Numerical Simulation of the Vortex-Induced Vibration of A Curved Flexible Riser in Shear Flow
Zhu, Hong-jun; Lin, Peng-zhi
2018-06-01
A series of fully three-dimensional (3D) numerical simulations of flow past a free-to-oscillate curved flexible riser in shear flow were conducted at Reynolds number of 185-1015. The numerical results obtained by the two-way fluid-structure interaction (FSI) simulations are in good agreement with the experimental results reported in the earlier study. It is further found that the frequency transition is out of phase not only in the inline (IL) and crossflow (CF) directions but also along the span direction. The mode competition leads to the non-zero nodes of the rootmean- square (RMS) amplitude and the relatively chaotic trajectories. The fluid-structure interaction is to some extent reflected by the transverse velocity of the ambient fluid, which reaches the maximum value when the riser reaches the equilibrium position. Moreover, the local maximum transverse velocities occur at the peak CF amplitudes, and the values are relatively large when the vibration is in the resonance regions. The 3D vortex columns are shed nearly parallel to the axis of the curved flexible riser. As the local Reynolds number increases from 0 at the bottom of the riser to the maximum value at the top, the wake undergoes a transition from a two-dimensional structure to a 3D one. More irregular small-scale vortices appeared at the wake region of the riser, undergoing large amplitude responses.
International Nuclear Information System (INIS)
Santos, Kamylla A.L. dos; Lima Filho, Hilario J.B. de; Benachour, Mohand; Dantas, Carlos C.; Santos, Valdemir A. dos
2013-01-01
Was obtained the radial profile of the catalyst volume fraction in a riser of the cold flow pilot unit of the Fluid Catalytic Cracking (FCC) unit, which was used for adjustment of the entrance conditions of the catalyst in a simulation program by Computational Fluid Dynamics (CFD). The height of the riser of the Cold Flow Pilot Unity (CFPU) utilized is 6.0m and its inner diameter is 0.097 m. A radiation-γ source of Am-241 and a NaI (Tl) detector, with shielding made of lead, have been installed on a steel backing that maintains the geometry of the source-detector-riser and allows to vary the distance from the source to the detector and the radial position in a given cross section of the riser. The data associated with the simulation of volume fraction radial profile of the catalyst were: Fluent software, version 12.0; preprocessor GAMBIT, version 2.3.16; Eulerian approach; structured mesh, cell number of 60000; turbulence model used was k-ε and kinetic theory of granular flow (KTGF) was implemented to describe the solid phase. Comparison of radial profiles simulated and experimental of the catalyst volumetric fraction in the CFPU riser allowed the identification of needs adjustments in the simulation for the input of catalyst, with consequent validation for the proposed model simulation. (author)
Mesh refinement of simulation with the AID riser transmission gamma
International Nuclear Information System (INIS)
Lima Filho, Hilario J.B. de; Benachour, Mohand; Dantas, Carlos C.; Brito, Marcio F.P.; Santos, Valdemir A. dos
2013-01-01
Type reactors Circulating Fluidized Bed (CFBR) vertical, in which the particulate and gaseous phases have flows upward (riser) have been widely used in gasification processes, combustion and fluid catalytic cracking (FCC). These biphasic reactors (gas-solid) efficiency depends largely on their hydrodynamic characteristics, and shows different behaviors in the axial and radial directions. The solids axial distribution is observed by the higher concentration in the base, getting more diluted toward the top. Radially, the solids concentration is characterized as core-annular, in which the central region is highly diluted, consisting of dispersed particles and fluid. In the present work developed a two-dimensional geometry (2D) techniques through simulations in computational fluid dynamics (CFD) to predict the gas-solid flow in the riser type CFBR through transient modeling, based on the kinetic theory of granular flow . The refinement of computational meshes provide larger amounts of information on the parameters studied, but may increase the processing time of the simulations. A minimum number of cells applied to the mesh construction was obtained by testing five meshes. The validation of the hydrodynamic parameters was performed using a range of 241Am source and detector NaI (Tl). The numerical results were provided consistent with the experimental data, indicating that the refined computational mesh in a controlled manner, improve the approximation of the expected results. (author)
DEFF Research Database (Denmark)
Hansen, Kim Granly; Solberg, Tron; Hjertager, Bjørn Helge
2004-01-01
The isothermal decomposition of ozone has been implemented in the CFD code FLOTRACS-MP-3D. The code is a 3D multiphase computational fluid dynamics code with an Eulerian description of both gas and particle phase. The turbulent motion of the particulate phase is modeled using the kinetic theory...... for granular flow, and the gas phase turbulence is modeled using a Sub-Grid-Scale model, cf. Ibsen et al. (2001). The decomposition reaction is studied in a 3D representation of a 0.254 m i.d. riser, which has been studied experimentally by Ouyang et al. (1993). The authors obtained profiles of ozone...
Oscillation of a rigid catenary riser due to the internal two-phase flow
Energy Technology Data Exchange (ETDEWEB)
Bordalo, Sergio N.; Morooka, Celso K.; Cavalcante, Cesar C.P. [Universidade Estadual de Campinas (UNICAMP), SP (Brazil); Matt, Cyntia G.C.; Franciss, Ricardo [PETROBRAS, Rio de Janeiro, RJ (Brazil). Centro de Pesquisas
2008-07-01
Production of petroleum reservoirs from deep and ultra-deep waters is of paramount importance in Brazil, and several researches are necessary to develop appropriated equipment and risers for those operational conditions. Risers are suspended pipes used to transport the petroleum fluids between the seabed and the floating production unit. The structural flexibility of riser's lines is conferred by its length when compared with the diameter, characterizing it as a slender body. The risers are submitted to large static and dynamic loads originated from its own weight, waves, currents, platform motions and the internal flow. These loadings may threaten, by fatigue, the structural integrity of the system, compromising its useful life, and so they must be considered in the riser's project. There is a large amount of knowledge in the literature about the effects of external loadings on these systems, but the effect of the internal flow remains vastly unexplored. The variation of the flow mass and momentum inside the riser causes a dynamic loading on this system, originating an oscillatory motion. Furthermore, the gas-liquid two-phase flow may assume several flow patterns (bubble, slug, intermittent or annular), each one possessing completely different characteristics. In this work, the influence of the internal flow on the oscillatory motion (whipping motion) of catenary risers is analyzed. To provide a better understanding of this physical phenomenon, a scaled apparatus was designed and built. The material used to manufacture the riser's model was a flexible silicone tube, and air and water were used to simulate the two-phase flow. The instrumentation used to measure the fluids flow rates and the sustaining force at the top of the model was installed in the apparatus. A video acquisition system was used to determine the displacements, and frequency spectrum, of color targets positioned throughout the model, under several flow conditions. The flow patterns
Mathematics of flexible risers including pressure and internal flow affects
Energy Technology Data Exchange (ETDEWEB)
Seyed, F.B. (John Brown Engineers and Constructors Ltd., London (GB)); Patel, M.H. (University Coll., London (GB). Dept. of Mechanical Engineering)
1992-01-01
Derivations are presented for calculation of pressure and internal flow induced forces on flexible risers and other curved pipes using a mathematically rigorous approach. Approximate and exact methods are presented for calculation of pressure forces on straight and curved pipes in two dimensions. The mathematical identity of these equations with those for effective tension is illustrated. The force arising from the flow of an internal fluid of constant density is then calculated and combined with those for pressure forces in derivation of the catenary equations including pressure and internal flow terms. It is shown that internal flow contributes a new term to the expression for effective tension. These governing equations are then reduced for the specific cases of simple catenary, steep-S, lazy-S, steep-wave and lazy-wave risers. In each case, the solution method has been presented and the governing equilibrium and geometric compatability conditions cited. (author).
Modelling and Simulation of Coking in the Riser of an Industrial ...
African Journals Online (AJOL)
Modelling and Simulation of Coking in the Riser of an Industrial Fluid Catalytic Cracking (FCC) Unit. ... Log in or Register to get access to full text downloads. ... The yields of LCO, gasoline, gas and coke that were predicted by the model for industrial risers were ... Full Text: EMAIL FREE FULL TEXT EMAIL FREE FULL TEXT
Duanmu, Yu; Zou, Lu; Wan, De-cheng
2017-12-01
This paper aimed at describing numerical simulations of vortex-induced vibrations (VIVs) of a long flexible riser with different length-to-diameter ratio (aspect ratio) in uniform and shear currents. Three aspect ratios were simulated: L/D = 500, 750 and 1 000. The simulation was carried out by the in-house computational fluid dynamics (CFD) solver viv-FOAM-SJTU developed by the authors, which was coupled with the strip method and developed on the OpenFOAM platform. Moreover, the radial basis function (RBF) dynamic grid technique is applied to the viv-FOAM-SJTU solver to simulate the VIV in both in-line (IL) and cross-flow (CF) directions of flexible riser with high aspect ratio. The validation of the benchmark case has been completed. With the same parameters, the aspect ratio shows a significant influence on VIV of a long flexible riser. The increase of aspect ratio exerted a strong effect on the IL equilibrium position of the riser while producing little effect on the curvature of riser. With the aspect ratio rose from 500 to 1 000, the maximum IL mean displacement increased from 3 times the diameter to 8 times the diameter. On the other hand, the vibration mode of the riser would increase with the increase of aspect ratio. When the aspect ratio was 500, the CF vibration was shown as a standing wave with a 3rd order single mode. When the aspect ratio was 1 000, the modal weights of the 5th and 6th modes are high, serving as the dominant modes. The effect of the flow profile on the oscillating mode becomes more and more apparent when the aspect ratio is high, and the dominant mode of riser in shear flow is usually higher than that in uniform flow. When the aspect ratio was 750, the CF oscillations in both uniform flow and shear flow showed multi-mode vibration of the 4th and 5th mode. While, the dominant mode in uniform flow is the 4th order, and the dominant mode in shear flow is the 5th order.
A case study in flow assurance of a pipeline-riser system using OLGA
Energy Technology Data Exchange (ETDEWEB)
Nemoto, Rafael Horschutz; Balino, Jorge Luis [Nucleo de Dinamica e Fluidos. Dept. de Engenharia Mecanica. Universidade de Sao Paulo (EP/USP), SP (Brazil)], e-mails: rafael.nemoto@usp.br, jlbalino@usp.br; Tanaka, Rafael Loureiro; Godinho, Carlos Alberto [Prysmian Cables and Systems, Cariacica, ES (Brazil)], e-mails: rafael.tanaka@prysmian.com, carlos.godinho@prysmian.com
2010-07-01
In this paper, a case study in flow assurance is performed considering an offshore operating system, using the software OLGA. As operating system we consider a pipeline-riser geometry with typical dimensions of offshore oil production systems, and a three-phase flow of oil, gas and water. The model developed in OLGA considers the composition and dimensions of the tubes, heat transfer parameters, process equipment and fluid sources. The fluids properties are calculated using the software PVTsim. Simulations are ran in order to determine the pipeline inner diameter and insulation required to satisfy pressure and temperature requirements. It is also possible to simulate the transient behavior of the system, which allows to evaluate if production instabilities are present. In case instabilities exist, two mitigation alternatives are evaluated: closure of a choke valve before the separator and gas lift. Considering a possible production shutdown, the tubes insulation is calculated in order to avoid hydrate formation. (author)
Fluid dynamics characterization of riser in a FCC cold flow model using gas radiotracer
International Nuclear Information System (INIS)
Santos, Valdemir A. dos; Lima, Emerson A.O.
2013-01-01
Was carried out the characterization of a diameter small riser of a cold flow model of a circulating fluidized bed (CFB), with aid of a radioactive tracer. Compressed air and catalytic cracking of petroleum flow through solids pneumatic transport regime, made of transparent material (glass, acrylic, PVC, polycarbonate) for study of problems in Fluid Catalytic Cracking (FCC) unit and development of methods of measurement of fluid dynamic parameters. The CFB model consisted of a mixer component solid-gas (compressed air at 25 deg C and 200 kN/m 2 ; cracking catalyst with an average diameter of 72μm and specific mass of 1,500 kg/m 3 ), comprising a riser pipe glass 0.02m internal diameter and 1.8m height, a gas solid separation vessel by flash effect, with the filter in the gas outlet, and a return column (a glass tube with an internal diameter of 0.0254m) to redirect the catalyst for the riser base. Recorded data allowed studies on residence time distribution of the gaseous phase in the riser, with the identification and characterization of the flow of gas-solid components in the CFB riser of small diameter. A plug flow type with deviations due to back mixing of catalyst close to the walls, associated with the density difference between this component was observed. (author)
Simulation of inlet and outlet riser break sequences in the N Reactor
International Nuclear Information System (INIS)
Bolander, M.A.; Fletcher, C.D.
1988-02-01
This report documents work performed at the Idaho National Engineering Laboratory (INEL) in support of the Westinghouse Hanford Company safety analyses of the N Reactor. The RELAP5/MOD2 computer code was used in analyzing two hypothetical transients. The computer code was modified specifically to simulate the refill behavior in the N Reactor process tubes. The transients analyzed were a double-ended rupture of an inlet riser column and a double-ended rupture of an outlet riser column
Flow Mapping in a Gas-Solid Riser via Computer Automated Radioactive Particle Tracking (CARPT)
Energy Technology Data Exchange (ETDEWEB)
Muthanna Al-Dahhan; Milorad P. Dudukovic; Satish Bhusarapu; Timothy J. O' hern; Steven Trujillo; Michael R. Prairie
2005-06-04
Statement of the Problem: Developing and disseminating a general and experimentally validated model for turbulent multiphase fluid dynamics suitable for engineering design purposes in industrial scale applications of riser reactors and pneumatic conveying, require collecting reliable data on solids trajectories, velocities ? averaged and instantaneous, solids holdup distribution and solids fluxes in the riser as a function of operating conditions. Such data are currently not available on the same system. Multiphase Fluid Dynamics Research Consortium (MFDRC) was established to address these issues on a chosen example of circulating fluidized bed (CFB) reactor, which is widely used in petroleum and chemical industry including coal combustion. This project addresses the problem of lacking reliable data to advance CFB technology. Project Objectives: The objective of this project is to advance the understanding of the solids flow pattern and mixing in a well-developed flow region of a gas-solid riser, operated at different gas flow rates and solids loading using the state-of-the-art non-intrusive measurements. This work creates an insight and reliable database for local solids fluid-dynamic quantities in a pilot-plant scale CFB, which can then be used to validate/develop phenomenological models for the riser. This study also attempts to provide benchmark data for validation of Computational Fluid Dynamic (CFD) codes and their current closures. Technical Approach: Non-Invasive Computer Automated Radioactive Particle Tracking (CARPT) technique provides complete Eulerian solids flow field (time average velocity map and various turbulence parameters such as the Reynolds stresses, turbulent kinetic energy, and eddy diffusivities). It also gives directly the Lagrangian information of solids flow and yields the true solids residence time distribution (RTD). Another radiation based technique, Computed Tomography (CT) yields detailed time averaged local holdup profiles at
modelling and modelling and simulation of coking in the riser
African Journals Online (AJOL)
eobe
into the modeling of FCC riser by predicting catalyst coke content as a function of reaction by predicting ... understanding of the process, hence restricting scale up to within the ... MATLAB (R2009a) on a Compaq HP CQ61 laptop. The following ...
Recreating Riser Slugging Flow Based on an Economic Lab-sized Setup
DEFF Research Database (Denmark)
Hansen, Lasse; Pedersen, Simon; Yang, Zhenyu
2013-01-01
As a kind of periodic phenomenon, the slugging flow in the offshore oil & gas production addresses a lot of attentions, due to its limitation of production rate, periodic overload processing facilities, and even direct cause of emergent shutdown. This work studies the emulation of the riser...... slugging flow in the offshore oil & gas production, by constructing an economical lab-sized setup in the university campus. Firstly, the construction and used components for the lab setup are illustrated; then, the constructed setup is validated by checking the consistency with some existing typical riser...
Energy Technology Data Exchange (ETDEWEB)
Kim, Sin-Yeob; Shin, Dong-Ho; Park, Goon-Cherl; Cho, Hyoung Kyu [Seoul National Univ., Seoul (Korea, Republic of); Kim, Chan-Soo [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2016-10-15
VHTR being developed at Korea Atomic Energy Research Institute adopts an air-cooled Reactor Cavity Cooling System (RCCS) incorporating rectangular riser channels to remove the afterheat emitted from the reactor vessel. Because the performance of RCCS is determined by heat removal rate through the RCCS riser, it is important to understand the heat transfer phenomena in the RCCS riser to ensure the safety of the reactor. In the mixed convection, due to the buoyance force induced by temperature and density differences, local flow structure and heat transfer mode near the heated wall have significantly dissimilar characteristics from both forced convection and free convection. In this study, benchmark calculation was conducted to reproduce the previous statements that V2F turbulence model can capture the mixed convection phenomena with the Shehata's experimental data. Then, the necessity of the model validation for the mixed convection phenomena was confirmed with the CFD analyses for the geometry of the prototype RCCS riser. For the purpose of validating the turbulence models for mixed convection phenomena in the heated rectangular riser duct, validation plan with three experimental tests was introduced. Among them, the flow visualization test facility with preserved cross-section geometry was introduced and a preliminary test result was shown.
Effect of flow on corrosion in catenary risers and its corrosion inhibitor performance
Energy Technology Data Exchange (ETDEWEB)
Ferreira, Pedro Altoe; Magalhaes, Alvaro Augusto Oliveira; Silva, Jussara de Mello [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil); Kang, Cheolho; More, Parimal P. [Det Norske Veritas (DNV), Oslo (Norway)
2009-07-01
In oil and gas production, multiphase flow is often encountered and a range of different flow patterns can be experienced in pipelines. The flow regime transition and flow characteristics can be changed with the change of pipeline topography, which affects the corrosion and the performance of corrosion inhibitor in these multiphase pipelines. This paper outlines on the effect of inclination on the flow characteristics and their subsequent effect on corrosion rates. Also, this paper presents on the performance of three candidate corrosion inhibitors under severe slugging conditions at low water cut. For the simulation of offshore flow lines and risers, the experiments were carried out in a 44 m long, 10 cm diameter, three different pipeline inclinations of 0, 3 and 45 degrees. Light condensate oil with a viscosity of 2.5 cP at room temperature was used and water cut was 20%. The results indicated that the baseline corrosion rate in 45 degrees showed higher than other inclinations. Each corrosion inhibitor showed a different inhibitor performance. (author)
Features of a time domain simulation tool for rigid riser design
Energy Technology Data Exchange (ETDEWEB)
Morooka, Celso K.; Brandt, Dustin M. [Universidade Estadual de Campinas (UNICAMP), SP (Brazil). Faculdade de Engenharia Mecanica. Dept. de Engenharia de Petroleo; Matt, Cyntia G.C.; Franciss, Ricardo [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil). Centro de Pesquisas
2008-07-01
This paper present a number of numerical implementations designed for the analysis of rigid riser's static and dynamic behavior that includes the effects of vortex induced vibrations (VIV) and marine hydrodynamic loads in time domain. Features include the ability to consider pipe with a free-span utilizing a soil/riser interaction model. An implementation of a numerical coupling scheme to couple the vertical riser and platform dynamics was developed to allow prediction of the sub sea Blow-Out Preventer (BOP) re-entry into a sub sea petroleum well when drilling different phases of deep and ultra-deep wells. The developments contains support for the consideration of the Self Standing Hybrid Riser (SSHR) configuration which has been shown to be a promising riser configuration in deep and ultra-deep waters. A graphical interface was also created to better grasp the results and aid in the modeling, processing and to help analyze the numerical simulations, contributing to enhance agility and quality of the riser design and analysis processes. (author)
Carlos Varas, Álvaro E; Peters, E A J F; Kuipers, J A M
2017-05-17
We report a computational fluid dynamics-discrete element method (CFD-DEM) simulation study on the interplay between mass transfer and a heterogeneous catalyzed chemical reaction in cocurrent gas-particle flows as encountered in risers. Slip velocity, axial gas dispersion, gas bypassing, and particle mixing phenomena have been evaluated under riser flow conditions to study the complex system behavior in detail. The most important factors are found to be directly related to particle cluster formation. Low air-to-solids flux ratios lead to more heterogeneous systems, where the cluster formation is more pronounced and mass transfer more influenced. Falling clusters can be partially circumvented by the gas phase, which therefore does not fully interact with the cluster particles, leading to poor gas-solid contact efficiencies. Cluster gas-solid contact efficiencies are quantified at several gas superficial velocities, reaction rates, and dilution factors in order to gain more insight regarding the influence of clustering phenomena on the performance of riser reactors.
International Nuclear Information System (INIS)
Murakawa, H.; Antal, S.P.; Lahey, R T.
2008-01-01
The object of this work was to simulate developing multidimensional velocity and void fraction distributions in bubbly and churn turbulent two-phase flows. An advanced Computational Multiphase Fluid Dynamics (CMFD) code, NPHASE, was used to perform three-dimensional, multi-field simulations of the developing phasic velocity and phase distributions in vertical adiabatic conduits. The NPHASE code employed a multi-field two-fluid model, in which, for churn turbulent flow, the vapor phase was divided into small and large, cap bubble fields. In addition, state-of-the-art interfacial area density and field-to-field mass transfer models were used for both the small and large, cap bubbles. In particular, the bubble breakup and coalescence processes were quantified using a two-group interfacial area density transport equation. This allowed the CMFD simulation of developing churn turbulent flows in an ESBWR with and without vertical riser channels in the chimney region above the core. Based on these simulations it was concluded that riser channels have little adverse effect on the induced natural circulation flow through the core and the stability characteristics of an ESBWR. (authors)
Directory of Open Access Journals (Sweden)
Zheng-Shou Chen
2012-03-01
Full Text Available This article presents a numerical investigation concerning the effect of two kinds of axially progressing internal flows (namely, upward and downward on fluid–structure interaction (FSI dynamics about a marine riser model which is subject to external shear current. The CAE technology behind the current research is a proposed FSI solution, which combines structural analysis software with CFD technology together. Efficiency validation for the CFD software was carried out first. It has been proved that the result from numerical simulations agrees well with the observation from relating model test cases in which the fluidity of internal flow is ignorable. After verifying the numerical code accuracy, simulations are conducted to study the vibration response that attributes to the internal progressive flow. It is found that the existence of internal flow does play an important role in determining the vibration mode (/dominant frequency and the magnitude of instantaneous vibration amplitude. Since asymmetric curvature along the riser span emerges in the case of external shear current, the centrifugal and Coriolis accelerations owing to up- and downward internal progressive flows play different roles in determining the fluid–structure interaction response. The discrepancy between them becomes distinct, when the velocity ratio of internal flow against external shear current is relatively high.
Energy Technology Data Exchange (ETDEWEB)
Fort, James A.; Pfund, David M.; Sheen, David M.; Pappas, Richard A.; Morgen, Gerald P.
2007-04-01
The MFDRC was formed in 1998 to advance the state-of-the-art in simulating multiphase turbulent flows by developing advanced computational models for gas-solid flows that are experimentally validated over a wide range of industrially relevant conditions. The goal was to transfer the resulting validated models to interested US commercial CFD software vendors, who would then propagate the models as part of new code versions to their customers in the US chemical industry. Since the lack of detailed data sets at industrially relevant conditions is the major roadblock to developing and validating multiphase turbulence models, a significant component of the work involved flow measurements on an industrial-scale riser contributed by Westinghouse, which was subsequently installed at SNL. Model comparisons were performed against these datasets by LANL. A parallel Office of Industrial Technology (OIT) project within the consortium made similar comparisons between riser measurements and models at NETL. Measured flow quantities of interest included volume fraction, velocity, and velocity-fluctuation profiles for both gas and solid phases at various locations in the riser. Some additional techniques were required for these measurements beyond what was currently available. PNNL’s role on the project was to work with the SNL experimental team to develop and test two new measurement techniques, acoustic tomography and millimeter-wave velocimetry. Acoustic tomography is a promising technique for gas-solid flow measurements in risers and PNNL has substantial related experience in this area. PNNL is also active in developing millimeter wave imaging techniques, and this technology presents an additional approach to make desired measurements. PNNL supported the advanced diagnostics development part of this project by evaluating these techniques and then by adapting and developing the selected technology to bulk gas-solids flows and by implementing them for testing in the SNL riser
Engineering Task Plan for simulated riser installation by use of rotary drilling
International Nuclear Information System (INIS)
Barnes, G.A.
1995-12-01
This task is being performed to demonstrate the feasibility of the best riser installation alternative identified in the Engineering Study. This Engineering Task Plan (ETP) will be the WHC project management plan for the riser installation demonstration activities
Energy Technology Data Exchange (ETDEWEB)
Tsukada, Raphael I.; Morooka, Celso K. [Universidade Estadual de Campinas (UNICAMP), SP (Brazil). Faculdade de Engenharia Mecanica; Franciss, Ricardo; Matt, Cyntia G.C. [Petroleo Brasileiro S.A. (PETROBRAS), Rio de Janeiro, RJ (Brazil). Centro de Pesquisas (CENPES)
2009-07-01
Hydrocarbon discoveries in ultra deep waters and the recent pre-salt deep carbonate reservoirs along the Brazilian coast demand further technological development in order to exploit these resources. These developments usually require new concepts for offshore sea surface structures and subsea systems for the petroleum and gas production, which means cost effective solutions that provides higher operational safety on drilling and production operations. In this scenario, the effect of the natural phenomenon of Vortex-Induced Vibration (VIV) on risers is one of the concerns for its design due to the tendency of VIV to increase levels of stresses in the riser structure. Therefore the correct prediction of stresses and displacements due to VIV is of great importance for designing riser systems. The present work presents new developments based on previous results for VIV in vertical risers extended to curved risers such as steel catenary risers (SCR). Numerical simulations have been performed in time domain, and experimental results from model tests with a scaled SCR in a towing tank have been used to evaluate the proposed developments. Finally, the conclusions from the analysis of the results bring very promising results. (author)
CFD Simulation of Vortex Induced Vibration for FRP Composite Riser with Different Modeling Methods
Directory of Open Access Journals (Sweden)
Chunguang Wang
2018-04-01
Full Text Available Steel risers are widely used in offshore oil and gas industry. However, the production capacity and depths are limited due to their extreme weight and poor fatigue and corrosion resistance. Nowadays, it is confirmed that fiber reinforced polymer (FRP composite risers have apparent advantages over steel risers. However, the study of vortex induced vibration (VIV for composite risers is rarely involved. Three different risers (one steel riser and two composite risers were compared for their VIV characteristics. The effects of 2D and 3D models and fluid–structure interaction (FSI were considered. The models of composite risers are established by effective modulus method (EMM and layered-structure method (LSM. It is found that 2D model are only suitable for ideal condition, while, for real situation, 3D model with FSI has to be considered. The results show that the displacements of the FRP composite risers are significantly larger than those of the steel riser, while the stresses are reversed. In addition, the distributions of the displacements and stresses depend on the geometries, material properties, top-tension force, constraints, etc. In addition, it is obvious that EMM are suitable to study the global working condition while LSM can be utilized to obtain the results in every single composite layer.
Energy Technology Data Exchange (ETDEWEB)
Apolonio, Adelia M.; Santos, Valdemir A. dos; Finkler, Christine L.L. [Universidade Catolica de Pernambuco (UNICAP), Recife, PE (Brazil); Dantas, Carlos C. [Universidade Federal de Pernambuco (UFPE), Recife, PE (Brazil). Dept. de Energia Nuclear
2008-07-01
Local variations in the catalyst/vacuum gas oils mixing can lead to low conversions in some parts of a fluid cracking catalytic riser, while in other parts, high conversions will produce undesirable fuel gas and coke quantities. Knowledge of the apparent solid concentration in a cross-section of the riser is then essential. A computational program to generate tri dimensional graphics and level curves of the radial catalyst density in FCC risers was elaborated. The algorithm is based on determinations of the polynomial coefficients with aid of least square method and was tested with literature data, obtained by applications of nuclear technique of gamma radiation attenuation. The simulation results showed convergence with the experimental data. The precision of the mapping depends on the number of measurements and promote better conditions of diagnostic of the distribution catalyst type in the riser. (author)
Severe Slugging in Air-Water Hybrid Riser System
Directory of Open Access Journals (Sweden)
Jing Gong
2014-11-01
Full Text Available In the subsea pipeline gathering system, severe slugging flow is prone to occur. Severe slugging flow brings major threat to production and flow assurance in oil and gas industry due to periodical pressure oscillation and large liquid volume. Currently many researchers pay much more attention on L-shaped riser, catenaries, and S-shaped riser; little research has been made on hybrid riser, which is applied in the Africa West and Gulf of Mexico oil fields. Flow characteristics simulation for hybrid riser is made in this paper, using the one-dimensional and quasi-equilibrium model to simulate not only the riser-base pressure, severe slugging period, and the liquid slug length of the whole system but also base-pressure in the flexible pipe section. The calculated results match well with the experiment data. Besides, the influence of flexible pipe to the severe slugging characteristics of hybrid riser system is analyzed, which are significant for the determination of riser structure.
Energy Technology Data Exchange (ETDEWEB)
Zakarian, E.
2000-03-10
Recent estimations predict that over half the remaining offshore oil and gas reserves are located in deep water and marginal fields. For such reserves, economic recovery methods are required. Then, multiphase flows are transported within pipelines and separated on treatment platforms built in shallow water or processed in onshore facilities. Unfortunately, hydrodynamic instabilities may occur whenever gas and liquid flow in a pipeline, generating serious operating problems. This dissertation presents a new way to model two-phase flows in pipelines such as pipeline-riser systems. Equations are algebraic and differential. Their smoothness depends on the closure laws of the problem such as slip or friction laws. Smooth forms of these closure laws are presented for the first time in this dissertation. Therefore, a mathematical analysis of our model fits into a classical frame: a linear analysis leads to an analytical expression of the boundary between stable and unstable flows. A nonlinear analysis provides for the first time, the bifurcation curves of gas-liquid flows in pipe-riser systems, locally round their stability boundary. (author)
Directory of Open Access Journals (Sweden)
Borsuk Grzegorz
2016-03-01
Full Text Available Clinker burning process has a decisive influence on energy consumption and the cost of cement production. A new problem is to use the process of decarbonization of alternative fuels from waste. These issues are particularly important in the introduction of a two-stage combustion of fuel in a rotary kiln without the typical reactor-decarbonizator. This work presents results of numerical studies on thermal-hydraulic phenomena in the riser chamber, which will be designed to burn fuel in the system where combustion air is supplied separately from the clinker cooler. The mathematical model is based on a combination of two methods of motion description: Euler description for the gas phase and Lagrange description for particles. Heat transfer between particles of raw material and gas was added to the numerical calculations. The main aim of the research was finding the correct fractional distribution of particles. For assumed particle distribution on the first stage of work, authors noted that all particles were carried away by the upper outlet to the preheater tower, what is not corresponding to the results of experimental studies. The obtained results of calculations can be the basis for further optimization of the design and operating conditions in the riser chamber with the implementation of the system.
Energy Technology Data Exchange (ETDEWEB)
Kallio, S. [Aabo Akademi, Turku (Finland). Inst. of Heat Engineering
1996-12-01
The aim of this work was to study the effects of different parameters on the flow behaviour in a CFB riser by means of empirical models based on measurement data and a computer code based on macroscopic equations for multiphase flow. The effects of primary air velocity and riser geometry have been observed in the results. Simulation of secondary air flow proved to be problematic with the software used. In the project, also analyses of measurement data from cold model experiments has been performed. Moreover, the possibilities to use commercial CFD codes for simulation of gas-solids flow were investigated. The code FLUENT seemed promising. (author)
International Nuclear Information System (INIS)
Spenik, J.; Ludlow, J.C.; Compston, R.; Breault, R.W.
2007-01-01
The local gas velocity and the intensity of the gas turbulence in a gas/solid flow are a required measurement in validating the gas and solids flow structure predicted by computational fluid dynamic (CFD) models in fluid bed and transport reactors. The high concentration and velocities of solids, however, make the use of traditional gas velocity measurement devices such as pitot tubes, hot wire anemometers and other such devices difficult. A method of determining these velocities has been devised at the National Energy Technology Laboratory employing tracer gas. The technique developed measures the time average local axial velocity gas component of a gas/solid flow using an injected tracer gas which induces changes in the heat transfer characteristics of the gas mixture. A small amount of helium is injected upstream a known distance from a self-heated thermistor. The thermistor, protected from the solids by means of a filter, is exposed to gases that are continuously extracted from the flow. Changes in the convective heat transfer characteristics of the gas are indicated by voltage variations across a Wheatstone bridge. When pulsed injections of helium are introduced to the riser flow the change in convective heat transfer coefficient of the gas can be rapidly and accurately determined with this instrument. By knowing the separation distance between the helium injection point and the thermistor extraction location as well as the time delay between injection and detection, the gas velocity can easily be calculated. Variations in the measured gas velocities also allow the turbulence intensity of the gas to be estimated
International Nuclear Information System (INIS)
Melo, Ana Cristina Bezerra Azedo de
2004-12-01
The fluid dynamic behavior of a riser in a cold type FCC model was investigated by means of catalyst concentration distribution measured with gamma attenuation and simulated with a mathematical model. In the riser of the cold model, MEF, 0,032 m in diameter, 2,30 m in length the fluidized bed, whose components are air and FCC catalyst, circulates. The MEF is operated by automatic control and instruments for measuring fluid dynamic variables. An axial catalyst concentration distribution was measured using an Am-241 gamma source and a NaI detector coupled to a multichannel provided with a software for data acquisition and evaluation. The MEF was adapted for a fluid dynamic model validation which describes the flow in the riser, for example, by introducing an injector for controlling the solid flow in circulation. Mathematical models were selected from literature, analyzed and tested to simulate the fluid dynamic of the riser. A methodology for validating fluid dynamic models was studied and implemented. The stages of the work were developed according to the validation methodology, such as data planning experiments, study of the equations which describe the fluidodynamic, computational solvers application and comparison with experimental data. Operational sequences were carried out keeping the MEF conditions for measuring catalyst concentration and simultaneously measuring the fluid dynamic variables, velocity of the components and pressure drop in the riser. Following this, simulated and experimental values were compared and statistical data treatment done, aiming at the required precision to validate the fluid dynamic model. The comparison tests between experimental and simulated data were carried out under validation criteria. The fluid dynamic behavior of the riser was analyzed and the results and the agreement with literature were discussed. The adopt model was validated under the MEF operational conditions, for a 3 to 6 m/s gas velocity in the riser and a slip
Energy Technology Data Exchange (ETDEWEB)
Bennett, W.; Jimenez, A.F.
1987-09-08
This patent describes a method for storing and retrieving a riser pipe, comprising the steps of: providing an upright annular magazine comprised of an inside annular wall and an outside annular wall, the magazine having an open top; storing the riser pipe in a substantially vertically oriented position within the annular magazine; and moving the riser pipe upwardly through the open top of the annular magazine at an angle to the vertical along at least a portion of the length of the riser pipe.
Liangjie, Mao; Qingyou, Liu; Shouwei, Zhou
2014-01-01
A considerable number of studies for VIV under the uniform flow have been performed. However, research on VIV under shear flow is scarce. An experiment for VIV under the shear flow with the same shear parameter at the two different Reynolds numbers was conducted in a deep-water offshore basin. Various measurements were obtained by the fiber bragg grating strain sensors. Experimental data were analyzed by modal analysis method. Results show several valuable features. First, the corresponding maximum order mode of the natural frequency for shedding frequency is the maximum dominant vibration mode and multi-modal phenomenon is appeared in VIV under the shear flow, and multi-modal phenomenon is more apparent at the same shear parameter with an increasing Reynolds number under the shear flow effect. Secondly, the riser vibrates at the natural frequency and the dominant vibration frequency increases for the effect of the real-time tension amplitude under the shear flow and the IL vibration frequency is the similar with the CF vibration frequency at the Reynolds number of 1105 in our experimental condition and the IL dominant frequency is twice the CF dominant frequency with an increasing Reynolds number. In addition, the displacement trajectories at the different locations of the riser appear the same shape and the shape is changed at the same shear parameter with an increasing Reynolds number under the shear flow. The diagonal displacement trajectories are observed at the low Reynolds number and the crescent-shaped displacement trajectories appear with an increasing Reynolds number under shear flow in the experiment.
Directory of Open Access Journals (Sweden)
Mao Liangjie
Full Text Available A considerable number of studies for VIV under the uniform flow have been performed. However, research on VIV under shear flow is scarce. An experiment for VIV under the shear flow with the same shear parameter at the two different Reynolds numbers was conducted in a deep-water offshore basin. Various measurements were obtained by the fiber bragg grating strain sensors. Experimental data were analyzed by modal analysis method. Results show several valuable features. First, the corresponding maximum order mode of the natural frequency for shedding frequency is the maximum dominant vibration mode and multi-modal phenomenon is appeared in VIV under the shear flow, and multi-modal phenomenon is more apparent at the same shear parameter with an increasing Reynolds number under the shear flow effect. Secondly, the riser vibrates at the natural frequency and the dominant vibration frequency increases for the effect of the real-time tension amplitude under the shear flow and the IL vibration frequency is the similar with the CF vibration frequency at the Reynolds number of 1105 in our experimental condition and the IL dominant frequency is twice the CF dominant frequency with an increasing Reynolds number. In addition, the displacement trajectories at the different locations of the riser appear the same shape and the shape is changed at the same shear parameter with an increasing Reynolds number under the shear flow. The diagonal displacement trajectories are observed at the low Reynolds number and the crescent-shaped displacement trajectories appear with an increasing Reynolds number under shear flow in the experiment.
DENSE MULTIPHASE FLOW SIMULATION: CONTINUUM MODEL FOR POLY-DISPERSED SYSTEMS USING KINETIC THEORY
Energy Technology Data Exchange (ETDEWEB)
Moses Bogere
2011-08-31
The overall objective of the project was to verify the applicability of the FCMOM approach to the kinetic equations describing the particle flow dynamics. For monodispersed systems the fundamental equation governing the particle flow dynamics is the Boltzmann equation. During the project, the FCMOM was successfully applied to several homogeneous and in-homogeneous problems in different flow regimes, demonstrating that the FCMOM has the potential to be used to solve efficiently the Boltzmann equation. However, some relevant issues still need to be resolved, i.e. the homogeneous cooling problem (inelastic particles cases) and the transition between different regimes. In this report, the results obtained in homogeneous conditions are discussed first. Then a discussion of the validation results for in-homogeneous conditions is provided. And finally, a discussion will be provided about the transition between different regimes. Alongside the work on development of FCMOM approach studies were undertaken in order to provide insights into anisotropy or particles kinetics in riser hydrodynamics. This report includes results of studies of multiphase flow with unequal granular temperatures and analysis of momentum re-distribution in risers due to particle-particle and fluid-particle interactions. The study of multiphase flow with unequal granular temperatures entailed both simulation and experimental studies of two particles sizes in a riser and, a brief discussion of what was accomplished will be provided. And finally, a discussion of the analysis done on momentum re-distribution of gas-particles flow in risers will be provided. In particular a discussion of the remaining work needed in order to improve accuracy and predictability of riser hydrodynamics based on two-fluid models and how they can be used to model segregation in risers.
Energy Technology Data Exchange (ETDEWEB)
Slagsvold, L. [ABB Offshore Systems (Norway)
2002-12-01
The industry is now looking at developing reserves in waters depths of up to 3000 m (10000 ft). When moving into deeper waters the un-bonded flexible riser becomes very heavy and introduces large hang-off forces on the vessel. We are therefore investigating riser concepts incorporating new materials and with a simpler cross section that can be used for floating production. Advanced composite materials have properties such as, low weight, high strength, good durability and very good fatigue performance. Composite materials are slowly being exploited in the oil industry; they are being prototype tested for drilling risers and small diameter lines. Part of the process for the industry to accept larger diameter production risers made out of composite materials is to understand both the advantages and limitations. A new continuous composite riser system is being developed which capitalizes on the technical benefits of this material while addressing the known constraints. The fully bonded riser is being developed for ultra deep waters and its' characteristics include high temperature (160 deg C), high pressure (500 barg min), light weight, chemical resistant, good insulation, excellent fatigue characteristics and installation by reeling. The concept is based on the use of a thermoplastic liner together with a thermoplastic carbon fibre composite. This paper summarises the ongoing development, which has a goal to manufacture and qualify an 8'' riser, and includes all the steps in a production process from material qualification to the winding process and analytical modelling. (author)
Advances in riser and pipeline technologies
Energy Technology Data Exchange (ETDEWEB)
Kan, Wan C.; Mortazavi, Mehrdad; Weir, Michael S. [ExxonMobil Development Company, Dallas, TX (United States)
2009-12-19
As oil and gas production continues to move into new frontier areas, novel applications of the existing riser and pipeline technologies need to be developed to meet the often more stringent requirements encountered in these environments. The challenges include ultra deep water, harsh environments, aggressive fluid conditions, and local content objectives, etc. They will require industry to constantly extend, expand, and enhance the broad range of solution options. Also, the existing design criteria in industry may need to be revised or new criteria may need to be developed to satisfy these needs. Exxon Mobil (Em) employs, and works with others in industry to promote robust design and operating practices. This approach requires in-depth understanding, sound engineering principles, advanced analysis, uncertainty management, and supportive qualification test data. It enables confident selection, extrapolation, and innovation of technologies to address new riser system and pipeline challenges. Focus on fundamental is imperative to ensure integrity of the selected systems during fabrication, installation, and operation phases. Recent and past project experience in deep water Gulf of Mexico and West Africa provides many successful examples of this approach. This paper reviews several examples of the key riser system and pipeline technology enhancements recently achieved by EM to provide confidence in addressing technical and project application challenges. Riser system technology enhancements addressed in this paper include steel catenary riser (SCR) application on turret-moored FPSO with severe motions, pipe-in-pipe (PIP) hybrid production riser to effectively manage gas lift and flow assurance requirements, irregular wave analysis methodology for flexible risers and umbilicals to reduce conservatism, and qualification of riser and pipeline VIV prediction and mitigation methods. Pipeline technology enhancements detailed in this paper include lateral buckling prediction
Hydrodynamics of a natural circulation loop in a scaled-down steam drum-riser-downcomer assembly
Energy Technology Data Exchange (ETDEWEB)
Basu, Dipankar N., E-mail: dnbasu@iitg.ernet.in; Patil, N.D.; Bhattacharyya, Souvik; Das, P.K.
2013-12-15
Highlights: • Experimental investigation of loop hydrodynamics in a scaled-down simulated AHWR. • Identification of flow regimes and transition analyzing conductance probe signal. • Downcomer flow maximizes with fully developed churn flow and lowest for bubbly flow. • Highest downcomer flow rate is achieved with identical air supply to both risers. • Interaction of varying flow patterns reduces downcomer flow for unequal operation. - Abstract: Complex interactions of different phases, widely varying frictional characteristics of different flow regimes and the involvement of multiple scales of transport make the modelling of a two-phase natural circulation loop (NCL) exceedingly difficult. The knowledge base about the dependency of downcomer flow rate on riser-side flow patterns, particularly for systems with multiple parallel channels is barely developed, necessitating the need for detailed experimentation. The present study focuses on developing a scaled-down test facility relevant to the Advanced Heavy Water Reactor conceived in the atomic energy programme of India to study the hydrodynamics of the NCL using air and water as test fluids. An experimental facility with two risers, one downcomer and a phase-separating drum was fabricated. Conductivity probes and photographic techniques are used to characterize the two phase flow. Normalized voltage signals obtained from the amplified output of conductivity probes and their subsequent analysis through probability distribution function reveal the presence of different two-phase flow patterns in the riser tubes. With the increase in air supply per riser void fraction in the two-phase mixture increases and gradually flow patterns transform from bubbly to fully developed annular through slug, churn and dispersed annular flow regimes. Downcomer flow rate increases rapidly with air supply till a maximum and then starts decreasing due to enhanced frictional forces. However, the maximum value of downcomer water
Energy Technology Data Exchange (ETDEWEB)
Melo, Ana Cristina Bezerra Azedo de
2004-12-15
The fluid dynamic behavior of a riser in a cold type FCC model was investigated by means of catalyst concentration distribution measured with gamma attenuation and simulated with a mathematical model. In the riser of the cold model, MEF, 0,032 m in diameter, 2,30 m in length the fluidized bed, whose components are air and FCC catalyst, circulates. The MEF is operated by automatic control and instruments for measuring fluid dynamic variables. An axial catalyst concentration distribution was measured using an Am-241 gamma source and a NaI detector coupled to a multichannel provided with a software for data acquisition and evaluation. The MEF was adapted for a fluid dynamic model validation which describes the flow in the riser, for example, by introducing an injector for controlling the solid flow in circulation. Mathematical models were selected from literature, analyzed and tested to simulate the fluid dynamic of the riser. A methodology for validating fluid dynamic models was studied and implemented. The stages of the work were developed according to the validation methodology, such as data planning experiments, study of the equations which describe the fluidodynamic, computational solvers application and comparison with experimental data. Operational sequences were carried out keeping the MEF conditions for measuring catalyst concentration and simultaneously measuring the fluid dynamic variables, velocity of the components and pressure drop in the riser. Following this, simulated and experimental values were compared and statistical data treatment done, aiming at the required precision to validate the fluid dynamic model. The comparison tests between experimental and simulated data were carried out under validation criteria. The fluid dynamic behavior of the riser was analyzed and the results and the agreement with literature were discussed. The adopt model was validated under the MEF operational conditions, for a 3 to 6 m/s gas velocity in the riser and a slip
Airport Network Flow Simulator
1978-10-01
The Airport Network Flow Simulator is a FORTRAN IV simulation of the flow of air traffic in the nation's 600 commercial airports. It calculates for any group of selected airports: (a) the landing and take-off (Type A) delays; and (b) the gate departu...
Energy Technology Data Exchange (ETDEWEB)
Araujo, Jairo B. de; Almeida, Jose Carlos L. de [PETROBRAS, Rio de Janeiro, RJ (Brazil); Rangel, Marcos; Fernandes, Antonio C.; Santos, Melquisedec F. dos; Sales Junior, Joel Sena [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil). Coordenacao dos Programas de Pos-graduacao de Engenharia (COPPE)
2004-07-01
This paper presents results, numeric and experimental, due to installation operation of a Risers Uphold Sub-Surface Buoy, (BSR). This kind of installation developed by PETROBRAS is unique in the world. The work of BSR installation was based on a numeric pre analysis to verify the system and determine the main parameters to be experimentally verified. The second phase of the work was the experimental analysis in a deep water ocean basin. s. The work describes the BSR and their main accessories, the experimental environment and the model constructed in aluminum in a 1:12 scale and the main results. (author)
Directory of Open Access Journals (Sweden)
Sparks C.
2006-11-01
Full Text Available Cet article a pour but de déterminer les principaux paramètres qui gouvernent le comportement mécanique des risers de forage et de production, et d'expliquer pourquoi et comment ils interviennent. Une compréhension claire de ces influences permet d'optimiser rapidement un riser donné sans avoir recours à un grand nombre d'analyses par ordinateur. Celui qui conçoit un riser est principalement préoccupé par les points suivants : - niveaux de contraintes dans la partie courante du riser ; - mouvements angulaires à la base du riser (ou moments, dans le cas d'une liaison rigide ; - mouvements relatifs au niveau de la liaison plate-forme/riser. La méthode utilisée dans cet article consiste à établir des expressions analytiques valables pour des risers simplifiés. Les conclusions tirées de ces expressions ont ensuite été verifiéés à l'aide d'un programme de calcul capable de simuler le comportement dynamique d'un riser dans des configurations variées. This paper attempts to identify the principal parameters, that influence the behavior of drilling and production risers and to explain how and why they do so. Clear understanding of these influences enable particular risers to be optimised rapidly without recourse to an inordinate number of computer analyses. The points of greatest concern, to the riser designer, are: a Stress levels in the main length of riser. (b Angular movement at sea bed (or moment, if the connection is rigid. (c Relative movement at riser/platform connection. The approach, used in the paper, has been ta derive analytical expressions, for simplified riser cases. Conclusions drawn from these expressions have then been checked for validity, by using a dynamic analysis computer program to simulate a wide range of cases.
Three-Dimensional Dynamics of a Flexible Marine Riser Undergoing Large Elastic Deformations
International Nuclear Information System (INIS)
Raman-Nair, W.; Baddour, R.E.
2003-01-01
The equations of the three dimensional motion of a marine riser undergoing large elastic deformations are formulated using Kane's formalism. The riser is modeled using lumped masses connected by extensional and rotational springs including structural damping. Surface waves are described by Stokes? second-order wave theory. Fluid-structure coupling is achieved by application of the hydrodynamic loads via Morison's equation and added-mass coefficients using the instantaneous relative velocities and accelerations between the fluid field and the riser segments. In the same way, a model for incorporating the effects of vortex-induced lift forces is included. The effect of internal flow is included in the model. The detailed algorithm is presented and the equations are solved using a robust implementation of the Runge-Kutta method provided in MATLAB. The mathematical model and associated algorithm are validated by comparing the steady-state equilibrium configuration of the riser with special cases of an elastic catenary mooring line and large deflection statics of a cantilever beam. The results of sample simulations are presented
Dynamic response of a riser under excitation of internal waves
Lou, Min; Yu, Chenglong; Chen, Peng
2015-12-01
In this paper, the dynamic response of a marine riser under excitation of internal waves is studied. With the linear approximation, the governing equation of internal waves is given. Based on the rigid-lid boundary condition assumption, the equation is solved by Thompson-Haskell method. Thus the velocity field of internal waves is obtained by the continuity equation. Combined with the modified Morison formula, using finite element method, the motion equation of riser is solved in time domain with Newmark-β method. The computation programs are compiled to solve the differential equations in time domain. Then we get the numerical results, including riser displacement and transfiguration. It is observed that the internal wave will result in circular shear flow, and the first two modes have a dominant effect on dynamic response of the marine riser. In the high mode, the response diminishes rapidly. In different modes of internal waves, the deformation of riser has different shapes, and the location of maximum displacement shifts. Studies on wave parameters indicate that the wave amplitude plays a considerable role in response displacement of riser, while the wave frequency contributes little. Nevertheless, the internal waves of high wave frequency will lead to a high-frequency oscillation of riser; it possibly gives rise to fatigue crack extension and partial fatigue failure.
Clashing of risers due to vortex induced vibrations
Energy Technology Data Exchange (ETDEWEB)
Teissier, D. [Ecole Superieure d' Ingenieurs de Marseille (ESIM), 13 - Marseille (France)]|[Institut Francais du Petrole (IFP), 92 - Rueil-Malmaison (France); Scolan, Y.M. [Ecole Superieure d' Ingenieurs de Marseille (ESIM), 13 - Marseille (France); Fontaine, E. [Institut Francais du Petrole (IFP), 92 - Rueil-Malmaison (France)
2004-07-01
Phenomena such as Vortex Induced Vibrations can potentially damage offshore risers, especially in ar ay configurations. Due to wake interferences, amplification of VIV is observed leading to large displacements which are no more self limited to one di meter as in the case of VIV. In this context, clash ng becomes also an issue. In order to study this problems, Institut Francais du Petrole is developing a Computational Fluid Dynamics code, DeepFlow, devoted to the simulation of two-dimensional flows around risers. The extension to three-dimensional configurations follows from a strip theory for the fluid flow, coupled to a structural model for flexible pipes (DeepLines). The numerical method (Etienne s 1999) developed in DeepFlow allows to solve the two-dimensional Reynolds Averaged Navier-Stokes equations through a mixed representation (Eulerian and Lagrangian) of the flow properties: vorticity and turbulence. The Eulerian method is necessary in the close vicinity of the bodies in order to capture the boundary layer effects with accuracy, whereas the Lagrangian representation, based on a grid-less method is suitable for the flow in the wake. In the present pa-per, this approach is applied to study the flow around two freely moving cylinders. For this test case, there are some numerical results (Sagatum et al, 2002), however instabilities have been experimentally identified (Paidoussis et al, 1998; Zdravkovich, 1985, 2003). The approach has also been improved to solve accurately the interstitial flow when the bodies are very close to each other. Results from a Chimera approach are presented. (authors)
Numerical Modeling and Mechanical Analysis of Flexible Risers
Li, J. Y.; Qiu, Z. X.; Ju, J. S.
2015-01-01
ABAQUS is used to create a detailed finite element model for a 10-layer unbonded flexible riser to simulate the riser’s mechanical behavior under three load conditions: tension force and internal and external pressure. It presents a technique to create detailed finite element model and to analyze flexible risers. In FEM model, all layers are modeled separately with contact interfaces; interaction between steel trips in certain layers has been considered as well. FEM model considering contact ...
Hopper Flow: Experiments and Simulation
Li, Zhusong; Shattuck, Mark
2013-03-01
Jamming and intermittent granular flow are important problems in industry, and the vertical hopper is a canonical example. Clogging of granular hoppers account for significant losses across many industries. We use realistic DEM simulations of gravity driven flow in a hopper to examine flow and jamming of 2D disks and compare with identical companion experiments. We use experimental data to validate simulation parameters and the form of the inter particle force law. We measure and compare flow rate, emptying times, jamming statistics, and flow fields as a function of opening angle and opening size in both experiment and simulations. Suppored by: NSF-CBET-0968013
Numerical Modeling and Mechanical Analysis of Flexible Risers
Directory of Open Access Journals (Sweden)
J. Y. Li
2015-01-01
Full Text Available ABAQUS is used to create a detailed finite element model for a 10-layer unbonded flexible riser to simulate the riser’s mechanical behavior under three load conditions: tension force and internal and external pressure. It presents a technique to create detailed finite element model and to analyze flexible risers. In FEM model, all layers are modeled separately with contact interfaces; interaction between steel trips in certain layers has been considered as well. FEM model considering contact interaction, geometric nonlinearity, and friction has been employed to accurately simulate the structural behavior of riser. The model includes the main features of the riser geometry with very little simplifying assumptions. The model was solved using a fully explicit time-integration scheme implemented in a parallel environment on an eight-processor cluster and 24 G memory computer. There is a very good agreement obtained from numerical and analytical comparisons, which validates the use of numerical model here. The results from the numerical simulation show that the numerical model takes into account various details of the riser. It has been shown that the detailed finite element model can be used to predict riser’s mechanics behavior under various load cases and bound conditions.
Monitoring catalyst flow rate in a FCC cold pilot unity by gamma ray transmission measurements
International Nuclear Information System (INIS)
Brito, Marcio F.P.; Netto, Wilson F.S.; Miranda, Marcia V.F.E.S.; Junior, Isacc A.S.; Dantas, Carlos C.; Melo, Silvio B.; Lima, Emerson A.O.
2013-01-01
A model for monitoring catalyst mass flow in riser of Fluid Catalytic Cracking - FCC, pilot unity as a function of air flow and solid injection is proposed. The fluidized FCC- catalyst bed system is investigated in an experimental setup the Cold Pilot Unity - CPU by means of gamma ray transmission measurements. Riser in CPU simulates the reactor in FCC process. By automation control air flow is instrumentally measured in riser and the solid injection is manually controlled by valve adjusting. Keeping a constant solid injection, catalyst level at the return column was measured by gamma transmission for several air flow values in riser. The operational condition reached a steady state regime before given to setup a new air flow value. A calibration of catalyst level as a function of air flow in riser is calculated, therefore, a model for solid feed rate is derived. Recent published work evaluates solid concentration in riser of the CPU by means of gamma ray transmission, and a correlation with air velocity is obtained. In this work, the model for solid feed rate was further investigated by carrying out experiments to measure catalyst concentration at the same air flow values. These experiments lead to a model for monitoring catalyst flow in riser as function of solid feed rate and air flow. Simulation with random numbers produced with Matlab software allows to define validation criteria for the model parameters. (author)
Flow lab.: flow visualization and simulation
International Nuclear Information System (INIS)
Park, Chung Kyun; Cho, Won Jin; Hahn, Pil Soo
2005-01-01
The experimental setups for flow visualization and processes identification in laboratory scale (so called Flow Lab.) has developed to get ideas and answer fundamental questions of flow and migration in geologic media. The setup was made of a granite block of 50x50cm scale and a transparent acrylate plate. The tracers used in this experiments were tritiated water, anions, and sorbing cations as well as an organic dye, eosine, to visualize migration paths. The migration plumes were taken with a digital camera as a function of time and stored as digital images. A migration model was also developed to describe and identify the transport processes. Computer simulation was carried out not only for the hydraulic behavior such as distributions of pressure and flow vectors in the fracture but also for the migration plume and the elution curves
The Sleipner riser platform experience
International Nuclear Information System (INIS)
Anon.
1993-01-01
The article discusses briefly the Norwegian Sleipner riser project. The project has provided new insight on how to handle smaller development projects in a time saving and cost effective way. Through active cooperation between the prime contractors, the total project time, which included engineering, fabrication ready to tow, was slashed to a record 11 months. Normally, such a project would take a couple of years to complete. 1 fig
Computer simulation of hopper flow
International Nuclear Information System (INIS)
Potapov, A.V.; Campbell, C.S.
1996-01-01
This paper describes two-dimensional computer simulations of granular flow in plane hoppers. The simulations can reproduce an experimentally observed asymmetric unsteadiness for monodispersed particle sizes, but also could eliminate it by adding a small amount of polydispersity. This appears to be a result of the strong packings that may be formed by monodispersed particles and is thus a noncontinuum effect. The internal stress state was also sampled, which among other things, allows an evaluation of common assumptions made in granular material models. These showed that the internal friction coefficient is far from a constant, which is in contradiction to common models based on plasticity theory which assume that the material is always at the point of imminent yield. Furthermore, it is demonstrated that rapid granular flow theory, another common modeling technique, is inapplicable to this problem even near the exit where the flow is moving its fastest. copyright 1996 American Institute of Physics
Steel catenary risers supported by subsurface buoy
Adebayo, Addayo
2011-01-01
Master's thesis in Offshore technology Oil and gas exploration and production activities in deep and ultra deep waters in hostile environments necessitates the need to develop innovative riser systems capable of ensuring transfer of fluids from the seabed to a floating vessel and vice versa, with little or no issues with respect to influences of environmental loads and vessel motions. Over the years, studies have shown that the conventional flexible riser and steel catenary riser config...
International Nuclear Information System (INIS)
Thummakul, Theeranan; Gidaspow, Dimitri; Piumsomboon, Pornpote; Chalermsinsuwan, Benjapon
2017-01-01
Highlights: • Circulating-turbulent fluidization was proved to be advantage on CO_2 sorption. • The novel regime was proven to capture CO_2 higher than the conventional regimes. • Uniform solid particle distribution was observed in the novel fluidization regime. • The system continuity had more effect in the system than the process system mixing. • Parametric experimental design analysis was studied to evaluate significant factor. - Abstract: In this study a high flux circulating-turbulent fluidized bed (CTFB) riser was confirmed to be advantageous for carbon dioxide (CO_2) sorption on a potassium carbonate solid sorbent. The effect of various parameters on the CO_2 removal level was evaluated using a statistical experimental design. The most appropriate fluidization regime was found to occur between the turbulent and fast fluidization regimes, which was shown to capture CO_2 more efficiently than conventional fluidization regimes. The highest CO_2 sorption level was 93.4% under optimized CTFB operating conditions. The important parameters for CO_2 capture were the inlet gas velocity and the interactions between the CO_2 concentration and the inlet gas velocity and water vapor concentration. The CTFB regime had a high and uniform solid particle distribution in both the axial and radial system directions and could transport the solid sorbent to the regeneration reactor. In addition, the process system continuity had a stronger effect on the CO_2 removal level in the system than the process system mixing.
Reliable Radiographic Inspection of Flexible Risers for the Oil Industry
Almeida, Rômulo M.; Rebello, Joao Marcos A.; Vaz, Murilo A.
2010-02-01
Flexible risers are composite tubular structures manufactured by the concentric assemblage of cylindrical polymeric and helically wound metallic layers employed to convey pressurized fluids such as oil, gas and water in the ocean environment. The metallic layers account for the flexible risers' structural strength and are dimensioned according to the static and dynamic loads. They are usually installed in a free hanging catenary configuration and are subjected to the direct action of waves and marine currents and wave induced motions from the oil production platform. The fatigue rupture of wire armours in the end fitting or within the riser segment protected by the bend stiffener is an object of major concern. Integrity models have been developed, however inspection techniques are mandatory to ensure that failure is detected. Gammagraphy has been used as a common inspection technique in all regions of the flexible riser, mainly with the single wall-single view method. On the other side, there is not any qualified radiographic procedure to this kind of structure. Radiographic simulation was adopted and its validation with actual gammagraphies and establishment of radiographic parameters to complex radiation geometries were done. Results show the viability of the radiographic inspection analyzing the armour wires' rupture and the displacement between wires.
RELIABLE RADIOGRAPHIC INSPECTION OF FLEXIBLE RISERS FOR THE OIL INDUSTRY
International Nuclear Information System (INIS)
Almeida, Romulo M.; Rebello, Joao Marcos A.; Vaz, Murilo A.
2010-01-01
Flexible risers are composite tubular structures manufactured by the concentric assemblage of cylindrical polymeric and helically wound metallic layers employed to convey pressurized fluids such as oil, gas and water in the ocean environment. The metallic layers account for the flexible risers' structural strength and are dimensioned according to the static and dynamic loads. They are usually installed in a free hanging catenary configuration and are subjected to the direct action of waves and marine currents and wave induced motions from the oil production platform. The fatigue rupture of wire armours in the end fitting or within the riser segment protected by the bend stiffener is an object of major concern. Integrity models have been developed, however inspection techniques are mandatory to ensure that failure is detected. Gammagraphy has been used as a common inspection technique in all regions of the flexible riser, mainly with the single wall-single view method. On the other side, there is not any qualified radiographic procedure to this kind of structure. Radiographic simulation was adopted and its validation with actual gammagraphies and establishment of radiographic parameters to complex radiation geometries were done. Results show the viability of the radiographic inspection analyzing the armour wires' rupture and the displacement between wires.
Simplified Model for Evaluation of VIV-induced Fatigue Damage of Deepwater Marine Risers
Institute of Scientific and Technical Information of China (English)
XUE Hong-xiang; TANG Wen-yong; ZHANG Sheng-kun
2009-01-01
A simplified empirical model for fatigue analysis of deepwater marine risers due to vortex-induced vibration (VIV) in non-uniform current is presented. A simplified modal vibration equation is employed according to the characteristics of deepwater top tensioned risers. The response amplitude of each mode is determined by a balance between the energy feeding into the riser over the lock-in regions and the energy dissipated by the fluid damping over the remainder based on the data from self-excited oscillation and forced oscillation experiments of rigid cylinders. Multi-modal VIV fatigue loading is obtained by the square root of the sum of squares approach.Compared with previous works, this model can take fully account of the main intrinsic natures of VIV for low mass ratio structures on lock-in regions, added mass and nonlinear fluid damping. In addition, a closed form solution of fatigue damage is presented for the case of a riser with uniform mass and cross-section oscillating in a uniform flow. Fatigue analysis of a typical deepwater riser operating in Gulf of Mexico and West Africa shows that the current velocity profiles affect the riser's fatigue life significantly and the most dangerous locations of the riser are also pointed out.
Prevention of pulsations caused by flexible risers
Belfroid S.P.C; Golliard, J.; Korst, H.J.C.
2013-01-01
In the last few decades, flexible risers have increasingly been used in the offshore oil and gas industry. In gas applications these risers can generate high amplitude tonal pressure fluctuations when the gas velocity reaches a threshold value. The resulting pressure fluctuations can then cause high
Riser configuration, Tank 241-A-105, light duty utility arm
International Nuclear Information System (INIS)
Boucher, T.D.
1994-01-01
The light-duty utility arm (LDUA) is a seven-joint stainless steel robotic arm with a payload capacity of 75 lb. The robotic arm is deployed vertically with a maximum vertical reach of 63 ft. and a maximum horizontal reach of 13.5 ft. The functional requirements of the LDUA system are mapping and characterization of waste in Hanford single-shell tanks (SST) before and during waste retrieval. The LDUA system consists of a mobile deployment system (MDS), a vertical positioning mast (VPM), a tank riser interface confinement (TRIC), the LDUA, and a controller subsystem or support trailer. Currently, the system is in design and is subject to change; however, the LDUA or robotic arm will be deployed through a 12-in. riser above the tank dome. Field trips were performed to gather specifics for future deployment of the LDUA in Tank 241-A-105. The purpose of this report is to support two previous reports for the investigation of SSTs for deployment of the LDUA system. The first report identified the availability of risers while the second report identified the availability of Tanks 241-A-105, 241-A-S-109, 241-A-T-101, and 241-A-T-109 for deployment of the LDUA system. The second report also identified those 4- and 12-in. risers that could be used for deployment of the LDUA and camera system. This report addresses accessibility to the 241-A Tank Farm and the usability of the Tank 241-A-105 risers. The following information for assisting in the design and deployment of the LDUA will be discussed in this report: radiation survey; flange identification; high resolution video; computer simulated model; and field survey
Reliability-based dynamic positioning of floating vessels with riser and mooring system
DEFF Research Database (Denmark)
Fang, Shaoji; Leira, Bernt J.; Blanke, Mogens
2011-01-01
To maintain safety of a floating vessel with associated slender components such as risers and mooring line, the vessel is normally kept within a limited region. To specify a safe position in that region, this paper suggests a new position chasing algorithm with the consideration of both riser ang...... to their criticality. An optimal position set-point is produced by minimization of the value of the cost function. Numerical simulations show the effectiveness of the proposed algorithm....
Experimental Plan for Crystal Accumulation Studies in the WTP Melter Riser
Energy Technology Data Exchange (ETDEWEB)
Miller, D. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Fowley, M. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
2015-04-28
This experimental plan defines crystal settling experiments to be in support of the U.S. Department of Energy – Office of River Protection crystal tolerant glass program. The road map for development of crystal-tolerant high level waste glasses recommends that fluid dynamic modeling be used to better understand the accumulation of crystals in the melter riser and mechanisms of removal. A full-scale version of the Hanford Waste Treatment and Immobilization Plant (WTP) melter riser constructed with transparent material will be used to provide data in support of model development. The system will also provide a platform to demonstrate mitigation or recovery strategies in off-normal events where crystal accumulation impedes melter operation. Test conditions and material properties will be chosen to provide results over a variety of parameters, which can be used to guide validation experiments with the Research Scale Melter at the Pacific Northwest National Laboratory, and that will ultimately lead to the development of a process control strategy for the full scale WTP melter. The experiments described in this plan are divided into two phases. Bench scale tests will be used in Phase 1 (using the appropriate solid and fluid simulants to represent molten glass and spinel crystals) to verify the detection methods and analytical measurements prior to their use in a larger scale system. In Phase 2, a full scale, room temperature mockup of the WTP melter riser will be fabricated. The mockup will provide dynamic measurements of flow conditions, including resistance to pouring, as well as allow visual observation of crystal accumulation behavior.
Energy Technology Data Exchange (ETDEWEB)
Rabelo, Alexandre S.; Motta, Antonio; Romero, Antonio; Nunes, Joao P.; Zaganelli Junior, Jose L.; Brack, Marcelo [PETROBRAS, Rio de Janeiro, RJ (Brazil)
2009-07-01
The main objective of this paper is to present the recent developments for monitoring and controlling the annulus conditions of flexible risers. PETROBRAS has been monitoring the pressure of permeated gas in the annulus region of some risers in order to infer the eventual occurrence of non-conformities as damage on the riser external sheath, for example. Such occurrence would affect the permeated gas flow pattern, the gas pressurization period and the relief valve opening frequencies. Furthermore, the mentioned occurrence would increase the susceptibility of the steel armors to experience the potential failure mechanism of corrosion. In PETROBRAS, the current monitoring method is characterized by visual and periodic manometer readings from a manometer set installed near each riser end-fitting. The data is recorded in a daily report and analyzed by personnel onshore, who are in charge of comparing data and requesting relief valve's actuation, whenever necessary. The paper illustrates Marlim-Sul Asset experience on monitoring and data processing to control the annulus conditions of flexible risers during operation. It presents the in-house developed methodology to data management and processing. This methodology is based on a daily analysis of the permeated gas data worksheet. Some examples are given to illustrate it. The paper also summarizes current developments, in progress, in order to improve riser integrity management. The first development is being done to implement, in the future, automatic data acquisition and control systems. The purpose of automating this process is to improve methods and techniques for data acquisition, transmission and processing. The second development focuses on applications in which riser top end-fittings are submerged. In this particular scenario, a special system - with a quick connection sub sea device - is under development to allow the connection, by divers, after the riser pull-in, of the riser annulus to the platform gas
Flow analysis of HANARO flow simulated test facility
International Nuclear Information System (INIS)
Park, Yong-Chul; Cho, Yeong-Garp; Wu, Jong-Sub; Jun, Byung-Jin
2002-01-01
The HANARO, a multi-purpose research reactor of 30 MWth open-tank-in-pool type, has been under normal operation since its initial critical in February, 1995. Many experiments should be safely performed to activate the utilization of the NANARO. A flow simulated test facility is being developed for the endurance test of reactivity control units for extended life times and the verification of structural integrity of those experimental facilities prior to loading in the HANARO. This test facility is composed of three major parts; a half-core structure assembly, flow circulation system and support system. The half-core structure assembly is composed of plenum, grid plate, core channel with flow tubes, chimney and dummy pool. The flow channels are to be filled with flow orifices to simulate core channels. This test facility must simulate similar flow characteristics to the HANARO. This paper, therefore, describes an analytical analysis to study the flow behavior of the test facility. The computational flow analysis has been performed for the verification of flow structure and similarity of this test facility assuming that flow rates and pressure differences of the core channel are constant. The shapes of flow orifices were determined by the trial and error method based on the design requirements of core channel. The computer analysis program with standard k - ε turbulence model was applied to three-dimensional analysis. The results of flow simulation showed a similar flow characteristic with that of the HANARO and satisfied the design requirements of this test facility. The shape of flow orifices used in this numerical simulation can be adapted for manufacturing requirements. The flow rate and the pressure difference through core channel proved by this simulation can be used as the design requirements of the flow system. The analysis results will be verified with the results of the flow test after construction of the flow system. (author)
Modelling and transient simulation of water flow in pipelines using WANDA Transient software
Directory of Open Access Journals (Sweden)
P.U. Akpan
2017-09-01
Full Text Available Pressure transients in conduits such as pipelines are unsteady flow conditions caused by a sudden change in the flow velocity. These conditions might cause damage to the pipelines and its fittings if the extreme pressure (high or low is experienced within the pipeline. In order to avoid this occurrence, engineers usually carry out pressure transient analysis in the hydraulic design phase of pipeline network systems. Modelling and simulation of transients in pipelines is an acceptable and cost effective method of assessing this problem and finding technical solutions. This research predicts the pressure surge for different flow conditions in two different pipeline systems using WANDA Transient simulation software. Computer models were set-up in WANDA Transient for two different systems namely; the Graze experiment (miniature system and a simple main water riser system based on some initial laboratory data and system parameters. The initial laboratory data and system parameters were used for all the simulations. Results obtained from the computer model simulations compared favourably with the experimental results at Polytropic index of 1.2.
Beyle, A. I.; Gustafson, C. G.; Kulakov, V. L.; Tarnopol'skii, Yu. M.
1997-09-01
Prospects for the application of advanced composites in the offshore technology of oil production are considered. The use of composites in vertical pipelines-risers seems to be the most efficient. The operating loads are studied and the attendant problems are formulated. A comparative analysis of the characteristics of metal, composite, and metal-composite deep-water risers is presented. A technique is developed for designing multilayered risers, taking into account the action of internal and external pressures, gravity, and the axial tensile force created by tensioners, as well as the residual technological stresses due to the difference in coefficients of thermal expansion, physical-chemical shrinkage, and force winding. Numerical estimations are given for a two-layered riser with an inner metal layer of steel, titanium, or aluminum alloys and a composite layer of glass- or carbon-fiber plastics formed by circumferential winding. It is shown that the technological stresses substantially affect the characteristics of the riser.
Model of a catalytic injection in a riser by means of gamma ray transmission measurements
Energy Technology Data Exchange (ETDEWEB)
Moura, Alex E.; Brito, Macio F.P.; Dantas, Carlos C.; Melo, Silvio B., E-mail: alex.emoura@ufpe.br, E-mail: sbm@ufpe.br [Universidade Federal de Pernambuco (DEN/UFPE), Recife, PE (Brazil); Barbosa, Enivaldo S., E-mail: Enivaldo.santos@ufcg.edu.br [Universidade Federal de Campina Grande (UFCG), PB (Brazil). Departamento de Engenharia Mecanica; Lima, Emerson A.O., E-mail: eal@poli.br [Universidade de Pernambuco, Recife, PE (Brazil). Departamento de Matematica
2015-07-01
In Gas solid process involving a solid circulation through a closed loop the knowledge of the Solids Circulation Rate (SCR) is fundamental to control and improve the operation of a circulating fluidized bed system. A valve controls the circulation rate of solids in the riser of a fluid catalytic cracking unit. Initially, to control the catalyst injection in the riser, a rotary valve controlled and measured solid flow injection, but with a limited working time. Due to the fine powder catalyst abrasive action on the valve steel axis, this device stop work. A lab made valve were design to avoiding direct contact of the catalyst with mechanical moving parts in while control solid injection in riser, but do not measure the solid flow like the rotary valve. To control the lab made device a fixed pressure measurement at riser bottom is provided by control setup which corresponds to a given mass/time solid injection. In the present work, we proposed a method to evaluate the control valve based on a non-invasive technique. With gamma ray transmission measurements, in a cross section of the pipe, we developed a model that was used in the control system of the Cold Pilot Unit (CPU). Therefore, the interaction of the gamma ray with solid flow in riser should yield the necessary information for the process control system. A first model approximation consider the solid flow rate injection and solid velocity in riser as proposed in literature. In the CPU control system a Programmable Logic Controller-PLC keeps steady state processing the airflow, pressure profile and solid flow inputs. Additionally to preexisting PLC platform, some LabVIEW algorithms were implemented to achieve a good system performance operational condition. (author)
Model of a catalytic injection in a riser by means of gamma ray transmission measurements
International Nuclear Information System (INIS)
Moura, Alex E.; Brito, Macio F.P.; Dantas, Carlos C.; Melo, Silvio B.; Barbosa, Enivaldo S.; Lima, Emerson A.O.
2015-01-01
In Gas solid process involving a solid circulation through a closed loop the knowledge of the Solids Circulation Rate (SCR) is fundamental to control and improve the operation of a circulating fluidized bed system. A valve controls the circulation rate of solids in the riser of a fluid catalytic cracking unit. Initially, to control the catalyst injection in the riser, a rotary valve controlled and measured solid flow injection, but with a limited working time. Due to the fine powder catalyst abrasive action on the valve steel axis, this device stop work. A lab made valve were design to avoiding direct contact of the catalyst with mechanical moving parts in while control solid injection in riser, but do not measure the solid flow like the rotary valve. To control the lab made device a fixed pressure measurement at riser bottom is provided by control setup which corresponds to a given mass/time solid injection. In the present work, we proposed a method to evaluate the control valve based on a non-invasive technique. With gamma ray transmission measurements, in a cross section of the pipe, we developed a model that was used in the control system of the Cold Pilot Unit (CPU). Therefore, the interaction of the gamma ray with solid flow in riser should yield the necessary information for the process control system. A first model approximation consider the solid flow rate injection and solid velocity in riser as proposed in literature. In the CPU control system a Programmable Logic Controller-PLC keeps steady state processing the airflow, pressure profile and solid flow inputs. Additionally to preexisting PLC platform, some LabVIEW algorithms were implemented to achieve a good system performance operational condition. (author)
Multiphase flow simulation in an annulus configuration
Friedemann, Christopher; Mortensen, Mikael; Nossen, Jan
2017-01-01
On the 20th of April 2010, explosion and fire killed 11 people on the Deepwater Horizon oil rig in the Gulf of Mexico. After two days in flames, the rig sank and left the riser (the pipe going up from the seabed) on the sea floor leaking oil and gas from the well through the gap between the drilling riser and the drill-string (rod holding the drillbit) inside it. The accident is known as the Macondo accident. Immediate concerns were raised regarding the amount of oil being released into the G...
Direct Numerical Simulation of Driven Cavity Flows
Verstappen, R.; Wissink, J.G.; Veldman, A.E.P.
Direct numerical simulations of 2D driven cavity flows have been performed. The simulations exhibit that the flow converges to a periodically oscillating state at Re=11,000, and reveal that the dynamics is chaotic at Re=22,000. The dimension of the attractor and the Kolmogorov entropy have been
The simulation of multidimensional multiphase flows
International Nuclear Information System (INIS)
Lahey, Richard T.
2005-01-01
This paper presents an assessment of various models which can be used for the multidimensional simulation of multiphase flows, such as may occur in nuclear reactors. In particular, a model appropriate for the direct numerical simulation (DNS) of multiphase flows and a mechanistically based, three-dimensional, four-field, turbulent, two-fluid computational multiphase fluid dynamics (CMFD) model are discussed. A two-fluid bubbly flow model, which was derived using potential flow theory, can be extended to other flow regimes, but this will normally involve ensemble-averaging the results from direct numerical simulations (DNS) of various flow regimes to provide the detailed numerical data necessary for the development of flow-regime-specific interfacial and wall closure laws
Simulation of 2D Granular Hopper Flow
Li, Zhusong; Shattuck, Mark
2012-02-01
Jamming and intermittent granular flow are big problems in industry, and the vertical hopper is a canonical example of these difficulties. We simulate gravity driven flow and jamming of 2D disks in a vertical hopper and compare with identical companion experiments presented in this session. We measure and compare the flow rate and probability for jamming as a function of particle properties and geometry. We evaluate the ability of standard Hertz-Mindlin contact mode to quantitatively predict the experimental flow.
Simulation of gas compressible flow by free surface water flow
International Nuclear Information System (INIS)
Altafini, C.R.; Silva Ferreira, R.T. da
1981-01-01
The analogy between the water flow with a free surface and the compressible fluid flow, commonly called hydraulic analogy, is analyzed and its limitations are identified. The water table is the equipment used for this simulation, which allows the quatitative analysis of subsonic and supersonic flow with a low cost apparatus. The hydraulic analogy is applied to subsonic flow around circular cylinders and supersonic flow around cones. The results are compared with available theoretical and experimental data and a good agreement is achieved. (Author) [pt
Visualization of numerically simulated aerodynamic flow fields
International Nuclear Information System (INIS)
Hian, Q.L.; Damodaran, M.
1991-01-01
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
Evaluation of riser 14 temperature response
International Nuclear Information System (INIS)
OGDEN, D.M.
1999-01-01
The initial sluicing activities of Project WRSS resulted in a two month increase in temperatures as measured by the Riser 14 thermocouple tree of tank 241-C-106. While this increase was anticipated, the maximum temperature was higher than expected. An evaluation was performed to determine if adequate subcooling exists in the waste to continue sluicing activities. It was determined that a minimum of 10 F subcooling exists in the waste and that the higher Riser 14 temperatures were the result of higher than assumed waste saturation temperature
Girassol, Riser Towers for ultra deep water
Energy Technology Data Exchange (ETDEWEB)
Rougier, Regis
1999-07-01
This is a brief presentation of the technical concept developed by ALTO MAR GIRASSOL (AMG) for the Girassol umbilical and flowlines system. In 1998 AMG was awarded a contract by Elf Exploration Angola for the engineering, procurement, construction and installation (EPCI) of the umbilical and flowline system. The technical concept is based around the use of sealine bundles and self-supporting hybrid riser towers which carry the production, water injection, gas injection, gas lift and service lines. The items discussed are: (1) selected field layout, (2) seabed flowlines, hybrid riser system, umbilicals, export lines, installation plan and overall project schedule.
Reliability analysis of wake-induced collision of flexible risers
Fu, Ping; Leira, Bernt Johan; Myrhaug, Dag
2017-01-01
Collision between risers is an important design and operational concern, especially in deep water since the probability of collision tends to increase as the riser length increases. Riser collision is due to the joint effects of many processes, i.e. environmental loads, hydrodynamic interference and surface floater motions and the most of them are stochastic processes. This paper provides an approach for estimating the failure probability of riser collision by considering these joint effects ...
Hydrodynamic simulation of elliptic flow
Kolb, P F; Ruuskanen, P V; Heinz, Ulrich W
1999-01-01
We use a hydrodynamic model to study the space-time evolution transverse to the beam direction in ultrarelativistic heavy-ion collisions with nonzero impact parameters. We focus on the influence of early pressure on the development of radial and elliptic flow. We show that at high energies elliptic flow is generated only during the initial stages of the expansion while radial flow continues to grow until freeze-out. Quantitative comparisons with SPS data from semiperipheral Pb+Pb collisions suggest the applicability of hydrodynamical concepts already $\\approx$ 1 fm/c after impact.
Reconstruction of Twist Torque in Main Parachute Risers
Day, Joshua D.
2015-01-01
The reconstruction of twist torque in the Main Parachute Risers of the Capsule Parachute Assembly System (CPAS) has been successfully used to validate CPAS Model Memo conservative twist torque equations. Reconstruction of basic, one degree of freedom drop tests was used to create a functional process for the evaluation of more complex, rigid body simulation. The roll, pitch, and yaw of the body, the fly-out angles of the parachutes, and the relative location of the parachutes to the body are inputs to the torque simulation. The data collected by the Inertial Measurement Unit (IMU) was used to calculate the true torque. The simulation then used photogrammetric and IMU data as inputs into the Model Memo equations. The results were then compared to the true torque results to validate the Model Memo equations. The Model Memo parameters were based off of steel risers and the parameters will need to be re-evaluated for different materials. Photogrammetric data was found to be more accurate than the inertial data in accounting for the relative rotation between payload and cluster. The Model Memo equations were generally a good match and when not matching were generally conservative.
Damage localization of marine risers using time series of vibration signals
Liu, Hao; Yang, Hezhen; Liu, Fushun
2014-10-01
Based on dynamic response signals a damage detection algorithm is developed for marine risers. Damage detection methods based on numerous modal properties have encountered issues in the researches in offshore oil community. For example, significant increase in structure mass due to marine plant/animal growth and changes in modal properties by equipment noise are not the result of damage for riser structures. In an attempt to eliminate the need to determine modal parameters, a data-based method is developed. The implementation of the method requires that vibration data are first standardized to remove the influence of different loading conditions and the autoregressive moving average (ARMA) model is used to fit vibration response signals. In addition, a damage feature factor is introduced based on the autoregressive (AR) parameters. After that, the Euclidean distance between ARMA models is subtracted as a damage indicator for damage detection and localization and a top tensioned riser simulation model with different damage scenarios is analyzed using the proposed method with dynamic acceleration responses of a marine riser as sensor data. Finally, the influence of measured noise is analyzed. According to the damage localization results, the proposed method provides accurate damage locations of risers and is robust to overcome noise effect.
NUMERICAL SIMULATION AND MODELING OF UNSTEADY FLOW ...
African Journals Online (AJOL)
2014-06-30
Jun 30, 2014 ... objective of this study is to control the simulation of unsteady flows around structures. ... Aerospace, our results were in good agreement with experimental .... Two-Equation Eddy-Viscosity Turbulence Models for Engineering.
FCC riser quick separation system: a review
Directory of Open Access Journals (Sweden)
Zhi Li
2016-10-01
Full Text Available Abstract The riser reactor is the key unit in the fluid catalytic cracking (FCC process. As the FCC feedstocks become heavier, the product mixture of oil, gas and catalysts must be separated immediately at the outlet of the riser to avoid excessive coking. The quick separation system is the core equipment in the FCC unit. China University of Petroleum (Beijing has developed many kinds of separation system including the fender-stripping cyclone and circulating-stripping cyclone systems, which can increase the separation efficiency and reduce the pressure drop remarkably. For the inner riser system, a vortex quick separation system has been developed. It contains a vortex quick separator and an isolated shell. In order to reduce the separation time, a new type of separator called the short residence time separator system was developed. It can further reduce the separation time to less than 1 s. In this paper, the corresponding design principles, structure and industrial application of these different kinds of separation systems are reviewed. A system that can simultaneously realize quick oil gas separation, quick oil gas extraction and quick pre-stripping of catalysts at the end of the riser is the trend in the future.
Numerical Simulation of Steady Supercavitating Flows
Ali Jafarian; Ahmad-Reza Pishevar
2016-01-01
In this research, the Supercavitation phenomenon in compressible liquid flows is simulated. The one-fluid method based on a new exact two-phase Riemann solver is used for modeling. The cavitation is considered as an isothermal process and a consistent equation of state with the physical behavior of the water is used. High speed flow of water over a cylinder and a projectile are simulated and the results are compared with the previous numerical and experimental results. The cavitation bubble p...
Large eddy simulation of bundle turbulent flows
International Nuclear Information System (INIS)
Hassan, Y.A.; Barsamian, H.R.
1995-01-01
Large eddy simulation may be defined as simulation of a turbulent flow in which the large scale motions are explicitly resolved while the small scale motions are modeled. This results into a system of equations that require closure models. The closure models relate the effects of the small scale motions onto the large scale motions. There have been several models developed, the most popular is the Smagorinsky eddy viscosity model. A new model has recently been introduced by Lee that modified the Smagorinsky model. Using both of the above mentioned closure models, two different geometric arrangements were used in the simulation of turbulent cross flow within rigid tube bundles. An inlined array simulations was performed for a deep bundle (10,816 nodes) as well as an inlet/outlet simulation (57,600 nodes). Comparisons were made to available experimental data. Flow visualization enabled the distinction of different characteristics within the flow such as jet switching effects in the wake of the bundle flow for the inlet/outlet simulation case, as well as within tube bundles. The results indicate that the large eddy simulation technique is capable of turbulence prediction and may be used as a viable engineering tool with the careful consideration of the subgrid scale model. (author)
International Nuclear Information System (INIS)
Aung, Nay Zar; Li, Songjing
2013-01-01
Highlights: • Optimum inclination for maximum heat flux changes with latitude of location. • Optimum inclination for maximum heat flux also changes local solar time. • Maximum flow rate increases with increasing of riser tube size. • Maximum mass flow rate is obtained at different inclinations for different risers. • Length of two-phase region depends on inclination angles but not riser tube size. - Abstract: In this work, the effect of riser diameter and its inclination angle on system parameters in a two-phase closed loop thermosyphon solar water heater has been numerically investigated. Here, receivable heat flux by the collector, circulating mass flow rate, driving pressure, total pressure drop, heat transfer coefficient in risers and collector efficiency are defined as system parameters. For this aim, a model of two-phase thermosyphon solar water heater that is acceptable for various inclinations is presented and variations of riser diameter and inclination are considered. The riser tube size is varied from 1.25 cm to 2.5 cm with inclination range 2–75°. The system absolute pressure is set as 3567 Pa and water is chosen as working fluid. The results show that higher inclination angle is required for higher latitude location to obtain maximum solar heat flux. At local solar noon of 21.996 north latitude, the optimum inclination angle increases in the range of 24–44° with increasing of riser diameter giving maximum circulating mass flow rate from 0.02288 kg/s to 0.03876 kg/s. The longer two-phase heat transfer characteristics can be obtained at smaller inclination angles and mass flow rate for all riser tube sizes. Therefore, it is observed that the optimum inclination angles and diameters for solar heat flux, circulating mass flow rate and heat transfer coefficient in two-phase thermosyphon systemdo not coincide. From this work, better understanding and useful information are provided for constructing two-phase thermosyphon solar heaters
????????????, ?. ?.; ????????, ?. ?.; ?????, ?. ?.
2012-01-01
? ?????? ???????? ??????? ??????? ???????? ?? ???????????? ??????????? ????????? SolidWorks/SolidWorks Flow Simulation (COSMOSFloWorks)/SolidWorks Simulation ??? ?????????? ???????? ?? ????????????? ???. ??? ???????? ????????? ???????? ?????????? ?? ?????? ???????? ??????? ? ????????????? ?????? ? ????????????? ????????????? ?????????? ???????????? SolidWorks Flow Simulation (COSMOSFloWorks). ??? ???????????? ??????????? ????????????? ?????? ?? ????????? ??????????? ??????? ?? ??????????? ...
The Airport Network Flow Simulator.
1976-05-01
The impact of investment at an individual airport is felt through-out the National Airport System by reduction of delays at other airports in the the system. A GPSS model was constructed to simulate the propagation of delays through a nine-airport sy...
Large Eddy Simulation for Compressible Flows
Garnier, E; Sagaut, P
2009-01-01
Large Eddy Simulation (LES) of compressible flows is still a widely unexplored area of research. The authors, whose books are considered the most relevant monographs in this field, provide the reader with a comprehensive state-of-the-art presentation of the available LES theory and application. This book is a sequel to "Large Eddy Simulation for Incompressible Flows", as most of the research on LES for compressible flows is based on variable density extensions of models, methods and paradigms that were developed within the incompressible flow framework. The book addresses both the fundamentals and the practical industrial applications of LES in order to point out gaps in the theoretical framework as well as to bridge the gap between LES research and the growing need to use it in engineering modeling. After introducing the fundamentals on compressible turbulence and the LES governing equations, the mathematical framework for the filtering paradigm of LES for compressible flow equations is established. Instead ...
Modeling and simulation of reactive flows
Bortoli, De AL; Pereira, Felipe
2015-01-01
Modelling and Simulation of Reactive Flows presents information on modeling and how to numerically solve reactive flows. The book offers a distinctive approach that combines diffusion flames and geochemical flow problems, providing users with a comprehensive resource that bridges the gap for scientists, engineers, and the industry. Specifically, the book looks at the basic concepts related to reaction rates, chemical kinetics, and the development of reduced kinetic mechanisms. It considers the most common methods used in practical situations, along with equations for reactive flows, and va
Stochastic dynamic analysis of marine risers considering Gaussian system uncertainties
Ni, Pinghe; Li, Jun; Hao, Hong; Xia, Yong
2018-03-01
This paper performs the stochastic dynamic response analysis of marine risers with material uncertainties, i.e. in the mass density and elastic modulus, by using Stochastic Finite Element Method (SFEM) and model reduction technique. These uncertainties are assumed having Gaussian distributions. The random mass density and elastic modulus are represented by using the Karhunen-Loève (KL) expansion. The Polynomial Chaos (PC) expansion is adopted to represent the vibration response because the covariance of the output is unknown. Model reduction based on the Iterated Improved Reduced System (IIRS) technique is applied to eliminate the PC coefficients of the slave degrees of freedom to reduce the dimension of the stochastic system. Monte Carlo Simulation (MCS) is conducted to obtain the reference response statistics. Two numerical examples are studied in this paper. The response statistics from the proposed approach are compared with those from MCS. It is noted that the computational time is significantly reduced while the accuracy is kept. The results demonstrate the efficiency of the proposed approach for stochastic dynamic response analysis of marine risers.
Li, Xiaomin; Guo, Xueli; Guo, Haiyan
2018-06-01
Robust numerical models that describe the complex behaviors of risers are needed because these constitute dynamically sensitive systems. This paper presents a simple and efficient algorithm for the nonlinear static and dynamic analyses of marine risers. The proposed approach uses the vector form intrinsic finite element (VFIFE) method, which is based on vector mechanics theory and numerical calculation. In this method, the risers are described by a set of particles directly governed by Newton's second law and are connected by weightless elements that can only resist internal forces. The method does not require the integration of the stiffness matrix, nor does it need iterations to solve the governing equations. Due to these advantages, the method can easily increase or decrease the element and change the boundary conditions, thus representing an innovative concept of solving nonlinear behaviors, such as large deformation and large displacement. To prove the feasibility of the VFIFE method in the analysis of the risers, rigid and flexible risers belonging to two different categories of marine risers, which usually have differences in modeling and solving methods, are employed in the present study. In the analysis, the plane beam element is adopted in the simulation of interaction forces between the particles and the axial force, shear force, and bending moment are also considered. The results are compared with the conventional finite element method (FEM) and those reported in the related literature. The findings revealed that both the rigid and flexible risers could be modeled in a similar unified analysis model and that the VFIFE method is feasible for solving problems related to the complex behaviors of marine risers.
OTEC riser cable model and prototype testing
Kurt, J. P.; Schultz, J. A.; Roblee, L. H. S.
1981-12-01
Two different OTEC riser cables have been developed to span the distance between a floating OTEC power plant and the ocean floor. The major design concerns for a riser cable in the dynamic OTEC environment are fatigue, corrosion, and electrical/mechanical aging of the cable components. The basic properties of the cable materials were studied through tests on model cables and on samples of cable materials. Full-scale prototype cables were manufactured and were tested to measure their electrical and mechanical properties and performance. The full-scale testing was culminated by the electrical/mechanical fatigue test, which exposes full-scale cables to simultaneous tension, bending and electrical loads, all in a natural seawater environment.
Riser equipment decontamination engineering task plan; TOPICAL
International Nuclear Information System (INIS)
BOGER, R.M.
1999-01-01
On October 15, 1998, two Characterization Project Operations (CPO) employees were found to have contaminated clothing. An operator had 300,000-dpm/100cm2 beta/gamma, no alpha, contamination on his coat sleeve and a Radiation Control Technician (RCT) had 10,000 dpm/100cm2 beta/gamma, no alpha, on his shirt sleeve. The CPO swing shift crew was working in TX tank farm, performing sampling activities at 241-TX-113. TX tank farm is a ''clean farm'' and does not require anti-contamination clothing for entry. The CPO personnel were dressed in normal work clothes. An operator and an RCT were performing a pre-job survey that involved removing bagging around the riser equipment. When the RCT saw that the contamination readings from smear samples of the riser equipment were greater than expected, the job was suspended. Crew members were then directed to areas of lower background radiation for personnel surveys. During personnel surveys, reportable contamination was found on the coat sleeve of the operator who had been involved in the pre-job survey and on the shirt sleeve of the RCT who had been involved in the pre-job survey. No other personnel were found to be contaminated. Because of this off normal event Characterization Engineering was given the following corrective action: Examine the process methodology used for core sampling operations to determine practicality and potential long-term advantages of reducing personnel contact with contaminated equipment. This Engineering Task Plan ensures that LMHC 1998a, Corrective Action No.7 is completely addressed by Characterization Engineering. The deliverable is an Engineering Study that evaluates decontamination of riser equipment components and considers additional engineered features to reduce potential exposure to workers operating the riser equipment. This engineering study shall also address any released design features that have failed to be implemented
Riser equipment decontamination engineering task plan
International Nuclear Information System (INIS)
BOGER, R.M.
1999-01-01
On October 15, 1998, two Characterization Project Operations (CPO) employees were found to have contaminated clothing. An operator had 300,000-dpm/100cm2 beta/gamma, no alpha, contamination on his coat sleeve and a Radiation Control Technician (RCT) had 10,000 dpm/100cm2 beta/gamma, no alpha, on his shirt sleeve. The CPO swing shift crew was working in TX tank farm, performing sampling activities at 241-TX-113. TX tank farm is a ''clean farm'' and does not require anti-contamination clothing for entry. The CPO personnel were dressed in normal work clothes. An operator and an RCT were performing a pre-job survey that involved removing bagging around the riser equipment. When the RCT saw that the contamination readings from smear samples of the riser equipment were greater than expected, the job was suspended. Crew members were then directed to areas of lower background radiation for personnel surveys. During personnel surveys, reportable contamination was found on the coat sleeve of the operator who had been involved in the pre-job survey and on the shirt sleeve of the RCT who had been involved in the pre-job survey. No other personnel were found to be contaminated. Because of this off normal event Characterization Engineering was given the following corrective action: Examine the process methodology used for core sampling operations to determine practicality and potential long-term advantages of reducing personnel contact with contaminated equipment. This Engineering Task Plan ensures that LMHC 1998a, Corrective Action No.7 is completely addressed by Characterization Engineering. The deliverable is an Engineering Study that evaluates decontamination of riser equipment components and considers additional engineered features to reduce potential exposure to workers operating the riser equipment. This engineering study shall also address any released design features that have failed to be implemented
Numerical simulation of real-world flows
Energy Technology Data Exchange (ETDEWEB)
Hayase, Toshiyuki, E-mail: hayase@ifs.tohoku.ac.jp [Institute of Fluid Science, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577 (Japan)
2015-10-15
Obtaining real flow information is important in various fields, but is a difficult issue because measurement data are usually limited in time and space, and computational results usually do not represent the exact state of real flows. Problems inherent in the realization of numerical simulation of real-world flows include the difficulty in representing exact initial and boundary conditions and the difficulty in representing unstable flow characteristics. This article reviews studies dealing with these problems. First, an overview of basic flow measurement methodologies and measurement data interpolation/approximation techniques is presented. Then, studies on methods of integrating numerical simulation and measurement, namely, four-dimensional variational data assimilation (4D-Var), Kalman filters (KFs), state observers, etc are discussed. The first problem is properly solved by these integration methodologies. The second problem can be partially solved with 4D-Var in which only initial and boundary conditions are control parameters. If an appropriate control parameter capable of modifying the dynamical structure of the model is included in the formulation of 4D-Var, unstable modes are properly suppressed and the second problem is solved. The state observer and KFs also solve the second problem by modifying mathematical models to stabilize the unstable modes of the original dynamical system by applying feedback signals. These integration methodologies are now applied in simulation of real-world flows in a wide variety of research fields. Examples are presented for basic fluid dynamics and applications in meteorology, aerospace, medicine, etc. (topical review)
Natural Frequencies and Mode Shapes of Statically Deformed Inclined Risers
Alfosail, Feras
2016-10-15
We investigate numerically the linear vibrations of inclined risers using the Galerkin approach. The riser is modeled as an Euler-Bernoulli beam accounting for the nonlinear mid-plane stretching and self-weight. After solving for the initial deflection of the riser due to self-weight, we use a Galerkin expansion employing 15 axially loaded beam mode shapes to solve the eigenvalue problem of the riser around the static equilibrium configuration. This yields the riser natural frequencies and corresponding exact mode shapes for various values of inclination angles and tension. The obtained results are validated against a boundary-layer analytical solution and are found to be in good agreement. This constitutes a basis to study the nonlinear forced vibrations of inclined risers.
Multiphase reacting flows modelling and simulation
Marchisio, Daniele L
2007-01-01
The papers in this book describe the most widely applicable modeling approaches and are organized in six groups covering from fundamentals to relevant applications. In the first part, some fundamentals of multiphase turbulent reacting flows are covered. In particular the introduction focuses on basic notions of turbulence theory in single-phase and multi-phase systems as well as on the interaction between turbulence and chemistry. In the second part, models for the physical and chemical processes involved are discussed. Among other things, particular emphasis is given to turbulence modeling strategies for multiphase flows based on the kinetic theory for granular flows. Next, the different numerical methods based on Lagrangian and/or Eulerian schemes are presented. In particular the most popular numerical approaches of computational fluid dynamics codes are described (i.e., Direct Numerical Simulation, Large Eddy Simulation, and Reynolds-Averaged Navier-Stokes approach). The book will cover particle-based meth...
Directory of Open Access Journals (Sweden)
Gabriela C. Lopes
2012-01-01
Full Text Available Fluid catalytic cracking (FCC riser reactors have complex hydrodynamics, which depend not only on operating conditions, feedstock quality, and catalyst particles characteristics, but also on the geometric configurations of the reactor. This paper presents a numerical study of the influence of different riser outlet designs on the dynamic of the flow and reactor efficiency. A three-dimensional, three-phase flow model and a four-lump kinetic scheme were used to predict the performance of the reactor. The phenomenon of vaporization of the liquid oil droplets was also analyzed. Results showed that small changes in the outlet configuration had a significant effect on the flow patterns and consequently, on the reaction yields.
Energy Technology Data Exchange (ETDEWEB)
Santos, Kamylla A.L. dos; Luna-Finkler, Christine L.; Lima Filho, Hilario J.B. de [Universidade Federal de Pernambuco (UFPE), Vitoria de Santo Antao, PE (Brazil); Benachour, Mohand; Dantas, Carlos Costa; Santos, Valdemir A. dos [Universidade Catolica de Pernambuco (UNICAP), Recife, PE (Brazil)
2012-07-01
It was planned and executed the implementation of a Central Composite Rotatable Design (CCRD) to the riser of a FCC (Fluid Catalytic Cracking) cold pilot plant, to identify the basic fluid dynamic characteristics of this type of reactor. The Fluid Catalytic Cracking is the major process in oil refineries in the world. It is realized in a vertical cylindrical reactor called riser, with a short contact time between the cracking catalyst and vacuum gas oil vapors. The constant evolution of the FCC process has required the analysis of fluid dynamics using computational fluid dynamics (CFD) software. However, analysis of images produced by the application of CFD to study of risers requires preliminary concepts of the relationship between response variables and independent variables. With the CCRD implementation was performed a total of 12 experiments, being 4 full factorial, 4 axial points and 4 central points. The dependent variables were the velocities of the components (cracking catalyst and compressed air) and the pressure drop in the riser. There was a great contribution of solids flow rate for the solid phase velocity and for the pressure drop. The effects of interaction between the flow rate phases are considerably senses in pressure drop through the riser, however, for the velocities of both phases this interaction becomes negligible. (author)
Reynolds averaged simulation of unsteady separated flow
International Nuclear Information System (INIS)
Iaccarino, G.; Ooi, A.; Durbin, P.A.; Behnia, M.
2003-01-01
The accuracy of Reynolds averaged Navier-Stokes (RANS) turbulence models in predicting complex flows with separation is examined. The unsteady flow around square cylinder and over a wall-mounted cube are simulated and compared with experimental data. For the cube case, none of the previously published numerical predictions obtained by steady-state RANS produced a good match with experimental data. However, evidence exists that coherent vortex shedding occurs in this flow. Its presence demands unsteady RANS computation because the flow is not statistically stationary. The present study demonstrates that unsteady RANS does indeed predict periodic shedding, and leads to much better concurrence with available experimental data than has been achieved with steady computation
CFD simulation on reactor flow mixing phenomena
International Nuclear Information System (INIS)
Kwon, T.S.; Kim, K.H.
2016-01-01
A pre-test calculation for multi-dimensional flow mixing in a reactor core and downcomer has been studied using a CFD code. To study the effects of Reactor Coolant Pump (RCP) and core zone on the boron mixing behaviors in a lower downcomer and core inlet, a 1/5-scale CFD model of flow mixing test facility for the APR+ reference plant was simulated. The flow paths of the 1/5-scale model were scaled down by the linear scaling method. The aspect ratio (L/D) of all flow paths was preserved to 1. To preserve a dynamic similarity, the ratio of Euler number was also preserved to 1. A single phase water flow at low pressure and temperature conditions was considered in this calculation. The calculation shows that the asymmetric effect driven by RCPs shifted the high velocity field to the failed pump's flow zone. The borated water flow zone at the core inlet was also shifted to the failed RCP side. (author)
Simulation of turbulent flows containing strong shocks
International Nuclear Information System (INIS)
Fryxell, Bruce; Menon, Suresh
2008-01-01
Simulation of turbulent flows with strong shocks is a computationally challenging problem. The requirements for a method to produce accurate results for turbulence are orthogonal to those needed to treat shocks properly. In order to prevent an unphysical rate of decay of turbulent structures, it is necessary to use a method with very low numerical dissipation. Because of this, central difference schemes are widely used. However, computing strong shocks with a central difference scheme can produce unphysical post-shock oscillations that corrupt the entire flow unless additional dissipation is added. This dissipation can be difficult to localize to the area near the shock and can lead to inaccurate treatment of the turbulence. Modern high-resolution shock-capturing methods usually use upwind algorithms to provide the dissipation necessary to stabilize shocks. However, this upwind dissipation can also lead to an unphysical rate of decay of the turbulence. This paper discusses a hybrid method for simulating turbulent flows with strong shocks that couples a high-order central difference scheme with a high-resolution shock-capturing method. The shock-capturing method is used only in the vicinity of discontinuities in the flow, whereas the central difference scheme is used in the remainder of the computational domain. Results of this new method will be shown for a variety of test problems. Preliminary results for a realistic application involving detonation in gas-particle flows will also be presented.
Fatigue Strength of Titanium Risers - Defect Sensitivity
Energy Technology Data Exchange (ETDEWEB)
Babalola, Olusegun Tunde
2001-07-01
This study is centred on assessment of the fatigue strength of titanium fusion welds for deep-water riser's applications. Deep-water risers are subjected to significant fatigue loading. Relevant fatigue data for titanium fusion welds are very scarce. Hence there is a need for fatigue data and life prediction models for such weldments. The study has covered three topics: Fatigue testing, Fractography and defect assessment, and Fracture Mechanics modelling of fatigue crack growth. Two series of welded grade of titanium consisting of 14 specimens in each series were fatigue tested under constant amplitude loading. Prior to fatigue testing, strain gauge measurements of some specimens was conducted to enable the definition of stress range in the fatigue assessment procedure. The results were compared with finite solid element analysis and related to fatigue stresses in a riser pipe wall. Distribution and geometry of internal and surface defects both in the as-welded and in the post-weld machined conditions were assessed using fractography. This served as a tool to determine the fatigue initiation point in the welds. Fracture mechanics was applied to model fatigue strength of titanium welds with initiation from weld defects. Two different stress intensity factor formulations for embedded eccentrically placed cracks were used for analysis of elliptical cracks with the major axis parallel and close to one of the free surfaces. The methods were combined to give a satisfactory model for crack growth analysis. The model analyses crack growth of elliptical and semi-elliptical cracks in two directions, with updating of the crack geometry. Fatigue strength assessment was conducted using two crack growth models, the Paris-Erdogan relation with no threshold and the Donahue et al. relation with an implied threshold. The model was validated against experimental data, with a discussion on the choice of crack growth model. (author)
Simulations of magnetorheological suspensions in Poiseuille flow
Energy Technology Data Exchange (ETDEWEB)
Pappas, Yannis; Klingenberg, Daniel J. [University of Wisconsin-Madison, Department of Chemical and Biological Engineering, Madison, WI (United States)
2006-06-15
Particle-level simulations are conducted to study magnetorheological fluids in plane Poiseuille flow. The importance of the boundary conditions for the particles at the channel walls is examined by considering two extreme cases: no friction and infinite coefficient of friction. The inclusion of friction produces Bingham fluid behavior, as commonly observed experimentally for MR suspensions. Lamellar structures, similar to those reported for electrorheological fluids in shear flow, are observed in the post-yield region for both particle boundary conditions. The formation of these lamellae is accompanied by an increase in the bulk fluid velocity. The slip boundary condition produces higher fluid velocities and thicker lamellar structures. (orig.)
Direct Simulation of Reentry Flows with Ionization
Carlson, Ann B.; Hassan, H. A.
1989-01-01
The Direct Simulation Monte Carlo (DSMC) method is applied in this paper to the study of rarefied, hypersonic, reentry flows. The assumptions and simplifications involved with the treatment of ionization, free electrons and the electric field are investigated. A new method is presented for the calculation of the electric field and handling of charged particles with DSMC. In addition, a two-step model for electron impact ionization is implemented. The flow field representing a 10 km/sec shock at an altitude of 65 km is calculated. The effects of the new modeling techniques on the calculation results are presented and discussed.
Dalia integrated production bundle (IPB): an innovative riser solution for deep water fields
Energy Technology Data Exchange (ETDEWEB)
Reals, Th Boscals de; Gloaguen, M.; Roche, F. [Total E and P (Angola); Marion, A.; Poincheval, A. [Technip, Paris (France)
2008-07-01
The Dalia field is located 210 km north west of Luanda (Angola), about 140 km from shore in 1400 meter water-depth. It was the second major discovery out of 15 made in the block 17 operated by Total. The Dalia Umbilical, Flow lines and Risers EPCI Contract was awarded in 2003. The sea-line network to connect and control the 71 wells and 9 manifolds consist of the following: 40 km of insulated pipe in pipe (12 inches into 17 inches) production flow lines; 45 km of 12 inches water and gas injection lines; 6 off 1.7 km flexible water and gas injection risers; 8 off 1.65 km flexible Integrated Production Bundle (IPB) risers; 75 km of control umbilicals. The flow assurance and associated insulation requirement of the production transport system was one of the main challenges of the project. With a crude temperature of 45 deg C at the wellhead and the required minimum temperature of 35 deg C on arrival at the FPSO, this problem was complex. Understanding that, due to the Joule Thompson effect of the riser gas lift, a 'built in' loss of about 5 deg C is induced and together with further losses through the sub sea pipelines, some up to 6 km long, the agreed solution was 'pipe in pipe' for the production flow lines. The innovative flexible IPB riser, incorporating gas lift and heating to keep the fluid temperature above hydrate formation zone, was the selected riser solution. The IPB is new technology for deep water, developed by Technip for Dalia, and consists of a 12 inches nominal central flexible, surrounded by layers of heat tracing cables, small bore gas lift lines, optical fibres and many insulation layers with an Overall Heat Transfer Coefficient of approximately 3,4 W/m{sup 2}K. After an earlier research and development programme, a further extensive qualification programme was conducted during the course of the project, culminating with the deep water testing phase offshore Brazil. The IPB was then approved for fabrication and installation
Adaptive LES Methodology for Turbulent Flow Simulations
Energy Technology Data Exchange (ETDEWEB)
Oleg V. Vasilyev
2008-06-12
Although turbulent flows are common in the world around us, a solution to the fundamental equations that govern turbulence still eludes the scientific community. Turbulence has often been called one of the last unsolved problem in classical physics, yet it is clear that the need to accurately predict the effect of turbulent flows impacts virtually every field of science and engineering. As an example, a critical step in making modern computational tools useful in designing aircraft is to be able to accurately predict the lift, drag, and other aerodynamic characteristics in numerical simulations in a reasonable amount of time. Simulations that take months to years to complete are much less useful to the design cycle. Much work has been done toward this goal (Lee-Rausch et al. 2003, Jameson 2003) and as cost effective accurate tools for simulating turbulent flows evolve, we will all benefit from new scientific and engineering breakthroughs. The problem of simulating high Reynolds number (Re) turbulent flows of engineering and scientific interest would have been solved with the advent of Direct Numerical Simulation (DNS) techniques if unlimited computing power, memory, and time could be applied to each particular problem. Yet, given the current and near future computational resources that exist and a reasonable limit on the amount of time an engineer or scientist can wait for a result, the DNS technique will not be useful for more than 'unit' problems for the foreseeable future (Moin & Kim 1997, Jimenez & Moin 1991). The high computational cost for the DNS of three dimensional turbulent flows results from the fact that they have eddies of significant energy in a range of scales from the characteristic length scale of the flow all the way down to the Kolmogorov length scale. The actual cost of doing a three dimensional DNS scales as Re{sup 9/4} due to the large disparity in scales that need to be fully resolved. State-of-the-art DNS calculations of isotropic
Fluid flow solidification simulation of molten alloys
International Nuclear Information System (INIS)
Kaschnitz, E.
1997-01-01
In an effort to minimize costs and to obtain optimum designs, computer simulation of shape casting processes is more and more used as a development tool. Accurate predictions are possible by means of three dimensional fluid flow and solidification modelling. The bases of the model are the transient laminar Navier-Stokes-equations for a Newtonian fluid including the tracking of the free surface. They are describing the melt flow pattern during the mold filling sequence. Simultaneously, the temperature development in the alloy and mold is calculated using Fourier's heat transfer equation. At OEGI, a commercial software package (MAGMAsoft) with a finite difference equation solver is used for improvement of casting processes. Different examples of industrial applications will be shown. (author)
Geometrical automata for two phase flow simulation
International Nuclear Information System (INIS)
Herrero, V.; Guido-Lavalle, G.; Clausse, A.
1996-01-01
An automaton is an entity defined by a mathematical state which changes following iterative rules representing the interaction with the neighborhood. A model of automata for two-phase flow simulation consisting in a field of disks which are allowed to change their radii and move in a plane is presented. The model is more general than the classical cellular automata in two respects: (1) the grid of cellular automata is dismissed in favor of a trajectory generator; and (2) the rules of interaction involve parameters intended to represent some of the most relevant variables governing the actual physical interactions between phases. Computational experiments show that the algorithm captures the essential physics underlying two-phase flow problems such as bubbly-slug pattern transition and void fraction development along tubes. A comparison with experimental data of void fraction profiles is presented, showing excellent agreement. (orig.)
Traffic flow dynamics data, models and simulation
Treiber, Martin
2013-01-01
This textbook provides a comprehensive and instructive coverage of vehicular traffic flow dynamics and modeling. It makes this fascinating interdisciplinary topic, which to date was only documented in parts by specialized monographs, accessible to a broad readership. Numerous figures and problems with solutions help the reader to quickly understand and practice the presented concepts. This book is targeted at students of physics and traffic engineering and, more generally, also at students and professionals in computer science, mathematics, and interdisciplinary topics. It also offers material for project work in programming and simulation at college and university level. The main part, after presenting different categories of traffic data, is devoted to a mathematical description of the dynamics of traffic flow, covering macroscopic models which describe traffic in terms of density, as well as microscopic many-particle models in which each particle corresponds to a vehicle and its driver. Focus chapters on ...
Direct numerical simulation of annular flows
Batchvarov, Assen; Kahouadji, Lyes; Chergui, Jalel; Juric, Damir; Shin, Seungwon; Craster, Richard V.; Matar, Omar K.
2017-11-01
Vertical counter-current two-phase flows are investigated using direct numerical simulations. The computations are carried out using Blue, a front-tracking-based CFD solver. Preliminary results show good qualitative agreement with experimental observations in terms of interfacial phenomena; these include three-dimensional, large-amplitude wave formation, the development of long ligaments, and droplet entrainment. The flooding phenomena in these counter current systems are closely investigated. The onset of flooding in our simulations is compared to existing empirical correlations such as Kutateladze-type and Wallis-type. The effect of varying tube diameter and fluid properties on the flooding phenomena is also investigated in this work. EPSRC, UK, MEMPHIS program Grant (EP/K003976/1), RAEng Research Chair (OKM).
Flexible riser integrity management: areas of concern and applications
Energy Technology Data Exchange (ETDEWEB)
Podskarbi, Mateusz [Schlumberger Servicos de Petroleo Ltda., Rio de Janeiro, RJ (Brazil)
2008-07-01
Flexible risers are key enables for both deep water and shallow water offshore production developments. Number of flexible risers installed worldwide is into several thousands with two main concentration areas - offshore Brazil and North Sea. Flexible risers are subject to significant loads including environmental impacts, vessel motions, internal temperature and pressure as well as substantial installation loads. Excessive loads of one type or a combination of various types of loads can cause damage to the flexible that can lead to a catastrophic failure. Industry observed number of failures increasing in recent years. Operators and manufacturing companies are taking various steps to address this issue. One of possible approaches is to use monitoring instrumentation to measure riser response and integrity in real time. This paper reviews various types of flexible riser damage mechanisms caused by impact damage, corrosion, excessive pressure, armor wire rupture, compromising flexible riser minimum bend radius, excessive fatigue loading, etc. Failure mechanisms are reviewed with particular focus on the consequences that it causes in terms of risk to the infrastructure and detectable changes. Further part of the paper is focused on monitoring techniques employed and available to detect particular types of failure mechanisms. Systematic review of the monitoring techniques is provided with specific attention given to ability of these techniques to provide early warnings of riser failure. Evaluation of monitoring techniques versus modes of operation and failure mechanism is key to selecting appropriate system that ensures effectiveness of the integrity management program. (author)
Two Phase Flow Simulation Using Cellular Automata
International Nuclear Information System (INIS)
Marcel, C.P.
2002-01-01
The classical mathematical treatment of two-phase flows is based on the average of the conservation equations for each phase.In this work, a complementary approach to the modeling of these systems based on statistical population balances of aut omata sets is presented.Automata are entities defined by mathematical states that change following iterative rules representing interactions with the neighborhood.A model of automata for two-phase flow simulation is presented.This model consists of fie lds of virtual spheres that change their volumes and move around a certain environment.The model is more general than the classical cellular automata in two respects: the grid of cellular automata is dismissed in favor of a trajectory generator, and the rules of interaction involve parameters representing the actual physical interactions between phases.Automata simulation was used to study unsolved two-phase flow problems involving high heat flux rates. One system described in this work consists of a vertical channel with saturated water at normal pressure heated from the lower surface.The heater causes water to boil and starts the bubble production.We used cellular automata to describe two-phase flows and the interaction with the heater.General rule s for such cellular automata representing bubbles moving in stagnant liquid were used, with special attention to correct modeling of different mechanisms of heat transfer.The results of the model were compared to previous experiments and correlations finding good agreement.One of the most important findings is the confirmation of Kutateladze's idea about a close relation between the start of critical heat flux and a change in the flow's topology.This was analyzed using a control volume located in the upper surface of the heater.A strong decrease in the interfacial surface just before the CHF start was encountered.The automata describe quite well some characteristic parameters such as the shape of the local void fraction in the
Distributed simulation of mixing flow of dough
International Nuclear Information System (INIS)
Baloch, A.
2005-01-01
This paper reports on a study concerned with the numerical simulation of incompressible complex mixing flows of viscoelastic fluids is of industrial importance, particularly relevance in the food processing industry, such as occurs in dough mixing. The flows considered are in a complex domain setting. The present problem is one of this form, expressed as the flow between an outer rotating cylindrical vessel all and a stationary cylindrical/stirrers. The context is one of mixing with in a cylindrical vessel, where stirrers are located on the mixing vessel lid, and placed in a concentric/eccentric position with respect to the central cylindrical axis of the vessel. Here, the motion is considered as driven by the rotation of the outer vessel wall, with various stirrer locations. Two dough mixers at various rotation speeds are studied; one with one stirrer and the other with two stirrers. With a singular circular stirrer, an eccentric configuration is adopted. A further eccentric case with two circular stirrers is also contrasted against the above, where a symmetrical arrangement is assumed. Numerical simulations are based on two dimensions in the cylindrical polar co-ordinates system. The results reflected close agreement with the equivalent experimental results. The motivation for this work is to develop and advance technology to model the mixing of dough. The ultimate target is to predict and adjust the design of dough mixers, so that optimal dough processing may be achieved notably, with reference to work input on the dough. The hardware platform is a network combination of homogeneous Intel Linux clusters of workstations. A semi-implicit time-stepping Taylor-Galerkin scheme is employed with PVM (Parallel Virtual Machine) message passing libraries as the message passing protocol. Parallel results are compared against single processor (sequentially) solutions, using the parallelism paradigm of domain decomposition. Linear speed-up with the number of processors is
Iversen, Alexander
2012-01-01
Master's thesis in Offshore technology The main concerns during drilling operations are riser integrity and maintaining well control. This thesis has mainly been focusing on the problems and challenges faced with the marine riser system to illuminate high risk areas related to riser integrity. A marine riser system consists generally of four main elements; the upper marine riser package, riser joints, lower marine riser package, and the blowout preventer, each playing an important par...
Single-shell tank riser resistance to ground test plan
International Nuclear Information System (INIS)
Kiewert, L.R.
1996-01-01
This Test Procedure provides the general directions for conducting Single-Shell Tank Riser to Earth Measurements which will be used by engineering as a step towards providing closure for the Lightning Hazard Issue
Liu, Huai-zeng; Wang, Fei; Jiang, Guo-sheng; Guo, Hai-yan; Li, Xiao-min
2016-03-01
The dynamic response of two flexible model risers in tandem arrangement immersed in a stepped current was analyzed. The risers, with an external diameter of 20 mm and a total length of 6200 mm, had an aspect ratio of 310. They were hinged to the support structure at the center-to-center distances away 3-12 times the external diameter. The top 1200 mm was exposed to a uniform current at a speed which was up to 0.9 m/s (the Reynolds number was 18000) and the rest in still water. The dynamic responses, which were obtained through the Fiber Bragg Grating strain gauges mounted on the surface, were analyzed by studying the cross-flow amplitudes and modal weights. The cross-flow vibration were observed up to the third mode, and the modal transformation from the second mode to the third mode was clearly observed. The experiment confirmed that the typical vortex-induced vibration (VIV) had occurred on the up-stream riser. But for the down-stream riser, the main excitation mechanism was wake-induced vibration (WIV). The modal transformation of WIV was more complex than that of VIV, which might be helpful for other researchers to study the interference effect.
Large eddy simulation of cavitating flows
Gnanaskandan, Aswin; Mahesh, Krishnan
2014-11-01
Large eddy simulation on unstructured grids is used to study hydrodynamic cavitation. The multiphase medium is represented using a homogeneous equilibrium model that assumes thermal equilibrium between the liquid and the vapor phase. Surface tension effects are ignored and the governing equations are the compressible Navier Stokes equations for the liquid/vapor mixture along with a transport equation for the vapor mass fraction. A characteristic-based filtering scheme is developed to handle shocks and material discontinuities in non-ideal gases and mixtures. A TVD filter is applied as a corrector step in a predictor-corrector approach with the predictor scheme being non-dissipative and symmetric. The method is validated for canonical one dimensional flows and leading edge cavitation over a hydrofoil, and applied to study sheet to cloud cavitation over a wedge. This work is supported by the Office of Naval Research.
Traffic flow dynamics. Data, models and simulation
Energy Technology Data Exchange (ETDEWEB)
Treiber, Martin [Technische Univ. Dresden (Germany). Inst. fuer Wirtschaft und Verkehr; Kesting, Arne [TomTom Development Germany GmbH, Berlin (Germany)
2013-07-01
First comprehensive textbook of this fascinating interdisciplinary topic which explains advances in a way that it is easily accessible to engineering, physics and math students. Presents practical applications of traffic theory such as driving behavior, stability analysis, stop-and-go waves, and travel time estimation. Presents the topic in a novel and systematic way by addressing both microscopic and macroscopic models with a focus on traffic instabilities. Revised and extended edition of the German textbook ''Verkehrsdynamik und -simulation''. This textbook provides a comprehensive and instructive coverage of vehicular traffic flow dynamics and modeling. It makes this fascinating interdisciplinary topic, which to date was only documented in parts by specialized monographs, accessible to a broad readership. Numerous figures and problems with solutions help the reader to quickly understand and practice the presented concepts. This book is targeted at students of physics and traffic engineering and, more generally, also at students and professionals in computer science, mathematics, and interdisciplinary topics. It also offers material for project work in programming and simulation at college and university level. The main part, after presenting different categories of traffic data, is devoted to a mathematical description of the dynamics of traffic flow, covering macroscopic models which describe traffic in terms of density, as well as microscopic many-particle models in which each particle corresponds to a vehicle and its driver. Focus chapters on traffic instabilities and model calibration/validation present these topics in a novel and systematic way. Finally, the theoretical framework is shown at work in selected applications such as traffic-state and travel-time estimation, intelligent transportation systems, traffic operations management, and a detailed physics-based model for fuel consumption and emissions.
Cerebral blood flow simulations in realistic geometries
Directory of Open Access Journals (Sweden)
Szopos Marcela
2012-04-01
Full Text Available The aim of this work is to perform the computation of the blood flow in all the cerebral network, obtained from medical images as angiographies. We use free finite elements codes as FreeFEM++. We first test the code on analytical solutions in simplified geometries. Then, we study the influence of boundary conditions on the flow and we finally perform first computations on realistic meshes. L’objectif est ici de simuler l’écoulement sanguin dans tout le réseau cérébral (artériel et veineux obtenu à partir d’angiographies cérébrales 3D à l’aide de logiciels d’éléments finis libres, comme FreeFEM++. Nous menons d’abord une étude détaillée des résultats sur des solutions analytiques et l’influence des conditions limites à imposer dans des géométries simplifiées avant de travailler sur les maillages réalistes.
Large-eddy simulations for turbulent flows
International Nuclear Information System (INIS)
Husson, S.
2007-07-01
The aim of this work is to study the impact of thermal gradients on a turbulent channel flow with imposed wall temperatures and friction Reynolds numbers of 180 and 395. In this configuration, temperature variations can be strong and induce significant variations of the fluid properties. We consider the low Mach number equations and carry out large eddy simulations. We first validate our simulations thanks to comparisons of some of our LES results with DNS data. Then, we investigate the influence of the variations of the conductivity and the viscosity and show that we can assume these properties constant only for weak temperature gradients. We also study the thermal sub-grid-scale modelling and find no difference when the sub-grid-scale Prandtl number is taken constant or dynamically calculated. The analysis of the effects of strongly increasing the temperature ratio mainly shows a dissymmetry of the profiles. The physical mechanism responsible of these modifications is explained. Finally, we use semi-local scaling and the Van Driest transformation and we show that they lead to a better correspondence of the low and high temperature ratios profiles. (author)
Helical wire stress analysis of unbonded flexible riser under irregular response
Wang, Kunpeng; Ji, Chunyan
2017-06-01
A helical wire is a critical component of an unbonded flexible riser prone to fatigue failure. The helical wire has been the focus of much research work in recent years because of the complex multilayer construction of the flexible riser. The present study establishes an analytical model for the axisymmetric and bending analyses of an unbonded flexible riser. The interlayer contact under axisymmetric loads in this model is modeled by setting radial dummy springs between adjacent layers. The contact pressure is constant during the bending response and applied to determine the slipping friction force per unit helical wire. The model tracks the axial stress around the angular position at each time step to calculate the axial force gradient, then compares the axial force gradient with the slipping friction force to judge the helical wire slipping region, which would be applied to determine the bending stiffness for the next time step. The proposed model is verified against the experimental data in the literature. The bending moment-curvature relationship under irregular response is also qualitatively discussed. The stress at the critical point of the helical wire is investigated based on the model by considering the local flexure. The results indicate that the present model can well simulate the bending stiffness variation during irregular response, which has significant effect on the stress of helical wire.
Composite Risers for Deepwater Applications Risers composites pour applications en mer profonde
Directory of Open Access Journals (Sweden)
Metivaud G.
2006-11-01
Full Text Available This paper is devoted to the high performance composite tubes developed by the Institut Français du Pétrole (IFP and Aerospatiale for deepwater risers applications. The design principles of the tubes are first presented, along with results of preliminary work carried out as part of the initial feasibility study. Applications of composite tubes to drilling riser Kill and Choke lines and to TLP production risers, both of which have been studied in detail, are then described. Technical and operational advantages obtained from such applications are discussed. Cet article présente les travaux réalisés par l'Institut Français du Pétrole et l'Aerospatiale dans le domaine des tubes composites haute performance pour les applications aux liaisons fond-surface de forage et de production en mer profonde. Les matériaux composites avancés sont une classe de matériaux très particulière, présentant à la fois des caractéristiques mécaniques élevées et une densité spécifique faible. Ils sont utilisés principalement par les industries de l'aéronautique et de l'espace, mais l'industrie pétrolière en mer profonde est un secteur où ils peuvent trouver dans l'avenir des applications très intéressantes, notamment les tubes de risers. Les tubes de risers pétroliers en mer présentent en effet une gamme de spécifications élevées (diamètres, pression, traction, fatigue dans un environnement sévère et leur poids suspendu peut pénaliser fortement les systèmes de forage ou de production par grande profondeur d'eau. Un premier concept de tube composite haute performance a été développé par IFP et Aerospatiale au début des années 1980 ; sa partie courante, réalisée par enroulement filamentaire de fibres de verre R ou de fibres de carbone, et son système d'embout ont été soumis à une série d'essais mécaniques (pression interne jusqu'à 105 MPa, traction supérieure à 1 000 kN pour un diamètre nominal de 0,1 m, millions de
New tools for steel catenary risers inspection; Novas ferramentas para inspecao de risers tipo SCR
Energy Technology Data Exchange (ETDEWEB)
Camerini, Claudio Soligo; Marinho, Carla Alves; Raphael, Fabiana N.; Maia, Carlos [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil); Freitas, Miguel [Pontificia Univ. Catolica do Rio de Janeiro, RJ (Brazil); Lopes, Ricardo Tadeu; Rocha, Henrique [Universidade Federal, Rio de Janeiro, RJ (Brazil). Coordenacao dos Programas de Pos-graduacao de Engenharia
2005-07-01
The Research Center of PETROBRAS and two of the Federal Brazilian Universities, PUC-Rio and UFRJ, have been developing two new projects in order to inspect risers of petroleum production. The first tool is an instrumented pig for profiling internal corrosion, having flexibility under diameter variations and independence related to thickness wall pipeline. The second one is a gammagraphy system remotely operated by ROVs, to be employed in alveoli corrosion and fatigue cracks detection in underwater pipelines. This work shows the trajectory of these two tools, describing laboratory and field tests and the future activities. (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.
Meshless Method for Simulation of Compressible Flow
Nabizadeh Shahrebabak, Ebrahim
In the present age, rapid development in computing technology and high speed supercomputers has made numerical analysis and computational simulation more practical than ever before for large and complex cases. Numerical simulations have also become an essential means for analyzing the engineering problems and the cases that experimental analysis is not practical. There are so many sophisticated and accurate numerical schemes, which do these simulations. The finite difference method (FDM) has been used to solve differential equation systems for decades. Additional numerical methods based on finite volume and finite element techniques are widely used in solving problems with complex geometry. All of these methods are mesh-based techniques. Mesh generation is an essential preprocessing part to discretize the computation domain for these conventional methods. However, when dealing with mesh-based complex geometries these conventional mesh-based techniques can become troublesome, difficult to implement, and prone to inaccuracies. In this study, a more robust, yet simple numerical approach is used to simulate problems in an easier manner for even complex problem. The meshless, or meshfree, method is one such development that is becoming the focus of much research in the recent years. The biggest advantage of meshfree methods is to circumvent mesh generation. Many algorithms have now been developed to help make this method more popular and understandable for everyone. These algorithms have been employed over a wide range of problems in computational analysis with various levels of success. Since there is no connectivity between the nodes in this method, the challenge was considerable. The most fundamental issue is lack of conservation, which can be a source of unpredictable errors in the solution process. This problem is particularly evident in the presence of steep gradient regions and discontinuities, such as shocks that frequently occur in high speed compressible flow
simulation of vertical water flow through vadose zone
African Journals Online (AJOL)
HOD
Simulation of vertical water flow representing the release of water from the vadose zone to the aquifer of surroundings ... ground water pollution from agricultural, industrial and municipal .... Peak Flow Characteristics of Wyoming. Streams: US ...
Energy Technology Data Exchange (ETDEWEB)
Roveri, Francisco E.; Pestana, Rafael G. [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil). Centro de Pesquisas
2008-07-01
This paper presents a set of structural and hydrodynamic analyses of a connected marine riser, in 1900 meter water depth. Operating windows are determined for one year return period environmental conditions and for a set of drilling fluid weight density values. Parametric analyses are carried out to study the riser response sensitivity to variations in environmental conditions, drilling fluid weight density, upper and lower flex joint rotational stiffness and vessel motion phase angles. Current, drilling fluid weight density and vessel motion phase angle changes affect significantly the system response, whereas the response is not significantly affected by changes in wave height, wave period and flex joint rotational stiffness. (author)
Simulation of the flow inside an annular can combustor
Alqaraghuli, W; Alkhafagiy, D; Shires, A
2014-01-01
In the gas turbine combustion system, the external flows in annuli play one of the key roles in controlling pressure loss, air flow distribution around the combustor liner, and the attendant effects on performance, durability, and stability. This paper describes a computational fluid dynamics (CFD) simulation of the flow in the outer annulus of a can combustor. Validating this simulation was done with experimental results obtained from analyzing the flow inside a can combustor annulus that w...
Continuum simulations of water flow past fullerene molecules
DEFF Research Database (Denmark)
Popadic, A.; Praprotnik, M.; Koumoutsakos, P.
2015-01-01
We present continuum simulations of water flow past fullerene molecules. The governing Navier-Stokes equations are complemented with the Navier slip boundary condition with a slip length that is extracted from related molecular dynamics simulations. We find that several quantities of interest...... as computed by the present model are in good agreement with results from atomistic and atomistic-continuum simulations at a fraction of the cost. We simulate the flow past a single fullerene and an array of fullerenes and demonstrate that such nanoscale flows can be computed efficiently by continuum flow...
Understanding casing flow in Pelton turbines by numerical simulation
Rentschler, M.; Neuhauser, M.; Marongiu, J. C.; Parkinson, E.
2016-11-01
For rehabilitation projects of Pelton turbines, the flow in the casing may have an important influence on the overall performance of the machine. Water sheets returning on the jets or on the runner significantly reduce efficiency, and run-away speed depends on the flow in the casing. CFD simulations can provide a detailed insight into this type of flow, but these simulations are computationally intensive. As in general the volume of water in a Pelton turbine is small compared to the complete volume of the turbine housing, a single phase simulation greatly reduces the complexity of the simulation. In the present work a numerical tool based on the SPH-ALE meshless method is used to simulate the casing flow in a Pelton turbine. Using improved order schemes reduces the numerical viscosity. This is necessary to resolve the flow in the jet and on the casing wall, where the velocity differs by two orders of magnitude. The results are compared to flow visualizations and measurement in a hydraulic laboratory. Several rehabilitation projects proved the added value of understanding the flow in the Pelton casing. The flow simulation helps designing casing insert, not only to see their influence on the flow, but also to calculate the stress in the inserts. In some projects, the casing simulation leads to the understanding of unexpected behavior of the flow. One such example is presented where the backsplash of a deflector hit the runner, creating a reversed rotation of the runner.
Numerical Simulation Of Flow Through An Artificial Heart
Rogers, Stuart; Kutler, Paul; Kwak, Dochan; Kiris, Centin
1991-01-01
Research in both artificial hearts and fluid dynamics benefits from computational studies. Algorithm that implements Navier-Stokes equations of flow extended to simulate flow of viscous, incompressible blood through articifial heart. Ability to compute details of such flow important for two reasons: internal flows with moving boundaries of academic interest in their own right, and many of deficiencies of artificial hearts attributable to dynamics of flow.
Implicit time accurate simulation of unsteady flow
van Buuren, René; Kuerten, Hans; Geurts, Bernard J.
2001-03-01
Implicit time integration was studied in the context of unsteady shock-boundary layer interaction flow. With an explicit second-order Runge-Kutta scheme, a reference solution to compare with the implicit second-order Crank-Nicolson scheme was determined. The time step in the explicit scheme is restricted by both temporal accuracy as well as stability requirements, whereas in the A-stable implicit scheme, the time step has to obey temporal resolution requirements and numerical convergence conditions. The non-linear discrete equations for each time step are solved iteratively by adding a pseudo-time derivative. The quasi-Newton approach is adopted and the linear systems that arise are approximately solved with a symmetric block Gauss-Seidel solver. As a guiding principle for properly setting numerical time integration parameters that yield an efficient time accurate capturing of the solution, the global error caused by the temporal integration is compared with the error resulting from the spatial discretization. Focus is on the sensitivity of properties of the solution in relation to the time step. Numerical simulations show that the time step needed for acceptable accuracy can be considerably larger than the explicit stability time step; typical ratios range from 20 to 80. At large time steps, convergence problems that are closely related to a highly complex structure of the basins of attraction of the iterative method may occur. Copyright
Flask fluid flow simulation using CFD
International Nuclear Information System (INIS)
Swindlehurst, W.E.; Livesey, E.; Worthington, D.
1989-01-01
BNFL and its subsidiary Company, PNTL, design and operate waterfilled LWR fuel transport flasks for the international transport of irradiated fuel. Although some 150 flasks are currently in operation, new flask designs are being developed. As part of the supporting R and D program, Computational Fluid Dynamics (CFD) codes are being investigated as a means of predicting fluid movements and temperatures within the complex internal geometry of flasks. The ability to simulate fluid flow is particularly important when convection heat transfer is significant. Although obviously relevant to water filled flasks, the technique is applicable to dry flask thermal assessments (where experience shows that convection heat transfer is often underestimated). Computational Fluid Dynamics has emerged in recent years as an important technique in engineering design and safety assessments. Cheaper computing and the development of general CFD codes allows complex engineering structures to be analyzed. However, because of this complexity, it is essential that the application and associated modeling assumptions are critically reviewed. To assess the ability of a CFD code to model flask internals, the code PHOENICS has been used to model the fluid movements in a BNFL Excellox-type flask and the results compared with test data
Computational fluid dynamics (CFD) simulation of hot air flow ...
African Journals Online (AJOL)
Computational Fluid Dynamics simulation of air flow distribution, air velocity and pressure field pattern as it will affect moisture transient in a cabinet tray dryer is performed using SolidWorks Flow Simulation (SWFS) 2014 SP 4.0 program. The model used for the drying process in this experiment was designed with Solid ...
Numerical simulations and mathematical models of flows in complex geometries
DEFF Research Database (Denmark)
Hernandez Garcia, Anier
The research work of the present thesis was mainly aimed at exploiting one of the strengths of the Lattice Boltzmann methods, namely, the ability to handle complicated geometries to accurately simulate flows in complex geometries. In this thesis, we perform a very detailed theoretical analysis...... and through the Chapman-Enskog multi-scale expansion technique the dependence of the kinetic viscosity on each scheme is investigated. Seeking for optimal numerical schemes to eciently simulate a wide range of complex flows a variant of the finite element, off-lattice Boltzmann method [5], which uses...... the characteristic based integration is also implemented. Using the latter scheme, numerical simulations are conducted in flows of different complexities: flow in a (real) porous network and turbulent flows in ducts with wall irregularities. From the simulations of flows in porous media driven by pressure gradients...
Flow Simulation and Performance Prediction of Centrifugal Pumps ...
African Journals Online (AJOL)
With the aid of computational fluid dynamics, the complex internal flows in water pump impellers can be well predicted, thus facilitating the product development process of pumps. In this paper a commercial CFD code was used to solve the governing equations of the flow field. A 2-D simulation of turbulent fluid flow is ...
Numerical simulation of two phase flows in heat exchangers
International Nuclear Information System (INIS)
Grandotto Biettoli, M.
2006-04-01
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)
Simulation of dendritic growth of magnesium alloys with fluid flow
Directory of Open Access Journals (Sweden)
Meng-wu Wu
2017-11-01
Full Text Available Fluid flow has a significant impact on the microstructure evolution of alloys during solidification. Based on the previous work relating simulation of the dendritic growth of magnesium alloys with hcp (hexagonal close-packed structure, an extension was made to the formerly established CA (cellular automaton model with the purpose of studying the effect of fluid flow on the dendritic growth of magnesium alloys. The modified projection method was used to solve the transport equations of flow field. By coupling the flow field with the solute field, simulation results of equiaxed and columnar dendritic growth of magnesium alloys with fluid flow were achieved. The simulated results were quantitatively compared with those without fluid flow. Moreover, a comparison was also made between the present work and previous works conducted by others. It can be concluded that a deep understanding of the dendritic growth of magnesium alloys with fluid flow can be obtained by applying the present numerical model.
Simulations of overall flow in gas centrifuge considering feed jet
International Nuclear Information System (INIS)
He Liang; Jiang Dongjun; Ying Chuntong
2010-01-01
A coupled method for the numerical solution of the flow in rapidly rotating gas centrifuge was presented. An iteration process of DSMC and CFD was performed to analyze the overall flow in radial direction, in which DSMC was adopted to simulate the rarefied region, and CFD was adopted to the counter-current of gas centrifuge to discrete the model equations. It was applied to simulate the 2D symmetrical flow model considering the rarefied region with the feed jet flow. A series of illustrative numerical examples were given. The flow structures of the feed jet in the rarefied gas flow region were shown. The results suggest that DSMC CFD coupled method is competent to the simulations of overall flow in a gas centrifuge. (authors)
Lattice gas automata simulations of flow through porous media
International Nuclear Information System (INIS)
Matsukuma, Yosuke; Abe, Yutaka; Adachi, Hiromichi; Takahashi, Ryoichi
1998-01-01
In the course of a severe accident, a debris bed may be formed from once- molten and fragmented fuel elements. In order to avoid further degradation of the reactor core, it is necessary to remove the heat from the debris bed since the debris bed still release the decay heat. So as to predict the coolability of the debris bed, it is important to precisely estimate flow patterns through complex geometry of debris bed in microscopic level. Lattice gas automata could be powerful tool to simulate such a complex geometry. As a first step of the study, fundamental numerical simulation were conducted in two dimensional systems by using the lattice gas automata method to clarify single phase flow patterns through porous media in mesoscopic level. Immiscible lattice gas model is one of the lattice gas automata method and utilized for spinodal decomposition simulation of binary fluids. This model was applied to generate the complex flow geometry simulating porous media. It was approved that the complex flow geometries were successfully generated by the present method. Flow concentration was observed in specified flow channels for lower Reynolds number. Two dimensional flow concentration was caused by the irregular flow geometry generated by the present method, since the flow selects the channels of lower friction. Two dimensional pressure distribution was observed relating to the concentrations of flow in specified channels. The simulating results of the flow through the porous media by the present method qualitatively agree with the Ergun's equation. Quantitatively, the present results approach to Ergun's equation in higher Reynolds number than 10, although concentration of the flow in a specified flow channels were observed in lower Reynolds number than 10. It can be concluded that this technique is useful is useful to simulate flow through complex geometry like porous media. (author)
An efficient structural finite element for inextensible flexible risers
Papathanasiou, T. K.; Markolefas, S.; Khazaeinejad, P.; Bahai, H.
2017-12-01
A core part of all numerical models used for flexible riser analysis is the structural component representing the main body of the riser as a slender beam. Loads acting on this structural element are self-weight, buoyant and hydrodynamic forces, internal pressure and others. A structural finite element for an inextensible riser with a point-wise enforcement of the inextensibility constrain is presented. In particular, the inextensibility constraint is applied only at the nodes of the meshed arc length parameter. Among the virtues of the proposed approach is the flexibility in the application of boundary conditions and the easy incorporation of dissipative forces. Several attributes of the proposed finite element scheme are analysed and computation times for the solution of some simplified examples are discussed. Future developments aim at the appropriate implementation of material and geometric parameters for the beam model, i.e. flexural and torsional rigidity.
A state space approach for the eigenvalue problem of marine risers
Alfosail, Feras; Nayfeh, Ali H.; Younis, Mohammad I.
2017-01-01
A numerical state-space approach is proposed to examine the natural frequencies and critical buckling limits of marine risers. A large axial tension in the riser model causes numerical limitations. These limitations are overcome by using
Flexible riser global analysis for very shallow water
Karegar, Sadjad
2013-01-01
Master's thesis in Offshore technology Flexible risers are widely used for a range of water depths and can accommodate large floater motions when using a buoyant system. A wide range of buoyancy solutions have been developed for very shallow water (e.g. 30-50 m), shallow water (e.g. 90-110 m) and semi-deep water (e.g. 300-400 m) and in the ranges between these depths. Flexible risers can have different configurations. These different solutions have different characteristics which influe...
Simulation and Verificaiton of Flow in Test Methods
DEFF Research Database (Denmark)
Thrane, Lars Nyholm; Szabo, Peter; Geiker, Mette Rica
2005-01-01
Simulations and experimental results of L-box and slump flow test of a self-compacting mortar and a self-compacting concrete are compared. The simulations are based on a single fluid approach and assume an ideal Bingham behavior. It is possible to simulate the experimental results of both tests...
Numerical simulation of random stresses on an annular turbulent flow
International Nuclear Information System (INIS)
Marti-Moreno, Marta
2000-01-01
The flow along a circular cylinder may induce structural vibrations. For the predictive analysis of such vibrations, the turbulent forcing spectrum needs to be characterized. The aim of this work is to study the turbulent fluid forces acting on a single tube in axial flow. More precisely we have performed numerical simulations of an annular flow. These simulations were carried out on a cylindrical staggered mesh by a finite difference method. We consider turbulent flow with Reynolds number up to 10 6 . The Large Eddy Simulation Method has been used. A survey of existent experiments showed that hydraulic diameter acts as an important parameter. We first showed the accuracy of the numerical code by reproducing the experiments of Mulcahy. The agreement between pressure spectra from computations and from experiments is good. Then, we applied this code to simulate new numerical experiments varying the hydraulic diameter and the flow velocity. (author) [fr
Morphometric methods for simulation of water flow
Booltink, H.W.G.
1993-01-01
Water flow in structured soils is strongly governed by the occurence of macropores. In this study emphasis was given to combined research of morphology of water- conducting macropores and soil physical measurements on bypass flow. Main research objectives were to: (i) develop and improve
Numerical simulation of flow in fluidized beds
Czech Academy of Sciences Publication Activity Database
Bauer, Petr; Beneš, M.; Fučík, R.; Dieu, H.H.; Klement, V.; Máca, R.; Mach, J.; Oberhuber, T.; Strachota, P.; Žabka, V.; Havlena, V.
2015-01-01
Roč. 8, č. 5 (2015), s. 833-846 ISSN 1937-1632 Institutional support: RVO:61388998 Keywords : Navier-Stokes equations * multi- phase flow * combustion * turbulence * reactive flow s Subject RIV: BK - Fluid Dynamics Impact factor: 0.737, year: 2015
Experimental study on low pressure flow instability
International Nuclear Information System (INIS)
Jiang Shengyao; Wu Xinxin; Wu Shaorong; Bo Jinhai; Zhang Youjie
1997-05-01
The experiment was performed on the test loop (HRTL-5), which simulates the geometry and system design of the 5 MW reactor. The flow behavior for a wide range of inlet subcooling, in which the flow undergoes from single phase to two phase, is described in a natural circulation system at low pressure (p = 0.1, 0.24 MPa). Several kinds of flow instability, e.g. subcooled boiling instability, subcooled boiling induced flashing instability, pure flashing instability as well as flashing coupled density wave instability and high frequency flow oscillation, are investigated. The mechanism of flashing and flashing concerned flow instability, which has never been studied well in this field, is especially interpreted. The experimental results show that, firstly, for a low pressure natural circulation system the two phase flow is unstable in most of inlet subcooling conditions, the two phase stable flow can only be reached at very low inlet subcooling; secondly, at high inlet subcooling the flow instability is dominated by subcooled boiling in the heated section, and at middle inlet subcooling is dominated by void flashing in the adiabatic long riser; thirdly, in two phase stable flow region the condition for boiling out of the core, namely, single phase flow in the heated section, two phase flow in the riser due to vapor flashing, can be realized. The experimental results are very important for the design and accident analysis of the vessel and swimming pool type natural circulation nuclear heating reactor. (7 refs., 10 figs., 1 tab.)
Preliminary optimal configuration on free standing hybrid riser
Directory of Open Access Journals (Sweden)
Kyoung-Su Kim
2018-05-01
Full Text Available Free Standing Hybrid Riser (FSHR is comprised of vertical steel risers and Flexible Jumpers (FJ. They are jointly connected to a submerged Buoyancy Can (BC. There are several factors that have influence on the behavior of FSHR such as the span distance between an offshore platform and a foundation, BC up-lift force, BC submerged location and FJ length.An optimization method through a parametric study is presented. Firstly, descriptions for the overall arrangement and characteristics of FSHR are introduced. Secondly, a flowchart for optimization of FSHR is suggested. Following that, it is described how to select reasonable ranges for a parametric study and determine each of optimal configuration options. Lastly, numerical analysis based on this procedure is performed through a case study. In conclusion, the relation among those parameters is analyzed and non-dimensional parametric ranges on optimal arrangements are suggested. Additionally, strength analysis is performed with variation in the configuration. Keywords: Free standing hybrid riser, Hybrid riser system, Buoyancy can, Flexible jumper, Deepwater, Multi-body dynamics
Spectral fatigue analysis of a tensioned riser compliant tower
Karadeniz, H.; Vrouwenvelder, A.C.W.M.; Shi, C.
1998-01-01
In this paper, the conceptual Tensioned Riser Compliant Tower (TRCT) structure of the Shell Oil, which is developed for a region of approximately 600 meter water depth of the West of Shetlands in the North Sea, is analyzed by using the SAPOS program of the Delft University of Technology. The fatigue
An analog simulation technique for distributed flow systems
DEFF Research Database (Denmark)
Jørgensen, Sten Bay; Kümmel, Mogens
1973-01-01
earlier[3]. This is an important extension since flow systems are frequently controlled through manipulation of the flow rate. Previously the technique has been applied with constant flows [4, 5]. Results demonstrating the new hardware are presented from simulation of a transportation lag and a double......Simulation of distributed flow systems in chemical engineering has been applied more and more during the last decade as computer techniques have developed [l]. The applications have served the purpose of identification of process dynamics and parameter estimation as well as improving process...... and process control design. Although the conventional analog computer has been expanded with hybrid techniques and digital simulation languages have appeared, none of these has demonstrated superiority in simulating distributed flow systems in general [l]. Conventional analog techniques are expensive...
A simple method for potential flow simulation of cascades
Indian Academy of Sciences (India)
vortex panel method to simulate potential flow in cascades is presented. The cascade ... The fluid loading on the blades, such as the normal force and pitching moment, may ... of such discrete infinite array singularities along the blade surface.
Digital Rock Simulation of Flow in Carbonate Samples
Klemin, D.; Andersen, M.
2014-12-01
Reservoir engineering has becomes more complex to deal with current challenges, so core analysts must understand and model pore geometries and fluid behaviors at pores scales more rapidly and realistically. We introduce an industry-unique direct hydrodynamic pore flow simulator that operates on pore geometries from digital rock models obtained using microCT or 3D scanning electron microscope (SEM) images. The PVT and rheological models used in the simulator represent real reservoir fluids. Fluid-solid interactions are introduced using distributed micro-scale wetting properties. The simulator uses density functional approach applied for hydrodynamics of complex systems. This talk covers selected applications of the simulator. We performed microCT scanning of six different carbonate rock samples from homogeneous limestones to vuggy carbonates. From these, we constructed digital rock models representing pore geometries for the simulator. We simulated nonreactive tracer flow in all six digital models using a digital fluid description that included a passive tracer solution. During the simulation, we evaluated the composition of the effluent. Results of tracer flow simulations corresponded well with experimental data of nonreactive tracer floods for the same carbonate rock types. This simulation data of the non-reactive tracer flow can be used to calculate the volume of the rock accessible by the fluid, which can be further used to predict response of a porous medium to a reactive fluid. The described digital core analysis workflow provides a basis for a wide variety of activities, including input to design acidizing jobs and evaluating treatment efficiency and EOR economics. Digital rock multiphase flow simulations of a scanned carbonate rock evaluated the effect of wettability on flow properties. Various wetting properties were tested: slightly oil wet, slightly water wet, and water wet. Steady-state relative permeability simulations yielded curves for all three
Energy Technology Data Exchange (ETDEWEB)
Braga, Mauro Jacinto Pastor
1990-07-01
A procedure to estimate the fatigue life of a TLP riser in 1000 meters water depth based on a hydro-elastic analysis of an integrated riser-TLP model in the time domain is presented . The computational architecture is shown that makes it feasible to process and store the great amount of data involved. The procedure is applied to a 1000 meters water depth TLP with a set of 40 risers 8 inches in diameter equipped with a floatation layer. (author)
Simulation based engineering in fluid flow design
Rao, J S
2017-01-01
This volume offers a tool for High Performance Computing (HPC). A brief historical background on the subject is first given. Fluid Statics dealing with Pressure in fluids at rest, Buoyancy and Basics of Thermodynamics are next presented. The Finite Volume Method, the most convenient process for HPC, is explained in one-dimensional approach to diffusion with convection and pressure velocity coupling. Adiabatic, isentropic and supersonic flows in quasi-one dimensional flows in axisymmetric nozzles is considered before applying CFD solutions. Though the theory is restricted to one-dimensional cases, three-dimensional CFD examples are also given. Lastly, nozzle flows with normal shocks are presented using turbulence models. Worked examples and exercises are given in each chapter. Fluids transport thermal energy for its conversion to kinetic energy, thus playing a major role that is central to all heat engines. With the advent of rotating machinery in the 20th century, Fluid Engineering was developed in the form o...
Wind flow simulation over flat terrain using CFD based software
International Nuclear Information System (INIS)
Petrov, Peter; Terziev, Angel; Genovski, Ivan
2009-01-01
Velocity distribution recognition over definite place (terrain) is very important because due to that the zones with high energy potential could be defined (the fields with high velocities). This is a precondition for optimal wind turbine generators micro-sitting. In current work a simulation of the open flow over the flat terrain using the CFD based software is reviewed. The simulations are made of a real fluid flow in order to be defined the velocity fields over the terrain
Numerical simulation of flow in Brush Creek Valley, Colorado
International Nuclear Information System (INIS)
Leone, J.M. Jr.; Lee, R.L.
1987-06-01
In this paper, we present some results from our three-dimensional, non-hydrostatic, finite element model applied to simulations of flow in Brush Creek Valley. These simulations are not intended to reproduce any particular experiment, but rather are to evaluate the qualitative performance of the model, to explore the major difficulties involved, and to begin sensitivity studies of the flows of interest. 2 refs., 11 figs
DSMC simulation of feed jet flow in gas centrifuge
International Nuclear Information System (INIS)
Jiang Dongjun; Zeng Shi
2011-01-01
Feed jet flow acts an important role for the counter-current in gas centrifuge. Direct simulation Monte-Carlo (DSMC) method was adopted to simulate the structure of the radial feed jet model. By setting the proper boundary conditions and the collision model of molecules, the flow distributions of the 2D radial feed jet were acquired under different feed conditions, including the wave structure of feed jet and the profile of the flow parameters. The analyses of the calculation results note the following flow phenomena: Near the radial outflow boundary, the obvious peaks of the flow parameters exist; higher speed of feed gas brings stronger influence on the flow field of the centrifuge; including the density, pressure and velocity of the gas, the distribution of the temperature is affected by the feed jet, at the outflow boundary, temperature to double times of the average value. (authors)
Friction dependence of shallow granular flows from discrete particle simulations
Thornton, Anthony Richard; Weinhart, Thomas; Luding, Stefan; Bokhove, Onno
2011-01-01
A shallow-layer model for granular flows is completed with a closure relation for the macroscopic bed friction or basal roughness obtained from micro-scale discrete particle simulations of steady flows. We systematically vary the bed friction by changing the contact friction coefficient between
Visualization and simulation of complex flows in biomedical engineering
Imai, Yohsuke; Ishikawa, Takuji; Oliveira, Mónica
2014-01-01
This book focuses on the most recent advances in the application of visualization and simulation methods to understand the flow behavior of complex fluids used in biomedical engineering and other related fields. It shows the physiological flow behavior in large arteries, microcirculation, respiratory systems and in biomedical microdevices.
Local grid refinement for free-surface flow simulations
van der Plas, Peter
2017-01-01
The principal goal of the current study is to explore and investigate the potential of local grid refinement for increasing the numerical efficiency of free-surface flow simulations in a practical context. In this thesis we propose a method for local grid refinement in the free-surface flow model
Theory, simulation, and experimental studies of zonal flows
International Nuclear Information System (INIS)
Hahm, T. S.; Burrell, K.H.; Lin, Z.; Nazikian, R.; Synakowski, E.J.
2000-01-01
The authors report on current theoretical understanding of the characteristics of self-generated zonal flows as observed in nonlinear gyrokinetic simulations of toroidal ITG turbulence [Science 281, 1835 (1998)], and discuss various possibilities for experimental measurements of signature of zonal flows
Simulations of flow induced ordering in viscoelastic fluids
Santos de Oliveira, I.S.
2012-01-01
In this thesis we report on simulations of colloidal ordering phenomena in shearthinning viscoelastic fluids under shear flow. Depending on the characteristics of the fluid, the colloids are observed to align in the direction of the flow. These string-like structures remain stable as long as the
Smoothed particle hydrodynamics simulations of flow separation at bends
Hou, Q.; Kruisbrink, A.C.H.; Pearce, F.R.; Tijsseling, A.S.; Yue, T.
2014-01-01
The separated flow in two-dimensional bends is numerically simulated for a right-angled bend with different ratios of the channel widths and for a symmetric bend with different turning angles. Unlike the potential flow solutions that have several restrictive assumptions, the Euler equations are
Smoothed particle hydrodynamics simulations of flow separation at bends
Hou, Q.; Kruisbrink, A.C.H.; Pearce, F.R.; Tijsseling, A.S.; Yue, T.
2013-01-01
The separated flow in two-dimensional bends is numerically simulated for a right-angled bend with different ratios of the channel widths and for a symmetric bend with different turning angles. Unlike the potential flow solutions that have several restrictive assumptions, the Euler equations are
Aldebeyan, Wassim; Liddell, Antony; Steffen, Thomas; Beckman, Lorne; Martineau, Paul A
2017-08-01
This is the first biomechanical study to examine the potential stress riser effect of the tibial tunnel or tunnels after ACL reconstruction surgery. In keeping with literature, the primary hypothesis tested in this study was that the tibial tunnel acts as a stress riser for fracture propagation. Secondary hypotheses were that the stress riser effect increases with the size of the tunnel (8 vs. 10 mm), the orientation of the tunnel [standard (STT) vs. modified transtibial (MTT)], and with the number of tunnels (1 vs. 2). Tibial tunnels simulating both single bundle hamstring graft (8 mm) and bone-patellar tendon-bone graft (10 mm) either STT or MTT position, as well as tunnels simulating double bundle (DB) ACL reconstruction (7, 6 mm), were drilled in fourth-generation saw bones. These five experimental groups and a control group consisting of native saw bones without tunnels were loaded to failure on a Materials Testing System to simulate tibial plateau fracture. There were no statistically significant differences in peak load to failure between any of the groups, including the control group. The fracture occurred through the tibial tunnel in 100 % of the MTT tunnels (8 and 10 mm) and 80 % of the DB tunnels specimens; however, the fractures never (0 %) occurred through the tibial tunnel of the standard tunnels (8 or 10 mm) (P = 0.032). In the biomechanical model, the tibial tunnel does not appear to be a stress riser for fracture propagation, despite suggestions to the contrary in the literature. Use of a standard, more vertical tunnel decreases the risk of ACL graft compromise in the event of a fracture. This may help to inform surgical decision making on ACL reconstruction technique.
Simulation of the groundwater flow of the Kivetty area
International Nuclear Information System (INIS)
Taivassalo, V.; Meszaros, F.
1994-02-01
Teollisuuden Voima Oy (TVO) is preparing for the final disposal of spent nuclear fuel into crystalline bedrock in Finland. Groundwater flow modelling is a part of the preliminary site investigation work. The aim is to simulate groundwater flow as realistically as possible in view of the experimental data available. Three dimensional groundwater flow modelling is based on a conceptual bedrock model. The modelling results will be used in the site evaluation process. Observations from flow simulations will also be used to identify and study uncertainties included in the site characterization. First a conceptual flow model for the Kivetty site in Konginkangas was developed. As a second stage the flow model was calibrated. The goal was to increase the reality of the model. To evaluate the reality of the flow model, the values of the input and output parameters were compared with the field data. Finally groundwater flow simulation results were computed and groundwater flow at the Kivetty area was analysed. (50 refs., 78 figs., 7 tabs.)
Interface tracking simulations of bubbly flows in PWR relevant geometries
Energy Technology Data Exchange (ETDEWEB)
Fang, Jun, E-mail: jfang3@ncsu.edu [Department of Nuclear Engineering, North Carolina State University, Raleigh, NC 27695 (United States); Rasquin, Michel, E-mail: michel.rasquin@colorado.edu [Aerospace Engineering Department, University of Colorado, Boulder, CO 80309 (United States); Bolotnov, Igor A., E-mail: igor_bolotnov@ncsu.edu [Department of Nuclear Engineering, North Carolina State University, Raleigh, NC 27695 (United States)
2017-02-15
Highlights: • Simulations were performed for turbulent bubbly flows in PWR subchannel geometry. • Liquid turbulence is fully resolved by direct numerical simulation approach. • Bubble behavior is captured using level-set interface tracking method. • Time-averaged single- and two-phase turbulent flow statistical quantities are obtained. - Abstract: The advances in high performance computing (HPC) have allowed direct numerical simulation (DNS) approach coupled with interface tracking methods (ITM) to perform high fidelity simulations of turbulent bubbly flows in various complex geometries. In this work, we have chosen the geometry of the pressurized water reactor (PWR) core subchannel to perform a set of interface tracking simulations (ITS) with fully resolved liquid turbulence. The presented research utilizes a massively parallel finite-element based code, PHASTA, for the subchannel geometry simulations of bubbly flow turbulence. The main objective for this research is to demonstrate the ITS capabilities in gaining new insight into bubble/turbulence interactions and assisting the development of improved closure laws for multiphase computational fluid dynamics (M-CFD). Both single- and two-phase turbulent flows were studied within a single PWR subchannel. The analysis of numerical results includes the mean gas and liquid velocity profiles, void fraction distribution and turbulent kinetic energy profiles. Two sets of flow rates and bubble sizes were used in the simulations. The chosen flow rates corresponded to the Reynolds numbers of 29,079 and 80,775 based on channel hydraulic diameter (D{sub h}) and mean velocity. The finite element unstructured grids utilized for these simulations include 53.8 million and 1.11 billion elements, respectively. This has allowed to fully resolve all the turbulence scales and the deformable interfaces of individual bubbles. For the two-phase flow simulations, a 1% bubble volume fraction was used which resulted in 17 bubbles in
Simulations of MHD flows with moving interfaces
Gerbeau, J F; Le Bris, C
2003-01-01
We report on the numerical simulation of a two-fluid magnetohydrodynamics problem arising in the industrial production of aluminium. The motion of the two non-miscible fluids is modeled through the incompressible Navier-Stokes equations coupled with the Maxwell equations. Stabilized finite elements techniques and an arbitrary Lagrangian-Eulerian formulation (for the motion of the interface separating the two fluids) are used in the numerical simulation. With a view to justifying our strategy, details on the numerical analysis of the problem, with a special emphasis on conservation and stability properties and on the surface tension discretization, as well as results on tests cases are provided. Examples of numerical simulations of the industrial case are eventually presented.
Numerical simulations of viscoelastic flows with free surfaces
DEFF Research Database (Denmark)
Comminal, Raphaël; Spangenberg, Jon; Hattel, Jesper Henri
2013-01-01
We present a new methodology to simulate viscoelastic flows with free-surfaces. These simulations are motivated by the modelling of polymers manufacturing techniques, such as extrusion and injection moulding. One of the consequences of viscoelasticity is that polymeric materials have a “memory...
Exploring Students' Flow Experiences in Business Simulation Games
Buil, I.; Catalán, S.; Martínez, E.
2018-01-01
Business simulation games are a motivational and engaging tool for teaching business management. However, relatively little is known about what factors contribute to their success. This study explores the role of flow experienced while using business simulation games. Specifically, this research investigates the influence of challenge, skills,…
Launch Environment Water Flow Simulations Using Smoothed Particle Hydrodynamics
Vu, Bruce T.; Berg, Jared J.; Harris, Michael F.; Crespo, Alejandro C.
2015-01-01
This paper describes the use of Smoothed Particle Hydrodynamics (SPH) to simulate the water flow from the rainbird nozzle system used in the sound suppression system during pad abort and nominal launch. The simulations help determine if water from rainbird nozzles will impinge on the rocket nozzles and other sensitive ground support elements.
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 flow behavior in tight lattice rod bundle
International Nuclear Information System (INIS)
Yu Yiqi; Yang Yanhua; Gu Hanyang; Cheng Xu; Song Xiaoming; Wang Xiaojun
2009-01-01
The Numerical investigation is performed on the air turbulent flow in triangular rod bundle array. Based on the experimental data, the eddy viscosity turbulent model and the Reynold stress turbulent model are evaluated to simulate the flow behavior in the tight lattice. The results show that SSG Reynolds Stress Model has shown superior predictive performance than other Reynolds-stress models, which indicates that the simulation of the anisotropy of the turbulence is significant in the tight lattice. The result with different Reynolds number and geometry shows that the magnitude of the secondary flow is almost independent of the Reynolds number, but it increases with the decrease of the P/D. (authors)
Large-Eddy Simulations of Flows in Complex Terrain
Kosovic, B.; Lundquist, K. A.
2011-12-01
Large-eddy simulation as a methodology for numerical simulation of turbulent flows was first developed to study turbulent flows in atmospheric by Lilly (1967). The first LES were carried by Deardorff (1970) who used these simulations to study atmospheric boundary layers. Ever since, LES has been extensively used to study canonical atmospheric boundary layers, in most cases flat plate boundary layers under the assumption of horizontal homogeneity. Carefully designed LES of canonical convective and neutrally stratified and more recently stably stratified atmospheric boundary layers have contributed significantly to development of better understanding of these flows and their parameterizations in large scale models. These simulations were often carried out using codes specifically designed and developed for large-eddy simulations of horizontally homogeneous flows with periodic lateral boundary conditions. Recent developments in multi-scale numerical simulations of atmospheric flows enable numerical weather prediction (NWP) codes such as ARPS (Chow and Street, 2009), COAMPS (Golaz et al., 2009) and Weather Research and Forecasting model, to be used nearly seamlessly across a wide range of atmospheric scales from synoptic down to turbulent scales in atmospheric boundary layers. Before we can with confidence carry out multi-scale simulations of atmospheric flows, NWP codes must be validated for accurate performance in simulating flows over complex or inhomogeneous terrain. We therefore carry out validation of WRF-LES for simulations of flows over complex terrain using data from Askervein Hill (Taylor and Teunissen, 1985, 1987) and METCRAX (Whiteman et al., 2008) field experiments. WRF's nesting capability is employed with a one-way nested inner domain that includes complex terrain representation while the coarser outer nest is used to spin up fully developed atmospheric boundary layer turbulence and thus represent accurately inflow to the inner domain. LES of a
Numerical simulations of seepage flow in rough single rock fractures
Directory of Open Access Journals (Sweden)
Qingang Zhang
2015-09-01
Full Text Available To investigate the relationship between the structural characteristics and seepage flow behavior of rough single rock fractures, a set of single fracture physical models were produced using the Weierstrass–Mandelbrot functions to test the seepage flow performance. Six single fractures, with various surface roughnesses characterized by fractal dimensions, were built using COMSOL multiphysics software. The fluid flow behavior through the rough fractures and the influences of the rough surfaces on the fluid flow behavior was then monitored. The numerical simulation indicates that there is a linear relationship between the average flow velocity over the entire flow path and the fractal dimension of the rough surface. It is shown that there is good a agreement between the numerical results and the experimental data in terms of the properties of the fluid flowing through the rough single rock fractures.
Numerical simulation of flow field in the China advanced research reactor flow-guide tank
International Nuclear Information System (INIS)
Xu Changjiang
2002-01-01
The flow-guide tank in China advanced research reactor (CARR) acts as a reactor inlet coolant distributor and play an important role in reducing the flow-induced vibration of the internal components of the reactor core. Numerical simulations of the flow field in the flow-guide tank under different conceptual designing configurations are carried out using the PHOENICS3.2. It is seen that the inlet coolant is well distributed circumferentially into the flow-guide tank with the inlet buffer plate and the flow distributor barrel. The maximum cross-flow velocity within the flow-guide tank is reduced significantly, and the reduction of flow-induced vibration of reactor internals is expected
Numerical Simulation of Flow Behavior within a Venturi Scrubber
Directory of Open Access Journals (Sweden)
M. M. Toledo-Melchor
2014-01-01
Full Text Available The present work details the three-dimensional numerical simulation of single-phase and two-phase flow (air-water in a venturi scrubber with an inlet and throat diameters of 250 and 122.5 mm, respectively. The dimensions and operating parameters correspond to industrial applications. The mass flow rate conditions were 0.483 kg/s, 0.736 kg/s, 0.861 kg/s, and 0.987 kg/s for the gas only simulation; the mass flow rate for the liquid was 0.013 kg/s and 0.038 kg/s. The gas flow was simulated in five geometries with different converging and diverging angles while the two-phase flow was only simulated for one geometry. The results obtained were validated with experimental data obtained by other researchers. The results show that the pressure drop depends significantly on the gas flow rate and that water flow rate does not have significant effects neither on the pressure drop nor on the fluid maximum velocity within the scrubber.
Numerical Simulation of Flow Behavior within a Venturi Scrubber
M. M. Toledo-Melchor; C. del C. Gutiérrez-Torres; J. A. Jiménez-Bernal; J. G. Barbosa-Saldaña; S. A. Martínez-Delgadillo; H. R. Mollinedo-Ponce de León; A. Yoguéz-Seoane; A. Alonzo-García
2014-01-01
The present work details the three-dimensional numerical simulation of single-phase and two-phase flow (air-water) in a venturi scrubber with an inlet and throat diameters of 250 and 122.5 mm, respectively. The dimensions and operating parameters correspond to industrial applications. The mass flow rate conditions were 0.483 kg/s, 0.736 kg/s, 0.861 kg/s, and 0.987 kg/s for the gas only simulation; the mass flow rate for the liquid was 0.013 kg/s and 0.038 kg/s. The gas flow was simulated in f...
Modeling and simulation of flow field in giant magnetostrictive pump
Zhao, Yapeng; Ren, Shiyong; Lu, Quanguo
2017-09-01
Recent years, there has been significant research in the design and analysis of giant magnetostrictive pump. In this paper, the flow field model of giant magnetostrictive pump was established and the relationship between pressure loss and working frequency of piston was studied by numerical simulation method. Then, the influence of different pump chamber height on pressure loss in giant magnetostrictive pump was studied by means of flow field simulation. Finally, the fluid pressure and velocity vector distribution in giant magnetostrictive pump chamber were simulated.
A particle-based method for granular flow simulation
Chang, Yuanzhang; Bao, Kai; Zhu, Jian; Wu, Enhua
2012-01-01
We present a new particle-based method for granular flow simulation. In the method, a new elastic stress term, which is derived from a modified form of the Hooke's law, is included in the momentum governing equation to handle the friction of granular materials. Viscosity force is also added to simulate the dynamic friction for the purpose of smoothing the velocity field and further maintaining the simulation stability. Benefiting from the Lagrangian nature of the SPH method, large flow deformation can be well handled easily and naturally. In addition, a signed distance field is also employed to enforce the solid boundary condition. The experimental results show that the proposed method is effective and efficient for handling the flow of granular materials, and different kinds of granular behaviors can be well simulated by adjusting just one parameter. © 2012 Science China Press and Springer-Verlag Berlin Heidelberg.
CFD simulation of subcooled flow boiling at low pressure
International Nuclear Information System (INIS)
Koncar, B.; Mavko, B.
2001-01-01
An increased interest to numerically simulate the subcooled flow boiling at low pressures (1 to 10 bar) has been aroused in recent years, pursued by the need to perform safety analyses of research nuclear reactors and to investigate the sump cooling concept for future light water reactors. In this paper the subcooled flow boiling has been simulated with a multidimensional two-fluid model used in a CFX-4.3 computational fluid dynamics (CFD) code. The existing model was adequately modified for low pressure conditions. It was shown that interfacial forces, which are usually used for adiabatic flows, need to be modeled to simulate subcooled boiling at low pressure conditions. Simulation results are compared against published experimental data [1] and agree well with experiments.(author)
A particle-based method for granular flow simulation
Chang, Yuanzhang
2012-03-16
We present a new particle-based method for granular flow simulation. In the method, a new elastic stress term, which is derived from a modified form of the Hooke\\'s law, is included in the momentum governing equation to handle the friction of granular materials. Viscosity force is also added to simulate the dynamic friction for the purpose of smoothing the velocity field and further maintaining the simulation stability. Benefiting from the Lagrangian nature of the SPH method, large flow deformation can be well handled easily and naturally. In addition, a signed distance field is also employed to enforce the solid boundary condition. The experimental results show that the proposed method is effective and efficient for handling the flow of granular materials, and different kinds of granular behaviors can be well simulated by adjusting just one parameter. © 2012 Science China Press and Springer-Verlag Berlin Heidelberg.
Simulation of Flow for an Immersed Sphere
2016-12-01
manufacture , use, or sell any patented invention that may relate to them. This report was cleared for public release by the 96th Air Base Wing, Public...failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE...capability for using the Large Eddy Simulation with LInear Eddy Modeling in 3 Dimensions (LESLIE3D) multiphase physics computer program. A high Reynolds
A flexible open-source toolkit for lava flow simulations
Mossoux, Sophie; Feltz, Adelin; Poppe, Sam; Canters, Frank; Kervyn, Matthieu
2014-05-01
Lava flow hazard modeling is a useful tool for scientists and stakeholders confronted with imminent or long term hazard from basaltic volcanoes. It can improve their understanding of the spatial distribution of volcanic hazard, influence their land use decisions and improve the city evacuation during a volcanic crisis. Although a range of empirical, stochastic and physically-based lava flow models exists, these models are rarely available or require a large amount of physical constraints. We present a GIS toolkit which models lava flow propagation from one or multiple eruptive vents, defined interactively on a Digital Elevation Model (DEM). It combines existing probabilistic (VORIS) and deterministic (FLOWGO) models in order to improve the simulation of lava flow spatial spread and terminal length. Not only is this toolkit open-source, running in Python, which allows users to adapt the code to their needs, but it also allows users to combine the models included in different ways. The lava flow paths are determined based on the probabilistic steepest slope (VORIS model - Felpeto et al., 2001) which can be constrained in order to favour concentrated or dispersed flow fields. Moreover, the toolkit allows including a corrective factor in order for the lava to overcome small topographical obstacles or pits. The lava flow terminal length can be constrained using a fixed length value, a Gaussian probability density function or can be calculated based on the thermo-rheological properties of the open-channel lava flow (FLOWGO model - Harris and Rowland, 2001). These slope-constrained properties allow estimating the velocity of the flow and its heat losses. The lava flow stops when its velocity is zero or the lava temperature reaches the solidus. Recent lava flows of Karthala volcano (Comoros islands) are here used to demonstrate the quality of lava flow simulations with the toolkit, using a quantitative assessment of the match of the simulation with the real lava flows. The
Detached Eddy Simulation of Flap Side-Edge Flow
Balakrishnan, Shankar K.; Shariff, Karim R.
2016-01-01
Detached Eddy Simulation (DES) of flap side-edge flow was performed with a wing and half-span flap configuration used in previous experimental and numerical studies. The focus of the study is the unsteady flow features responsible for the production of far-field noise. The simulation was performed at a Reynolds number (based on the main wing chord) of 3.7 million. Reynolds Averaged Navier-Stokes (RANS) simulations were performed as a precursor to the DES. The results of these precursor simulations match previous experimental and RANS results closely. Although the present DES simulations have not reached statistical stationary yet, some unsteady features of the developing flap side-edge flowfield are presented. In the final paper it is expected that statistically stationary results will be presented including comparisons of surface pressure spectra with experimental data.
Simulation and Modeling of Flow in a Gas Compressor
Directory of Open Access Journals (Sweden)
Anna Avramenko
2015-01-01
Full Text Available The presented research demonstrates the results of a series of numerical simulations of gas flow through a single-stage centrifugal compressor with a vaneless diffuser. Numerical results were validated with experiments consisting of eight regimes with different mass flow rates. The steady-state and unsteady simulations were done in ANSYS FLUENT 13.0 and NUMECA FINE/TURBO 8.9.1 for one-period geometry due to periodicity of the problem. First-order discretization is insufficient due to strong dissipation effects. Results obtained with second-order discretization agree with the experiments for the steady-state case in the region of high mass flow rates. In the area of low mass flow rates, nonstationary effects significantly influence the flow leading stationary model to poor prediction. Therefore, the unsteady simulations were performed in the region of low mass flow rates. Results of calculation were compared with experimental data. The numerical simulation method in this paper can be used to predict compressor performance.
Numerical simulation of flow fields and particle trajectories
DEFF Research Database (Denmark)
Mayer, Stefan
2000-01-01
. 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......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...... in 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 mechanical...
Hydrodynamic analysis and simulation of a flow cell ammonia electrolyzer
International Nuclear Information System (INIS)
Diaz, Luis A.; Botte, Gerardine G.
2015-01-01
Highlights: • NH_3 electrooxidation mechanism was validated in a bench scale electrolyzer. • All kinetic parameters for NH_3 electro-oxidation were calculated and verified. • Hydrodynamic behavior of the NH_3 electrolyzer was properly described as a CSTR. • CSTR model was successfully applied to simulate a flow ammonia electrolyzer. - Abstract: The hydrodynamic analysis and simulation of a non-ideal single pass flow cell alkaline ammonia electrolyzer was performed after the scale-up of a well-characterized deposited polycrystalline Pt on Ni anode. The hydrodynamic analysis was performed using the residence time distribution (RTD) test. The results of the hydrodynamic investigation provide additional insights for the kinetic analysis of the ammonia electrooxidation reaction on polycrystalline Pt electrocatalysts -which are typically obtained under controlled flow regime, e.g., rotating disk electrode- by including the flow non-uniformity present in the electrolyzer. Based on the RTD function, the ammonia electrolyzer performance was simulated as a non-steady stirred tank reactor (CSTR) and the unknown kinetic parameters were obtained by fitting the simulation results with an experimental current profile, obtaining an adequate prediction of the ammonia conversion. This simplified approach for the simulation of the ammonia electrolyzer could be implemented in process simulation packages and could be used for the design and scale-up of the process for hydrogen production and wastewater remediation.
Large eddy simulation of a wing-body junction flow
Ryu, Sungmin; Emory, Michael; Campos, Alejandro; Duraisamy, Karthik; Iaccarino, Gianluca
2014-11-01
We present numerical simulations of the wing-body junction flow experimentally investigated by Devenport & Simpson (1990). Wall-junction flows are common in engineering applications but relevant flow physics close to the corner region is not well understood. Moreover, performance of turbulence models for the body-junction case is not well characterized. Motivated by the insufficient investigations, we have numerically investigated the case with Reynolds-averaged Naiver-Stokes equation (RANS) and Large Eddy Simulation (LES) approaches. The Vreman model applied for the LES and SST k- ω model for the RANS simulation are validated focusing on the ability to predict turbulence statistics near the junction region. Moreover, a sensitivity study of the form of the Vreman model will also be presented. This work is funded under NASA Cooperative Agreement NNX11AI41A (Technical Monitor Dr. Stephen Woodruff)
Remote installation of risers on underground nuclear waste storage tanks
International Nuclear Information System (INIS)
Jackson, J.P.; Gessner, R.F.
1988-03-01
The West Valley Demonstration Project was established to solidify 2120 m 3 (560,000) gallons of high-level nuclear waste generated during six years of commercial nuclear fuel reprocessing. This liquid will be processed to remove radioactive elements which, with the remaining sludge, will be combined with glass formers and be converted into borosilicate glass. Risers were installed on the high-level tank for installation of pumps which will be used to remove the liquid and sludge. The extensive use of remote technology was required to install the risers and to minimize operator exposure to high levels of radiation and contamination. The riser installation required remotely: drilling through two feet of concrete shielding; installing pump access pipes which are welded to the tank top; and cutting holes in tanks located 3658 mm (12) feet below ground. These operations were successfully completed 13 times without exposing personnel to high-level radiation or contamination. Specially designed remote equipment was developed for each step of this operation. Extensive operator training in the use of this equipment was performed on a tank with low radiation prior to work on the high-level tank. This paper discusses the application of remote technology that assured a quality job was safely accomplished. 3 refs., 18 figs., 2 tabs
Computational fluid dynamics simulations of light water reactor flows
International Nuclear Information System (INIS)
Tzanos, C.P.; Weber, D.P.
1999-01-01
Advances in computational fluid dynamics (CFD), turbulence simulation, and parallel computing have made feasible the development of three-dimensional (3-D) single-phase and two-phase flow CFD codes that can simulate fluid flow and heat transfer in realistic reactor geometries with significantly reduced reliance, especially in single phase, on empirical correlations. The objective of this work was to assess the predictive power and computational efficiency of a CFD code in the analysis of a challenging single-phase light water reactor problem, as well as to identify areas where further improvements are needed
Stochastic simulation of regional groundwater flow in Beishan area
International Nuclear Information System (INIS)
Dong Yanhui; Li Guomin
2010-01-01
Because of the hydrogeological complexity, traditional thinking of aquifer characteristics is not appropriate for groundwater system in Beishan area. Uncertainty analysis of groundwater models is needed to examine the hydrologic effects of spatial heterogeneity. In this study, fast Fourier transform spectral method (FFTS) was used to generate the random horizontal permeability parameters. Depth decay and vertical anisotropy of hydraulic conductivity were included to build random permeability models. Based on high-performance computers, hundreds of groundwater flow models were simulated. Through stochastic simulations, the effect of heterogeneity to groundwater flow pattern was analyzed. (authors)
Numerical Simulation of Two Dimensional Flows in Yazidang Reservoir
Huang, Lingxiao; Liu, Libo; Sun, Xuehong; Zheng, Lanxiang; Jing, Hefang; Zhang, Xuande; Li, Chunguang
2018-01-01
This paper studied the problem of water flow in the Yazid Ang reservoir. It built 2-D RNG turbulent model, rated the boundary conditions, used the finite volume method to discrete equations and divided the grid by the advancing-front method. It simulated the two conditions of reservoir flow field, compared the average vertical velocity of the simulated value and the measured value nearby the water inlet and the water intake. The results showed that the mathematical model could be applied to the similar industrial water reservoir.
Multiscale simulation of water flow past a C540 fullerene
DEFF Research Database (Denmark)
Walther, Jens Honore; Praprotnik, Matej; Kotsalis, Evangelos M.
2012-01-01
We present a novel, three-dimensional, multiscale algorithm for simulations of water flow past a fullerene. We employ the Schwarz alternating overlapping domain method to couple molecular dynamics (MD) of liquid water around the C540 buckyball with a Lattice–Boltzmann (LB) description for the Nav......We present a novel, three-dimensional, multiscale algorithm for simulations of water flow past a fullerene. We employ the Schwarz alternating overlapping domain method to couple molecular dynamics (MD) of liquid water around the C540 buckyball with a Lattice–Boltzmann (LB) description...
Construction and simulation of a novel continuous traffic flow model
International Nuclear Information System (INIS)
Hwang, Yao-Hsin; Yu, Jui-Ling
2017-01-01
In this paper, we aim to propose a novel mathematical model for traffic flow and apply a newly developed characteristic particle method to solve the associate governing equations. As compared with the existing non-equilibrium higher-order traffic flow models, the present one is put forward to satisfy the following three conditions: 1.Preserve the equilibrium state in the smooth region. 2.Yield an anisotropic propagation of traffic flow information. 3.Expressed with a conservation law form for traffic momentum. These conditions will ensure a more practical simulation in traffic flow physics: The current traffic will not be influenced by the condition in the behind and result in unambiguous condition across a traffic shock. Through analyses of characteristics, stability condition and steady-state solution adherent to the equation system, it is shown that the proposed model actually conform to these conditions. Furthermore, this model can be cast into its characteristic form which, incorporated with the Rankine-Hugoniot relation, is appropriate to be simulated by the characteristic particle method to obtain accurate computational results. - Highlights: • The traffic model expressed with the momentum conservation law. • Traffic flow information propagate anisotropically and preserve the equilibrium state in the smooth region. • Computational particles of two families are invented to mimic forward-running and backward-running characteristics. • Formation of shocks will be naturally detected by the intersection of computational particles of same family. • A newly developed characteristic particle method is used to simulate traffic flow model equations.
Numerical simulation of internal flow in mixed-flow waterjet propulsion
International Nuclear Information System (INIS)
Wu, T T; Pan, Z Y; Zhang, D Q; Jia, Y Y
2012-01-01
In order to reveal the internal flow characteristic of a mixed-flow waterjet propulsion, a mixed-flow waterjet propulsion under different conditions was simulated based on multi-reference frame(MRF), the standard k − ε turbulent model and SIMPLEC algorithm. The relationship between pump performance instability and internal flow was obtained. The numerical results showed that characteristic instability occurred at 0.65-0.67Q BEP , the reason is that the backflow on the vaned diffuser hub-side blocks the downstream flow from the impeller. Therefore, the flow separates on the pressure surface of the impeller outlet and a strong vortex is generated, then the characteristic instability appeared due to the instability of internal flow. Backflow was found in diffuser passage at 0.65 Q BEP and 0.85 Q BEP , as flow rate decreases, the backflow region and velocity increases. Pressure fluctuation at diffuser inlet and diffuser passages was severe at at 0.65 Q BEP . According to the numerical simulation, the mixed-flow waterjet propulsion has characteristic instability at partial flow rate condition.
Advanced Algebraic Multigrid Solvers for Subsurface Flow Simulation
Chen, Meng-Huo
2015-09-13
In this research we are particularly interested in extending the robustness of multigrid solvers to encounter complex systems related to subsurface reservoir applications for flow problems in porous media. In many cases, the step for solving the pressure filed in subsurface flow simulation becomes a bottleneck for the performance of the simulator. For solving large sparse linear system arising from MPFA discretization, we choose multigrid methods as the linear solver. The possible difficulties and issues will be addressed and the corresponding remedies will be studied. As the multigrid methods are used as the linear solver, the simulator can be parallelized (although not trivial) and the high-resolution simulation become feasible, the ultimately goal which we desire to achieve.
Large Eddy Simulation of Turbulent Flows in Wind Energy
DEFF Research Database (Denmark)
Chivaee, Hamid Sarlak
This research is devoted to the Large Eddy Simulation (LES), and to lesser extent, wind tunnel measurements of turbulent flows in wind energy. It starts with an introduction to the LES technique associated with the solution of the incompressible Navier-Stokes equations, discretized using a finite......, should the mesh resolution, numerical discretization scheme, time averaging period, and domain size be chosen wisely. A thorough investigation of the wind turbine wake interactions is also conducted and the simulations are validated against available experimental data from external sources. The effect...... Reynolds numbers, and thereafter, the fully-developed infinite wind farm boundary later simulations are performed. Sources of inaccuracy in the simulations are investigated and it is found that high Reynolds number flows are more sensitive to the choice of the SGS model than their low Reynolds number...
Large-eddy simulation of atmospheric flow over complex terrain
DEFF Research Database (Denmark)
Bechmann, Andreas
2007-01-01
The present report describes the development and validation of a turbulence model designed for atmospheric flows based on the concept of Large-Eddy Simulation (LES). The background for the work is the high Reynolds number k - #epsilon# model, which has been implemented on a finite-volume code...... turbulence model is able to handle both engineering and atmospheric flows and can be run in both RANS or LES mode. For LES simulations a time-dependent wind field that accurately represents the turbulent structures of a wind environment must be prescribed at the computational inlet. A method is implemented...... where the turbulent wind field from a separate LES simulation can be used as inflow. To avoid numerical dissipation of turbulence special care is paid to the numerical method, e.g. the turbulence model is calibrated with the specific numerical scheme used. This is done by simulating decaying isotropic...
CFD Numerical Simulation of the Complex Turbulent Flow Field in an Axial-Flow Water Pump
Directory of Open Access Journals (Sweden)
Wan-You Li
2014-09-01
Full Text Available Further optimal design of an axial-flow water pump calls for a thorough recognition of the characteristics of the complex turbulent flow field in the pump, which is however extremely difficult to be measured using the up-to-date experimental techniques. In this study, a numerical simulation procedure based on computational fluid dynamics (CFD was elaborated in order to obtain the fully three-dimensional unsteady turbulent flow field in an axial-flow water pump. The shear stress transport (SST k-ω model was employed in the CFD calculation to study the unsteady internal flow of the axial-flow pump. Upon the numerical simulation results, the characteristics of the velocity field and pressure field inside the impeller region were discussed in detail. The established model procedure in this study may provide guidance to the numerical simulations of turbomachines during the design phase or the investigation of flow and pressure field characteristics and performance. The presented information can be of reference value in further optimal design of the axial-flow pump.
Direct numerical simulation of laminar-turbulent flow over a flat plate at hypersonic flow speeds
Egorov, I. V.; Novikov, A. V.
2016-06-01
A method for direct numerical simulation of a laminar-turbulent flow around bodies at hypersonic flow speeds is proposed. The simulation is performed by solving the full three-dimensional unsteady Navier-Stokes equations. The method of calculation is oriented to application of supercomputers and is based on implicit monotonic approximation schemes and a modified Newton-Raphson method for solving nonlinear difference equations. By this method, the development of three-dimensional perturbations in the boundary layer over a flat plate and in a near-wall flow in a compression corner is studied at the Mach numbers of the free-stream of M = 5.37. In addition to pulsation characteristic, distributions of the mean coefficients of the viscous flow in the transient section of the streamlined surface are obtained, which enables one to determine the beginning of the laminar-turbulent transition and estimate the characteristics of the turbulent flow in the boundary layer.
Simulation of blood flow through an artificial heart
Kiris, Cetin; Chang, I-Dee; Rogers, Stuart E.; Kwak, Dochan
1991-01-01
A numerical simulation of the incompressible viscous flow through a prosthetic tilting disk heart valve is presented in order to demonstrate the current capability to model unsteady flows with moving boundaries. Both steady state and unsteady flow calculations are done by solving the incompressible Navier-Stokes equations in 3-D generalized curvilinear coordinates. In order to handle the moving boundary problems, the chimera grid embedding scheme which decomposes a complex computational domain into several simple subdomains is used. An algebraic turbulence model for internal flows is incorporated to reach the physiological values of Reynolds number. Good agreement is obtained between the numerical results and experimental measurements. It is found that the tilting disk valve causes large regions of separated flow, and regions of high shear.
Energy Technology Data Exchange (ETDEWEB)
Sobrinho, L.L.; Bastian, F.L. [Federal University of Rio de Janeiro, RJ (Brazil). Dept. of Metallurgical and Materials Engineering], e-mail: ledjane@metalmat.ufrj.br; Calado, V.M.A. [Federal University of Rio de Janeiro, RJ (Brazil). Escola de Quimica
2008-07-01
Industry has been challenged to provide riser systems which are more cost effective and which can fill the technology gaps with respect to water depth, riser diameter and high temperatures left open by flexible, steel catenary risers (SCRs) and hybrid risers. Composite materials present advantages over conventional steel risers because composite materials are lighter, more fatigue and corrosion resistant, better thermal insulators and can be designed for improving the structural and mechanical response. Besides, composite materials present some attractive attributes for the offshore service, such as: high specific strength and stiffness. This paper focuses on the development and characterization of a polymer matrix (epoxy) and of material composite (epoxy/fiber glass), which will be used in a development for composites risers by the filament winding process (wet winding). (author)
Acceleration of coupled granular flow and fluid flow simulations in pebble bed energy systems
International Nuclear Information System (INIS)
Li, Yanheng; Ji, Wei
2013-01-01
Highlights: ► Fast simulation of coupled pebble flow and coolant flow in PBR systems is studied. ► Dimension reduction based on axisymmetric geometry shows significant speedup. ► Relaxation of coupling frequency is investigated and an optimal range is determined. ► A total of 80% efficiency increase is achieved by the two fast strategies. ► Fast strategies can be applied to simulating other general fluidized bed systems. -- Abstract: Fast and accurate approaches to simulating the coupled particle flow and fluid flow are of importance to the analysis of large particle-fluid systems. This is especially needed when one tries to simulate pebble flow and coolant flow in Pebble Bed Reactor (PBR) energy systems on a routine basis. As one of the Generation IV designs, the PBR design is a promising nuclear energy system with high fuel performance and inherent safety. A typical PBR core can be modeled as a particle-fluid system with strong interactions among pebbles, coolants and reactor walls. In previous works, the coupled Discrete Element Method (DEM)-Computational Fluid Dynamics (CFD) approach has been investigated and applied to modeling PBR systems. However, the DEM-CFD approach is computationally expensive due to large amounts of pebbles in PBR systems. This greatly restricts the PBR analysis for the real time prediction and inclusion of more physics. In this work, based on the symmetry of the PBR geometry and the slow motion characteristics of the pebble flow, two acceleration strategies are proposed. First, a simplified 3D-DEM/2D-CFD approach is proposed to speed up the DEM-CFD simulation without loss of accuracy. Pebble flow is simulated by a full 3D DEM, while the coolant flow field is calculated with a 2D CFD simulation by averaging variables along the annular direction in the cylindrical and annular geometries. Second, based on the slow motion of pebble flow, the impact of the coupling frequency on the computation accuracy and efficiency is
Acceleration of coupled granular flow and fluid flow simulations in pebble bed energy systems
Energy Technology Data Exchange (ETDEWEB)
Li, Yanheng, E-mail: liy19@rpi.edu [Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY (United States); Ji, Wei, E-mail: jiw2@rpi.edu [Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY (United States)
2013-05-15
Highlights: ► Fast simulation of coupled pebble flow and coolant flow in PBR systems is studied. ► Dimension reduction based on axisymmetric geometry shows significant speedup. ► Relaxation of coupling frequency is investigated and an optimal range is determined. ► A total of 80% efficiency increase is achieved by the two fast strategies. ► Fast strategies can be applied to simulating other general fluidized bed systems. -- Abstract: Fast and accurate approaches to simulating the coupled particle flow and fluid flow are of importance to the analysis of large particle-fluid systems. This is especially needed when one tries to simulate pebble flow and coolant flow in Pebble Bed Reactor (PBR) energy systems on a routine basis. As one of the Generation IV designs, the PBR design is a promising nuclear energy system with high fuel performance and inherent safety. A typical PBR core can be modeled as a particle-fluid system with strong interactions among pebbles, coolants and reactor walls. In previous works, the coupled Discrete Element Method (DEM)-Computational Fluid Dynamics (CFD) approach has been investigated and applied to modeling PBR systems. However, the DEM-CFD approach is computationally expensive due to large amounts of pebbles in PBR systems. This greatly restricts the PBR analysis for the real time prediction and inclusion of more physics. In this work, based on the symmetry of the PBR geometry and the slow motion characteristics of the pebble flow, two acceleration strategies are proposed. First, a simplified 3D-DEM/2D-CFD approach is proposed to speed up the DEM-CFD simulation without loss of accuracy. Pebble flow is simulated by a full 3D DEM, while the coolant flow field is calculated with a 2D CFD simulation by averaging variables along the annular direction in the cylindrical and annular geometries. Second, based on the slow motion of pebble flow, the impact of the coupling frequency on the computation accuracy and efficiency is
New approach for simulating groundwater flow in discrete fracture network
Fang, H.; Zhu, J.
2017-12-01
In this study, we develop a new approach to calculate groundwater flowrate and hydraulic head distribution in two-dimensional discrete fracture network (DFN) where both laminar and turbulent flows co-exist in individual fractures. The cubic law is used to calculate hydraulic head distribution and flow behaviors in fractures where flow is laminar, while the Forchheimer's law is used to quantify turbulent flow behaviors. Reynolds number is used to distinguish flow characteristics in individual fractures. The combination of linear and non-linear equations is solved iteratively to determine flowrates in all fractures and hydraulic heads at all intersections. We examine potential errors in both flowrate and hydraulic head from the approach of uniform flow assumption. Applying the cubic law in all fractures regardless of actual flow conditions overestimates the flowrate when turbulent flow may exist while applying the Forchheimer's law indiscriminately underestimate the flowrate when laminar flows exist in the network. The contrast of apertures of large and small fractures in the DFN has significant impact on the potential errors of using only the cubic law or the Forchheimer's law. Both the cubic law and Forchheimer's law simulate similar hydraulic head distributions as the main difference between these two approaches lies in predicting different flowrates. Fracture irregularity does not significantly affect the potential errors from using only the cubic law or the Forchheimer's law if network configuration remains similar. Relative density of fractures does not significantly affect the relative performance of the cubic law and Forchheimer's law.
International Nuclear Information System (INIS)
Santos, Valdemir A. dos; Lima, Emerson A.O.
2013-01-01
Nuclear techniques of gamma transmission and radioactive tracer were used to estimate the catalyst circulation rate in a cold flow pilot plant unit of Fluid Catalytic Cracking (FCC). Catalyst circulation rate in a FCC unit, allow to determine operating conditions of the exchange catalyst and inlet data for fluid dynamic simulation computational program. The pilot unit was fabricated obeying geometrical parameters provided by the Petrobras Research Center (CENPES), based on hot pilot units to existing in that center. The cold flow pilot unit has a transfer line, two separation vessels flash type, a return column, a riser and a regenerator. The vertical sections as riser, return column, regenerator column and transfer line are made of transparent material (glass). The two separation vessels have bases with tapered cylindrical shapes and are made of steel plates. The riser is divided into four sections of different diameters (0.005 m, 0.010 m, 0.018 m and 0.025 m) and rising upwards, to simulate the increasing flow rate caused by the increase of volume with the increase of the number of moles due to molecules breakage. The radioactive tracer used was the catalyst itself (intrinsic tracer) irradiated by neutron activation, yielding the radioisotope 59 Fe. The velocity measurements were also obtained with aid of an electronic clock triggered by certain radiation levels across the two detectors. Besides estimates for the catalyst circulation rate was possible to identify the type of flow relative to the catalyst in return column. (author)
Response prediction of long flexible risers subject to forced harmonic vibration
Riveros, Carlos Alberto; Utsunomiya, Tomoaki; Maeda, Katsuya; Itoh, Kazuaki
2010-01-01
Several research efforts have been directed toward the development of models for response prediction of flexible risers. The main difficulties arise from the fact that the dynamic response of flexible risers involves highly nonlinear behavior and a self-regulated process. This article presents a quasi-steady approach for response prediction of oscillating flexible risers. Amplitude-dependent lift coefficients are considered, as is an increased mean drag coefficient model during synchronizatio...
Large eddy simulation of the flow through a swirl generator
Energy Technology Data Exchange (ETDEWEB)
Conway, Stephen
1998-12-01
The advances made in computer technology over recent years have led to a great increase in the engineering problems that can be studied using CFD. The computation of flows over and through complex geometries at relatively high Reynolds numbers is becoming more common using the Large Eddy Simulation (LES) technique. Direct numerical simulations of such flows is still beyond the capacity of todays fastest supercomputers, requiring excessive computational times and memory. In addition, traditional Reynolds Averaged Navier Stokes (RANS) methods are known to have limited applicability in a wide range of engineering flow situations. In this thesis LES has been used to simulate the flow through a cascade of guidance vanes, more commonly known as a swirl generator, positioned at the inlet to a gas turbine combustion chamber. This flow case is of interest because of the complex flow phenomena which occur within the swirl generator, which include compressibility effects, different types of flow instabilities, transition, laminar and turbulent separation and near wall turbulence. It is also of interest because it fits very well into the range of engineering applications that can be studied using LES. Two computational grids with different resolutions and two subgrid scale stress models were used in the study. The effects of separation and transition are investigated. A vortex shedding frequency from the guidance vanes is determined which is seen to be dependent on the angle of incident air flow. Interaction between the movement of the separation region and the shedding frequency is also noted. Such vortex shedding phenomena can directly affect the quality of fuel and air mixing within the combustion chamber and can in some cases induce vibrations in the gas turbine structure. Comparisons between the results obtained using different grid resolutions with an implicit and a dynamic divergence (DDM) subgrid scale stress models are also made 32 refs, 35 figs, 2 tabs
Molecular dynamics simulations of oscillatory flows in microfluidic channels
DEFF Research Database (Denmark)
Hansen, J.S.; Ottesen, Johnny T.
2006-01-01
In this paper we apply the direct non-equilibrium molecular dynamics technique to oscillatory flows of fluids in microscopic channels. Initially, we show that the microscopic simulations resemble the macroscopic predictions based on the Navier–Stokes equation very well for large channel width, high...... density and low temperature. Further simulations for high temperature and low density show that the non-slip boundary condition traditionally used in the macroscopic equation is greatly compromised when the fluid–wall interactions are the same as the fluid–fluid interactions. Simulations of a system...
Moving least squares simulation of free surface flows
DEFF Research Database (Denmark)
Felter, C. L.; Walther, Jens Honore; Henriksen, Christian
2014-01-01
In this paper a Moving Least Squares method (MLS) for the simulation of 2D free surface flows is presented. The emphasis is on the governing equations, the boundary conditions, and the numerical implementation. The compressible viscous isothermal Navier–Stokes equations are taken as the starting ...
Direct Numerical Simulations of turbulent flow in a driven cavity
Verstappen, R.; Wissink, J.G.; Cazemier, W.; Veldman, A.E.P.
Direct numerical simulations (DNS) of 2 and 3D turbulent flows in a lid-driven cavity have been performed. DNS are numerical solutions of the unsteady (here: incompressible) Navier-Stokes equations that compute the evolution of all dynamically significant scales of motion. In view of the large
Application of HPCN to direct numerical simulation of turbulent flow
Verstappen, RWCP; Veldman, AEP; van Waveren, GM; Hertzberger, B; Sloot, P
1997-01-01
This poster shows how HPCN can be used as a path-finding tool for turbulence research. The parallelization of direct numerical simulation of turbulent flow using the data-parallel model and Fortran 95 constructs is treated, both on a shared memory and a distributed memory computer.
CFD Simulations of Pb-Bi Two-Phase Flow
International Nuclear Information System (INIS)
Dostal, Vaclav; Zelezny, Vaclav; Zacha, Pavel
2008-01-01
In a Pb-Bi cooled direct contact steam generation fast reactor water is injected directly above the core, the produced steam is separated at the top and is send to the turbine. Neither the direct contact phenomenon nor the two-phase flow simulations in CFD have been thoroughly described yet. A first attempt in simulating such two-phase flow in 2D using the CFD code Fluent is presented in this paper. The volume of fluid explicit model was used. Other important simulation parameters were: pressure velocity relation PISO, discretization scheme body force weighted for pressure, second order upwind for momentum and CISCAM for void fraction. Boundary conditions were mass flow inlet (Pb-Bi 0 kg/s and steam 0.07 kg/s) and pressure outlet. The effect of mesh size (0.5 mm and 0.2 mm cells) was investigated as well as the effect of the turbulent model. It was found that using a fine mesh is very important in order to achieve larger bubbles and the turbulent model (k-ε realizable) is necessary to properly model the slug flow. The fine mesh and unsteady conditions resulted in computationally intense problem. This may pose difficulties in 3D simulations of the real experiments. (authors)
Capabilities of current wildfire models when simulating topographical flow
Kochanski, A.; Jenkins, M.; Krueger, S. K.; McDermott, R.; Mell, W.
2009-12-01
Accurate predictions of the growth, spread and suppression of wild fires rely heavily on the correct prediction of the local wind conditions and the interactions between the fire and the local ambient airflow. Resolving local flows, often strongly affected by topographical features like hills, canyons and ridges, is a prerequisite for accurate simulation and prediction of fire behaviors. In this study, we present the results of high-resolution numerical simulations of the flow over a smooth hill, performed using (1) the NIST WFDS (WUI or Wildland-Urban-Interface version of the FDS or Fire Dynamic Simulator), and (2) the LES version of the NCAR Weather Research and Forecasting (WRF-LES) model. The WFDS model is in the initial stages of development for application to wind flow and fire spread over complex terrain. The focus of the talk is to assess how well simple topographical flow is represented by WRF-LES and the current version of WFDS. If sufficient progress has been made prior to the meeting then the importance of the discrepancies between the predicted and measured winds, in terms of simulated fire behavior, will be examined.
Unsteady 3D flow simulations in cranial arterial tree
Grinberg, Leopold; Anor, Tomer; Madsen, Joseph; Karniadakis, George
2008-11-01
High resolution unsteady 3D flow simulations in major cranial arteries have been performed. Two cases were considered: 1) a healthy volunteer with a complete Circle of Willis (CoW); and 2) a patient with hydrocephalus and an incomplete CoW. Computation was performed on 3344 processors of the new half petaflop supercomputer in TACC. Two new numerical approaches were developed and implemented: 1) a new two-level domain decomposition method, which couples continuous and discontinuous Galerkin discretization of the computational domain; and 2) a new type of outflow boundary conditions, which imposes, in an accurate and computationally efficient manner, clinically measured flow rates. In the first simulation, a geometric model of 65 cranial arteries was reconstructed. Our simulation reveals a high degree of asymmetry in the flow at the left and right parts of the CoW and the presence of swirling flow in most of the CoW arteries. In the second simulation, one of the main findings was a high pressure drop at the right anterior communicating artery (PCA). Due to the incompleteness of the CoW and the pressure drop at the PCA, the right internal carotid artery supplies blood to most regions of the brain.
Numerical convergence improvements for porflow unsaturated flow simulations
Energy Technology Data Exchange (ETDEWEB)
Flach, Greg [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
2017-08-14
Section 3.6 of SRNL (2016) discusses various PORFLOW code improvements to increase modeling efficiency, in preparation for the next E-Area Performance Assessment (WSRC 2008) revision. This memorandum documents interaction with Analytic & Computational Research, Inc. (http://www.acricfd.com/default.htm) to improve numerical convergence efficiency using PORFLOW version 6.42 for unsaturated flow simulations.
Direct numerical simulation of particulate flow with heat transfer
Tavassoli Estahbanati, H; Kriebitzsch, S.H.L.; Hoef, van der M.A.; Peters, E.A.J.F.; Kuipers, J.A.M.
2013-01-01
The Immersed Boundary (IB) method proposed by Uhlmann for Direct Numerical Simulation (DNS) of fluid flow through dense fluid-particle systems is extended to systems with interphase heat transport. A fixed Eulerian grid is employed to solve the momentum and energy equations by traditional
A direct simulation method for flows with suspended paramagnetic particles
Kang, T.G.; Hulsen, M.A.; Toonder, den J.M.J.; Anderson, P.D.; Meijer, H.E.H.
2008-01-01
A direct numerical simulation method based on the Maxwell stress tensor and a fictitious domain method has been developed to solve flows with suspended paramagnetic particles. The numerical scheme enables us to take into account both hydrodynamic and magnetic interactions between particles in a
Adaptive Multiscale Finite Element Method for Subsurface Flow Simulation
Van Esch, J.M.
2010-01-01
Natural geological formations generally show multiscale structural and functional heterogeneity evolving over many orders of magnitude in space and time. In subsurface hydrological simulations the geological model focuses on the structural hierarchy of physical sub units and the flow model addresses
Water Flow Simulation using Smoothed Particle Hydrodynamics (SPH)
Vu, Bruce; Berg, Jared; Harris, Michael F.
2014-01-01
Simulation of water flow from the rainbird nozzles has been accomplished using the Smoothed Particle Hydrodynamics (SPH). The advantage of using SPH is that no meshing is required, thus the grid quality is no longer an issue and accuracy can be improved.
Control algorithm for multiscale flow simulations of water
DEFF Research Database (Denmark)
Kotsalis, E. M.; Walther, Jens Honore; Kaxiras, E.
2009-01-01
We present a multiscale algorithm to couple atomistic water models with continuum incompressible flow simulations via a Schwarz domain decomposition approach. The coupling introduces an inhomogeneity in the description of the atomistic domain and prevents the use of periodic boundary conditions...
Development of an adaptive sawmill- flow simulator template for ...
African Journals Online (AJOL)
Development of an adaptive sawmill- flow simulator template for predicting results ... including: raw materials, personnel, equipment, product mix, product quality, orders ... Profitable sawing of small diameter logs requires high speed processing, use of ... performance measures due to changes in mill layout, raw material and ...
Influence of riser-induced slugs on the downstream separation processes
DEFF Research Database (Denmark)
Pedersen, Simon; Løhndorf, Petar Durdevic; Yang, Zhenyu
2017-01-01
In Oil & Gas installations the severe slug is an undesired flow regime due to the negative impact on the production rate and facility safety. This study will evaluate the severe riser-induced slugs’ influence to a typical separation process, consisting of a 3-phase gravity separator physically...... linked to a de-oiling hydrocyclone, based on experimental tests performed on a laboratory testing facility. Several scenarios are compared, while three PID controllers’ coefficients are kept constant for all the tests: The separator pressure, water level, and hydrocyclone pressure-drop-ratio (PDR......) controllers. Each respective scenario makes a comparison between uncontrolled, open-, and closed-loop anti-slug control configurations. It is concluded that both open- and closed-loop anti-slug control strategies improve the water level and PDR setpoint tracking equally well, but that the closed-loop strategy...
Tools for in service monitoring and testing of riser to prevent failure and extend service life
Energy Technology Data Exchange (ETDEWEB)
Ward, Haakon; Bondevik, Jon Olav; Skjerve, Haavard; Tveit, Oeyvind [SeaFlex AS, Asker (Norway)
2005-07-01
Exploration and development of new oil and gas fields is heavily dependant on use of flexible pipes and many field developments would not have been possible without them. The number of flexible risers in service is constantly increasing since relatively few offshore projects have reached the estimated operational life and the operational lifetime of several fields in-service has been extended due to new and improved technology. Many risers have been in service over a large number of years. Some risers have been operated under demanding conditions such as severe dynamic loads, high pressure and temperatures. One may in some cases find that risers actually have shorter service life than estimated in the design phase due to the severe operational conditions. In order to extend the use of the riser, some risers may have to be modified and re-terminated and prepared for a new and less demanding application. In order to operate risers safely, it is important to re-assess the fatigue life in order to prevent potential riser failure. The operator should implement methods and tools for in-service monitoring and testing. This paper addresses efficient and reliable methods and tools for monitoring of critical operational parameters as well as in-service riser testing. A brief description of structural failure modes will also be given in order to understand how to interpret test results in view of potential failure modes. (author)
Tripathi, Anurag; Prasad, Mahesh; Kumar, Puneet
2017-11-01
The saturation of the effective friction coefficient for granular flows at high inertial numbers has been assumed widely by researchers, despite little simulation/experimental evidence. In contrast, a recent simulation study of plane shear flows by Mandal and Khakhar, suggests that the effective friction coefficient becomes maximum and then starts to decrease with increase in the inertial number for I > 0.5 . In order to investigate whether such a dip at higher inertial numbers is indeed a feature of granular rheology, we perform DEM simulations of chute flow of highly inelastic disks. We show that steady, fully developed flows are possible at inclinations much higher than those normally reported in literature. At such high inclinations, the flow is characterised by a significant slip at the base; the height of the layer increases by more than 300 % and kinetic energy of the layer increases by nearly 5 orders of magnitude. We observe, for the first time, steady chute flows at inertial number I 2 and show that the dip at higher inertial numbers can be observed in case of chute flow as well. The predictions of modified μ - I rheology, however, seem to remain valid in the bulk of the layer for packing fractions as low as 0.2. AT acknowledges the funding obtained from IIT Kanpur through the initiation Grant for this study.
An evaluation of Dynamic TOPMODEL for low flow simulation
Coxon, G.; Freer, J. E.; Quinn, N.; Woods, R. A.; Wagener, T.; Howden, N. J. K.
2015-12-01
Hydrological models are essential tools for drought risk management, often providing input to water resource system models, aiding our understanding of low flow processes within catchments and providing low flow predictions. However, simulating low flows and droughts is challenging as hydrological systems often demonstrate threshold effects in connectivity, non-linear groundwater contributions and a greater influence of water resource system elements during low flow periods. These dynamic processes are typically not well represented in commonly used hydrological models due to data and model limitations. Furthermore, calibrated or behavioural models may not be effectively evaluated during more extreme drought periods. A better understanding of the processes that occur during low flows and how these are represented within models is thus required if we want to be able to provide robust and reliable predictions of future drought events. In this study, we assess the performance of dynamic TOPMODEL for low flow simulation. Dynamic TOPMODEL was applied to a number of UK catchments in the Thames region using time series of observed rainfall and potential evapotranspiration data that captured multiple historic droughts over a period of several years. The model performance was assessed against the observed discharge time series using a limits of acceptability framework, which included uncertainty in the discharge time series. We evaluate the models against multiple signatures of catchment low-flow behaviour and investigate differences in model performance between catchments, model diagnostics and for different low flow periods. We also considered the impact of surface water and groundwater abstractions and discharges on the observed discharge time series and how this affected the model evaluation. From analysing the model performance, we suggest future improvements to Dynamic TOPMODEL to improve the representation of low flow processes within the model structure.
Simulation and experimental study of resin flow in fibre fabrics
Yan, Fei; Yan, Shilin; Li, Yongjing
2017-06-01
Liquid Composite Moulding (LCM) is gradually becoming the most competitive manufacturing technology for producing large composite parts with complex geometry with high quality and low cost. These parts include those for airplanes, wind turbine blades and automobile components. Fibre fabrics in liquid composite moulding can be considered as dual-scale porous media. In different gap scales, an unsaturated flow is produced during the mould filling process. This particular flow behaviour deviates from the traditional Darcy’s law, which is used to calculate the filling pressure and will cause errors. According to sink theory, the unsaturated flow characteristics of this dual-scale porous media were studied in this paper, and a FEM solution program was developed. The results showed that the pressure curves against the position which simulated by sink functions were departure from the position of traditional theory. In addition, the simulation results of partially-saturated region were consistent with the experimental data.
Computer simulations of magnetic fluids in laminar pipe flows
International Nuclear Information System (INIS)
Ramos, D.M.; Cunha, F.R.; Sobral, Y.D.; Fontoura Rodrigues, J.L.A.
2005-01-01
Finite volume method is adapted to simulate momentum and magnetic coupled equations of a laminar magnetic fluid flow. An evolution equation is used to calculate the fluid magnetization. Pressure-driven flow under steady and oscillatory magnetic field is investigated. The magnetostatic limit of the Maxwell's equations is treated in terms of a Poisson equation numerically integrated. The SIMPLE algorithm is used to calculate the pressure-velocity coupling when the pressure field is not prescribed. Suitable boundary conditions for velocity, magnetization and field intensity on the pipe wall are described. Results are obtained for velocity and pressure response under several conditions of the identified physical parameters of the flow. The simulations are verified by comparing numerical results and asymptotic theory, and they show a very good agreement
Unsteady flow simulations of Pelton turbine at different rotational speeds
Directory of Open Access Journals (Sweden)
Minsuk Choi
2015-11-01
Full Text Available This article presents numerical simulations of a small Pelton turbine suitable for desalination system. A commercial flow solver was adopted to resolve difficulties in the numerical simulation for Pelton turbine such as the relative motion of the turbine runner to the injector and two-phase flow of water and air. To decrease the numerical diffusion of the water jet, a new topology with only hexagonal mesh was suggested for the computational mesh around the complex geometry of a bucket. The predicted flow coefficient, net head coefficient, and overall efficiency showed a good agreement with the experimental data. Based on the validation of the numerical results, the pattern of wet area on the bucket inner surface has been analyzed at different rotational speeds, and an attempt to find the connection between rotational speeds, torque, and efficiency has been made.
Simulation of flooding waves in vertical churn flow
Energy Technology Data Exchange (ETDEWEB)
Tekavčič, Matej, E-mail: matej.tekavcic@ijs.si; Končar, Boštjan; Kljenak, Ivo
2016-04-01
Highlights: • Flooding waves in air–water churn flow in a vertical pipe were studied. • Simulations using two-fluid model with interface sharpening were performed. • Calculated wave amplitudes agree with existing experimental data. • Contributions of force terms in the liquid momentum balance equation are presented. - Abstract: A transient simulation of flooding waves in the churn flow of air and water in a vertical pipe is performed by the means of two-fluid modelling approach with interface sharpening. The gas and liquid phases are considered immiscible and incompressible with no mass transfer between them. Inter-phase coupling of momentum is realized via interface drag force which is based on the interface area density and the relative velocity between the phases. Surface tension effects are modelled with the Continuum Surface Model. The flow is assumed isothermal. Turbulence is modelled for each phase separately using the two-equation eddy viscosity approach. Results are compared with the reported experimental data for churn flow regime in a vertical pipe (Wang et al., 2011a). Reynolds numbers of the gas flow are in the range from 6000 to 10,000, while the liquid mass flow rate upwards ranges from 25 to 32 g/s. Prediction of critical and maximum amplitudes of the flooding waves show good agreement with experimental values. Results for wave frequencies indicate significant deviations, which can be attributed to the choice of the liquid inlet model.
Cellular automaton simulation of counter flow with paired pedestrians
Directory of Open Access Journals (Sweden)
Hui Xiong
2011-12-01
Full Text Available Knowledge on pedestrian behavior is the basis to build decision support system for crowd evacuation management in emergency. In this paper, the impact of paired walking behavior on pedestrian counter flow in a channel is studied. The pedestrian walking behaviors are simulated by the cellular automaton model and the pedestrians are classified as single right walker, single left walker, paired right walker, and paired left walker. Single walker can move forward, leftward, rightward or stand still. The paired pedestrians are considered as a combined unit similar to the single walker in terms of route choice and they can move to the same direction simultaneously. It is found that flow and velocity decrease with increase of the paired rate in case of stable density. Simulation results reveal the phase transitions in terms of density from free flow to the unstable flow and from the unstable flow to the congestion flow. However, the critical densities of phase transition are unaffected by the channel size.
Simulation of flooding waves in vertical churn flow
International Nuclear Information System (INIS)
Tekavčič, Matej; Končar, Boštjan; Kljenak, Ivo
2016-01-01
Highlights: • Flooding waves in air–water churn flow in a vertical pipe were studied. • Simulations using two-fluid model with interface sharpening were performed. • Calculated wave amplitudes agree with existing experimental data. • Contributions of force terms in the liquid momentum balance equation are presented. - Abstract: A transient simulation of flooding waves in the churn flow of air and water in a vertical pipe is performed by the means of two-fluid modelling approach with interface sharpening. The gas and liquid phases are considered immiscible and incompressible with no mass transfer between them. Inter-phase coupling of momentum is realized via interface drag force which is based on the interface area density and the relative velocity between the phases. Surface tension effects are modelled with the Continuum Surface Model. The flow is assumed isothermal. Turbulence is modelled for each phase separately using the two-equation eddy viscosity approach. Results are compared with the reported experimental data for churn flow regime in a vertical pipe (Wang et al., 2011a). Reynolds numbers of the gas flow are in the range from 6000 to 10,000, while the liquid mass flow rate upwards ranges from 25 to 32 g/s. Prediction of critical and maximum amplitudes of the flooding waves show good agreement with experimental values. Results for wave frequencies indicate significant deviations, which can be attributed to the choice of the liquid inlet model.
Analysis on flow characteristic of nuclear heating reactor
International Nuclear Information System (INIS)
Jiang Shengyao; Wu Xinxin
1997-06-01
The experiment was carried out on the test loop HRTL-5, which simulates the geometry and system design of a 5 MW Nuclear heating reactor. The analysis was based on a one-dimensional two-phase flow drift model with conservation equations for mass, steam mass, energy and momentum. Clausius-Clapeyron equation was used for the calculation of flashing front in the riser. A set of ordinary equation, which describes the behavior of two-phase flow in the natural circulation system, was derived through integration of the above conservation equations in subcooled boiling region, bulk boiling region in the heated section and in the riser. The method of time-domain was used for the calculation. Both static and dynamic results are presented. System pressure, inlet subcooling and heat flux are varied as input parameters. The results show that, firstly, subcooled boiling in the heated section and void flashing in the riser have significant influence on the distribution of the void fraction, mass flow rate and stability of the system, especially at lower pressure, secondly, in a wide range of two-phase flow conditions, only subcooled boiling occurs in the heated section. For the designed two-phase regime operation of the 5 MW nuclear heating reactor, the temperature at the core exit has not reaches its saturation value. Thirdly, the mechanism of two-phase flow oscillation, namely, 'zero-pressure-drop', is described. In the wide range of inlet subcooling (0 K<ΔT<28 K) there exists three regions for system flow condition, namely, (1) stable two-phase flow, (2) bulk and subcooled boiling unstable flow, (3) subcooled boiling and single phase stable flow. The response of mass flow rate, after a small disturbance in the heat flux, is showed in the above inlet subcooling range, and based on it the instability map of the system is given through experiment and calculation. (3 refs., 9 figs.)
Large-eddy simulation of unidirectional turbulent flow over dunes
Omidyeganeh, Mohammad
We performed large eddy simulation of the flow over a series of two- and three-dimensional dune geometries at laboratory scale using the Lagrangian dynamic eddy-viscosity subgrid-scale model. First, we studied the flow over a standard 2D transverse dune geometry, then bedform three-dimensionality was imposed. Finally, we investigated the turbulent flow over barchan dunes. The results are validated by comparison with simulations and experiments for the 2D dune case, while the results of the 3D dunes are validated qualitatively against experiments. The flow over transverse dunes separates at the dune crest, generating a shear layer that plays a crucial role in the transport of momentum and energy, as well as the generation of coherent structures. Spanwise vortices are generated in the separated shear; as they are advected, they undergo lateral instabilities and develop into horseshoe-like structures and finally reach the surface. The ejection that occurs between the legs of the vortex creates the upwelling and downdrafting events on the free surface known as "boils". The three-dimensional separation of flow at the crestline alters the distribution of wall pressure, which may cause secondary flow across the stream. The mean flow is characterized by a pair of counter-rotating streamwise vortices, with core radii of the order of the flow depth. Staggering the crestlines alters the secondary motion; two pairs of streamwise vortices appear (a strong one, centred about the lobe, and a weaker one, coming from the previous dune, centred around the saddle). The flow over barchan dunes presents significant differences to that over transverse dunes. The flow near the bed, upstream of the dune, diverges from the centerline plane; the flow close to the centerline plane separates at the crest and reattaches on the bed. Away from the centerline plane and along the horns, flow separation occurs intermittently. The flow in the separation bubble is routed towards the horns and leaves
Numerical simulation of interior flow field of nuclear model pump
International Nuclear Information System (INIS)
Wang Chunlin; Peng Na; Kang Can; Zhao Baitong; Zhang Hao
2009-01-01
Reynolds time-averaged N-S equations and the standard k-ε turbulent model were adopted, and three-dimensional non-structural of tetrahedral mesh division was used for modeling. Multiple reference frame model of rotating fluid mechanical model was used, under the design condition, the three-dimensional incompressible turbulent flow of nuclear model pump was simulated, and the results preferably post the characteristics of the interior flow field. This paper first analyzes the total pressure and velocity distribution in the flow field, and then describes the interior flow field characteristics of each part such as the impeller, diffuser and spherical shell, and also discusses the reasons that cause these characteristics. The study results can be used to estimate the performance of nuclear model pump, and will provide some useful references for its hydraulic optimized design. (authors)
Hydrodynamic stability of inverted annular flow in an adiabatic simulation
International Nuclear Information System (INIS)
De Jarlais, G.; Ishii, M.; Linehan, J.
1986-01-01
Inverted annular flow was simulated adiabatically with turbulent water jets, issuing downward from large aspect ratio nozzles, enclosed in gas annuli. Velocities, diameters, and gas species were varied, and core jet length, shape, breakup mode, and dispersed core droplet sizes were recorded at approximately 750 data points. Inverted annular flow destabilization led to inverted slug flow at low relative velocities, and to dispersed droplet flow, core breakup length correlations were developed by extending work on free liquid jets to include this coaxial, jet disintegration phenomenon. The results show length dependence upon D/sub J/, Re/sub J/, We/sub J/, α, and We/sub G/,rel. Correlations for core shape, breakup mechanisms, and dispersed core droplet size were also developed, by extending the results of free jet stability, roll wave entrainment, and churn turbulent droplet stability studies
Topics in the numerical simulation of high temperature flows
International Nuclear Information System (INIS)
Cheret, R.; Dautray, R.; Desgraz, J.C.; Mercier, B.; Meurant, G.; Ovadia, J.; Sitt, B.
1984-06-01
In the fields of inertial confinement fusion, astrophysics, detonation, or other high energy phenomena, one has to deal with multifluid flows involving high temperatures, high speeds and strong shocks initiated e.g. by chemical reactions or even by thermonuclear reactions. The simulation of multifluid flows is reviewed: first are Lagrangian methods which have been successfully applied in the past. Then we describe our experience with newer adaptive mesh methods, originally designed to increase the accuracy of Lagrangian methods. Finally, some facts about Eulerian methods are recalled, with emphasis on the EAD scheme which has been recently extended to the elasto-plastic case. High temperature flows is then considered, described by the equations of radiation hydrodynamics. We show how conservation of energy can be preserved while solving the radiative transfer equation via the Monte Carlo method. For detonation, some models, introduced to describe the initiation of detonation in heterogeneous explosives. Finally we say a few words about instability of these flows
Directory of Open Access Journals (Sweden)
Muhammad Ahsan
2015-07-01
Full Text Available Fluid catalytic cracking (FCC is an essential process for the conversion of gas oil to gasoline. This study is an effort to model the phenomenon numerically using commercial computational fluid dynamics (CFD software, heavy density catalyst and 4-lump kinetic model. Geometry, boundary conditions and dimensions of industrial riser for catalytic cracking unit are conferred for 2D simulation using commercial CFD code FLUENT 6.3. Continuity, momentum, energy and species transport equations, applicable to two phase solid and gas flow, are used to simulate the physical phenomenon as efficient as possible. This study implements and predicts the use of the granular Eulerian multiphase model with species transport. Time accurate transient problem is solved with the prediction of mass fraction profiles of gas oil, gasoline, light gas and coke. The output curves demonstrate the breaking of heavy hydrocarbon in the presence of catalyst. An approach proposed in this study shows good agreement with the experimental and numerical data available in the literature.
Evaluating Mesoscale Simulations of the Coastal Flow Using Lidar Measurements
Floors, R.; Hahmann, A. N.; Peña, A.
2018-03-01
The atmospheric flow in the coastal zone is investigated using lidar and mast measurements and model simulations. Novel dual-Doppler scanning lidars were used to investigate the flow over a 7 km transect across the coast, and vertically profiling lidars were used to study the vertical wind profile at offshore and onshore positions. The Weather, Research and Forecasting model is set up in 12 different configurations using 2 planetary boundary layer schemes, 3 horizontal grid spacings and varied sources of land use, and initial and lower boundary conditions. All model simulations describe the observed mean wind profile well at different onshore and offshore locations from the surface up to 500 m. The simulated mean horizontal wind speed gradient across the shoreline is close to that observed, although all simulations show wind speeds that are slightly higher than those observed. Inland at the lowest observed height, the model has the largest deviations compared to the observations. Taylor diagrams show that using ERA-Interim data as boundary conditions improves the model skill scores. Simulations with 0.5 and 1 km horizontal grid spacing show poorer model performance compared to those with a 2 km spacing, partially because smaller resolved wave lengths degrade standard error metrics. Modeled and observed velocity spectra were compared and showed that simulations with the finest horizontal grid spacing resolved more high-frequency atmospheric motion.
A new approach to flow simulation using hybrid models
Solgi, Abazar; Zarei, Heidar; Nourani, Vahid; Bahmani, Ramin
2017-11-01
The necessity of flow prediction in rivers, for proper management of water resource, and the need for determining the inflow to the dam reservoir, designing efficient flood warning systems and so forth, have always led water researchers to think about models with high-speed response and low error. In the recent years, the development of Artificial Neural Networks and Wavelet theory and using the combination of models help researchers to estimate the river flow better and better. In this study, daily and monthly scales were used for simulating the flow of Gamasiyab River, Nahavand, Iran. The first simulation was done using two types of ANN and ANFIS models. Then, using wavelet theory and decomposing input signals of the used parameters, sub-signals were obtained and were fed into the ANN and ANFIS to obtain hybrid models of WANN and WANFIS. In this study, in addition to the parameters of precipitation and flow, parameters of temperature and evaporation were used to analyze their effects on the simulation. The results showed that using wavelet transform improved the performance of the models in both monthly and daily scale. However, it had a better effect on the monthly scale and the WANFIS was the best model.
Numerical simulations of the IPPE target geometry flows
International Nuclear Information System (INIS)
Prakash, Akshay; Kakarantzas, Sotiris; Bernardi, Davide; Micciche, Gioacchino; Massaut, Vincent; Knaepen, Bernard
2013-01-01
Highlights: ► We performed numerical simulation of flow over IPPE geometry using turbulence models in FLUENT. ► Stable free surface profile well within the required design limits was predicted by the models. ► Velocity profiles across the liquid jet and jet thickness different for different models. ► There were some 3D effects noticeable for the velocity profiles but the predicted jet thickness similar to 2D models. ► TKE predicted by different models close to each other and compare will with published data. -- Abstract: A high speed water and liquid lithium (Li) flow is computed over the IPPE geometry to evaluate the performance of different turbulence models in 2D and 3D simulations. Results reported are the thickness of the liquid jet, irregularities in the surface, transient phenomena at the wall which can affect fluid surface and effect of the variation in bulk velocity on these quantities. All models show good near wall resolution of the boundary layer and expected profiles for the free surface flow. Predicted turbulent kinetic energy compare well with published data. Fluctuations of the flow surface at the control location (center of the curved section) and elsewhere are well within 1 mm for all models. However it was observed that the predictions are strongly dependent on the model used. Overall, the predictions of RANS models are close to each other whereas predictions of laminar simulations are close to those obtained with LES models
Uncertainty quantification tools for multiphase gas-solid flow simulations using MFIX
Energy Technology Data Exchange (ETDEWEB)
Fox, Rodney O. [Iowa State Univ., Ames, IA (United States); Passalacqua, Alberto [Iowa State Univ., Ames, IA (United States)
2016-02-01
Computational fluid dynamics (CFD) has been widely studied and used in the scientific community and in the industry. Various models were proposed to solve problems in different areas. However, all models deviate from reality. Uncertainty quantification (UQ) process evaluates the overall uncertainties associated with the prediction of quantities of interest. In particular it studies the propagation of input uncertainties to the outputs of the models so that confidence intervals can be provided for the simulation results. In the present work, a non-intrusive quadrature-based uncertainty quantification (QBUQ) approach is proposed. The probability distribution function (PDF) of the system response can be then reconstructed using extended quadrature method of moments (EQMOM) and extended conditional quadrature method of moments (ECQMOM). The report first explains the theory of QBUQ approach, including methods to generate samples for problems with single or multiple uncertain input parameters, low order statistics, and required number of samples. Then methods for univariate PDF reconstruction (EQMOM) and multivariate PDF reconstruction (ECQMOM) are explained. The implementation of QBUQ approach into the open-source CFD code MFIX is discussed next. At last, QBUQ approach is demonstrated in several applications. The method is first applied to two examples: a developing flow in a channel with uncertain viscosity, and an oblique shock problem with uncertain upstream Mach number. The error in the prediction of the moment response is studied as a function of the number of samples, and the accuracy of the moments required to reconstruct the PDF of the system response is discussed. The QBUQ approach is then demonstrated by considering a bubbling fluidized bed as example application. The mean particle size is assumed to be the uncertain input parameter. The system is simulated with a standard two-fluid model with kinetic theory closures for the particulate phase implemented into
Vectorization of a particle simulation method for hypersonic rarefied flow
Mcdonald, Jeffrey D.; Baganoff, Donald
1988-01-01
An efficient particle simulation technique for hypersonic rarefied flows is presented at an algorithmic and implementation level. The implementation is for a vector computer architecture, specifically the Cray-2. The method models an ideal diatomic Maxwell molecule with three translational and two rotational degrees of freedom. Algorithms are designed specifically for compatibility with fine grain parallelism by reducing the number of data dependencies in the computation. By insisting on this compatibility, the method is capable of performing simulation on a much larger scale than previously possible. A two-dimensional simulation of supersonic flow over a wedge is carried out for the near-continuum limit where the gas is in equilibrium and the ideal solution can be used as a check on the accuracy of the gas model employed in the method. Also, a three-dimensional, Mach 8, rarefied flow about a finite-span flat plate at a 45 degree angle of attack was simulated. It utilized over 10 to the 7th particles carried through 400 discrete time steps in less than one hour of Cray-2 CPU time. This problem was chosen to exhibit the capability of the method in handling a large number of particles and a true three-dimensional geometry.
Vectorization of a particle simulation method for hypersonic rarefied flow
International Nuclear Information System (INIS)
Mcdonald, J.D.; Baganoff, D.
1988-01-01
An efficient particle simulation technique for hypersonic rarefied flows is presented at an algorithmic and implementation level. The implementation is for a vector computer architecture, specifically the Cray-2. The method models an ideal diatomic Maxwell molecule with three translational and two rotational degrees of freedom. Algorithms are designed specifically for compatibility with fine grain parallelism by reducing the number of data dependencies in the computation. By insisting on this compatibility, the method is capable of performing simulation on a much larger scale than previously possible. A two-dimensional simulation of supersonic flow over a wedge is carried out for the near-continuum limit where the gas is in equilibrium and the ideal solution can be used as a check on the accuracy of the gas model employed in the method. Also, a three-dimensional, Mach 8, rarefied flow about a finite-span flat plate at a 45 degree angle of attack was simulated. It utilized over 10 to the 7th particles carried through 400 discrete time steps in less than one hour of Cray-2 CPU time. This problem was chosen to exhibit the capability of the method in handling a large number of particles and a true three-dimensional geometry. 14 references
Entrainment in Laboratory Simulations of Cumulus Cloud Flows
Narasimha, R.; Diwan, S.; Subrahmanyam, D.; Sreenivas, K. R.; Bhat, G. S.
2010-12-01
A variety of cumulus cloud flows, including congestus (both shallow bubble and tall tower types), mediocris and fractus have been generated in a water tank by simulating the release of latent heat in real clouds. The simulation is achieved through ohmic heating, injected volumetrically into the flow by applying suitable voltages between diametral cross-sections of starting jets and plumes of electrically conducting fluid (acidified water). Dynamical similarity between atmospheric and laboratory cloud flows is achieved by duplicating values of an appropriate non-dimensional heat release number. Velocity measurements, made by laser instrumentation, show that the Taylor entrainment coefficient generally increases just above the level of commencement of heat injection (corresponding to condensation level in the real cloud). Subsequently the coefficient reaches a maximum before declining to the very low values that characterize tall cumulus towers. The experiments also simulate the protected core of real clouds. Cumulus Congestus : Atmospheric cloud (left), simulated laboratory cloud (right). Panels below show respectively total heat injected and vertical profile of heating in the laboratory cloud.
Large eddy simulation of turbulent and stably-stratified flows
International Nuclear Information System (INIS)
Fallon, Benoit
1994-01-01
The unsteady turbulent flow over a backward-facing step is studied by mean of Large Eddy Simulations with structure function sub grid model, both in isothermal and stably-stratified configurations. Without stratification, the flow develops highly-distorted Kelvin-Helmholtz billows, undergoing to helical pairing, with A-shaped vortices shed downstream. We show that forcing injected by recirculation fluctuations governs this oblique mode instabilities development. The statistical results show good agreements with the experimental measurements. For stably-stratified configurations, the flow remains more bi-dimensional. We show with increasing stratification, how the shear layer growth is frozen by inhibition of pairing process then of Kelvin-Helmholtz instabilities, and the development of gravity waves or stable density interfaces. Eddy structures of the flow present striking analogies with the stratified mixing layer. Additional computations show the development of secondary Kelvin-Helmholtz instabilities on the vorticity layers between two primary structures. This important mechanism based on baroclinic effects (horizontal density gradients) constitutes an additional part of the turbulent mixing process. Finally, the feasibility of Large Eddy Simulation is demonstrated for industrial flows, by studying a complex stratified cavity. Temperature fluctuations are compared to experimental measurements. We also develop three-dimensional un-stationary animations, in order to understand and visualize turbulent interactions. (author) [fr
Numerical simulation for gas-liquid two-phase flow in pipe networks
International Nuclear Information System (INIS)
Li Xiaoyan; Kuang Bo; Zhou Guoliang; Xu Jijun
1998-01-01
The complex pipe network characters can not directly presented in single phase flow, gas-liquid two phase flow pressure drop and void rate change model. Apply fluid network theory and computer numerical simulation technology to phase flow pipe networks carried out simulate and compute. Simulate result shows that flow resistance distribution is non-linear in two phase pipe network
Anchoring FRP Composite Armor in Flexible Offshore Riser Systems
DEFF Research Database (Denmark)
Costache, Andrei
things, they serve for the transportation of hydrocarbons from the subsea facilities to the production and drilling equipment at the sea surface. Flexible risers are the prime choice for connecting floating production, storage and offloading facilities, because they are specially designed for dynamic...... counterpart. A new double grip design with flat faces is proposed, in which the loads are transferred through friction. The behavior of such grip is studied by means of experimental testing and finite element modeling. Several iterations of the grip system were evaluated over the course of the project...
CFD Simulation of Flow Tones from Grazing Flow past a Deep Cavity
International Nuclear Information System (INIS)
T Bagwell
2006-01-01
Locked-in flow tones due to shear flow over a deep cavity are investigated using Large Eddy Simulation (LES). An isentropic form of the compressible Navier-Stokes equations (pseudo-compressibility) is used to couple the vertical flow over the cavity mouth with the deep cavity resonances (1). Comparisons to published experimental data (2) show that the pseudo-compressible LES formulation is capable of predicting the feedforward excitation of the deep cavity resonator, as well as the feedback process from the resonator to the flow source. By systematically increasing the resonator damping level, it is shown that strong lock-in results in a more organized shear layer than is observed for the locked-out flow state. By comparison, weak interactions (non-locked-in) produce no change in the shear layer characteristics. This supports the 40 dB definition of lock-in defined in the experiment
Large-eddy simulation of atmospheric flow over complex terrain
Energy Technology Data Exchange (ETDEWEB)
Bechmann, A.
2006-11-15
The present report describes the development and validation of a turbulence model designed for atmospheric flows based on the concept of Large-Eddy Simulation (LES). The background for the work is the high Reynolds number k - epsilon model, which has been implemented on a finite-volume code of the incompressible Reynolds-averaged Navier-Stokes equations (RANS). The k - epsilon model is traditionally used for RANS computations, but is here developed to also enable LES. LES is able to provide detailed descriptions of a wide range of engineering flows at low Reynolds numbers. For atmospheric flows, however, the high Reynolds numbers and the rough surface of the earth provide difficulties normally not compatible with LES. Since these issues are most severe near the surface they are addressed by handling the near surface region with RANS and only use LES above this region. Using this method, the developed turbulence model is able to handle both engineering and atmospheric flows and can be run in both RANS or LES mode. For LES simulations a time-dependent wind field that accurately represents the turbulent structures of a wind environment must be prescribed at the computational inlet. A method is implemented where the turbulent wind field from a separate LES simulation can be used as inflow. To avoid numerical dissipation of turbulence special care is paid to the numerical method, e.g. the turbulence model is calibrated with the specific numerical scheme used. This is done by simulating decaying isotropic and homogeneous turbulence. Three atmospheric test cases are investigated in order to validate the behavior of the presented turbulence model. Simulation of the neutral atmospheric boundary layer, illustrates the turbulence model ability to generate and maintain the turbulent structures responsible for boundary layer transport processes. Velocity and turbulence profiles are in good agreement with measurements. Simulation of the flow over the Askervein hill is also
Site scale groundwater flow in Olkiluoto - complementary simulations
International Nuclear Information System (INIS)
Loefman, J.
2000-06-01
This work comprises of the complementary simulations to the previous groundwater flow analysis at the Olkiluoto site. The objective is to study the effects of flow porosity, conceptual model for solute transport, fracture zones, land uplift and initial conditions on the results. The numerical simulations are carried out up to 10000 years into the future employing the same modelling approach and site-specific flow and transport model as in the previous work except for the differences in the case descriptions. The result quantities considered are the salinity and the driving force in the vicinity of the repository. The salinity field and the driving force are sensitive to the flow porosity and the conceptual model for solute transport. Ten-fold flow porosity and the dual-porosity approach retard the transport of solutes in the bedrock resulting in brackish groundwater conditions at the repository at 10000 years A.P. (in the previous work the groundwater in the repository turned into fresh). The higher driving forces can be attributed to the higher concentration gradients resulting from the opposite effects of the land uplift, which pushes fresh water deeper and deeper into the bedrock, and the higher flow porosity and the dual-porosity model, which retard the transport of solutes. The cases computed (unrealistically) without fracture zones and postglacial land uplift show that they both have effect on the results and can not be ignored in the coupled and transient groundwater flow analyses. The salinity field and the driving force are also sensitive to the initial salinity field especially at the beginning during the first 500 years A.P. The sensitivity will, however, diminish as soon as fresh water dilutes brackish and saline water and decreases the concentration gradients. Fresh water conditions result in also a steady state for the driving force in the repository area. (orig.)
Directory of Open Access Journals (Sweden)
A. V. Rusanov
2016-12-01
Full Text Available The results of numerical investigation of spatial flow of viscous incompressible fluid in flow part of Kaplan turbine PL20 Kremenchug HPP at optimum setting angle of runner blade φb = 15° and at maximum setting angle φb = 35° are shown. The flow simulation has been carried out on basis of numerical integration of the Reynolds equations with an additional term containing artificial compressibility. The differential two-parameter model of Menter (SST has been applied to take into account turbulent effects. Numerical integration of the equations is carried out using an implicit quasi-monotone Godunov type scheme of second - order accuracy in space and time. The calculations have been conducted with the help of the software system IPMFlow. The analysis of fluid flow in the flow part elements is shown and the values of hydraulic losses and local cavitation coefficient have been obtained. Comparison of calculated and experimental results has been carried out.
Numerical simulation of low Mach number reacting flows
International Nuclear Information System (INIS)
Bell, J B; Aspden, A J; Day, M S; Lijewski, M J
2007-01-01
Using examples from active research areas in combustion and astrophysics, we demonstrate a computationally efficient numerical approach for simulating multiscale low Mach number reacting flows. The method enables simulations that incorporate an unprecedented range of temporal and spatial scales, while at the same time, allows an extremely high degree of reaction fidelity. Sample applications demonstrate the efficiency of the approach with respect to a traditional time-explicit integration method, and the utility of the methodology for studying the interaction of turbulence with terrestrial and astrophysical flame structures
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 simulation of lava flow using a GPU SPH model
Directory of Open Access Journals (Sweden)
Eugenio Rustico
2011-12-01
Full Text Available A smoothed particle hydrodynamics (SPH method for lava-flow modeling was implemented on a graphical processing unit (GPU using the compute unified device architecture (CUDA developed by NVIDIA. This resulted in speed-ups of up to two orders of magnitude. The three-dimensional model can simulate lava flow on a real topography with free-surface, non-Newtonian fluids, and with phase change. The entire SPH code has three main components, neighbor list construction, force computation, and integration of the equation of motion, and it is computed on the GPU, fully exploiting the computational power. The simulation speed achieved is one to two orders of magnitude faster than the equivalent central processing unit (CPU code. This GPU implementation of SPH allows high resolution SPH modeling in hours and days, rather than in weeks and months, on inexpensive and readily available hardware.
Simulations of ductile flow in brittle material processing
Energy Technology Data Exchange (ETDEWEB)
Luh, M.H.; Strenkowski, J.S.
1988-12-01
Research is continuing on the effects of thermal properties of the cutting tool and workpiece on the overall temperature distribution. Using an Eulerian finite element model, diamond and steel tools cutting aluminum have been simulated at various, speeds, and depths of cut. The relative magnitude of the thermal conductivity of the tool and the workpiece is believed to be a primary factor in the resulting temperature distribution in the workpiece. This effect is demonstrated in the change of maximum surface temperatures for diamond on aluminum vs. steel on aluminum. As a preliminary step toward the study of ductile flow in brittle materials, the relative thermal conductivities of diamond on polycarbonate is simulated. In this case, the maximum temperature shifts from the rake face of the tool to the surface of the machined workpiece, thus promoting ductile flow in the workpiece surface.
Simulation of turbulent flow in a packed bed
Energy Technology Data Exchange (ETDEWEB)
Guo, B.; Yu, A. [Centre for Simulation and Modelling of Particulate Systems and School of Material Science and Engineering, The University of New South Wales, Sydney 2052 (Australia); Wright, B.; Zulli, P. [BlueScope Steel Research Laboratories, P.O. Box 202, Port Kembla, NSW 2505 (Australia)
2006-05-15
Numerous models for simulating the flow and transport in packed beds have been proposed in the literature with few reported applications. In this paper, several turbulence models for porous media are applied to the gas flow through a randomly packed bed and are examined by means of a parametric study against some published experimental data. These models predict widely different turbulent eddy viscosity. The analysis also indicates that deficiencies exist in the formulation of some model equations and selection of a suitable turbulence model is important. With this realization, residence time distribution and velocity distribution are then simulated by considering a radial profile of porosity and turbulence induced dispersion, and the results are in good agreement with the available experimental data. (Abstract Copyright [2006], Wiley Periodicals, Inc.)
Singing mitigation in an export riser via liquid injection: a field case study
Belfroid, S.P.C.; Korst, H.J.C.; Beek, P.J.G. van; Lunde, K.; Eidsvik, I.G.; Hansen, F.; Olsen, B.
2014-01-01
Flexible Risers are prone to the generation of high amplitude tonal noise, i.e. a so-called singing riser. Recently, severe vibrations and high noise levels were encountered on the turret of an FPSO in the Norwegian Sea, resulting in significantly reduced production. The vibrations could be
An analytic solution of the static problem of inclined risers conveying fluid
Alfosail, Feras; Nayfeh, Ali H.; Younis, Mohammad I.
2016-01-01
We use the method of matched asymptotic expansion to develop an analytic solution to the static problem of clamped–clamped inclined risers conveying fluid. The inclined riser is modeled as an Euler–Bernoulli beam taking into account its self
Numerical simulation of groundwater flow in LILW Repository site:I. Groundwater flow modeling
Energy Technology Data Exchange (ETDEWEB)
Park, Koung Woo; Ji, Sung Hoon; Kim, Chun Soo; Kim, Kyoung Su [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Kim, Ji Yeon [Korea Hydro and Nuclear Power Co. Ltd., Seoul (Korea, Republic of)
2008-12-15
Based on the site characterization works in a low and intermediate level waste (LILW) repository site, the numerical simulations for groundwater flow were carried out in order to understand the groundwater flow system of repository site. To accomplish the groundwater flow modeling in the repository site, the discrete fracture network (DFN) model was constructed using the characteristics of fracture zones and background fractures. At result, the total 10 different hydraulic conductivity(K) fields were obtained from DFN model stochastically and K distributions of constructed mesh were inputted into the 10 cases of groundwater flow simulations in FEFLOW. From the total 10 numerical simulation results, the simulated groundwater levels were strongly governed by topography and the groundwater fluxes were governed by locally existed high permeable fracture zones in repository depth. Especially, the groundwater table was predicted to have several tens meters below the groundwater table compared with the undisturbed condition around disposal silo after construction of underground facilities. After closure of disposal facilities, the groundwater level would be almost recovered within 1 year and have a tendency to keep a steady state of groundwater level in 2 year.
Go with the Flow. Moving meshes and solution monitoring for compressible flow simulation
van Dam, A.
2009-01-01
The simulation of time-dependent physical problems, such as flows of some kind, places high demands on the domain discretization in order to obtain high accuracy of the numerical solution. We present a moving mesh method in which the mesh points automatically move towards regions where high spatial
Diagnosis of Catalyst Cooler and Riser in RFCC using Sealed gamma-ray Source
International Nuclear Information System (INIS)
Kim, Jin Seop; Kim, Jong Bum; Jung, Sung Hee; Kim, Jae Ho
2005-12-01
With a quantitative growth of the petroleum industry, a lot of budget are spent for the maintenance and repairs of facilities related to the process annually. Among them, the RFCC(residual fluid catalytic cracking) is a highly value-added unit which converts gas oil and heavier streams to lighter, more valuable products such as propylene, gasoline by an injection of atmospheric residue into the fluided catalyst. In this study, field experiments were performed to analyze the reasons of an abnormal operation in the catalyst cooler and the catalyst riser belonged to the RFCC unit respectively and to estimate the amount of seriousness using sealed gamma-ray source( 60 Co). The catalyst cooler functions cooling for the regeneration of a catalyst, which will be used to a new media in the RFCC unit. The catalyst riser, while, plays an important part in transporting to next cyclotron steps by mixing of an oil, steam and a catalyst mechanically. The purposes of this study is what was the condition of catalyst flow pattern and whether the coke was produced in an inside process or not. Gamma radiation counts were measured by the detector(NaI) positioned outside the pipe-wall diametrically opposite to the gamma source with a regular space. From the results, the section different from the distribution pattern of nearby catalyst in a facility was found. And this became the definitive information to a process operator. Diagnosis technique using gamma radiation source is proved to be the effective and reliable method in providing information on the media distribution in a facility
DEM simulation of granular flows in a centrifugal acceleration field
Cabrera, Miguel Angel; Peng, Chong; Wu, Wei
2017-04-01
The main purpose of mass-flow experimental models is abstracting distinctive features of natural granular flows, and allow its systematic study in the laboratory. In this process, particle size, space, time, and stress scales must be considered for the proper representation of specific phenomena [5]. One of the most challenging tasks in small scale models, is matching the range of stresses and strains among the particle and fluid media observed in a field event. Centrifuge modelling offers an alternative to upscale all gravity-driven processes, and it has been recently employed in the simulation of granular flows [1, 2, 3, 6, 7]. Centrifuge scaling principles are presented in Ref. [4], collecting a wide spectrum of static and dynamic models. However, for the case of kinematic processes, the non-uniformity of the centrifugal acceleration field plays a major role (i.e., Coriolis and inertial effects). In this work, we discuss a general formulation for the centrifugal acceleration field, implemented in a discrete element model framework (DEM), and validated with centrifuge experimental results. Conventional DEM simulations relate the volumetric forces as a function of the gravitational force Gp = mpg. However, in the local coordinate system of a rotating centrifuge model, the cylindrical centrifugal acceleration field needs to be included. In this rotating system, the centrifugal acceleration of a particle depends on the rotating speed of the centrifuge, as well as the position and speed of the particle in the rotating model. Therefore, we obtain the formulation of centrifugal acceleration field by coordinate transformation. The numerical model is validated with a series of centrifuge experiments of monodispersed glass beads, flowing down an inclined plane at different acceleration levels and slope angles. Further discussion leads to the numerical parameterization necessary for simulating equivalent granular flows under an augmented acceleration field. The premise of
TO THE QUESTION ABOUT THE SIMULATION OF TURBULENT THERMAL FLOWS
Directory of Open Access Journals (Sweden)
2016-01-01
Full Text Available The main purpose of this work was the simulation of turbulent thermal flows, which is aimed at improving the visualization and the modeling of the flow fields of wind flows, which are necessary for aviation. The physical-mathematical model of gas flow in thermal is proposed on the basis of thermodynamic model and dynamic model under the assumption that the condensation energy, when the movement of the thermal is upward, becomes the turbulent fluctuations. A thermal is an air mass, which goes up and is capable to intermix with ambient air. In the work the thermodynamic model of thermal is presented, the equations and the system of equations are derived, that describe the main characteristics of wind flow, which are required for the modeling of airflows. The generation of vertical turbulent gust with von Karman spectrum is shown. The basic assumption in the construction of the dynamic model of generation was that the energy, which is stood out in the thermal due to the condensation of steam, is converted into the energy of turbulent pulsations. Some examples of numerical simulation are given in the article. The visualizations of the generation of the vertical velocity of random wind gust are given depending on the size of the considered space and depending on the pitch of cell partition. The analysis and comparison of the obtained results of the calculation are presented. The conducted studies are aimed at the simulation of the atmospheric background and atmospheric processes and, in the final result, at the increasing of flight safety.
Optimal Results and Numerical Simulations for Flow Shop Scheduling Problems
Directory of Open Access Journals (Sweden)
Tao Ren
2012-01-01
Full Text Available This paper considers the m-machine flow shop problem with two objectives: makespan with release dates and total quadratic completion time, respectively. For Fm|rj|Cmax, we prove the asymptotic optimality for any dense scheduling when the problem scale is large enough. For Fm‖ΣCj2, improvement strategy with local search is presented to promote the performance of the classical SPT heuristic. At the end of the paper, simulations show the effectiveness of the improvement strategy.
Numerical simulation of liquid droplet breakup in supersonic flows
Liu, Nan; Wang, Zhenguo; Sun, Mingbo; Wang, Hongbo; Wang, Bing
2018-04-01
A five-equation model based on finite-difference frame was utilized to simulate liquid droplet breakup in supersonic flows. To enhance the interface-capturing quality, an anti-diffusion method was introduced as a correction of volume-fraction after each step of calculation to sharpen the interface. The robustness was guaranteed by the hybrid variable reconstruction in which the second-order and high-order method were respectively employed in discontinuous and continuous flow fields. According to the recent classification of droplet breakup regimes, the simulations lay in the shear induced entrainment regime. Comparing to the momentum of the high-speed air flows, surface tension and viscid force were negligible in both two-dimensional and three-dimensional simulations. The inflow conditions were set as Mach 1.2, 1.5 and 1.8 to reach different dynamic pressure with the liquid to gas density ratio being 1000 initially. According to the results of simulations, the breakup process was divided into three stages which were analyzed in details with the consideration of interactions between gas and liquid. The shear between the high-speed gas flow and the liquid droplet was found to be the sources of surface instabilities on windward, while the instabilities on the leeward side were originated by vortices. Movement of the liquid mass center was studied, and the unsteady acceleration was observed. In addition, the characteristic breakup time was around 1.0 based on the criterion of either droplet thickness or liquid volume fraction.
Target Lagrangian kinematic simulation for particle-laden flows.
Murray, S; Lightstone, M F; Tullis, S
2016-09-01
The target Lagrangian kinematic simulation method was motivated as a stochastic Lagrangian particle model that better synthesizes turbulence structure, relative to stochastic separated flow models. By this method, the trajectories of particles are constructed according to synthetic turbulent-like fields, which conform to a target Lagrangian integral timescale. In addition to recovering the expected Lagrangian properties of fluid tracers, this method is shown to reproduce the crossing trajectories and continuity effects, in agreement with an experimental benchmark.
Simulation of uncompressible fluid flow through a porous media
Energy Technology Data Exchange (ETDEWEB)
Ramirez, A. [Instituto Politecnico Nacional (SEPI-ESIQIE-IPN), Unidad Profesional Zacatenco, Laboratorio de Analisis Met. (Edif. ' Z' y Edif. ' 6' P.B.), Mexico City (Mexico)], E-mail: adaramil@yahoo.com.mx; Gonzalez, J.L. [Instituto Politecnico Nacional (SEPI-ESIQIE-IPN), Unidad Profesional Zacatenco, Laboratorio de Analisis Met. (Edif. ' Z' y Edif. ' 6' P.B.), Mexico City (Mexico); Carrillo, F. [Instituto Politecnico Nacional (SEPI-CICATA-IPN), Unidad Altamira Tamaulipas, Mexico (Mexico); Lopez, S. [Instituto Mexicano del Petroleo (I.M.P.-D.F.), Mexico (Mexico)
2009-02-28
Recently, a great interest has been focused for investigations about transport phenomena in disordered systems. One of the most treated topics is fluid flow through anisotropic materials due to the importance in many industrial processes like fluid flow in filters, membranes, walls, oil reservoirs, etc. In this work is described the formulation of a 2D mathematical model to simulate the fluid flow behavior through a porous media (PM) based on the solution of the continuity equation as a function of the Darcy's law for a percolation system; which was reproduced using computational techniques reproduced using a random distribution of the porous media properties (porosity, permeability and saturation). The model displays the filling of a partially saturated porous media with a new injected fluid showing the non-defined advance front and dispersion of fluids phenomena.
Simulation of uncompressible fluid flow through a porous media
International Nuclear Information System (INIS)
Ramirez, A.; Gonzalez, J.L.; Carrillo, F.; Lopez, S.
2009-01-01
Recently, a great interest has been focused for investigations about transport phenomena in disordered systems. One of the most treated topics is fluid flow through anisotropic materials due to the importance in many industrial processes like fluid flow in filters, membranes, walls, oil reservoirs, etc. In this work is described the formulation of a 2D mathematical model to simulate the fluid flow behavior through a porous media (PM) based on the solution of the continuity equation as a function of the Darcy's law for a percolation system; which was reproduced using computational techniques reproduced using a random distribution of the porous media properties (porosity, permeability and saturation). The model displays the filling of a partially saturated porous media with a new injected fluid showing the non-defined advance front and dispersion of fluids phenomena.
Application of corrosion screening tools for riser inspection
International Nuclear Information System (INIS)
Zamir Mohamed Daud; Vijayan, S.
2003-01-01
As offshore facilities approach the end of their design life, owners would like to assess the condition and integrity of plant and equipment. Detailed inspection, including non-destructive testing (NDT), are implemented and results are utilised for predictive maintenance and estimating useful remaining life. Except for risk based inspection, the extent of surface coverage required would be more compared to inspection of pre-determined spots. Risers, for example, usually have several layers of coating that prevent use of conventional techniques for inspection of corrosion. Complete coverage requires access (including removal coatings and insulation). Inspection utilising the conventional NDT tools can be very slow and expensive. However, recent advances have forwarded the use of specialised NDT techniques that were developed for inspection of corrosion under insulation (CUI). This paper details two screening inspection tools, LIXI Profiler and RTD-INCOTEST that have been applied to inspection of risers. LIXI Profiler is based on attenuation of penetrating radiation by materials, and RTD-INCOTEST is based on decay of pulsed eddy current in materials. (Author)
Lattice Boltzmann model for simulating immiscible two-phase flows
International Nuclear Information System (INIS)
Reis, T; Phillips, T N
2007-01-01
The lattice Boltzmann equation is often promoted as a numerical simulation tool that is particularly suitable for predicting the flow of complex fluids. This paper develops a two-dimensional 9-velocity (D2Q9) lattice Boltzmann model for immiscible binary fluids with variable viscosities and density ratio using a single relaxation time for each fluid. In the macroscopic limit, this model is shown to recover the Navier-Stokes equations for two-phase flows. This is achieved by constructing a two-phase component of the collision operator that induces the appropriate surface tension term in the macroscopic equations. A theoretical expression for surface tension is determined. The validity of this analysis is confirmed by comparing numerical and theoretical predictions of surface tension as a function of density. The model is also shown to predict Laplace's law for surface tension and Poiseuille flow of layered immiscible binary fluids. The spinodal decomposition of two fluids of equal density but different viscosity is then studied. At equilibrium, the system comprises one large low viscosity bubble enclosed by the more viscous fluid in agreement with theoretical arguments of Renardy and Joseph (1993 Fundamentals of Two-Fluid Dynamics (New York: Springer)). Two other simulations, namely the non-equilibrium rod rest and the coalescence of two bubbles, are performed to show that this model can be used to simulate two fluids with a large density ratio
An Improved Simulation of the Diurnally Varying Street Canyon Flow
Yaghoobian, Neda; Kleissl, Jan; Paw U, Kyaw Tha
2012-11-01
The impact of diurnal variation of temperature distribution over building and ground surfaces on the wind flow and scalar transport in street canyons is numerically investigated using the PArallelized LES Model (PALM). The Temperature of Urban Facets Indoor-Outdoor Building Energy Simulator (TUF-IOBES) is used for predicting urban surface heat fluxes as boundary conditions for a modified version of PALM. TUF-IOBES dynamically simulates indoor and outdoor building surface temperatures and heat fluxes in an urban area taking into account weather conditions, indoor heat sources, building and urban material properties, composition of the building envelope (e.g. windows, insulation), and HVAC equipment. Temperature (and heat flux) distribution over urban surfaces of the 3-D raster-type geometry of TUF-IOBES makes it possible to provide realistic, high resolution boundary conditions for the numerical simulation of flow and scalar transport in an urban canopy. Compared to some previous analyses using uniformly distributed thermal forcing associated with urban surfaces, the present analysis shows that resolving non-uniform thermal forcings can provide more detailed and realistic patterns of the local air flow and pollutant dispersion in urban canyons.
Numerical simulation on coolant flow and heat transfer in core
International Nuclear Information System (INIS)
Yao Zhaohui; Wang Xuefang; Shen Mengyu
1997-01-01
To simulate the coolant flow and the heat transfer characteristics of a core, a computer code, THAPMA (Thermal Hydraulic Analysis Porous Medium Analysis) has been developed. In THAPMA code, conservation equations are based on a porous-medium formulation, which uses four parameters, i.e, volume porosity, directional surface porosity, distributed resistance, and distributed heat source (sink), to model the effects of fuel rods and other internal solid structures on flow and heat transfer. Because the scheme and the solution are very important in accuracy and speed of calculation, a new difference scheme (WSUC) has been used in the energy equation, and a modified PISO solution method have been employed to simulate the steady/transient states. The code has been proved reliable and can effectively solve the transient state problem by several numerical tests. According to the design of Qinshan NPP-II, the flow and heat transfer phenomena in reactor core have been numerically simulated. The distributions of the velocity and the temperature can provide a theoretical basis for core design and safety analysis
Framework for simulating droplet vaporization in turbulent flows
Palmore, John; Desjardins, Olivier
2017-11-01
A framework for performing direct numerical simulations of droplet vaporization is presented. The work is motivated by spray combustion in engines wherein fuel droplets vaporize in a turbulent gas flow. The framework is built into a conservative finite volume code for simulating low Mach number turbulent multiphase flows. Phase tracking is performed using a discretely conservative geometric volume of fluid method, while the transport of mass fraction and temperature is performed using the BQUICK scheme. Special attention is given to the implementation of transport equations near the interface to ensure the consistency between fluxes of mass, momentum, and scalars. The effect of evaporation on the flow appears as a system of coupled source terms which depend on the local thermodynamic equilibrium between the phases. The sources are implemented implicitly using an unconditionally stable, monotone scheme. Two methodologies for resolving the system's thermodynamic equilibrium are compared for their accuracy, robustness, and computational expense. Verification is performed by comparing results to known solutions in one and three dimensions. Finally, simulations of droplets vaporizing in turbulence are demonstrated, and trends for mass fraction and temperature fields are discussed.
Numerical simulation of secondary flow in bubbly turbulent flow in sub-channel
International Nuclear Information System (INIS)
Ikeno, Tsutomu; Kataoka, Isao
2009-01-01
Secondary flow in bubbly turbulent flow in sub-channel was simulated by using an algebraic turbulence stress model. The mass, momentum, turbulence energy and bubble diffusion equations were used as fundamental equation. The basis for these equations was the two-fluid model: the equation of liquid phase was picked up from the equation system theoretically derived for the gas-liquid two-fluid turbulent flow. The fundamental equation was transformed onto a generalized coordinate system fitted to the computational domain in sub-channel. It was discretized for the SIMPLE algorism using the finite-volume method. The shape of sub-channel causes a distortion of the computational mesh, and orthogonal nature of the mesh is sometimes broken. An iterative method to satisfy a requirement for the contra-variant velocity was introduced to represent accurate symmetric boundary condition. Two-phase flow at a steady state was simulated for different magnitude of secondary flow and void fraction. The secondary flow enhanced the momentum transport in sub-channel and accelerated the liquid phase in the rod gap. This effect was slightly mitigated when the void fraction increased. The acceleration can contribute to effective cooling in the rod gap. The numerical result implied a phenomenon of industrial interest. This suggested that experimental approach is necessary to validate the numerical model and to identify the phenomenon. (author)
Leakage flow simulation in a specific pump model
International Nuclear Information System (INIS)
Dupont, P; Bayeul-Lainé, A C; Dazin, A; Bois, G; Roussette, O; Si, Q
2014-01-01
This paper deals with the influence of leakage flow existing in SHF pump model on the analysis of internal flow behaviour inside the vane diffuser of the pump model performance using both experiments and calculations. PIV measurements have been performed at different hub to shroud planes inside one diffuser channel passage for a given speed of rotation and various flow rates. For each operating condition, the PIV measurements have been trigged with different angular impeller positions. The performances and the static pressure rise of the diffuser were also measured using a three-hole probe. The numerical simulations were carried out with Star CCM+ 8.06 code (RANS frozen and unsteady calculations). Comparisons between numerical and experimental results are presented and discussed for three flow rates. The performances of the diffuser obtained by numerical simulation results are compared to the performances obtained by three-hole probe indications. The comparisons show few influence of fluid leakage on global performances but a real improvement concerning the efficiency of the impeller, the pump and the velocity distributions. These results show that leakage is an important parameter that has to be taken into account in order to make improved comparisons between numerical approaches and experiments in such a specific model set up
SIPSON--simulation of interaction between pipe flow and surface overland flow in networks.
Djordjević, S; Prodanović, D; Maksimović, C; Ivetić, M; Savić, D
2005-01-01
The new simulation model, named SIPSON, based on the Preissmann finite difference method and the conjugate gradient method, is presented in the paper. This model simulates conditions when the hydraulic capacity of a sewer system is exceeded, pipe flow is pressurized, the water flows out from the piped system to the streets, and the inlets cannot capture all the runoff. In the mathematical model, buried structures and pipelines, together with surface channels, make a horizontally and vertically looped network involving a complex interaction of flows. In this paper, special internal boundary conditions related to equivalent inlets are discussed. Procedures are described for the simulation of manhole cover loss, basement flooding, the representation of street geometry, and the distribution of runoff hydrographs between surface and underground networks. All these procedures are built into the simulation model. Relevant issues are illustrated on a set of examples, focusing on specific parameters and comparison with field measurements of flooding of the Motilal ki Chal catchment (Indore, India). Satisfactory agreement of observed and simulated hydrographs and maximum surface flooding levels is obtained. It is concluded that the presented approach is an improvement compared to the standard "virtual reservoir" approach commonly applied in most of the models.
Numerical simulation of travelling wave induced electrothermal fluid flow
International Nuclear Information System (INIS)
Perch-Nielsen, Ivan R; Green, Nicolas G; Wolff, Anders
2004-01-01
Many microdevices for manipulating particles and cells use electric fields to produce a motive force on the particles. The movement of particles in non-uniform electric fields is called dielectrophoresis, and the usual method of applying this effect is to pass the particle suspension over a microelectrode structure. If the suspension has a noticeable conductivity, one important side effect is that the electric field drives a substantial conduction current through the fluid, causing localized Joule-heating. The resulting thermal gradient produces local conductivity and permittivity changes in the fluid. Dielectrophoretic forces acting upon these pockets of fluid will then produce motion of both the fluid and the particles. This paper presents a numerical solution of the electrical force and the resulting electrothermal driven fluid flow on a travelling wave structure. This common electrode geometry consists of interdigitated electrodes laid down in a long array, with the phase of the applied potential shifted by 90 0 on each subsequent electrode. The resulting travelling electric field was simulated and the thermal field and electrical body force on the fluid calculated, for devices constructed from two typical materials: silicon and glass. The electrothermal fluid flow in the electrolyte over the electrode array was then numerically simulated. The model predicts that the thermal field depends on the conductivity and applied voltage, but more importantly on the geometry of the system and the material used in the construction of the device. The velocity of the fluid flow depends critically on the same parameters, with slight differences in the thermal field for glass and silicon leading to diametrically opposite flow direction with respect to the travelling field for the two materials. In addition, the imposition of slight external temperature gradients is shown to have a large effect on the fluid flow in the device, under certain conditions leading to a reversal of
Direct Numerical Simulation of Low Capillary Number Pore Scale Flows
Esmaeilzadeh, S.; Soulaine, C.; Tchelepi, H.
2017-12-01
The arrangement of void spaces and the granular structure of a porous medium determines multiple macroscopic properties of the rock such as porosity, capillary pressure, and relative permeability. Therefore, it is important to study the microscopic structure of the reservoir pores and understand the dynamics of fluid displacements through them. One approach for doing this, is direct numerical simulation of pore-scale flow that requires a robust numerical tool for prediction of fluid dynamics and a detailed understanding of the physical processes occurring at the pore-scale. In pore scale flows with a low capillary number, Eulerian multiphase methods are well-known to produce additional vorticity close to the interface. This is mainly due to discretization errors which lead to an imbalance of capillary pressure and surface tension forces that causes unphysical spurious currents. At the pore scale, these spurious currents can become significantly stronger than the average velocity in the phases, and lead to unphysical displacement of the interface. In this work, we first investigate the capability of the algebraic Volume of Fluid (VOF) method in OpenFOAM for low capillary number pore scale flow simulations. Afterward, we compare VOF results with a Coupled Level-Set Volume of Fluid (CLSVOF) method and Iso-Advector method. It has been shown that the former one reduces the VOF's unphysical spurious currents in some cases, and both are known to capture interfaces sharper than VOF. As the conclusion, we will investigate that whether the use of CLSVOF or Iso-Advector will lead to less spurious velocities and more accurate results for capillary driven pore-scale multiphase flows or not. Keywords: Pore-scale multiphase flow, Capillary driven flows, Spurious currents, OpenFOAM
CFD simulation of neutral ABL flows; Atmospheric Boundary Layer
Energy Technology Data Exchange (ETDEWEB)
Xiaodong Zhang
2009-04-15
This work is to evaluate the CFD prediction of Atmospheric Boundary Layer flow field over different terrains employing Fluent 6.3 software. How accurate the simulation could achieve depend on following aspects: viscous model, wall functions, agreement of CFD model with inlet wind velocity profile and top boundary condition. Fluent employ wall function roughness modifications based on data from experiments with sand grain roughened pipes and channels, describe wall adjacent zone with Roughness Height (Ks) instead of Roughness Length (z{sub 0}). In a CFD simulation of ABL flow, the mean wind velocity profile is generally described with either a logarithmic equation by the presence of aerodynamic roughness length z{sub 0} or an exponential equation by the presence of exponent. As indicated by some former researchers, the disagreement between wall function model and ABL velocity profile description will result in some undesirable gradient along flow direction. There are some methods to improve the simulation model in literatures, some of them are discussed in this report, but none of those remedial methods are perfect to eliminate the streamwise gradients in mean wind speed and turbulence, as EllipSys3D could do. In this paper, a new near wall treatment function is designed, which, in some degree, can correct the horizontal gradients problem. Based on the corrected model constants and near wall treatment function, a simulation of Askervein Hill is carried out. The wind condition is neutrally stratified ABL and the measurements are best documented until now. Comparison with measured data shows that the CFD model can well predict the velocity field and relative turbulence kinetic energy field. Furthermore, a series of artificial complex terrains are designed, and some of the main simulation results are reported. (au)
Shear flow simulations of biaxial nematic liquid crystals
Sarman, Sten
1997-08-01
We have calculated the viscosities of a biaxial nematic liquid crystal phase of a variant of the Gay-Berne fluid [J. G. Gay and B. J. Berne, J. Chem. Phys. 74, 3316 (1981)] by performing molecular dynamics simulations. The equations of motion have been augmented by a director constraint torque that fixes the orientation of the directors. This makes it possible to fix them at different angles relative to the stream lines in shear flow simulations. In equilibrium simulations the constraints generate a new ensemble. One finds that the Green-Kubo relations for the viscosities become linear combinations of time correlation function integrals in this ensemble whereas they are complicated rational functions in the conventional canonical ensemble. We have evaluated these Green-Kubo relations for all the shear viscosities and all the twist viscosities. We have also calculated the alignment angles, which are functions of the viscosity coefficients. We find that there are three real alignment angles but a linear stability analysis shows that only one of them corresponds to a stable director orientation. The Green-Kubo results have been cross checked by nonequilibrium shear flow simulations. The results from the different methods agree very well. Finally, we have evaluated the Miesowicz viscosities [D. Baalss, Z. Naturforsch. Teil A 45, 7 (1990)]. They vary by more than 2 orders of magnitude. The viscosity is consequently highly orientation dependent.
Simulation of flow in dual-scale porous media
Tan, Hua
Liquid composite molding (LCM) is one of the most effective processes for manufacturing near net-shaped parts from fiber-reinforced polymer composites. The quality of LCM products and the efficiency of the process depend strongly on the wetting of fiber preforms during the mold-filling stage of LCM. Mold-filling simulation is a very effective approach to optimize the LCM process and mold design. Recent studies have shown that the flow modeling for the single-scale fiber preforms (made from random mats) has difficulties in accurately predicting the wetting in the dual-scale fiber preforms (made from woven and stitched fabrics); the latter are characterized by the presence of unsaturated flow created due to two distinct length-scales of pores (i.e., large pores outside the tows and small pores inside the tows) in the same media. In this study, we first develop a method to evaluate the accuracy of the permeability-measuring devices for LCM, and conduct a series of 1-D mold-filling experiments for different dual-scale fabrics. The volume averaging method is then applied to derive the averaged governing equations for modeling the macroscopic flow through the dual-scale fabrics. The two sets of governing equations are coupled with each other through the sink terms representing the absorptions of mass, energy, and species (degree of resin cure) from the global flow by the local fiber tows. The finite element method (FEM) coupled with the control volume method, also known as the finite element/control volume (FE/CV) method, is employed to solve the governing equations and track the moving boundary signifying the moving liquid-front. The numerical computations are conducted with the help of an in-house developed computer program called PORE-FLOW(c). We develop the flux-corrected transport (FCT) based FEM to stabilize the convection-dominated energy and species equations. A fast methodology is proposed to simulate the dual-scale flow under isothermal conditions, where flow
Numerical simulation of fluid flow in microporous media
International Nuclear Information System (INIS)
Xu Ruina; Jiang Peixue
2008-01-01
The flow characteristics of water and air in microporous media with average diameters of 200 μm, 125 μm, 90 μm, 40 μm, 20 μm, and 10 μm were studied numerically. The calculated friction factors for water and air in the non-slip-flow regime in the microporous media agree well with the known correlation suitable for normal size porous media. The numerically predicted friction factors for air in the slip-flow regime in the microporous media with 90 μm, 40 μm, 20 μm, and 10 μm diameter particles were less than the correlation for normal size porous media but close to experimental data and a modified correlation that accounts for rarefaction. Comparisons of the numerical results with the experimental data and the modified correlations show that rarefaction effects occur in air flows in the microporous media with particle diameters less than 90 μm and that the numerical calculations with velocity slip on the boundary can properly simulate the fluid flow in microporous media
Water flow simulation and analysis in HMA microstructure
Directory of Open Access Journals (Sweden)
Can Chen
2014-10-01
Full Text Available This paper introduces a new method for reconstructing virtual two-dimensional (2-D microstructure of hot mix asphalt (HMA. Based on the method, the gradation of coarse aggregates and the film thickness of the asphalt binder can be defined by the user. The HMA microstructure then serves as the input to the computational fluid dynamic (CFD software (ANSYS-FLUENT to investigate the water flow pattern through it. It is found that the realistic flow fields can be simulated in the 2-D micro-structure and the flow patterns in some typical air void structures can be identified. These flow patterns can be used to explain the mechanism that could result in moisture damage in HMA pavement. The one-dimensional numerical permeability values are also derived from the flow fields of the 2-D HMA microstructure and compared with the measured values obtained by the Karol-Warner permeameter. Because the interconnected air voids channels in actual HMA samples cannot be fully represented in a 2-D model, some poor agreements need to be improved.
The inhomogeneous MUSIG model for the simulation of polydispersed flows
International Nuclear Information System (INIS)
Krepper, Eckhard; Lucas, Dirk; Frank, Thomas; Prasser, Horst-Michael; Zwart, Phil J.
2008-01-01
A generalized inhomogeneous multiple size group (MUSIG) model based on the Eulerian modeling framework was developed in close cooperation of ANSYS-CFX and Forschungszentrum Dresden-Rossendorf and implemented into the CFD code CFX. The model enables the subdivision of the dispersed phase into a number of size groups regarding the mass balance as well as regarding the momentum balance. In this work, the special case of polydispersed bubbly flow is considered. By simulating such flows, the mass exchanged between bubble size classes by bubble coalescence and bubble fragmentation, as well as the momentum transfer between the bubbles and the surrounding liquid due to bubble size dependent interfacial forces have to be considered. Particularly the lift force has been proven to play an important role in establishing a certain bubble size distribution dependent flow regime. In a previous study [Krepper, E., Lucas, D., Prasser, H.-M., 2005. On the modeling of bubbly flow in vertical pipes. Nucl. Eng. Des. 235, 597-611] the application of such effects were considered and justified and a general outline of such a model concept was given. In this paper the model and its validation for several vertical pipe flow situations is presented. The experimental data were obtained from the TOPFLOW test facility at the Forschungszentrum Dresden-Rossendorf (FZD). The wire-mesh technology measuring local gas volume fractions, bubble size distributions and velocities of gas and liquid phases were employed. The inhomogeneous MUSIG model approach was shown as capable of describing bubbly flows with higher gas content. Particularly the separation phenomenon of small and large bubbles is well described. This separation has been proven as a key phenomenon in the establishment of the corresponding flow regime. Weaknesses in this approach can be attributed to the characterization of bubble coalescence and bubble fragmentation, which must be further investigated
Adapting HYDRUS-1D to Simulate Overland Flow and Reactive Transport During Sheet Flow Deviations
Liang, J.; Bradford, S. A.; Simunek, J.; Hartmann, A.
2017-12-01
The HYDRUS-1D code is a popular numerical model for solving the Richards equation for variably-saturated water flow and solute transport in porous media. This code was adapted to solve rather than the Richards equation for subsurface flow the diffusion wave equation for overland flow at the soil surface. The numerical results obtained by the new model produced an excellent agreement with the analytical solution of the kinematic wave equation. Model tests demonstrated its applicability to simulate the transport and fate of many different solutes, such as non-adsorbing tracers, nutrients, pesticides, and microbes. However, the diffusion wave or kinematic wave equations describe surface runoff as sheet flow with a uniform depth and velocity across the slope. In reality, overland water flow and transport processes are rarely uniform. Local soil topography, vegetation, and spatial soil heterogeneity control directions and magnitudes of water fluxes, and strongly influence runoff characteristics. There is increasing evidence that variations in soil surface characteristics influence the distribution of overland flow and transport of pollutants. These spatially varying surface characteristics are likely to generate non-equilibrium flow and transport processes. HYDRUS-1D includes a hierarchical series of models of increasing complexity to account for both physical equilibrium and non-equilibrium, e.g., dual-porosity and dual-permeability models, up to a dual-permeability model with immobile water. The same conceptualization as used for the subsurface was implemented to simulate non-equilibrium overland flow and transport at the soil surface. The developed model improves our ability to describe non-equilibrium overland flow and transport processes and to improves our understanding of factors that cause this behavior. The HYDRUS-1D overland flow and transport model was additionally also extended to simulate soil erosion. The HYDRUS-1D Soil Erosion Model has been verified by
Multiscale Simulation Framework for Coupled Fluid Flow and Mechanical Deformation
Energy Technology Data Exchange (ETDEWEB)
Hou, Thomas [California Inst. of Technology (CalTech), Pasadena, CA (United States); Efendiev, Yalchin [Stanford Univ., CA (United States); Tchelepi, Hamdi [Texas A & M Univ., College Station, TX (United States); Durlofsky, Louis [Stanford Univ., CA (United States)
2016-05-24
Our work in this project is aimed at making fundamental advances in multiscale methods for flow and transport in highly heterogeneous porous media. The main thrust of this research is to develop a systematic multiscale analysis and efficient coarse-scale models that can capture global effects and extend existing multiscale approaches to problems with additional physics and uncertainties. A key emphasis is on problems without an apparent scale separation. Multiscale solution methods are currently under active investigation for the simulation of subsurface flow in heterogeneous formations. These procedures capture the effects of fine-scale permeability variations through the calculation of specialized coarse-scale basis functions. Most of the multiscale techniques presented to date employ localization approximations in the calculation of these basis functions. For some highly correlated (e.g., channelized) formations, however, global effects are important and these may need to be incorporated into the multiscale basis functions. Other challenging issues facing multiscale simulations are the extension of existing multiscale techniques to problems with additional physics, such as compressibility, capillary effects, etc. In our project, we explore the improvement of multiscale methods through the incorporation of additional (single-phase flow) information and the development of a general multiscale framework for flows in the presence of uncertainties, compressible flow and heterogeneous transport, and geomechanics. We have considered (1) adaptive local-global multiscale methods, (2) multiscale methods for the transport equation, (3) operator-based multiscale methods and solvers, (4) multiscale methods in the presence of uncertainties and applications, (5) multiscale finite element methods for high contrast porous media and their generalizations, and (6) multiscale methods for geomechanics.
Energy Technology Data Exchange (ETDEWEB)
Wang, Shiming; Ren, Cheng; Sun, Yangfei [Institute of Nuclear and New Energy Technology of Tsinghua University, Collaborative Innovation Center of Advanced Nuclear Energy Technology, Key Laboratory of Advanced Reactor Engineering and Safety of Ministry of Education, Beijing 100084 (China); Tu, Jiyuan [Institute of Nuclear and New Energy Technology of Tsinghua University, Collaborative Innovation Center of Advanced Nuclear Energy Technology, Key Laboratory of Advanced Reactor Engineering and Safety of Ministry of Education, Beijing 100084 (China); School of Aerospace, Mechanical & Manufacturing Engineering, RMIT University, Melbourne, VIC 3083 (Australia); Yang, Xingtuan, E-mail: yangxt107@sina.com [Institute of Nuclear and New Energy Technology of Tsinghua University, Collaborative Innovation Center of Advanced Nuclear Energy Technology, Key Laboratory of Advanced Reactor Engineering and Safety of Ministry of Education, Beijing 100084 (China)
2016-08-15
Highlights: • The flow confluence process in the steam generator is very important for HTR-PM. • The complicated flow in the unique pipeline configuration is studied by both of experimental and numerical method. • The pressure uniformity at the bottom of the model was tested to evaluate the accuracy of the experimental results. • Flow separation and the secondary flow is described for explaining the nonuniformity of the flow distribution. - Abstract: The helium flow measurement method is very important for the design of HTR-PM. Water experiments and numerical simulation with a 1/5 scaled model are conducted to investigate the flow measurement method utilized in the steam generator of HTR-PM. Pressure information at specific location of the 90° elbows with the diameter of 46.75 mm and radius ratio of 1.5 is measured to evaluate the flow rate in the riser-pipes. Pressure uniformity at the bottom of the experimental apparatus is tested to evaluate the influence of the equipment error on the final experimental results. Numerical results obtained by using the realizable k–ε model are compared with the experimental data. The results reveal that flow oscillation does not occur in the confluence system. For every single riser-pipe, the flow is stable despite the nonuniformity of the flow distribution. The average flow rates of the two pipe series show good repeatability regardless of the increases and decreases of the average velocity. In the header box, the flows out of the riser-pipes encounter with each other and finally distort the pressure distribution and the nonuniformity of the flow distribution becomes more significant along with the increasing Reynolds number.
Numerical simulation of flow-induced vibrations in tube bundles
International Nuclear Information System (INIS)
Elisabeth Longatte; Zaky Bendjeddou; Mhamed Souli
2005-01-01
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
Cao, Guoliang; Han, Dongmei; Currell, Matthew J.; Zheng, Chunmiao
2016-09-01
Groundwater flow in deep sedimentary basins results from complex evolution processes on geological timescales. Groundwater flow systems conceptualized according to topography and/or groundwater table configuration generally assume a near-equilibrium state with the modern landscape. However, the time to reach such a steady state, and more generally the timescales of groundwater flow system evolution are key considerations for large sedimentary basins. This is true in the North China Basin (NCB), which has been studied for many years due to its importance as a groundwater supply. Despite many years of study, there remain contradictions between the generally accepted conceptual model of regional flow, and environmental tracer data. We seek to reconcile these contractions by conducting simulations of groundwater flow, age and heat transport in a three dimensional model, using an alternative conceptual model, based on geological, thermal, isotope and historical data. We infer flow patterns under modern hydraulic conditions using this new model and present the theoretical maximum groundwater ages under such a flow regime. The model results show that in contrast to previously accepted conceptualizations, most groundwater is discharged in the vicinity of the break-in-slope of topography at the boundary between the piedmont and central plain. Groundwater discharge to the ocean is in contrast small, and in general there are low rates of active flow in the eastern parts of the basin below the central and coastal plain. This conceptualization is more compatible with geochemical and geothermal data than the previous model. Simulated maximum groundwater ages of ∼1 Myrs below the central and coastal plain indicate that residual groundwater may be retained in the deep parts of the basin since being recharged during the last glacial period or earlier. The groundwater flow system has therefore probably not reached a new equilibrium state with modern-day hydraulic conditions. The
Direct Numerical Simulations of Particle-Laden Turbulent Channel Flow
Jebakumar, Anand Samuel; Premnath, Kannan; Abraham, John
2017-11-01
In a recent experimental study, Lau and Nathan (2014) reported that the distribution of particles in a turbulent pipe flow is strongly influenced by the Stokes number (St). At St lower than 1, particles migrate toward the wall and at St greater than 10 they tend to migrate toward the axis. It was suggested that this preferential migration of particles is due to two forces, the Saffman lift force and the turbophoretic force. Saffman lift force represents a force acting on the particle as a result of a velocity gradient across the particle when it leads or lags the fluid flow. Turbophoretic force is induced by turbulence which tends to move the particle in the direction of decreasing turbulent kinetic energy. In this study, the Lattice Boltzmann Method (LBM) is employed to simulate a particle-laden turbulent channel flow through Direct Numerical Simulations (DNS). We find that the preferential migration is a function of particle size in addition to the St. We explain the effect of the particle size and St on the Saffman lift force and turbophoresis and present how this affects particle concentration at different conditions.
Rarefield gas dynamics fundamentals, simulations and micro flows
Shen, Ching
2006-01-01
This book elucidates the methods of molecular gas dynamics or rarefied gas dynamics which treat the problems of gas flows when the discrete molecular effects of the gas prevail under the circumstances of low density, the emphasis being on the basis of the methods, the direct simulation Monte Carlo method applied to the simulation of non-equilibrium effects and the frontier subjects related to low speed microscale rarefied gas flows. It provides a solid basis for the study of molecular gas dynamics for senior students and graduates in the aerospace and mechanical engineering departments of universities and colleges. It gives a general acquaintance of modern developments of rarefied gas dynamics in various regimes and leads to the frontier topics of non-equilibrium rarefied gas dynamics and low speed microscale gas dynamics. It will be also of benefit to the scientific and technical researchers engaged in aerospace high altitude aerodynamic force and heating design and in the research on gas flow in MEMS.
Uncertainty in simulated groundwater-quality trends in transient flow
Starn, J. Jeffrey; Bagtzoglou, Amvrossios; Robbins, Gary A.
2013-01-01
In numerical modeling of groundwater flow, the result of a given solution method is affected by the way in which transient flow conditions and geologic heterogeneity are simulated. An algorithm is demonstrated that simulates breakthrough curves at a pumping well by convolution-based particle tracking in a transient flow field for several synthetic basin-scale aquifers. In comparison to grid-based (Eulerian) methods, the particle (Lagrangian) method is better able to capture multimodal breakthrough caused by changes in pumping at the well, although the particle method may be apparently nonlinear because of the discrete nature of particle arrival times. Trial-and-error choice of number of particles and release times can perhaps overcome the apparent nonlinearity. Heterogeneous aquifer properties tend to smooth the effects of transient pumping, making it difficult to separate their effects in parameter estimation. Porosity, a new parameter added for advective transport, can be accurately estimated using both grid-based and particle-based methods, but predictions can be highly uncertain, even in the simple, nonreactive case.
Stochastic Rotation Dynamics simulations of wetting multi-phase flows
Hiller, Thomas; Sanchez de La Lama, Marta; Brinkmann, Martin
2016-06-01
Multi-color Stochastic Rotation Dynamics (SRDmc) has been introduced by Inoue et al. [1,2] as a particle based simulation method to study the flow of emulsion droplets in non-wetting microchannels. In this work, we extend the multi-color method to also account for different wetting conditions. This is achieved by assigning the color information not only to fluid particles but also to virtual wall particles that are required to enforce proper no-slip boundary conditions. To extend the scope of the original SRDmc algorithm to e.g. immiscible two-phase flow with viscosity contrast we implement an angular momentum conserving scheme (SRD+mc). We perform extensive benchmark simulations to show that a mono-phase SRDmc fluid exhibits bulk properties identical to a standard SRD fluid and that SRDmc fluids are applicable to a wide range of immiscible two-phase flows. To quantify the adhesion of a SRD+mc fluid in contact to the walls we measure the apparent contact angle from sessile droplets in mechanical equilibrium. For a further verification of our wettability implementation we compare the dewetting of a liquid film from a wetting stripe to experimental and numerical studies of interfacial morphologies on chemically structured surfaces.
The PDF method for Lagrangian two-phase flow simulations
International Nuclear Information System (INIS)
Minier, J.P.; Pozorski, J.
1996-04-01
A recent turbulence model put forward by Pope (1991) in the context of PDF modelling has been used. In this approach, the one-point joint velocity-dissipation pdf equation is solved by simulating the instantaneous behaviour of a large number of Lagrangian fluid particles. Closure of the evolution equations of these Lagrangian particles is based on stochastic models and more specifically on diffusion processes. Such models are of direct use for two-phase flow modelling where the so-called fluid seen by discrete inclusions has to be modelled. Full Lagrangian simulations have been performed for shear-flows. It is emphasized that this approach gives far more information than traditional turbulence closures (such as the K-ε model) and therefore can be very useful for situations involving complex physics. It is also believed that the present model represents the first step towards a complete Lagrangian-Lagrangian model for dispersed two-phase flow problems. (authors). 21 refs., 6 figs
Simulation of swimming strings immersed in a viscous fluid flow
Huang, Wei-Xi; Sung, Hyung Jin
2006-11-01
In nature, many phenomena involve interactions between flexible bodies and their surrounding viscous fluid, such as a swimming fish or a flapping flag. The intrinsic dynamics is complicate and not well understood. A flexible string can be regarded as a one-dimensional flag model. Many similarities can be found between the flapping string and swimming fish, although different wake speed results in a drag force for the flapping string and a propulsion force for the swimming fish. In the present study, we propose a mathematical formulation for swimming strings immersed in a viscous fluid flow. Fluid motion is governed by the Navier-Stokes equations and a momentum forcing is added in order to bring the fluid to move at the same velocity with the immersed surface. A flexible inextensible string model is described by another set of equations with an additional momentum forcing which is a result of the fluid viscosity and the pressure difference across the string. The momentum forcing is calculated by a feedback loop. Simulations of several numerical examples are carried out, including a hanging string which starts moving under gravity without ambient fluid, a swinging string immersed in a quiescent viscous fluid, a string swimming within a uniform surrounding flow, and flow over two side-by-side strings. The numerical results agree well with the theoretical analysis and previous experimental observations. Further simulation of a swimming fish is under consideration.
Simulation of dilated heart failure with continuous flow circulatory support.
Directory of Open Access Journals (Sweden)
Yajuan Wang
Full Text Available Lumped parameter models have been employed for decades to simulate important hemodynamic couplings between a left ventricular assist device (LVAD and the native circulation. However, these studies seldom consider the pathological descending limb of the Frank-Starling response of the overloaded ventricle. This study introduces a dilated heart failure model featuring a unimodal end systolic pressure-volume relationship (ESPVR to address this critical shortcoming. The resulting hemodynamic response to mechanical circulatory support are illustrated through numerical simulations of a rotodynamic, continuous flow ventricular assist device (cfVAD coupled to systemic and pulmonary circulations with baroreflex control. The model further incorporated septal interaction to capture the influence of left ventricular (LV unloading on right ventricular function. Four heart failure conditions were simulated (LV and bi-ventricular failure with/without pulmonary hypertension in addition to normal baseline. Several metrics of LV function, including cardiac output and stroke work, exhibited a unimodal response whereby initial unloading improved function, and further unloading depleted preload reserve thereby reducing ventricular output. The concept of extremal loading was introduced to reflect the loading condition in which the intrinsic LV stroke work is maximized. Simulation of bi-ventricular failure with pulmonary hypertension revealed inadequacy of LV support alone. These simulations motivate the implementation of an extremum tracking feedback controller to potentially optimize ventricular recovery.
Energy Technology Data Exchange (ETDEWEB)
Bahiense, Rodrigo A.; Rodrigues, Marcos V. [Det Norske Veritas (DNV), Rio de Janeiro, RJ (Brazil)
2008-07-01
Due to adoption of oil and gas production systems to deep and ultra-deep water, achieving frontiers that were not conceivable before, research in computational methods has contributed to implementation of sophisticated and efficient numerical tools in order to perform simulations considering those operational conditions. Thus, this work presents a steel catenary riser (SCR) design which is connected to a semi-submersible platform where the applied motions to SCR are obtained from analyses based on de-coupled and coupled methodologies. With increase of the line number of the system and water depth, the effects due to coupling of the lines on the platform motions are significant. It can be observed from performed evaluations for a floating production system, comparing the obtained results for SCR under extreme and fatigue conditions when it was submitted to the platform motions considering both methodologies mentioned. So, from the results obtained it can be concluded that for production system evaluated the adoption of decoupled methodology presents more conservative results. Thus the adoption of the coupled model associated to design practice of production lines presents as an alternative more realist and accurate to provide the optimization in the design of these structures. (author)
Computer simulation of two-phase flow in nuclear reactors
International Nuclear Information System (INIS)
Wulff, W.
1993-01-01
Two-phase flow models dominate the requirements of economic resources for the development and use of computer codes which serve to analyze thermohydraulic transients in nuclear power plants. An attempt is made to reduce the effort of analyzing reactor transients by combining purpose-oriented modelling with advanced computing techniques. Six principles are presented on mathematical modeling and the selection of numerical methods, along with suggestions on programming and machine selection, all aimed at reducing the cost of analysis. Computer simulation is contrasted with traditional computer calculation. The advantages of run-time interactive access operation in a simulation environment are demonstrated. It is explained that the drift-flux model is better suited than the two-fluid model for the analysis of two-phase flow in nuclear reactors, because of the latter's closure problems. The advantage of analytical over numerical integration is demonstrated. Modeling and programming techniques are presented which minimize the number of needed arithmetical and logical operations and thereby increase the simulation speed, while decreasing the cost. (orig.)
Fluid Flow Simulation and Energetic Analysis of Anomalocarididae Locomotion
Mikel-Stites, Maxwell; Staples, Anne
2014-11-01
While an abundance of animal locomotion simulations have been performed modeling the motions of living arthropods and aquatic animals, little quantitative simulation and reconstruction of gait parameters has been done to model the locomotion of extinct animals, many of which bear little physical resemblance to their modern descendants. To that end, this project seeks to analyze potential swimming patterns used by the anomalocaridid family, (specifically Anomalocaris canadensis, a Cambrian Era aquatic predator), and determine the most probable modes of movement. This will serve to either verify or cast into question the current assumed movement patterns and properties of these animals and create a bridge between similar flexible-bodied swimmers and their robotic counterparts. This will be accomplished by particle-based fluid flow simulations of the flow around the fins of the animal, as well as an energy analysis of a variety of sample gaits. The energy analysis will then be compared to the extant information regarding speed/energy use curves in an attempt to determine which modes of swimming were most energy efficient for a given range of speeds. These results will provide a better understanding of how these long-extinct animals moved, possibly allowing an improved understanding of their behavioral patterns, and may also lead to a novel potential platform for bio-inspired underwater autonomous vehicles (UAVs).
Lattice Boltzmann accelerated direct simulation Monte Carlo for dilute gas flow simulations.
Di Staso, G; Clercx, H J H; Succi, S; Toschi, F
2016-11-13
Hybrid particle-continuum computational frameworks permit the simulation of gas flows by locally adjusting the resolution to the degree of non-equilibrium displayed by the flow in different regions of space and time. In this work, we present a new scheme that couples the direct simulation Monte Carlo (DSMC) with the lattice Boltzmann (LB) method in the limit of isothermal flows. The former handles strong non-equilibrium effects, as they typically occur in the vicinity of solid boundaries, whereas the latter is in charge of the bulk flow, where non-equilibrium can be dealt with perturbatively, i.e. according to Navier-Stokes hydrodynamics. The proposed concurrent multiscale method is applied to the dilute gas Couette flow, showing major computational gains when compared with the full DSMC scenarios. In addition, it is shown that the coupling with LB in the bulk flow can speed up the DSMC treatment of the Knudsen layer with respect to the full DSMC case. In other words, LB acts as a DSMC accelerator.This article is part of the themed issue 'Multiscale modelling at the physics-chemistry-biology interface'. © 2016 The Author(s).
Macro-Micro Simulation for Polymer Crystallization in Couette Flow
Directory of Open Access Journals (Sweden)
Chunlei Ruan
2017-12-01
Full Text Available Polymer crystallization in manufacturing is a process where quiescent crystallization and flow-induced crystallization coexists, and heat/mass transfer on a macroscopic level interacts with crystal morphology evolution on a microscopic level. Previous numerical studies on polymer crystallization are mostly concentrated at a single scale; they only calculate macroscale parameters, e.g., temperature and relative crystallinity, or they only predict microstructure details, e.g., crystal morphology and mean size of crystals. The multi-scale numerical works that overcome these disadvantages are unfortunately based on quiescent crystallization, in which flow effects are neglected. The objective of this work is to build up a macro-micro model and a macro-micro algorithm to consider both the thermal and flow effects on the crystallization. Our macro-micro model couples two parts: mass and heat transfer of polymeric flow at the macroscopic level, and nucleation and growth of spherulites and shish-kebabs at the microscopic level. Our macro-micro algorithm is a hybrid finite volume/Monte Carlo method, in which the finite volume method is used at the macroscopic level to calculate the flow and temperature fields, while the Monte Carlo method is used at the microscopic level to capture the development of spherulites and shish-kebabs. The macro-micro model and the macro-micro algorithm are applied to simulate polymer crystallization in Couette flow. The effects of shear rate, shear time, and wall temperature on the crystal morphology and crystallization kinetics are also discussed.
Periodic transonic flow simulation using fourier-based algorithm
International Nuclear Information System (INIS)
Mohaghegh, Mohammad Reza; Malekjafarian, Majid
2014-01-01
The present research simulates time-periodic unsteady transonic flow around pitching airfoils via the solution of unsteady Euler and Navier-Stokes equations, using time spectral method (TSM) and compares it with the traditional methods like BDF and explicit structured adaptive grid method. The TSM uses a Fourier representation in time and hence solves for the periodic state directly without resolving transients (which consume most of the resources in a time-accurate scheme). Mathematical tools used here are discrete Fourier transformations. The TSM has been validated with 2D external aerodynamics test cases. These test cases are NACA 64A010 (CT6) and NACA 0012 (CT1 and CT5) pitching airfoils. Because of turbulent nature of flow, Baldwin-Lomax turbulence model has been used in viscous flow analysis with large oscillation amplitude (CT5 type). The results presented by the TSM are compared with experimental data and the two other methods. By enforcing periodicity and using Fourier representation in time that has a spectral accuracy, tremendous reduction of computational cost has been obtained compared to the conventional time-accurate methods. Results verify the small number of time intervals per pitching cycle (just four time intervals) required to capture the flow physics with small oscillation amplitude (CT6) and large oscillation amplitude (CT5) as compared to the other two methods.
Transient simulation in interior flow field of lobe pump
International Nuclear Information System (INIS)
Li, Y B; Sang, X H; Shen, H; Jia, K; Meng, Q W
2013-01-01
The subject of this paper is mainly focused on the development and control of the double folium and trifolium lobe pump profiles by using the principle of involute engagement and use CAD to get an accurate involute profile. We use the standard k-ε turbulence model and PISO algorithm based on CFD software FLUENT. The dynamic mesh and UDF technology is introduced to simulate the interior flow field inside a lobe pump, and the variation of interior flow field under the condition of the lobe rotating is analyzed. We also analyse the influence produced by the difference in lobes, and then reveal which lobe is best. The results show that dynamic variation of the interior flow field is easily obtained by dynamic mesh technology and the distribution of its pressure and velocity. Because of the small gaps existing between the rotors and pump case, the higher pressure area will flow into the lower area though the small gaps which cause the working area keep with higher pressure all the time. Both of the double folium and trifolium are existing the vortex during the rotting time and its position, size and shape changes all the time. The vortexes even disappear in a circle period and there are more vortexes in double folium lobe pump. The velocity and pressure pulsation of trifolium pump are lower than that of the double folium
Numerical simulation of a cross flow Marine Hydrokinetic turbine.
Hall, Taylor; Aliseda, Alberto
2011-11-01
In the search for alternative sources of energy, the kinetic energy of water currents in oceans, rivers and estuaries is being explored as predictable and environmentally benign. We are investigating the flow past a cross flow turbine in which a helical blade under hydrodynamic forces turns around a shaft perpendicular to the free stream. This type of turbine, while very different from the classical horizontal axis turbine commonly used in the wind energy field, presents advantages for stacking in very narrow constricted channels where the water currents are consistently high and therefore turbine installation may be economically feasible. We use a model of a helical four-bladed turbine in cross flow to investigate the efficiency of the energy capture and the dynamics of the turbulent wake. Scale model experiments in a flume are used to validate the numerical results on a stationary configuration as an initial step towards creating an accurate numerical model of the turbine. The simulation of the rotating turbine provides a full perspective on the effect of angular position on flow detachment and vortex shedding from the blade, as well as on the fluctuations of the shaft torque produced (a problematic feature of this type of turbine). The results are analyzed in terms of hydrodynamic optimization of the blade and its structural loading. Supported by DOE through the Northwest National Marine Renewable Energy Center.
Direct numerical simulation of turbulent channel flow with deformed bubbles
International Nuclear Information System (INIS)
Yamamoto, Yoshinobu; Kunugi, Tomoaki
2010-01-01
In this study, the direct numerical simulation of a fully-developed turbulent channel flow with deformed bubbles were conducted by means of the refined MARS method, turbulent Reynolds number 150, and Bubble Reynolds number 120. As the results, large-scale wake motions were observed round the bubbles. At the bubble located region, mean velocity was degreased and turbulent intensities and Reynolds shear stress were increased by the effects of the large-scale wake motions round bubbles. On the other hands, near wall region, bubbles might effect on the flow laminarlize and drag reduction. Two types of drag coefficient of bubble were estimated from the accelerated velocity of bubble and correlation equation as a function of Particle Reynolds number. Empirical correlation equation might be overestimated the drag effects in this Particle Reynolds number range. (author)
Application of mathematical model for simulation of groundwater flow
International Nuclear Information System (INIS)
Carvalho Filho, Carlos Alberto de; Branco, Otavio Eurico de Aquino; Loureiro, Celso de Oliveira
2000-01-01
The main purpose of the present research work is the groundwater flow characterization of the aquifer system of the Engenho Nogueira Creek watershed basin, particularly within the limits of the Pampulha Campus of the Federal University of Minas Gerais and nearby. In order to reach the aforementioned goal, a numerical model was implemented for simulation the groundwater flow, using the MODFLOW code. The local hydrogeology consists of a porous granular aquifer placed above and hydraulically connected to a fractured aquifer, constituting a unique aquifer system, mixed and phreatic type, heterogeneous and anisotropic. The local hydrogeological system is strongly influenced by a complex drain system and by the Engenho Nogueira Creek. After calibration, it was possible to predict the average phreatic depth measured in the observation wells for the period in study with a standard deviation of 1.65 m and a correlation coefficient of 0.94. (author)
Numerical simulation of magnetohydrodynamic (MHD) flow with internal heat generation
International Nuclear Information System (INIS)
Bokade, Vipin; Bhandarkar, U.V.; Bodi, Kowsik
2016-01-01
A strong magnetic field is used to confine the plasma in a fusion reactor. This magnetic field also affects the flow of Lead-Lithium (breeder/coolant) in the breeding blanket. So it is important to study MHD flow of Lead-Lithium (Pb-Li). Open-source toolbox, OpenFOAM, is used to study single phase behaviour of Pb-Li. As the induced magnetic field is very small, Ni et al. electric potential algorithm is employed in OpenFOAM and validated with analytical results. This solver can also solve the temperature field with heat source term. Simulations are carried out in 2D straight channel for various values of Hartmann Number ranging from 100 to 5000 and velocity profile, temperature, current density and pressure drop are studied. (author)
Monitoring system of depressurization valves of migrated gas in annular space of flexible risers
Energy Technology Data Exchange (ETDEWEB)
Mesquita, Luiz A.; Santos, Joilson M.; Carvalho, Antonio L.; Loureiro, Patricia [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil)
2005-07-01
PETROBRAS Research and Development Center - CENPES developed an automatic system for monitoring pressure of annular space due to permeation of gas in flexible risers to inspect continuously integrity of such lines. To help maintaining physical integrity of flexible risers, two PSV's are installed to end fittings on top of riser, so that operation of any valve grants the maximum admissible gas pressure within the riser annular space, as overpressure might cause damages to external polymeric layer of flexible riser. Due to the fact that there is no mechanism allowing operation to verify correct PSV performance and frequency of valve's closings and openings, we felt to be necessary the development and implement an automatic instrumented system, integrated to platform's automation and control infrastructure. The objective of this instrumentation is to monitor and register pressure of annular space in flexible riser, as well as XV's depressurization frequency. Having such information registered and monitored, can infer some riser structural conditions, anticipating repairs and preventive maintenance. In this paper we present developed system details including instruments required, application, operation of associated screens that are used in the ECOS, with events, alarms and industrial automation services required (Application development and system integration). (author)
Multiport riser and flange assemblies acceptance test report
International Nuclear Information System (INIS)
Precechtel, D.R.; Schroeder, B.K.
1994-01-01
This document presents the results of the acceptance test for the multiport riser (MPR) and multiport flange (MPF) assemblies. The accepted MPR and MPF assemblies will be used in support of the hydrogen mitigation project for double-shell waste tank 241-SY-101 and other related projects. The testing described in this document verifies that the mechanical and interface features are operating as designed and that the unit is ready for field service. The objectives of the acceptance testing were as follows: Basic equipment functions and mechanical interfaces were verified; Installation and removal of equipment were demonstrated to the degree possible; Operation of the decon spray system and all valving was confirmed; and the accumulated leak rate of the MPR and MPF assemblies was determined
Two-riser system improves drilling at Auger prospect
International Nuclear Information System (INIS)
Gonzalez, R.; Marsh, G.L.; Ritter, P.B.; Mendel, P.E.
1992-01-01
This paper reports on a two-rise system (TRS) for drilling deepwater development wells which eliminates some of the limitations of conventional subsea technology and allows flexibility in well programs. Shell Offshore Inc.'s deep exploratory wells in Garden Banks 426 and 471 have encountered drilling problems that were attributed to limitations in casing sizes imposed by conventional subsea drilling systems. These problems are not uncommon in exploratory deepwater, deep well drilling in the Gulf of Mexico. Reservoir depths of up to 19,500 ft true vertical depth (TVD) and 7-in. production casing requirements led to potentially troublesome and expensive well plans. Because of the constraints placed on the development drilling program by completion requirements and directional drilling, a two-riser system was designed and fabricated. Solving such significant drilling problems has reduced overall development costs
New Results on the Simulation of Particulate Flows
Energy Technology Data Exchange (ETDEWEB)
Uhlmann, M.
2004-07-01
We propose a new immersed boundary method for the simulation of particulate flows. The fluid solid interaction force is formulate din a direct manner, without resorting to a feed-back mechanisms and thereby avoiding the introduction of additional free parameters. The regularized delta function of Peskin (Acta Numerica, 2002) is used to pass variables between Lagrangian and Eulerian representations, providing for a smooth variation of the hydrodynamic forces while particles are in motion relative to the fixed grid. The application of this scheme to several benchmark problems in two space dimensions demonstrates its feasibility and efficiency. (Author) 9 refs.
On the numerical simulation of tracer flows in porous media
International Nuclear Information System (INIS)
Aquino, J.; Pereira, F.; Amaral Souto, H.P.; Francisco, A.S.
2007-01-01
We discuss in detail a new Lagrangian, locally conservative procedure which has been proposed for the numerical solution of linear transport problems in porous media. The new scheme is computationally efficient, virtually free of numerical diffusion, and can be applied to investigate numerically the time evolution of radionuclide contaminant plumes. Results of two-dimensional simulations of tracer flows will be presented to show the influence on the computed solutions of distinct interpolation functions for evaluating the velocity field at any position of the physical domain, as required by the Lagrangian scheme. (author)
New Results on the Simulation of Particulate Flows
International Nuclear Information System (INIS)
Uhlmann, M.
2004-01-01
We propose a new immersed boundary method for the simulation of particulate flows. The fluid solid interaction force is formulated in a direct manner, without resorting to a feed-back mechanism and thereby avoiding the introduction of additional free parameters. The regularized delta function of Pekin (Acta Numerical, 2002) is used to pass variables between Lagrangian and Eulerian representations, providing for a smooth variation of the hydrodynamic forces while particles are in motion relative to the fixed grid. The application of this schemer to several benchmark problems in two space dimensions demonstrates its feasibility and efficiency. (Author) 9 refs
Efficient Parallel Algorithm For Direct Numerical Simulation of Turbulent Flows
Moitra, Stuti; Gatski, Thomas B.
1997-01-01
A distributed algorithm for a high-order-accurate finite-difference approach to the direct numerical simulation (DNS) of transition and turbulence in compressible flows is described. This work has two major objectives. The first objective is to demonstrate that parallel and distributed-memory machines can be successfully and efficiently used to solve computationally intensive and input/output intensive algorithms of the DNS class. The second objective is to show that the computational complexity involved in solving the tridiagonal systems inherent in the DNS algorithm can be reduced by algorithm innovations that obviate the need to use a parallelized tridiagonal solver.
Numerical Simulation of Turbulent Convective Flow Over Wavy Terrain
Dörnbrack, A.; Schumann, U.
1993-01-01
By means of a large-eddy simulation, the convective boundary layer is investigated for flows over wavy terrain. The lower surface varies sinusoidalty in the downstream direction while remaining constant in the other. Several cases are considered with amplitude 6 up to 0.15H and wavelength A of H to 8H, where H is the mean fluid-layer height. At the lower surface, the vertical heat flux is prescribed to be constant and the momentum flux is determined locally from the Monin-Obukhov relationship...
Numerical simulation of air hypersonic flows with equilibrium chemical reactions
Emelyanov, Vladislav; Karpenko, Anton; Volkov, Konstantin
2018-05-01
The finite volume method is applied to solve unsteady three-dimensional compressible Navier-Stokes equations on unstructured meshes. High-temperature gas effects altering the aerodynamics of vehicles are taken into account. Possibilities of the use of graphics processor units (GPUs) for the simulation of hypersonic flows are demonstrated. Solutions of some test cases on GPUs are reported, and a comparison between computational results of equilibrium chemically reacting and perfect air flowfields is performed. Speedup of solution on GPUs with respect to the solution on central processor units (CPUs) is compared. The results obtained provide promising perspective for designing a GPU-based software framework for practical applications.
Directory of Open Access Journals (Sweden)
Brac J.
2012-09-01
Full Text Available Offshore transportation of gaseous fluids frequently relies on flexible pipes. Flexible pipes are obtained from the helicoidal rolling of steel tape which induces a geometrical cavity from edge to edge. Along the pipe, the gas infinitely encounters the edge to edge cavity of the same shape at regular interval. In some service conditions, acoustic vibrations of huge amplitude can arise. Indeed, in front of each cavity, there is a shear layer where Kelvin-Helmholtz instability can occur. The flow encounters a large number of cavities on its path which gives rise to a new specific problem: is there a stabilized flow? Results of large eddy scale simulations are presented as a reference but they are very costly. This gives reason to develop a numerical solution of the Orr-Sommerfeld equation in order to analyze the temporal and spatial wave lengths generated by the shear layers in front of the cavities. First, we introduce the problem of flexible risers and the analysis of some RANS and LES modeling. Second, a bibliographical study describes the state of the art about vibrations induced by cavity. Third, we state the Orr-Sommerfeld equation and set the problem we want to solve in terms of generalized eigen values Numerical discretizations are based on finite difference approaches of fourth orders. The choice of the relevant eigen values among all those provided by the solutions of the numerical problem is the main difficulty to be tackled. Le transport offshore de gaz utilise souvent des conduites flexibles. Elles sont fabriquées en enroulant en hélice un ruban d’acier; au contact bord à bord des tours d’hélice, une cavité apparaît. Le gaz s’écoule en conduite et rencontre cette cavité à intervalles réguliers, toujours avec la même forme. Dans certaines conditions d’usage, des vibrations acoustiques de grandes amplitudes apparaissent. En effet, devant chaque cavité, il y a une couche de cisaillement où une instabilité de type
Structural analysis of multiport riser 5A installation on tank 241SY101
Energy Technology Data Exchange (ETDEWEB)
Strehlow, J.P.
1994-09-16
The Tank 101-SY multiport riser assembly in the 241-SY-101 waste tank will replace the existing 42 inch riser with four smaller ports. Each smaller port can be used independently to access the tank interior with equipment and instruments needed to mitigate the concentration of hydrogen in the tank. This document provides a design report on the structural evaluation of the multiport riser assembly as well as its anchorage. The multiport riser assembly is a steel structure installed directly above the 42-inch riser and sealed at the existing riser flange. The assembly is structurally supported by the concrete pad placed around the 42 inch riser. The multiport riser assembly will provide two 8-inch penetrations, one 12-inch penetration and one 24-inch penetration. Each penetration will have a shielding plate. These penetrations will be used to insert equipment such as a sonic probe into the tank. In addition to normal loads, non-reactor Safety Class 1 structures, systems and components are to withstand the effects of extreme environmental loads including Design Basis Earthquake (DBE), Design Basis Wind (DBW), Design Basis Flood, Volcanic Eruptions and other abnormal loads considered on a case by case basis. Non-reactor Safety Class 2, 3 and 4 structures, systems and components are those that are not Safety Class 1 and are respectively specified as onsite safety related, occupational safety related and non-safety related items. The 241-SY-101 tank is considered as a non-reactor Safety Class 1 structure. The multiport riser assembly is considered as a non-reactor Safety Class 2 structure since it serves to contain the radioactive and toxic materials under normal operating conditions. However, the pressure relief doors provided on the assembly are considered as Safety Class 1 structures.
HYDRASTAR - a code for stochastic simulation of groundwater flow
International Nuclear Information System (INIS)
Norman, S.
1992-05-01
The computer code HYDRASTAR was developed as a tool for groundwater flow and transport simulations in the SKB 91 safety analysis project. Its conceptual ideas can be traced back to a report by Shlomo Neuman in 1988, see the reference section. The main idea of the code is the treatment of the rock as a stochastic continuum which separates it from the deterministic methods previously employed by SKB and also from the discrete fracture models. The current report is a comprehensive description of HYDRASTAR including such topics as regularization or upscaling of a hydraulic conductivity field, unconditional and conditional simulation of stochastic processes, numerical solvers for the hydrology and streamline equations and finally some proposals for future developments
Numerical simulation of cavitation surge and vortical flows in a diffuser with swirling flow
Energy Technology Data Exchange (ETDEWEB)
Ji, Bin; Wang, Jiong; Xiao, L. Z.; Long, X. [Wuhan University, Hubei (China); Luo, X. [Tsinghua University, Beijing (China); Miyagawa, K. [Waseda University, Tokyo (Japan); Tsujimoto, Yoshinobu [Osaka University, Osaka (Japan)
2016-06-15
The strong swirling flow at the exit of the runner of a Francis turbine at part load causes flow instabilities and cavitation surges in the draft tube, deteriorating the performance of the hydraulic power system. The unsteady cavitating turbulent flow in the draft tube is simplified and modeled by a diffuser with swirling flow using the Scale-adaptive simulation method. Unsteady characteristics of the vortex rope structure and the underlying mechanisms for the interactions between the cavitation and the vortices are both revealed. The generation and evolution of the vortex rope structures are demonstrated with the help of the iso-surfaces of the vapor volume fraction and the Qcriterion. Analysis based on the vorticity transport equation suggests that the vortex dilatation term is much larger along the cavity interface in the diffuser inlet and modifies the vorticity field in regions with high density and pressure gradients. The present work is validated by comparing two types of cavitation surges observed experimentally in the literature with further interpretations based on simulations.
Direct numerical simulations of flow and heat transfer over a circular cylinder at Re = 2000
Vidya, Mahening Citra; Beishuizen, N.A.; van der Meer, Theodorus H.
2016-01-01
Unsteady direct numerical simulations of the flow around a circular cylinder have been performed at Re = 2000. Both two-dimensional and three-dimensional simulations were validated with laminar cold flow simulations and experiments. Heat transfer simulations were carried out and the time-averaged
An optical sensor for the detection of leaks from subsea pipelines and risers
International Nuclear Information System (INIS)
McStay, D; Kerlin, J; Acheson, R
2007-01-01
An optical sensor for the rapid detection of detect leaks of oil, hydraulic fluids or leak detection chemicals from underwater pipelines and risers is reported. The sensor is designed to be deployed on ROVs or AUVs for the rapid survey of underwater pipelines and risers. The system employs ultra-bright LEDs to project a sensing light beam into the water to allow real time detection of ppm concentration plumes of material leaking from pipelines or riser in real time. Typically the system is deployed on an ROV which inspects a pipeline at a height of 2-3m
Engineering study - installation of new risers in Single-Shell Tanks
International Nuclear Information System (INIS)
Magruder, W.J.
1994-08-01
A sampling program is being developed to characterize the 149 underground SSTs on the Hanford Site. The sampling effort will require access to the tank interior in a minimum of two locations per tank. Some of the risers suitable for sampling are either unavailable or are not in locations for proper characterization of the tank contents. Additional risers will be required in the SSTs to support the tank characterization sampling program. The purpose of this engineering study is to review alternatives for installation of new riser in the SSTs
Approaches to the simulation of unconfined flow and perched groundwater flow in MODFLOW
Bedekar, Vivek; Niswonger, Richard G.; Kipp, Kenneth; Panday, Sorab; Tonkin, Matthew
2012-01-01
Various approaches have been proposed to manage the nonlinearities associated with the unconfined flow equation and to simulate perched groundwater conditions using the MODFLOW family of codes. The approaches comprise a variety of numerical techniques to prevent dry cells from becoming inactive and to achieve a stable solution focused on formulations of the unconfined, partially-saturated, groundwater flow equation. Keeping dry cells active avoids a discontinuous head solution which in turn improves the effectiveness of parameter estimation software that relies on continuous derivatives. Most approaches implement an upstream weighting of intercell conductance and Newton-Raphson linearization to obtain robust convergence. In this study, several published approaches were implemented in a stepwise manner into MODFLOW for comparative analysis. First, a comparative analysis of the methods is presented using synthetic examples that create convergence issues or difficulty in handling perched conditions with the more common dry-cell simulation capabilities of MODFLOW. Next, a field-scale three-dimensional simulation is presented to examine the stability and performance of the discussed approaches in larger, practical, simulation settings.
Equivalence of two models in single-phase multicomponent flow simulations
Wu, Yuanqing
2016-02-28
In this work, two models to simulate the single-phase multicomponent flow in reservoirs are introduced: single-phase multicomponent flow model and two-phase compositional flow model. Because the single-phase multicomponent flow is a special case of the two-phase compositional flow, the two-phase compositional flow model can also simulate the case. We compare and analyze the two models when simulating the single-phase multicomponent flow, and then demonstrate the equivalence of the two models mathematically. An experiment is also carried out to verify the equivalence of the two models.
Equivalence of two models in single-phase multicomponent flow simulations
Wu, Yuanqing; Sun, Shuyu
2016-01-01
In this work, two models to simulate the single-phase multicomponent flow in reservoirs are introduced: single-phase multicomponent flow model and two-phase compositional flow model. Because the single-phase multicomponent flow is a special case of the two-phase compositional flow, the two-phase compositional flow model can also simulate the case. We compare and analyze the two models when simulating the single-phase multicomponent flow, and then demonstrate the equivalence of the two models mathematically. An experiment is also carried out to verify the equivalence of the two models.
Assessing continuum postulates in simulations of granular flow
Energy Technology Data Exchange (ETDEWEB)
Rycroft, Chris; Kamrin, Ken; Bazant, Martin
2008-08-26
Continuum mechanics relies on the fundamental notion of a mesoscopic volume"element" in which properties averaged over discrete particles obey deterministic relationships. Recent work on granular materials suggests a continuum law may be inapplicable, revealing inhomogeneities at the particle level, such as force chains and slow cage breaking. Here, we analyze large-scale three-dimensional Discrete-Element Method (DEM) simulations of different granular flows and show that an approximate"granular element" defined at the scale of observed dynamical correlations (roughly three to five particle diameters) has a reasonable continuum interpretation. By viewing all the simulations as an ensemble of granular elements which deform and move with the flow, we can track material evolution at a local level. Our results confirm some of the hypotheses of classical plasticity theory while contradicting others and suggest a subtle physical picture of granular failure, combining liquid-like dependence on deformation rate and solid-like dependence on strain. Our computational methods and results can be used to guide the development of more realistic continuum models, based on observed local relationships betweenaverage variables.
Laboratory simulations of cumulus cloud flows explain the entrainment anomaly
Narasimha, Roddam; Diwan, Sourabh S.; Subrahmanyam, Duvvuri; Sreenivas, K. R.; Bhat, G. S.
2010-11-01
In the present laboratory experiments, cumulus cloud flows are simulated by starting plumes and jets subjected to off-source heat addition in amounts that are dynamically similar to latent heat release due to condensation in real clouds. The setup permits incorporation of features like atmospheric inversion layers and the active control of off-source heat addition. Herein we report, for the first time, simulation of five different cumulus cloud types (and many shapes), including three genera and three species (WMO Atlas 1987), which show striking resemblance to real clouds. It is known that the rate of entrainment in cumulus cloud flows is much less than that in classical plumes - the main reason for the failure of early entrainment models. Some of the previous studies on steady-state jets and plumes (done in a similar setup) have attributed this anomaly to the disruption of the large-scale turbulent structures upon the addition of off-source heat. We present estimates of entrainment coefficients from these measurements which show a qualitatively consistent variation with height. We propose that this explains the observed entrainment anomaly in cumulus clouds; further experiments are planned to address this question in the context of starting jets and plumes.
Direct numerical simulation of stratified gas-liquid flow
International Nuclear Information System (INIS)
Lombardi, P.; De Angelis, V.; Banerjee, S.
1996-01-01
Interactions through an interface between two turbulent flows play an important role in many environmental and industrial problems, e.g. in determining the coupling fluxes of heat mass and momentum, between the ocean and atmosphere, and in the design of gas-liquid contractors for the chemical industry, as well as in determining interactions between phases in nuclear transients that are accompanied by system voiding e.g. LOCAs. Here, the Direct Numerical Simulation (DNS) of the interaction of two turbulent fluids through a flat interface has been simulated. The flow and the temperature fields are computed using a pseudospectral method. This study shows that shear stress at the interface correlates well with the heat flux. Extensive analysis of the near interface turbulence structure has been performed using quadrant analysis. From this it is clear that gas-side sweeps dominate over the high shear stress regions. This suggests that simple parameterizations based on sweep frequency may be adequate for predictions of scalar transport rates
Direct Numerical Simulation of Flow Over Passive Geometric Disturbances
Vizard, Alexander
It is well understood that delaying flow separation on a bluff body allows significant drag reduction, which is attractive in many applications. With this in mind, many separation control mechanisms, both active and passive, have been developed and tested to optimize the effects of this phenomenon. Although this idea is generally accepted, the physical occurrences in the near-wall region during transition that lead to separation delay are not well understood. The current study evaluates the impact of both spherical dimples, and sandgrain style roughness on downstream flow by performing direct numerical simulations over such geometries on a zero pressure gradient flat plate. It is shown that although dimples and random roughness of similar characteristic length scales exhibit similar boundary layer characteristics, dimples are more successful in developing high momentum in the vicinity of the wall. Additionally it is shown that increasing the relative size of the rough elements does not increase the near-wall momentum, and is undesirable in controlling separation. Finally, it is shown that the impact of roughness elements on the flow is more immediate, and that, for the case of one row of dimples and an equivalent area of roughness, the roughness patch is more successful in transitioning the near-wall region to a non-laminar state. It can be concluded from variation in the span of the flowfield for a single row of dimples that the size and orientation of the disturbance region is significant to the results.
Loss of flow incident - Simulation and measurements in the MPR
International Nuclear Information System (INIS)
Doval, A.; Hesham Abdou
1999-01-01
As part of the Probabilistic Safety Analysis of the Multi Purpose Reactor, MPR, the list of Postulated Initiating Events was analyzed and one of these PIEs corresponds to the Loss of Coolant Flow. It is well known that during the operation life of a research reactor a LOFA could eventually occur and, once this event takes place, in time detection and automatic actions, thanks to the engineering safety features of the system, will mitigate the incident evolution. The postulated event corresponds to a loss of flow due to a total loss of power supply. The goal of the present work is to provide a general description and the engineering safety features of the MPR, as well as describe the sequence of scenarios during a LOFA. Temporal evolution of main parameters is presented, also. During Stage A of the Commissioning Program measurements of the core cooling system pump coast-down were performed in order to validate previous simulation results, as well as, flap valves opening time. In this way it was verified that engineering safety features worked properly. On Stage B of the Commissioning Program the upward natural convection flow was verified and results comparison against analytical calculation, showed that the reactor core was cooled within the adopted design goals. (author)
Flow Simulation of Supersonic Inlet with Bypass Annular Duct
Kim, HyoungJin; Kumano, Takayasu; Liou, Meng-Sing; Povinelli, Louis A.; Conners, Timothy R.
2011-01-01
A relaxed isentropic compression supersonic inlet is a new concept that produces smaller cowl drag than a conventional inlet, but incurs lower total pressure recovery and increased flow distortion in the (radially) outer flowpath. A supersonic inlet comprising a bypass annulus to the relaxed isentropic compression inlet dumps out airflow of low quality through the bypass duct. A reliable computational fluid dynamics solution can provide considerable useful information to ascertain quantitatively relative merits of the concept, and further provide a basis for optimizing the design. For a fast and reliable performance evaluation of the inlet performance, an equivalent axisymmetric model whose area changes accounts for geometric and physical (blockage) effects resulting from the original complex three-dimensional configuration is proposed. In addition, full three-dimensional calculations are conducted for studying flow phenomena and verifying the validity of the equivalent model. The inlet-engine coupling is carried out by embedding numerical propulsion system simulation engine data into the flow solver for interactive boundary conditions at the engine fan face and exhaust plane. It was found that the blockage resulting from complex three-dimensional geometries in the bypass duct causes significant degradation of inlet performance by pushing the terminal normal shock upstream.
Direct Numerical Simulation of Fingering Instabilities in Coating Flows
Eres, Murat H.; Schwartz, Leonard W.
1998-11-01
We consider stability and finger formation in free surface flows. Gravity driven downhill drainage and temperature gradient driven climbing flows are two examples of such problems. The former situation occurs when a mound of viscous liquid on a vertical wall is allowed to flow. Constant surface shear stress due to temperature gradients (Marangoni stress) can initiate the latter problem. The evolution equations are derived using the lubrication approximation. We also include the effects of finite-contact angles in the evolution equations using a disjoining pressure model. Evolution equations for both problems are solved using an efficient alternating-direction-implicit method. For both problems a one-dimensional base state is established, that is steady in a moving reference frame. This base state is unstable to transverse perturbations. The transverse wavenumbers for the most rapidly growing modes are found through direct numerical solution of the nonlinear evolution equations, and are compared with published experimental results. For a range of finite equilibrium contact angles, the fingers can grow without limit leading to semi-finite steady fingers in a moving coordinate system. A computer generated movie of the nonlinear simulation results, for several sets of input parameters, will be shown.
Scalar conservation and boundedness in simulations of compressible flow
Subbareddy, Pramod K.; Kartha, Anand; Candler, Graham V.
2017-11-01
With the proper combination of high-order, low-dissipation numerical methods, physics-based subgrid-scale models, and boundary conditions it is becoming possible to simulate many combustion flows at relevant conditions. However, non-premixed flows are a particular challenge because the thickness of the fuel/oxidizer interface scales inversely with Reynolds number. Sharp interfaces can also be present in the initial or boundary conditions. When higher-order numerical methods are used, there are often aphysical undershoots and overshoots in the scalar variables (e.g. passive scalars, species mass fractions or progress variable). These numerical issues are especially prominent when low-dissipation methods are used, since sharp jumps in flow variables are not always coincident with regions of strong variation in the scalar fields: consequently, special detection mechanisms and dissipative fluxes are needed. Most numerical methods diffuse the interface, resulting in artificial mixing and spurious reactions. In this paper, we propose a numerical method that mitigates this issue. We present methods for passive and active scalars, and demonstrate their effectiveness with several examples.
Numerical simulation of turbulent convective flow over wavy terrain
Dörnbrack, A.; Schumann, U.
1993-09-01
By means of a large-eddy simulation, the convective boundary layer is investigated for flows over wavy terrain. The lower surface varies sinusoidally in the downstream direction while remaining constant in the other. Several cases are considered with amplitude δ up to 0.15 H and wavelength λ of H to 8 H, where H is the mean fluid-layer height. At the lower surface, the vertical heat flux is prescribed to be constant and the momentum flux is determined locally from the Monin-Obukhov relationship with a roughness length z o=10-4 H. The mean wind is varied between zero and 5 w *, where w * is the convective velocity scale. After rather long times, the flow structure shows horizontal scales up to 4 H, with a pattern similar to that over flat surfaces at corresponding shear friction. Weak mean wind destroys regular spatial structures induced by the surface undulation at zero mean wind. The surface heating suppresses mean-flow recirculation-regions even for steep surface waves. Short surface waves cause strong drag due to hydrostatic and dynamic pressure forces in addition to frictional drag. The pressure drag increases slowly with the mean velocity, and strongly with δ/ H. The turbulence variances increase mainly in the lower half of the mixed layer for U/w *>2.
Transient Simulation of Accumulating Particle Deposition in Pipe Flow
Hewett, James; Sellier, Mathieu
2015-11-01
Colloidal particles that deposit in pipe systems can lead to fouling which is an expensive problem in both the geothermal and oil & gas industries. We investigate the gradual accumulation of deposited colloids in pipe flow using numerical simulations. An Euler-Lagrangian approach is employed for modelling the fluid and particle phases. Particle transport to the pipe wall is modelled with Brownian motion and turbulent diffusion. A two-way coupling exists between the fouled material and the pipe flow; the local mass flux of depositing particles is affected by the surrounding fluid in the near-wall region. This coupling is modelled by changing the cells from fluid to solid as the deposited particles exceed each local cell volume. A similar method has been used to model fouling in engine exhaust systems (Paz et al., Heat Transfer Eng., 34(8-9):674-682, 2013). We compare our deposition velocities and deposition profiles with an experiment on silica scaling in turbulent pipe flow (Kokhanenko et al., 19th AFMC, 2014).
Direct Numerical Simulation of Turbulent Flow Over Complex Bathymetry
Yue, L.; Hsu, T. J.
2017-12-01
Direct numerical simulation (DNS) is regarded as a powerful tool in the investigation of turbulent flow featured with a wide range of time and spatial scales. With the application of coordinate transformation in a pseudo-spectral scheme, a parallelized numerical modeling system was created aiming at simulating flow over complex bathymetry with high numerical accuracy and efficiency. The transformed governing equations were integrated in time using a third-order low-storage Runge-Kutta method. For spatial discretization, the discrete Fourier expansion was adopted in the streamwise and spanwise direction, enforcing the periodic boundary condition in both directions. The Chebyshev expansion on Chebyshev-Gauss-Lobatto points was used in the wall-normal direction, assuming there is no-slip on top and bottom walls. The diffusion terms were discretized with a Crank-Nicolson scheme, while the advection terms dealiased with the 2/3 rule were discretized with an Adams-Bashforth scheme. In the prediction step, the velocity was calculated in physical domain by solving the resulting linear equation directly. However, the extra terms introduced by coordinate transformation impose a strict limitation to time step and an iteration method was applied to overcome this restriction in the correction step for pressure by solving the Helmholtz equation. The numerical solver is written in object-oriented C++ programing language utilizing Armadillo linear algebra library for matrix computation. Several benchmarking cases in laminar and turbulent flow were carried out to verify/validate the numerical model and very good agreements are achieved. Ongoing work focuses on implementing sediment transport capability for multiple sediment classes and parameterizations for flocculation processes.
Burkhardt, Z.; Ramachandran, N.; Majumdar, A.
2017-01-01
Fluid Transient analysis is important for the design of spacecraft propulsion system to ensure structural stability of the system in the event of sudden closing or opening of the valve. Generalized Fluid System Simulation Program (GFSSP), a general purpose flow network code developed at NASA/MSFC is capable of simulating pressure surge due to sudden opening or closing of valve when thermodynamic properties of real fluid are available for the entire range of simulation. Specifically GFSSP needs an accurate representation of pressure-density relationship in order to predict pressure surge during a fluid transient. Unfortunately, the available thermodynamic property programs such as REFPROP, GASP or GASPAK does not provide the thermodynamic properties of Monomethylhydrazine (MMH). This paper will illustrate the process used for building a customized table of properties of state variables from available properties and speed of sound that is required by GFSSP for simulation. Good agreement was found between the simulations and measured data. This method can be adopted for modeling flow networks and systems with other fluids whose properties are not known in detail in order to obtain general technical insight. Rigorous code validation of this approach will be done and reported at a future date.
Efficient algorithms for flow simulation related to nuclear reactor safety
International Nuclear Information System (INIS)
Gornak, Tatiana
2013-01-01
Safety analysis is of ultimate importance for operating Nuclear Power Plants (NPP). The overall modeling and simulation of physical and chemical processes occuring in the course of an accident is an interdisciplinary problem and has origins in fluid dynamics, numerical analysis, reactor technology and computer programming. The aim of the study is therefore to create the foundations of a multi-dimensional non-isothermal fluid model for a NPP containment and software tool based on it. The numerical simulations allow to analyze and predict the behavior of NPP systems under different working and accident conditions, and to develop proper action plans for minimizing the risks of accidents, and/or minimizing the consequences of possible accidents. A very large number of scenarios have to be simulated, and at the same time acceptable accuracy for the critical parameters, such as radioactive pollution, temperature, etc., have to be achieved. The existing software tools are either too slow, or not accurate enough. This thesis deals with developing customized algorithm and software tools for simulation of isothermal and non-isothermal flows in a containment pool of NPP. Requirements to such a software are formulated, and proper algorithms are presented. The goal of the work is to achieve a balance between accuracy and speed of calculation, and to develop customized algorithm for this special case. Different discretization and solution approaches are studied and those which correspond best to the formulated goal are selected, adjusted, and when possible, analysed. Fast directional splitting algorithm for Navier-Stokes equations in complicated geometries, in presence of solid and porous obstacles, is in the core of the algorithm. Developing suitable pre-processor and customized domain decomposition algorithms are essential part of the overall algorithm amd software. Results from numerical simulations in test geometries and in real geometries are presented and discussed.
Simulation of two-phase flows by domain decomposition
International Nuclear Information System (INIS)
Dao, T.H.
2013-01-01
This thesis deals with numerical simulations of compressible fluid flows by implicit finite volume methods. Firstly, we studied and implemented an implicit version of the Roe scheme for compressible single-phase and two-phase flows. Thanks to Newton method for solving nonlinear systems, our schemes are conservative. Unfortunately, the resolution of nonlinear systems is very expensive. It is therefore essential to use an efficient algorithm to solve these systems. For large size matrices, we often use iterative methods whose convergence depends on the spectrum. We have studied the spectrum of the linear system and proposed a strategy, called Scaling, to improve the condition number of the matrix. Combined with the classical ILU pre-conditioner, our strategy has reduced significantly the GMRES iterations for local systems and the computation time. We also show some satisfactory results for low Mach-number flows using the implicit centered scheme. We then studied and implemented a domain decomposition method for compressible fluid flows. We have proposed a new interface variable which makes the Schur complement method easy to build and allows us to treat diffusion terms. Using GMRES iterative solver rather than Richardson for the interface system also provides a better performance compared to other methods. We can also decompose the computational domain into any number of sub-domains. Moreover, the Scaling strategy for the interface system has improved the condition number of the matrix and reduced the number of GMRES iterations. In comparison with the classical distributed computing, we have shown that our method is more robust and efficient. (author) [fr
Magnetic non-destructive evaluation of ruptures of tensile armor in oil risers
International Nuclear Information System (INIS)
Pérez-Benitez, J A; Padovese, L R
2012-01-01
Risers are flexible multilayered pipes formed by an inner flexible metal structure surrounded by polymer layers and spiral wound steel ligaments, also known as armor wires. Since these risers are used to link subsea pipelines to floating oil and gas production installations, and their failure could produce catastrophic consequences, some methods have been proposed to monitor the armor integrity. However, until now there is no practical method that allows the automatic non-destructive detection of individual armor wire rupture. In this work we show a method using magnetic Barkhausen noise that has shown high efficiency in the detection of armor wire rupture. The results are examined under the cyclic and static load conditions of the riser. This work also analyzes the theory behind the singular dependence of the magnetic Barkhausen noise on the applied tension in riser armor wires. (paper)
Directory of Open Access Journals (Sweden)
2016-01-01
Full Text Available The article is devoted to the validation and application of CFD code for turbulent flows. Two-dimensional un- steady flows in the cavities and compartments and three-dimensional flow in the compartment of complex geometry have been considered. Two turbulence parameter oriented models are used.Numerical simulation of unsteady transonic flow (Mоо=0.74 in a narrow channel with a cavity inside has been conducted. The dependence of the static pressure on time at fixed points in space has been obtained. The fast Fourier trans- form has been applied for processing data of static pressure. The difference of 6-10% between the numerical and experi-mental data has been obtained.The computations of unsteady transonic cavity flow with Mach number Mоо=0.85 have been performed. Low fre- quency oscillations of the static pressure in several fixed points in space have been obtained. Power spectrum of oscilla- tions at the center of the cavity is compared with experimental data and Rossiter modes. An acceptable agreement between experimental and computed data has been achieved. The influence of geometrical factors on the frequency characteristics of the flow has been investigated. For this purpose two round flaps have been added to the cavity. The most low-frequency oscillation modes changed by the presence of the flaps. The first mode was gone, the second mode amplitude decreased and the third mode amplitude significantly decreased. The changes in height of protruding part of the geometry to the external flow have led to changes in pressure pulsation amplitude without changing the frequency. The spectral functions obtained while using the two considered models of turbulence have been compared for this case. It is found that the frequency values are only slightly different; the main difference is present at the amplitude of pulsations.The effect of deflection of flat flap on the non-stationary subsonic flow parameters in a cylindrical body with an inner
Pressured drilling riser design for drilling in ultra deep water with surface bop
Energy Technology Data Exchange (ETDEWEB)
Zhang, J.; Morrison, D.; Efthymiou, M.; Lo, K.H. [Shell Global Solutions, 78 - Velizy Villacoublay (France); Magne, E.; Leach, C. [Shell Internationale Exploration and Production (Netherlands)
2002-12-01
In conventional drilling with a semi-submersible rig valuable rig time is used to run and retrieve the BOP and its accessories on the seabed, and this time increases with water depth. Furthermore, use of the conventional sub-sea BOP requires a large-diameter riser, which requires substantial rig storage and deck load capacity prior to installation. It also requires high riser-tensioning capacity or additional buoyancy. Thus as the water depth increases, it leads to a need for heavy duty 4. and 5. generation rigs with escalation in costs. The high cost of deep-water drill rigs is leading to the development of Surface BOP technology. In this development, the BOP is placed above sea level and the riser is simply a continuation of the casing (typical diameter 13-3/8''). This eliminates the need for a heavy 21'' riser and for running the BOP to the sea bed and retrieving it. Moreover, the reduced tension requirement for the smaller riser extends the water depth capability of 3. generation drilling semi-submersibles, enabling them to drill in deeper waters. A critical success factor for this development is the ability to design the riser/casing to withstand high internal pressures due to well kicks, in addition to environmental loads, and to restrict vessel offsets within certain limits so as not to overload the riser under the prevailing weather conditions. This paper addresses the design considerations of a pressured drilling riser that can be used with a surface BOP in deep-water. Key design issues that are sensitive to ultra-deep-water applications are discussed. The technical aspects of using (disposable) standard casing with threaded connector for the drilling riser are discussed, with a particular emphasis on the connector fatigue-testing program to quantify the stress concentration factor for fatigue design. Emerging composite material offers some alternatives to the steel riser when drilling in ultra-deep water Design issues related to the
Direct numerical simulation of turbulent, chemically reacting flows
Doom, Jeffrey Joseph
This dissertation: (i) develops a novel numerical method for DNS/LES of compressible, turbulent reacting flows, (ii) performs several validation simulations, (iii) studies auto-ignition of a hydrogen vortex ring in air and (iv) studies a hydrogen/air turbulent diffusion flame. The numerical method is spatially non-dissipative, implicit and applicable over a range of Mach numbers. The compressible Navier-Stokes equations are rescaled so that the zero Mach number equations are discretely recovered in the limit of zero Mach number. The dependent variables are co--located in space, and thermodynamic variables are staggered from velocity in time. The algorithm discretely conserves kinetic energy in the incompressible, inviscid, non--reacting limit. The chemical source terms are implicit in time to allow for stiff chemical mechanisms. The algorithm is readily applicable to complex chemical mechanisms. Good results are obtained for validation simulations. The algorithm is used to study auto-ignition in laminar vortex rings. A nine species, nineteen reaction mechanism for H2/air combustion proposed by Mueller et al. [37] is used. Diluted H 2 at ambient temperature (300 K) is injected into hot air. The simulations study the effect of fuel/air ratio, oxidizer temperature, Lewis number and stroke ratio (ratio of piston stroke length to diameter). Results show that auto--ignition occurs in fuel lean, high temperature regions with low scalar dissipation at a 'most reactive' mixture fraction, zeta MR (Mastorakos et al. [32]). Subsequent evolution of the flame is not predicted by zetaMR; a most reactive temperature TMR is defined and shown to predict both the initial auto-ignition as well as subsequent evolution. For stroke ratios less than the formation number, ignition in general occurs behind the vortex ring and propagates into the core. At higher oxidizer temperatures, ignition is almost instantaneous and occurs along the entire interface between fuel and oxidizer. For stroke
An experimental study on the key fretting variables for flexible marine risers
O’Halloran, S.M.; Harte, A.M.; Shipway, P.H.; Leen, S.B.
2018-01-01
This paper presents an experimental investigation into the effects of contact conformity, contact pressure and displacement amplitude on the gross-slip fretting behaviour grease-lubricated cylinder-on-flat contacts in the context of flexible marine riser pressure armour wire, and compares behaviour with that observed in unlubricated conditions. Characterisation of friction and wear is critical to fretting fatigue life prediction in flexible risers since friction directly controls trailing-edg...
Inspection and monitoring techniques for un-bonded flexible risers and pipelines
Simonsen, Anders
2014-01-01
Master's thesis in Offshore technology Un-bonded flexible pipelines and risers are an alternative to conventional rigid steel pipes. The use of flexible pipes has enabled development of several offshore fields that seemed unfeasible with the use of rigid pipes due to extensive seabed preparation and large dynamic motions. The lack of knowledge and integrity management tools for flexible pipes is a limiting factor and cause pipelines and risers to be replaced before their service life has ...
Network Flow Simulation of Fluid Transients in Rocket Propulsion Systems
Bandyopadhyay, Alak; Hamill, Brian; Ramachandran, Narayanan; Majumdar, Alok
2011-01-01
Fluid transients, also known as water hammer, can have a significant impact on the design and operation of both spacecraft and launch vehicle propulsion systems. These transients often occur at system activation and shutdown. The pressure rise due to sudden opening and closing of valves of propulsion feed lines can cause serious damage during activation and shutdown of propulsion systems. During activation (valve opening) and shutdown (valve closing), pressure surges must be predicted accurately to ensure structural integrity of the propulsion system fluid network. In the current work, a network flow simulation software (Generalized Fluid System Simulation Program) based on Finite Volume Method has been used to predict the pressure surges in the feed line due to both valve closing and valve opening using two separate geometrical configurations. The valve opening pressure surge results are compared with experimental data available in the literature and the numerical results compared very well within reasonable accuracy (< 5%) for a wide range of inlet-to-initial pressure ratios. A Fast Fourier Transform is preformed on the pressure oscillations to predict the various modal frequencies of the pressure wave. The shutdown problem, i.e. valve closing problem, the simulation results are compared with the results of Method of Characteristics. Most rocket engines experience a longitudinal acceleration, known as "pogo" during the later stage of engine burn. In the shutdown example problem, an accumulator has been used in the feed system to demonstrate the "pogo" mitigation effects in the feed system of propellant. The simulation results using GFSSP compared very well with the results of Method of Characteristics.
Zhang, Xujie; Booij, Martijn J.; Xu, YuePing
2015-01-01
Climate change is expected to have large impacts on peak flows. However, there may be bias in the simulation of peak flows by hydrological models. This study aims to improve the simulation of peak flows under climate change in Lanjiang catchment, east China, by comparing two approaches:
Energy Technology Data Exchange (ETDEWEB)
Baldessar, Fabio; Negrao, Cezar O. Ribeiro; Palu, Claudia [Centro Federal de Educacao Tecnologica do Parana (CEFET-PR), Curitiba, PR (Brazil)
2004-07-01
The current work presents a mathematical model of an ascendant flow vertical reactor (riser) of a Fluid Catalytic Cracking Unit. The two-phase flow (gas-solid) and the cracking reactions are admitted one-dimensional and steady state. Mass, momentum and energy conservation equations are considered for each phase (solid and gas). A six-lump kinetic model is employed to evaluate gasoil, gasoline, GLP, fuel gas, light cycle oil and coke fractions. The model results are compared to experimental values from a pilot plant and to another model found in the literature. The results are in good agreement, showing the model has great potential. (author)
The Simulation Study of Horizontal Axis Water Turbine Using Flow Simulation Solidworks Application
Prasetyo, H.; Budiana, EP; Tjahjana, DDDP; Hadi, S.
2018-02-01
The design of Horizontal Axis Water Turbine in pico hydro power plants involves many parameters. To simplify that, usually using computer simulation is applied. This research performs simulation process variation on turbine blade number, turbine blade curvature angle, turbine bucket angle and blocking system tilt angle. Those four variations were combined in order to obtain the best design of turbine. The study used Flow Simulation Solidworks application, and obtain data on turbine speed, pressure, force, and torque. However, this research focused on turbine torque value. The best design of turbine was obtained in the turbine with 6 blades, blade curvature angle of 65° and bucket angle of 10°, and blocking system tilt angle of 40°. In the best turbine, the produced torque value was 8.464 Nm.
The Architecture and Beyond of Tread and Riser
Directory of Open Access Journals (Sweden)
Sai Sanath
2016-01-01
The primary constitution of stairs is the arrangement of horizontal and vertical measures known as tread and riser. This is the simplest arrangement that essentially conveys people from one level to the other with required comfort and safety. Steps are a universal symbol with multiple interpretations. They are the most generally used similes in art, philosophy and psychology. Stairs occupy a unique status in the built environment because they not only convey people, but also symbolize the psychological, spiritual and artistic aspects of human nature. The mental significance and symbolic connotations of steps are deeply rooted. Understanding the role of stairs in different spheres of human need and expression is crucial in approaching its design. The pattern of stairs is dependent on the type of materials and other related design considerations. It is one of the unique architectural entities that reflect the various facets of social, psychological, artistic, metaphysical and religious dimensions. The importance of physical activity in the rising sedentary life styles is linked to the design of building elements, especially the staircases. The advancement in technology has displaced the role of stairs into an inconsequential means of emergency escape. But the importance of physical activity in the rising sedentary lifestyle has revitalized the concept of stairs as an active building component. The mono functional approach to staircases in high-rise buildings, especially as the means of escape in emergency situations, indicates that the design of staircases as multi functional element is still under the confines of design explorations. This paper is an attempt to understand the concept of stairs not only from the evolutionary point of view, but also the associated metaphoric meanings and its emerging multi facet identity. The concept of vertical accessibility in the form of tread and riser arrangement makes stairs a timeless phenomenon. The approach to multi utility
Simulation of neutral gas flow in a tokamak divertor using the Direct Simulation Monte Carlo method
International Nuclear Information System (INIS)
Gleason-González, Cristian; Varoutis, Stylianos; Hauer, Volker; Day, Christian
2014-01-01
Highlights: • Subdivertor gas flows calculations in tokamaks by coupling the B2-EIRENE and DSMC method. • The results include pressure, temperature, bulk velocity and particle fluxes in the subdivertor. • Gas recirculation effect towards the plasma chamber through the vertical targets is found. • Comparison between DSMC and the ITERVAC code reveals a very good agreement. - Abstract: This paper presents a new innovative scientific and engineering approach for describing sub-divertor gas flows of fusion devices by coupling the B2-EIRENE (SOLPS) code and the Direct Simulation Monte Carlo (DSMC) method. The present study exemplifies this with a computational investigation of neutral gas flow in the ITER's sub-divertor region. The numerical results include the flow fields and contours of the overall quantities of practical interest such as the pressure, the temperature and the bulk velocity assuming helium as model gas. Moreover, the study unravels the gas recirculation effect located behind the vertical targets, viz. neutral particles flowing towards the plasma chamber. Comparison between calculations performed by the DSMC method and the ITERVAC code reveals a very good agreement along the main sub-divertor ducts
Low-Mach number simulations of transcritical flows
Lapenna, Pasquale E.
2018-01-08
A numerical framework for the direct simulation, in the low-Mach number limit, of reacting and non-reacting transcritical flows is presented. The key feature are an efficient and detailed representation of the real fluid properties and an high-order spatial discretization. The latter is of fundamental importance to correctly resolve the largely non-linear behavior of the fluid in the proximity of the pseudo-boiling. The validity of the low-Mach number assumptions is assessed for a previously developed non-reacting DNS database of transcritical and supercritical mixing. Fully resolved DNS data employing high-fidelity thermodynamical models are also used to investigate the spectral characteristic as well as the differences between transcritical and supercritical jets.
Large Eddy Simulations of turbulent flows at supercritical pressure
Energy Technology Data Exchange (ETDEWEB)
Kunik, C.; Otic, I.; Schulenberg, T., E-mail: claus.kunik@kit.edu, E-mail: ivan.otic@kit.edu, E-mail: thomas.schulenberg@kit.edu [Karlsruhe Inst. of Tech. (KIT), Karlsruhe (Germany)
2011-07-01
A Large Eddy Simulation (LES) method is used to investigate turbulent heat transfer to CO{sub 2} at supercritical pressure for upward flows. At those pressure conditions the fluid undergoes strong variations of fluid properties in a certain temperature range, which can lead to a deterioration of heat transfer (DHT). In this analysis, the LES method is applied on turbulent forced convection conditions to investigate the influence of several subgrid scale models (SGS-model). At first, only velocity profiles of the so-called inflow generator are considered, whereas in the second part temperature profiles of the heated section are investigated in detail. The results are statistically analyzed and compared with DNS data from the literature. (author)
First Experiments with the Simulation of Particulate Flows
Energy Technology Data Exchange (ETDEWEB)
Uhlmann, M.
2003-07-01
Several variants of a Eulerian-Lagrangian method for the simulation of particulate flows are implemented in a finite-difference framework. All methods have in common that they represent the presence of the solid fraction by means of artificial volume forces in the momentum equation of the fluid phase. Thereby, explicit griddling of the moving particles is avoided and a fixed grid can be used. The computations show that the direct forcing method (Kin et a/., 2001) is not adequate for a our purposes due to large oscillations in the hydro-dynamical forces. The immersed method of Pekin (2002) does provide accurate predictions of particle motion,however at the cost of a small time step. (Author) 33 refs.
First Experiments with the Simulation of Particulate Flows
International Nuclear Information System (INIS)
Uhlmann, M.
2003-01-01
Several variants of a Eulerian-Lagrangian method for the simulation of particulate flows are implemented in a finite-difference framework. All methods have in common that they represent the presence of the solid fraction by means of artificial volume forces in the momentum equation of the fluid phase. Thereby, explicit griddling of the moving particles is avoided and a fixed grid can be used. The computations show that the direct forcing method (Kin et a/., 2001) is not adequate for a our purposes due to large oscillations in the hydro-dynamical forces. The immersed method of Pekin (2002) does provide accurate predictions of particle motion,however at the cost of a small time step. (Author) 33 refs
Large-Eddy-Simulation of turbulent magnetohydrodynamic flows
Directory of Open Access Journals (Sweden)
Woelck Johannes
2017-01-01
Full Text Available A magnetohydrodynamic turbulent channel flow under the influence of a wallnormal magnetic field is investigated using the Large-Eddy-Simulation technique and k-equation subgrid-scale-model. Therefore, the new solver MHDpisoFoam is implemented in the OpenFOAM CFD-Code. The temporal decay of an initial turbulent field for different magnetic parameters is investigated. The rms values of the averaged velocity fluctuations show a similar, trend for each coordinate direction. 80% of the fluctuations are damped out in the range between 0 < Ha < < 75 at Re = 6675. The trend can be approximated via an exponential of the form exp(−a·Ha, where a is a scaling parameter. At higher Hartmann numbers the fluctuations decrease in an almost linear way. Therefore, the results of this study show that it may be possible to construct a general law for the turbulence damping due to action of magnetic fields.
Energy Technology Data Exchange (ETDEWEB)
Grandotto Biettoli, M
2006-04-15
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)
Simulation of water flows in multiple columns with small outlets
International Nuclear Information System (INIS)
Suh, Yong Kweon; Li, Zi Lu; Jeong, Jong Hyun; Lee, Jun Hee
2006-01-01
High-pressure die casting such as thixocasting and rheocasting is an effective process in the manufacturing automotive parts. Following the recent trend in the automotive manufacturing technologies, the product design subject to the die casting becomes more and more complex. Simultaneously the injection speed is also designed to be very high to establish a short cycle-time. Thus, the requirement of the die design becomes more demanding than ever before. In some cases the product's shape can have multiple slender manifolds. In such cases, design of the inlet and outlet parts of the die is very important in the whole manufacturing process. The main issues required for the qualified products are to attain gentle and uniform flow of the molten liquid within the passages of the die. To satisfy such issues, the inlet cylinder ('bed cylinder' in this paper) must be as large as possible and simultaneously the outlet opening at the end of each passage must be as small as possible. However these in turn obviously bring additional manufacturing costs caused by re-melting of the bed cylinder and increased power due to the small outlet-openings. The purpose of this paper is to develop effective simulation methods of calculation for fluid flows in multiple columns, which mimic the actual complex design, and to get some useful information which can give some contributions to the die-casting industry. We have used a commercial code CFX in the numerical simulation. The primary parameter involved is the size of the bed cylinder. We will show how the very small opening of the outlet can be treated with the aid of the porous model provided in the code. To check the validity of the numerical results we have also conducted a simple experiment by using water
Mathematics of large eddy simulation of turbulent flows
Energy Technology Data Exchange (ETDEWEB)
Berselli, L.C. [Pisa Univ. (Italy). Dept. of Applied Mathematics ' ' U. Dini' ' ; Iliescu, T. [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Mathematics; Layton, W.J. [Pittsburgh Univ., PA (United States). Dept. of Mathematics
2006-07-01
Large eddy simulation (LES) is a method of scientific computation seeking to predict the dynamics of organized structures in turbulent flows by approximating local, spatial averages of the flow. Since its birth in 1970, LES has undergone an explosive development and has matured into a highly-developed computational technology. It uses the tools of turbulence theory and the experience gained from practical computation. This book focuses on the mathematical foundations of LES and its models and provides a connection between the powerful tools of applied mathematics, partial differential equations and LES. Thus, it is concerned with fundamental aspects not treated so deeply in the other books in the field, aspects such as well-posedness of the models, their energy balance and the connection to the Leray theory of weak solutions of the Navier-Stokes equations. The authors give a mathematically informed and detailed treatment of an interesting selection of models, focusing on issues connected with understanding and expanding the correctness and universality of LES. This volume offers a useful entry point into the field for PhD students in applied mathematics, computational mathematics and partial differential equations. Non-mathematicians will appreciate it as a reference that introduces them to current tools and advances in the mathematical theory of LES. (orig.)
Large-eddy simulations of unidirectional water flow over dunes
Grigoriadis, D. G. E.; Balaras, E.; Dimas, A. A.
2009-06-01
The unidirectional, subcritical flow over fixed dunes is studied numerically using large-eddy simulation, while the immersed boundary method is implemented to incorporate the bed geometry. Results are presented for a typical dune shape and two Reynolds numbers, Re = 17,500 and Re = 93,500, on the basis of bulk velocity and water depth. The numerical predictions of velocity statistics at the low Reynolds number are in very good agreement with available experimental data. A primary recirculation region develops downstream of the dune crest at both Reynolds numbers, while a secondary region develops at the toe of the dune crest only for the low Reynolds number. Downstream of the reattachment point, on the dune stoss, the turbulence intensity in the developing boundary layer is weaker than in comparable equilibrium boundary layers. Coherent vortical structures are identified using the fluctuating pressure field and the second invariant of the velocity gradient tensor. Vorticity is primarily generated at the dune crest in the form of spanwise "roller" structures. Roller structures dominate the flow dynamics near the crest, and are responsible for perturbing the boundary layer downstream of the reattachment point, which leads to the formation of "horseshoe" structures. Horseshoe structures dominate the near-wall dynamics after the reattachment point, do not rise to the free surface, and are distorted by the shear layer of the next crest. The occasional interaction between roller and horseshoe structures generates tube-like "kolk" structures, which rise to the free surface and persist for a long time before attenuating.
Direct numerical simulation of incompressible multiphase flow with phase change
Lee, Moon Soo; Riaz, Amir; Aute, Vikrant
2017-09-01
Simulation of multiphase flow with phase change is challenging because of the potential for unphysical pressure oscillations, spurious velocity fields and mass flux errors across the interface. The resulting numerical errors may become critical when large density contrasts are present. To address these issues, we present a new approach for multiphase flow with phase change that features, (i) a smooth distribution of sharp velocity jumps and mass flux within a narrow region surrounding the interface, (ii) improved mass flux projection from the implicit interface onto the uniform Cartesian grid and (iii) post-advection velocity correction step to ensure accurate velocity divergence in interfacial cells. These new features are implemented in combination with a sharp treatment of the jumps in pressure and temperature gradient. A series of 1-D, 2-D, axisymmetric and 3-D problems are solved to verify the improvements afforded by the new approach. Axisymmetric film boiling results are also presented, which show good qualitative agreement with heat transfer correlations as well as experimental observations of bubble shapes.
International Nuclear Information System (INIS)
Wang Haijun; He Huining; Luo Yushan; Wang Weishu
2011-01-01
In the present work, a numerical simulation was performed to study the flow characteristics of lean jet to cross flow in a main tube in the safety injection of reactor cooling system. The influence scope and mixing characteristics of the confined lean jet in cross-flow were studied. It can be concluded that three basic flow regimes are marked, namely the attached lean jet, lift-off lean jet and impinging lean jet. The velocity ratio V R is the key factor in the flow state. The depth and region of jet to main flow are enhanced with the increase of the velocity ratio. The jet flow penetrates through the main flow with the increase of the velocity ratio. At higher velocity ratio, the jet flow strikes the main flow bottom and circumfluence happens in upriver of main flow. The vortex flow characteristics dominate the flow near region of jet to cross-flow and the mixture of jet to cross-flow. At different velocity ratio V R , the vortex grows from the same displacement, but the vortex type and the vortex is different. At higher velocity ratio, the vortex develops fleetly, wears off sharp and dies out sharp. The study is very important to the heat transfer experiments of cross-flow jet and thermal stress analysis in the designs of nuclear engineering. (authors)
Numerical flow simulation over clean and iced wind turbine blades
Energy Technology Data Exchange (ETDEWEB)
Villalpando, F.; Reggio, M. [Ecole Polytechnique, Montreal, PQ (Canada); Ilinca, A. [Quebec Univ., Rimouski, PQ (Canada). Wind Energy Group
2009-07-01
The impact of ice accretion on the drag and lift coefficients of a wind turbine blade was studied. Computerized simulations were conducted for both clean and ice-accreted 2-D airfoils at various angles of attack. The finite volume-based commercial computational fluid dynamics (CFD) program FLUENT was used to simulate the 2-D geometries of turbulent, unsteady and incompressible flow around the airfoils. Pressure coefficients and the contribution of pressure and friction forces to the lift and drag coefficients were analyzed. The study showed that traditional calculations over-predict the lift and drag of ice-accreted airfoil profiles. Ice accreted over the profile's pressure side provoked a bigger lift reduction and drag increase than that caused by ice accreted on the suction side. The poor performance of the aerodynamic coefficients was attributed to the contribution of pressure forces. Further experimentation is required to determine if de-icing systems for turbine blades should be developed to prevent or melt ice over the profile pressure side. 11 refs., 7 tabs., 15 figs.
Two-phase flow field simulation of horizontal steam generators
Energy Technology Data Exchange (ETDEWEB)
Rabiee, Ataollah; Kamalinia, Amir Hossein; Hadad, Kamal [School of Mechanical Engineering, Shiraz University, Shiraz (Iran, Islamic Republic of)
2017-02-15
The analysis of steam generators as an interface between primary and secondary circuits in light water nuclear power plants is crucial in terms of safety and design issues. VVER-1000 nuclear power plants use horizontal steam generators which demand a detailed thermal hydraulics investigation in order to predict their behavior during normal and transient operational conditions. Two phase flow field simulation on adjacent tube bundles is important in obtaining logical numerical results. However, the complexity of the tube bundles, due to geometry and arrangement, makes it complicated. Employment of porous media is suggested to simplify numerical modeling. This study presents the use of porous media to simulate the tube bundles within a general-purpose computational fluid dynamics code. Solved governing equations are generalized phase continuity, momentum, and energy equations. Boundary conditions, as one of the main challenges in this numerical analysis, are optimized. The model has been verified and tuned by simple two-dimensional geometry. It is shown that the obtained vapor volume fraction near the cold and hot collectors predict the experimental results more accurately than in previous studies.
Flow MRI simulation in complex 3D geometries: Application to the cerebral venous network.
Fortin, Alexandre; Salmon, Stéphanie; Baruthio, Joseph; Delbany, Maya; Durand, Emmanuel
2018-02-05
Develop and evaluate a complete tool to include 3D fluid flows in MRI simulation, leveraging from existing software. Simulation of MR spin flow motion is of high interest in the study of flow artifacts and angiography. However, at present, only a few simulators include this option and most are restricted to static tissue imaging. An extension of JEMRIS, one of the most advanced high performance open-source simulation platforms to date, was developed. The implementation of a Lagrangian description of the flow allows simulating any MR experiment, including both static tissues and complex flow data from computational fluid dynamics. Simulations of simple flow models are compared with real experiments on a physical flow phantom. A realistic simulation of 3D flow MRI on the cerebral venous network is also carried out. Simulations and real experiments are in good agreement. The generality of the framework is illustrated in 2D and 3D with some common flow artifacts (misregistration and inflow enhancement) and with the three main angiographic techniques: phase contrast velocimetry (PC), time-of-flight, and contrast-enhanced imaging MRA. The framework provides a versatile and reusable tool for the simulation of any MRI experiment including physiological fluids and arbitrarily complex flow motion. © 2018 International Society for Magnetic Resonance in Medicine.
A new algorithm for extended nonequilibrium molecular dynamics simulations of mixed flow
Hunt, T.A.; Hunt, Thomas A.; Bernardi, Stefano; Todd, B.D.
2010-01-01
In this work, we develop a new algorithm for nonequilibrium molecular dynamics of fluids under planar mixed flow, a linear combination of planar elongational flow and planar Couette flow. To date, the only way of simulating mixed flow using nonequilibrium molecular dynamics techniques was to impose
GPU accelerated flow solver for direct numerical simulation of turbulent flows
Energy Technology Data Exchange (ETDEWEB)
Salvadore, Francesco [CASPUR – via dei Tizii 6/b, 00185 Rome (Italy); Bernardini, Matteo, E-mail: matteo.bernardini@uniroma1.it [Department of Mechanical and Aerospace Engineering, University of Rome ‘La Sapienza’ – via Eudossiana 18, 00184 Rome (Italy); Botti, Michela [CASPUR – via dei Tizii 6/b, 00185 Rome (Italy)
2013-02-15
Graphical processing units (GPUs), characterized by significant computing performance, are nowadays very appealing for the solution of computationally demanding tasks in a wide variety of scientific applications. However, to run on GPUs, existing codes need to be ported and optimized, a procedure which is not yet standardized and may require non trivial efforts, even to high-performance computing specialists. In the present paper we accurately describe the porting to CUDA (Compute Unified Device Architecture) of a finite-difference compressible Navier–Stokes solver, suitable for direct numerical simulation (DNS) of turbulent flows. Porting and validation processes are illustrated in detail, with emphasis on computational strategies and techniques that can be applied to overcome typical bottlenecks arising from the porting of common computational fluid dynamics solvers. We demonstrate that a careful optimization work is crucial to get the highest performance from GPU accelerators. The results show that the overall speedup of one NVIDIA Tesla S2070 GPU is approximately 22 compared with one AMD Opteron 2352 Barcelona chip and 11 compared with one Intel Xeon X5650 Westmere core. The potential of GPU devices in the simulation of unsteady three-dimensional turbulent flows is proved by performing a DNS of a spatially evolving compressible mixing layer.
Lattice Boltzmann Simulations in the Slip and Transition Flow Regime with the Peano Framework
Neumann, Philipp; Rohrmann, Till
2012-01-01
We present simulation results of flows in the finite Knudsen range, which is in the slip and transition flow regime. Our implementations are based on the Lattice Boltzmann method and are accomplished within the Peano framework. We validate our code
How to inspect platform risers: an effective approach and new challenges
International Nuclear Information System (INIS)
Agthoven, Robert van
2007-01-01
Ageing risers on offshore platforms, designed and built several decades ago, were until recently hard to inspect or not inspectable at all. This was due to their layout or ID geometry changes prohibiting the use of product propelled intelligent pigs, which are frequently used, on long distance pipelines. Growing concerns about reliability and safety, as well as environmental pressure, are the impetus for operators of offshore platforms to check the condition of the risers, which until now could not be inspected. This paper describes a few solutions to enter these 'non-inspect-able' risers to check their condition by using special small diameter cable operated tools. These new miniature cable tools are spin-offs from the well-known cable (tether, umbilical) tools introduced more than two decades ago by RTD for the inspection of (off)-loading lines. The first generation gravity driven small diameter riser inspection tools were designed to inspect the vertical section of the riser only. On-going development has resulted in a second generation of riser inspection tools which can now enter a few hundred metres into the horizontal connecting pipeline on the sea-floor by using a small, but powerful, crawler. With this ability these tools are the only solution for riser-pipes and relatively short connecting pipelines which terminate at a T-or Y-connection in the vicinity of the platform. All riser inspection tools apply ultrasonics to quantify wall thickness and corrosion. A novel TOFD (Time Of Flight Diffraction) module can be applied as an option to inspect in the circumferential weld area. All cable tools have a reinforced cable, which is used for tool control and retrieval. A strong advantage of these cable tools is that they provide on-line results and allow on-site evaluation. Since the introduction of these new tools considerable experience has been gained. The history of development and several typical cases of applications are given in this paper. In addition
Kellogg, Kevin; Liu, Peiyuan; Lamarche, Casey; Hrenya, Christine
2017-11-01
In flows of cohesive particles, agglomerates will readily form and break. These agglomerates are expected to complicate how particles interact with the surrounding fluid in multiphase flows, and consequently how the solids flow. In this work, a dilute flow of particles driven by gas against gravity is studied. A continuum framework, composed of a population balance to predict the formation of agglomerates, and kinetic-theory-based balances, is used to predict the flow of particles. The closures utilized for the birth and death rates due to aggregation and breakage in the population balance take into account how the impact velocity (the granular temperature) affects the outcome of a collision as aggregation, rebound, or breakage. The agglomerate size distribution and solids velocity predicted by the continuum framework are compared to discrete element method (DEM) simulations, as well to experimental results of particles being entrained from the riser of a fluidized bed. Dow Corning Corporation.
Dietterich, Hannah; Lev, Einat; Chen, Jiangzhi; Richardson, Jacob A.; Cashman, Katharine V.
2017-01-01
Numerical simulations of lava flow emplacement are valuable for assessing lava flow hazards, forecasting active flows, designing flow mitigation measures, interpreting past eruptions, and understanding the controls on lava flow behavior. Existing lava flow models vary in simplifying assumptions, physics, dimensionality, and the degree to which they have been validated against analytical solutions, experiments, and natural observations. In order to assess existing models and guide the development of new codes, we conduct a benchmarking study of computational fluid dynamics (CFD) models for lava flow emplacement, including VolcFlow, OpenFOAM, FLOW-3D, COMSOL, and MOLASSES. We model viscous, cooling, and solidifying flows over horizontal planes, sloping surfaces, and into topographic obstacles. We compare model results to physical observations made during well-controlled analogue and molten basalt experiments, and to analytical theory when available. Overall, the models accurately simulate viscous flow with some variability in flow thickness where flows intersect obstacles. OpenFOAM, COMSOL, and FLOW-3D can each reproduce experimental measurements of cooling viscous flows, and OpenFOAM and FLOW-3D simulations with temperature-dependent rheology match results from molten basalt experiments. We assess the goodness-of-fit of the simulation results and the computational cost. Our results guide the selection of numerical simulation codes for different applications, including inferring emplacement conditions of past lava flows, modeling the temporal evolution of ongoing flows during eruption, and probabilistic assessment of lava flow hazard prior to eruption. Finally, we outline potential experiments and desired key observational data from future flows that would extend existing benchmarking data sets.
Analysis of the effects of corrosion probe on riser 241-AN-102-WST-16 during seismic event
International Nuclear Information System (INIS)
ZIADA, H.H.
1998-01-01
This analysis supports the installation activity of the corrosion probe in Tank 241-AN-102. The probe is scheduled to be installed in Riser 241-AN-102-WST-16 (formerly known as Riser 15B). The purpose of this analysis is to evaluate the potential effect of the corrosion probe on the riser during a credible seismic event. The previous analysis (HNF 1997a) considered only pump jet impingement loading
National Research Council Canada - National Science Library
Behrman, Robert; Carley, Kathleen
2003-01-01
This paper describes the Dynamic Information Flow Simulation (DIFS), an abstract model for analyzing the structure and function of intelligence support organizations and the activities of entities within...
NUMERICAL SIMULATION AND MODELING OF UNSTEADY FLOW AROUND AN AIRFOIL. (AERODYNAMIC FORM
Directory of Open Access Journals (Sweden)
M. Y. Habib
2015-07-01
Full Text Available During this work, we simulated an unsteady flow around an airfoil type NACA0012 using the Fluent software. The objective is to control the code on the one hand and on the other hand the simulation of unsteady flows. By simulating an unsteady flow Reynolds number (Re = 6.85 * 106 and Mach number (M = 0.3, we have the flowing with a grid (mesh adequate numerical results and experimental data are in good agreement. To represent the results of the simulation we have validated by comparing the values of aerodynamic coefficients with those of experimental data.
Direct numerical simulations of nucleate boiling flows of binary mixtures
International Nuclear Information System (INIS)
Didier Jamet; Celia Fouillet
2005-01-01
Full text of publication follows: Better understand the origin and characteristics of boiling crisis is still a scientific challenge despite many years of valuable studies. One of the reasons why boiling crisis is so difficult to understand is that local and coupled physical phenomena are believed to play a key role in the trigger of instabilities which lead to the dry out of large portions of the heated solid phase. Nucleate boiling of a single bubble is fairly well understood compared to boiling crisis. Therefore, the numerical simulation of a single bubble growth during nucleate boiling is a good candidate to evaluate the capabilities of a numerical method to deal with complex liquid-vapor phenomena with phase-change and eventually to tackle the boiling crisis problem. In this paper, we present results of direct numerical simulations of nucleate boiling. The numerical method used is the second gradient method, which is a diffuse interface method dedicated to liquid vapor flows with phase-change. This study is not intended to provide quantitative results, partly because all the simulations are two-dimensional. However, particular attention is paid to the influence of some parameters on the main features of nucleate boiling, i.e. the radius of departure and the frequency of detachment of bubbles. In particular, we show that, as the contact angle increases, the radius of departure increases whereas the frequency of detachment decreases. Moreover, the influence of the existence of quasi non-condensable gas is studied. Numerical results show an important decrease of the heat exchange coefficient when a small amount of a quasi non-condensable gas is added to the pure liquid-vapor water system. This result is in agreement with experimental observations. Beyond these qualitative results, this numerical study allows to get insight into some important physical phenomena and to confirm that during nucleate boiling, large scale quantities are influenced by small scale
Global Qualitative Flow-Path Modeling for Local State Determination in Simulation and Analysis
Malin, Jane T. (Inventor); Fleming, Land D. (Inventor)
1998-01-01
For qualitative modeling and analysis, a general qualitative abstraction of power transmission variables (flow and effort) for elements of flow paths includes information on resistance, net flow, permissible directions of flow, and qualitative potential is discussed. Each type of component model has flow-related variables and an associated internal flow map, connected into an overall flow network of the system. For storage devices, the implicit power transfer to the environment is represented by "virtual" circuits that include an environmental junction. A heterogeneous aggregation method simplifies the path structure. A method determines global flow-path changes during dynamic simulation and analysis, and identifies corresponding local flow state changes that are effects of global configuration changes. Flow-path determination is triggered by any change in a flow-related device variable in a simulation or analysis. Components (path elements) that may be affected are identified, and flow-related attributes favoring flow in the two possible directions are collected for each of them. Next, flow-related attributes are determined for each affected path element, based on possibly conflicting indications of flow direction. Spurious qualitative ambiguities are minimized by using relative magnitudes and permissible directions of flow, and by favoring flow sources over effort sources when comparing flow tendencies. The results are output to local flow states of affected components.
Directory of Open Access Journals (Sweden)
Ledjane Lima Sobrinho
2011-09-01
Full Text Available Industry has been challenged to provide riser systems which are more cost effective and which can fill the technology gaps with respect to water depth, riser diameter and high temperatures left open by flexibles, steel catenary risers (SCRs and hybrid risers. Composite materials present advantages over conventional steel risers because composite materials are lighter, more fatigue and corrosion resistant, better thermal insulators and can be designed for improving the structural and mechanical response. This paper contains a study of the toughening mechanism of an epoxy resin under rubber addition by means of fractographic analysis and its relation with the fracture process and increase of strength of a composite riser employing this polymeric matrix. Initially, an epoxy resin system was toughened by rubber CTBN addition (10 wt. (% as a way of improving the flexibility of future risers. Mechanical and thermal analyses were carried out for characterizing the polymeric systems. Later, composite tubes were prepared and mechanically characterized. The influence of matrix toughening on the mechanical behavior of the tubes was also studied. Split-disk tests were used to determine the hoop tensile strength of these specimens. The results indicate that the matrix plays an important role in composite fracture processes. The adding rubber to the polymeric matrix promoted a simultaneous increase of stress and elongation at fracture of the tubes manufactured herein, which is not often reported. These results, probably, is function of better adhesion between fibers and polymeric matrix observed in the CTBN-modified composite rings, which was evidenced in the fractografic analysis by SEM after the split-disk tests.
A test section design to simulate horizontal two-phase air-water flow
International Nuclear Information System (INIS)
Faccini, Jose Luiz H.; Cesar, Silvia B.G.; Coutinho, Jorge A.; Freitas, Sergio Carlos; Addor, Pedro N.
2002-01-01
In this work an air-water two-phase flow horizontal test section assembling at Nuclear Engineering Institute (IEN) is presented. The test section was designed to allow four-phase flow patterns to be simulated: bubble flow, stratified flow, wave flow and slug flow. These flow patterns will be identified by non-conventional ultrasonic techniques which have been developed to meet this particular application. Based on the separated flow and drift-flux models the test section design steps are shown. A description of the test section and its instrumentation and data acquisition system is also provided. (author)
Three-dimensional simulation of viscous-flow agglomerate sintering.
Kirchhof, M J; Schmid, H -J; Peukert, W
2009-08-01
The viscous-flow sintering of different agglomerate particle morphologies is studied by three-dimensional computer simulations based on the concept of fractional volume of fluid. For a fundamental understanding of particle sintering characteristics, the neck growth kinetics in agglomerate chains and in doublets consisting of differently sized primary particles is investigated. Results show that different sintering contacts in agglomerates even during the first stages are not completely independent from each other, even though differences are small. The neck growth kinetics of differently sized primary particles is determined by the smaller one up to a size difference by a factor of approximately 2, whereas for larger size differences, the kinetics becomes faster. In particular, the agglomerate sintering kinetics is investigated for particle chains of different lengths and for different particle morphologies each having ten primary particles and nine initial sintering contacts. For agglomerate chains, the kinetics approximately can be normalized by using the radius of the fully coalesced sphere. In general, different agglomerate morphologies show equal kinetics during the first sintering stages, whereas during advanced stages, compact morphologies show significantly faster sintering progress than more open morphologies. Hence, the overall kinetics cannot be described by simply using constant morphology correction factors such as fractal dimension or mean coordination number which are used in common sintering models. However, for the first stages of viscous-flow agglomerate sintering, which are the most important for many particle processes, a sintering equation is presented. Although we use agglomerates consisting of spherical primary particles, our methodology can be applied to other aggregate geometries as well.
Numerical simulation of turbulent buoyant flows in horizontal channels
International Nuclear Information System (INIS)
Seiter, C.
1995-09-01
A numerical method is presented, to calculate the three-dimensional, time-dependent large scale structure of turbulent buoyant flows. The subject of the study is the Rayleigh-Benard-convection with air (Pr=0.71, Ra=2.5 10 6 , 10 7 ) and sodium (Pr=0.006, Ra=8.4 10 4 , 2.5 10 5 , 10 6 , 10 7 ) and a fluid layer with water and an internal heat source (Pr=7.0, Ra I =1.5 10 10 ) at moderate and high Rayleigh-numbers. The goal of the work is both, the analysis of structures of instantaneous as well as the statistical analysis of spatially and/or time averaged data, to give a contribution to the investigation of the characteristics of turbulent natural convection mainly in fluids with small Prandtl-numbers. The large eddy simulation of natural convection requires the development of appropriate momentum and heat subgrid scale models and the formulation of new boundary conditions. The used energy-length-models in the computer code TURBIT are extended methodically by modification of the characteristic length scales of the sub scale turbulence. The reduction or the increase of the sub scale turbulence correlations, caused by the influence of solid boundaries or the stratification, is considered. In the same way the new boundary conditions for the diffusive terms of the conservation equations are seen to be necessary, when the thermal or in the case of liquid metals the more critical hydrodynamic boundary layer is resolved insufficiently or not at all. The extended and new methods, models and boundary conditions, which enabled the realization of the planned simulations, are presented. (orig.)
A Finite Element Method for Simulation of Compressible Cavitating Flows
Shams, Ehsan; Yang, Fan; Zhang, Yu; Sahni, Onkar; Shephard, Mark; Oberai, Assad
2016-11-01
This work focuses on a novel approach for finite element simulations of multi-phase flows which involve evolving interface with phase change. Modeling problems, such as cavitation, requires addressing multiple challenges, including compressibility of the vapor phase, interface physics caused by mass, momentum and energy fluxes. We have developed a mathematically consistent and robust computational approach to address these problems. We use stabilized finite element methods on unstructured meshes to solve for the compressible Navier-Stokes equations. Arbitrary Lagrangian-Eulerian formulation is used to handle the interface motions. Our method uses a mesh adaptation strategy to preserve the quality of the volumetric mesh, while the interface mesh moves along with the interface. The interface jump conditions are accurately represented using a discontinuous Galerkin method on the conservation laws. Condensation and evaporation rates at the interface are thermodynamically modeled to determine the interface velocity. We will present initial results on bubble cavitation the behavior of an attached cavitation zone in a separated boundary layer. We acknowledge the support from Army Research Office (ARO) under ARO Grant W911NF-14-1-0301.
3D code for simulations of fluid flows
International Nuclear Information System (INIS)
Skandera, D.
2004-01-01
In this paper, a present status in the development of the new numerical code is reported. The code is considered for simulations of fluid flows. The finite volume approach is adopted for solving standard fluid equations. They are treated in a conservative form to ensure a correct conservation of fluid quantities. Thus, a nonlinear hyperbolic system of conservation laws is numerically solved. The code uses the Eulerian description of the fluid and is designed as a high order central numerical scheme. The central approach employs no (approximate) Riemann solver and is less computational expensive. The high order WENO strategy is adopted in the reconstruction step to achieve results comparable with more accurate Riemann solvers. A combination of the central approach with an iterative solving of a local Riemann problem is tested and behaviour of such numerical flux is reported. An extension to three dimensions is implemented using a dimension by dimension approach, hence, no complicated dimensional splitting need to be introduced. The code is fully parallelized with the MPI library. Several standard hydrodynamic tests in one, two and three dimensions were performed and their results are presented. (author)
Flow and air conditioning simulations of computer turbinectomized nose models.
Pérez-Mota, J; Solorio-Ordaz, F; Cervantes-de Gortari, J
2018-04-16
Air conditioning for the human respiratory system is the most important function of the nose. When obstruction occurs in the nasal airway, turbinectomy is used to correct such pathology. However, mucosal atrophy may occur sometime after this surgery when it is overdone. There is not enough information about long-term recovery of nasal air conditioning performance after partial or total surgery. The purpose of this research was to assess if, based on the flow and temperature/humidity characteristics of the air intake to the choana, partial resection of turbinates is better than total resection. A normal nasal cavity geometry was digitized from tomographic scans and a model was printed in 3D. Dynamic (sinusoidal) laboratory tests and computer simulations of airflow were conducted with full agreement between numerical and experimental results. Computational adaptations were subsequently performed to represent six turbinectomy variations and a swollen nasal cavity case. Streamlines along the nasal cavity and temperature and humidity distributions at the choana indicated that the middle turbinate partial resection is the best alternative. These findings may facilitate the diagnosis of nasal obstruction and can be useful both to plan a turbinectomy and to reduce postoperative discomfort. Graphical Abstract ᅟ.
Numerical Simulation of 3D Viscous MHD Flows
National Research Council Canada - National Science Library
Golovachov, Yurii P; Kurakin, Yurii A; Schmidt, Alexander A; Van Wie, David M
2003-01-01
.... Flows in hypersonic intakes are considered. Preliminary results showed that local MHD interaction in the inlet part of the intake model was the most effective for control over plasma flow field...
Immersed boundary simulation of flow through arterial junctions
Indian Academy of Sciences (India)
Dwaipayan Sarkar
haemodynamic activities in regions like carotid arteries, encephalic regions and ... immersed boundary method (IBM), has gained attention in the last few years .... the flow from left inlet and the flow is subsequently divided among the two ...
Project Evaluation and Cash Flow Forecasting by Stochastic Simulation
Directory of Open Access Journals (Sweden)
Odd A. Asbjørnsen
1983-10-01
Full Text Available The net present value of a discounted cash flow is used to evaluate projects. It is shown that the LaPlace transform of the cash flow time function is particularly useful when the cash flow profiles may be approximately described by ordinary linear differential equations in time. However, real cash flows are stochastic variables due to the stochastic nature of the disturbances during production.
Accurate analysis of water flow pathways from rainfall to streams is critical for simulating water use, climate change impact, and contaminant transport. In this study, we developed a new scheme to simultaneously calibrate surface flow (SF) and baseflow (BF) simulations of Soil and Water Assessment ...
Numerical simulations of concrete flow: A benchmark comparison
DEFF Research Database (Denmark)
Roussel, Nicolas; Gram, Annika; Cremonesi, Massimiliano
2016-01-01
First, we define in this paper two benchmark flows readily usable by anyone calibrating a numerical tool for concrete flow prediction. Such benchmark flows shall allow anyone to check the validity of their computational tools no matter the numerical methods and parameters they choose. Second, we ...
Simulation and validation of concentrated subsurface lateral flow paths in an agricultural landscape
Zhu, Q.; Lin, H. S.
2009-08-01
The importance of soil water flow paths to the transport of nutrients and contaminants has long been recognized. However, effective means of detecting concentrated subsurface flow paths in a large landscape are still lacking. The flow direction and accumulation algorithm based on single-direction flow algorithm (D8) in GIS hydrologic modeling is a cost-effective way to simulate potential concentrated flow paths over a large area once relevant data are collected. This study tested the D8 algorithm for simulating concentrated lateral flow paths at three interfaces in soil profiles in a 19.5-ha agricultural landscape in central Pennsylvania, USA. These interfaces were (1) the interface between surface plowed layers of Ap1 and Ap2 horizons, (2) the interface with subsoil water-restricting clay layer where clay content increased to over 40%, and (3) the soil-bedrock interface. The simulated flow paths were validated through soil hydrologic monitoring, geophysical surveys, and observable soil morphological features. The results confirmed that concentrated subsurface lateral flow occurred at the interfaces with the clay layer and the underlying bedrock. At these two interfaces, the soils on the simulated flow paths were closer to saturation and showed more temporally unstable moisture dynamics than those off the simulated flow paths. Apparent electrical conductivity in the soil on the simulated flow paths was elevated and temporally unstable as compared to those outside the simulated paths. The soil cores collected from the simulated flow paths showed significantly higher Mn content at these interfaces than those away from the simulated paths. These results suggest that (1) the D8 algorithm is useful in simulating possible concentrated subsurface lateral flow paths if used with appropriate threshold value of contributing area and sufficiently detailed digital elevation model (DEM); (2) repeated electromagnetic surveys can reflect the temporal change of soil water storage
Numerical simulation of flow in De-NOx catalyst honeycomb with NOx reduction reaction
Energy Technology Data Exchange (ETDEWEB)
Tanno, K.; Makino, H. [Electric Power Industry, Kanagawa (Japan). Energy Engineering Research Lab.; Kurose, R.; Komori, S. [Kyoto Univ. (Japan). Dept. of Mechanical Engineering and Science
2013-07-01
The effect of flow behavior in a De-NOx honeycomb with NOx reduction reaction is investigated by direct numerical simulation (DNS). As the inlet flow, fully developed turbulent or laminar flow is given. The results show that the surface reaction is strongly affected by inner flow behavior. The surface reaction rate for the turbulent flow is higher than that for the laminar flow. This is due to the difference of inner flow behavior that the diffusion of NOx in the vicinity of the wall is dominated only by molecular diffusion for the laminar flow, whereas it is enhanced by turbulent motions for the turbulent flow. Moreover, surface reaction is suppressed towards downstream even though inlet flow is turbulent. This is due to the flow transition from turbulent to laminar.
Multiphase flows with phase change
Indian Academy of Sciences (India)
Multiphase flows with phase change are ubiquitous in many industrial sectors ranging from energy and infra-structure to specialty chemicals and pharmaceuticals. My own interest in mul- tiphase flows with phase change started more than 15 years ago when I had initiated work on riser reactor for fluid catalytic cracking and ...
Numerical Simulation on Forced Convective Condensation of Steam Upward Flow in a Vertical Pipe
Directory of Open Access Journals (Sweden)
Guo-Dong Qiu
2014-05-01
Full Text Available A transient three-dimensional volume of fluid (VOF simulation on condensation of upward flow of wet steam inside a 12 mm i.d. vertical pipe is presented. The effect of gravity and surface tension are taken into account. A uniform wall temperature has been fixed as boundary conditions. The mass flux is 130~6400 kg m−2's−1 and the turbulence inside the vapor phase and liquid phase have been handled by Reynolds stress model (RSM. The vapor quality of fluid is 0~0.4. The numerical simulation results show that, in all the simulation conditions, the bubbly flow, slug flow, churn flow, wispy annular flow, and annular flow are observed; in addition, the results of flow pattern are in good agreement with the regime map from Hewitt and Roberts. The typical velocity field characteristic of each flow pattern and the effect of velocity field on heat transfer of condensation are analyzed, indicating that the slug flow and churn flow have obvious local eddy. However, no obvious eddy is observed in other flow patterns and the streamlines are almost parallel to the flow direction. The simulation results of heat transfer coefficients and frictional pressure drop show good agreement with the correlations from existing literatures.
Large eddy simulation and direct numerical simulation of high speed turbulent reacting flows
Adumitroaie, V.; Frankel, S. H.; Madnia, C. K.; Givi, P.
The objective of this research is to make use of Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) for the computational analyses of high speed reacting flows. Our efforts in the first phase of this research conducted within the past three years have been directed in several issues pertaining to intricate physics of turbulent reacting flows. In our previous 5 semi-annual reports submitted to NASA LaRC, as well as several technical papers in archival journals, the results of our investigations have been fully described. In this progress report which is different in format as compared to our previous documents, we focus only on the issue of LES. The reason for doing so is that LES is the primary issue of interest to our Technical Monitor and that our other findings were needed to support the activities conducted under this prime issue. The outcomes of our related investigations, nevertheless, are included in the appendices accompanying this report. The relevance of the materials in these appendices are, therefore, discussed only briefly within the body of the report. Here, results are presented of a priori and a posterior analyses for validity assessments of assumed Probability Density Function (PDF) methods as potential subgrid scale (SGS) closures for LES of turbulent reacting flows. Simple non-premixed reacting systems involving an isothermal reaction of the type A + B yields Products under both chemical equilibrium and non-equilibrium conditions are considered. A priori analyses are conducted of a homogeneous box flow, and a spatially developing planar mixing layer to investigate the performance of the Pearson Family of PDF's as SGS models. A posteriori analyses are conducted of the mixing layer using a hybrid one-equation Smagorinsky/PDF SGS closure. The Smagorinsky closure augmented by the solution of the subgrid turbulent kinetic energy (TKE) equation is employed to account for hydrodynamic fluctuations, and the PDF is employed for modeling the
CFD for subcooled flow boiling: Simulation of DEBORA experiments
International Nuclear Information System (INIS)
Krepper, Eckhard; Rzehak, Roland
2011-01-01
Highlights: → In the DEBORA subcooled boiling tests using R12 are investigated. → Radial profiles of void fraction, liquid velocity, temperature and bubble sizes at the end of the heated length were measured. → The theoretical and experimental basis of correlations used in the wall boiling model are reviewed. → An assessment of the necessary recalibrations to describe the DEBORA tests is given. → With increased generated vapour the gas fraction profile changes from wall to core peaking, not captured by the present modelling. - Abstract: In this work we investigate the present capabilities of CFD for wall boiling. The computational model used combines the Euler/Euler two-phase flow description with heat flux partitioning. Very similar modelling was previously applied to boiling water under high pressure conditions relevant to nuclear power systems. Similar conditions in terms of the relevant non-dimensional numbers have been realized in the DEBORA tests using dichlorodifluoromethane (R12) as the working fluid. This facilitated measurements of radial profiles for gas volume fraction, gas velocity, liquid temperature and bubble size. After reviewing the theoretical and experimental basis of correlations used in the model, give a careful assessment of the necessary recalibrations to describe the DEBORA tests. It is then shown that within a certain range of conditions different tests can be simulated with a single set of model parameters. As the subcooling is decreased and the amount of generated vapour increases the gas fraction profile changes from wall to core peaking. This is a major effect not captured by the present modelling. Some quantitative deviations are assessed as well and directions for further model improvement are outlined.
Directory of Open Access Journals (Sweden)
Bogdanović-Jovanović Jasmina B.
2012-01-01
Full Text Available In the increasing need for energy saving worldwide, the designing process of turbomachinery, as an essential part of thermal and hydroenergy systems, goes in the direction of enlarging efficiency. Therefore, the optimization of turbomachinery designing strongly affects the energy efficiency of the entire system. In the designing process of turbomachinery blade profiling, the model of axisymmetric fluid flows is commonly used in technical practice, even though this model suits only the profile cascades with infinite number of infinitely thin blades. The actual flow in turbomachinery profile cascades is not axisymmetric, and it can be fictively derived into the axisymmetric flow by averaging flow parameters in the blade passages according to the circular coordinate. Using numerical simulations of flow in turbomachinery runners, its operating parameters can be preliminarily determined. Furthermore, using the numerically obtained flow parameters in the blade passages, averaged axisymmetric flow surfaces in blade profile cascades can also be determined. The method of determination of averaged flow parameters and averaged meridian streamlines is presented in this paper, using the integral continuity equation for averaged flow parameters. With thus obtained results, every designer can be able to compare the obtained averaged flow surfaces with axisymmetric flow surfaces, as well as the specific work of elementary stages, which are used in the procedure of blade designing. Numerical simulations of flow in an exemplary axial flow pump, used as a part of the thermal power plant cooling system, were performed using Ansys CFX. [Projekat Ministarstva nauke Republike Srbije, br. TR33040: Revitalization of existing and designing new micro and mini hydropower plants (from 100 kW to 1000 kW in the territory of South and Southeast Serbia
DEFF Research Database (Denmark)
Yang, Yang; Kær, Søren Knudsen
2012-01-01
The flow structure of one isothermal swirling case in the Sydney swirl flame database was studied using two numerical methods. Results from the Reynolds-averaged Navier-Stokes (RANS) approach and large eddy simulation (LES) were compared with experimental measurements. The simulations were applied...
Hybrid simulations of current-carrying instabilities in Z-pinch plasmas with sheared axial flow
International Nuclear Information System (INIS)
Sotnikov, Vladimir I.; Makhin, Volodymyr; Bauer, Bruno S.; Hellinger, Petr; Travnicek, Pavel; Fiala, Vladimir; Leboeuf, Jean-Noel
2002-01-01
The development of instabilities in z-pinch plasmas has been studied with three-dimensional (3D) hybrid simulations. Plasma equilibria without and with sheared axial flow have been considered. Results from the linear phase of the hybrid simulations compare well with linear Hall magnetohydrodynamics (MHD) calculations for sausage modes. The hybrid simulations show that sheared axial flow has a stabilizing effect on the development of both sausage and kink modes
Bokhorst, E. van; Blokland, H.
2012-01-01
Deep-sea oil and gas production normally involves the use of flexible risers that comprise a metal carcass with a large number of enveloping layers that safeguard the integrity of the pipe system. The flexible risers are hung from a floating platform and may be supported by several floating buoys to
Advanced Algebraic Multigrid Solvers for Subsurface Flow Simulation
Chen, Meng-Huo; Sun, Shuyu; Salama, Amgad
2015-01-01
and issues will be addressed and the corresponding remedies will be studied. As the multigrid methods are used as the linear solver, the simulator can be parallelized (although not trivial) and the high-resolution simulation become feasible, the ultimately
Simulation of horizontal pipe two-phase slug flows using the two-fluid model
Energy Technology Data Exchange (ETDEWEB)
Ortega Malca, Arturo J. [Pontificia Univ. Catolica do Rio de Janeiro, RJ (Brazil). Dept. de Engenharia Mecanica. Nucleo de Simulacao Termohidraulica de Dutos (SIMDUT); Nieckele, Angela O. [Pontificia Univ. Catolica do Rio de Janeiro, RJ (Brazil). Dept. de Engenharia Mecanica
2005-07-01
Slug flow occurs in many engineering applications, mainly in the transport of hydrocarbon fluids in pipelines. The intermittency of slug flow causes severe unsteady loading on the pipelines carrying the fluids, which gives rise to design problems. Therefore, it is important to be able to predict the onset and development of slug flow as well as slug characteristics. The present work consists in the simulation of two-phase flow in slug pattern through horizontal pipes using the two-fluid model in its transient and one-dimensional form. The advantage of this model is that the flow field is allowed to develop naturally from a given initial conditions as part of the transient calculation; the slug evolves automatically as a product of the computed flow development. Simulations are then carried out for a large number of flow conditions that lead a slug flow. (author)
Simulation-based patient flow analysis in an endoscopy unit
DEFF Research Database (Denmark)
Koo, Pyung-Hoi; Nielsen, Karl Brian; Jang, Jaejin
2010-01-01
One of the major elements in improving efficiency of healthcare services is patient flow. Patients require a variety of healthcare resources as they receive healthcare services. Poor management of patient flow results in long waiting time of patients, under/over utilization of medical resources......, low quality of care and high healthcare cost. This article addresses patient flow problems at a Gastrointestinal endoscopy unit. We attempt to analyze the main factors that contribute to the inefficient patient flow and process bottlenecks and to propose efficient patient scheduling and staff...
High definition graphics application in fluid flow simulations
International Nuclear Information System (INIS)
Bancroft, G.; Merritt, F.; Buning, P.; Watson, V.
1987-01-01
NASA Ames is using high spatial/color-resolution computer graphics to interactively visualize flow fields generated by supercomputer solutions for the flow about such vehicles as the Space Shuttle. The scientist's viewing position in three-dimensional space can be interactively changed while the fluid flow is either frozen or moving in time. Animated sequences can then be made for workstation viewing with the aid of specialized software that allows easy editing and automatic tweening of the sequences. Attention is presently given to the software generating the three-dimensional flow field displays, as well as that for creating the animation sequences
CFD simulations of a bubbly flow in a vertical pipe
International Nuclear Information System (INIS)
Krepper, E.
1999-01-01
Even at the very simple conditions of two phase flow in a vertical pipe, strong 3D effects are observed. The distribution of the gas phase over the cross section varies significantly between the different flow patterns, which are known for the vertical two-phase flow. The air water flow in a vertical tube having a diameter of 50 mm and a length of about 3 m was investigated in steady state tests for different liquid and gas superficial velocities. Several two phase flow measuring techniques were used. Applying a wire mesh sensor, developed in FZR, the void fraction could be determined over the whole cross section of the pipe. The working principle is based on the measurement of the local instantaneous conductivity of the two-phase mixture. At the investigated flow velocities, the rate of the image acquisition is sufficient to record the same bubble several times. This enables to determine bubble diameter distributions. Applying two similar wire mesh sensors with a distance of 50 mm one above the other, the influence of the wire mesh to the flow could be investigated. No essential disturbances of the two-phase flow by the mesh could be found for the investigated flow regimes. Performing an auto correlation between the signals of both sensors, also profiles of the gas velocity were determined. (orig.)
CFD simulations of a bubbly flow in a vertical pipe
International Nuclear Information System (INIS)
Krepper, E.
2000-01-01
Even at the very simple conditions of two phase flow in a vertical pipe, strong 3D effects are observed. The distribution of the gas phase over the cross section varies significantly between the different flow patterns, which are known for the vertical two-phase flow. The air water flow in a vertical tube having a diameter of 50 mm and a length of about 3 m was investigated in steady state tests for different liquid and gas superficial velocities. Several two phase flow measuring techniques were used. Applying a wire mesh sensor, developed in FZR, the void fraction could be determined over the whole cross section of the pipe. The working principle is based on the measurement of the local instantaneous conductivity of the two-phase mixture. At the investigated flow velocities, the rate of the image acquisition is sufficient to record the same bubble several times. This enables to determine bubble diameter distributions. Applying two similar wire mesh sensors with a distance of 50 mm one above the other, the influence of the wire mesh to the flow could be investigated. No essential disturbances of the two-phase flow by the mesh could be found for the investigated flow regimes. Performing an auto correlation between the signals of both sensors, also profiles of the gas velocity were determined. In the CFD code CFX-4.2 several two-phase flow models were available. Using the code, volume fraction profiles were calculated and compared to the measured results for bubble flow regimes, to investigate the capability of these models (see also Krepper and Prasser [4] (1999)). (orig.)
Clearance gap flow: Simulations by discontinuous Galerkin method and experiments
Czech Academy of Sciences Publication Activity Database
Hála, Jindřich; Luxa, Martin; Bublík, O.; Prausová, H.; Vimmr, J.
2016-01-01
Roč. 92, May (2016), 02073-02073 ISSN 2100-014X. [EFM14 – Experimental Fluid Mechanics 2014. Český Krumlov, 18.11.2014-21.11.2014] Institutional support: RVO:61388998 Keywords : compressible fluid flow * narrow channel flow * discontinuous Galerkin finite element method Subject RIV: BK - Fluid Dynamics
Simulation of three-demensional unsteady flow in hydraulic pumps
van Esch, B.P.M.; van Esch, Bartholomeus Petrus Maria
1997-01-01
In this thesis it is shown that the flow in hydraulic pumps of the radial and mixedflow type, operating at conditions not too far from design point, can be considered as an incompressible potential flow, where the influence of viscosity is restricted to thin boundary layers, wakes and mixing areas.
Simulation of the air flows in many industrial pleated filters
International Nuclear Information System (INIS)
Del Fabbro, L.; Brun, P.; Laborde, J.C.; Lacan, J.; Ricciardi, L.; Renoux, A.
2000-01-01
The study presents results concerning the characterization of the charge loss and the air flow in nuclear and automobile type pleated filters. The experimental studies in correlation with the numerical models showed an homogenous distribution of the air flows in a THE nuclear type filter, whereas the distribution is heterogenous in the case of an automobile filter. (A.L.B.)
Simulation of the regional groundwater-flow system of the Menominee Indian Reservation, Wisconsin
Juckem, Paul F.; Dunning, Charles P.
2015-01-01
A regional, two-dimensional, steady-state groundwater-flow model was developed to simulate the groundwater-flow system and groundwater/surface-water interactions within the Menominee Indian Reservation. The model was developed by the U.S. Geological Survey (USGS), in cooperation with the Menominee Indian Tribe of Wisconsin, to contribute to the fundamental understanding of the region’s hydrogeology. The objectives of the regional model were to improve understanding of the groundwater-flow system, including groundwater/surface-water interactions, and to develop a tool suitable for evaluating the effects of potential regional water-management programs. The computer code GFLOW was used because of the ease with which the model can simulate groundwater/surface-water interactions, provide a framework for simulating regional groundwater-flow systems, and be refined in a stepwise fashion to incorporate new data and simulate groundwater-flow patterns at multiple scales. Simulations made with the regional model reproduce groundwater levels and stream base flows representative of recent conditions (1970–2013) and illustrate groundwater-flow patterns with maps of (1) the simulated water table and groundwater-flow directions, (2) probabilistic areas contributing recharge to high-capacity pumped wells, and (3) estimation of the extent of infiltrated wastewater from treatment lagoons.
A Level-set based framework for viscous simulation of particle-laden supersonic flows
Das, Pratik; Sen, Oishik; Jacobs, Gustaaf; Udaykumar, H. S.
2017-06-01
Particle-laden supersonic flows are important in natural and industrial processes, such as, volcanic eruptions, explosions, pneumatic conveyance of particle in material processing etc. Numerical study of such high-speed particle laden flows at the mesoscale calls for a numerical framework which allows simulation of supersonic flow around multiple moving solid objects. Only a few efforts have been made toward development of numerical frameworks for viscous simulation of particle-fluid interaction in supersonic flow regime. The current work presents a Cartesian grid based sharp-interface method for viscous simulations of interaction between supersonic flow with moving rigid particles. The no-slip boundary condition is imposed at the solid-fluid interfaces using a modified ghost fluid method (GFM). The current method is validated against the similarity solution of compressible boundary layer over flat-plate and benchmark numerical solution for steady supersonic flow over cylinder. Further validation is carried out against benchmark numerical results for shock induced lift-off of a cylinder in a shock tube. 3D simulation of steady supersonic flow over sphere is performed to compare the numerically obtained drag co-efficient with experimental results. A particle-resolved viscous simulation of shock interaction with a cloud of particles is performed to demonstrate that the current method is suitable for large-scale particle resolved simulations of particle-laden supersonic flows.
Low-Gravity Mimicking Simulants and Evaluation of Simulant Flow, Phase I
National Aeronautics and Space Administration — This project will provide a new method for testing flow/no-flow conditions and other gravity-driven flow behavior of Lunar or planetary regolith under reduced...
Lattice Boltzmann simulations of heat transfer in fully developed periodic incompressible flows
Wang, Zimeng; Shang, Helen; Zhang, Junfeng
2017-06-01
Flow and heat transfer in periodic structures are of great interest for many applications. In this paper, we carefully examine the periodic features of fully developed periodic incompressible thermal flows, and incorporate them in the lattice Boltzmann method (LBM) for flow and heat transfer simulations. Two numerical approaches, the distribution modification (DM) approach and the source term (ST) approach, are proposed; and they can both be used for periodic thermal flows with constant wall temperature (CWT) and surface heat flux boundary conditions. However, the DM approach might be more efficient, especially for CWT systems since the ST approach requires calculations of the streamwise temperature gradient at all lattice nodes. Several example simulations are conducted, including flows through flat and wavy channels and flows through a square array with circular cylinders. Results are compared to analytical solutions, previous studies, and our own LBM calculations using different simulation techniques (i.e., the one-module simulation vs. the two-module simulation, and the DM approach vs. the ST approach) with good agreement. These simple, however, representative simulations demonstrate the accuracy and usefulness of our proposed LBM methods for future thermal periodic flow simulations.
EDDA 1.0: integrated simulation of debris flow erosion, deposition and property changes
Chen, H. X.; Zhang, L. M.
2015-03-01
Debris flow material properties change during the initiation, transportation and deposition processes, which influences the runout characteristics of the debris flow. A quasi-three-dimensional depth-integrated numerical model, EDDA (Erosion-Deposition Debris flow Analysis), is presented in this paper to simulate debris flow erosion, deposition and induced material property changes. The model considers changes in debris flow density, yield stress and dynamic viscosity during the flow process. The yield stress of the debris flow mixture determined at limit equilibrium using the Mohr-Coulomb equation is applicable to clear water flow, hyper-concentrated flow and fully developed debris flow. To assure numerical stability and computational efficiency at the same time, an adaptive time stepping algorithm is developed to solve the governing differential equations. Four numerical tests are conducted to validate the model. The first two tests involve a one-dimensional debris flow with constant properties and a two-dimensional dam-break water flow. The last two tests involve erosion and deposition, and the movement of multi-directional debris flows. The changes in debris flow mass and properties due to either erosion or deposition are shown to affect the runout characteristics significantly. The model is also applied to simulate a large-scale debris flow in Xiaojiagou Ravine to test the performance of the model in catchment-scale simulations. The results suggest that the model estimates well the volume, inundated area, and runout distance of the debris flow. The model is intended for use as a module in a real-time debris flow warning system.
Bayesian inference in mass flow simulations - from back calculation to prediction
Kofler, Andreas; Fischer, Jan-Thomas; Hellweger, Valentin; Huber, Andreas; Mergili, Martin; Pudasaini, Shiva; Fellin, Wolfgang; Oberguggenberger, Michael
2017-04-01
Mass flow simulations are an integral part of hazard assessment. Determining the hazard potential requires a multidisciplinary approach, including different scientific fields such as geomorphology, meteorology, physics, civil engineering and mathematics. An important task in snow avalanche simulation is to predict process intensities (runout, flow velocity and depth, ...). The application of probabilistic methods allows one to develop a comprehensive simulation concept, ranging from back to forward calculation and finally to prediction of mass flow events. In this context optimized parameter sets for the used simulation model or intensities of the modeled mass flow process (e.g. runout distances) are represented by probability distributions. Existing deterministic flow models, in particular with respect to snow avalanche dynamics, contain several parameters (e.g. friction). Some of these parameters are more conceptual than physical and their direct measurement in the field is hardly possible. Hence, parameters have to be optimized by matching simulation results to field observations. This inverse problem can be solved by a Bayesian approach (Markov chain Monte Carlo). The optimization process yields parameter distributions, that can be utilized for probabilistic reconstruction and prediction of avalanche events. Arising challenges include the limited amount of observations, correlations appearing in model parameters or observed avalanche characteristics (e.g. velocity and runout) and the accurate handling of ensemble simulations, always taking into account the related uncertainties. Here we present an operational Bayesian simulation framework with r.avaflow, the open source GIS simulation model for granular avalanches and debris flows.
LENUS (Irish Health Repository)
Hargrove, M
2008-07-01
Errors in blood flow delivery due to shunting have been reported to reduce flow by, potentially, up to 40-83% during cardiopulmonary bypass. The standard roller-pump measures revolutions per minute and a calibration factor for different tubing sizes calculates and displays flow accordingly. We compared displayed roller-pump flow with ultrasonically measured flow to ascertain if measured flow correlated with the heart-lung pump flow reading. Comparison of flows was measured under varying conditions of pump run duration, temperature, viscosity, varying arterial\\/venous loops, occlusiveness, outlet pressure, use of silicone or polyvinyl chloride (PVC) in the roller race, different tubing diameters, and use of a venous vacuum-drainage device.
Simulation of granular and gas-solid flows using discrete element method
Boyalakuntla, Dhanunjay S.
2003-10-01
In recent years there has been increased research activity in the experimental and numerical study of gas-solid flows. Flows of this type have numerous applications in the energy, pharmaceuticals, and chemicals process industries. Typical applications include pulverized coal combustion, flow and heat transfer in bubbling and circulating fluidized beds, hopper and chute flows, pneumatic transport of pharmaceutical powders and pellets, and many more. The present work addresses the study of gas-solid flows using computational fluid dynamics (CFD) techniques and discrete element simulation methods (DES) combined. Many previous studies of coupled gas-solid flows have been performed assuming the solid phase as a continuum with averaged properties and treating the gas-solid flow as constituting of interpenetrating continua. Instead, in the present work, the gas phase flow is simulated using continuum theory and the solid phase flow is simulated using DES. DES treats each solid particle individually, thus accounting for its dynamics due to particle-particle interactions, particle-wall interactions as well as fluid drag and buoyancy. The present work involves developing efficient DES methods for dense granular flow and coupling this simulation to continuum simulations of the gas phase flow. Simulations have been performed to observe pure granular behavior in vibrating beds. Benchmark cases have been simulated and the results obtained match the published literature. The dimensionless acceleration amplitude and the bed height are the parameters governing bed behavior. Various interesting behaviors such as heaping, round and cusp surface standing waves, as well as kinks, have been observed for different values of the acceleration amplitude for a given bed height. Furthermore, binary granular mixtures (granular mixtures with two particle sizes) in a vibrated bed have also been studied. Gas-solid flow simulations have been performed to study fluidized beds. Benchmark 2D
URANS simulations of separated flow with stall cells over an NREL S826 airfoil
DEFF Research Database (Denmark)
Sarlak Chivaee, Hamid; Nishino, T.; Sørensen, Jens Nørkær
2016-01-01
airfoil using unsteady Reynolds-averaged Navier-Stokes (URANS) approach. Results of the simulations are demonstrated in terms of mean flow velocity, lift and drag, as well as pressure distribution, and validated against available experimental data. The simulations are carried out with a wide computational......A series of wind tunnel measurements and oil flow visualization was recently carried out at the Technical University of Denmark in order to investigate flow characteristics over a 14% thick NREL S826 airfoil at low Reynolds numbers. This paper aims at presenting numerical simulations of the same...
Modeling, Identification, Estimation, and Simulation of Urban Traffic Flow in Jakarta and Bandung
Directory of Open Access Journals (Sweden)
Herman Y. Sutarto
2015-06-01
Full Text Available This paper presents an overview of urban traffic flow from the perspective of system theory and stochastic control. The topics of modeling, identification, estimation and simulation techniques are evaluated and validated using actual traffic flow data from the city of Jakarta and Bandung, Indonesia, and synthetic data generated from traffic micro-simulator VISSIM. The results on particle filter (PF based state estimation and Expectation-Maximization (EM based parameter estimation (identification confirm the proposed model gives satisfactory results that capture the variation of urban traffic flow. The combination of the technique and the simulator platform assembles possibility to develop a real-time traffic light controller.
A PISO-like algorithm to simulate superfluid helium flow with the two-fluid model
Soulaine, Cyprien; Allain, Hervé; Baudouy, Bertrand; Van Weelderen, Rob
2015-01-01
This paper presents a segregated algorithm to solve numerically the superfluid helium (He II) equations using the two-fluid model. In order to validate the resulting code and illustrate its potential, different simulations have been performed. First, the flow through a capillary filled with He II with a heated area on one side is simulated and results are compared to analytical solutions in both Landau and Gorter–Mellink flow regimes. Then, transient heat transfer of a forced flow of He II is investigated. Finally, some two-dimensional simulations in a porous medium model are carried out.
Numerical simulation of the two-phase flows in a hydraulic coupling by solving VOF model
International Nuclear Information System (INIS)
Luo, Y; Zuo, Z G; Liu, S H; Fan, H G; Zhuge, W L
2013-01-01
The flow in a partially filled hydraulic coupling is essentially a gas-liquid two-phase flow, in which the distribution of two phases has significant influence on its characteristics. The interfaces between the air and the liquid, and the circulating flows inside the hydraulic coupling can be simulated by solving the VOF two-phase model. In this paper, PISO algorithm and RNG k–ε turbulence model were employed to simulate the phase distribution and the flow field in a hydraulic coupling with 80% liquid fill. The results indicate that the flow forms a circulating movement on the torus section with decreasing speed ratio. In the pump impeller, the air phase mostly accumulates on the suction side of the blades, while liquid on the pressure side; in turbine runner, air locates in the middle of the flow passage. Flow separations appear near the blades and the enclosing boundaries of the hydraulic coupling
Tsukamoto, Kaname; Okada, Mizuki; Inokuchi, Yuzo; Yamasaki, Nobuhiko; Yamagata, Akihiro
2017-04-01
For centrifugal compressors used in automotive turbochargers, the extension of the surge margin is demanded because of lower engine speed. In order to estimate the surge line exactly, it is required to acquire the compressor characteristics at small or negative flow rate. In this paper, measurement and numerical simulation of the characteristics at small or negative flow rate are carried out. In the measurement, an experimental facility with a valve immediately downstream of the compressor is used to suppress the surge. In the numerical work, a new boundary condition that specifies mass flow rate at the outlet boundary is used to simulate the characteristics around the zero flow rate region. Furthermore, flow field analyses at small or negative flow rate are performed with the numerical results. The separated and re-circulated flow fields are investigated by visualization to identify the origin of losses.
Gyrokinetic simulations in general geometry and applications to collisional damping of zonal flows
International Nuclear Information System (INIS)
Lin, Z.; Hahm, T.S.; Lee, W.W.; Tang, W.M.; White, R.B.
2000-01-01
A fully three-dimensional gyrokinetic particle code using magnetic coordinates for general geometry has been developed and applied to the investigation of zonal flows dynamics in toroidal ion-temperature-gradient turbulence. Full torus simulation results support the important conclusion that turbulence-driven zonal flows significantly reduce the turbulent transport. Linear collisionless simulations for damping of an initial poloidal flow perturbation exhibit an asymptotic residual flow. The collisional damping of this residual causes the dependence of ion thermal transport on the ion-ion collision frequency even in regimes where the instabilities are collisionless
Enhanced Mesh-Free Simulation of Regolith Flow, Phase I
National Aeronautics and Space Administration — NASA needs simulation tools capable of predicting the behavior of regolith in proposed excavation, transport, and handling or sample acquisition systems. For...
EDDA: integrated simulation of debris flow erosion, deposition and property changes
Chen, H. X.; Zhang, L. M.
2014-11-01
Debris flow material properties change during the initiation, transportation and deposition processes, which influences the runout characteristics of the debris flow. A quasi-three-dimensional depth-integrated numerical model, EDDA, is presented in this paper to simulate debris flow erosion, deposition and induced material property changes. The model considers changes in debris flow density, yield stress and dynamic viscosity during the flow process. The yield stress of debris flow mixture is determined at limit equilibrium using the Mohr-Coulomb equation, which is applicable to clear water flow, hyper-concentrated flow and fully developed debris flow. To assure numerical stability and computational efficiency at the same time, a variable time stepping algorithm is developed to solve the governing differential equations. Four numerical tests are conducted to validate the model. The first two tests involve a one-dimensional dam-break water flow and a one-dimensional debris flow with constant properties. The last two tests involve erosion and deposition, and the movement of multi-directional debris flows. The changes in debris flow mass and properties due to either erosion or deposition are shown to affect the runout characteristics significantly. The model is also applied to simulate a large-scale debris flow in Xiaojiagou Ravine to test the performance of the model in catchment-scale simulations. The results suggest that the model estimates well the volume, inundated area, and runout distance of the debris flow. The model is intended for use as a module in a real-time debris flow warning system.
Optimal design and uncertainty quantification in blood flow simulations for congenital heart disease
Marsden, Alison
2009-11-01
Recent work has demonstrated substantial progress in capabilities for patient-specific cardiovascular flow simulations. Recent advances include increasingly complex geometries, physiological flow conditions, and fluid structure interaction. However inputs to these simulations, including medical image data, catheter-derived pressures and material properties, can have significant uncertainties associated with them. For simulations to predict clinically useful and reliable output information, it is necessary to quantify the effects of input uncertainties on outputs of interest. In addition, blood flow simulation tools can now be efficiently coupled to shape optimization algorithms for surgery design applications, and these tools should incorporate uncertainty information. We present a unified framework to systematically and efficient account for uncertainties in simulations using adaptive stochastic collocation. In addition, we present a framework for derivative-free optimization of cardiovascular geometries, and layer these tools to perform optimization under uncertainty. These methods are demonstrated using simulations and surgery optimization to improve hemodynamics in pediatric cardiology applications.
Kumar, Mayank
2012-01-19
In this two-part paper, we describe the construction, validation, and application of a multiscale model of entrained flow gasification. The accuracy of the model is demonstrated by (1) rigorously constructing and validating the key constituent submodels against relevant canonical test cases from the literature and (2) validating the integrated model against experimental data from laboratory scale and commercial scale gasifiers. In part I, the flow solver and particle turbulent dispersion models are validated against experimental data from nonswirling flow and swirling flow test cases in an axisymmetric sudden expansion geometry and a two-phase flow test case in a cylindrical bluff body geometry. Results show that while the large eddy simulation (LES) performs best among all tested models in predicting both swirling and nonswirling flows, the shear stress transport (SST) k-ω model is the best choice among the commonly used Reynolds-averaged Navier-Stokes (RANS) models. The particle turbulent dispersion model is accurate enough in predicting particle trajectories in complex turbulent flows when the underlying turbulent flow is well predicted. Moreover, a commonly used modeling constant in the particle dispersion model is optimized on the basis of comparisons with particle-phase experimental data for the two-phase flow bluff body case. © 2011 American Chemical Society.
Probabilistic Power Flow Simulation allowing Temporary Current Overloading
W.S. Wadman (Wander); G. Bloemhof; D.T. Crommelin (Daan); J.E. Frank (Jason)
2012-01-01
htmlabstractThis paper presents a probabilistic power flow model subject to connection temperature constraints. Renewable power generation is included and modelled stochastically in order to reflect its intermittent nature. In contrast to conventional models that enforce connection current
Probablistic Power Flow Simulations Allowing Temporary Current Overloading
Wadman, W.; Bloemhof, G.; Crommelin, D.; Frank, J.; Ozdemir, A.
2013-01-01
This paper presents a probabilistic power flow model subject to connection temperature constraints. Renewable power generation is included and modelled stochastically in order to reflect its intermittent nature. In contrast to conventional models that enforce connection current constraints,
Simulations of Steady Cavitating Flow in a Small Francis Turbine
Directory of Open Access Journals (Sweden)
Ahmed Laouari
2016-01-01
Full Text Available The turbulent flow through a small horizontal Francis turbine is solved by means of Ansys-CFX at different operating points, with the determination of the hydrodynamic performance and the best efficiency point. The flow structures at different regimes reveal a large flow eddy in the runner and a swirl in the draft tube. The use of the mixture model for the cavity/liquid two-phase flow allowed studying the influence of cavitation on the hydrodynamic performance and revealed cavitation pockets near the trailing edge of the runner and a cavitation vortex rope in the draft tube. By maintaining a constant dimensionless head and a distributor vane opening while gradually increasing the cavitation number, the output power and efficiency reached a critical point and then had begun to stabilize. The cavitation number corresponding to the safety margin of cavitation is also predicted for this hydraulic turbine.
Direct numerical simulation of solidification microstructures affected by fluid flow
International Nuclear Information System (INIS)
Juric, D.
1997-12-01
The effects of fluid flow on the solidification morphology of pure materials and solute microsegregation patterns of binary alloys are studied using a computational methodology based on a front tracking/finite difference method. A general single field formulation is presented for the full coupling of phase change, fluid flow, heat and solute transport. This formulation accounts for interfacial rejection/absorption of latent heat and solute, interfacial anisotropies, discontinuities in material properties between the liquid and solid phases, shrinkage/expansion upon solidification and motion and deformation of the solid. Numerical results are presented for the two dimensional dendritic solidification of pure succinonitrile and the solidification of globulitic grains of a plutonium-gallium alloy. For both problems, comparisons are made between solidification without fluid flow and solidification within a shear flow
Turbulent flow simulation of the NREL S809 airfoil
Energy Technology Data Exchange (ETDEWEB)
Guerri, Ouahiba; Bouhadef, Khadidja; Harhad, Ameziane
2006-05-15
Numerical computations are carried out for the NREL S809 airfoil. The flow is modelled using an unsteady incompressible Reynolds Averaged Navier-Stokes solver. Two turbulence models (SST {kappa}/{omega}of Menter and RNG {kappa}/{epsilon}) are applied to close the RANS equations. All computations are performed assuming fully turbulent flow. The flow field is analyzed at various angles of attack from 0 to 20 degrees. Lift and drag forces are obtained from the computations by integrating the pressure and shear stress over the blade surface. The performance of the two turbulence models is compared and the influence of the free stream turbulence intensity is checked. The results confirm the satisfactory performance of the SST {kappa}/{omega} model of Menter for modelling turbulent flow around airfoils. (author)
Labour flows in a simulation model of the firm
Butter, F.A.G. den; Gameren, E. van
1998-01-01
A hierarchical model is calibrated and used to illustrate labour market flows within a firm. The model establishes a link between the models of the firm from the literature on industrial organisation and the description of labour market dynamics in the flow approach to labour markets. It describes the decision of the personnel management of the firm whether to fire workers, and/or whether to hire workers from the internal or external labour market. The decision is based on firing costs, hirin...
Real gas flow simulation in damaged distribution pipelines
International Nuclear Information System (INIS)
Kostowski, Wojciech J.; Skorek, Janusz
2012-01-01
The paper discusses chosen issues concerning damaged gas pipelines. Attention is paid to modelling the steady-state flow of natural gas in distribution pipelines, and the most commonly applied models of isothermal and adiabatic flow are evaluated for both the ideal and the real gas properties. A method of accounting for a leakage by means of a reference flow equation with a discharge coefficient is presented, and the dependency of the discharge coefficient on pressure is demonstrated both with literature data and the authors' experimental results. A relevant computational study of a pipeline failure is presented for a high- and a medium pressure pipeline. The importance of an appropriate choice of the flow model (isothermal or adiabatic flow of real or ideal gas) is demonstrated by the results of the study. It is shown that accounting for the variability of the discharge coefficient is required if medium pressure pipelines are analysed. However, it is eventually shown that the impact of the discharge coefficient on the predicted outflow rate is of lesser importance than that of the applied flow model. -- Highlights: ► Comparison of real/ideal gas, isothermal/adiabatic gas flow in a damaged pipeline. ► Variability of the discharge coefficient with pressure is demonstrated. ► Isothermal model predicts wrong values of downstream pressure, not just temperature. ► Isothermal model may cause significant error (for 2 case studies is >20%). ► Error in the discharge coefficient has a weak influence on the predicted flow rate.
Energy Technology Data Exchange (ETDEWEB)
Priere, C
2005-01-15
Nowadays, environmental and economic constraints require considerable research efforts from the gas turbine industry. Objectives aim at lowering pollutants emissions and fuel consumption. These efforts take a primary importance to satisfy a continue growth of energy production and to obey to stringent environmental legislations. Recorded progresses are linked to mixing enhancement in combustors running at lean premixed operating point. Indeed, industry shows itself to be attentive in the mixing enhancement and during the last years, efforts are concentrated on fresh and burned gas dilution. The Jet In Cross Flow (JICF), which constitutes a representative case to further the research effort. It has been to be widely studied both in experimentally and numerically, and is particularly well suited for the evaluation of Large Eddy Simulations (LES). This approach, where large scale phenomena are naturally taken into account in the governing equation while the small scales are modelled, offers the means to well-predict such flows. The main objective of this work is to gauge and to enhance the quality of the LES predictions in JICF configurations by means of numerical tools developed in the compressible AVBP code. Physical and numerical parameters considered in the JICF modelization are taken into account and strategies that are able to enhance quality of LES results are proposed. Configurations studied in this work are the following: - Influences of the boundary conditions and jet injection system on a free JICF - Study of static mixing device in an industrial gas turbine chamber. - Study of a JICF configuration represented a dilution zone in low emissions combustors. (author)
Direct numerical simulation of MHD flow with electrically conducting wall
International Nuclear Information System (INIS)
Satake, S.; Kunugi, T.; Naito, N.; Sagara, A.
2006-01-01
The 2D vortex problem and 3D turbulent channel flow are treated numerically to assess the effect of electrically conducting walls on turbulent MHD flow. As a first approximation, the twin vortex pair is considered as a model of a turbulent eddy near the wall. As the eddy approaches and collides with the wall, a high value electrical potential is induced inside the wall. The Lorentz force, associated with the potential distribution, reduces the velocity gradient in the near-wall region. When considering a fully developed turbulent channel flow, a high electrical conductivity wall was chosen to emphasize the effect of electromagnetic coupling between the wall and the flow. The analysis was performed using DNS. The results are compared with a non-MHD flow and MHD flow in the insulated channel. The mean velocity within the logarithmic region in the case of the electrically conducting wall is slightly higher than that in the non-conducting wall case. Thus, the drag is smaller compared to that in the non-conducting wall case due to a reduction of the Reynolds stress in the near wall region through the Lorentz force. This mechanism is explained via reduction of the production term in the Reynolds shear stress budget
A graphical interface to the TOUGH family of flow simulators
Energy Technology Data Exchange (ETDEWEB)
O`Sullivan, M.J.; Bullivant, D.P. [Univ. of Auckland (New Zealand)
1995-03-01
A graphical interface for the TOUGH family of simulators is presented. The interface allows the user to graphically create or modify a computer model and then to graphically examine the simulation results. The package uses the X Window System, enabling it to be used on many computer platforms.
International Nuclear Information System (INIS)
Nance, T.A.
1998-01-01
Underground storage tanks with 2 inches to 3 inches diameter access ports at the Department of Energy's Savannah River Site have been used to store radioactive solvents and sludge. In order to close these tanks, the contents of the tanks need to first be quantified in terms of volume and chemical and radioactive characteristics. To provide information on the volume of waste contained within the tanks, a small remote inspection system was needed. This inspection system was designed to provide lighting and provide pan and tilt capabilities in an inexpensive package with zoom abilities and color video. This system also needed to be utilized inside of a plastic tent built over the access port to contain any contamination exiting from the port. This system had to be build to travel into the small port opening, through the riser pipe, into the tank evacuated space, and out of the riser pipe and access port with no possibility of being caught and blocking the access riser. Long thin plates were found in many access riser pipes that blocked the inspection system from penetrating into the tank interiors. Retrieval tools to clear the plates from the tanks using developed sampling devices while providing safe containment for the samples. This paper will discuss the inspection systems, tools for clearing access pipes, and solvent sampling tools developed to evaluate the tank contents of the underground solvent storage tanks
Countercurrent Flow of Molten Glass and Air during Siphon Tests
International Nuclear Information System (INIS)
Guerrero, H.N.
2001-01-01
Siphon tests of molten glass were performed to simulate potential drainage of a radioactive waste melter, the Defense Waste Processing Facility (DWPF) at the Savannah River Site. Glass is poured from the melter through a vertical downspout that is connected to the bottom of the melter through a riser. Large flow surges have the potential of completely filling the downspout and creating a siphon effect that has the potential for complete draining of the melter. Visual observations show the exiting glass stream starts as a single-phase pipe flow, constricting into a narrow glass stream. Then a half-spherical bubble forms at the exit of the downspout. The bubble grows, extending upwards into the downspout, while the liquid flows counter-currently to one side of the spout. Tests were performed to determine what are the spout geometry and glass properties that would be conducive to siphoning, conditions for terminating the siphon, and the total amount of glass drained
Large eddy simulations of flow and mixing in jets and swirl flows: application to a gas turbine
Energy Technology Data Exchange (ETDEWEB)
Schluter, J.U.
2000-07-01
Large Eddy Simulations (LES) are an accepted tool in turbulence research. Most LES investigations deal with low Reynolds-number flows and have a high spatial discretization, which results in high computational costs. To make LES applicable to industrial purposes, the possibilities of LES to deliver results with low computational costs on high Reynolds-number flows have to be investigated. As an example, the cold flow through the Siemens V64.3A.HR gas turbine burner shall be examined. It is a gas turbine burner of swirl type, where the fuel is injected on the surface of vanes perpendicular to the main air flow. The flow regime of an industrial gas turbine is governed by several flow phenomena. The most important are the fuel injection in form of a jet in cross flow (JICF) and the swirl flow issuing into a combustion chamber. In order to prove the ability of LES to deal with these flow phenomena, two numerical investigations were made in order to reproduce the results of experimental studies. The first one deals with JICF. It will be shown that the reproduction of three different JICF is possible with LES on meshes with a low number of mesh points. The results are used to investigate the flow physics of the JICF, especially the merging of two adjacent JICFs. The second fundamental investigation deals with swirl flows. Here, the accuracy of an axisymmetric assumption is examined in detail by comparing it to full 3D LES computations and experimental data. Having demonstrated the ability of LES and the flow solver to deal with such complex flows with low computational efforts, the LES approach is used to examine some details of the burner. First, the investigation of the fuel injection on a vane reveals that the vane flow tends to separate. Furthermore the tendency of the fuel jets to merge is shown. Second, the swirl flow in the combustion chamber is computed. For this investigation the vanes are removed from the burner and swirl is imposed as a boundary condition. As
Numerical simulation of 3-D turbulent flow through entire stage in a multistage centrifugal pump
International Nuclear Information System (INIS)
Huang, S.; Islam, M.F.; Liu, P.
2005-01-01
A three-dimensional turbulent flow through a multistage centrifugal pump is numerically simulated using a commercial CFD software package. The simulation and analysis include flow fields in rotating impeller and stationary diffuser and is completed in a multiple reference frame. The standard k-ε turbulence model is applied. The analysis of the simulation reveals that the reverse flows exist in the zone near the impeller exit and diffuser entrance, resulting in flow field asymmetric and unsteady. There is a considerable interference on velocity field at impeller exit due to the interaction between impeller blades and diffuser vanes. The hydraulic performance is connected and evaluated with the 3-D computational flow field. The current computation is verified by comparing predicted and measured head. (author)
Directory of Open Access Journals (Sweden)
Baocheng Shi
2014-06-01
Full Text Available For numerically simulating 3D solid-liquid turbulent flow in low specific speed centrifugal pumps, the iteration convergence problem caused by complex internal structure and high rotational speed of pump is always a problem for numeral simulation researchers. To solve this problem, the combination of three measures of dynamic underrelaxation factor adjustment, step method, and rotational velocity control means according to residual curves trends of operating parameters was used to improve the numerical convergence. Numeral simulation of 3D turbulent flow in a low specific speed solid-liquid centrifugal pump was performed, and the results showed that the improved solution strategy is greatly helpful to the numerical convergence. Moreover, the 3D turbulent flow fields in pumps have been simulated for the bottom ash-particles with the volume fraction of 10%, 20%, and 30% at the same particle diameter of 0.1 mm. The two-phase calculation results are compared with those of single-phase clean water flow. The calculated results gave the main region of the abrasion of the impeller and volute casing and improve the hydraulic design of the impeller in order to decrease the abrasion and increase the service life of the pump.
Unsteady Simulations of the Flow in a Channel Flow and a Ventilated Room Using the SST-SAS Model
DEFF Research Database (Denmark)
Davidson, Lars; Nielsen, Peter V.
The SAS model (Scale Adapted Simulation) was invented by Menter and his co-workers. The idea behind the SST-SAS model is to add an additional production term - the SAS term - in the w equation which is sensitive to resolved (i.e. unsteady) fluctuations. In regions where the flow is on the limit...
Scale-adaptive simulation of a hot jet in cross flow
Energy Technology Data Exchange (ETDEWEB)
Duda, B M; Esteve, M-J [AIRBUS Operations S.A.S., Toulouse (France); Menter, F R; Hansen, T, E-mail: benjamin.duda@airbus.com [ANSYS Germany GmbH, Otterfing (Germany)
2011-12-22
The simulation of a hot jet in cross flow is of crucial interest for the aircraft industry as it directly impacts aircraft safety and global performance. Due to the highly transient and turbulent character of this flow, simulation strategies are necessary that resolve at least a part of the turbulence spectrum. The high Reynolds numbers for realistic aircraft applications do not permit the use of pure Large Eddy Simulations as the spatial and temporal resolution requirements for wall bounded flows are prohibitive in an industrial design process. For this reason, the hybrid approach of the Scale-Adaptive Simulation is employed, which retains attached boundary layers in well-established RANS regime and allows the resolution of turbulent fluctuations in areas with sufficient flow instabilities and grid refinement. To evaluate the influence of the underlying numerical grid, three meshing strategies are investigated and the results are validated against experimental data.
Scale-adaptive simulation of a hot jet in cross flow
International Nuclear Information System (INIS)
Duda, B M; Esteve, M-J; Menter, F R; Hansen, T
2011-01-01
The simulation of a hot jet in cross flow is of crucial interest for the aircraft industry as it directly impacts aircraft safety and global performance. Due to the highly transient and turbulent character of this flow, simulation strategies are necessary that resolve at least a part of the turbulence spectrum. The high Reynolds numbers for realistic aircraft applications do not permit the use of pure Large Eddy Simulations as the spatial and temporal resolution requirements for wall bounded flows are prohibitive in an industrial design process. For this reason, the hybrid approach of the Scale-Adaptive Simulation is employed, which retains attached boundary layers in well-established RANS regime and allows the resolution of turbulent fluctuations in areas with sufficient flow instabilities and grid refinement. To evaluate the influence of the underlying numerical grid, three meshing strategies are investigated and the results are validated against experimental data.
An Improved Ghost-cell Immersed Boundary Method for Compressible Inviscid Flow Simulations
Chi, Cheng
2015-01-01
This study presents an improved ghost-cell immersed boundary approach to represent a solid body in compressible flow simulations. In contrast to the commonly used approaches, in the present work ghost cells are mirrored through the boundary
Numerical simulation in a two dimensional turbulent flow over a backward-facing step
International Nuclear Information System (INIS)
Silveira Neto, A. da; Grand, D.
1991-01-01
Numerical simulations of turbulent flows in complex geometries are generally restricted to the prediction of the mean flow and use semi-empirical turbulence models. The present study is devoted to the simulation of the coherence structures which develop in a flow submitted to a velocity change, downstream of a backward facing step. Two aspect ratios (height of the step over height of the channel) have been explored and the values of the Reynolds number vary from (6000 to 90000). In the isothermal case coherent structures have been obtained by the numerical simulation in the mixing layer downstream of the step. The numerical simulations provides results in fairly good agreement with available experimental results. In a second step a thermal stratification is imposed on this flow for one value of Richardson number (0.5) the coherent structures disappear downstream for increasing values of Richardson number. (author)
Scalable Methods for Eulerian-Lagrangian Simulation Applied to Compressible Multiphase Flows
Zwick, David; Hackl, Jason; Balachandar, S.
2017-11-01
Multiphase flows can be found in countless areas of physics and engineering. Many of these flows can be classified as dispersed two-phase flows, meaning that there are solid particles dispersed in a continuous fluid phase. A common technique for simulating such flow is the Eulerian-Lagrangian method. While useful, this method can suffer from scaling issues on larger problem sizes that are typical of many realistic geometries. Here we present scalable techniques for Eulerian-Lagrangian simulations and apply it to the simulation of a particle bed subjected to expansion waves in a shock tube. The results show that the methods presented here are viable for simulation of larger problems on modern supercomputers. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1315138. This work was supported in part by the U.S. Department of Energy under Contract No. DE-NA0002378.
International Nuclear Information System (INIS)
Rockhold, M.L.
1993-02-01
A field-scale, unsaturated flow and solute transport experiment at the Las Cruces trench site in New Mexico was simulated as part of a ''blind'' modeling exercise to demonstrate the ability or inability of uncalibrated models to predict unsaturated flow and solute transport in spatially variable porous media. Simulations were conducted using a recently developed multiphase flow and transport simulator. Uniform and heterogeneous soil models were tested, and data from a previous experiment at the site were used with an inverse procedure to estimate water retention parameters. A spatial moment analysis was used to provide a quantitative basis for comparing the mean observed and simulated flow and transport behavior. The results of this study suggest that defensible predictions of waste migration and fate at low-level waste sites will ultimately require site-specific data for model calibration
An improved ghost-cell immersed boundary method for compressible flow simulations
Chi, Cheng; Lee, Bok Jik; Im, Hong G.
2016-01-01
This study presents an improved ghost-cell immersed boundary approach to represent a solid body in compressible flow simulations. In contrast to the commonly used approaches, in the present work ghost cells are mirrored through the boundary
Numerical simulation of the effect of upstream swirling flow on swirl meter performance
Chen, Desheng; Cui, Baoling; Zhu, Zuchao
2018-04-01
Flow measurement is important in the fluid process and transmission system. For the need of accuracy measurement of fluid, stable flow is acquired. However, the elbows and devices as valves and rotary machines may produce swirling flow in the natural gas pipeline networks system and many other industry fields. In order to reveal the influence of upstream swirling flow on internal flow fields and the metrological characteristics, numerical simulations are carried out on the swirl meter. Using RNG k-ɛ turbulent model and SIMPLE algorithm, the flow field is numerically simulated under swirling flows generated from co-swirl and counter-swirl flow. Simulation results show fluctuation is enhanced or weakened depending on the rotating direction of swirling flow. A counter- swirl flow increases the entropy production rate at the inlet and outlet of the swirler, the junction region between throat and divergent section, and then the pressure loss is increased. The vortex precession dominates the static pressure distributions on the solid walls and in the channel, especially at the end region of the throat.
Experimental research and numerical simulation on flow resistance of integrated valve
International Nuclear Information System (INIS)
Cai Wei; Bo Hanliang; Qin Benke
2008-01-01
The flow resistance of the integrated valve is one of the key parameters for the design of the control rod hydraulic drive system (CRHDS). Experimental research on the improved new integrated valve was performed, and the key data such as pressure difference, volume flow, resistance coefficient and flow coefficient of each flow channel were obtained. With the computational fluid dynamics software CFX, numerical simulation was executed to analyze the effect of Re on the flow resistance. On the basis of experimental and numerical results, fitting empirical formulas of resistance coefficient were obtained, which provide experimental and theoretical foundations for CRHDS's optimized design and theoretical analysis. (authors)
Kozu, Hiroyuki; Kobayashi, Isao; Neves, Marcos A; Nakajima, Mitsutoshi; Uemura, Kunihiko; Sato, Seigo; Ichikawa, Sosaku
2014-08-01
This study quantitatively analyzed the flow phenomena in model gastric contents induced by peristalsis using a human gastric flow simulator (GFS). Major functions of the GFS include gastric peristalsis simulation by controlled deformation of rubber walls and direct observation of inner flow through parallel transparent windows. For liquid gastric contents (water and starch syrup solutions), retropulsive flow against the direction of peristalsis was observed using both particle image velocimetry (PIV) and computational fluid dynamics (CFD). The maximum flow velocity was obtained in the region occluded by peristalsis. The maximum value was 9 mm s(-1) when the standard value of peristalsis speed in healthy adults (UACW = 2.5 mm s(-1)) was applied. The intragastric flow-field was laminar with the maximum Reynolds number (Re = 125). The viscosity of liquid gastric contents hardly affected the maximum flow velocity in the applied range of this study (1 to 100 mPa s). These PIV results agreed well with the CFD results. The maximum shear rate in the liquid gastric contents was below 20 s(-1) at UACW = 2.5 mm s(-1). We also measured the flow-field in solid-liquid gastric contents containing model solid food particles (plastic beads). The direction of velocity vectors was influenced by the presence of the model solid food particle surface. The maximum flow velocity near the model solid food particles ranged from 8 to 10 mm s(-1) at UACW = 2.5 mm s(-1). The maximum shear rate around the model solid food particles was low, with a value of up to 20 s(-1).
Simulation of blood flow in a small-diameter vascular graft model with a swirl (spiral) flow guider.
Zhang, ZhiGuo; Fan, YuBo; Deng, XiaoYan; Wang, GuiXue; Zhang, He; Guidoin, Robert
2008-10-01
Small-diameter vascular grafts are in large demand for coronary and peripheral bypass procedures, but present products still fail in long-term clinical application. In the present communication, a new type of small-diameter graft with a swirl flow guider was proposed to improve graft patency rate. Flow pattern in the graft was simulated numerically and compared with that in a conventional graft. The numerical results revealed that the swirl flow guider could indeed make the blood flow rotate in the new graft. The swirling flow distal to the flow guider significantly altered the flow pattern in the new graft and the velocity profiles were re-distributed. Due to the swirling flow, the blood velocity near the vessel wall and wall shear rate were greatly enhanced. We believe that the increased blood velocity near the wall and the wall shear rate can impede the occurrence of acute thrombus formation and intimal hyperplasia, hence can improve the graft patency rate for long-term clinical use.
Simulation of groundwater flows in unsaturated porous media
International Nuclear Information System (INIS)
Musy, A.
1976-01-01
Groundwater flow in unsaturated porous media is caused by a potential gradient where the total potential consists of the sum of a gravitational and a suction component. The partial differential equations which result from the general analysis of groundwater flow in unsaturated soil are solved by succesive approximations with the finite-element method. General boundary and initial conditions, linear or curvilinear shaped elements (isoparametric elements) and steady-state or transient flow can be introduced into the numerical computer program. The results of this mathematical model are compared with experimental data established in the laboratory with a physical groundwater model. This is a rectangular testing tank of dimension 3 x 1.5 x 0.15 m and contains a silty clay loam. The variation of the bulk density and the volumetric moisture of the soil as a function of time and space are measured by gamma absorption from a 137 Cs source with 300 mCi intensity
Numerical simulations of bistable flows in precessing spheroidal shells
Vormann, J.; Hansen, U.
2018-05-01
Precession of the rotation axis is an often neglected mechanical driving mechanism for flows in planetary interiors, through viscous coupling at the boundaries and topographic forcing in non-spherical geometries. We investigate precession-driven flows in spheroidal shells over a wide range of parameters and test the results against theoretical predictions. For Ekman numbers down to 8.0 × 10-7, we see a good accordance with the work of Busse, who assumed the precession-driven flow to be dominated by a rigid rotation component that is tilted to the main rotation axis. The velocity fields show localized small-scale structures for lower Ekman numbers and clear signals of inertial waves for some parameters. For the case of moderate viscosity and strong deformation, we report the realization of multiple solutions at the same parameter combination, depending on the initial condition.
Simulation of non-isothermal transient flow in gas pipeline
Energy Technology Data Exchange (ETDEWEB)
Ferreira Junior, Luis Carlos; Soares, Matheus; Lima, Enrique Luis; Pinto, Jose Carlos [Coordenacao dos Programas de Pos-graduacao de Engenharia (COPPE/UFRJ), Rio de Janeiro, RJ (Brazil). Programa de Engenharia Quimica; Muniz, Cyro; Pires, Clarissa Cortes; Rochocz, Geraldo [ChemTech, Rio de Janeiro, RJ (Brazil)
2009-07-01
Modeling of gas pipeline usually considers that the gas flow is isothermal (or adiabatic) and that pressure changes occur instantaneously (quasi steady state approach). However, these assumptions are not valid in many important transient applications (changes of inlet and outlet flows/pressures, starting and stopping of compressors, changes of controller set points, among others). Besides, the gas properties are likely to depend simultaneously on the pipe position and on the operation time. For this reason, a mathematical model is presented and implemented in this paper in order to describe the gas flow in pipeline when pressure and temperature transients cannot be neglected. The model is used afterwards as a tool for reconciliation of available measured data. (author)
Implementation of a Large Eddy Simulation Method Applied to Recirculating Flow in a Ventilated Room
DEFF Research Database (Denmark)
Davidson, Lars
In the present work Large Eddy Simulations are presented. The flow in a ventilated enclosure is studied. We use an explicit, two-steps time-advancement scheme where the pressure is solved from a Poisson equation.......In the present work Large Eddy Simulations are presented. The flow in a ventilated enclosure is studied. We use an explicit, two-steps time-advancement scheme where the pressure is solved from a Poisson equation....
Numerical Simulation of Unsteady Large Scale Separated Flow around Oscillating Airfoil
Isogai, Koji; 磯貝, 紘二
1991-01-01
Numerical simulations of dynamic stall phenomenon of NACA0012 airfoil oscillating in pitch near static stalling angle are performed by using the compressible Navier-Stokes equations. In the present computations, a TVD scheme and an algebraic turbulence model are employed for the simulations of the unsteady separated flows at Reynolds number of 1.1x105. The hysteresis loops of the unsteady pitching moment during dynamic stall are compared with the existing experimental data. The flow pattern a...
High-Reynolds Number Viscous Flow Simulations on Embedded-Boundary Cartesian Grids
2016-05-05
AFRL-AFOSR-VA-TR-2016-0192 High- Reynolds Number Viscous Flow Simulations on Embedded-Boundary Cartesian Grids Marsha Berger NEW YORK UNIVERSITY Final...TO THE ABOVE ORGANIZATION. 1. REPORT DATE (DD-MM-YYYY) 30/04/2016 2. REPORT TYPE Final 3. DATES COVERED (From - To) High- Reynolds 4. TITLE AND...SUBTITLE High- Reynolds Number Viscous Flow Simulations on Embedded-Boundary Cartesian Grids 5a. CONTRACT NUMBER 5b. GRANT NUMBER FA9550-13-1
Numerical simulation of steady cavitating flow of viscous fluid in a Francis hydroturbine
Panov, L. V.; Chirkov, D. V.; Cherny, S. G.; Pylev, I. M.; Sotnikov, A. A.
2012-09-01
Numerical technique was developed for simulation of cavitating flows through the flow passage of a hydraulic turbine. The technique is based on solution of steady 3D Navier—Stokes equations with a liquid phase transfer equation. The approch for setting boundary conditions meeting the requirements of cavitation testing standard was suggested. Four different models of evaporation and condensation were compared. Numerical simulations for turbines of different specific speed were compared with experiment.
First-principles molecular dynamics simulation study on electrolytes for use in redox flow battery
Choe, Yoong-Kee; Tsuchida, Eiji; Tokuda, Kazuya; Ootsuka, Jun; Saito, Yoshihiro; Masuno, Atsunobu; Inoue, Hiroyuki
2017-11-01
Results of first-principles molecular dynamics simulations carried out to investigate structural aspects of electrolytes for use in a redox flow battery are reported. The electrolytes studied here are aqueous sulfuric acid solutions where its property is of importance for dissolving redox couples in redox flow battery. The simulation results indicate that structural features of the acid solutions depend on the concentration of sulfuric acid. Such dependency arises from increase of proton dissociation from sulfuric acid.
Numerical Simulation of Natural Gas Flow in Anisotropic Shale Reservoirs
Negara, Ardiansyah
2015-11-09
Shale gas resources have received great attention in the last decade due to the decline of the conventional gas resources. Unlike conventional gas reservoirs, the gas flow in shale formations involves complex processes with many mechanisms such as Knudsen diffusion, slip flow (Klinkenberg effect), gas adsorption and desorption, strong rock-fluid interaction, etc. Shale formations are characterized by the tiny porosity and extremely low-permeability such that the Darcy equation may no longer be valid. Therefore, the Darcy equation needs to be revised through the permeability factor by introducing the apparent permeability. With respect to the rock formations, several studies have shown the existence of anisotropy in shale reservoirs, which is an essential feature that has been established as a consequence of the different geological processes over long period of time. Anisotropy of hydraulic properties of subsurface rock formations plays a significant role in dictating the direction of fluid flow. The direction of fluid flow is not only dependent on the direction of pressure gradient, but it also depends on the principal directions of anisotropy. Therefore, it is very important to take into consideration anisotropy when modeling gas flow in shale reservoirs. In this work, the gas flow mechanisms as mentioned earlier together with anisotropy are incorporated into the dual-porosity dual-permeability model through the full-tensor apparent permeability. We employ the multipoint flux approximation (MPFA) method to handle the full-tensor apparent permeability. We combine MPFA method with the experimenting pressure field approach, i.e., a newly developed technique that enables us to solve the global problem by breaking it into a multitude of local problems. This approach generates a set of predefined pressure fields in the solution domain in such a way that the undetermined coefficients are calculated from these pressure fields. In other words, the matrix of coefficients
FullSWOF: a software for overland flow simulation
Delestre, Olivier; Cordier, Stéphane; Darboux, Frédéric; Du, Mingxuan; James, Francois; Laguerre, Christian; Lucas, Carine; Planchon, Olivier
2012-01-01
Overland flow on agricultural fields may have some undesirable effects such as soil erosion, flood and pollutant transport. To better understand this phenomenon and limit its consequences, we developed a code using state-of-the-art numerical methods: FullSWOF (Full Shallow Water equations for Overland Flow), an object oriented code written in C++. It has been made open-source and can be downloaded from http://www.univ-orleans.fr/mapmo/soft/FullSWOF/. The model is based on the classical system...
Numerical Simulation of Natural Gas Flow in Anisotropic Shale Reservoirs
Negara, Ardiansyah; Salama, Amgad; Sun, Shuyu; Elgassier, Mokhtar; Wu, Yu-Shu
2015-01-01
Shale gas resources have received great attention in the last decade due to the decline of the conventional gas resources. Unlike conventional gas reservoirs, the gas flow in shale formations involves complex processes with many mechanisms such as Knudsen diffusion, slip flow (Klinkenberg effect), gas adsorption and desorption, strong rock-fluid interaction, etc. Shale formations are characterized by the tiny porosity and extremely low-permeability such that the Darcy equation may no longer be valid. Therefore, the Darcy equation needs to be revised through the permeability factor by introducing the apparent permeability. With respect to the rock formations, several studies have shown the existence of anisotropy in shale reservoirs, which is an essential feature that has been established as a consequence of the different geological processes over long period of time. Anisotropy of hydraulic properties of subsurface rock formations plays a significant role in dictating the direction of fluid flow. The direction of fluid flow is not only dependent on the direction of pressure gradient, but it also depends on the principal directions of anisotropy. Therefore, it is very important to take into consideration anisotropy when modeling gas flow in shale reservoirs. In this work, the gas flow mechanisms as mentioned earlier together with anisotropy are incorporated into the dual-porosity dual-permeability model through the full-tensor apparent permeability. We employ the multipoint flux approximation (MPFA) method to handle the full-tensor apparent permeability. We combine MPFA method with the experimenting pressure field approach, i.e., a newly developed technique that enables us to solve the global problem by breaking it into a multitude of local problems. This approach generates a set of predefined pressure fields in the solution domain in such a way that the undetermined coefficients are calculated from these pressure fields. In other words, the matrix of coefficients
Numerical simulation of two phase flows in heat exchangers
International Nuclear Information System (INIS)
Grandotto Biettoli, M.
2006-04-01
The author gives an overview of his research activity since 1981. He first gives a detailed presentation of properties and equations of two-phase flows in heat exchangers, and of their mathematical and numerical investigation: semi-local equations (mass conservation, momentum conservation and energy conservation), homogenized conservation equations (mass, momentum and enthalpy conservation, boundary conditions), equation closures, discretization, resolution algorithm, computational aspects and applications. Then, he reports the works performed in the field of turbulent flows, hyperbolic methods, low Mach methods, the Neptune project, and parallel computing
Directory of Open Access Journals (Sweden)
Snorri Donaldsson
Full Text Available The ability to determine airflow during nasal CPAP (NCPAP treatment without adding dead space or resistance would be useful when investigating the physiologic effects of different NCPAP systems on breathing. The aim of this study was to investigate the effect on pressure stability of different flow measuring devices at the in-line and flow-through position, using simulated neonatal breathing.Six different flow measure devices were evaluated by recording pressure changes and imposed work of breathing for breaths with 16 and 32 ml tidal volumes. The tests were performed initially with the devices in an in line position and with 5 and 10 L/min using flow through technique, without CPAP. The flow meters were then subsequently tested with an Infant Flow CPAP system at 3, 5 and 8 cm H2O pressure using flow through technique. The quality of the recorded signals was compared graphically.The resistance of the measuring devices generated pressure swings and imposed work of breathing. With bias flow, the resistance also generated CPAP pressure. Three of the devices had low resistance and generated no changes in pressure stability or CPAP pressure. The two devices intended for neonatal use had the highest measured resistance.The importance of pressure stability and increased work of breathing during non-invasive respiratory support are insufficiently studied. Clinical trials using flow-through technique have not focused on pressure stability. Our results indicate that a flow-through technique might be a way forward in obtaining a sufficiently high signal quality without the added effects of rebreathing and increased work of breathing. The results should stimulate further research and the development of equipment for dynamic flow measurements in neonates.
Donaldsson, Snorri; Falk, Markus; Jonsson, Baldvin; Drevhammar, Thomas
2015-01-01
The ability to determine airflow during nasal CPAP (NCPAP) treatment without adding dead space or resistance would be useful when investigating the physiologic effects of different NCPAP systems on breathing. The aim of this study was to investigate the effect on pressure stability of different flow measuring devices at the in-line and flow-through position, using simulated neonatal breathing. Six different flow measure devices were evaluated by recording pressure changes and imposed work of breathing for breaths with 16 and 32 ml tidal volumes. The tests were performed initially with the devices in an in line position and with 5 and 10 L/min using flow through technique, without CPAP. The flow meters were then subsequently tested with an Infant Flow CPAP system at 3, 5 and 8 cm H2O pressure using flow through technique. The quality of the recorded signals was compared graphically. The resistance of the measuring devices generated pressure swings and imposed work of breathing. With bias flow, the resistance also generated CPAP pressure. Three of the devices had low resistance and generated no changes in pressure stability or CPAP pressure. The two devices intended for neonatal use had the highest measured resistance. The importance of pressure stability and increased work of breathing during non-invasive respiratory support are insufficiently studied. Clinical trials using flow-through technique have not focused on pressure stability. Our results indicate that a flow-through technique might be a way forward in obtaining a sufficiently high signal quality without the added effects of rebreathing and increased work of breathing. The results should stimulate further research and the development of equipment for dynamic flow measurements in neonates.
Numerical simulation of two-phase flow behavior in Venturi scrubber by interface tracking method
Energy Technology Data Exchange (ETDEWEB)
Horiguchi, Naoki, E-mail: s1430215@u.tsukuba.ac.jp [Japan Atomic Energy Agency, 2-4, Shirakata, Tokai-mura, Naka-gun, Ibaraki 319-1195 (Japan); University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki, 305-8577 (Japan); Yoshida, Hiroyuki [Japan Atomic Energy Agency, 2-4, Shirakata, Tokai-mura, Naka-gun, Ibaraki 319-1195 (Japan); Abe, Yutaka [University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki, 305-8577 (Japan)
2016-12-15
Highlights: • Self-priming occur because of pressure balance between inside and outside of throat is confirmed. • VS has similar flow with a Venturi tube except of disturbance and burble flow is considered. • Some of atomization simulated are validated qualitatively by comparison with previous studies. - Abstract: From the viewpoint of protecting a containment vessel of light water reactor and suppressing the diffusion of radioactive materials from a light water reactor, it is important to develop the device which allows a filtered venting of contaminated high pressure gas. In the filtered venting system that used in European reactors, so called Multi Venturi scrubbers System is used to realize filtered venting without any power supply. This system is able to define to be composed of Venturi scrubbers (VS) and a bubble column. In the VS, scrubbing of contaminated gas is promoted by both gas releases through the submerged VS and gas-liquid contact with splay flow formed by liquid suctioned through a hole provided by the pressure difference between inner and outer regions of a throat part of the VS. However, the scrubbing mechanism of the self-priming VS including effects of gas mass flow rate and shape of the VS are understood insufficiently in the previous studies. Therefore, we started numerical and experimental study to understand the detailed two-phase flow behavior in the VS. In this paper, to understand the VS operation characteristics for the filtered venting, we performed numerical simulations of two-phase flow behavior in the VS. In the first step of this study, we perform numerical simulations of supersonic flow by the TPFIT to validate the applicability of the TPFIT for high velocity flow like flow in the VS. In the second step, numerical simulation of two-phase flow behavior in the VS including self-priming phenomena. As the results, dispersed flow in the VS was reproduced in the numerical simulation, as same as the visualization experiments.
Numerical simulation of two-phase flow behavior in Venturi scrubber by interface tracking method
International Nuclear Information System (INIS)
Horiguchi, Naoki; Yoshida, Hiroyuki; Abe, Yutaka
2016-01-01
Highlights: • Self-priming occur because of pressure balance between inside and outside of throat is confirmed. • VS has similar flow with a Venturi tube except of disturbance and burble flow is considered. • Some of atomization simulated are validated qualitatively by comparison with previous studies. - Abstract: From the viewpoint of protecting a containment vessel of light water reactor and suppressing the diffusion of radioactive materials from a light water reactor, it is important to develop the device which allows a filtered venting of contaminated high pressure gas. In the filtered venting system that used in European reactors, so called Multi Venturi scrubbers System is used to realize filtered venting without any power supply. This system is able to define to be composed of Venturi scrubbers (VS) and a bubble column. In the VS, scrubbing of contaminated gas is promoted by both gas releases through the submerged VS and gas-liquid contact with splay flow formed by liquid suctioned through a hole provided by the pressure difference between inner and outer regions of a throat part of the VS. However, the scrubbing mechanism of the self-priming VS including effects of gas mass flow rate and shape of the VS are understood insufficiently in the previous studies. Therefore, we started numerical and experimental study to understand the detailed two-phase flow behavior in the VS. In this paper, to understand the VS operation characteristics for the filtered venting, we performed numerical simulations of two-phase flow behavior in the VS. In the first step of this study, we perform numerical simulations of supersonic flow by the TPFIT to validate the applicability of the TPFIT for high velocity flow like flow in the VS. In the second step, numerical simulation of two-phase flow behavior in the VS including self-priming phenomena. As the results, dispersed flow in the VS was reproduced in the numerical simulation, as same as the visualization experiments.
Study for discharge coefficient of flow nozzles. Prediction by using numerical simulation
International Nuclear Information System (INIS)
Ikeda, Hiroshi; Sakai, Norio; Yamamoto, Yasushi; Arai, Kenji; Matsumoto, Masaaki
2008-01-01
In nuclear plant, as water feeding into reactor have much effect on thermal power of plant, it is important to measure accurately the flow rate of water. Flow nozzle is on of typical differential pressure type flow meters and the discharge coefficient is used to calculate the flow rate. This coefficient is given by actual experiment and theory. We studied the theoretical assumption of the discharge coefficient curve using numerical simulation and evaluated the effect of flow nozzle configuration on the coefficient numerically and experimentally. As the result, numerical simulation can predict the discharge coefficient of theoretical curve within 0.3%. And we found that the throat length and throat tapping location of flow nozzle have much effect on the coefficient. (author)
Unsteady Flow Simulation of a Sweeping Jet Actuator Using a Lattice-Boltzmann Method
Duda, B.; Wessels, M.; Fares, E.; Vatsa, V.
2016-01-01
Active flow control technology is increasingly used in aerospace applications to control flow separation and to improve aerodynamic performance. In this paper, PowerFLOW is used to simulate the flow through a sweeping jet actuator at two different pressure ratios. The lower pressure ratio leads to a high subsonic flow, whereas the high pressure ratio produces a choked flow condition. Comparison of numerical results with experimental data is shown, which includes qualitatively good agreement of pressure histories and spectra. PIV measurements are also available but the simulation overestimates mean and fluctuation quantities outside the actuator. If supply pressure is matched at one point inside the mixing chamber a good qualitative agreement is achieved at all other monitor points.
Vibrational energy flow in the villin headpiece subdomain: Master equation simulations
International Nuclear Information System (INIS)
Leitner, David M.; Buchenberg, Sebastian; Brettel, Paul; Stock, Gerhard
2015-01-01
We examine vibrational energy flow in dehydrated and hydrated villin headpiece subdomain HP36 by master equation simulations. Transition rates used in the simulations are obtained from communication maps calculated for HP36. In addition to energy flow along the main chain, we identify pathways for energy transport in HP36 via hydrogen bonding between residues quite far in sequence space. The results of the master equation simulations compare well with all-atom non-equilibrium simulations to about 1 ps following initial excitation of the protein, and quite well at long times, though for some residues we observe deviations between the master equation and all-atom simulations at intermediate times from about 1–10 ps. Those deviations are less noticeable for hydrated than dehydrated HP36 due to energy flow into the water
Vibrational energy flow in the villin headpiece subdomain: Master equation simulations
Energy Technology Data Exchange (ETDEWEB)
Leitner, David M., E-mail: dml@unr.edu, E-mail: stock@physik.uni-freiburg.de [Department of Chemistry and Chemical Physics Program, University of Nevada, Reno, Nevada 89557 (United States); Freiburg Institute for Advanced Studies (FRIAS), University of Freiburg, Freiburg (Germany); Buchenberg, Sebastian; Brettel, Paul [Biomolecular Dynamics, Institute of Physics, University of Freiburg, Freiburg (Germany); Stock, Gerhard, E-mail: dml@unr.edu, E-mail: stock@physik.uni-freiburg.de [Freiburg Institute for Advanced Studies (FRIAS), University of Freiburg, Freiburg (Germany); Biomolecular Dynamics, Institute of Physics, University of Freiburg, Freiburg (Germany)
2015-02-21
We examine vibrational energy flow in dehydrated and hydrated villin headpiece subdomain HP36 by master equation simulations. Transition rates used in the simulations are obtained from communication maps calculated for HP36. In addition to energy flow along the main chain, we identify pathways for energy transport in HP36 via hydrogen bonding between residues quite far in sequence space. The results of the master equation simulations compare well with all-atom non-equilibrium simulations to about 1 ps following initial excitation of the protein, and quite well at long times, though for some residues we observe deviations between the master equation and all-atom simulations at intermediate times from about 1–10 ps. Those deviations are less noticeable for hydrated than dehydrated HP36 due to energy flow into the water.
Grid dependency of wall heat transfer for simulation of natural convection flow problems
Loomans, M.G.L.C.; Seppänen, O.; Säteri, J.
2007-01-01
In the indoor environment natural convection is a well known air flow phenomenon. In numerical simulations applying the CFD technique it is also known as a flow problem that is difficult to solve. Alternatives are available to overcome the limitations of the default approach (standard k-e model with
Effectiveness of Side Force Models for Flow Simulations Downstream of Vortex Generators
Florentie, L.; van Zuijlen, A.H.; Hulshoff, S.J.; Bijl, H.
2017-01-01
Vortex generators (VGs) are a widely used means of flow control, and predictions of their influence are vital for efficient designs. However, accurate CFD simulations of their effect on the flow field by means of a body fitted mesh are computationally expensive. Therefore the BAY and jBAY models,
The stress generated by non-Brownian fibers in turbulent channel flow simulations
Gillissen, J.J.J.; Boersma, B.J.; Mortensen, P.H.; Andersson, H.I.
2007-01-01
Turbulent fiber suspension channel flow is studied using direct numerical simulation. The effect of the fibers on the fluid mechanics is governed by a stress tensor, involving the distribution of fiber position and orientation. Properties of this function in channel flow are studied by computing the
Simulating sanitation and waste flows and their environmental impacts in East African urban centres
Oyoo, R.
2014-01-01
Simulating Sanitation and Waste Flows and their Environmental Impacts in East African Urban Centres
Abstract
If improperly managed, urban waste flows can pose a significant threat to the quality of both the natural environment and public health.
Numerical simulation for a two-phase porous medium flow problem with rate independent hysteresis
Brokate, M.; Botkin, N.D.; Pykhteev, O.A.
2012-01-01
The paper is devoted to the numerical simulation of a multiphase flow in porous medium with a hysteretic relation between the capillary pressures and the saturations of the phases. The flow model we use is based on Darcys law. The hysteretic
Simulations of Micro Gas Flows by the DS-BGK Method
Li, Jun
2011-01-01
For gas flows in micro devices, the molecular mean free path is of the same order as the characteristic scale making the Navier-Stokes equation invalid. Recently, some micro gas flows are simulated by the DS-BGK method, which is convergent
Lattice Boltzmann simulation of flow around a confined circular cyclinder
International Nuclear Information System (INIS)
Ashrafizaadeh, M.; Zadehgol, A.
2002-01-01
A two dimensional lattice Boltzmann model (LBM) based on a single time relaxation BGK model has been developed. Several benchmark problems including the Poiseuille flow, the lid driven cavity flow and the flow around a circular cylinder have been performed employing a d2q9 lattice. The laminar flow around a circular cylinder within a channel has been extensively investigated using the present lattice Boltzmann model. Both symmetric and asymmetric placement configurations of the circular cylinder within the channel have been considered. A new treatment for the outlet velocity and pressure (density) boundary conditions has been proposed and validated. The present LBM results are in excellent agreement with those of the other existing CFD results. Careful examination of the LBM results and an appropriate calculation of the lift coefficient based on the rectangular lattice representation of the circular cylinder reveals that the periodic oscillation of the lift coefficient has a second harmonic when the cylinder is placed asymmetrically within the channel. The second harmonic could be associated with an asymmetrical shedding pattern of the vortices behind the cylinder from the upper and lower sides of the cylinder. (author)
Simulating unsteady conduit flows with smoothed particle hydrodynamics
Hou, Q.
2012-01-01
Pipelines are widely used for transport and cooling in industries such as oil and gas, chemical, water supply and sewerage, and hydro, fossil-fuel and nuclear power plants. Unsteady pipe flows with large pressure variations may cause a range of problems such as pipe rapture, support failure, pipe
Numerical simulation methods for phase-transitional flow
Pecenko, A.
2010-01-01
The object of the present dissertation is a numerical study of multiphase flow of one fluid component. In particular, the research described in this thesis focuses on the development of numerical methods that are based on a diffuse-interface model (DIM). With this approach, the modeling problem
Simulation of fluid flow in fractured rock: a probabilistic approach
International Nuclear Information System (INIS)
Samaniego, J.A.; Priest, S.D.
1985-02-01
This report describes the results of a research project designed to investigate the influence of discontinuities on fluid flow through fractured rock masses. The aim has been to provide a rational basis for the assessment of prospective intermediate level radioactive waste repository sites. The results of this work are presented in the form of two groups of FORTRAN computer programs. The first of these is designed to process data obtained from exposed rock faces and thereby provide an unbiased estimate of discontinuity characteristics. The resulting data are input to the second group of programs which generate a two-dimensional random realisation of discontinuity geometry. When appropriate boundary conditions have been specified, the resulting network of channels is solved numerically to determine nodal potentials, flow quantities and equivalent permeabilities. A number of validation runs are presented, together with some parametric studies, to investigate the influence of excavation size and discontinuity geometry on fluid flow. A practical application is given in the form of a case study involving the prediction of fluid flow into a 2.8 m diameter tunnel in water bearing, fractured rock. Finally, the applications and limitations of the programs in site assessment for radioactive waste repositories are discussed. (author)
Fast Multilevel Panel Method for Wind Turbine Rotor Flow Simulations
van Garrel, Arne; Venner, Cornelis H.; Hoeijmakers, Hendrik Willem Marie
2017-01-01
A fast multilevel integral transform method has been developed that enables the rapid analysis of unsteady inviscid flows around wind turbines rotors. A low order panel method is used and the new multi-level multi-integration cluster (MLMIC) method reduces the computational complexity for
Numerical simulations of flux flow in stacked Josephson junctions
DEFF Research Database (Denmark)
Madsen, Søren Peder; Pedersen, Niels Falsig
2005-01-01
We numerically investigate Josephson vortex flux flow states in stacked Josephson junctions, motivated by recent experiments trying to observe the vortices in a square vortex lattice when a magnetic field is applied to layered high-Tc superconductors of the Bi2Sr2CaCu2Ox type. By extensive...
Simulation of acoustic pressure and flow velocity in human glottis
Czech Academy of Sciences Publication Activity Database
Šidlof, Petr; Chaigne, A.; Doaré, O.; Cadot, O.
2008-01-01
Roč. 123, - (2008), s. 3664-3664 ISSN 0001-4966 R&D Projects: GA AV ČR KJB200760801 Institutional research plan: CEZ:AV0Z20760514 Keywords : flow separation * Navier-Stokes equations * vocal fold s Subject RIV: BI - Acoustics
Computational simulation of heat transfer in laser melted material flow
International Nuclear Information System (INIS)
Shankar, V.; Gnanamuthu, D.
1986-01-01
A computational procedure has been developed to study the heat transfer process in laser-melted material flow associated with surface heat treatment of metallic alloys to improve wear-and-tear and corrosion resistance. The time-dependent incompressible Navier-Stokes equations are solved, accounting for both convective and conductive heat transfer processes. The convection, induced by surface tension and high surface temperature gradients, sets up a counterrotating vortex flow within the molten pool. This recirculating material flow is responsible for determining the molten pool shape and the associated cooling rates which affect the solidifying material composition. The numerical method involves an implicit triple-approximate factorization scheme for the energy equation, and an explicit treatment for the momentum and the continuity equations. An experimental setup, using a continuous wave CO 2 laser beam as a heat source, has been carried out to generate data for validation of the computational model. Results in terms of the depth, width, and shape of the molten pool and the heat-affected zone for various power settings and shapes of the laser, and for various travel speeds of the workpiece, compare very well with experimental data. The presence of the surface tension-induced vortex flow is demonstrated
Numerical simulations of rarefied gas flows in thin film processes
Dorsman, R.
2007-01-01
Many processes exist in which a thin film is deposited from the gas phase, e.g. Chemical Vapor Deposition (CVD). These processes are operated at ever decreasing reactor operating pressures and with ever decreasing wafer feature dimensions, reaching into the rarefied flow regime. As numerical
Numerical Simulation of Airfoil Vibrations Induced by Turbulent Flow
Czech Academy of Sciences Publication Activity Database
Feistauer, M.; Horáček, Jaromír; Sváček, P.
2015-01-01
Roč. 17, č. 1 (2015), s. 146-188 ISSN 1815-2406 R&D Projects: GA ČR(CZ) GAP101/11/0207 Institutional support: RVO:61388998 Keywords : fluid-structure interaction * flow induced vibrations * turbulence models * finite element method Subject RIV: BI - Acoustics Impact factor: 1.778, year: 2015
Numerical simulation of particle-laden turbulent channel flow
Li, Y.; McLaughlin, J.B.; Kontomaris, K.; Portela, L.
2001-01-01
This paper presents results for the behavior of particle-laden gases in a small Reynolds number vertical channel down flow. Results will be presented for the effects of particle feedback on the gas-phase turbulence and for the concentration profile of the particles. The effects of density ratio,
Lattice Boltzmann simulation of flow across a staggered tube bundle array
Energy Technology Data Exchange (ETDEWEB)
Tiftikçi, A.; Kocar, C., E-mail: ckocar@hacettepe.edu.tr
2016-04-15
Highlights: • Large eddy simulation of the cross-flow in a staggered tube bundle array in 3D was made. • LBM and FVM are used separately as numerical solvers and the results of each method compared with experimental data. • Effect of lattice model is studied for tube bundle flow. • Filter size effects, mesh size effects are studied for VLES turbulence model. - Abstract: The decision on the magnitude of the grid size is a crucial problem in large eddy simulations. Finer mesh requires excessive memory and causes long simulation time. Large eddy simulation model becomes inefficient when the extent of the flow geometry to be simulated with the lattice-Boltzmann method is large. Thus, in this study, it is proposed to investigate the capabilities of three turbulence models, namely, very large eddy simulation, Van Driest and Smagorinsky–Lilly. As a test case, a staggered tube bundle flow experiment is used for the validation and comparison purposes. Sensitivity analyses (including mesh and filter size) have been made. Furthermore, the effect of lattice model is investigated and it is showed that the D3Q27 and D3Q19 models do not differ significantly in lattice-Boltzmann method for this type of flow. The results of turbulence model comparisons for staggered tube bundle flow showed that very large eddy simulation is superior at low resolution. This paper might be considered as a good validation of the lattice-Boltzmann method. In turbulent flow conditions, the code successfully captures the velocity and stress profiles even if the flow is quite complicated.
Evaluating Mesoscale Simulations of the Coastal Flow Using Lidar Measurements
DEFF Research Database (Denmark)
Floors, Rogier Ralph; Hahmann, Andrea N.; Pena Diaz, Alfredo
2018-01-01
observed height, the model has the largest deviations compared to the observations. Taylor diagrams show that using ERA-Interim data as boundary conditions improves the model skill scores. Simulations with 0.5 and 1 km horizontal grid spacing show poorer model performance compared to those with a 2 km...... spacing, partially because smaller resolved wave lengths degrade standard error metrics. Modeled and observed velocity spectra were compared and showed that simulations with the ﬁnest horizontal grid spacing resolved more high-frequency atmospheric motion....
Simulation techniques for spatially evolving instabilities in compressible flow over a flat plate
Wasistho, B.; Geurts, Bernardus J.; Kuerten, Johannes G.M.
1997-01-01
In this paper we present numerical techniques suitable for a direct numerical simulation in the spatial setting. We demonstrate the application to the simulation of compressible flat plate flow instabilities. We compare second and fourth order accurate spatial discretization schemes in combination
UF6 fissile mass flow simulation at Oak Ridge National Laboratory
International Nuclear Information System (INIS)
Mihalczo, J.T.; March-Leuba, J.; Valentine, T.E.; Mattingly, J.K.; Uckan, T.; McEvers, J.A.
1997-01-01
Basis for measuring fissile mass flow in slurries, liquid, and gaseous streams is activation of a fissile stream by neutrons and then detection of delayed radiation from resulting fission products. This paper describes recent simulation measurements with the first prototype of the system for fissile mass flow measurements with HEU UF 6 gas for use in blenddown facilities. Theory was only 15% higher than actual measured; thus calibration factor would be 0.85. This simulation of HEU gas flow confirms well the understanding of the physical phenomena associated with this measurement system
Numerical simulation of 3D backward facing step flows at various Reynolds numbers
Directory of Open Access Journals (Sweden)
Louda Petr
2015-01-01
Full Text Available The work deals with the numerical simulation of 3D turbulent flow over backward facing step in a narrow channel. The mathematical model is based on the RANS equations with an explicit algebraic Reynolds stress model (EARSM. The numerical method uses implicit finite volume upwind discretization. While the eddy viscosity models fail in predicting complex 3D flows, the EARSM model is shown to provide results which agree well with experimental PIV data. The reference experimental data provide the 3D flow field. The simulations are compared with experiment for 3 values of Reynolds number.
Some recent developments of the immersed interface method for flow simulation
Xu, Sheng
2017-11-01
The immersed interface method is a general methodology for solving PDEs subject to interfaces. In this talk, I will give an overview of some recent developments of the method toward the enhancement of its robustness for flow simulation. In particular, I will present with numerical results how to capture boundary conditions on immersed rigid objects, how to adopt interface triangulation in the method, and how to parallelize the method for flow with moving objects. With these developments, the immersed interface method can achieve accurate and efficient simulation of a flow involving multiple moving complex objects. Thanks to NSF for the support of this work under Grant NSF DMS 1320317.
Energy Technology Data Exchange (ETDEWEB)
Teles, Francisco A.S.; Santos, Ebenezer F.; Dantas, Carlos C., E-mail: francisco.teles@ufpe.br [Universidade Federal de Pernambuco (UFPE), Recife, PE (Brazil). Centro de Tecnologia e Geociencias. Departamento de Energia Nuclear; Melo, Silvio B., E-mail: sbm@cin.ufpe.br [Universidade Federal de Pernambuco (CIN/UFPE), Recife, PE (Brazil). Centro de Informatica; Santos, Valdemir A. dos, E-mail: vas@unicap.br [Universidade Catolica de Pernambuco (UNICAP), Recife, PE (Brazil). Dept. de Quimica; Lima, Emerson A.O., E-mail: emathematics@gmail.com [Universidade de Pernambuco (POLI/UPE), Recife, PE (Brazil). Escola Politecnica
2013-07-01
In this paper, fluid dynamics of Fluid Catalytic Cracking (FCC) process is investigated by means of a Cold Flow Pilot Unit (CFPU) constructed in Plexiglas to visualize operational conditions. Axial and radial catalyst profiles were measured by gamma ray transmission in the riser of the CFPU. Standard uncertainty was evaluated in volumetric solid fraction measurements for several concentrations at a given point of axial profile. Monitoring of the pressure drop in riser shows a good agreement with measured standard uncertainty data. A further evaluation of the combined uncertainty was applied to volumetric solid fraction equation using gamma transmission data. Limit condition of catalyst concentration in riser was defined and simulation with random numbers provided by MATLAB software has tested uncertainty evaluation. The Guide to the expression of Uncertainty in Measurement (GUM) is based on the law of propagation of uncertainty and on the characterization of the quantities measured by means of either a Gaussian distribution or a t-distribution, which allows measurement uncertainty to be delimited by means of a confidence interval. A variety of supplements to GUM are being developed, which will progressively enter into effect. The first of these supplements [3] describes an alternative procedure for the calculation of uncertainties: the Monte Carlo Method (MCM).MCM is an alternative to GUM, since it performs a characterization of the quantities measured based on the random sampling of the probability distribution functions. This paper also explains the basic implementation of the MCM method in MATLAB. (author)