The Experts below are selected from a list of 8124 Experts worldwide ranked by ideXlab platform
Bart Ripperda - One of the best experts on this subject based on the ideXlab platform.
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general relativistic resistive magnetohydrodynamics with robust Primitive Variable recovery for accretion disk simulations
Astrophysical Journal Supplement Series, 2019Co-Authors: Bart Ripperda, Fabio Bacchini, Oliver Porth, Elias R Most, Hector Olivares, Antonios Nathanail, Luciano RezzollaAbstract:Recent advances in black hole astrophysics, particularly the first visual evidence of a supermassive black hole at the center of the galaxy M87 by the Event Horizon Telescope, and the detection of an orbiting "hot spot" nearby the event horizon of Sgr A* in the Galactic center by the Gravity Collaboration, require the development of novel numerical methods to understand the underlying plasma microphysics. Non-thermal emission related to such hot spots is conjectured to originate from plasmoids that form due to magnetic reconnection in thin current layers in the innermost accretion zone. Resistivity plays a crucial role in current sheet formation, magnetic reconnection, and plasmoid growth in black hole accretion disks and jets. We included resistivity in the three-dimensional general-relativistic magnetohydrodynamics (GRMHD) code BHAC and present the implementation of an implicit–explicit scheme to treat the stiff resistive source terms of the GRMHD equations. The algorithm is tested in combination with adaptive mesh refinement to resolve the resistive scales and a constrained transport method to keep the magnetic field solenoidal. Several novel methods for Primitive-Variable recovery, a key part in relativistic magnetohydrodynamics codes, are presented and compared for accuracy, robustness, and efficiency. We propose a new inversion strategy that allows for resistive-GRMHD simulations of low gas-to-magnetic pressure ratio and highly magnetized regimes as applicable for black hole accretion disks, jets, and neutron-star magnetospheres. We apply the new scheme to study the effect of resistivity on accreting black holes, accounting for dissipative effects as reconnection.
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general relativistic resistive magnetohydrodynamics with robust Primitive Variable recovery for accretion disk simulations
arXiv: Computational Physics, 2019Co-Authors: Bart Ripperda, Fabio Bacchini, Oliver Porth, Elias R Most, Hector Olivares, Antonios Nathanail, Luciano RezzollaAbstract:Recent advances in black hole astrophysics, particularly the first visual evidence of a supermassive black hole at the center of the galaxy M87 by the Event Horizon Telescope (EHT), and the detection of an orbiting "hot spot" nearby the event horizon of Sgr A* in the Galactic center by the Gravity Collaboration, require the development of novel numerical methods to understand the underlying plasma microphysics. Non-thermal emission related to such hot spots is conjectured to originate from plasmoids that form due to magnetic reconnection in thin current layers in the innermost accretion zone. Resistivity plays a crucial role in current sheet formation, magnetic reconnection, and plasmoid growth in black hole accretion disks and jets. We included resistivity in the three-dimensional general-relativistic magnetohydrodynamics (GRMHD) code BHAC and present the implementation of an Implicit-Explicit scheme to treat the stiff resistive source terms of the GRMHD equations. The algorithm is tested in combination with adaptive mesh refinement to resolve the resistive scales and a constrained transport method to keep the magnetic field solenoidal. Several novel methods for Primitive Variable recovery, a key part in relativistic magnetohydrodynamics codes, are presented and compared for accuracy, robustness, and efficiency. We propose a new inversion strategy that allows for resistive-GRMHD simulations of low gas-to-magnetic pressure ratio and highly magnetized regimes as applicable for black hole accretion disks, jets, and neutron star magnetospheres. We apply the new scheme to study the effect of resistivity on accreting black holes, accounting for dissipative effects as reconnection.
Vali Enjilela - One of the best experts on this subject based on the ideXlab platform.
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natural convection heat transfer at high rayleigh numbers extended meshless local petrov galerkin mlpg Primitive Variable method
Engineering Analysis With Boundary Elements, 2014Co-Authors: Mohammad Najafi, Vali EnjilelaAbstract:Abstract The meshless local Petrov–Galerkin (MLPG) method is extended using an improved Primitive Variable formulation to solve the two-dimensional laminar natural convection equations. The extended method solves the natural convection heat transfer problems at high Rayleigh numbers. The method uses the fractional step scheme for discretization, and the moving least square (MLS) interpolation for approximation of the field Variables. For the proposed technique, a weighting function of unity is used. The improved method considers the natural convection in a square cavity for up to and including Ra = 10 8 , in a concentric square outer cylinder and circular inner cylinder annulus for up to and including Ra = 10 7 , and in a two concentric circular cylinders annulus for up to and including Ra = 10 5 . Comparing the results of the three test cases obtained using the present method with those obtained using the conventional methods shows very good agreement existing among the appropriate results, hence, verifying the proposed improved meshless numerical technique.
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extending mlpg Primitive Variable based method for implementation in fluid flow and natural forced and mixed convection heat transfer
Engineering Analysis With Boundary Elements, 2013Co-Authors: Mohammad Najafi, A Arefmanesh, Vali EnjilelaAbstract:Abstract The purpose of the current study is to empower the MLPG Primitive Variable-based method using the characteristic-based split (CBS) scheme to solve the laminar fluid flow and natural, forced, and mixed convection heat transfer at, respectively, higher Rayleigh, Reynolds and Peclet, and Reynolds and Grashof numbers than those that the MLPG approach has ever solved. In this work, the CBS scheme with unity test function is employed for discretization and the moving least square (MLS) method is used for interpolation. As some test cases, natural convection within a square cavity, forced convection by fluid flow over a bundle of tubes, and mixed convection within a lid-driven square cavity are solved by the proposed method. For verifications, the obtained results are compared with those of the conventional numerical methods in the literature. Being entirely meshless, strong in nature, and able to give accurate and stable results for the broadest range of laminar fluid flow involving any of the three modes of convection heat transfer, the proposed method shows to be a flexible and reliable technique which can replace many available meshfree methods in the literature.
W R Briley - One of the best experts on this subject based on the ideXlab platform.
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a Primitive Variable riemann method for solution of the shallow water equations with wetting and drying
Journal of Computational Physics, 2009Co-Authors: P Sivakumar, Daniel Hyams, Lafayette K Taylor, W R BrileyAbstract:A Riemann flux that uses Primitive Variables rather than conserved Variables is developed for the shallow water equations with nonuniform bathymetry. This Primitive-Variable flux is both conservative and well behaved at zero depth. The unstructured finite-volume discretization used is suitable for highly nonuniform grids that provide resolution of complex geometries and localized flow structures. A source-term discretization is derived for nonuniform bottom that balances the discrete flux integral both for still water and in dry regions. This Primitive-Variable formulation is uniformly valid in wet and dry regions with embedded wetting and drying fronts. A fully nonlinear implicit scheme and both nonlinear and time-linearized explicit schemes are developed for the time integration. The implicit scheme is solved by a parallel Newton-iterative algorithm with numerically computed flux Jacobians. A concise treatment of characteristic-Variable boundary conditions with source terms is also given. Computed results obtained for the one-dimensional dam break on wet and dry beds and for normal-mode oscillations in a circular parabolic basin are in very close agreement with the analytical solutions. Other results for a forced breaking wave with friction interacting with a sloped bottom demonstrate a complex wave motion with wetting, drying and multiple interacting wave fronts. Finally, a highly nonuniform, coastline-conforming unstructured grid is used to demonstrate an unsteady simulation that models an artificial coastal flooding due to a forced wave entering the Gulf of Mexico.
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high resolution viscous flow simulations at arbitrary mach number
Journal of Computational Physics, 2003Co-Authors: W R Briley, Lafayette K Taylor, David L WhitfieldAbstract:A characteristic-based unsteady viscous flow solver is developed with preconditioning that is uniformly applicable for Mach numbers ranging from essentially incompressible to supersonic. A preconditioned flux-difference formulation for nondimensional Primitive Variables is a key element of the present approach. The simple Primitive-Variable numerical flux is related to Roe's flux-difference scheme and preserves contact discontinuities using Primitive Variables, with or without preconditioning. Preconditioning by a single-parameter diagonal matrix conditions the system eigenvalues in terms of nondimensional local velocity and local temperature. An iterative implicit solution algorithm is given for the preconditioned formulation and is used for several simple test and validation cases. These include an inviscid shock-tube case, flat-plate boundary layer flow at low Mach number, viscous flow past a circular cylinder at low Reynolds number and with different thermal boundary conditions, and validation cases for incompressible and transonic flows.
Luciano Rezzolla - One of the best experts on this subject based on the ideXlab platform.
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general relativistic resistive magnetohydrodynamics with robust Primitive Variable recovery for accretion disk simulations
Astrophysical Journal Supplement Series, 2019Co-Authors: Bart Ripperda, Fabio Bacchini, Oliver Porth, Elias R Most, Hector Olivares, Antonios Nathanail, Luciano RezzollaAbstract:Recent advances in black hole astrophysics, particularly the first visual evidence of a supermassive black hole at the center of the galaxy M87 by the Event Horizon Telescope, and the detection of an orbiting "hot spot" nearby the event horizon of Sgr A* in the Galactic center by the Gravity Collaboration, require the development of novel numerical methods to understand the underlying plasma microphysics. Non-thermal emission related to such hot spots is conjectured to originate from plasmoids that form due to magnetic reconnection in thin current layers in the innermost accretion zone. Resistivity plays a crucial role in current sheet formation, magnetic reconnection, and plasmoid growth in black hole accretion disks and jets. We included resistivity in the three-dimensional general-relativistic magnetohydrodynamics (GRMHD) code BHAC and present the implementation of an implicit–explicit scheme to treat the stiff resistive source terms of the GRMHD equations. The algorithm is tested in combination with adaptive mesh refinement to resolve the resistive scales and a constrained transport method to keep the magnetic field solenoidal. Several novel methods for Primitive-Variable recovery, a key part in relativistic magnetohydrodynamics codes, are presented and compared for accuracy, robustness, and efficiency. We propose a new inversion strategy that allows for resistive-GRMHD simulations of low gas-to-magnetic pressure ratio and highly magnetized regimes as applicable for black hole accretion disks, jets, and neutron-star magnetospheres. We apply the new scheme to study the effect of resistivity on accreting black holes, accounting for dissipative effects as reconnection.
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general relativistic resistive magnetohydrodynamics with robust Primitive Variable recovery for accretion disk simulations
arXiv: Computational Physics, 2019Co-Authors: Bart Ripperda, Fabio Bacchini, Oliver Porth, Elias R Most, Hector Olivares, Antonios Nathanail, Luciano RezzollaAbstract:Recent advances in black hole astrophysics, particularly the first visual evidence of a supermassive black hole at the center of the galaxy M87 by the Event Horizon Telescope (EHT), and the detection of an orbiting "hot spot" nearby the event horizon of Sgr A* in the Galactic center by the Gravity Collaboration, require the development of novel numerical methods to understand the underlying plasma microphysics. Non-thermal emission related to such hot spots is conjectured to originate from plasmoids that form due to magnetic reconnection in thin current layers in the innermost accretion zone. Resistivity plays a crucial role in current sheet formation, magnetic reconnection, and plasmoid growth in black hole accretion disks and jets. We included resistivity in the three-dimensional general-relativistic magnetohydrodynamics (GRMHD) code BHAC and present the implementation of an Implicit-Explicit scheme to treat the stiff resistive source terms of the GRMHD equations. The algorithm is tested in combination with adaptive mesh refinement to resolve the resistive scales and a constrained transport method to keep the magnetic field solenoidal. Several novel methods for Primitive Variable recovery, a key part in relativistic magnetohydrodynamics codes, are presented and compared for accuracy, robustness, and efficiency. We propose a new inversion strategy that allows for resistive-GRMHD simulations of low gas-to-magnetic pressure ratio and highly magnetized regimes as applicable for black hole accretion disks, jets, and neutron star magnetospheres. We apply the new scheme to study the effect of resistivity on accreting black holes, accounting for dissipative effects as reconnection.
Fabio Bacchini - One of the best experts on this subject based on the ideXlab platform.
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general relativistic resistive magnetohydrodynamics with robust Primitive Variable recovery for accretion disk simulations
Astrophysical Journal Supplement Series, 2019Co-Authors: Bart Ripperda, Fabio Bacchini, Oliver Porth, Elias R Most, Hector Olivares, Antonios Nathanail, Luciano RezzollaAbstract:Recent advances in black hole astrophysics, particularly the first visual evidence of a supermassive black hole at the center of the galaxy M87 by the Event Horizon Telescope, and the detection of an orbiting "hot spot" nearby the event horizon of Sgr A* in the Galactic center by the Gravity Collaboration, require the development of novel numerical methods to understand the underlying plasma microphysics. Non-thermal emission related to such hot spots is conjectured to originate from plasmoids that form due to magnetic reconnection in thin current layers in the innermost accretion zone. Resistivity plays a crucial role in current sheet formation, magnetic reconnection, and plasmoid growth in black hole accretion disks and jets. We included resistivity in the three-dimensional general-relativistic magnetohydrodynamics (GRMHD) code BHAC and present the implementation of an implicit–explicit scheme to treat the stiff resistive source terms of the GRMHD equations. The algorithm is tested in combination with adaptive mesh refinement to resolve the resistive scales and a constrained transport method to keep the magnetic field solenoidal. Several novel methods for Primitive-Variable recovery, a key part in relativistic magnetohydrodynamics codes, are presented and compared for accuracy, robustness, and efficiency. We propose a new inversion strategy that allows for resistive-GRMHD simulations of low gas-to-magnetic pressure ratio and highly magnetized regimes as applicable for black hole accretion disks, jets, and neutron-star magnetospheres. We apply the new scheme to study the effect of resistivity on accreting black holes, accounting for dissipative effects as reconnection.
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general relativistic resistive magnetohydrodynamics with robust Primitive Variable recovery for accretion disk simulations
arXiv: Computational Physics, 2019Co-Authors: Bart Ripperda, Fabio Bacchini, Oliver Porth, Elias R Most, Hector Olivares, Antonios Nathanail, Luciano RezzollaAbstract:Recent advances in black hole astrophysics, particularly the first visual evidence of a supermassive black hole at the center of the galaxy M87 by the Event Horizon Telescope (EHT), and the detection of an orbiting "hot spot" nearby the event horizon of Sgr A* in the Galactic center by the Gravity Collaboration, require the development of novel numerical methods to understand the underlying plasma microphysics. Non-thermal emission related to such hot spots is conjectured to originate from plasmoids that form due to magnetic reconnection in thin current layers in the innermost accretion zone. Resistivity plays a crucial role in current sheet formation, magnetic reconnection, and plasmoid growth in black hole accretion disks and jets. We included resistivity in the three-dimensional general-relativistic magnetohydrodynamics (GRMHD) code BHAC and present the implementation of an Implicit-Explicit scheme to treat the stiff resistive source terms of the GRMHD equations. The algorithm is tested in combination with adaptive mesh refinement to resolve the resistive scales and a constrained transport method to keep the magnetic field solenoidal. Several novel methods for Primitive Variable recovery, a key part in relativistic magnetohydrodynamics codes, are presented and compared for accuracy, robustness, and efficiency. We propose a new inversion strategy that allows for resistive-GRMHD simulations of low gas-to-magnetic pressure ratio and highly magnetized regimes as applicable for black hole accretion disks, jets, and neutron star magnetospheres. We apply the new scheme to study the effect of resistivity on accreting black holes, accounting for dissipative effects as reconnection.