
2004-05-01
Laboratory studies of granular shear zones have provided significant insight into fault zone processes and the mechanics of earthquakes, including important contributions to our understanding of earthquake nucleation, the seismic-aseismic stability transition, dynamic rupture, and fault interactions. Numerical simulations using particle dynamics methods can offer unique views into deforming fault zones, particularly regarding the micromechanisms of deformation in shearing materials. Recently, significant advances in our understanding of granular shear have been gained by integrating these two approaches to better model the frictional behavior of tectonic faults. We describe a series of comparative laboratory and numerical experiments of granular shear carried out under identical initial and boundary conditions, using idealized granular materials, i.e., glass beads and rods. Phenomenologically, the two sets of experiments are very similar, demonstrating shear strength fluctuations that can be related to variations in particle size distribution, shear zone thickness, and imposed normal stress. Observed discrepancies in absolute shear strength and stress-strain behavior, then, allow us to calibrate and update the numerical interparticle contact laws to gain improved fits to the laboratory results. The numerical simulations serve to clarify the active deformation processes, demonstrating the role of shear localization, and partitioning between deformation mechanisms, including grain boundary sliding, rolling, and changes in particle size distribution. This integrated study offers great promise to improve our understanding of fault mechanics and earthquake physics. We describe results of the combined study and development of the next generation of particle-based numerical models, including realistic, physico-chemically based contact laws.
Numerical simulation in material science: principles and applications
International Nuclear Information System (INIS)
The objective is here to describe the main simulation techniques currently used in material science. After a presentation of the concepts of modelling and simulation, of their objectives and uses, of the issue of simulation scale, and of means of numeric simulation, the author addresses simulations performed at a nano-scopic scale: 'ab-initio' methods, molecular dynamics, examples of applications of ab-initio methods to energy issues or to the study of surface properties of nano-materials. The next chapter addresses various Monte Carlo methods (Metropolis, atomic kinetics, objects kinetics, transport with the simulation of particle trajectories, generation of random numbers). The next parts address simulations performed at a mesoscopic scale (simulation and microstructure, phase field methods, dynamics of discrete dislocations, homogeneous chemical kinetics) and at a macroscopic scale (medium discretization with the notion of mesh, simulation of structure mechanics and of fluid behaviour). The issues of code coupling and scale coupling are then discussed. The last part proposes an overview of virtual metallurgy and modelling of industrial processes (welding, vacuum arc re-fusion, rolling, forming)
Direct numerical simulation of 3D transitional fluid flows
International Nuclear Information System (INIS)
Full text: For the numerical simulation of the 2D-3D transitional homogeneous and stratified incompressible viscous fluid flows, characterizing by the full Navier-Stokes equations, the splitting on physical factors method is used. The explicit hybrid finite difference scheme of the method has the following behaviors: the second order of accuracy in space, minimum scheme viscosity and dispersion, workable in wide range of Reynolds and Froude numbers and monotonicity. The efficiency of the developed numerical method and the advanced performance of the supercomputers allowed simulating 2D-3D transitional uncompressible viscous fluid flows around the bluff bodies in particular around a cylinder. By the numerical simulation of the fluid flows around 3D circular cylinder it was found that the transition to 3D regime arrives at Re>200. At 200< Re<300 the mode A with wavelength 3.5 d<λ<4.0 d (where d is the diameter of the cylinder) for 3D structures along the axis of a cylinder was observed. At 300< Re<400 the mode B with wavelength 0.8 d<λ<0.9 d was observed. At Re=300 the both modes A and B were observed simultaneously. The regime with large dislocations previously discovered experimentally was first obtained numerically at 210< Re<260. This regime is characterized by flow phase dislocation along the axis of the cylinder and as the effect by the amplitude fall of the lift force coefficient and the variations in the drag coefficient. There was simulated numerically the initiation of the attached internal waves behind the circular cylinder and upstream disturbance area at low Froude and moderate Reynolds numbers. (author)
Numerical simulation of the sucker-rod pumping system
Oldrich Joel Romero; Paula Almeida
2014-01-01
The sucker rod pump is an artificial lift method frequently applied in onshore petroleum wells. This system can be described using a numerical simulation based on the behavior of a rod string. In the past, the elastic behavior of the rod string made it difficult to model the system. However, since the 1960s and with the advent of digital computers, it has been modeled numerically. The rod string be-haves like a slender bar, and thus, the propagation of elastic waves along the bar can be repre...
Numerical Simulation of Impacts on Marine Environment by Sewage Discharge
Directory of Open Access Journals (Sweden)
Chen Honglingyao
2015-01-01
Full Text Available Numerical simulation on tidal field of sewage marine disposal engineering area was carried out by using the MIKE3 numerical model. The impact of volatile phenol of waste water, cyanide and COD on water environment was predicted. Results show that great changes of pollutant content have taken place in each water layer because of pollution discharge. The pollution discharge into deep water has the greatest effect on bottom water quality, and the impact decreases gradually from the bottom to the surface. It shows that pollution discharge into deep water is helpful to control the pollutant increment of surface water.
Numerical simulations of the Euler system with congestion constraint
Degond, Pierre; Navoret, Laurent
2010-01-01
In this paper, we study the numerical simulations for Euler system with maximal density constraint. This model is developed in [1, 3] with the constraint introduced into the system by a singular pressure law, which causes the transition of different asymptotic dynamics between different regions. To overcome these difficulties, we adapt and implement two asymptotic preserving (AP) schemes originally designed for low Mach number limit [2,4] to our model. These schemes work for the different dynamics and capture the transitions well. Several numerical tests both in one dimensional and two dimensional cases are carried out for our schemes.
Numerical simulation of the flow field around a complete aircraft
Shang, J. S.; Scherr, S. J.
1986-01-01
The present effort represents a first attempt of numerical simulation of the flow field around a complete aircraft-like, lifting configuration utilizing the Reynolds averaged Navier-Stokes equations. The numerical solution generated for the experimental aircraft concept X24C-10D at a Mach number of 5.95 not only exhibited accurate prediction of detailed flow properties but also of the integrated aerodynamic coefficients. In addition, the present analysis demonstrated that a page structure of data collected into cyclic blocks is an efficient and viable means for processing the Navier-Stokes equations on the CRAY XMP-22 computer with external memory device.
Advances in numerical simulation of nonlinear water waves
Ma, Qingwei
2014-01-01
Most of the Earth's surface is covered by water. Our everyday lives and activities are affected by water waves in oceans, such as the tsunami that occurred in the Indian Ocean on 26 December 2004. This indicates how important it is for us to fully understand water waves, in particular the very large ones. One way to do so is to perform numerical simulation based on the nonlinear theory. Considerable research advances have been made in this area over the past decade by developing various numerical methods and applying them to emerging problems; however, until now there has been no comprehensive
Recent Advances in the Numerical Simulations of Binary Black Holes
Marronetti, Pedro
2011-01-01
Since the breakthrough papers from 2005/2006, the field of numerical relativity has experienced a growth spurt that took the two-body problem in general relativity from the category of "really-hard-problems" to the realm of "things-we-know-how-to-do". Simulations of binary black holes in circular orbits, the holy grail of numerical relativity, are now tractable problems that lead to some of the most spectacular results in general relativity in recent years. We cover here some of the latest achievements and highlight the field's next challenges.
Graphics interfaces and numerical simulations: Mexican Virtual Solar Observatory
Hernández, L.; González, A.; Salas, G.; Santillán, A.
2007-08-01
Preliminary results associated to the computational development and creation of the Mexican Virtual Solar Observatory (MVSO) are presented. Basically, the MVSO prototype consists of two parts: the first, related to observations that have been made during the past ten years at the Solar Observation Station (EOS) and at the Carl Sagan Observatory (OCS) of the Universidad de Sonora in Mexico. The second part is associated to the creation and manipulation of a database produced by numerical simulations related to solar phenomena, we are using the MHD ZEUS-3D code. The development of this prototype was made using mysql, apache, java and VSO 1.2. based GNU and `open source philosophy'. A graphic user interface (GUI) was created in order to make web-based, remote numerical simulations. For this purpose, Mono was used, because it is provides the necessary software to develop and run .NET client and server applications on Linux. Although this project is still under development, we hope to have access, by means of this portal, to other virtual solar observatories and to be able to count on a database created through numerical simulations or, given the case, perform simulations associated to solar phenomena.
Numerical simulations of internal wave generation by convection in water
Lecoanet, Daniel; Le Bars, Michael; Burns, Keaton J.; Vasil, Geoffrey M.; Brown, Benjamin P.; Quataert, Eliot; Oishi, Jeffrey S.
2015-06-01
Water's density maximum at 4 ∘C makes it well suited to study internal gravity wave excitation by convection: an increasing temperature profile is unstable to convection below 4 ∘C,but stably stratified above 4 ∘C . We present numerical simulations of a waterlike fluid near its density maximum in a two-dimensional domain. We successfully model the damping of waves in the simulations using linear theory, provided we do not take the weak damping limit typically used in the literature. To isolate the physical mechanism exciting internal waves, we use the spectral code dedalus to run several simplified model simulations of our more detailed simulation. We use data from the full simulation as source terms in two simplified models of internal-wave excitation by convection: bulk excitation by convective Reynolds stresses, and interface forcing via the mechanical oscillator effect. We find excellent agreement between the waves generated in the full simulation and the simplified simulation implementing the bulk excitation mechanism. The interface forcing simulations overexcite high-frequency waves because they assume the excitation is by the "impulsive" penetration of plumes, which spreads energy to high frequencies. However, we find that the real excitation is instead by the "sweeping" motion of plumes parallel to the interface. Our results imply that the bulk excitation mechanism is a very accurate heuristic for internal-wave generation by convection.
Numerical simulation of H2/air detonation using unstructured mesh
Togashi, Fumiya; Löhner, Rainald; Tsuboi, Nobuyuki
2009-06-01
To explore the capability of unstructured mesh to simulate detonation wave propagation phenomena, numerical simulation of H2/air detonation using unstructured mesh was conducted. The unstructured mesh has several adv- antages such as easy mesh adaptation and flexibility to the complicated configurations. To examine the resolution dependency of the unstructured mesh, several simulations varying the mesh size were conducted and compared with a computed result using a structured mesh. The results show that the unstructured mesh solution captures the detailed structure of detonation wave, as well as the structured mesh solution. To capture the detailed detonation cell structure, the unstructured mesh simulations required at least twice, ideally 5times the resolution of structured mesh solution.
Design and numerical simulation of thermionic electron gun
Hosseinzadeh, M
2015-01-01
This paper reports the simulation of an electron gun. The effects of some parameters on the beam quality were studied and optimal choices were identified. It gives numerical beam qualities in common electrostatic triode gun, and the dependences on design parameters such as electrode geometries and bias voltages to these electrodes are shown. An electron beam of diameter 5 mm with energy of five kilo electron volt was assumed for simulation process. Some design parameters were identified as variable parameters in the presence of space charge. These parameters are the inclination angle of emission electrode, the applied voltage to focusing electrode, the gap width between the emission electrode and the focusing electrode and the diameter of the focusing electrode. The triode extraction system is designed and optimized by using CST software (for Particle Beam Simulations). The physical design of the extraction system is given in this paper. From the simulation results, it is concluded that the inclination angle ...
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...
Numerical simulation of cloud rise phenomena associated with nuclear bursts
International Nuclear Information System (INIS)
We present numerical simulations of cloud evolution from nuclear explosions using high-resolution numerical methods. Our numerical approach includes a fluid mechanical model that is a combination of a compressible code (GEODYN) and a low Mach code (LMC). Early stages of nuclear explosions that are characterized by the blust wave propagation are simulated with an explicit code (GEODYN) that solves the compressible Navier-Stokes equations via a high-order Godunov scheme. As soon as the blust wave weakens (∼10 s) the subsequent cloud rise due to buoyancy forces can be effectively simulated by the LMC code. LMC is an implicit code based on a pressure projection technique, and derived from the compressible Navier-Stokes equations using an asymptotic analysis in Mach number. It analytically eliminates time step restrictions based on sound wave propagation and it is computationally efficient and accurate for simulations of cloud rise dynamics at later stages. We perform a series of cloud rise scenarios ranging from an idealized bubble rise problem to realistic air bursts. We analyze effects of compressible dynamics on cloud evolution at different stages. It is found that in a realistic configuration, interaction of the reflected shock wave from the ground with the fireball significantly affects cloud evolution, in contrast to the equivalent idealized bubble rise simulations. We validate the code predictions against available experimental data. It is demonstrated that, by providing the initial source from the compressible GEODYN code, late time flow evolution can be successfully simulated with the fast, efficient and accurate LMC code.
Numerical simulation of cloud rise phenomena associated with nuclear bursts
Energy Technology Data Exchange (ETDEWEB)
Kanarska, Y. [Lawrence Livermore National Laboratory, P.O. Box 808, L-231, Livermore, CA 94551 (United States)], E-mail: kanarska1@llnl.gov; Lomov, I.; Glenn, L.; Antoun, T. [Lawrence Livermore National Laboratory, P.O. Box 808, L-231, Livermore, CA 94551 (United States)
2009-10-15
We present numerical simulations of cloud evolution from nuclear explosions using high-resolution numerical methods. Our numerical approach includes a fluid mechanical model that is a combination of a compressible code (GEODYN) and a low Mach code (LMC). Early stages of nuclear explosions that are characterized by the blust wave propagation are simulated with an explicit code (GEODYN) that solves the compressible Navier-Stokes equations via a high-order Godunov scheme. As soon as the blust wave weakens ({approx}10 s) the subsequent cloud rise due to buoyancy forces can be effectively simulated by the LMC code. LMC is an implicit code based on a pressure projection technique, and derived from the compressible Navier-Stokes equations using an asymptotic analysis in Mach number. It analytically eliminates time step restrictions based on sound wave propagation and it is computationally efficient and accurate for simulations of cloud rise dynamics at later stages. We perform a series of cloud rise scenarios ranging from an idealized bubble rise problem to realistic air bursts. We analyze effects of compressible dynamics on cloud evolution at different stages. It is found that in a realistic configuration, interaction of the reflected shock wave from the ground with the fireball significantly affects cloud evolution, in contrast to the equivalent idealized bubble rise simulations. We validate the code predictions against available experimental data. It is demonstrated that, by providing the initial source from the compressible GEODYN code, late time flow evolution can be successfully simulated with the fast, efficient and accurate LMC code.
Numerical Simulation of nZVI at the Field Scale
Chowdhury, A. I.; Krol, M.; Sleep, B. E.; O'Carroll, D. M.
2014-12-01
Nano-scale zero valent iron (nZVI) has been used at a number of contaminated sites over the last decade. At most of these sites, significant decreases in contaminant concentrations have resulted from the application of nZVI. However, limited work has been completed investigating nZVI mobility at the field-scale. In this study a three dimensional, three phase, finite difference numerical simulator (CompSim) was used to simulate nZVI and polymer transport in a variably saturated site. The model was able to accurately predict the field observed head data without parameter fitting. In addition, the numerical simulator estimated the amount of nZVI delivered to the saturated and unsaturated zones as well as the phase of nZVI (i.e., attached or aqueous phase). The simulation results showed that the injected slurry migrated radially outward from the injection well, and therefore nZVI transport was governed by injection velocity as well as viscosity of the injected solution. A suite of sensitivity analyses was performed to investigate the impact of different injection scenarios (e.g. different volume and injection rate) on nZVI migration. Simulation results showed that injection of a higher volume of nZVI delivered more iron particles at a given distance; however, not necessarily to a greater distance proportionate to the increase in volume. This study suggests that on-site synthesized nZVI particles are mobile in the subsurface and the numerical simulator can be a valuable tool for optimum design of nZVI applications.
Linking numerical simulations of molecular cloud structure with observations.
Kainulainen, Jouni
2015-08-01
Understanding the physical processes that control the life-cycle of the cold interstellar medium (ISM) is one of the key themes in the astrophysics of galaxies today. This importance derives from the role of the cold ISM as the birthplace of new stars, and consequently, as an indivisible constituent of galaxy evolution. In the current paradigm of turbulence-regulated ISM, star formation is controlled by the internal structure of individual molecular clouds, which in turn is set by a complex interplay of turbulence, gravity, and magnetic fields in the clouds. It is in the very focus of the field to determine how these processes give rise to the observed structure of molecular clouds. In this talk, I will review our current efforts to confront this paradigm with the goal of observationally constraining how different processes regulate molecular cloud structure and star formation. At the heart of these efforts lies the use of numerical simulations of gravo-turbulent media to A) define physically meaningful characteristics that are sensitive to the different cloud-shaping processes, and B) determine if and how such characteristics can be recovered by observations. I will show in my talk how this approach has recently led to new constraints for some fundamental measures of the molecular cloud structure. Such constraints allow us to assess the roles of turbulence and gravity in controlling the ISM structure and star formation. I will also highlight specific recent results, focusing on the nature of filamentary structures within molecular clouds. These results may provide a novel set of observational constraints with which to challenge the turbulence-regulated ISM paradigm. Finally, I will discuss the current challenges and open questions in understanding the link between molecular cloud structure and star formation, and speculate on key directions to aim the near-future studies.
Numerical simulation and experimental investigation of incremental sheet forming process
Institute of Scientific and Technical Information of China (English)
HAN Fei; MO Jian-hua
2008-01-01
In order to investigate the process of incremental sheet forming (ISF) through both experimental and numerical approaches, a three-dimensional elasto-plastic finite element model (FEM) was developed to simulate the process and the simulated results were compared with those of experiment. The results of numerical simulations, such as the strain history and distribution, the stress state and distribution, sheet thickness distribution, etc, were discussed in details, and the influences of process parameters on these results were also analyzed. The simulated results of the radial strain and the thickness distribution are in good agreement with experimental results. The simulations reveal that the deformation is localized around the tool and constantly remains close to a plane strain state. With decreasing depth step, increasing tool diameter and wall inclination angle, the axial stress reduces, leading to less thinning and more homogeneous plastic strain and thickness distribution. During ISF, the plastic strain increases stepwise under the action of the tool. Each increase in plastic strain is accompanied by hydrostatic pressure, which explains why obtainable deformation using ISF exceeds the forming limits of conventional sheet forming.
Characterizing Electron Temperature Gradient Turbulence Via Numerical Simulation
Energy Technology Data Exchange (ETDEWEB)
Nevins, W M; Candy, J; Cowley, S; Dannert, T; Dimits, A; Dorland, W; Estrada-Mila, C; Hammett, G W; Jenko, F; Pueschel, M J; Shumaker, D E
2006-05-22
Numerical simulations of electron temperature gradient (ETG) turbulence are presented which characterize the ETG fluctuation spectrum, establish limits to the validity of the adiabatic ion model often employed in studying ETG turbulence, and support the tentative conclusion that plasmaoperating regimes exist in which ETG turbulence produces sufficient electron heat transport to be experimentally relevant. We resolve prior controversies regarding simulation techniques and convergence by benchmarking simulations of ETG turbulence from four microturbulence codes, demonstrating agreement on the electron heat flux, correlation functions, fluctuation intensity, and rms flow shear at fixed simulation cross section and resolution in the plane perpendicular to the magnetic field. Excellent convergence of both continuum and particle-in-cell codes with time step and velocity-space resolution is demonstrated, while numerical issues relating to perpendicular (to the magnetic field) simulation dimensions and resolution are discussed. A parameter scan in the magnetic shear, s, demonstrates that the adiabatic ion model is valid at small values of s (s < 0.4 for the parameters used in this scan) but breaks down at higher magnetic shear. A proper treatment employing gyrokinetic ions reveals a steady increase in the electron heat transport with increasing magnetic shear, reaching electron heat transport rates consistent with analyses of experimental tokamak discharges.
Numerical simulations of thin accretion discs with PLUTO
Parthasarathy, Varadarajan; Kluzniak, Wlodek
2014-01-01
Our goal is to perform global simulations of thin accretion discs around compact bodies like neutron stars with dipolar magnetic profile and black holes by exploiting the facilities provided by state-of-the-art grid-based, high resolution shock capturing (HRSC) and finite volume codes. We have used the Godunov-type code PLUTO to simulate a thin disc around a compact object prescribed with a pseudo-Newtonian potential in a purely hydrodynamical (HD) regime, with numerical viscosity as a first ...
Numerical simulations of thin accretion discs with PLUTO
Parthasarathy, Varadarajan
2014-01-01
Our goal is to perform global simulations of thin accretion discs around compact bodies like neutron stars with dipolar magnetic profile and black holes by exploiting the facilities provided by state-of-the-art grid-based, high resolution shock capturing (HRSC) and finite volume codes. We have used the Godunov-type code PLUTO to simulate a thin disc around a compact object prescribed with a pseudo-Newtonian potential in a purely hydrodynamical (HD) regime, with numerical viscosity as a first step towards achieving our goal as mentioned above.
Numerical simulations on a twin-plate wake
DEFF Research Database (Denmark)
Fernández-Gámiz, U.; Velte, Clara Marika; Egusquiza, E.
2013-01-01
In this work, a detailed numerical analysis of two dimensional mean velocity profiles downstream of two parallel flat plates was carried out at a Reynolds number of 3.2x104 (based on the plate length and free stream velocity) using Reynolds Averaged Navier-Stokes (RANS) and have been compared wit...... experimental data. Furthermore, a self-similar study of the wake behind the twin plate was carried out based on the computer simulations. The main objective is to investigate how well the simulations can reproduce the physics of the flow behind a twin plate....
Numerical Simulation and Innovation on Magnesium Reduction Process
Institute of Scientific and Technical Information of China (English)
Dehong XIA; Gang ZHANG; Liang GUO
2006-01-01
The thermal process of L.M.Pidgeon's reduction art, widely used in magnesium production, is numerically simulated. It is shown that the thermal efficiency will be highly enhanced with the increase of heat-exchange area or the intensification of heat exchange between flame and the outer surface of the reduction jars. An innovation has been made by fuel-shifting (from coal to Coal-Water Mixture), up-draft reduction furnace configuration,multi-layer jars installation and waste heat recovery. A bench scale furnace has been constructed and put into operation to identify the simulation and new design.
Numerical simulation and mechanism analysis of freak waves
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
A numerical wave model based on the modified fourth-order nonlinear Schroe dinger equation (mNLSE) in deep water was developed to simulate the formation of freak waves and a standard split-step, pseudo-spectral method was used to solve the equation. The validation of the model is firstly verified, then the simulation of freak waves was performed by changing sideband conditions, and the variation of wave energy was also analyzed in the evolution. The results indicate that Benjamin-Feir instability (sideband instability) is an important mechanism for freak wave formation.
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
Numerical simulation of fluid particle transport through porous media
Najam, S
1999-01-01
The work presented in this report aims at the numerical simulation of fluid particle transport through porous medium. For this purpose various mathematical models and numerical schemes are studied. A mathematical model is derived based on Darcy's Law and continuity equation, it is discretized using finite difference schemes and Guass Seidal iterative procedure is used as a solver. For transient problems Crank Nicolson's method is used. Finally a software in Visual Basic 3.0 is developed that can simulate fluid transport through porous medium by promoting the user to specify the material and geometrical properties of the medium. The unknown pressure heads can be determined at various nodal points and the results are visualized by the colored grid display or by the surface plots.
Numerical Simulation of BJMOSFET on Current-Voltage Characteristics
Institute of Scientific and Technical Information of China (English)
曾云; 金湘亮; 颜永红; 刘久玲; 成世明
2000-01-01
A new power MOSFET Structure with a pn junction--Bipolar Junction MOSFET (BJMOSFET) has been proposed. The device has the advantages of both BJT and FET. The numerical model of the I-V characteristics of BJMOSFET has been obtained on the basis of both numerical and analytical methods. With the software package of Mathematic, we firstly calculate the gain factor, and then simulate the voltage tranmission, voltage output and voltage transfer's characteristic graphs of the BJMOSFET. The simulation result indicates that BJMOSFET has the current density, which is about 25% larger than the power MOSFET, under the same operating conditions and with the same structure parameters, except that the threshold voltage increase a little.
Numerical Relativity Simulations for Black Hole Merger Astrophysics
Baker, John G.
2010-01-01
Massive black hole mergers are perhaps the most energetic astronomical events, establishing their importance as gravitational wave sources for LISA, and also possibly leading to observable influences on their local environments. Advances in numerical relativity over the last five years have fueled the development of a rich physical understanding of general relativity's predictions for these events. Z will overview the understanding of these event emerging from numerical simulation studies. These simulations elucidate the pre-merger dynamics of the black hole binaries, the consequent gravitational waveform signatures ' and the resulting state, including its kick velocity, for the final black hole produced by the merger. Scenarios are now being considered for observing each of these aspects of the merger, involving both gravitational-wave and electromagnetic astronomy.
Numerical simulation of draft tube flow of a bulb turbine
Energy Technology Data Exchange (ETDEWEB)
Coelho, J.G. [Federal University of Triangulo Mineiro, Institute of Technological and Exact Sciences, Avenida Doutor Randolfo Borges Junior, 1250 – Uberaba – MG (Brazil); Brasil, A.C.P. Jr. [University of Brasilia, Department of Mechanical Engineering, Campus Darcy Ribeiro, Brasilia – DF (Brazil)
2013-07-01
In this work a numerical study of draft tube of a bulb hydraulic turbine is presented, where a new geometry is proposed. This new proposal of draft tube has the unaffected ratio area, a great reduction in his length and approximately the same efficiency of the draft tube conventionally used. The numerical simulations were obtained in commercial software of calculation of flow (CFX-14), using the turbulence model SST, that allows a description of the field fluid dynamic near to the wall. The simulation strategy has an intention of identifying the stall of the boundary layer precisely limits near to the wall and recirculations in the central part, once those are the great causes of the decrease of efficiency of a draft tube. Finally, it is obtained qualitative and quantitative results about the flow in draft tubes.
Numerical simulations of a diode laser BPH treatment system
Energy Technology Data Exchange (ETDEWEB)
Esch, V; London, R A; Papademetriou, S
1999-02-23
Numerical simulations are presented of the laser-tissue interaction of a diode laser system for treating benign prostate hyperplasia. The numerical model includes laser light transport, heat transport, cooling due to blood perfusion, thermal tissue damage, and enthalpy of tissue damage. Comparisons of the simulation results to clinical data are given. We report that a reasonable variation from a standard set of input data produces heating times which match those measured in the clinical trials. A general trend of decreasing damage volume with increasing heating time is described. We suggest that the patient-to- patient variability seen in the data can be explained by differences in fundamental biophysical properties such as the optical coefficients. Further work is identified, including the measurement and input to the model of several specific data parameters such as optical coefficients, blood perfusion cooling rate, and coagulation rates.
3D numerical simulation and analysis of railgun gouging mechanism
Directory of Open Access Journals (Sweden)
Jin-guo Wu
2016-04-01
Full Text Available A gouging phenomenon with a hypervelocity sliding electrical contact in railgun not only shortens the rail lifetime but also affects the interior ballistic performance. In this paper, a 3-D numerical model was introduced to simulate and analyze the generation mechanism and evolution of the rail gouging phenomenon. The results show that a rail surface bulge is an important factor to induce gouging. High density and high pressure material flow on the contact surface, obliquely extruded into the rail when accelerating the armature to a high velocity, can produce gouging. Both controlling the bulge size to a certain range and selecting suitable materials for rail surface coating will suppress the formation of gouging. The numerical simulation had a good agreement with experiments, which validated the computing model and methodology are reliable.
Numerical simulation of asymmetric particle precipitation by pitch angle diffusion
Thorne, Richard M.; Abel, Robert W.; Summers, Danny
1996-11-01
A numerical simulation code is developed to evaluate the loss rate of particles trapped in a mirror magnetic field geometry with asymmetric loss cones. The one-dimensional model can accommodate particle diffusion at any prescribed rate and loss cones of any prescribed sizes, and it incorporates the important effect of atmospheric backscattering. Numerical solutions for the loss cone particle distribution function calculated for the case of equal loss cones provide an acceptable simulation of the well-known modified Bessel function solution. The code provides the first quantitative solutions for any specified rate of pitch angle scattering for the general case of arbitrary asymmetry in loss cone size. In the case of weak or moderate diffusion the ratio of particle precipitation fluxes into the two loss cones can provide a sensitive measurement of the rate of particle scattering, but to utilize this important diagnostic property, one must also have information on the fraction of particles that are backscattered from the atmosphere.
Numerical Relativity Towards Simulations of 3D Black Hole Coalescence
Seidel, E
1998-01-01
I review recent developments in numerical relativity, focussing on progress made in 3D black hole evolution. Progress in development of black hole initial data, apparent horizon boundary conditions, adaptive mesh refinement, and characteristic evolution is highlighted, as well as full 3D simulations of colliding and distorted black holes. For true 3D distorted holes, with Cauchy evolution techniques, it is now possible to extract highly accurate, nonaxisymmetric waveforms from fully nonlinear simulations, which are verified by comparison to pertubration theory, and with characteristic techniques extremely long term evolutions of 3D black holes are now possible. I also discuss a new code designed for 3D numerical relativity, called Cactus, that will be made public.
Numerical simulation of the nonlinear optical response of bacteriorhodopsin
Kowalski, Gregory J.
1996-10-01
The numerical simulation of the nonlinear optical behavior of bacteriorhodopsin in a solution of water is described. Relationships for the intensity dependent absorption coefficient and index of refraction are developed and used in the numerical simulation of bacteriorhodopsin as an optical limiter and as defocussing element for laser pulses in the picosecond regime. The algorithm is a transient finite volume method that is coupled with a 'ray model' of the radiation which simultaneously solves the heat transfer and Maxwell's equations. The nonlinear behavior of the material is included in this analysis using a modified Euler predictor-corrector integration technique. Calculated power limiting and z-scan curves are in qualitative agreement with experiments. These results indicate that the code can be used to investigate and optimize optical systems which use the nonlinear behavior of bacteriorhodopsin.
Numerical simulation of interfacial reaction between titanium and zirconia
Directory of Open Access Journals (Sweden)
Liu Aihui
2010-11-01
Full Text Available Based on the conservation laws of energy and mass, and taking into account the effect of chemical reaction between liquid titanium and zirconia ceramic mold on the concentration field and the temperature field, a comprehensive mathematical model for numerical simulation of heat and mass transfer has been established to study the interfacial reaction between liquid Ti and ZrO2 ceramic mold. With the proposed model, numerical simulations were preformed to investigate the effects of pouring temperature and holding time on the oxygen concentrations and reactive layer thickness in metal. The results showed that both the oxygen concentration and the thickness of reactive layer in metal increase with the increase of the holding time and the pouring temperature. The development of reactive layer thickness with time consists of three stages: inoculation (0-1 s, linear increase (1-5 s and parabolic increase (after 5 s.
Numerical model for learning concepts of streamflow simulation
DeLong, L.L.
1993-01-01
Numerical models are useful for demonstrating principles of open-channel flow. Such models can allow experimentation with cause-and-effect relations, testing concepts of physics and numerical techniques. Four PT is a numerical model written primarily as a teaching supplement for a course in one-dimensional stream-flow modeling. Four PT options particularly useful in training include selection of governing equations, boundary-value perturbation, and user-programmable constraint equations. The model can simulate non-trivial concepts such as flow in complex interconnected channel networks, meandering channels with variable effective flow lengths, hydraulic structures defined by unique three-parameter relations, and density-driven flow.The model is coded in FORTRAN 77, and data encapsulation is used extensively to simplify maintenance and modification and to enhance the use of Four PT modules by other programs and programmers.
Experimentation and numerical simulation of steel fibre reinforced concrete pipes
International Nuclear Information System (INIS)
The results concerning on an experimental and a numerical study related to SFRCP are presented. Eighteen pipes with an internal diameter of 600 mm and fibre dosages of 10, 20 and 40 kg/m3 were manufactured and tested. Some technological aspects were concluded. Likewise, a numerical parameterized model was implemented. With this model, the simulation of the resistant behaviour of SFRCP can be performed. In this sense, the results experimentally obtained were contrasted with those suggested by means MAP reaching very satisfactory correlations. Taking it into account, it could be said that the numerical model is a useful tool for the optimal design of the SFRCP fibre dosages, avoiding the need of the systematic employment of the test as an indirect design method. Consequently, the use of this model would reduce the overall cost of the pipes and would give fibres a boost as a solution for this structural typology. (Author) 27 refs.
Numerical simulation of a magnetic reconnection in the solar corona
International Nuclear Information System (INIS)
In this paper, a kind of magnetic reconnection process caused by the local heating in the closed magnetic field region over the equator in the solar corona is discussed. At first, we use a method in combination with analytical and numerical methods to obtain a coronal magnetic configuration with X-type neutral point. Furthermore we solve numerically the magnetohydrodynamic equations by using the full-implicit continuous Eulerian scheme in the spherical coordinates. The results of numerical simulation show that three different processes of magnetic reconnection are existed. On the other hand, the upward plasma velocity is small when the effect of solar gravitational field is considered. Hence, we suggest that the magnetic reconnection caused by the pure resistivity tearing mode may be unimportant for the coronal mass ejections. (author). 37 refs, 2 figs
Numerical simulation of ceramic breeder pebble bed thermal creep behavior
International Nuclear Information System (INIS)
The evolution of ceramic breeder pebble bed thermal creep deformation subjected to an external load and a differential thermal stress was studied using a modified discrete numerical code previously developed for the pebble bed thermomechanical evaluation. The rate change of creep deformation was modeled at the particle contact based on a diffusion creep mechanism. Numerical results of strain histories have compared reasonably well with those of experimentally observed data at 740 C using activation energy of 180 KJ/mole. Calculations also show that, at this activation energy level, a particle bed at an elevated temperature of 800 C may cause undesired local sintering at a later time when it is subjected to an external load of 6.3 MPa. Thus, by tracking the stress histories inside a breeder pebble bed the numerical simulation provides an indication of whether the bed may encounter an undesired condition under a typical operating condition. (orig.)
Numerical simulation of piston leakage over hermetic reciprocating compressors behavior.
Rigola Serrano, Joaquim; Pérez Segarra, Carlos David; Oliva Llena, Asensio
2009-01-01
Instantaneous flow leakage between piston and cylinder is numerically evaluated. Reynolds equation is solved to calculate the pressure leakage distribution through the piston in the compressor. Piston movement inside the cylinder is simulated from kinematic analysis of the connecting rod mechanical system and the respective force balances. An updated version of this model is here presented for different working range compressors and fluid refrigerants compressor chamber pressures distribution...
NUMERICAL SIMULATIONS OF β-GYRES IN TROPICAL CYCLONES
Institute of Scientific and Technical Information of China (English)
杨洪波; 张铭
2003-01-01
The circulation of β-gyres in tropical cyclones is studied using numerical simulations. As shown in the result, there is clear circulation of β-gyres in the deviation flow field of the middle layer of the model,i.e. there is cyclone current west of the vortex center but anticyclone current east of it. The theory analysis shows that the circulation of β-gyres is formed by the advection of geostrophic vorticity.
Numerical simulations of gravitational collapse in Einstein-aether theory
Garfinkle, D; Jacobson, T; Garfinkle, David; Eling, Christopher; Jacobson, Ted
2007-01-01
We study gravitational collapse of a spherically symmetric scalar field in Einstein-aether theory (general relativity coupled to a dynamical unit timelike vector field). The initial value formulation is developed, and numerical simulations are performed. The collapse produces regular, stationary black holes, as long as the aether coupling constants are not too large. For larger couplings a finite area singularity occurs. These results are shown to be consistent with the stationary solutions found previously.
Electromagnetic Pulse Propagation over Nonuniform Earth Surface: Numerical Simulation
Popov, Alexei V.; Kopeikin, Vladimir V.
2007-01-01
We simulate EM pulse propagation along the nonuniform earth surface using so called time-domain parabolic equation. To solve it by finite differences, we introduce a time-domain analog of the impedance boundary condition and a nonlocal BC of transparency reducing open computational domain to a strip of finite width. Numerical examples demonstrate influence of soil conductivity on the wide-band pulse waveform. For a high-frequency modulated EM pulse, we develop an asymptotic approach based on ...
Numerical simulation methods for wave propagation through optical waveguides
International Nuclear Information System (INIS)
The simulation of the field propagation through waveguides requires numerical solutions of the Helmholtz equation. For this purpose a method based on the principle of orthogonal collocation was recently developed. The method is also applicable to nonlinear pulse propagation through optical fibers. Some of the salient features of this method and its application to both linear and nonlinear wave propagation through optical waveguides are discussed in this report. 51 refs, 8 figs, 2 tabs
The numerical simulation of plate-type windborne debris flight
Kakimpa, Bruce
2012-01-01
Wind borne debris is one of the principal causes of building envelope failure during severe storms. It is often of interest in windstorm risk modelling to estimate the potential flight trajectories and impact energy of a piece of debris. This thesis presents research work aimed at the development and validation of a numerical model for the simulation of plate-type windborne debris. While a number of quasi-steady analytical models are available at present, these models are unable to account fo...
Numerical simulations of the Euler system with congestion constraint
Degond, Pierre; Hua, Jiale; Navoret, Laurent
2010-01-01
In this paper, we study the numerical simulations for Euler system with maximal density constraint. This model is developed in [1, 3] with the constraint introduced into the system by a singular pressure law, which causes the transition of different asymptotic dynamics between different regions. To overcome these difficulties, we adapt and implement two asymptotic preserving (AP) schemes originally designed for low Mach number limit [2,4] to our model. These schemes work for the different dyn...
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.
Direct Numerical Simulation Of Turbulent Combustion Near Solid Surfaces
Gruber, Andrea
2006-01-01
This study uses Direct Numerical Simulation of turbulent reacting compressible plane channel flow at low Reynolds number in order to understand the physics of the interaction of a flame with the turbulent boundary layer near a solid inert surface.Better insight into the process of flame quenching near a solid surface, of the influence of turbulence on this process, and of its relation to the maximum and average wall heat fluxes, pollutant formation and incomplete fuel consumption is crucial t...
Do numerical simulation and optimization results improve management? : experimental evidence
Brekke, Kjell Arne; Moxnes, Erling
2000-01-01
Models of different forms are the core tool of economic analysis. The advises econo-mists give decision makers may represent general insights derived from stylized models. Alternatively, economists may construct complex large scale models to simu-late the consequences of different policy option, often without any definite conclusion as to what option is best. Decision makers are likely to blend the results from numerous analyses, focusing on different facets of the real world. We asked the qu...
Blast Loaded Aluminium Plates : Experiments and numerical simulations
Melby, Emil Arne; Eide, Hilde Olaug Stakvik
2013-01-01
Light and flexible protective constructions in aluminium could be subjected to a blast load. In this thesis the effect of blast loading on aluminium plates of the type 1050A ? H14 was studied through experiments and numerical simulations. The effect of fragmentation was idealized with predrilled holes. The thesis was written at the Structural Impact Laboratory (SIMLab) at NTNU in collaboration with the Norwegian Defence Estates Agency (NDEA).Tensile tests revealed a clearly anisotropic behavi...
Numerical Simulation of thePorous Structure of Biomaterials
Institute of Scientific and Technical Information of China (English)
WANGHui-min; YANYu-hua; LIShi-pu
2004-01-01
Porous biomaterials are widely used as bone replacement materials because of thers high biocompatibility and osteoconductivity property. Understanding of their porous structure (i. e. geometrical and topological characteristic) and studying how to the body fluid flow through them are essential to investigate thed egradation behaviour at the surface-liquid interface. This research develops a numerical model to simulate the porous structure of biomaterials based on the stochastic approach in pore size distribution and interconnectivity.
Numerical Simulations of Settlement of Jet Grouting Columns
Directory of Open Access Journals (Sweden)
Juzwa Anna
2016-03-01
Full Text Available The paper presents the comparison of results of numerical analyses of interaction between group of jet grouting columns and subsoil. The analyses were conducted for single column and groups of three, seven and nine columns. The simulations are based on experimental research in real scale which were carried out by authors. The final goal for the research is an estimation of an influence of interaction between columns working in a group.
Numerical Simulation on Zonal Disintegration in Deep Surrounding Rock Mass
Xuguang Chen; Yuan Wang; Yu Mei; Xin Zhang
2014-01-01
Zonal disintegration have been discovered in many underground tunnels with the increasing of embedded depth. The formation mechanism of such phenomenon is difficult to explain under the framework of traditional rock mechanics, and the fractured shape and forming conditions are unclear. The numerical simulation was carried out to research the generating condition and forming process of zonal disintegration. Via comparing the results with the geomechanical model test, the zonal disintegration p...
Numerical simulation of flow in the wet scrubber for desulfurization
Directory of Open Access Journals (Sweden)
Novosád Jan
2015-01-01
Full Text Available This article deals with numerical simulation of flow and chemical reactions in absorber for desulfurization of flue-gas. The objective of the work is the investigation of effect of different nozzles types and their placement in spray layers. These nozzles distribute lime suspension into flue gas stream. The research includes two types of nozzles and four different arrangements of nozzles and spray layers. Conclusion describes the effect of nozzle types and their arrangements on the suspension concentration in absorber.
Developing a numerical simulation for fading in feldspar
DEFF Research Database (Denmark)
Larsen, A.; Greilich, Steffen; Jain, Mayank;
2009-01-01
Most models describing anomalous fading in feldspars are based on analytical solutions. As an alternative approach we present an entirely numerical model based on statistical sampling that simulates stepwise the charge creation/trapping and recombination in a given phosphor. We assume the number...... of nearest-neighbor distances with time. The best agreement with experimental data is achieved if we assume the crystal to consist of small subvolumes (nanocrystals) only within which charge carriers are allowed to recombine....
Numerical simulation of flow in the wet scrubber for desulfurization
Novosád, Jan; Vít, Tomáš
2015-05-01
This article deals with numerical simulation of flow and chemical reactions in absorber for desulfurization of flue-gas. The objective of the work is the investigation of effect of different nozzles types and their placement in spray layers. These nozzles distribute lime suspension into flue gas stream. The research includes two types of nozzles and four different arrangements of nozzles and spray layers. Conclusion describes the effect of nozzle types and their arrangements on the suspension concentration in absorber.
Numerical simulation of flow in the wet scrubber for desulfurization
Novosád Jan; Vít Tomáš
2015-01-01
This article deals with numerical simulation of flow and chemical reactions in absorber for desulfurization of flue-gas. The objective of the work is the investigation of effect of different nozzles types and their placement in spray layers. These nozzles distribute lime suspension into flue gas stream. The research includes two types of nozzles and four different arrangements of nozzles and spray layers. Conclusion describes the effect of nozzle types and their arrangements on the suspension...
Numerical simulation of underexpanded air jet using OpenFOAM
Talukdar, Mohammad
2015-01-01
It is of utmost importance for the awareness of safety issues involved in high pressure gas storage to perceive the adjacent field of high pressure gas jet release for the establishment of the decomposition laws in the far field. The numerical simulations of the first cell of an underexpanded gas jet can be performed executing finite volume solver which can be validated later by means of available literature source. The prominence of OpenFoam is irrefutable fact especially in the research fie...
Ditching Numerical Simulations: Recent Steps in Industrial Applications
Benítez Montañés, Luis; Climent Máñez, Héctor; Siemann, Martin; Kohlgrueber, Dieter
2012-01-01
Ditching is an aircraft emergency condition that ends with planned impact of the aircraft on water. The high forward velocity in fixed-wing aircraft ditching affects the aircraft dynamics and its structural response due to complex hydrodynamic effects. Therefore, analysis of ditching impact is particularly relevant to satisfy the airworthiness regulations for modern aircraft. Numerical methods for simulating ditching take advantage of the computational capacity allowing industry to deal w...
Numerical Simulation of a Planing Vessel at High Speed
Institute of Scientific and Technical Information of China (English)
Yumin Su; Qingtong Chen; Hailong Shen; Wei Lu
2012-01-01
Planing vessels are applied widely in civil and military situations.Due to their high speed,the motion of planning vessels is complex.In order to predict the motion of planning vessels,it is important to analyze the hydrodynamic performance of planning vessels at high speeds.The computational fluid dynamic method (CFD) has been proposed to calculate hydrodynamic performance of planning vessels.However,in most traditional CFD approaches,model tests or empirical formulas are needed to obtain the running attitude of the planing vessels before calculation.This paper presents a new CFD method to calculate hydrodynamic forces of planing vessels.The numerical method was based on Reynolds-Averaged Navier-Stokes (RANS)equations.The volume of fluid (VOF) method and the six-degrees-of-freedom equation were applied.An effective process was introduced to solve the numerical divergence problem in numerical simulation.Compared with experimental results,numerical simulation results indicate that both the running attitude and hydrodynamic performance can be predicted well at high speeds.
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.
Numerical Simulation of Microbiological Growth in the Capillary Fringe
Hron, P.; Jost, D.; Engwer, C.; Ippisch, O.; Bastian, P.
2012-04-01
The capillary fringe (CF) is a highly dynamic zone in a porous media at the interface between water-saturated aquifer and vadose zone, where steep biogeochemical gradients and thus high bioactivities are expected. In recent years, considerable effort has been undertaken to deepen the understanding of the physical (flow, diffusion, dispersion), geochemical (dissolution, precipitation) and biological (metabolism, excretion, biofilm formation) processes in the CF. We developed a numerical simulator for multiphase multicomponent flow in porous media which is able to consider simultaneously multiphase flow, component transport, phase exchange, geochemical reactions and microbiological processes. A splitting approach for phase transport, component transport and reaction/phase exchanges allows the usage of higher-order discretizations for the component transport. This reduces numerical dispersion significantly, which is especially important in the simulation of reactive flow. In a flow-through laboratory experiment performed at the Karlsruhe Institute of Technology, Germany, within the project "Dynamic Capillary Fringes - A Multidisciplinary Approach", the oxygen phase transfer, the growth and the transport of a bacteria (green fluorescent Escherichia coli) were investigated. The results of numerical simulations of the E. coli growth in the CF with a high nutrient supply under steady-state and transient flow conditions are compared to the experimental data.
The numerical simulation based on CFD of hydraulic turbine pump
Duan, X. H.; Kong, F. Y.; Liu, Y. Y.; Zhao, R. J.; Hu, Q. L.
2016-05-01
As the functions of hydraulic turbine pump including self-adjusting and compensation with each other, it is far-reaching to analyze its internal flow by the numerical simulation based on CFD, mainly including the pressure field and the velocity field in hydraulic turbine and pump.The three-dimensional models of hydraulic turbine pump are made by Pro/Engineer software;the internal flow fields in hydraulic turbine and pump are simulated numerically by CFX ANSYS software. According to the results of the numerical simulation in design condition, the pressure field and the velocity field in hydraulic turbine and pump are analyzed respectively .The findings show that the static pressure decreases systematically and the pressure gradient is obvious in flow area of hydraulic turbine; the static pressure increases gradually in pump. The flow trace is regular in suction chamber and flume without spiral trace. However, there are irregular traces in the turbine runner channels which contrary to that in flow area of impeller. Most of traces in the flow area of draft tube are spiral.
Transient productivity index for numerical well test simulations
Energy Technology Data Exchange (ETDEWEB)
Blanc, G.; Ding, D.Y.; Ene, A. [Institut Francais du Petrole, Pau (France)] [and others
1997-08-01
The most difficult aspect of numerical simulation of well tests is the treatment of the Bottom Hole Flowing (BHF) Pressure. In full field simulations, this pressure is derived from the Well-block Pressure (WBP) using a numerical productivity index which accounts for the grid size and permeability, and for the well completion. This productivity index is calculated assuming a pseudo-steady state flow regime in the vicinity of the well and is therefore constant during the well production period. Such a pseudo-steady state assumption is no longer valid for the early time of a well test simulation as long as the pressure perturbation has not reached several grid-blocks around the well. This paper offers two different solutions to this problem: (1) The first one is based on the derivation of a Numerical Transient Productivity Index (NTPI) to be applied to Cartesian grids; (2) The second one is based on the use of a Corrected Transmissibility and Accumulation Term (CTAT) in the flow equation. The representation of the pressure behavior given by both solutions is far more accurate than the conventional one as shown by several validation examples which are presented in the following pages.
Calculation of residual stresses by means of a 3D numerical weld simulation
Energy Technology Data Exchange (ETDEWEB)
Nicak, Tomas; Huemmer, Matthias [AREVA NP GmbH, Postfach 1109 (Germany)
2008-07-01
The numerical weld simulation has developed very fast in recent years. The problem complexity has increased from simple 2D models to full 3D models, which can describe the entire welding process more realistically. As recent research projects indicate, a quantitative assessment of the residual stresses by means of a 3D analysis is possible. The structure integrity can be assessed based on the weld simulation results superimposed with the operating load. Moreover, to support the qualification of welded components parametric studies for optimization of the residual stress distribution in the weld region can be performed. In this paper a full 3D numerical weld simulation for a man-hole drainage nozzle in a steam generator will be presented. The residual stresses are calculated by means of an uncoupled transient thermal and mechanical FE analysis. The paper will present a robust procedure allowing reasonable predictions of the residual stresses for complex structures in industrial practice. (authors)
Numerical simulation of flow-induced vibrations in tube bundles
International Nuclear Information System (INIS)
Full text of publication follows: In many industrial components mechanical structures like rod cluster control assembly, fuel assembly and heat exchanger tube bundles are submitted to complex flows causing possible vibrations and damage. Fluid forces are usually split into two parts: structure motion independent forces and fluid-elastic forces coupled with tube motion and responsible for possible dynamic instability development leading to possible short term failures through high amplitude vibrations. Most classical fluid force identification methods rely on structure response experimental measurements associated with convenient data processes. Owing to recent improvements in Computational Fluid Dynamics (C.F.D.), numerical fluid force identification is now practicable in the presence of industrial configurations. The present paper is devoted to numerical simulation of flow-induced vibrations of tube bundles submitted to single-phase cross flows by using C.F.D. codes. Direct Numerical Simulation (D.N.S.), Arbitrary Lagrange Euler formulation (A.L.E.) and code coupling process are involved to predict fluid forces responsible for tube bundle vibrations in the presence of fluid structure and fluid-elastic coupling effects. In the presence of strong multi-physics coupling, simulation of flow-induced vibrations requires a fluid structure code coupling process. The methodology consists in solving in the same time thermohydraulics and mechanics problems by using an A.L.E. formulation for the fluid computation. The purpose is to take into account coupling between flow and structure motions in order to be able to capture coupling effects. From a numerical point of view, there are three steps in the computation: the fluid problem is solved on the computational domain; fluid forces acting on the moving tube are estimated; finally they are introduced in the structure solver providing the tube displacement that is used to actualize the fluid computational domain. Specific
Numerical simulations of rubber bearing tests and shaking table tests
International Nuclear Information System (INIS)
Test data concerning rubber bearing tests and shaking table tests of base-isolated model conducted by CRIEPI are provided to the participants of Coordinated Research Program (CRP) on 'Intercomparison of Analysis Methods for predicting the behaviour of Seismically Isolated Nuclear Structure', which is organized by International Atomic Energy Agency (IAEA), for the comparison study of numerical simulation of base-isolated structure. In this paper outlines of the test data provided and the numerical simulations of bearing tests and shaking table tests are described. Using computer code ABAQUS, numerical simulations of rubber bearing tests are conducted for NRBs, LRBs (data provided by CRIEPI) and for HDRs (data provided by ENEA/ENEL and KAERI). Several strain energy functions are specified according to the rubber material test corresponding to each rubber bearing. As for lead plug material in LRB, mechanical characteristics are reevaluated and are made use of. Simulation results for these rubber bearings show satisfactory agreement with the test results. Shaking table test conducted by CRIEPI is of a base isolated rigid mass supported by LRB. Acceleration time histories, displacement time histories of the isolators as well as cyclic loading test data of the LRB used for the shaking table test are provided to the participants of the CRP. Simulations of shaking table tests are conducted for this rigid mass, and also for the steel frame model which is conducted by ENEL/ENEA. In the simulation of the rigid mass model test, where LRBs are used, isolators are modeled either by bilinear model or polylinear model. In both cases of modeling of isolators, simulation results show good agreement with the test results. In the case of the steel frame model, where HDRs are used as isolators, bilinear model and polylinear model are also used for modeling isolators. The response of the model is simulated comparatively well in the low frequency range of the floor response, however, in
Numerical simulations of fragmentation of the Affleck-Dine condensate
Enqvist, Kari; Multamaki, T P; Vilja, I
2001-01-01
We present numerical simulations of fragmentation of the Affleck-Dine condensate in two spatial dimensions. We argue analytically that the final state should consist of both Q-balls and anti-Q-balls in a state of maximum entropy, with most of the balls small and relativistic. Such a behaviour is found in simulations on a 100x100 lattice with cosmologically realistic parameter values. During fragmentation process, we observe filament-like texture in the spatial distribution of charge. The total charge in Q-balls is found to be almost equal to the charge in anti-Q-balls and typically orders of magnitude larger than charge asymmetry. Analytical considerations indicate that, apart from geometrical factors, the results of the simulated two dimensional case should apply also to the fully realistic three dimensional case.
Study on the numerical simulation of batch sieving process
Institute of Scientific and Technical Information of China (English)
JIAO Hong-guang; MA Jiao; ZHAO Yue-min; CHEN Lun-jian
2006-01-01
Screening was widely used in many sectors of industry. However, it is rather incomplete to the cognition of the sieving process for us due to the daedal separation process involving interactions of thousands of particulates. To address this problem, two dimensional numerical simulation of batch sieving process was performed by adopting advanced discrete element method (DEM), which is one of the highly nonlinear digitized dynamic simulative methods and can be used to reveal the quantitative change from particle dimension level. DEM simulation results show that the jam phenomena of sieve-plate apertures of the "blinding particles" in the screen feed can be demonstrated vividly and results also reveal that the velocity of particle moving on the screen plate will vary along with the screen length. This conclusion will be helpful to the design and operation of screen.
Hygrothermal Numerical Simulation Tools Applied to Building Physics
Delgado, João M P Q; Ramos, Nuno M M; Freitas, Vasco Peixoto
2013-01-01
This book presents a critical review on the development and application of hygrothermal analysis methods to simulate the coupled transport processes of Heat, Air, and Moisture (HAM) transfer for one or multidimensional cases. During the past few decades there has been relevant development in this field of study and an increase in the professional use of tools that simulate some of the physical phenomena that are involved in Heat, Air and Moisture conditions in building components or elements. Although there is a significant amount of hygrothermal models referred in the literature, the vast majority of them are not easily available to the public outside the institutions where they were developed, which restricts the analysis of this book to only 14 hygrothermal modelling tools. The special features of this book are (a) a state-of-the-art of numerical simulation tools applied to building physics, (b) the boundary conditions importance, (c) the material properties, namely, experimental methods for the measuremen...
NUMERICAL SIMULATION OF A PODDED PROPULSOR IN VISCOUS FLOW
Institute of Scientific and Technical Information of China (English)
GUO Chun-yu; MA Ning; YANG Chen-jun
2009-01-01
A podded propulsor in viscous flow is numerically simulated in this article.The region of fluid is divided into efficient calculation grids.The pressure and viscous force of blades,pod and strut are obtained as functions of an advance coefficient.The steady result is used as a base in the unsteady simulation to obtain a solution more quickly.The distributions of the thrust and torque fluctuations of the key blade in one revolution are obtained.The calculation results from the mixing plane on steady conditions are compared with those obtained from the sliding mesh model on unsteady conditions.The User-Defined Function(UDF)method is used to simulate the influence of ship hull on the non-uniform wake of the propeller.
A Numerical Simulation of a Plunging Breaking Wave
Adams, Paul; Stephens, Mike; Brucker, Kyle A; O'Shea, Thomas; Dommermuth, Douglas
2009-01-01
This article describes the fluid dynamics video, "A Numerical Simulation of a Plunging Breaking Wave", which was submitted to the gallery of fluid motion at the 2009 APS/DFD conference. The simulation was of a deep-water plunging breaking wave. It was a two-phase calculation which used a Volume of Fluid (VOF) method to simulate the interface between the two immiscible fluids. Surface tension and viscous effects were not considered. The initial wave was generated by applying a spatio-temporal pressure forcing on the free surface. The video shows the 50% isocontour of the volume fraction from several different perspectives. Significant air entrainment is observed as well as the presence of stream-wise vortex structures.
Numerical simulation of a compressible homogeneous, turbulent shear flow
Feiereisen, W. J.; Reynolds, W. C.; Ferziger, J. H.
1981-03-01
A direct, low Reynolds number, numerical simulation was performed on a homogeneous turbulent shear flow. The full compressible Navier-Stokes equations were used in a simulation on the ILLIAC IV computer with a 64,000 mesh. The flow fields generated by the code are used as an experimental data base, to examine the behavior of the Reynols stresses in this simple, compressible flow. The variation of the structure of the stresses and their dynamic equations as the character of the flow changed is emphasized. The structure of the tress tensor is more heavily dependent on the shear number and less on the fluctuating Mach number. The pressure-strain correlation tensor in the dynamic uations is directly calculated in this simulation. These correlations are decomposed into several parts, as contrasted with the traditional incompressible decomposition into two parts. The performance of existing models for the conventional terms is examined, and a model is proposed for the 'mean fluctuating' part.
Fluent-based numerical simulation of flow centrifugal fan
Institute of Scientific and Technical Information of China (English)
LI Xian-zhang
2011-01-01
Testing centrifugal fan flow field by physical laboratory is difficult because the testing system is complex and the workload is heavy, and the results observed by naked-eye deviates far from the actual value. To address this problem, the computational fluid dynamics software FLUENT was applied to establish three-dimensional model of the centrifugal fan. The numeral model was verified by comparing simulation data to experimental data. The pressure centrifugal fan and the speed changes in distribution in centrifugal fan was simulated by computational fluid dynamics software FLUENT. The simulation results show that the gas flow velocity in the impeller increases with impeller radius increase. Static pressure gradually increases when gas from the fan access is imported through fan impeller leaving fans.
Real-Time Numerical Simulation of the Carnot Cycle
International Nuclear Information System (INIS)
We developed a highly interactive, multi-windows Java applet which made it possible to simulate and visualize within any platform and internet the Carnot cycle (or engine) in a real-time computer experiment. We extended our previous model and algorithm to simulate not only the heat flow but also the macroscopic movement of the piston. since in reality it is impossible to construct a reversible Carnot engine, the question arises whether it is possible to simulate it at least in a numerical experiment? The positive answer to this question which we found is related to our model and algorithm which make it possible to omit the many-body problem arising when many gas particles simultaneously interact with the mobile piston. As usually the considerations of phenomenomenological thermodynamics began with a study of the basic properties of heat engines hence our approach, beside intrinsic physical significance, is also important from the educational, technological and even environmental points of view. (author)
Direct numerical simulation of bubbles with parallelized adaptive mesh refinement
International Nuclear Information System (INIS)
The study of two-phase Thermal-Hydraulics is a major topic for Nuclear Engineering for both security and efficiency of nuclear facilities. In addition to experiments, numerical modeling helps to knowing precisely where bubbles appear and how they behave, in the core as well as in the steam generators. This work presents the finest scale of representation of two-phase flows, Direct Numerical Simulation of bubbles. We use the 'Di-phasic Low Mach Number' equation model. It is particularly adapted to low-Mach number flows, that is to say flows which velocity is much slower than the speed of sound; this is very typical of nuclear thermal-hydraulics conditions. Because we study bubbles, we capture the front between vapor and liquid phases thanks to a downward flux limiting numerical scheme. The specific discrete analysis technique this work introduces is well-balanced parallel Adaptive Mesh Refinement (AMR). With AMR, we refined the coarse grid on a batch of patches in order to locally increase precision in areas which matter more, and capture fine changes in the front location and its topology. We show that patch-based AMR is very adapted for parallel computing. We use a variety of physical examples: forced advection, heat transfer, phase changes represented by a Stefan model, as well as the combination of all those models. We will present the results of those numerical simulations, as well as the speed up compared to equivalent non-AMR simulation and to serial computation of the same problems. This document is made up of an abstract and the slides of the presentation. (author)
Numerical Simulation of Waves Generated by Seafloor Movements
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
Waves generated by vertical seafloor movements are simulated by use of a fully nonlinear two-dimensional numerical wave tank. In the source region, the seafloor lifts to a designated height by a generation function. The numerical tests show that the linear theory is only valid for estimating the wave behaviors induced by the seafloor movements with a small amplitude, and the fully nonlinear numerical model should be adopted in the simulation of the wave generation by the large amplitude seafloor movements. Without the background surface waves, many numerical tests on the stable maximum elevations ηmax0 are carried out by both the linear theory and the fully nonlinear model. The results of two models are compared and analyzed. For the fully nonlinear model, the influences of the amplitudes and the horizontal lengths on ηmax0 are stronger than that of the characteristic duration times. Furthermore, results reveal that there are significant differences between the linear theory and the fully nonlinear model. When the influences of the background surface waves are considered, the corresponding numerical analyses reveal that with the fully nonlinear model the ηmax0 near-linearly varies with the wave amplitudes of the surface waves, and the ηmax0 has significant depndences on the wave lengths and the wave phases of the surface waves. In addition, the differences between the linear theory and the fully nonlinear model are still obvious, and these differences are significantly affected by the wave parameters of the background surface waves, such as the wave amplitude, the wave length and the wave phase.
Numerical simulations of clinical focused ultrasound functional neurosurgery
Pulkkinen, Aki; Werner, Beat; Martin, Ernst; Hynynen, Kullervo
2014-04-01
A computational model utilizing grid and finite difference methods were developed to simulate focused ultrasound functional neurosurgery interventions. The model couples the propagation of ultrasound in fluids (soft tissues) and solids (skull) with acoustic and visco-elastic wave equations. The computational model was applied to simulate clinical focused ultrasound functional neurosurgery treatments performed in patients suffering from therapy resistant chronic neuropathic pain. Datasets of five patients were used to derive the treatment geometry. Eight sonications performed in the treatments were then simulated with the developed model. Computations were performed by driving the simulated phased array ultrasound transducer with the acoustic parameters used in the treatments. Resulting focal temperatures and size of the thermal foci were compared quantitatively, in addition to qualitative inspection of the simulated pressure and temperature fields. This study found that the computational model and the simulation parameters predicted an average of 24 ± 13% lower focal temperature elevations than observed in the treatments. The size of the simulated thermal focus was found to be 40 ± 13% smaller in the anterior-posterior direction and 22 ± 14% smaller in the inferior-superior direction than in the treatments. The location of the simulated thermal focus was off from the prescribed target by 0.3 ± 0.1 mm, while the peak focal temperature elevation observed in the measurements was off by 1.6 ± 0.6 mm. Although the results of the simulations suggest that there could be some inaccuracies in either the tissue parameters used, or in the simulation methods, the simulations were able to predict the focal spot locations and temperature elevations adequately for initial treatment planning performed to assess, for example, the feasibility of sonication. The accuracy of the simulations could be improved if more precise ultrasound tissue properties (especially of the
Numerical simulations of clinical focused ultrasound functional neurosurgery
International Nuclear Information System (INIS)
A computational model utilizing grid and finite difference methods were developed to simulate focused ultrasound functional neurosurgery interventions. The model couples the propagation of ultrasound in fluids (soft tissues) and solids (skull) with acoustic and visco-elastic wave equations. The computational model was applied to simulate clinical focused ultrasound functional neurosurgery treatments performed in patients suffering from therapy resistant chronic neuropathic pain. Datasets of five patients were used to derive the treatment geometry. Eight sonications performed in the treatments were then simulated with the developed model. Computations were performed by driving the simulated phased array ultrasound transducer with the acoustic parameters used in the treatments. Resulting focal temperatures and size of the thermal foci were compared quantitatively, in addition to qualitative inspection of the simulated pressure and temperature fields. This study found that the computational model and the simulation parameters predicted an average of 24 ± 13% lower focal temperature elevations than observed in the treatments. The size of the simulated thermal focus was found to be 40 ± 13% smaller in the anterior–posterior direction and 22 ± 14% smaller in the inferior–superior direction than in the treatments. The location of the simulated thermal focus was off from the prescribed target by 0.3 ± 0.1 mm, while the peak focal temperature elevation observed in the measurements was off by 1.6 ± 0.6 mm. Although the results of the simulations suggest that there could be some inaccuracies in either the tissue parameters used, or in the simulation methods, the simulations were able to predict the focal spot locations and temperature elevations adequately for initial treatment planning performed to assess, for example, the feasibility of sonication. The accuracy of the simulations could be improved if more precise ultrasound tissue properties (especially of the
Direct numerical simulation of sharkskin denticles in turbulent channel flow
Boomsma, A.; Sotiropoulos, F.
2016-03-01
The hydrodynamic function of sharkskin has been under investigation for the past 30 years. Current literature conflicts on whether sharkskin is able to reduce skin friction similar to riblets. To contribute insights toward reconciling these conflicting views, direct numerical simulations are carried out to obtain detailed flow fields around realistic denticles. A sharp interface immersed boundary method is employed to simulate two arrangements of actual sharkskin denticles (from Isurus oxyrinchus) in a turbulent boundary layer at Reτ ≈ 180. For comparison, turbulent flow over drag-reducing scalloped riblets is also simulated with similar flow conditions and with the same numerical method. Although the denticles resemble riblets, both sharkskin arrangements increase total drag by 44%-50%, while the riblets reduce drag by 5%. Analysis of the simulated flow fields shows that the turbulent flow around denticles is highly three-dimensional and separated, with 25% of the total drag being form drag. The complex three-dimensional shape of the denticles gives rise to a mean flow dominated by strong secondary flows in sharp contrast with the mean flow generated by riblets, which is largely two-dimensional. The so resulting three-dimensionality of sharkskin flows leads to an increase in the magnitude of the turbulent statistics near the denticles, which further contributes to increasing the total drag. The simulations also show that, at least for the simulated arrangements, sharkskin, in sharp contrast with drag-reducing riblets, is unable to isolate high shear stress near denticle ridges causing a significant portion of the denticle surface to be exposed to high mean shear.
Numerical simulation of microstructure of the GeSi alloy
Energy Technology Data Exchange (ETDEWEB)
Rasin, I.
2006-09-08
The goal of this work is to investigate pattern formation processes on the solid-liquid interface during the crystal growth of GeSi. GeSi crystals with cellular structure have great potential for applications in -ray and neutron optics. The interface patterns induce small quasi-periodic distortions of the microstructure called mosaicity. Existence and properties of this mosaicity are important for the application of the crystals. The properties depend on many factors; this dependence, is currently not known even not qualitatively. A better understanding of the physics near the crystal surface is therefore required, in order to optimise the growth process. There are three main physical processes in this system: phase-transition, diffusion and melt flow. Every process is described by its own set of equations. Finite difference methods and lattice kinetic methods are taken for solving these governing equations. We have developed a modification of the kinetic methods for the advectiondiffusion and extended this method for simulations of non-linear reaction diffusion equations. The phase-field method was chosen as a tool for describing the phase-transition. There are numerous works applied for different metallic alloys. An attempt to apply the method directly to simulation GeSi crystal growth showed that this method is unstable. This instability has not been observed in previous works due to the much smaller scale of simulations. We introduced a modified phase-field scheme, which enables to simulate pattern formation with the scale observed in experiment. A flow in the melt was taken in to account in the numerical model. The developed numerical model allows us to investigate pattern formation in GeSi crystals. Modelling shows that the flow near the crystal surface has impact on the patterns. The obtained patterns reproduce qualitatively and in some cases quantitatively the experimental results. (orig.)
Numerical simulations of waves in a magnetically structured atmosphere
Espinola, Thomas Peter
A physical model for simulating waves in a stellar atmosphere was developed from a combination of basic fluid mechanics, plasma physics, and electrodynamics. The model was three dimensional and included the effects of gravity, magnetic fields, and viscosity. An algorithm was developed to numerically implement this model. The resulting program used an explicit time integration scheme based on Runge-Kutta and a combination of finite difference and spectral methods to evaluate the spatial derivatives. A number of numerical boundary conditions were developed—the most successful used a modified Sommerfeld radiation condition. The program was written and coded in Fortran on a Vax computer. Additional routines were written to evaluate the required fast fourier transforms and to graph and display the data. The program was tested on a large number of one and two dimensional problems for which the solutions were known. These problems included acoustic waves, Alfvén waves, magnetoacoustic waves, shocks, rarefactions, and contact discontinuities. The numerical results agreed with the analytic solutions of the physical problems to within the precision requested of the simulation. The program proved to be stable and robust for all the problems attempted. This program was then used to simulate three problems for which analytic solutions are not known. All three simulations concerned the propagation of waves in magnetically structured atmospheres and may be applied to outstanding problems in solar physics. First, the interactions of non-linear waves and a flux slab were studied. From the result it is apparent that sources of shocks and rarefactions, such as the solar convection zone, do not concentrate the magnetic field in flux sheaths. Next I used the program to simulate the interaction of non-linear waves with a flux tube. The results suggest that the magnetic fields in flux tubes are also not concentrated by pairs of passing shocks and rarefactions; however, a complete
Towards direct numerical simulation of freely swimming fish.
Curet, Oscar; Patankar, Neelesh; Maciver, Malcolm
2006-11-01
Swimming mechanisms employed by fish are currently inspiring unique underwater vehicles and robotic devices as well as basic science research into the neural control of movement. Key engineering issues include propulsion efficiency, precise motion control and maneuverability. A numerical scheme that simulates the motion of freely swimming fish will be a valuable design and research tool. We are working towards this goal. In particular we are interested in simulating the motion of a gymnotiform fish that swims by producing undulations of a ventral ribbon fin while keeping its body rigid. We model the fish as a rigid body with an attached undulating membrane. In our numerical scheme the key idea is to assume that the entire fluid-fish domain is a fluid. Then we impose two constraints: the first requires that the fluid in the region occupied by the fish body moves rigidly (a fictitious domain approach), and the second requires that the fluid at the location of the fin has the traveling wave velocity of the fin (an immersed boundary approach). Given the traveling wave form of the fin, the objective is for the numerical scheme to give the swimming velocity of the fish by solving the coupled fluid-fish problem. We will present results for the forces generated by a fin attached to a fixed body and preliminary results for freely swimming fish.
Progress in numerical simulation of cavitating water jets
Institute of Scientific and Technical Information of China (English)
PENG Guoyi; SHMIZU Seiji
2013-01-01
This paper reviews recent progress made toward modeling of cavitation and numerical simulation of cavitating water jets.Properties of existing cavitation models are discussed and a compressible mixture flow method for the numerical simulation of highspeed water jets accompanied by intensive cavitation is introduced.Two-phase fluids media of cavitating flow are treated as a homogeneous bubbly mixture and the mean flow is computed by solving Reynolds-Averaged Navier-Stokes (RANS) equations for compressible fluid.The intensity of cavitation is evaluated by the gas volume fraction,which is governed by the compressibility of bubble-liquid mixture corresponding to the status of mean flow field.Numerical results of cavitating water jet issuing from an orifice nozzle are presented and its applicability to intensively cavitating jets is demonstrated.However,the effect of impact pressure caused by collapsing of bubbles is neglected,and effectively coupling of the present compressible mixture flow method with the dynamics of bubbles remains to be a challenge.
Numerical simulation of the sucker-rod pumping system
Directory of Open Access Journals (Sweden)
Oldrich Joel Romero
2014-11-01
Full Text Available The sucker rod pump is an artificial lift method frequently applied in onshore petroleum wells. This system can be described using a numerical simulation based on the behavior of a rod string. In the past, the elastic behavior of the rod string made it difficult to model the system. However, since the 1960s and with the advent of digital computers, it has been modeled numerically. The rod string be-haves like a slender bar, and thus, the propagation of elastic waves along the bar can be represented by a one-dimensional equation. Gibbs (1963 presented a mathematical model based on the wave equation, which is described on the basis of the analysis of forces on the rod string and is incorporated into a boundary value problem involving partial differential equations. The use of the finite differ-ence method allows for a numerical solution by the discretization of the wave equation developed in the mathematical formulation with appropriate boundary and initial conditions. This work presents a methodology for implementing an academic computer code that allows simulation of the upstroke and downstroke motion of the rod string described by the wave equation under ideal operating conditions, assuming a harmonic motion of the rod at one end and downhole pump at the other end. The goal of this study is to generate the downhole dynamometer card, an important and consolidated tool that controls the pump system by diagnosing oper-ational conditions of the downhole pump.
High accuracy mantle convection simulation through modern numerical methods
Kronbichler, Martin
2012-08-21
Numerical simulation of the processes in the Earth\\'s mantle is a key piece in understanding its dynamics, composition, history and interaction with the lithosphere and the Earth\\'s core. However, doing so presents many practical difficulties related to the numerical methods that can accurately represent these processes at relevant scales. This paper presents an overview of the state of the art in algorithms for high-Rayleigh number flows such as those in the Earth\\'s mantle, and discusses their implementation in the Open Source code Aspect (Advanced Solver for Problems in Earth\\'s ConvecTion). Specifically, we show how an interconnected set of methods for adaptive mesh refinement (AMR), higher order spatial and temporal discretizations, advection stabilization and efficient linear solvers can provide high accuracy at a numerical cost unachievable with traditional methods, and how these methods can be designed in a way so that they scale to large numbers of processors on compute clusters. Aspect relies on the numerical software packages deal.II and Trilinos, enabling us to focus on high level code and keeping our implementation compact. We present results from validation tests using widely used benchmarks for our code, as well as scaling results from parallel runs. © 2012 The Authors Geophysical Journal International © 2012 RAS.
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 SIMULATION OF A PREMIXED TURBULENT V-SHAPED FLAME
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M I El Khazen
2011-01-01
Full Text Available In this paper we simulate a turbulent premixed V-shape flame stabilized on a hot wire. The device used is composed of a vertical combustion chamber where the methane-air mixture is convected upwards with a mean velocity of 4ms-1. The flow was simulated running Fluent 6.3, which numerically solved the stationary Favre-averaged mass balance; Navier-Stokes equations; combustion progress variable, and k-ε equations on a two-dimensional numerical mesh. We model gaseous mixture, ignoring Soret and Dufour effects and radiation heat transfer. The progress variable balance equation was closed using Eddy Break Up model. The results of our simulations allow us to analyze the influence of equivalence ratio and the turbulent intensity on the properties of the flame (velocity, fluctuation, progress variable and Thickness of flame.This work gives us an idea on the part which turbulence can play to decrease the risks of extinction and instabilities caused by the lean premixed combustion.
Numerical simulation of plasmas on an unstructured grid
International Nuclear Information System (INIS)
The use of unstructured grids provides some inherent advantages in the accurate simulation of plasma problems which involve complex configurations and where the treatment of complicated boundaries is important. The use of a triangular grid in two dimensions, and of a tetrahedral grid with arbitrary connectivity in three dimensions, allows a straightforward representation of complex geometries and naturally allows the resolution of the mesh to vary according to the requirements of a problem. We have constructed a very simple and efficient data structure to represent unstructured grids for geometries with arbitrarily shaped boundaries. The data contains information about the location of vertices, edges, sides, and cells and permits with one degree of indirectness the implementation of algorithms for field solvers and for particle orbit integration. The numerical algorithms that have been constructed include a potential solver, an electromagnetic solver for both the time and frequency domain, and a particle-in-cell simulation. The efficiency and vectorization of the basic code functions are retained and yield timing results comparable with structured mesh codes. They describe the method of grid generation, the numerical algorithm's for a variety of applications, and present typical results. These include particle-in-cell plasma simulations as well as purely electromagnetic cases which illustrate powerful features of local grid refinement for cavity and scattering problems
Numerical Simulation on Interface Evolution and Impact of Flooding Flow
Directory of Open Access Journals (Sweden)
J. Hu
2015-01-01
Full Text Available A numerical model based on Navier-Stokes equation is developed to simulate the interface evolution of flooding flows. The two-dimensional fluid domain is discretised by structured rectangular elements according to finite volume method (FVM. The interface between air and liquid is captured through compressive interface capturing scheme for arbitrary meshes (CICSAM based on the idea of volume of fluid (VOF. semiimplicit method for pressure linked equations (SIMPLE scheme is used for the pressure-velocity coupling. A second order upwind discretization scheme is applied for the momentum equations. Both laminar flow model and turbulent flow model have been studied and the results have been compared. Previous experiments and other numerical solutions are employed to verify the present results on a single flooding liquid body. Then the simulation is extended to two colliding flooding liquid bodies. The impacting force of the flooding flow on an obstacle has been also analyzed. The present results show a favourable agreement with those by previous simulations and experiments.
Numerical simulation of free water surface in pump intake
International Nuclear Information System (INIS)
The purpose of this paper is to verify the volume of fluid (VOF) method for simulating the free water surface flow in pump intake. With the increasing computer power, VOF method has been becoming a more flexible and accurate choice to replace the conventional fixed water surface method, because it does not require assumptions on the nature of air-water interface. Two examples are presented in this paper. The first example is presented for simulating the growth of air-entrained vortices. LES (Large Eddy Simulation) model, instead of RANS (Reynolds averaged Navier-Stokes) turbulence model, is used to capture the peak of circular velocity around the vortex core. Numerical result shows good agreement with the benchmark experiment carried by the Turbomachinery Society of Japan. The second example predicts the flow rate distribution in the pump intake consisting of one opened and two closed channels. VOF result is compared with the conventional fixed water surface method assuming free-slip boundary condition on the fluid interface. The difference of flow pattern in the opened channel indicates that numerical flow field is affected remarkably by the setup of boundary condition at air-water interface.
Numerical Simulation Multicomponent Ion Beam Transport form ECR Ion Source
Institute of Scientific and Technical Information of China (English)
MaLei; SongMingtao; ZhangZimin; CaoYun
2003-01-01
In order to simulate the transport of multi-components ion beam extracted from an ECR ion source, we have developed a multi-charged ion beam transport program named MCIBS 1.0. The program is dedicated to numerical simulation of the behavior of highly-charged ion beam and optimization of beam optics in transport lines and is realized on a PC with Windows user interface of Microsoft Visual Basic. Among all the ions with different charge states in the beam, the exchanges of electrons between highly charged ions and low charged ions or neutral,atoms of residual gas are taken into account by using classical Molecular Over-barrier Model and Monte Carlo method. An advanced Windows graphical interface makes it; comfortable and friendly for the user to operate in an interactive mode. The present program is used for the numerical calculation and optimization of beam optics in a transport line consisting of various magnetic elements, such as dipole magnet, quadrupole and so on. It is possible to simultaneously simulate 200,000 particles, in a transport line of 340 m at most, and show every particle orbit. Beam cross section graphics and emittance phase pictures can be also shown at any position in the transport line.
Numerical simulation of multi-layered textile composite reinforcement forming
International Nuclear Information System (INIS)
One important perspective in aeronautics is to produce large, thick or/and complex structural composite parts. The forming stage presents an important role during the whole manufacturing process, especially for LCM processes (Liquid Composites Moulding) or CFRTP (Continuous Fibre Reinforcements and Thermoplastic resin). Numerical simulations corresponding to multi-layered composite forming allow the prediction for a successful process to produce the thick parts, and importantly, the positions of the fibres after forming to be known. This paper details a set of simulation examples carried out by using a semi-discrete shell finite element made up of unit woven cells. The internal virtual work is applied on all woven cells of the element taking into account tensions, in-plane shear and bending effects. As one key problem, the contact behaviours of tool/ply and ply/ply are described in the numerical model. The simulation results not only improve our understanding of the multi-layered composite forming process but also point out the importance of the fibre orientation and inter-ply friction during formability.
Numerical simulation of nanoparticle pattern fabricated by electrostatic spray deposition
Institute of Scientific and Technical Information of China (English)
Wei Wei; Zhaolin Gu; Sheng Wang; Takeshi Fukuda; Kiwamu Kase; Jungmyoung Ju; Yutaka Yamagata
2013-01-01
Electrospray deposition (ESD) as a patterning method of nanoparticles deposited on a substrate has attracted much attention due to several advantages over other methods.However,obtaining an optimum ESD processing condition for nanoparticle pattern relies much on trial experiments because of the lack of reliable numerical simulation.In this study,the deposition characteristics of nanoparticle generated by electrospray were investigated by using a three-dimensional Lagrangian model.Three important process parameters,including solution dielectric constant,applied voltage and surface charge density on mask were considered by fixing the geometrical parameters of the ESD device.Simulation result showed that under the condition of without a mask,the spray diameter increases with increasing solvent dielectric constant,and higher applied voltage makes the spray area wider.Controllability of focusing by changing surface charge density on the mask was confirmed:higher surface charge density on the mask results in more focused deposition.Validity of the numerical simulation developed in this study was verified by comparison with experimental data.
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.
NUMERICAL SIMULATION OF AN AGRICULTURAL SOIL SHEAR STRESS TEST
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Andrea Formato
2007-03-01
Full Text Available In this work a numerical simulation of agricultural soil shear stress tests was performed through soil shear strength data detected by a soil shearometer. We used a soil shearometer available on the market to measure soil shear stress and constructed special equipment that enabled automated detection of soil shear stress. It was connected to an acquisition data system that displayed and recorded soil shear stress during the full field tests. A soil shearometer unit was used to the in situ measurements of soil shear stress in full field conditions for different types of soils located on the right side of the Sele river, at a distance of about 1 km from each other, along the perpendicular to the Sele river in the direction of the sea. Full field tests using the shearometer unit were performed alongside considered soil characteristic parameter data collection. These parameter values derived from hydrostatic compression and triaxial tests performed on considered soil samples and repeated 4 times and we noticed that the difference between the maximum and minimum values detected for every set of performed tests never exceeded 4%. Full field shear tests were simulated by the Abaqus program code considering three different material models of soils normally used in the literature, the Mohr-Coulomb, Drucker-Prager and Cam-Clay models. We then compared all data outcomes obtained by numerical simulations with those from the experimental tests. We also discussed any further simulation data results obtained with different material models and selected the best material model for each considered soil to be used in tyre/soil contact simulation or in soil compaction studies.
Numerical simulation of heat exchangers elliptical tubes and corrugated fins
International Nuclear Information System (INIS)
The intensified heat exchangers fins are widely used in the automotive and domestic industry. The low heat transfer coefficients on the air side are the main reason why these fins of heat exchangers need to be intensified. In this paper, the numerical simulation of a wavy fin type is made with elliptical tubes. The dimensions of the fin is in the range of those used in air conditioning equipment. The friction factor and the mass transfer coefficient as a function of the Reynolds number for this type of fin, always within the laminar regime is determined. The numerical model against experimental results published in the literature is validated. In addition the mechanisms that produce intensified heat transfer fin in such occur. (full text)
Mechanical characterisation of Dacron graft: Experiments and numerical simulation.
Bustos, Claudio A; García-Herrera, Claudio M; Celentano, Diego J
2016-01-01
Experimental and numerical analyses focused on the mechanical characterisation of a woven Dacron vascular graft are presented. To that end, uniaxial tensile tests under different orientations have been performed to study the anisotropic behaviour of the material. These tests have been used to adjust the parameters of a hyperelastic anisotropic constitutive model which is applied to predict through numerical simulation the mechanical response of this material in the ring tensile test. The obtained results show that the model used is capable of representing adequately the nonlinear elastic region and, in particular, it captures the progressive increase of the rigidity and the anisotropy due to the stretching of the Dacron. The importance of this research lies in the possibility of predicting the graft׳s mechanical response under generalized loading such as those that occur under physiological conditions after surgical procedures. PMID:26627367
Numerical Simulation for Ventilated Supercavitation High Speed Underwater Vehicle
Institute of Scientific and Technical Information of China (English)
YANG Wu-gang; YANG Zhen-cai; CHU Yan; DENG Qiu-xia; LI Ya-rong; ZHANG Yu-wen
2009-01-01
Supercavitation is a revolutionary technique to achieve high drag reduction for underwater vehicle. It can help us to break through the conventional speed barrier. This article presents a numerical algorithm for ventilated supercavitation flow field based on mixture multiphase flow model, briefs the calculation results and compares them with that tested in high-speed water tunnel and towing tank. The mathematical model, its numerical calculation method, computational region and boundary conditions are discussed in detail. Some pertinent nondimensional parameters about the ventilated supercavitation, such as geometrical configuration of supercavity, drag coefficient and ventilation rate are investigated. Reynolds number is selected to predict gas ventilation rate instead of Froude number. Finally, based on the test and simulation results, a semi-empirical formula of the ventilation rate estimation suitable for different conical angle caritators is proposed.
Various numerical simulation methods for acoustic emission in rock
International Nuclear Information System (INIS)
Acoustic Emission (AE) or Microseismicity (MS) is a very useful method to understand fracture mechanism and to predict serious rock fracture like rockburst. This method can be applied to monitor reservoirs where water and gas are injected, for example, in underground sequestration of carbon dioxide and in Enhanced Oil Recovery (EOR) of petroleum industry. If a numerical simulation helps to interpret AE monitoring results, AE monitoring would become much more powerful tool for the rock engineering. Thus, in this paper, the authors review various methods that can simulate occurrence of AE events incorporating inhomogeneity of rock. A code of Finite Element Method (FEM) developed by Tang et al., those of Boundary Element Method (BEM) by Napier's and Stephansson's groups and those of Distinct Element Method (DEM) by Shimizu et. al., Fakhimi et al. and Cai et al. are briefly introduced as simulation methods of brittle fracture like rockburst. For simulation of AE events induced by water or gas injection, DEM incorporating Fluid Flow Algorism by Shimizu et al. are introduced, with showing their simulation results of hydraulic fracturing. (author)
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...
Polarity Reversals from Paleomagnetic Observations and Numerical Dynamo Simulations
Amit, Hagay; Leonhardt, Roman; Wicht, Johannes
2010-08-01
Recent advances in the study of geomagnetic field reversals are reviewed. These include studies of the transitional field during the last geomagnetic reversal and the last geomagnetic excursion based on paleomagnetic observations, and analysis of reversals in self-consistent 3D numerical dynamo simulations. Field models inferred from observations estimate reversal duration in the range of 1-10 kyr (depending on site location). The transitional fields during both the Matuyama/Brunhes reversal and the Laschamp excursion are characterized by low-latitude reversed flux formation and subsequent poleward migration. During both events the dipole as well as the non-dipole field energies decrease. However, while the non-dipole energy dominates the dipole energy for a period of 2 kyr in the reversal, the non-dipole energy merely exceeds the dipole energy for a very brief period during the excursion. Numerical dynamo simulations show that stronger convection, slower rotation, and lower electrical conductivity provide more favorable conditions for reversals. A non-dimensional number that depends on the typical length scale of the flow and represents the relative importance of inertial effects, termed the local Rossby number, seems to determine whether a dynamo will reverse or not. Stable polarity periods in numerical dynamos may last about 1 Myr, whereas reversals may last about 10 kyr. Numerical dynamo reversals often involve prolonged dipole collapse followed by shorter directional instability of the dipole axis, with advective processes governing the field variation. Magnetic upwellings from the equatorial inner-core boundary that produce reversed flux patches at low-latitudes of the core-mantle boundary could be significant in triggering reversals. Inferences from the observational and modeling sides are compared. We summarize with an outlook on some open questions and future prospects.
Numerical simulation of motion and deformation of ring bubble along body surface
Institute of Scientific and Technical Information of China (English)
倪宝玉; 张阿漫
2013-01-01
Numerical simulation for fluid flow over an attached rigid body with a deformable ring bubble is analyzed based on the velocity potential theory together with the boundary element method (BEM). The analysis is focused on the axisymmetric case. The bubble surface is treated as a well defined air-liquid interface and is tracked by a mixed Eulerian-Lagrangian method. The points of intersection between the bubble and body are treated, specially in the numerical procedure. The auxiliary function method is adopted to calculate the pressure on the body surface and in the flow field. The convergence study is undertaken to assess the developed numerical method and the computation code. Some case studies are undertaken in which the interactions between the bubble/body and the incoming flow field are simulated. The effects of various physical parameters on the interactions are investigated.
Springback Simulation: Impact of Some Advanced Constitutive Models and Numerical Parameters
Haddag, Badis; Balan, Tudor; Abed-Meraim, Farid
2005-08-01
The impact of material models on the numerical simulation of springback is investigated. The study is focused on the strain-path sensitivity of two hardening models. While both models predict the Bauschinger effect, their response in the transient zone after a strain-path change is fairly different. Their respective predictions are compared in terms of sequential test response and of strip-drawing springback. For this purpose, an accurate and general time integration algorithm has been developed and implemented in the Abaqus code. The impact of several numerical parameters is also studied in order to assess the overall accuracy of the finite element prediction. For some test geometries, both material and numerical parameters are shown to clearly influence the springback behavior at a large extent. Moreover, a general trend cannot always be extracted, thus justifying the need for the finite element simulation of the stamping process.
Numerical simulation of a liquid propellant rocket motor
Salvador, Nicolas M. C.; Morales, Marcelo M.; Migueis, Carlos E. S. S.; Bastos-Netto, Demétrio
2001-03-01
This work presents a numerical simulation of the flow field in a liquid propellant rocket engine chamber and exit nozzle using techniques to allow the results to be taken as starting points for designing those propulsive systems. This was done using a Finite Volume method simulating the different flow regimes which usually take place in those systems. As the flow field has regions ranging from the low subsonic to the supersonic regimes, the numerical code used, initially developed for compressible flows only, was modified to work proficiently in the whole velocity range. It is well known that codes have been developed in CFD, for either compressible or incompressible flows, the joint treatment of both together being complex even today, given the small number of references available in this area. Here an existing code for compressible flow was used and primitive variables, the pressure, the Cartesian components of the velocity and the temperature instead of the conserved variables were introduced in the Euler and Navier-Stokes equations. This was done to permit the treatment at any Mach number. Unstructured meshes with adaptive refinements were employed here. The convective terms were treated with upwind first and second order methods. The numerical stability was kept with artificial dissipation and in the spatial coverage one used a five stage Runge-Kutta scheme for the Fluid Mechanics and the VODE (Value of Ordinary Differential Equations) scheme along with the Chemkin II in the chemical reacting solution. During the development of this code simulating the flow in a rocket engine, comparison tests were made with several different types of internal and external flows, at different velocities, seeking to establish the confidence level of the techniques being used. These comparisons were done with existing theoretical results and with other codes already validated and well accepted by the CFD community.
Numerical simulation of morphodynamic diversity in the World's largest rivers
Nicholas, A.
2012-04-01
The World's largest rivers share many common properties, including gentle longitudinal bed gradients (~ 0.01-0.1 m per km), high mean annual discharges (~ >10,000 cumecs), and sand-sized bed sediment (D50 ~ 0.1-0.4 mm), yet despite these similarities they are characterised by diverse planform patterns and morphodynamic behaviour (including meandering, braided and anabranching river styles). Recent studies have shown that this diversity cannot be explained using existing channel pattern classification schemes that apply to small rivers. Indeed at present, the causes of morphodynamic diversity in the World's largest rivers remain unclear. Moreover, elucidation of process-form interactions in large rivers is hampered by logistical difficulties involved in field data collection, and by the time period over which satellite imagery is available, which is short given the slow rates of channel change in many large rivers. Numerical models provide a further possible approach for investigating large river morphodynamics. However, although many such models exist, they have generally been developed or applied to simulate either meandering or braided rivers, rather than to investigate a range of channel styles. This paper aims to address this shortcoming using a new numerical simulation model, which is applied to explore the controls on morphodynamic diversity in large sand-bed rivers. This model is based on the 2D shallow water equations with secondary circulation correction, with model components representing total sand transport, suspended transport of silt and clay, bank erosion, vegetation growth and floodplain development. Numerical simulations representing time periods of c. 200 years illustrate how a wide range of channel morphologies, including meandering, braided and anabranching channels, may develop from the same initial conditions and external forcing (valley gradient and discharge regime). These results shed light on the process controls on morphodynamic diversity
Numerical Simulation of a Liquid Propellant Rocket Motor
Institute of Scientific and Technical Information of China (English)
Nicolas M.C. Salvador; Marcelo M. Morales; Carlos E.S.S. Migueis; Demétrio Bastos-Netto
2001-01-01
This work presents a numerical simulation of the flow field in a liquid propellant rocket engine chamber and exit nozzle using techniques to allow the results to be taken as starting points for designing those propulsive systems.This was done using a Finite Volume method simulating the different flow regimes which usually take place in those systems. As the flow field has regions ranging from the low subsonic to the supersonic regimes, the numerical code used, initially developed for compressible flows only, was modified to work, proficiently in the whole velocity range. It is well known that codes have been developed in CFD, for either compressible or incompressible flows, the joint treatment of both together being complex even today, given the small number of references available in this area. Here an existing code for compressible flow was used and primitive variables,the pressure, the Cartesian components of the velocity and the temperature instead of the conserved variables were introduced in the Euler and Navier-Stokes equations. This was done to permit the treatment at any Mach number. Unstructured meshes with adaptive refinements were employed here. The convective terms were treated with upwind first and second order methods. The numerical stability was kept with artificial dissipation and in the spatial coverage one used a five stage Runge-Kutta scheme for the Fluid Mechanics and the VODE (Value of Ordinary Differential Equations) scheme along with the Chemkin II in the chemical reacting solution. During the development of this code simulating the flow in a rocket engine, comparison tests were made with several different types of internal and extemal flows, at different velocities, seeking to establish the confidence level of the techniques being used. These comparisons were done with existing theoretical results and with other codes already validated and well accepted by the CFD community.
Recent Development in Numerical Simulation of Enhanced Geothermal Reservoirs
Institute of Scientific and Technical Information of China (English)
Huilin Xing; Yan Liu; Jinfang Gao; Shaojie Chen
2015-01-01
This paper briefly introduces the current state in computer modelling of geothermal reservoir system and then focuses on our research efforts in high performance simulation of en-hanced geothermal reservoir system. A novel supercomputer simulation tool has been developing towards simulating the highly non-linear coupled geomechanical-fluid flow-thermal systems involv-ing heterogeneously fractured geomaterials at different spatial and temporal scales. It is applied here to simulate and visualise the enhanced geothermal system (EGS), such as (1) visualisation of the microseismic events to monitor and determine where/how the underground rupture proceeds during a hydraulic stimulation, to generate the mesh using the recorded data for determining the domain of the ruptured zone and to evaluate the material parameters (i.e., the permeability) for the further numerical analysis and evaluation of the enhanced geothermal reservoir; (2) converting the avail-able fractured rock image/fracture data as well as the reservoir geological geometry to suitable meshes/grids and further simulating the fluid flow in the complicated fractures involving the de-tailed description of fracture dimension and geometry by the lattice Boltzmann method and/or finite element method;(3) interacting fault system simulation to determine the relevant complicated rup-ture process for evaluating the geological setting and the in-situ reservoir properties; (4) coupled thermo-fluid flow analysis of a geothermal reservoir system for an optimised geothermal reservoir design and management. A few of application examples are presented to show its usefulness in simu-lating the enhanced geothermal reservoir system.
Numerical Simulation of Particle Flow in a Sand Trap
Araújo, A D; Maia, L P; Herrmann, H J
2008-01-01
Sand traps are used to measure Aeolian flux. Since they modify the surrounding wind velocity field their gauging represents an important challenge. We use numerical simulations under the assumption of homogeneous turbulence based on FLUENT to systematically study the flow field and trapping efficiency of one of the most common devices based on a hollow cylinder with two slits. In particular, we investigate the dependence on the wind speed, the Stokes number, the permeability of the membrane on the slit and the saltation height.
Numerical Simulations of Static Tested Ramjet Dump Combustor
Javed, Afroz; Chakraborty, Debasis
2016-06-01
The flow field of a Liquid Fuel Ram Jet engine side dump combustor with kerosene fuel is numerically simulated using commercial CFD code CFX-11. Reynolds Averaged 3-D Navier-Stokes equations are solved alongwith SST turbulence model. Single step infinitely fast reaction is assumed for kerosene combustion. The combustion efficiency is evaluated in terms of the unburnt kerosene vapour leaving the combustor. The comparison of measured pressures with computed values show that the computation underpredicts (~5 %) pressures for non reacting cases but overpredicts (9-7 %) for reacting cases.
Modelisation and numerical simulation for bulk crystal growth processes
Energy Technology Data Exchange (ETDEWEB)
Duffar, F.; Dusserre, P.; Barat, C.; Nabot, J.P.
1993-12-31
The aim of this work is to study the relevance of numerical simulation for improving the process control in the field of crystal growth. This investigation focused on the growth of semiconductor and halide crystals by the Bridgman solidification technique, the principle of which is to cool a seeded feed material contained in a crucible, either by pulling the crucible or by decreasing the temperature in the furnace. Calculations are performed with the finite element method, and for comparison, experiments are carried out on Bridgman pulling machines operating either in a laboratory or in industrial plants. Calculations and experimental data have shown a good agreement and a satisfactory reliability.
Numerical Simulation of Chip Formation in Metal Cutting Process
Directory of Open Access Journals (Sweden)
HUANG Meixia
2012-07-01
Full Text Available In order to study the chip formation mechanism in metal cutting process, based on finite element software ABAQUS, establish finite element model, and carry out numerical simulation on serrated chip formation of Ni-base superalloy GH4169 and ribbon chip formation of 45# steel respectively.In addition, analyze the influence law of three factors (cutting speed, feed rate, back cutting depth on cutting force and the distribution rule of cutting heat in serrated chip formation of GH4169.
Numerical simulation of bosonic-superconducting-string interactions
Energy Technology Data Exchange (ETDEWEB)
Laguna, P. (Department of Physics and Atomspheric Science, Drexel University, Philadelphia, Pennsylvania 19104 (USA)); Matzner, R.A. (Department of Physics, University of Texas, Austin, Texas 78712 (USA) Center for Relativity, The University of Texas at Austin, Austin, Texas 78712 (USA))
1990-03-15
Numerical simulations show that bosonic superconducting U(1) gauge cosmic strings interact by reconnecting and chopping off in a fashion similar to nonconducting strings. Cancellation of the electromagnetic current occurs when, in one of the strings, the direction of the U(1) gauge magnetic field is opposite to the electromagnetic current flow. Electric charge accumulates on the segments of the reconnected strings where the current is discontinuous or vanishes. A {ital virtual} {ital photon} appears after the collision and intercommutation, and a bubble of electromagnetic radiation emerges as the currents in the reconnected strings equalize. These phenomena suggest new possible mechanisms for void production in the large-scale distribution of galaxies.
Numerical Simulation of mobile BEC-impurity interaction
Lausch, Tobias; Grusdt, Fabian; Fleischhauer, Michael; Widera, Artur
2016-05-01
Cooling atoms to temperatures, where quantum effects become dominant, has become a standard in cold atom experiments. Especially interactions of quantum baths such as fermi gases and the implementation of impurities, which form fermi polarons, have been studied theoretically and experimentally in detail. However, detailed experiments on the bose polaron and the interaction between impurities and a bose gas are still elusive. We consider a model, where we immerse a single impurity into a BEC, which is described by Bogoliubov approximation. From the master equation, we derived the impurity's momentum resolved scattering and cooling dynamics for numerical simulations. Such cooling processes should enable momentum resolved radio-frequency spectroscopy of the BEC polaron.
NUMERICAL SIMULATION FOR DEFORMATION OF NANO-GRAINED METALS
Institute of Scientific and Technical Information of China (English)
杨卫; 洪伟
2002-01-01
Electro-deposition technique is capable of producing nano-grainedbulk copper specimens that exhibit superplastic extensibility at room temperature.Metals of such small grain sizes deform by grains sliding, with little distortion occur-ring in the grain cores. Accommodation mechanisms such as grain boundary diffusion,sliding and grain rotation control the kinetics of the process. Actual deformation min-imizes the plastic dissipation and stored strain energy for representative steps of grainneighbor switching. Numerical simulations based on these principles are discussed inthis paper.
Numerical Simulation of Phenolic Sheet Molding Compound in Compression Molding
Institute of Scientific and Technical Information of China (English)
MEI Qi-lin; YAN Shi-lin; HUANG Zhi-xiong
2003-01-01
Based on generalized Hele-Shaw (GHS) model, a numerical simulation of phenolic sheet molding compound (P-SMC) in compression molding is realized by finite element step-by-step computing method. Finite elemental computing and post analysis programs have been written. The compression mold filling process, time and pressure requirements of P-SMC in a closed mold are predicted, and a good agreement is shown when compared with experiments. It will be of theoretical significance for the mold design and the optimization of the technological parameters in the compression molding of sheet molding compound.
High performance Python for direct numerical simulations of turbulent flows
2016-01-01
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 v...
2D numerical simulation of the resistive reconnection layer
International Nuclear Information System (INIS)
In this paper the authors present a two-dimensional numerical simulation of a reconnection current layer in incompressible resistive magnetohydrodynamics with uniform resistivity in the limit of very large Lundquist numbers. They use realistic boundary conditions derived consistently from the outside magnetic field, and they also take into account the effect of the backpressure from flow into the separatrix region. They find that within a few Alfven times the system reaches a steady state consistent with the Sweet-Parker model, even if the initial state is Petschek-like
Numerical simulation of lava flows: Applications to the terrestrial planets
Zimbelman, James R.; Campbell, Bruce A.; Kousoum, Juliana; Lampkin, Derrick J.
1993-03-01
Lava flows are the visible expression of the extrusion of volcanic materials on a variety of planetary surfaces. A computer program described by Ishihara et al. appears to be well suited for application to different environments, and we have undertaken tests to evaluate their approach. Our results are somewhat mixed; the program does reproduce reasonable lava flow behavior in many situations, but we have encountered some conditions common to planetary environments for which the current program is inadequate. Here we present our initial efforts to identify the 'parameter space' for reasonable numerical simulations of lava flows.
Direct numerical simulations of high speed reactive mixing layers
International Nuclear Information System (INIS)
The present work is devoted to the analysis of ignition phenomena in high speed turbulent reactive flows. From the computational modelling point of view, this requires to account accurately for the competition between molecular diffusion effects and chemical kinetics as well as complex flowfield structures that may feature shock and expansion waves. Some results of direct numerical simulations of the multicomponent, compressible, reactive Navier-Stokes equations are reported here for the particular case of a two-dimensional mixing layer. Special emphasis is placed on the effects associated with heat release.
Numerical simulation of compact intracloud discharge and generated electromagnetic pulse
Babich, L. P.; Bochkov, E. I.; Kutsyk, I. M.
2015-06-01
Using the concept of the relativistic runaway electron avalanche, numerical simulation of compact intracloud discharge as a generator of powerful natural electromagnetic pulses (EMPs) in the HF-UHF range was conducted. We evaluated the numbers of electrons initiating the avalanche, with which the calculated EMP characteristics are consistent with measured ones. The discharge capable of generating EMPs produces runaway electrons in numbers close to those in the source of terrestrial γ-flashes (TGF) registered in the nearest space, which may be an argument for a joint EMP and TGF source.
Numerical Simulation Model of Laminar Hydrogen/Air Diffusion Flame
Institute of Scientific and Technical Information of China (English)
于溯源; 吕雪峰
2002-01-01
A numerical simulation model is developed for a laminar hydrogen/air diffusion flame. Nineteen species and twenty chemical reactions are considered. The chemical kinetics package (CHEMKIN) subroutines are employed to calculate species thermodynamic properties and chemical reaction rate constants. The flow field is calculated by simultaneously solving a continuity equation, an axial momentum equation and an energy equation in a cylindrical coordinate system. Thermal diffusion and Brownian diffusion are considered in the radial direction while they are neglected in the axial direction. The results suggest that the main flame is buoyancy-controlled.
Diffusive mesh relaxation in ALE finite element numerical simulations
Energy Technology Data Exchange (ETDEWEB)
Dube, E.I.
1996-06-01
The theory for a diffusive mesh relaxation algorithm is developed for use in three-dimensional Arbitary Lagrange/Eulerian (ALE) finite element simulation techniques. This mesh relaxer is derived by a variational principle for an unstructured 3D grid using finite elements, and incorporates hourglass controls in the numerical implementation. The diffusive coefficients are based on the geometric properties of the existing mesh, and are chosen so as to allow for a smooth grid that retains the general shape of the original mesh. The diffusive mesh relaxation algorithm is then applied to an ALE code system, and results from several test cases are discussed.
Modelisation and numerical simulation for bulk crystal growth processes
International Nuclear Information System (INIS)
The aim of this work is to study the relevance of numerical simulation for improving the process control in the field of crystal growth. This investigation focused on the growth of semiconductor and halide crystals by the Bridgman solidification technique, the principle of which is to cool a seeded feed material contained in a crucible, either by pulling the crucible or by decreasing the temperature in the furnace. Calculations are performed with the finite element method, and for comparison, experiments are carried out on Bridgman pulling machines operating either in a laboratory or in industrial plants. Calculations and experimental data have shown a good agreement and a satisfactory reliability
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 [1]. 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 Simulation of Wakes in a Weakly Stratified Fluid
Rottman, James W; Innis, George E; O'Shea, Thomas T; Novikov, Evgeny
2014-01-01
This paper describes some preliminary numerical studies using large eddy simulation of full-scale submarine wakes. Submarine wakes are a combination of the wake generated by a smooth slender body and a number of superimposed vortex pairs generated by various control surfaces and other body appendages. For this preliminary study, we attempt to gain some insight into the behavior of full-scale submarine wakes by computing separately the evolution the self-propelled wake of a slender body and the motion of a single vortex pair in both a non-stratified and a stratified environment. An important aspect of the simulations is the use of an iterative procedure to relax the initial turbulence field so that turbulent production and dissipation are in balance.
Numerical simulation of spinning detonation in square tube
Tsuboi, Nobuyuki; Asahara, Makoto; Eto, Keitaro; Hayashi, A. Koichi
2008-09-01
A single spinning detonation wave propagating in a square tube is simulated three-dimensionally with the detailed chemical reaction mechanism for hydrogen/air mixture proposed by Petersen and Hanson. The spinning detonation is composed of a transverse detonation rotating around the wall normal to the tube axis, triple lines propagating partially out of phase, and a short pressure trail. The formation of an unburned gas pocket behind the detonation front was not observed in the present simulations because the rotating transverse detonation completely consumed the unburned gas. The calculated profiles of instantaneous OH mass fraction have a keystone shape behind the detonation front. The numerical results for the pitch and track angle on the tube wall agree well with the experimental results.
Numerical simulations of heat transfer in plane channel flow
Gharbi, Najla El; Benzaoui, Ahmed
2010-01-01
Reynolds-averaged Navier-Stokes (RANS) turbulence models (such as k-{\\epsilon} models) are still widely used for engineering applications because of their relatively simplicity and robustness. In fully developed plane channel flow (i.e. the flow between two infinitely large plates), even if available models and near-wall treatments provide adequate mean flow velocities, they fail to predict suitable turbulent kinetic energy "TKE" profiles near walls. TKE is involved in determination of eddy viscosity/diffusivity and could therefore provide inaccurate concentrations and temperatures. In order to improve TKE a User Define Function "UDF" based on an analytical profile for TKE was developed and implemented in Fluent. Mean streamwise velocity and turbulent kinetic energy "TKE" profiles were compared to DNS data for friction Reynolds number $Re_{\\tau}$ = 150. Simulation results for TKE show accurate profiles. Simulation results for horizontal heated channel flows obtained with Fluent are presented. Numerical result...
Numerical simulation of the evolution of glacial valley cross sections
Seddik, Hakime; Sugiyama, Shin; Naruse, Renji
2009-01-01
A numerical model was developed for simulating the formation of U-shaped glacial valleys by coupling a two-dimensional ice flow model with an erosion model for a transverse cross section. The erosion model assumes that the erosion rate varies quadratically with sliding speed. We compare the two-dimensional model with a simple shallow-ice approximation model and show the differences in the evolution of a pre-glacial V-shaped valley profile using the two models. We determine the specific role of the lateral shear stresses acting on the glacier side walls in the formation of glacial valleys. By comparing the model results with field data, we find that U-shaped valleys can be formed within 50 ka. A shortcoming of the model is that it primarily simulates the formation of glacial valleys by deepening, whereas observed valleys apparently have formed mainly by widening.
Numerical simulation of low pressure die-casting aluminum wheel
Institute of Scientific and Technical Information of China (English)
Mi Guofa; Liu Xiangyu; Wang Kuangfei; Fu Hengzhi
2009-01-01
The FDM numerical simulation software, ViewCast system, was employed to simulate the low pressure die casting (LPDC) of an aluminum wheel. By analyzing the mold-filling and solidification stage of the LPDC process, the distribution of liquid fraction, temperature field and solidification pattern of castings were studied. The potential shrinkage defects were predicted to be formed at the rim/spoke junctions, which is in consistence with the X-ray detection result. The distribution pattern of the defects has also been studied. A solution towards reducing such defects has been presented. The cooling capacity of the mold was improved by installing water pipes both in the side mold and the top mold. Analysis on the shrinkage defects under forced cooling mode proved that adding the cooling system in the mold is an effective method for reduction of shrinkage defects.
Numerical simulations of undulatory swimming at moderate Reynolds number.
Eldredge, Jeff D
2006-12-01
We perform numerical simulations of the swimming of a three-linkage articulated system in a moderately viscous regime. The computational methodology focuses on the creation, diffusion and transport of vorticity from the surface of the bodies into the fluid. The simulations are dynamically coupled, in that the motion of the three-linkage swimmer is computed simultaneously with the dynamics of the fluid. The novel coupling scheme presented in this work is the first to exploit the relationship between vorticity creation and body dynamics. The locomotion of the system, when subject to undulatory inputs of the hinges, is computed at Reynolds numbers of 200 and 1000. It is found that the forward swimming speed increases with the Reynolds number, and that in both cases the swimming is slower than in an inviscid medium. The vortex shedding is examined, and found to exhibit behavior consistent with experimental flow visualizations of fish. PMID:17671314
Numerical simulations of the 'jet' in the Crab nebula
International Nuclear Information System (INIS)
Observations and earlier models of the 'jet' in the Crab nebula are reviewed, and a new model, in which the 'jet' is formed by material from the supernova remnant propagating up the interior of a cooled star trail left by the progenitor, is described. This model is similar to a previous model for the 'jet', but differs in that the 'jet' lies in the plane of the sky, and the Crab's progenitor moves supersonically rather than subsonically through the interstellar medium. Numerical simulations indicate that the model offers a successful description of the structure of the 'jet'. In the light of these simulation we conclude that the nebula is situated within the warm component of the interstellar medium, and that its proposed outer halo does not exist. (author)
Numerical simulations of ultrasimple ultrashortlaser-pulse measurement.
Liu, Xuan; Trebino, Rick; Smith, Arlee V
2007-04-16
We numerically simulate the performance of the ultrasimple frequency-resolved-optical-gating (FROG) technique, GRENOUILLE, for measuring ultrashort laser pulses. While simple in practice, GRENOUILLE has many theoretical subtleties because it involves the second-harmonic generation of relatively tightly focused and broadband pulses. In addition, these processes occur in a thick crystal, in which the phase-matching bandwidth is deliberately made narrow compared to the pulse bandwidth. In these simulations, we include all sum-frequency-generation processes, both collinear and noncollinear. We also include dispersion using the Sellmeier equation for the crystal BBO. Working in the frequency domain, we compute the GRENOUILLE trace for practical-and impractical- examples and show that accurate measurements are easily obtained for properly designed devices. PMID:19532705
Numerical simulation of low pressure die-casting aluminum wheel
Directory of Open Access Journals (Sweden)
Mi Guofa
2009-02-01
Full Text Available The FDM numerical simulation software, ViewCast system, was employed to simulate the low pressure die casting (LPDC of an aluminum wheel. By analyzing the mold-fi lling and solidifi cation stage of the LPDC process, the distribution of liquid fraction, temperature field and solidification pattern of castings were studied. The potential shrinkage defects were predicted to be formed at the rim/spoke junctions, which is in consistence with the X-ray detection result. The distribution pattern of the defects has also been studied. A solution towards reducing such defects has been presented. The cooling capacity of the mold was improved by installing water pipes both in the side mold and the top mold. Analysis on the shrinkage defects under forced cooling mode proved that adding the cooling system in the mold is an effective method for reduction of shrinkage defects.
A Physical Numerical Ionospheric Model and Its Simulation Results
Institute of Scientific and Technical Information of China (English)
ZHANG Man-Lian; Radicella Sandro M.; SHANG She-Ping
2004-01-01
This paper describes the construction of a one-dimensional time-dependent theoretical ionospheric model,which is based onnumerical solution of continuity and momentum equations for O+, O+2, N+2, and NO+. The model is designed to have an option to incorporate the observational ionospheric characteristic parameters into the numerical model to indirectly determine the upper boundary condition when solving the transport equations of O+. A preliminary simulation result of the model when used to simulate the ionosphere during April 18 ～ May 10, 1998, which includes both quiet and disturbed periods, showed that the model constructed is able to reproduce the observational results reasonably well both for quiet and disturbed periods.
Numerical simulations of energy transfer in counter-streaming plasmas
International Nuclear Information System (INIS)
Collisionless shock formation is investigated with large scale fully electromagnetic two-dimensional Particle-in-Cell numerical simulations. Two plasmas are colliding in the center of mass reference frame at sub-relativistic velocities. Their interaction leads to collisionless stochastic electron heating, ion slowing down and formation of a shock front. We focus here on the initial stage of evolution where electron heating is due to the Weibel-like micro-instability driven by the high-speed ion flow. A two stage process is described in the detailed analysis of our simulation results. Filament generation, followed by turbulent mixing, constitute the dominant mechanism for energy repartition. The global properties are illustrated by examination of single filament evolution in terms of energy/particle density and fields. (authors)
Hassan, D.; Ritter, Markus
2011-01-01
The present paper deals with steady and unsteady aeroelastic simulation results obtained on the High Reynolds Number Aero-Structural Dynamics (HIRENASD) wind tunnel configuration [1], selected as common test case in the numerical aeroelasticity ONERA/DLR cooperation project “NLAS2”. In order to assess the aeroelastic prediction capabilities of the flow solvers elsA (ONERA) and TAU (DLR), 3 types of simulations have been realized: static coupling, harmonic forced motion and dynamic coupling...
Numerical simulation and design of a thermionic electron gun
Hoseinzade, M.; Nijatie, M.; Sadighzadeh, A.
2016-05-01
This paper reports the simulation of an electron gun. The effects on the beam quality of some parameters on the beam quality were studied and optimal choices were identified. It gives numerical beam qualities for a common electrostatic triode gun, and the dependencies on design parameters such as electrode geometries and bias voltages to these electrodes are shown. An electron beam of diameter 5 mm with energy of 5 keV was assumed for the simulation process. Some design parameters were identified as variable parameters in the presence of space charge. These parameters are the inclination angle of emission electrode, the applied voltage to the focusing electrode, the gap width between the emission electrode and the focusing electrode and the diameter of the focusing electrode. The triode extraction system is designed and optimized by using CST software (for Particle Beam Simulations). The physical design of the extraction system is given in this paper. From the simulation results, it is concluded that the inclination angle of the emission electrode is optimized at 22.5°, the applied voltage to the focusing electrode was optimized and found to be V foc = ‑600 V, the optimal separation distance (gap between emission electrode and focusing electrode) is 4 mm, and the optimal diameter of the emission electrode is 14 mm. Initial results for these efforts aimed at emittance improvement are also given.
Real-time numerical simulation of the Carnot cycle
International Nuclear Information System (INIS)
We developed a highly interactive, multi-windows Java applet which made it possible to simulate and visualize within any platform and internet the Carnot cycle (or engine) in a real-time computer experiment. We extended our previous model and algorithm (Galant et al 2003 Heat Transfer, Newton's Law of Cooling and the Law of Entropy Increase Simulated by the Real-Time Computer Experiments in Java (Lecture Notes in Computer Science vol 2657) pp 45-53, Gall and Kutner 2005 Molecular mechanisms of heat transfer: Debye relaxation versus power-law Physica A 352 347-78) to simulate not only the heat flow but also the macroscopic movement of the piston. Since in reality it is impossible to construct a reversible Carnot engine, the question arises whether it is possible to simulate it at least in a numerical experiment? The positive answer to this question which we found is related to our model and algorithm which make it possible to omit the many-body problem arising when many gas particles simultaneously interact with the mobile piston. As usual, the considerations of phenomenological thermodynamics began with a study of the basic properties of heat engines, hence our approach, besides intrinsic physical significance, is also important from the educational, technological and even environmental points of view
Direct numerical simulation of water droplet coalescence in the oil
International Nuclear Information System (INIS)
Highlights: ► VOF computational technique has been used to simulate coalescence of two water droplets in oil. ► The model was validated with the experimental data for binary droplet coalescence. ► Based on the CFD simulation results a correlation has been proposed to predict the coalescence time. - Abstract: Coalescence of two water droplets in the oil was simulated using Computational Fluid Dynamics (CFD) techniques. The finite volume numerical method was applied to solve the Navier–Stokes equations in conjunction with the Volume of Fluid (VOF) approach for interface tracking. The effects of some parameters consisting of the collision velocity, off-center collision parameter, oil viscosity and water–oil interfacial tension on the coalescence time were investigated. The simulation results were validated against the experimental data available in the literature. The results revealed that quicker coalescence could be achieved if the head-on collisions occur or the droplets approach each other with a high velocity. In addition, low oil viscosities or large water–oil interfacial tensions cause less coalescence time. Moreover, a correlation was developed to predict coalescence efficiency as a function of the mentioned parameters.
Numerical Simulation of Transient Gauss pulse Coupling through Small Apertures
Directory of Open Access Journals (Sweden)
Jinshi Xiao
2011-08-01
Full Text Available Transient electromagnetic pulse (EMP can easily couple into equipments through small apertures in its shells. To study the coupling effects of transient Gauss pulse to a cubic cavity with openings, coupling course is simulated using sub-gridding finite difference in time domain (FDTD algorithm in this paper. A new grid partition approach is provided to simulate each kind of apertures with complex shapes. With this approach, the whole calculation space is modeled, and six kinds of aperture with different shapes are simulated. Coupling course is simulate in the whole time domain using sub-gridding FDTD approach. Selecting apertures with dimension of several millimeters to research, coupled electric field waveform, power density and coupling coefficient are calculated. The affect on coupling effects by varied incident angle and varied pulse width are also analyzed. The main conclusion includes interior resonance phenomenon, increase effect around rectangle aperture and several distributing rules of coupled electric field in the cavity. The correctness of these results is validated by comparing with other scholars’ results. These numerical results can help us to understand coupling mechanism of the transient Gauss pulse.
Numerical simulation of a DFB - fiber laser sensor (part 1
Directory of Open Access Journals (Sweden)
Dan SAVASTRU
2010-06-01
Full Text Available This paper presents the preliminary results obtained in developing a numerical simulationanalysis of fiber optic bending sensitivity aiming to improve the design of fiber lasers. The developednumerical simulation method relies on an analysis of both the fundamental mode propagation alongan optical fiber and of how bending of this fiber influence the optical radiation losses. The cases ofsimple, undoped and of doped with Er3+ ions optical fibers are considered. The presented results arebased on numerical simulation of eigen-modes of a laser intensity distribution by the use of finiteelement method (FEM developed in the frame of COMSOL software package. The numericalsimulations are performed by considering the cases of both normal, non-deformed optic fiber and ofsymmetrically deformed optic fiber resembling micro-bending of it. Both types of fiber optic bendinglosses are analyzed, namely: the transition loss, associated with the abrupt or rapid change incurvature at the beginning and the end of a bend, and pure bend loss is associated with the loss fromthe bend of constant curvature in between.
The Numerical Simulation of Infrasound Generated by Convective Storms
Schecter, D.; Nicholls, M. E.
2009-12-01
Recent observations and theoretical considerations suggest that a developing tornado has a detectable signature in the infrasound of a severe weather system [A.J. Bedard Jr., Mon. Weather Rev., 133, 241 (2005)]. In order to reliably distinguish the vortex signal from extraneous noise, it is essential to advance current understanding of the various mechanisms that produce infrasound in atmospheric convection. Without detailed observations of the acoustic sources within a storm, numerical modeling may be the best method of investigation. Here, we consider the feasibility of using a special version of the Regional Atmospheric Modeling System (RAMS) that is customized to simulate aeroacoustics. Comparison to analytical results demonstrates that the customized model adequately generates the infrasound of tornado-like vortices, and of basic diabatic cloud processes. Sensitivity to the microphysics parameterization is briefly addressed. Provisional simulations suggest that a moderate-to-strong tornado can adiabatically generate infrasound of much greater intensity than the infrasound of a generic hail-producing thunderstorm, in the 0.1-3 Hz frequency range [D.A. Schecter et al., J. Atmos. Sci., 65, 685 (2008)]. More detailed numerical studies are underway to verify this conclusion, and to further understand the production of infrasound in a broad spectrum of convective systems, ranging from non-precipitating cumuli to tornadic thunderstorms.
Three-dimensional numerical simulation of detonations in coaxial tubes
Tsuboi, Nobuyuki; Daimon, Yu; Hayashi, A. Koichi
2008-10-01
Three-dimensional numerical simulation of detonations in both a circular tube and a coaxial tube are simulated to reveal characteristics of single spinning and two-headed detonations. The numerical results show a feature of a single spinning detonation which was discovered in 1926. Transverse detonations are observed in both tubes, however, the single spinning mode maintains the complex Mach reflection whereas the two-headed mode develops periodically from the single Mach reflection to the complex one. The calculated cell aspect ratio for the two-headed mode changes from 1.09 to 1.34 as the radius of axial insert increases from r 1/ R = 0.1 to 0.9. The calculated cell aspect ratio for r 1/ R = 0.1 is close to the experimental results without an axial insert. The formation of an unreacted gas pocket behind the detonation front was not observed in the single spinning mode; however, the two-headed mode has unreacted gas pocket behind the front near the axial insert.
Modelling and numerical simulation of liquid-vapor phase transitions
International Nuclear Information System (INIS)
This work deals with the modelling and numerical simulation of liquid-vapor phase transition phenomena. The study is divided into two part: first we investigate phase transition phenomena with a Van Der Waals equation of state (non monotonic equation of state), then we adopt an alternative approach with two equations of state. In the first part, we study the classical viscous criteria for selecting weak solutions of the system used when the equation of state is non monotonic. Those criteria do not select physical solutions and therefore we focus a more recent criterion: the visco-capillary criterion. We use this criterion to exactly solve the Riemann problem (which imposes solving an algebraic scalar non linear equation). Unfortunately, this step is quite costly in term of CPU which prevent from using this method as a ground for building Godunov solvers. That is why we propose an alternative approach two equations of state. Using the least action principle, we propose a phase changing two-phase flow model which is based on the second thermodynamic principle. We shall then describe two equilibrium submodels issued from the relaxations processes when instantaneous equilibrium is assumed. Despite the weak hyperbolicity of the last sub-model, we propose stable numerical schemes based on a two-step strategy involving a convective step followed by a relaxation step. We show the ability of the system to simulate vapor bubbles nucleation. (author)
Numerical Simulation of Oil Jet Lubrication for High Speed Gears
Directory of Open Access Journals (Sweden)
Tommaso Fondelli
2015-01-01
Full Text Available The Geared Turbofan technology is one of the most promising engine configurations to significantly reduce the specific fuel consumption. In this architecture, a power epicyclical gearbox is interposed between the fan and the low pressure spool. Thanks to the gearbox, fan and low pressure spool can turn at different speed, leading to higher engine bypass ratio. Therefore the gearbox efficiency becomes a key parameter for such technology. Further improvement of efficiency can be achieved developing a physical understanding of fluid dynamic losses within the transmission system. These losses are mainly related to viscous effects and they are directly connected to the lubrication method. In this work, the oil injection losses have been studied by means of CFD simulations. A numerical study of a single oil jet impinging on a single high speed gear has been carried out using the VOF method. The aim of this analysis is to evaluate the resistant torque due to the oil jet lubrication, correlating the torque data with the oil-gear interaction phases. URANS calculations have been performed using an adaptive meshing approach, as a way of significantly reducing the simulation costs. A global sensitivity analysis of adopted models has been carried out and a numerical setup has been defined.
Numerical simulation system for environmental studies: SPEEDI-MP
International Nuclear Information System (INIS)
A numerical simulation system SPEEDI-MP has been developed to apply for various environmental studies. SPEEDI-MP consists of dynamical models and material transport models for the atmospheric, terrestrial, and oceanic environments, meteorological and geographical database for model inputs, and system utilities for file management, visualization, analysis, etc., using graphical user interfaces (GUIs). As a numerical simulation tool, a model coupling program (model coupler) has been developed. It controls parallel calculations of several models and data exchanges among them to realize the dynamical coupling of the models. A coupled model system for water circulation has been constructed with atmosphere, ocean, wave, hydrology, and land-surface models using the model coupler. System utility GUIs are based on the Web technology, allowing users to manipulate all the functions on the system using their own PCs via the internet. In this system, the source estimation function in the atmospheric transport model can be executed on the grid computer system. Performance tests of the coupled model system for water circulation were also carried out for the flood event at Saudi Arabia in January 2005 and the storm surge case by the hurricane KATRINA in August 2005. (author)
Constitutive Modeling and Numerical Simulation of Frp Confined Concrete Specimens
Smitha, Gopinath; Ramachandramurthy, Avadhanam; Nagesh, Ranganatha Iyer; Shahulhameed, Eduvammal Kunhimoideen
2014-09-01
Fiber-reinforced polymer (FRP) composites are generally used for the seismic retrofit of concrete members to enhance their strength and ductility. In the present work, the confining effect of Carbon Fiber-Reinforced Polymer (CFRP) composite layers has been investigated by numerical simulation. The numerical simulation has been carried out using nonlinear finite element analysis (FEA) to predict the response behaviour of CFRP-wrapped concrete cylinders. The nonlinear behaviour of concrete in compression and the linear elastic behaviour of CFRP has been modeled using an appropriate constitutive relationship. A cohesive model has been developed for modeling the interface between the concrete and CFRP. The interaction and damage failure criteria between the concrete to the cohesive element and the cohesive element to the CFRP has also been accounted for in the modeling. The response behaviour of the wrapped concrete specimen has been compared with the proposed interface model and with a perfectly bonded condition. The results obtained from the present study showed good agreement with the experimental load-displacement response and the failure pattern in the literature. Further, a sensitivity analysis has been carried out to study the effect of the number of layers of CFRP on the concrete specimens. It has been observed that wrapping with two layers was found to be the optimum, beyond which the response becomes flexible but with a higher load-carrying capacity
Numerical simulation of pressure fluctuation in Kaplan turbine
Institute of Scientific and Technical Information of China (English)
2008-01-01
As it is almost impossible to carry out the prototype hydro-turbine experiment be- fore the power plant is built up, rational prediction of pressure fluctuations in the prototype turbine is very important at the design stage. From this viewpoint, we at first treated the unsteady turbulent flow computation based on the modified RNG k-ε turbulence model through the whole flow passage to simulate the pressure fluctuation in a model turbine. Since fair agreement was recognized between the numerical results and the experimental data, this numerical method was applied to simulate the pressure fluctuations in the prototype turbine. From the comparison of them with the model turbine results, it is seen that their qualitative trend of pres- sure fluctuations are similar, but an appreciable difference is observed between the amplitudes of pressure fluctuation of the prototype turbine and that of the model turbine. Though the present findings may be explained by the effect of Reynolds number, further studies are expected for quantitative interpretation. We paid atten- tion to the interaction between the fluid and turbine structure. Adopting a weak fluid-solid coupling method, we studied the pressure fluctuation in the prototype turbine to clarify how the elastic behavior of runner blades influenced the charac- teristics of pressure fluctuation.
Numerical simulation of mechanical breakup of river ice-cover
Institute of Scientific and Technical Information of China (English)
WANG Jun; HE Liang; CHEN Pang-pang; SUI Jueyi
2013-01-01
Ice jams and ice dams in rivers will cause significant rises of water levels.Under extreme conditions,the ice flooding during winter or early spring may occur.In this paper,by considering the fluid-solid coupling effect caused by the water and the ice cover,the mechanisms of the mechanical breakup of the river ice cover are studied.A formula is obtained for determining whether or not the mechanical breakup process would happen under the hydraulic pressure of the flow.Combined with the hydraulic model under the ice covered flow,a numerical model is built and the interaction between the discharge,the hydraulic pressure under the ice cover and the date for the mechanical breakup of the river ice cover is simulated.The simulated results of the dates for the mechanical breakup of the river ice cover agree very well with the field observations of the breakups of the river ice cover in the Hequ Reach of the Yellow River.Therefore,the numerical model might serve as a good preliminary step in studying the breakup of the river ice-cover,evidencing many important parameters that affect the ice-cover process.
Numerical simulation static-bed drying of barley
Energy Technology Data Exchange (ETDEWEB)
Mandas, N. [Universita di Cagliari (Italy). Dipartimento d' Ingegneria Meccanica; Habte, M. [Addis Ababa University (Ethiopia). Mechanical Engineering Department
2002-07-01
The last decade has seen enormous progress in mathematical modelling and numerical simulation in areas related with fluid dynamics and heat and mass transfer. This is because of the increasingly widespread use of powerful, low-cost digital computers. Future efforts should be directed towards developing computer codes that can be implemented by users who may not be well versed in computational skills. Here a computer program has been developed, for simulating a non-equilibrium mathematical model for static-deep-bed drying of barley. The model consists of a set of four non-linear partial differential equations as a result of mass and energy balances and heat transfer equations, together with appropriate diffusion equation. The set of equations is solved by means of a finite-difference method, using a second-order iterative predictor-corrector process to solve the first two equations in the time domain, and a first-order iterative process for the second two, in the space domain. Published experimental results are used to validate the model. The numerical results are in good agreement with the experimental data relative to heated-air drying system, and the prediction accuracy is enhanced with respect to equilibrium models. (author)
Numerical simulation of deep-level rockburst in Fuxin coalfield
Institute of Scientific and Technical Information of China (English)
TANG Ju-peng; PAN Yi-shan; LI Ying-jie
2005-01-01
On the basis of ANSYS finite element model(FEM) software, the deep-leve lrockburst in Fuxin coalfield was simulated numerically. Based on Haizhou Mine and Wulong Mine as two typical deep-level rockburst examples in Fuxin coalfield, the rules and characteristics of the deep-level rockburst were analyzed. And the models were established. For Haizhou mine, the relationship between mining distance and rockburst was presented when 100, 300, 600 m were mined in 3313 working face. When 300 mwere mined, the rockburst began to emerge. When 600 m were mined, the rockburst was the most possible to happen and the compression stress of the working face reached to the maximum value. The effect of tectonic stress on synclinal axis is also a key factor to rockburst occurrence. This was verified by the rockburst happened when 496 m were mined. For Wulong mine, based on the 311 working face as an example,the contours of Y stress in the roof and floor were obtained when the mining distance were 100, 200, 300 and 400 m. When 100 and 400 m were mined, the high stress concentration regions occurred in the front of working face. This shows the rockburst is easy to happen. It is confirmed by the rockburst when 91m were mined in 311 working plane.The above indicates that the numerical simulation has instructive rule to study the deep-level rockburst in Fuxin coalfield.
STOCHASTIC ALGORITHM AND NUMERICAL SIMULATION FOR DROP SCAVENGING OF AEROSOLS
Institute of Scientific and Technical Information of China (English)
ZHAO Hai-bo; ZHENG Chu-guang
2006-01-01
The time evolution of aerosol size distribution during precipitation, which is founded mathematically by general dynamic equation (GDE) for wet removal, describes quantitatively the process of aerosol wet scavenging. The equation depends on aerosol size distribution, raindrop size distribution and the complicated model of scavenging coefficient which is induced by taking account of the important wet removal mechanisms such as Brownian diffusion, interception and inertial impaction. Normal numerical methods can hardly solve GDE, which is a typical partially integro-differential equation. A new multi-Monte Carlo method was introduced to solve GDE for wet removal, and then was used to simulate the wet scavenging of aerosols in the real atmospheric environment. The results of numerical simulation show that, the smaller lognormal raindrop size distribution and lognormal initial aerosol size distribution, the smaller geometric mean diameter or geometric standard deviation of raindrops can help scavenge small aerosols and intermediate size aerosols better, though large aerosols are prevented from being collected in some ways.
Internal waves generated by unsteady impulsive forcing - numerical simulations
Paoletti, Matthew; Shipley, Kara; Brandt, Alan
2014-11-01
Numerical simulations of the generation of internal waves by an unsteady impulse are presented. While extensive work has examined the generation of internal waves by steady flow, such as winds over mountains, or periodic flow, an example being tidal flow over bathymetry, internal waves can also be generated by transient events like those produced by local instabilities. The studies presented here focus on the generation of internal waves by the release of a patch of miscible fluid of constant density into a stably stratified water column. The fluid descends owing to its initial momentum, spreads in the lateral direction, and vertically displaces the isopycnals, leading to the generation of internal waves. The transfer of energy from the impulse to the internal wave field is characterized by the energy flux of the radiated internal waves. While the impulse is initially axisymmetric, the effects of the three-dimensional nature of the turbulent evolution are examined by comparing the results of two-dimensional and three-dimensional numerical simulations. Supported by the Office of Navel Research.
Fast ignition physics and its requirements to numerical simulation
International Nuclear Information System (INIS)
Fast ignition is a new igniting scheme for inertial confinement fusion (ICF). However, the theoretical and experimental researches show that the ignition phase of the fast ignition is very complicated and difficult. The fast ignition research needs a deep and thorough numerical simulation. Based on physical analysis, the requirements of the fast ignition for the numerical simulation are explored, and, at the same time, the problem in the light of the specific conditions of our institute is discussed. The fast ignition mainly includes three processes, those are implosive pre-compression, ultra-intense laser propagation in sub-critical and super-critical plasmas (channeling and boring), and the generation and transportation of hot electrons in plasma, especially in dense plasma, with producing the high-temperature ignition zone. The research considers that for target pre-compression, not only 1D, 2D, but also three-dimensional laser target coupling code are needed; to describe the behavior of hot electron the Fokker-Planck equation considering electric and magnetic fields is suitable, whereas the hydrodynamic motion of the plasma should be two-streaming, with the electrical and magnetic effects included. PIC code could be used to investigate the local details and supply the data needed for solving the mentioned equations. Furthermore, some countries-planed future projects for realizing the fast ignition in a concise way are still stated. (authors)
Shock Simulation of the Optics Mirror Assembly By Numerical Method
Directory of Open Access Journals (Sweden)
Mr. Brijeshkumar Patel
2015-09-01
Full Text Available Satellite faces many extreme types of loading throughout their life time from the harsh launch environment to the critical space environment. Launch load mainly dynamic is the main design concern for space structure. Shocks are the one of the most critical dynamic load occurs in spacecraft. Optics Mirror Assembly (OMA is used in the telescope of the satellite. The telescope performance relies on dimensional control & the geometric positioning of the mirror, pointing accuracy and controlled surface deformation of the mirror; Mirror fixation device (MFD is used for controlling all these factors. It should not distort due to launch loads mainly shocks as well as loads during operation of the telescope. In the present work an attempt has been made to perform experimental and computational analysis of the shock load on Optics Mirror Assembly. The FE modal for Shock Analysis purpose has been analysed with a specific Linear Transient Response Analysis in order to obtain the time history of acceleration in several output points. The analysis has been conducted over the time interval 0 to 62 ms and frequency band between 10 - 10 KHz. In order to verify the feasibility and reliability of the numerical (Implicit Finite Element Code, Nastran analysis, the numerical results obtained by Nastran have been compared with those obtained experimentally in the form of SRS. The overall outcome of the simulation method has proven its reliability in simulating Satellite payloads subjected to shocks.
Influence of clearance model on numerical simulation of centrifugal pump
Wang, Z.; Gao, B.; Yang, L.; Du, W. Q.
2016-05-01
Computing models are always simplified to save the computing resources and time. Particularly, the clearance that between impeller and pump casing is always ignored. But the completer model is, the more precise result of numerical simulation is in theory. This paper study the influence of clearance model on numerical simulation of centrifugal pump. We present such influence via comparing performance, flow characteristic and pressure pulsation of two cases that the one of two cases is the model pump with clearance and the other is not. And the results show that the head decreases and power increases so that efficiency decreases after computing with front and back cavities. Then no-leakage model would improve absolute velocity magnitude in order to reach the rated flow rate. Finally, more disturbance induced by front cavity flow and wear-ring flow would change the pressure pulsation of impeller and volute. The performance of clearance flow is important for the whole pump in performance, flow characteristic, pressure pulsation and other respects.
Numerical simulation of small section rectangular tube in parallel welding
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The welding temperature field and deformation of parallel arrangement small-section rectangular tubes is calculated by using a non-contact model. After comparing the computed results with the experimentally measured results, it shows that there exist big errors when applying this model to the numerical simulation of small-section rectangular tube's welding temperature field and deformation. Based on a simple analysis of the errors, a contact model is presented. The heat transfer and stress analysis between small-section rectangular tubes and clamping fixture are simulated by using direct constraints method, and then the laws of the temperature distribution, which coincide with experiment, are obtained. A further numerical analysis of the stress and deformation are made, it shows that a "T" shaped stress-field is formed in the vicinity of the weld. As the stress-field departs from the centroid of tubes', this leads to the small rectangular tubes not only have a longitudinal deflection, but also have a transverse bending and deformation.
Numerical simulation of tungsten alloy in powder injection molding process
Institute of Scientific and Technical Information of China (English)
ZHENG Zhen-xing; XIA Wei; ZHOU Zhao-yao; ZHU Quan-li
2008-01-01
The flow behavior of feedstock for the tungsten alloy powder in the mold cavity was approximately described using Hele-Shaw flow model. The math model consisting of momentum equation, consecutive equation and thermo-conduction equation for describing the injection process was established. The equations are solved by the finite element/finite difference hybrid method that means dispersing the feedstock model with finite element method, resolving the model along the depth with finite difference methpd, and tracking the movable boundary with control volume method, then the pressure equation and energy equation can be resolved in turn. The numerical simulation of the injection process and the identification of the process parameters were realized by the Moldflow software. The results indicate that there is low temperature gradient in the cavity while the pressure and shear rate gradient are high at high flow rate. The selection of the flow rate is affected by the structure of the gate. The shear rate and the pressure near the gate can be decreased by properly widening the dimension of the gate. There is a good agreement between the process parameters obtained by the numerical simulation and the actual ones.
Numerical simulation of ceramic breeder pebble bed thermal creep behavior
International Nuclear Information System (INIS)
The evolution of ceramic breeder pebble bed thermal creep deformation subjected to an external load and a differential thermal stress was studied using a modified discrete numerical code previously developed for the pebble bed thermomechanical evaluation. The rate change of creep deformation was modeled at the particle contact based on a diffusion creep mechanism. Numerical results of strain histories have shown lower values as compared to those of experimentally observed data at 740 deg. C using an activation energy of 180 kJ/mol. Calculations also show that, at this activation energy level, a particle bed at an elevated temperature of 800 deg. C may cause too much particle overlapping with a contact radius growth beyond 0.65 radius at a later time, when it is subjected to an external load of 6.3 MPa. Thus, by tracking the stress histories inside a breeder pebble bed the numerical simulation provides an indication of whether the bed may encounter an undesired condition under a typical operating condition
Numerical Simulation of Wind Turbine Blade-Tower Interaction
Institute of Scientific and Technical Information of China (English)
Qiang Wang; Hu Zhou; Decheng Wan
2012-01-01
Numerical simulations of wind turbine blade-tower interaction by using the open source OpenFOAM tools coupled with arbitrary mesh interface (AMI) method were presented.The governing equations were the unsteady Reynolds-averaged Navier-Stokes (PANS) which were solved by the pimpleDyMFoam solver,and the AMI method was employed to handle mesh movements.The National Renewable Energy Laboratory (NREL) phase Ⅵ wind turbine in upwind configuration was selected for numerical tests with different incoming wind speeds (5,10,15,and 25 m/s) at a fixed blade pitch and constant rotational speed.Detailed numerical results of vortex structure,time histories of thrust,and pressure distribution on the blade and tower were presented.The findings show that the wind turbine tower has little effect on the whole aerodynamic performance of an upwind wind turbine,while the rotating rotor will induce an obvious cyclic drop in the front pressure of the tower.Also,strong interaction of blade tip vortices with separation from the tower was observed.
Numerical simulation of impact tests on reinforced concrete beams
International Nuclear Information System (INIS)
Highlights: ► Predictions using advanced concrete model compare well with the impact test results. ► Several important behavior of concrete is discussed. ► Two mesh ways incorporating rebar into concrete mesh is also discussed. ► Gives a example of using EPDC model and references to develop new constitutive models. -- Abstract: This paper focuses on numerical simulation of impact tests of reinforced concrete (RC) beams by the LS-DYNA finite element (FE) code. In the FE model, the elasto-plastic damage cap (EPDC) model, which is based on continuum damage mechanics in combination with plasticity theory, is used for concrete, and the reinforcement is assumed to be elasto-plastic. The numerical results compares well with the experimental values reported in the literature, in terms of impact force history, mid-span deflection history and crack patterns of RC beams. By comparing the numerical and experimental results, several important behavior of concrete material is investigated, which includes: damage variable to describe the strain softening section of stress–strain curve; the cap surface to describe the plastic volume change; the shape of the meridian and deviatoric plane to describe the yield surface as well as two methods of incorporating rebar into concrete mesh. This study gives a good example of using EPDC model and can be utilized for the development new constitutive models for concrete in future.
Numerical simulation of nonlinear dynamical systems driven by commutative noise
International Nuclear Information System (INIS)
The local linearization (LL) approach has become an effective technique for the numerical integration of ordinary, random and stochastic differential equations. One of the reasons for this success is that the LL method achieves a convenient trade-off between numerical stability and computational cost. Besides, the LL method reproduces well the dynamics of nonlinear equations for which other classical methods fail. However, in the stochastic case, most of the reported works has been focused in Stochastic Differential Equations (SDE) driven by additive noise. This limits the applicability of the LL method since there is a number of interesting dynamics observed in equations with multiplicative noise. On the other hand, recent results show that commutative noise SDEs can be transformed into a random differential equation (RDE) by means of a random diffeomorfism (conjugacy). This paper takes advantages of such conjugacy property and the LL approach for defining a LL scheme for SDEs driven by commutative noise. The performance of the proposed method is illustrated by means of numerical simulations
International Nuclear Information System (INIS)
The accident to which the secondary system piping of the Mihama Power Station Unit-3 was damaged in August, 2004 happened. This is due to thinning of the pipe, and it is thought to be flow accelerated corrosion mechanism (FAC). The turbulence kinetic energy is considered as one of the flow factors in FAC. This is because the location where the amount of thinning is large and the parts where the turbulence kinetic energy is high are corresponding comparatively well. However, the causal relation between both parts is not clarified enough and the research advances now. Then, the flow field in the orifice downstream is calculated by the numerical simulation. The numerical simulation of LES in flow field (Re=25000) in the orifice downstream is performed. The distribution of the turbulence kinetic energy indicates the maximum value at the position that depended on β of the open area ratio of the orifice. In the rough side shape, the position in which the turbulence kinetic energy shows the maximum changes depending on the distance from the wall. (author)
Numerical simulation of the hydrodynamic instability experiments and flow mixing
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
Based on the numerical methods of volume of fluid (VOF) and piecewise parabolic method (PPM) and parallel circumstance of Message Passing Interface (MPI),a parallel multi-viscosity-fluid hydrodynamic code MVPPM (Multi-Viscosity-Fluid Piecewise Parabolic Method) is developed and performed to study the hydrodynamic instability and flow mixing. Firstly,the MVPPM code is verified and validated by simulating three instability cases:The first one is a Riemann problem of viscous flow on the shock tube; the second one is the hydrodynamic instability and mixing of gaseous flows under re-shocks; the third one is a half height experiment of interfacial instability,which is conducted on the AWE’s shock tube. By comparing the numerical results with experimental data,good agreement is achieved. Then the MVPPM code is applied to simulate the two cases of the interfacial instabilities of jelly models acceler-ated by explosion products of a gaseous explosive mixture (GEM),which are adopted in our experi-ments. The first is implosive dynamic interfacial instability of cylindrical symmetry and mixing. The evolving process of inner and outer interfaces,and the late distribution of mixing mass caused by Rayleigh-Taylor (RT) instability in the center of different radius are given. The second is jelly layer ex-periment which is initialized with one periodic perturbation with different amplitude and wave length. It reveals the complex processes of evolution of interface,and presents the displacement of front face of jelly layer,bubble head and top of spike relative to initial equilibrium position vs. time. The numerical results are in excellent agreement with that experimental images,and show that the amplitude of initial perturbations affects the evolvement of fluid mixing zone (FMZ) growth rate extremely,especially at late times.
Excavation-induced microseismicity: microseismic monitoring and numerical simulation
Institute of Scientific and Technical Information of China (English)
Nu-wen XU; Chun-an TANG; Hong LI; Feng DAI; Ke MA; Jing-dong SHAO; Ji-chang WU
2012-01-01
The volume of influence of excavation at the right bank slope of Dagangshan Hydropower Station,southwest China,is essentially determined from microseismic monitoring,numerical modeling and conventional measurements as well as in situ observations.Microseismic monitoring is a new application technique for investigating microcrackings in rock slopes.A microseismic monitoring network has been systematically used to monitor rock masses unloading relaxation due to continuous excavation of rock slope and stress redistribution caused by dam impoundment later on,and to idemify and delineate the potential slippage regions since May,2010.An important database of seismic source locations is available.The analysis of microseismic events showed a particular tempo-spatial distribution.Seismic events predominantly occurred around the upstream slope of 1180 m elevation,especially focusing on the hanging wall of fault XL316-1.Such phenomenon was interpreted by numerical modeling using RFPA-SRM code (realistic failure process analysis-strength reduction method).By comparing microseismic activity and results of numerical simulation with in site observation and conventional measurements results,a strong correlation can be obtained between seismic source locations and excavation-induced stress distribution in the working areas.The volume of influence of the rock slope is thus determined.Engineering practices show microseismic monitoring can accurately diagnose magnitude,intensity and associated tempo-spatial characteristics of tectonic activities such as faults and unloading zones.The integrated technique combining seismic monitoring with numerical modeling,as well as in site observation and conventional surveying,leads to a better understanding of the internal effect and relationship between microseisrnic activity and stress field in the right bank slope from different perspectives.
In search of discernible infrasound emitted by numerically simulated tornadoes
Schecter, David A.
2012-09-01
The comprehensive observational study of Bedard (2005) provisionally found that the infrasound of a tornado is discernible from the infrasound of generic cloud processes in a convective storm. This paper discusses an attempt to corroborate the reported observations of distinct tornado infrasound with numerical simulations. Specifically, this paper investigates the infrasound of an ordinary tornado in a numerical experiment with the Regional Atmospheric Modeling System, customized to simulate acoustic phenomena. The simulation has no explicit parameterization of microphysical cloud processes, but creates an unsteady tornado of moderate strength by constant thermal forcing in a rotational environment. Despite strong fluctuations in the lower corner flow and upper outflow regions, a surprisingly low level of infrasound is radiated by the vortex. Infrasonic pressure waves in the 0.1 Hz frequency regime are less intense than those which could be generated by core-scale vortex Rossby (VR) waves of modest amplitude in similar vortices. Higher frequency infrasound is at least an order of magnitude weaker than expected based on infrasonic observations of tornadic thunderstorms. Suppression of VR waves (and their infrasound) is explained by the gradual decay of axial vorticity with increasing radius from the center of the vortex core. Such non-Rankine wind-structure is known to enable the rapid damping of VR waves by inviscid mechanisms, including resonant wave-mean flow interaction and "spiral wind-up" of vorticity. Insignificant levels of higher frequency infrasound may be due to oversimplifications in the computational setup, such as the neglect of thermal fluctuations caused by phase transitions of moisture in vigorous cloud turbulence.
Ogive Nose Hard Missile Penetrating Concrete Slab Numerical Simulation Approach
Directory of Open Access Journals (Sweden)
Qadir Bux
2011-01-01
Full Text Available Great demand exists for more efficient design to protect delicate and serious structures such as nuclear plants, Power plants, Weapon Industries, weapons storage places, water retaining structures, & etc, against impact of kinetic missiles generated both accidentally and deliberately such as dynamic loading, incident occurs in nuclear plants, terrorist attack, Natural disasters like tsunami and etc., in various impact and blast scenarios for both civilian and military activities. In many cases, projectiles can be treated as rigid bodies when their damage and erosion are not severe. Due to the intricacy of the local impact damages, investigations are generally based on experimental data. Conclusions of the experimental observations are then used to guide engineering models. Local damages studies normally fall into three categories, i.e. empirical formulae based on data fitting, idealised analytical models based on physic laws and numerical simulations based on computational mechanics and material models. In the present study, 2D asymmetrical numerical simulation have done on concrete slab against the impact of ogive nose hard missile of 26.90mm and 76.20mm diameter with CRH ratio 2.0 and 6.0 respectively, for penetration by using Concrete Damaged Plasticity Model, and ABAQUS/Explicit dynamic analysis in ABAQUS. It is found that the strains/stresses are induced in the concrete slab and a very nicely propagation of the stresses inside the concrete slab in the form of waves, which is a clear indication for vibrations of the concrete. The lack of failure criterion in concrete damaged plasticity model does not allow the removal of elements during the analyses. This means that spalling, scabbing, and perforation cannot be modelled with the Concrete Damage Plasticity Model. The penetration depth results shows that the deeper penetration requires higher critical impact kinetic energies, and comparison shows the simulation results are more accurate
Direct numerical simulation of supersonic turbulent boundary layers
Guarini, Stephen
The objectives of this research were to develop a method by which the spatially developing compressible turbulent boundary layer could be simulated using a temporally developing numerical simulation and to study the physics of the compressible turbulent boundary layer. We take advantage of the technique developed by Spalart (1987, 1988) for the incompressible case. In this technique, it is recognized that the boundary layer exhibits slow growth in the streamwise direction, so the turbulence can be treated as approximately homogeneous in this direction. The slow growth is accounted for with a coordinate transformation and a multiple scale analysis. The result is a modified system of equations (Navier-Stokes plus some extra terms, which we call "slow growth terms") that are homogeneous in both the streamwise and spanwise directions and represent the state of the boundary layer at a given streamwise location (or, equivalently, a given thickness). The compressible Navier-Stokes equations are solved using a mixed Fourier and B-spline "spectral" method. The dependent variables are expanded in terms of a Fourier representation in the horizontal directions and a B-spline representation in the wall-normal direction. In the wall-normal direction non-reflecting boundary conditions are used at the freestream boundary, and zero-heat-flux no-slip boundary conditions are used at the wall. This combination of splines and Fourier methods produces a very accurate numerical method. Mixed implicit/explicit time discretization is used. Results are presented for a case with a Mach number of 2.5, and a Reynolds number, based on momentum integral thickness and wall viscosity, of Rsb{thetasp'} = 840. The results show that the van Driest transformed velocity satisfies the incompressible scalings and a narrow logarithmic region is obtained. The results for the turbulence intensities compare well with the incompressible simulations of Spalart. Pressure fluctuations are found to be higher than
Numerical Simulation of Laminar Flow Field in a Stirred Tank
Institute of Scientific and Technical Information of China (English)
范茏; 王卫京; 杨超; 毛在砂
2004-01-01
Stirred tanks are used extensively in process industry and one of the most commonly used impellers in stirred tanks is the R.ushton disk turbine. Surprisingly few data are available regarding flow and mixing in stirred-tank reactors with Rushton turbine in the laminar regime, in particular the laminar flow in baffled tanks.In this paper, the laminar flow field in a baffled tank stirred by a standard R.ushton turbine is simulated with the improved inner-outer iterative method. The non-inertial coordinate system is used for the impeller region, which is in turn used as the boundary conditions for iteration. It is found that the simulation results are in good agreement with previous experiments. In addition, the flow number and impeller power number calculated from the simulated flow field are in satisfactory agreement with experimental data. This numerical method allows prediction of flow structure requiring no experimental data as the boundary conditions and has the potential of being used to scale-up and design of related process equipment.
Numerical simulation of non-equilibrium transient flow during inhalation
Marxen, Olaf; Magin, Thierry
2012-11-01
The flow in human upper airways may be laminar, transitional, or turbulent. Breadth-by-breadth and patient-specific variability is expected to have a significant influence on laminar-turbulent transition. The flow path of therapeutic drug aerosols may be strongly affected by the transition-induced unsteady structures. The unsteady Navier-Stokes equations are solved numerically to simulate the flow through a channel-flow geometry representative of an airway segment. In order to trigger transition, small-amplitude disturbances are forced via wall blowing/suction. We perform multiple simulations with varying phase of the forced disturbances. Ensemble averaging then allows to compute mean and RMS values. A time-dependent channel center-line velocity serves to model the change in flow velocity during inhalation. The uncertainty associated with variability during breathing is quantified using non-intrusive stochastic collocation. Simulation results reveal that we have intervals in time and space with quasi-steady equilibrium and with strong non-equilibrium flow. The uncertainty associated with the breathing pattern may strongly affect the occurrence of laminar-turbulent transition, leading to large uncertainties when RMS values are peaking.
NUMERICAL SIMULATION FOR A PROCESS ANALYSIS OF A COKE OVEN
Institute of Scientific and Technical Information of China (English)
Zhancheng Guo; Huiqing Tang
2005-01-01
A computational fluid dynamic model is established for a coking process analysis of a coke oven using PHOENICS CFD package. The model simultaneously calculates the transient composition, temperatures of the gas and the solid phases, velocity of the gas phase and porosity and density of the semi-coke phase. Numerical simulation is illustrated in predicting the evolution of volatile gases, gas flow paths, profiles of density, porosity of the coke oven charge,profiles of temperatures of the coke oven gas and the semi-coke bed. On the basis of above modeling, the flow of coke oven gas (COG) blown from the bottom of the coke oven into the porous semi-coke bed is simulated to reveal whether or not and when the blown COG can uniformly flow through the porous semi-coke bed for the purpose of desulfurizing the semi-coke by recycling the COG. The simulation results show that the blown COG can uniformly flow through the semi-coke bed only after the temperature at the center of the semi-coke bed has risen to above 900 ℃.
Direct Numerical Simulation of Soot Particle Dynamics using DQMOM
Blanquart, Guillaume; Pitsch, Heinz; Fox, Rodney
2006-11-01
The understanding of soot particle dynamics in combustion systems is a key issue in the development of low emission engines. Of particular importance are the processes shaping the soot particle size distribution function (PSDF). However, it is not always necessary to represent exactly the full distribution but rather some of its moments. The Direct Quadrature Method of Moments (DQMOM) allows for a very accurate prediction of the moments of the soot PSDF without the cost of expensive methods like Direct Simulation Monte-Carlo (DSMC). This method has been validated for laminar premixed and diffusion flames with detailed chemistry and is now implemented in a semi-implicit low Mach number Navier-Stokes solver. A Direct Numerical Simulation (DNS) of an ethylene jet diffusion flame is performed to study the dynamics of soot particles in a turbulent environment. Soot particles are formed in very rich regions of the flames and are then transported to lean regions where they get oxidized. The time evolution of the soot PSDF will be analyzed and compared to similar distributions from laminar simulations.
Numerical Simulations of Coronal Heating through Footpoint Braiding
Hansteen, Viggo; De Pontieu, Bart; Carlsson, Mats
2015-01-01
Advanced 3D radiative MHD simulations now reproduce many properties of the outer solar atmosphere. When including a domain from the convection zone into the corona, a hot chromosphere and corona are self-consistently maintained. Here we study two realistic models, with different simulated area, magnetic field strength and topology, and numerical resolution. These are compared in order to characterize the heating in the 3D-MHD simulations which self-consistently maintains the structure of the atmosphere. We analyze the heating at both large and small scales and find that heating is episodic and highly structured in space, but occurs along loop shaped structures, and moves along with the magnetic field. On large scales we find that the heating per particle is maximal near the transition region and that widely distributed opposite-polarity field in the photosphere leads to a greater heating scale height in the corona. On smaller scales, heating is concentrated in current sheets, the thicknesses of which are set ...
Numerical resolution effects on simulations of massive black hole seeds
Regan, John A; Haehnelt, Martin G
2013-01-01
We have performed high-resolution numerical simulations with the hydrodynamical AMR code Enzo to investigate the formation of massive seed black holes in a sample of six dark matter haloes above the atomic cooling threshold. The aim of this study is to illustrate the effects of varying the maximum refinement level on the final object formed. The virial temperatures of the simulated haloes range from $\\rm{T} \\sim 10000\\ \\rm{K} - 16000\\ \\rm{K}$ and they have virial masses in the range $\\rm{M} \\sim 2 \\times 10^7 \\rm{M_{\\odot}}$ to $\\rm{M} \\sim 7 \\times 10^7 \\rm{M_{\\odot}}$ at $z \\sim 15$. The outcome of our six fiducial simulations is both generic and robust. A rotationally supported, marginally gravitationally stable, disk forms with an exponential profile. The mass and scale length of this disk depends strongly on the maximum refinement level used. Varying the maximum refinement level by factors between 1 / 64 to 256 times the fiducial level illustrates the care that must be taken in interpreting the results. ...
Numerical simulation of plasma transport driven by the Io torus
Yang, Y. S.; Wolf, R. A.; Spiro, R. W.; Dessler, A. J.
1992-01-01
The Rice convection model (RCM) has been modified to a form suitable for Jupiter (RCM-J) to study plasma interchange motion in and near the Io plasma torus. The net result of the interchange is that flux tubes, heavily loaded with torus plasma, are transported outward, to be replaced by tubes containing little low-energy (less than 1 keV) plasma. The process is numerically simulated in terms of time evolution from an initial torus that is longitudinally asymmetric and with gradually decreasing density outward from Io's orbit. In the simulations, the nonlinear stage of the instability characteristically exhibits outreaching fingers of heavily-loaded flux tubes that lengthen at an accelerating rate. The principal finding is that the primary geometrical form of outward transport of torus plasma in Jupiter's magnetosphere is through long, outward-moving fingers of plasma. In the simulations, the fingers mainly form in the active sector of the Io torus (the heavier side of the asymmetric torus), and they are spaced longitudinally roughly 20 deg apart.
Numerical Relativity in Spherical Polar Coordinates: Off-center Simulations
Baumgarte, Thomas W; Müller, Ewald
2015-01-01
We have recently presented a new approach for numerical relativity simulations in spherical polar coordinates, both for vacuum and for relativistic hydrodynamics. Our approach is based on a reference-metric formulation of the BSSN equations, a factoring of all tensor components, as well as a partially implicit Runge-Kutta method, and does not rely on a regularization of the equations, nor does it make any assumptions about the symmetry across the origin. In order to demonstrate this feature we present here several off-centered simulations, including simulations of single black holes and neutron stars whose center is placed away from the origin of the coordinate system, as well as the asymmetric head-on collision of two black holes. We also revisit our implementation of relativistic hydrodynamics and demonstrate that a reference-metric formulation of hydrodynamics together with a factoring of all tensor components avoids problems related to the coordinate singularities at the origin and on the axes. As a parti...
Numerical simulation of separated flows past bluff bodies
Alexandrou, Andreas Neophytou
1986-12-01
The steady two-dimensional flow past bluff bodies is simulated numerically using a hybrid Eulerian-Lagrangian model. The boundary layer effects, such as the location of the separation points and the rate of the generation of vorticity, are determined by a boundary layer solver. This solver uses Prandtl's boundary layer equations transformed by the Falkner-Skan transformation and then solved using a cubic spline approximation and a mean weighted residual technique. The vorticity generated at separation is discretized into elemental point vortices and convected downstream into the wake in a Lagrangian manner. The wake is modeled in a finite Eulerian computational domain using a modified Cloud-in-Cell (CIC) method. The velocity field at each time step is obtained as a solution to the rotationality condition using the finite element method in a cartesian mesh with nine-node elements and biquadratic shape functions. The biquadratic shape functions introduce a higher order interpolation scheme for the distribution of the vorticity at the nodal points than the bilinear (area) interpolation used in the original CIC method. The higher order interpolation as used in the CIC formulation performs better than the bilinear interpolation of the original method. This is demonstrated by the simulation of an isolated Rankine vortex. The ability of the CIC method to simulate the dynamics of vortex structures is also tested for the cases of flow past a flat plate and a circular cylinder.
Numerical Simulation of a Solar Domestic Hot Water System
International Nuclear Information System (INIS)
An innovative transient numerical model is presented for the simulation of a solar Domestic Hot Water (DHW) system. The solar collectors have been simulated by using a zerodimensional analytical model. The temperature distributions in the heat transfer fluid and in the water inside the tank have been evaluated by one-dimensional models. The reversion elimination algorithm has been used to include the effects of natural convection among the water layers at different heights in the tank on the thermal stratification. A finite difference implicit scheme has been implemented to solve the energy conservation equation in the coil heat exchanger, and the energy conservation equation in the tank has been solved by using the finite difference Euler implicit scheme. Energy conservation equations for the solar DHW components models have been coupled by means of a home-made implicit algorithm. Results of the simulation performed using as input data the experimental values of the ambient temperature and the solar irradiance in a summer day are presented and discussed
Direct Numerical Simulation of a Weakly Stratified Turbulent Wake
Redford, J. A.; Lund, T. S.; Coleman, Gary N.
2014-01-01
Direct numerical simulation (DNS) is used to investigate a time-dependent turbulent wake evolving in a stably stratified background. A large initial Froude number is chosen to allow the wake to become fully turbulent and axisymmetric before stratification affects the spreading rate of the mean defect. The uncertainty introduced by the finite sample size associated with gathering statistics from a simulation of a time-dependent flow is reduced, compared to earlier simulations of this flow. The DNS reveals the buoyancy-induced changes to the turbulence structure, as well as to the mean-defect history and the terms in the mean-momentum and turbulence-kinetic-energy budgets, that characterize the various states of this flow - namely the three-dimensional (essentially unstratified), non-equilibrium (or 'wake-collapse') and quasi-two-dimensional (or 'two-component') regimes observed elsewhere for wakes embedded in both weakly and strongly stratified backgrounds. The wake-collapse regime is not accompanied by transfer (or 'reconversion') of the potential energy of the turbulence to the kinetic energy of the turbulence, implying that this is not an essential feature of stratified-wake dynamics. The dependence upon Reynolds number of the duration of the wake-collapse period is demonstrated, and the effect of the details of the initial/near-field conditions of the wake on its subsequent development is examined.
Numerical Simulation of Density Current Evolution in a Diverging Channel
Directory of Open Access Journals (Sweden)
Mitra Javan
2012-01-01
Full Text Available When a buoyant inflow of higher density enters a reservoir, it sinks below the ambient water and forms an underflow. Downstream of the plunge point, the flow becomes progressively diluted due to the fluid entrainment. This study seeks to explore the ability of 2D width-averaged unsteady Reynolds-averaged Navier-Stokes (RANS simulation approach for resolving density currents in an inclined diverging channel. 2D width-averaged unsteady RANS equations closed by a buoyancy-modified − turbulence model are integrated in time with a second-order fractional step approach coupled with a direct implicit method and discretized in space on a staggered mesh using a second-order accurate finite volume approach incorporating a high-resolution semi-Lagrangian technique for the convective terms. A series of 2D width-averaged unsteady simulations is carried out for density currents. Comparisons with the experimental measurements and the other numerical simulations show that the predictions of velocity and density field are with reasonable accuracy.
Numerical simulation of wheel wear evolution for heavy haul railway
Institute of Scientific and Technical Information of China (English)
王璞; 高亮
2015-01-01
The prediction of the wheel wear is a fundamental problem in heavy haul railway. A numerical methodology is introduced to simulate the wheel wear evolution of heavy haul freight car. The methodology includes the spatial coupling dynamics of vehicle and track, the three-dimensional rolling contact analysis of wheel-rail, the Specht’s material wear model, and the strategy for reproducing the actual operation conditions of railway. The freight vehicle is treated as a full 3D rigid multi-body model. Every component is built detailedly and various contact interactions between parts are accurately simulated, taking into account the real clearances. The wheel−rail rolling contact calculation is carried out based on Hertz’s theory and Kalker’s FASTSIM algorithm. The track model is built based on field measurements. The material loss due to wear is evaluated according to the Specht’s model in which the wear coefficient varies with the wear intensity. In order to exactly reproduce the actual operating conditions of railway, dynamic simulations are performed separately for all possible track conditions and running velocities in each iterative step. Dimensionless weight coefficients are introduced that determine the ratios of different cases and are obtained through site survey. For the wheel profile updating, an adaptive step strategy based on the wear depth is introduced, which can effectively improve the reliability and stability of numerical calculation. At last, the wear evolution laws are studied by the numerical model for different wheels of heavy haul freight vehicle running in curves. The results show that the wear of the front wheelset is more serious than that of the rear wheelset for one bogie, and the difference is more obvious for the outer wheels. The wear of the outer wheels is severer than that of the inner wheels. The wear of outer wheels mainly distributes near the flange and the root;while the wear of inner wheels mainly distributes around the
Directory of Open Access Journals (Sweden)
Mottyll Stephan
2014-03-01
Full Text Available This paper reports the outcome of a numerical study of ultrasonic cavitation using a CFD flow algorithm based on a compressible density-based finite volume method with a low-Machnumber consistent flux function and an explicit time integration [15; 18] in combination with an erosion-detecting flow analysis procedure. The model is validated against erosion data of an ultrasonic horn for different gap widths between the horn tip and a counter sample which has been intensively investigated in previous material studies at the Ruhr University Bochum [23] as well as on first optical in-house flow measurement data which is presented in a companion paper [13]. Flow features such as subharmonic cavitation oscillation frequencies as well as constricted vapour cloud structures can also be observed by the vapour regions predicted in our simulation as well as by the detected collapse event field (collapse detector [12]. With a statistical analysis of transient wall loads we can determine the erosion sensitive areas qualitatively. Our simulation method can reproduce the influence of the gap width on vapour structure and on location of cavitation erosion.
Understanding disordered systems through numerical simulation and algorithm development
Sweeney, Sean Michael
Disordered systems arise in many physical contexts. Not all matter is uniform, and impurities or heterogeneities can be modeled by fixed random disorder. Numerous complex networks also possess fixed disorder, leading to applications in transportation systems, telecommunications, social networks, and epidemic modeling, to name a few. Due to their random nature and power law critical behavior, disordered systems are difficult to study analytically. Numerical simulation can help overcome this hurdle by allowing for the rapid computation of system states. In order to get precise statistics and extrapolate to the thermodynamic limit, large systems must be studied over many realizations. Thus, innovative algorithm development is essential in order reduce memory or running time requirements of simulations. This thesis presents a review of disordered systems, as well as a thorough study of two particular systems through numerical simulation, algorithm development and optimization, and careful statistical analysis of scaling properties. Chapter 1 provides a thorough overview of disordered systems, the history of their study in the physics community, and the development of techniques used to study them. Topics of quenched disorder, phase transitions, the renormalization group, criticality, and scale invariance are discussed. Several prominent models of disordered systems are also explained. Lastly, analysis techniques used in studying disordered systems are covered. In Chapter 2, minimal spanning trees on critical percolation clusters are studied, motivated in part by an analytic perturbation expansion by Jackson and Read that I check against numerical calculations. This system has a direct mapping to the ground state of the strongly disordered spin glass. We compute the path length fractal dimension of these trees in dimensions d = {2, 3, 4, 5} and find our results to be compatible with the analytic results suggested by Jackson and Read. In Chapter 3, the random bond Ising
The North Sea Andrea storm and numerical simulations
Bitner-Gregersen, E. M.; Fernandez, L.; Lefèvre, J. M.; Monbaliu, J.; Toffoli, A.
2014-06-01
A coupling of a spectral wave model with a nonlinear phase-resolving model is used to reconstruct the evolution of wave statistics during a storm crossing the North Sea on 8-9 November 2007. During this storm a rogue wave (named the Andrea wave) was recorded at the Ekofisk field. The wave has characteristics comparable to the well-known New Year wave measured by Statoil at the Draupner platform 1 January 1995. Hindcast data of the storm at the nearest grid point to the Ekofisk field are here applied as input to calculate the evolution of random realizations of the sea surface and its statistical properties. Numerical simulations are carried out using the Euler equations with a higher-order spectral method (HOSM). Results are compared with some characteristics of the Andrea wave record measured by the down-looking lasers at Ekofisk.
Reinforcement Corrosion: Numerical Simulation and Service Life Prediction
DEFF Research Database (Denmark)
Michel, Alexander
substances in concrete a heat and mass transport model was applied, which is based on thermodynamic principles. To incorporate the influence of temperature and chloride on the moisture sorption extensions were made using experimental results. The impact ofchlorides on the moisture sorption was accounted for...... concrete specimens was demonstrated comparing experimental ingress results and numerical simulations. The corrosion model, which is coupled to the transport model, was used to describe electrochemical processes at the reinforcement surface. The corrosion model was based on generally accepted physical laws...... describing thermodynamics and kinetics of electrochemical processes. The applicabilityof the model to capture various reinforcement corrosion phenomena, such as activation, resistance, and concentration polarisation as well as the impact of temperature and relative humidity was demonstrated comparing...
The Numerical Simulation of Ship Waves using Cartesian Grid Methods
Sussman, Mark
2014-01-01
Two different cartesian-grid methods are used to simulate the flow around the DDG 5415. The first technique uses a "coupled level-set and volume-of-fluid" (CLS) technique to model the free-surface interface. The no-flux boundary condition on the hull is imposed using a finite-volume technique. The second technique uses a level-set technique (LS) to model the free-surface interface. A body-force technique is used to impose the hull boundary condition. The predictions of both numerical techniques are compared to whisker-probe measurements of the DDG 5415. The level-set technique is also used to investigate the breakup of a two-dimensional spray sheet.
Numerical simulation of the channel flow affected by synthetic jet
Czech Academy of Sciences Publication Activity Database
Dančová, Petra; Vít, T.
Kyjev: Міністерство Освіти і Науки України, 2009, s. 14-15. [Міжнародної науково-методичної конференції ВИВЧЕННЯ САПР УКРАЇНСЬКИМИ ІНЖЕНЕРАМИ. Kyjev (UA), 25.06.2009-27.06.2009] R&D Projects: GA AV ČR(CZ) IAA200760801 Institutional research plan: CEZ:AV0Z20760514 Keywords : numerical simulation * synthetic jet * channel flow Subject RIV: BK - Fluid Dynamics
Automated continuous verification and validation for numerical simulation
Directory of Open Access Journals (Sweden)
P. E. Farrell
2010-09-01
Full Text Available Verification and validation are crucially important for the final users of a computational model: code is useless if its results cannot be relied upon. Typically, undergoing these processes is seen as a discrete event, performed once and for all after development is complete. However, this does not reflect the reality that many geoscientific codes undergo continuous development of the mathematical model, discretisation and software implementation. Therefore, we advocate that in such cases verification and validation must be continuous and happen in parallel with development. The desirability of their automation follows immediately. This paper discusses a framework for automated continuous verification and validation of wide applicability to any kind of numerical simulation. It also documents a range of rigorous test cases for use in computational and geophysical fluid dynamics.
Numerical simulation of streak ICT electron optics focusing characteristics
International Nuclear Information System (INIS)
The image converter tube is a core component in the streak cameras. Its operation was introduced and the model for its internal electronic optical system was built. Numerical simulations were done by ANSYS based on the finite element method, in which the functional is solved by Hamilton principle. The distribution of the electrostatic field was calculated in an operation voltage and the tracks of electrons were calculated in different operation voltages. The results agree well with that of the symmetric electrostatic field theoretical analysis. They also indicate that the size and shape of electrode has a slight influence on imaging, and the proper voltages(containing accelerating, focusing and anode voltages) has more. (authors)
A numerical simulation of photothermal response in laser medicine
Institute of Scientific and Technical Information of China (English)
Xiaoxia Li(李小霞); Shifu Fan(范世福); Youquan Zhao(赵友全); Songshan Xiao(肖松山)
2004-01-01
In this paper, we reported a numerical solution of laser induced thermal effect in the bio-tissue. The model of photothermal effect and classical Pennes bio-heat transfer equation were introduced. Finite element method (FEM), which was realized by Matlab software, was used to calculate the temperature distribution. He-Ne laser (633 nm) was used to simulate the physical therapy in in vivo skin tissue. Under the cylinder coordinates, the three-dimension(3-D) geometry of tissue was reduced to two-dimension(2-D)computation. The results contained the radial, axial and temperature 3-D color plot. Combining the time animation display was possible. By changing the laser and tissue parameters we can get different results.This will be the initial and indispensable work of the non-destructive evaluation of the laser induced injury.
Planar and cylindrical active microwave temperature imaging: numerical simulations.
Rius, J M; Pichot, C; Jofre, L; Bolomey, J C; Joachimowicz, N; Broquetas, A; Ferrando, M
1992-01-01
A comparative study at 2.45 GHz concerning both measurement and reconstruction parameters for planar and cylindrical configurations is presented. For the sake of comparison, a numerical model consisting of two nonconcentric cylinders is considered and reconstructed using both geometries from simulated experimental data. The scattered fields and reconstructed images permit extraction of very useful information about dynamic range, sensitivity, resolution, and quantitative image accuracy for the choice of the configuration in a particular application. Both geometries can measure forward and backward scattered fields. The backscattering measurement improves the image resolution and reconstruction in lossy mediums, but, on the other hand, has several dynamic range difficulties. This tradeoff between forward only and forward-backward field measurement is analyzed. As differential temperature imaging is a weakly scattering problem, Born approximation algorithms can be used. The simplicity of Born reconstruction algorithms and the use of FFT make them very attractive for real-time biomedical imaging systems. PMID:18222887
Numerical simulation of plane target in airflow under laser irradiation
International Nuclear Information System (INIS)
A model of a plane target under laser irradiation is used to numerically simulate the temperature distribution in different speed airflow, using the thermal coupling method of gas and solid. The results show that there is a higher equilibrium temperature over the plane target when there is no laser irradiation, and the heat transfer coefficient between air and the plane target increases with the airflow speed; with a maximum value occurring at the front edge of the target, it declines along the target length. When under laser irradiation in different cases, the temperature distribution in the plane is analyzed carefully, and the influence of aerodynamic heating, forced convection cooling and laser heating is focused to compare their thermal competition, which shows that the temperature distributions in the target results from several thermal competition ultimately. (authors)
Numerical simulation of rising bubble with chemical reaction
Sahu, Kirti; Tripathi, Manoj; Matar, Omar; Karapetsas, George
2014-11-01
The dynamics of a rising bubble under the action of gravity and in the presence of an exothermic chemical reaction at the interface is investigated via direct numerical simulation using Volume-of-Fluid (VOF) method. The product of the chemical reaction, and temperature rise due to the exothermic chemical reaction influence the local viscosity and surface tension near the interfacial region, which in turn give rise to many interesting dynamics. The flow is governed by continuity, Navier-Stokes equations along with the convection equation of the volume fraction of the outer fluid and the energy equation. The effects of the Bond, Damkohler, and Reynolds numbers, and of the dimensionless heat of reaction are investigated. The results of this parametric study will be presented at the meeting.
Numerical simulations of magnetic reconnection in the lower solar atmosphere
Institute of Scientific and Technical Information of China (English)
Xiao-Yan Xu; Cheng Fang; Ming-De Ding; Dan-Hui Gao
2011-01-01
Observations indicate that Ellerman bombs (EBs) and chromospheric microflares both occur in the lower solar atmosphere, and share many common features,such as temperature enhancements, accompanying jet-like mass motions, short lifetime, and so on. These strongly suggest that EBs and chromospheric microflares could both probably be induced by magnetic reconnection in the lower solar atmosphere.With gravity, ionization and radiation considered, we perform two-dimensional numerical simulations of magnetic reconnection in the lower solar atmosphere. The influence of different parameters, such as intensity of the magnetic field and anomalous resistivity, on the results are investigated. Our result demonstrates that the temperature increases are mainly due to the joule dissipation caused by magnetic reconnection.The spectral profiles of EBs and chromospheric microflares are calculated with the non-LTE radiative transfer theory and compared with observations. It is found that the typical features of the two phenomena can be qualitatively reproduced.
Direct numerical simulation of MHD turbulent free surface flow
International Nuclear Information System (INIS)
A direct numerical simulation (DNS) of turbulent free surface flow with a constant magnetic field has been carried out to grasp and understand the effects of electromagnetic suppression of turbulence. In this study, the Reynolds number based on bulk velocity and a film depth was set to be constant, Reb=2300. The constant static magnetic field at Ha=20 and 30 for the streamwise orientation and at Ha=5 and 10 for the spanwise orientation were considered in the electrical potential equation. The number of computational grids used in this study was 256x128x128 in the x-, y- and z-directions, respectively. The turbulent quantities such as the mean flow, turbulent stresses and the turbulent statistics were obtained. The mean velocity and turbulent intensities distributed from the wall to the free surface are damped quickly near wall region, because of the electromagnetic effects. (author)
NUMERICAL SIMULATION OF FISH SWIMMING WITH RIGID PECTORAL FINS
Institute of Scientific and Technical Information of China (English)
XU Yi-gang; WAN De-cheng
2012-01-01
The numerical simulation of the self-propelled motion of a fish with a pair of rigid pectoral fins is presented.A Navier-Stokes equation solver incorporating with the multi-block and overset grid method is developed to deal with the multi-body and moving body problems.The lift-based swimming mode is selected for the fin motion.In the lift-based swimming mode,the fin can generate great thrust and at the same tune have no generation of lift force.It can be found when a pair of rigid pectoral fins generates the hydrodynamic moment,it may also generate a lateral force opposite to the centripetal direction,which has adverse effect on the turn motion of the fish.Furthermore,the periodic vortex structure generation and shedding,and their effects on the generation of hydrodynamic force are also demonstrated in this article.
Numerical simulation of high Reynolds number bubble motion
International Nuclear Information System (INIS)
This paper presents the results of numerical simulations of bubble motion. All the results are for single bubbles in unbounded fluids. The liquid phase is quiescent except for the motion created by the bubble, which is axisymmetric. The main focus of the paper is on bubbles that are of order 1 mm in diameter in water. Of particular interest is the effect of surfactant molecules on bubble motion. Results for the open-quotes insoluble surfactantclose quotes model will be presented. These results extend research by other investigators to finite Reynolds numbers. The results indicate that, by assuming complete coverage of the bubble surface, one obtains good agreement with experimental observations of bubble motion in tap water. The effect of surfactant concentration on the separation angle is discussed
Numerical simulation on micromixer based on synthetic jet
Institute of Scientific and Technical Information of China (English)
Minghou Liu; Chen Xie; Xiangfeng Zhang; Yiliang Chen
2008-01-01
This paper studied a concept of micromixer with a synthetic jet placed at the bottom of a rectangular channel. Due to periodic ejections from and suctions into the chan-nel, the fluids are mixed effectively. To study the effects of the inlet velocity, the jet intensity and frequency, and the jet location on the mixing efficiency, 3-D numerical simulations of the micromixer have been carried out. It has been found that when the jet intensity and the frequency are fixed, the mixing efficiency increases when Re 50 with the best mixing efficiency achieved at Re = 50. When the ratio of the jet velocity magnitude to the inlet velocity is taken as 10 and the jet frequency is 100 Hz, the mixing index reaches the highest value. It has also been found that to get better mixing efficiency, the orifice of the synthetic jet should be asymmetrically located away from the channel's centerline.
Heterogeneous individuals' behavioral biases model and numerical simulation
Institute of Scientific and Technical Information of China (English)
ZHANG Da-yong; LIANG Guo-wei
2010-01-01
A model of the relationships between individual cognitive biases and individual decision-making based on the analysis of cognitive biases of bonded rationality individual,has been established in this paper by introducing a set of new variables callod overconfidence coefficient and attribution bias coefficient to the sentiment model.The irrational expectation and irrational risk aversion as two inseparable aspects of bonded rationality are expressed in an unified model,and a method of measuring individual cognitive biases is proposed,which overcomes the shortcomings of traditional normative models that can not describe the differences of behaviors among heterogeneous individuals.As a result,numerical simulations show that individual cognitive risk is a positive interaction with overconfidence coefficient,and a negative interaction with attribution bias coefficient.
Numerical simulation based cold tests for a tangentially fired boiler
Institute of Scientific and Technical Information of China (English)
XIANG Yuhua; ZHANG Jiayuan; ZHANG Xiaohui
2012-01-01
Such problems as flameout and serious slagging frequently occurred in a 170 t/h tangentially fired boiler burning inferior coals and with low load.Thus,cold tests were carried out to comprehensively investigate the performance of each air tube and the size and position of the tangential circle.Therefore,the cause and area of slagging in furnace can be determined.Thus,by numerical simulation on combustion,the optimal operation parameters for the boiler burning different coals under various loads conditions can be provided.The actual application showed that,the boiler fed with present coal can be long-term operated stably at 60％ load,and its heat efficiency was up to 91％.Moreover,the abnormal flameout no longer occurred,and the slagging was alleviated a lot.
Numerical Simulation of Flow Interference Between Two Circular Cylinders
Gao, F.; Mingham, C. G.; Causon, D. M.
2011-09-01
Viscous flow past two circular cylinders in tandem and side-by-side arrangements is investigated numerically. The solution to the Navier-Stokes equations is obtained by means of a cell-centred finite volume method (FVM) based on a structured Cartesian grid with collocated variable arrangement. The pressure-velocity coupling is evaluated by using the SIMPLE algorithm. The 2D Cartesian cut cell mesh is generated on the horizontal plane, which is extended vertically to form the 3D grid. The simulations are based on the Reynolds number of 200, and the gap between the two cylinders are 1.5-3D for side-by-side arrangement and 3-4D for tandem. Instantaneous velocity contours of the flow around the cylinders and time histories of force coefficients are presented.
Numerical simulation of low emittance tuning at SuperKEKB
International Nuclear Information System (INIS)
SuperKEKB is a double ring e+e- collider aimed to reach new luminosity frontier. The target peak luminosity is 8x103 cm-2s-1, which is 40 times higher than the world recored achieved by the KEKB machine. The basic strategy to break the KEKB's record is 2 times higher beam current and 20 times smaller beam size at the interaction point. In order to obtain the required beam size, we have to stably storage high quality beams and squeez the beta function. Therefore, one of important accelerator topic in the project is the Low Emittance Tuning (LET) as in high brightness light source projects. We have conducted LET study, shush as error sensitivity, alignment strategy and beam optics correction by using numerical approach. Some remarkable simulation results obtained so far are reported. (author)
Numerical simulation of the passive gas mixture flow
Directory of Open Access Journals (Sweden)
Kyncl Martin
2015-01-01
Full Text Available We work with the system of equations describing non-stationary compressible turbulent multicomponent flow in the gravitational field, and we focus on the numerical solution of these equations. In these computations we assume the mixture of perfect inert gases. The thermodynamic constants are functions in time and space. The finite volume method is used. In order to solve the local boundary problem at each mesh face, we use the original analysis of the exact solution of the Riemann problem. The roughness of the surface is simulated via the specific dissipation at the wall. We show the computational results obtained with the own-developed code (C,FORTRAN for the solution of the 3D compressible turbulent mixture flow. The originality of this work lies with the special handling of the boundary conditions, which shows superior behavior, and own computational code.
Numerical simulation of the passive gas mixture flow
Kyncl, Martin; Pelant, Jaroslav
2016-03-01
The aim of this paper is the numerical solution of the equations describing the non-stationary compressible turbulent multicomponent flow in gravitational field. The mixture of perfect inert gases is assumed. We work with the RANS equations equipped with the k-omega and the EARSM turbulence models. For the simulation of the wall roughness we use the modification of the specific turbulent dissipation. The finite volume method is used, with thermodynamic constants being functions in time and space. In order to compute the fluxes through the boundary faces we use the modification of the Riemann solver, which is the original result. We present the computational results, computed with the own-developed code (C, FORTRAN, multiprocessor, unstructured meshes in general).
Numerical simulation of flow fields and particle trajectories
DEFF Research Database (Denmark)
Mayer, Stefan
2000-01-01
A model describing the ciliary driven flow and motion of suspended particles in downstream suspension feeders is developed. The quasi-steady Stokes equations for creeping flow are solved numerically in an unbounded fluid domain around cylindrical bodies using a boundary integral formulation. The...... time-dependent flow is approximated with a continuous sequence of steady state creeping flow fields, where metachronously beating ciliary bands are modelled by linear combinations of singularity solutions to the Stokes equations. Generally, the computed flow fields can be divided into an unsteady...... the simulated unsteady ciliary driven flow. A fraction of particles appear to follow trajectories, that resemble experimentally observed particle capture events in the downstream feeding system of the polycheate Sabella penicillus, indicating that particles can be captured by ciliary systems without...
Isentropic 'shock waves' in numerical simulations of astrophysical bodies
Bisnovatyi-Kogan, G S
2016-01-01
Strong discontinuities in solutions of the gas dynamic equations under isentropic conditions, i.e., with continuity of entropy at the discontinuity, are examined. Solutions for a standard shock wave with continuity of energy at the discontinuity are compared with those for an isentropic 'shock wave'. It is shown that numerical simulation of astrophysical problems in which high-amplitude shock waves are encountered (supernova explosions, modelling of jets) with conservation of entropy, rather than of energy, leads to large errors in the shock calculations. The isentropic equations of gas dynamics can be used only when there are no strong discontinuities in the solution or when the intensity of the shocks is not high and they do not significantly affect the flow.
Numerical Simulation of Cylindrical Solitary Waves in Periodic Media
Quezada de Luna, Manuel
2013-07-14
We study the behavior of nonlinear waves in a two-dimensional medium with density and stress relation that vary periodically in space. Efficient approximate Riemann solvers are developed for the corresponding variable-coefficient first-order hyperbolic system. We present direct numerical simulations of this multiscale problem, focused on the propagation of a single localized perturbation in media with strongly varying impedance. For the conditions studied, we find little evidence of shock formation. Instead, solutions consist primarily of solitary waves. These solitary waves are observed to be stable over long times and to interact in a manner approximately like solitons. The system considered has no dispersive terms; these solitary waves arise due to the material heterogeneity, which leads to strong reflections and effective dispersion.
Numerical simulation of the passive gas mixture flow
Directory of Open Access Journals (Sweden)
Kyncl Martin
2016-01-01
Full Text Available The aim of this paper is the numerical solution of the equations describing the non-stationary compressible turbulent multicomponent flow in gravitational field. The mixture of perfect inert gases is assumed. We work with the RANS equations equipped with the k-omega and the EARSM turbulence models. For the simulation of the wall roughness we use the modification of the specific turbulent dissipation. The finite volume method is used, with thermodynamic constants being functions in time and space. In order to compute the fluxes through the boundary faces we use the modification of the Riemann solver, which is the original result. We present the computational results, computed with the own-developed code (C, FORTRAN, multiprocessor, unstructured meshes in general.
Numerical Simulations of Intraband Crosstalk in Optical Cross Connect
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
All optical network based on wavelength division multiplexing transmission system with optical cross connect (OXC) is an essential approach for optical commumications.Crosstalk introduced by OXC (specially large scale one) is a key limiting factor for its capacity. Optical signal passing through a typical OXC is analyzed in this paper, followed by description of the generation and effect of intraband crosstalk.The power penalties induced by intraband crosstalk versus the number of multiplexed wavelengths M and the number of input fibers N have been given by numerical simulations. The results show that the coherent crosstalk is the most critical limitation on OXC and depends more closely on the number of multiplexed wavelengths M than the number of input fibers N. Crosstalk is suppressed by doubly filtering, fixing optimum decision-threshold and appropriately choosing the number of multiplexed wavelengths M.
Numerical simulation of the resonantly excited capillary-gravity waves
Hanazaki, Hideshi; Hirata, Motonori; Okino, Shinya
2015-11-01
Capillary gravity waves excited by an obstacle are investigated by a direct numerical simulation. In the flow without capillary effects, it is well known that large-amplitude upstream advancing solitary waves are generated periodically under the resonant condition, i.e., when the phase velocity of the long surface waves and the mean flow velocity agrees. With capillary effects, solutions of the Euler equations show the generation of very short waves further upstream of the solitary waves and also in the depression region downstream of the obstacle. The overall characteristics of these waves agree with the solutions of the forced fifth-order KdV equation, while the weakly nonlinear theory generally overestimates the wavelength of the short waves.
Numerical Simulations of the Physical Process for Hailstone Growth
Institute of Scientific and Technical Information of China (English)
FANG Wen; ZHENG Guoguang; HU Zhijin
2005-01-01
Theoretical and experimental studies show that during hail growth the heat and mass transfers play a determinant role in growth rates and different structures. However, many numerical model researchers made extrapolation of the key heat transfer coefficient of the thermal balance expression from measurements of evaporating water droplets obtained under small Renolds numbers (Re ≤ 200) introduced by Ranz and Marshall, leading to great difference from reality. This paper is devoted to the parameterization of measured heat transfer coefficients under Renolds numbers related to actual hail scales proposed by Zheng, which are then applied, to Hu-He 1D and 3D models for hail growth respectively, indicating that the melting rate of a hailstone is 12%-50% bigger, the evaporation rate is 10%-200% higher and the dry-wet growth rate is 10%-40% larger from the present simulations than from the prototype models.
Emitter Design and Numerical Simulation Based on the Extenics Theory
Directory of Open Access Journals (Sweden)
Jiang Fan
2014-05-01
Full Text Available In order to improve the performance of emitter, the extenics theory is introduced, whose divergent thinking is used to resolve the conflict of anti-clogging and energy dissipation and a new structure is proposed. The wide triangular areas are designed to reduce the flow rate behind of the each orifice and be easy to precipitation of impurities. The orifices are set to gradually decrease water kinetic energy and the flow channel is designed to be dismantle. The numerical simulation technology is used to analyze the internal flow field of emitter, the flow field results show that the improved emitter has great effect of energy dissipation and anti-clogging. As the same time, the structure of emitter is optimized and L1 = 31 mm, L2 = 21 mm, L3 = 8 mm and L4 = 5 mm are the optimization size values.
Many-body localization: Entanglement and efficient numerical simulations
Pollmann, Frank
Many-body localization (MBL) occurs in isolated quantum systems when Anderson localization persists in the presence of finite interactions. To understand this phenomenon, the development of new efficient numerical methods to find highly excited many-body eigenstates is essential. In this talk, we will discuss two complimentary approaches to simulate MBL systems: First, we introduce a variant of the density-matrix renormalization group (DMRG) method that obtains individual highly excited eigenstates of MBL systems to machine precision accuracy at moderate to large disorder. This method explicitly takes advantage of the local spatial structure and the low entanglement which is characteristic for MBL eigenstates. Second, we propose an approach to directly find an approximate compact representation of the diagonalizing unitary by using a variational unitary matrix-product operator.
CLOUDY 90: Numerical Simulation of Plasmas and Their Spectra
Ferland, G. J.; Korista, K. T.; Verner, D. A.; Ferguson, J. W.; Kingdon, J. B.; Verner, E. M.
1998-07-01
CLOUDY is a large-scale spectral synthesis code designed to simulate fully physical conditions within an astronomical plasma and then predict the emitted spectrum. Here we describe version 90 (C90) of the code, paying particular attention to changes in the atomic database and numerical methods that have affected predictions since the last publicly available version, C84. The computational methods and uncertainties are outlined together with the direction future development will take. The code is freely available and is widely used in the analysis and interpretation of emission-line spectra. Web access to the Fortran source for CLOUDY, its documentation Hazy, and an independent electronic form of the atomic database is also described.
Numerical simulation of high Reynolds number bubble motion
Energy Technology Data Exchange (ETDEWEB)
McLaughlin, J.B. [Clarkson Univ., Potsdam, NY (United States)
1995-12-31
This paper presents the results of numerical simulations of bubble motion. All the results are for single bubbles in unbounded fluids. The liquid phase is quiescent except for the motion created by the bubble, which is axisymmetric. The main focus of the paper is on bubbles that are of order 1 mm in diameter in water. Of particular interest is the effect of surfactant molecules on bubble motion. Results for the {open_quotes}insoluble surfactant{close_quotes} model will be presented. These results extend research by other investigators to finite Reynolds numbers. The results indicate that, by assuming complete coverage of the bubble surface, one obtains good agreement with experimental observations of bubble motion in tap water. The effect of surfactant concentration on the separation angle is discussed.
Numerical Simulations of Driven Supersonic Relativistic MHD Turbulence
Zrake, Jonathan; 10.1063/1.3621748
2011-01-01
Models for GRB outflows invoke turbulence in relativistically hot magnetized fluids. In order to investigate these conditions we have performed high-resolution three-dimensional numerical simulations of relativistic magneto-hydrodynamical (RMHD) turbulence. We find that magnetic energy is amplified to several percent of the total energy density by turbulent twisting and folding of magnetic field lines. Values of epsilon_B near 1% are thus naturally expected. We study the dependence of saturated magnetic field energy fraction as a function of Mach number and relativistic temperature. We then present power spectra of the turbulent kinetic and magnetic energies. We also present solenoidal (curl-like) and dilatational (divergence-like) power spectra of kinetic energy. We propose that relativistic effects introduce novel couplings between these spectral components. The case we explore in most detail is for equal amounts of thermal and rest mass energy, corresponding to conditions after collisions of shells with re...