The Experts below are selected from a list of 15603 Experts worldwide ranked by ideXlab platform
Christian B Allen - One of the best experts on this subject based on the ideXlab platform.
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parallel efficient Mesh Motion using radial basis functions with application to multi bladed rotors
International Journal for Numerical Methods in Engineering, 2010Co-Authors: Thomas Rendall, Christian B AllenAbstract:Radial basis functions are used to provide a solution to the problem of Mesh Motion for unsteady aerodynamic simulation. The method is independent of connectivity and produces high-quality Meshes, but is expensive for large Meshes in its full form. Hence, the efficiency of the technique has been greatly improved here by reducing the number of surface points used to define deformations of the surface, and the minor error in position that this implies at other surface points is corrected with a simple decaying perturbation, thus splitting the method into a primary basis function method and a secondary local correction method. This means that the exact surface is retained, but the Mesh Motion is significantly faster, while splitting the Motion into two stages allows both the methods to work on appropriate problems given their relative strengths. An example deformation for a 5×106 cell helicopter rotor Mesh with an exaggerated cyclic pitch Motion shows excellent Mesh quality, thus validating a scheme that is also simple, robust and readily parallelized. Copyright © 2009 John Wiley & Sons, Ltd.
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Parallel efficient Mesh Motion using radial basis functions with application to multi-bladed rotors
International Journal for Numerical Methods in Engineering, 2009Co-Authors: Thomas Rendall, Christian B AllenAbstract:Radial basis functions are used to provide a solution to the problem of Mesh Motion for unsteady aerodynamic simulation. The method is independent of connectivity and produces high-quality Meshes, but is expensive for large Meshes in its full form. Hence, the efficiency of the technique has been greatly improved here by reducing the number of surface points used to define deformations of the surface, and the minor error in position that this implies at other surface points is corrected with a simple decaying perturbation, thus splitting the method into a primary basis function method and a secondary local correction method. This means that the exact surface is retained, but the Mesh Motion is significantly faster, while splitting the Motion into two stages allows both the methods to work on appropriate problems given their relative strengths. An example deformation for a 5 x10 6 cell helicopter rotor Mesh with an exaggerated cyclic pitch Motion shows excellent Mesh quality, thus validating a scheme that is also simple, robust and readily parallelized.
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Point Selection Approaches for Reduced Surface Representation in Mesh Motion
27th AIAA Applied Aerodynamics Conference, 2009Co-Authors: Thomas Rendall, Christian B AllenAbstract:Previous work by the authors has developed an efficient methodfor using radial basis functions to achieve high quality Mesh Motion for large Meshes. This method starts by using a chosen error function on the surface Mesh to select a subset of the surface points; this subset gives a low surface position error and contains a sufficiently small number of points so as to make the volume Motion fast. However, alternatives exist for the error function, so here a comparison is made between three different options: the surface error function, the unit function and the power function. Tests run on a structured wing Mesh and an unstructured aircraft Mesh show that the surface error function gives the lowest errors, but this also requires a deformed surface shape to be known in advance of the simulation. The unit and power functions both avoid the need for a deformed surface, and the unit function is superior as it leads to lower errors.
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Improved radial basis function fluid–structure coupling via efficient localized implementation
International Journal for Numerical Methods in Engineering, 2009Co-Authors: Thomas Rendall, Christian B AllenAbstract:Previous work by the authors has developed a universal interpolation scheme, using radial basis functions (RBFs), which results in a unified formulation for robust fluid-structure interpolation and high-quality Mesh Motion. The method has several significant advantages. Primarily, all volume Mesh, structural Mesh, and flow-solver-type dependence is removed entirely, as all operations are performed on totally arbitrary point clouds of any form. Hence, all connectivity requirements are removed from both the coupling and Mesh Motion problems. Furthermore, only matrix-vector multiplications are required during unsteady simulation because dependence relations are computed once prior to any simulation and then remain constant. This property means that the method is both perfectly parallel and totally independent from the flow-solver. However, the full method is expensive, since the dependence matrix between two sets of points is N points1 × N points2 . The fluid-structure coupling behaviour can also be influenced by parameters used in the interpolation. To alleviate these difficulties a more efficient form of the RBF fluid-structure coupling is presented, which also greatly reduces the interpolation parameter influence. A pointwise form of the partition of unity approach is developed that localizes the interpolation, with results presented for static aeroelastic simulations of the Brite-Euram multi-disciplinary optimization wing using a very fine Mesh containing 58000 surface points. It is shown that a 58 × reduction in data size is achieved, and equally importantly the interpolation has a much smaller influence on final aeroelastic results. .
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Efficient Mesh Motion using radial basis functions with data reduction algorithms
Journal of Computational Physics, 2009Co-Authors: Thomas Rendall, Christian B AllenAbstract:Mesh Motion using radial basis functions has been demonstrated previously by the authors to produce high quality Meshes suitable for use within unsteady and aeroelastic CFD codes. In the aeroelastic case the structural Mesh may be used as the set of control points governing the deformation, which is efficient since the structural Mesh is usually small. However, as a stand alone Mesh Motion tool, where the surface Mesh points control the Motion, radial basis functions may be restricted by the size of the surface Mesh, as an update of a single volume point depends on all surface points. In this paper a method is presented that allows an arbitrary deformation to be represented to within a desired tolerance by using a significantly reduced set of surface points intelligently identified in a fashion that minimises the error in the interpolated surface. This method may be used on much larger cases and is successfully demonstrated here for a 10^6 cell Mesh, where the initial solve phase cost reduces by a factor of eight with the new scheme and the Mesh update by a factor of 55. It has also been shown that the number of surface points required to represent the surface is only geometry dependent (i.e. grid size independent), and so this reduction factor actually increases for larger Meshes.
Garry Rodrigue - One of the best experts on this subject based on the ideXlab platform.
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Large eddy simulation and ALE Mesh Motion in Rayleigh-Taylor instability simulation ✩
Computer Physics Communications, 2002Co-Authors: Rebecca M. Darlington, Thomas L. Mcabee, Garry RodrigueAbstract:Abstract Many large eddy simulation (LES) techniques have been developed for stationary computational Meshes. This study applies a single equation LES to Arbitrary Lagrangian–Eulerian (ALE) simulations of Rayleigh–Taylor instability and investigates its effects. Behavior of LES is similar for Eulerian and ALE simulations for the test problem studied. However, the Motion of the Mesh can be tied to the subgrid scale model in the form of a relaxation weight based on subgrid scale energy. This increases Mesh resolution in areas of high subgrid scale energy.
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A study of ALE simulations of Rayleigh–Taylor instability☆
Computer Physics Communications, 2001Co-Authors: Rebecca M. Darlington, Thomas L. Mcabee, Garry RodrigueAbstract:Abstract This paper investigates the use of an Arbitrary Lagrangian–Eulerian (ALE) technique on a single-mode Rayleigh–Taylor instability simulation in two dimensions. A finite volume approach on a simply connected quadrilateral grid is used. The effect of various modifications in the ALE method on instability growth, energy balance, and Mesh distortion are investigated. It is shown that ALE Mesh Motion can be used to improve single mode Rayleigh–Taylor Instability simulations.
Thomas Rendall - One of the best experts on this subject based on the ideXlab platform.
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parallel efficient Mesh Motion using radial basis functions with application to multi bladed rotors
International Journal for Numerical Methods in Engineering, 2010Co-Authors: Thomas Rendall, Christian B AllenAbstract:Radial basis functions are used to provide a solution to the problem of Mesh Motion for unsteady aerodynamic simulation. The method is independent of connectivity and produces high-quality Meshes, but is expensive for large Meshes in its full form. Hence, the efficiency of the technique has been greatly improved here by reducing the number of surface points used to define deformations of the surface, and the minor error in position that this implies at other surface points is corrected with a simple decaying perturbation, thus splitting the method into a primary basis function method and a secondary local correction method. This means that the exact surface is retained, but the Mesh Motion is significantly faster, while splitting the Motion into two stages allows both the methods to work on appropriate problems given their relative strengths. An example deformation for a 5×106 cell helicopter rotor Mesh with an exaggerated cyclic pitch Motion shows excellent Mesh quality, thus validating a scheme that is also simple, robust and readily parallelized. Copyright © 2009 John Wiley & Sons, Ltd.
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Parallel efficient Mesh Motion using radial basis functions with application to multi-bladed rotors
International Journal for Numerical Methods in Engineering, 2009Co-Authors: Thomas Rendall, Christian B AllenAbstract:Radial basis functions are used to provide a solution to the problem of Mesh Motion for unsteady aerodynamic simulation. The method is independent of connectivity and produces high-quality Meshes, but is expensive for large Meshes in its full form. Hence, the efficiency of the technique has been greatly improved here by reducing the number of surface points used to define deformations of the surface, and the minor error in position that this implies at other surface points is corrected with a simple decaying perturbation, thus splitting the method into a primary basis function method and a secondary local correction method. This means that the exact surface is retained, but the Mesh Motion is significantly faster, while splitting the Motion into two stages allows both the methods to work on appropriate problems given their relative strengths. An example deformation for a 5 x10 6 cell helicopter rotor Mesh with an exaggerated cyclic pitch Motion shows excellent Mesh quality, thus validating a scheme that is also simple, robust and readily parallelized.
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Point Selection Approaches for Reduced Surface Representation in Mesh Motion
27th AIAA Applied Aerodynamics Conference, 2009Co-Authors: Thomas Rendall, Christian B AllenAbstract:Previous work by the authors has developed an efficient methodfor using radial basis functions to achieve high quality Mesh Motion for large Meshes. This method starts by using a chosen error function on the surface Mesh to select a subset of the surface points; this subset gives a low surface position error and contains a sufficiently small number of points so as to make the volume Motion fast. However, alternatives exist for the error function, so here a comparison is made between three different options: the surface error function, the unit function and the power function. Tests run on a structured wing Mesh and an unstructured aircraft Mesh show that the surface error function gives the lowest errors, but this also requires a deformed surface shape to be known in advance of the simulation. The unit and power functions both avoid the need for a deformed surface, and the unit function is superior as it leads to lower errors.
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Improved radial basis function fluid–structure coupling via efficient localized implementation
International Journal for Numerical Methods in Engineering, 2009Co-Authors: Thomas Rendall, Christian B AllenAbstract:Previous work by the authors has developed a universal interpolation scheme, using radial basis functions (RBFs), which results in a unified formulation for robust fluid-structure interpolation and high-quality Mesh Motion. The method has several significant advantages. Primarily, all volume Mesh, structural Mesh, and flow-solver-type dependence is removed entirely, as all operations are performed on totally arbitrary point clouds of any form. Hence, all connectivity requirements are removed from both the coupling and Mesh Motion problems. Furthermore, only matrix-vector multiplications are required during unsteady simulation because dependence relations are computed once prior to any simulation and then remain constant. This property means that the method is both perfectly parallel and totally independent from the flow-solver. However, the full method is expensive, since the dependence matrix between two sets of points is N points1 × N points2 . The fluid-structure coupling behaviour can also be influenced by parameters used in the interpolation. To alleviate these difficulties a more efficient form of the RBF fluid-structure coupling is presented, which also greatly reduces the interpolation parameter influence. A pointwise form of the partition of unity approach is developed that localizes the interpolation, with results presented for static aeroelastic simulations of the Brite-Euram multi-disciplinary optimization wing using a very fine Mesh containing 58000 surface points. It is shown that a 58 × reduction in data size is achieved, and equally importantly the interpolation has a much smaller influence on final aeroelastic results. .
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Efficient Mesh Motion using radial basis functions with data reduction algorithms
Journal of Computational Physics, 2009Co-Authors: Thomas Rendall, Christian B AllenAbstract:Mesh Motion using radial basis functions has been demonstrated previously by the authors to produce high quality Meshes suitable for use within unsteady and aeroelastic CFD codes. In the aeroelastic case the structural Mesh may be used as the set of control points governing the deformation, which is efficient since the structural Mesh is usually small. However, as a stand alone Mesh Motion tool, where the surface Mesh points control the Motion, radial basis functions may be restricted by the size of the surface Mesh, as an update of a single volume point depends on all surface points. In this paper a method is presented that allows an arbitrary deformation to be represented to within a desired tolerance by using a significantly reduced set of surface points intelligently identified in a fashion that minimises the error in the interpolated surface. This method may be used on much larger cases and is successfully demonstrated here for a 10^6 cell Mesh, where the initial solve phase cost reduces by a factor of eight with the new scheme and the Mesh update by a factor of 55. It has also been shown that the number of surface points required to represent the surface is only geometry dependent (i.e. grid size independent), and so this reduction factor actually increases for larger Meshes.
Rebecca M. Darlington - One of the best experts on this subject based on the ideXlab platform.
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Large eddy simulation and ALE Mesh Motion in Rayleigh-Taylor instability simulation ✩
Computer Physics Communications, 2002Co-Authors: Rebecca M. Darlington, Thomas L. Mcabee, Garry RodrigueAbstract:Abstract Many large eddy simulation (LES) techniques have been developed for stationary computational Meshes. This study applies a single equation LES to Arbitrary Lagrangian–Eulerian (ALE) simulations of Rayleigh–Taylor instability and investigates its effects. Behavior of LES is similar for Eulerian and ALE simulations for the test problem studied. However, the Motion of the Mesh can be tied to the subgrid scale model in the form of a relaxation weight based on subgrid scale energy. This increases Mesh resolution in areas of high subgrid scale energy.
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A study of ALE simulations of Rayleigh–Taylor instability☆
Computer Physics Communications, 2001Co-Authors: Rebecca M. Darlington, Thomas L. Mcabee, Garry RodrigueAbstract:Abstract This paper investigates the use of an Arbitrary Lagrangian–Eulerian (ALE) technique on a single-mode Rayleigh–Taylor instability simulation in two dimensions. A finite volume approach on a simply connected quadrilateral grid is used. The effect of various modifications in the ALE method on instability growth, energy balance, and Mesh distortion are investigated. It is shown that ALE Mesh Motion can be used to improve single mode Rayleigh–Taylor Instability simulations.
Andrei N. Simakov - One of the best experts on this subject based on the ideXlab platform.
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A conservative phase-space moving-grid strategy for a 1D-2V Vlasov–Fokker–Planck Solver
Computer Physics Communications, 2021Co-Authors: William Taitano, Luis Chacon, Andrei N. Simakov, Steven E. AndersonAbstract:Abstract We develop a conservative configuration- and velocity-space (i.e., phase-space) moving-grid strategy for the Vlasov–Fokker–Planck (VFP) equation in a planar geometry. The velocity-space grid is normalized and shifted in terms of the thermal speed and the bulk-fluid velocity, respectively. The configuration-space grid is moved according to a Mesh-Motion-partial-differential equation (MMPDE), which equidistributes a monitor function that is inversely proportional to the gradient-length scales of the macroscopic plasma quantities. The resulting inertial terms in the transformed VFP equations are discretized to ensure the discrete conservation of mass, momentum, and energy. To satisfy the discrete conservation theorems in the presence of phase-space Mesh Motion, we employ the method of discrete nonlinear constraints – explored in previous studies – but the underlying symmetries are determined in a much more efficient manner than before. The conservative grid-adaptivity strategy provides an efficient scheme that resolves important physical structures in the phase-space while controlling the computational complexity at all times. We demonstrate the favorable features of the proposed algorithm through a set of test cases of increasing complexity. The problems test independent components of the algorithms, as well as the integrated capability on settings relevant to inertial confinement fusion.
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An Eulerian Vlasov-Fokker-Planck Algorithm for Spherical Implosion Simulations of Inertial Confinement Fusion Capsules
arXiv: Computational Physics, 2020Co-Authors: William Taitano, Luis Chacon, Steven E. Anderson, Brett Keenan, Hans Hammer, Andrei N. SimakovAbstract:We present a numerical algorithm that enables a phase-space adaptive Eulerian Vlasov-Fokker-Planck (VFP) simulation of an inertial confinement fusion (ICF) capsule implosion. The approach relies on extending a recent mass, momentum, and energy conserving phase-space moving-Mesh adaptivity strategy to spherical geometry. In configuration space, we employ a Mesh Motion partial differential equation (MMPDE) strategy while, in velocity space, the Mesh is expanded/contracted and shifted with the plasma's evolving temperature and drift velocity. The Mesh Motion is dealt with by transforming the underlying VFP equations into a computational (logical) coordinate, with the resulting inertial terms carefully discretized to ensure conservation. To deal with the spatial and temporally varying dynamics in a spherically imploding system, we have developed a novel nonlinear stabilization strategy for MMPDE in the configuration space. The strategy relies on a nonlinear optimization procedure that optimizes between Mesh quality and the volumetric rate change of the Mesh to ensure both accuracy and stability of the solution. Implosions of ICF capsules are driven by several boundary conditions: 1) an elastic moving wall boundary; 2) a time-dependent Maxwellian Dirichlet boundary; and 3) a pressure-driven Lagrangian boundary. Of these, the pressure-driven Lagrangian boundary driver is new to our knowledge. The implementation of our strategy is verified through a set of test problems, including the Guderley and Van-Dyke implosion problems --the first-ever reported using a Vlasov-Fokker-Planck model.
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An Eulerian Vlasov-Fokker–Planck algorithm for spherical implosion simulations of inertial confinement fusion capsules
Computer Physics Communications, 1Co-Authors: William Taitano, Luis Chacon, Steven E. Anderson, Brett Keenan, Hans Hammer, Andrei N. SimakovAbstract:Abstract We present a numerical algorithm that enables a phase-space adaptive Eulerian Vlasov-Fokker–Planck (VFP) simulation of inertial confinement fusion (ICF) capsule implosions. The approach relies on extending a recent mass, momentum, and energy conserving phase-space moving-Mesh adaptivity strategy to spherical geometry. In configuration space, we employ a Mesh Motion partial differential equation (MMPDE) strategy while, in velocity space, the Mesh is expanded/contracted and shifted with the plasma’s evolving temperature and drift velocity. The Mesh Motion is dealt with by transforming the underlying VFP equations into a computational (logical) coordinate, with the resulting inertial terms carefully discretized to ensure conservation. To deal with the spatial and temporally varying dynamics in a spherically imploding system, we have developed a novel nonlinear stabilization strategy for MMPDE in the configuration space. The strategy relies on a nonlinear optimization procedure that optimizes between Mesh quality and the volumetric rate change of the Mesh to ensure both accuracy and stability of the solution. Implosions of ICF capsules are driven by several boundary conditions: (1) an elastic moving wall boundary; (2) a time-dependent Maxwellian Dirichlet boundary; and (3) a pressure-driven Lagrangian boundary. Of these, the pressure-driven Lagrangian boundary driver is new to our knowledge. The implementation of our strategy is verified through a set of test problems, including the Guderley and Van-Dyke implosion problems –the first-ever reported using a Vlasov-Fokker–Planck model.