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Using the feasible set method for rezoning in ALE

Procedia Computer Science 2010年第1期1卷 1885-1892页

作者： Markus Berndt Milan Kucharik Mikhail J. Shashkov Los Alamos National Laboratory Computational Physics and Methods Group Mail Stop D413 Los Alamos NM 87545 USA Department of Physical Electronics Faculty of Nuclear Sciences and Physical Engineering Czech Technical University in Prague Brehova 7 Praha 1 115 19 Czech Republic Los Alamos National Laboratory Applied Mathematics and Plasma Physics Group Mail Stop B284 Los Alamos NM 87545 USA

One of the steps in the Arbitrary Lagrangian Eulerian (ALE) algorithm is the improvement of the quality of the computational mesh. This step, commonly referred to as rezoning, is essential for maintaining a mesh that does not become invalid during a simulation. In this paper, we present a new robust and computationally efficient 2D mesh relaxation method. This feasible set method is a geometric method for finding the convex polygon that represents the region of coordinates that a vertex in a mesh can occupy while the mesh around it remains valid. After the feasible set has been computed for a vertex in a mesh, a new vertex location can be chosen that lies inside this feasible set. As a result, the mesh after relaxation is guaranteed to be valid. We present an example ALE simulation, that highlights the robustness of the feasible set method when used as a rezoning method in ALE.

关键词： Mesh smoothing Arbitrary Lagrangian Eulerian method ALE Rezoning Feasible set

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Stochastic methods for uncertainty quantification in radiation transport

Stochastic methods for uncertainty quantification in radiati...

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International Conference on Mathematics, computational methods and Reactor Physics 2009, M and C 2009

作者： Fichtl, Erin D. Prinja, Anil K. Warsa, James S. Los Alamos National Laboratory Computational Physics and Methods Group Los Alamos NM 87545 United States Department of Chemical and Nuclear Engineering University of New Mexico Albuquerque NM 87131 United States

ISBN: (纸本)9781615673490

The use of generalized polynomial chaos (gPC) expansions is investigated for uncertainty quantification in radiation transport. The gPC represents second-order random processes in terms of an expansion of orthogonal polynomials of random variables and is used to represent the uncertain input(s) and unknown(s). We assume a single uncertain input - the total macroscopic cross section - although this does not represent a limitation of the approaches considered here. Two solution methods are examined: The Stochastic Finite Element Method (SFEM) and the Stochastic Collocation Method (SCM). The SFEM entails taking Galerkin projections onto the orthogonal basis, which, for fixed source problems, yields a linear system of fully-coupled equations for the PC coefficients of the unknown. For k-eigenvalue calculations, the SFEM system is non-linear and a Newton-Krylov method is employed to solve it. The SCM utilizes a suitable quadrature rule to compute the moments or PC coefficients of the unknown(s), thus the SCM solution involves a series of independent deterministic transport solutions. The accuracy and efficiency of the two methods are compared and contrasted. The PC coefficients are used to compute the moments and probability density functions of the unknown(s), which are shown to be accurate by comparing with Monte Carlo results. Our work demonstrates that stochastic spectral expansions are a viable alternative to sampling-based uncertainty quantification techniques since both provide a complete characterization of the distribution of the flux and the k-eigenvalue. Furthermore, it is demonstrated that, unlike perturbation methods, SFEM and SCM can handle large parameter uncertainty.

关键词： Linear systems

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Effects of the temperature discretization on numerical methods for thermal radiation transport

Effects of the temperature discretization on numerical metho...

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International Conference on Mathematics, computational methods and Reactor Physics 2009, M and C 2009

作者： McClarren, Ryan G. Lowrie, Robert B. Dept. of Nuclear Engineering Texas A and M University College Station TX 77843-3133 United States Computational Physics and Methods Group Los Alamos National Laboratory MS D413 P.O. Box 1663 Los Alamos NM 87545 United States

ISBN: (纸本)9781615673490

We present an analysis of three means of treating the material energy equation coupled with the nonlinear radiation transport equation in slab geometry. The radiation transport equation is discretized using a linear discontinuous Galerkin method. The material temperature is then treated with either 1) two temperature unknowns per cell, 2) one temperature unknown per cell, or 3) one temperature unknown per cell with a linear reconstruction of the emission source. Only the two temperatures per cell discretization is robust in the equilibrium diffusion limit. Though it is not robust in the diffusion limit, the reconstructed emission treatment is much more accurate than the one temperature per cell treatment. We use all three methods to solve a diffusive Marshak wave problem. These numerical solutions agree with the analysis. On a problem representing an ablating hohlraum where the solution is strongly influenced by a transport boundary layer between an optically thick and thin region, both the two temperature and reconstructed emission source treatments required 10 μm resolution to resolve the solution. The one temperature per cell solution was not yet converged at this fine resolution.

关键词： Radiation effects

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Filtered spherical harmonics methods for transport problems

Filtered spherical harmonics methods for transport problems

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International Conference on Mathematics, computational methods and Reactor Physics 2009, M and C 2009

作者： McClarren, Ryan G. Hauck, Cory D. Lowrie, Robert B. Dept. of Nuclear Engineering Texas A and M University College Station TX 77843-3133 United States Computational Physics and Methods Group Los Alamos National Laboratory MS D413 P.O. Box 1663 Los Alamos NM 87545 United States

ISBN: (纸本)9781615673490

We present a new way of using spherical harmonics expansions to solve transport problems. Our approach uses filtered expansions to give positive solutions and reduce wave effects in the solutions. We present two specific filters: one based on maintaining positivity in a P1 expansion, and the other that is a function of the total cross-section and the order of the expansion. We compare solutions using our filtered expansions to the standard spherical harmonics expansions, Monte Carlo, diffusion, discrete or-dinates, and analytic transport solutions. These numerical results suggest that our filtered expansions give solutions that are comparable to other methods in terms of accuracy. Additionally, we point out how filtered spherical harmonics expansions could be improved.

关键词： Harmonic analysis

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Linearized stability analysis of two time discretizations for the compton-scattering fokker-planck equation

Linearized stability analysis of two time discretizations fo...

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2008 Winter Meeting and Nuclear Technology Expo: Nuclear Power-Ready, Steady, Go

作者： Densmore, Jeffery D. Warsa, James S. Lowrie, Robert B. Morel, Jim E. Computational Physics and Methods Group Los Alamos National Laboratory Los Alamos NM United States Department of Nuclear Engineering Texas A and M University College Station TX United States

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A finite element model for the numerical simulation of hydrodynamic transport phenomena: An effective tool for the evaluation of human-induced impacts in coastal areas of high environmental and economical value

A finite element model for the numerical simulation of hydro...

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11th International Conference on Civil, Structural and Environmental engineering Computing, Civil-Comp 2007

作者： Colominas, I. Navarrina, F. Casteleiro, M. Cueto-Felgueroso, L. Gómez, H. Fe, J. Soage, A. Group of Numerical Methods in Engineering University of la Coruña Spain Aerospace Computational Design Laboratory Massachusetts Institute of Technology United States

ISBN: (纸本)9781905088157

This paper presents a numerical model for the simulation of the hydrodynamic and of the evolution of the salinity in shallow water estuaries. The mathematical model consists of the equations to model the evolution of the depth and of the velocity field ("shallow water hydrodynamic equations") and the equation that describes the evolution of the salinity level ("shallow water advective-diffusive transport equation"). Some important issues that must be taken into account are the effects of the tides (including the possible exposition of the seabed), the volume of fresh water provided by the rivers and the effects of the winds. Consequently, different types of boundary conditions must be considered. The numerical model proposed for solving this complex problem is a second-order Taylor-Galerkin Finite Element formulation. The proposed formulation has been applied to predict effects of human actions on the marine habitat in coastal areas and to evaluate their environmental impact under different meteorological conditions. The example presented in this paper is Los Lombos del Ulla within the Arousa Estuary in northwestern Spain, which is an area with high environmental, economical and social value. © 2007 Civil-Comp Press.

关键词： Estuaries

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A Fokker-Planck method for modeling compton scattering in implicit Monte Carlo simulations

A Fokker-Planck method for modeling compton scattering in im...

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Joint International Topical Meeting on Mathematics and Computations and Supercomputing in Nuclear Applications, M and C + SNA 2007

作者： Densmore, Jeffery D. Warsa, James S. Morel, Jim E. Computational Physics and Methods Group Los Alamos National Laboratory MS D409 P.O. Box 1663 Los Alamos NM 87545 United States Department of Nuclear Engineering Texas A and M University 3133 TAMU College Station TX 77843 United States

ISBN: (纸本)0894480596

We present a new method for modeling Compton scattering in Implicit Monte Carlo (IMC) simulations that implicitly evaluates the radiation-matter energy coupling due to photon-electron scattering. In this technique, the scattering physics are split from the radiative-transfer process and represented by a Fokker-Planck approximation. In each time step, radiative transfer, minus Compton scattering, is simulated using the usual IMC method. The results of this calculation are then used to solve the Fokker-Planck equation deterministically and update the material temperature and radiation intensity accordingly. With a set of numerical examples, we demonstrate that our new Fokker-Planck method is able to employ larger time steps than an analog technique for simulating Compton scattering that evaluates the material temperature explicitly.

关键词： Compton scattering

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An object-oriented systems engineering model design for integrating spent fuel treatment facility and chemical separation processes

An object-oriented systems engineering model design for inte...

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2006 ASME International Mechanical engineering Congress and Exposition, IMECE2006

作者： Chang, Ming Hodges, Matthew Kwan, Kenny Hsieh, Hsuan-Tsung Chen, Yitung Vandegrift, George Copple, Jackie Laidler, James Nevada Center for Advanced Computational Methods College of Engineering University of Nevada Las Vegas United States Argonne National Laboratory 9700 S. Cass Avenue Argonne IL 60439 United States

ISBN: (纸本)0791837904

The mission of the Transmutation Research Program (TRP) at University of Nevada, Las Vegas (UNLV) is to establish a nuclear engineering test bed that can carry out effective transmutation and advanced reactor research and development effort. TRPSEMPro package, developed from previous project period, integrated a chemical separation code from the Argonne National Laboratories (ANL). Current research focus has two folds: development of simulation system processes applied to Spent Fuel Treatment Facility (SFTF) using ASPEN-plus and further interaction of ASPEN+ program from TRPSEMPro interface. More details will be discussed below. ANL has identified three processes simulations using their separation technologies. The first process is to separate aqueous acid streams of acetic acid, nitric acid, water and a variety of fission product nitric salts. Distillation separation method is used to remove the desired components from the streams. The second simulation is to convert plutonium nitrate to plutonium metal. Steps used for the process simulation are precipitation, calcinations, fluorination and reduction. The third process currently under development is vitrification of fission product of raffinate streams. During the process, various waste streams from the plant are mixed and fed to a process that converts them to a solid state glass phase. The vitrification process used by the Hanford and Savannah River facilities was selected as a guideline to develop the prototype simulation process using ASPEN-Plus. Current research is focusing on identifying unit operations required to perform the vitrification of the waste streams. The first two processes are near completion stage. Microsoft Visual Basic (MS VB) has been used to develop the entire system engineering model package, TRPSEMPro. Currently a user friendly interface is under development to facilitate direct execution of ASPEN-plus within TRPSEMPro. The major purpose for the implementation is to create iterative intera

关键词： Spent fuels

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CFD-based method for simulation of marine-vehicle maneuvering

CFD-based method for simulation of marine-vehicle maneuverin...

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35th AIAA Fluid Dynamics Conference and Exhibit

作者： Racine, Benjamin J. Paterson, Eric G. Pennsylvania State University Computational Methods Development Department Applied Research Laboratory Department of Mechanical and Nuclear Engineering State College PA 16804 United States

ISBN: (纸本)9781624100598

A physics-based methodology for predicting marine-vehicle maneuvering has been developed. The work is motivated by the need for a simulation tool which is suitable for preliminary design of vehicles with novel hull forms, propulsion systems, and flow-control schemes. The approach is based upon a nonlinear coefficient-based maneuvering model and unsteady Reynolds-averaged Naviers Stokes (URANS) computational fluid dynamics (CFD) simulations. To guide and reduce the size of the CFD simulation matrix, a sensitivity analysis is performed that rank orders the importance of each coefficient for definitive maneuvers such as turning circles and horizontal- and vertical-plane overshoots. CFD is then used to simulate traditional experiments, i.e., towing-tank tests at static drift angles, rotating-arm tests, and prescribed harmonic motions via a planar-motion mechanism. The resultant forces and moments are then post-processed to compute the various model coefficients, which then permits both assessment of dynamic straight-line stability and simulation of vehicle trajectories given control-surface inputs. The overall approach is applied to the Newport News Experimental Model (NNEMO). Thirteen bare-hull and 16 complete-vehicle CFD simulations are performed. This permits computation of the stability coefficients and 11 significant maneuvering coefficients. It is shown from the CFD results that the hull is stable in the vertical plane, but unstable in the horizontal plane, whereas the complete vehicle is stable in both planes. Maneuvering simulations are performed with both baseline (from theoretical and empirical methods) and CFD-computed coefficients and the trajectories, velocities, and Euler angles for several maneuvers are compared. It is shown that the maneuvers in the horizontal plane exhibit both roll instability and significant out-of-plane motion when using the CFD-computed coefficients, whereas the vertical-plane maneuver showed almost no sensitivity to the updated coe

关键词： computational fluid dynamics

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A survey and taxonomy of 3D visualization resources for bioinformatics

A survey and taxonomy of 3D visualization resources for bioi...

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Summer Computer Simulation Conference 2005, SCSC 2005, Part of the 2005 Summer Simulation Multiconference, SummerSim 2005

作者： Dos Santos, Carlos Luiz N. Hill, David R. C. Blaise Pascal University ISIMA/LIMOS UMR CNRS 6158 Computer Science and Modeling Laboratory Campus des Cézeaux BP 10125 63177 Aubière Cedex France Federal University of Rio de Janeiro COPPE Civil Engineering Department Laboratory of Computational Methods in Engineering P.O. BOX 68.552 CEP 21949-900 Rio de Janeiro RJ Brazil

ISBN: (纸本)9781622763511

We will present in this article a survey of 3D visualization resources for Bioinformatics. A taxonomy is proposed based on some aspects in visualization evolution. Details of the taxonomy retained are presented with definitions to help understanding the differences between the five categories exposed. We have then listed a sub-set of bioinformatics tools, taking benefit of 3D visualization systems and classified according to the previously established taxonomy.

关键词： Visualization

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