The Experts below are selected from a list of 222 Experts worldwide ranked by ideXlab platform

Christine Jones - One of the best experts on this subject based on the ideXlab platform.

  • Standoff distance of bow shocks in galaxy clusters as proxy for Mach number
    Monthly Notices of the Royal Astronomical Society, 2018
    Co-Authors: Congyao Zhang, Eugene Churazov, William R. Forman, Christine Jones
    Abstract:

    X-ray observations of merging clusters provide many examples of bow shocks leading merging subclusters. While the Mach number of a shock can be estimated from the observed density jump using Rankine-Hugoniot Condition, it reflects only the velocity of the shock itself and is generally not equal to the velocity of the infalling subcluster dark matter halo or to the velocity of the contact discontinuity separating gaseous atmospheres of the two subclusters. Here we systematically analyze additional information that can be obtained by measuring the standoff distance, i.e. the distance between the leading edge of the shock and the contact discontinuity that drives this shock. The standoff distance is influenced by a number of additional effects, e.g. (1) the gravitational pull of the main cluster (causing acceleration/deceleration of the infalling subcluster), (2) the density and pressure gradients of the atmosphere in the main cluster, (3) the non-spherical shape of the subcluster, and (4) projection effects. The first two effects tend to bias the standoff distance in the same direction, pushing the bow shock closer to (farther away from) the subcluster during the pre- (post-)merger stages. Particularly, in the post-merger stage, the shock could be much farther away from the subcluster than predicted by a model of a body moving at a constant speed in a uniform medium. This implies that a combination of the standoff distance with measurements of the Mach number from density/temperature jumps can provide important information on the merger, e.g. differentiating between the pre- and post-merger stages.

S. V. Raghurama Rao - One of the best experts on this subject based on the ideXlab platform.

  • A central Rankine-Hugoniot solver for hyperbolic conservation laws
    Journal of Computational Physics, 2009
    Co-Authors: S. Jaisankar, S. V. Raghurama Rao
    Abstract:

    A numerical method in which the Rankine-Hugoniot Condition is enforced at the discrete level is developed. The simple format of central discretization in a finite volume method is used together with the jump Condition to develop a simple and yet accurate numerical method free of Riemann solvers and complicated flux splittings. The steady discontinuities are captured accurately by this numerical method. The basic idea is to fix the coefficient of numerical dissipation based on the Rankine-Hugoniot (jump) Condition. Several numerical examples for scalar and vector hyperbolic conservation laws representing the inviscid Burgers equation, the Euler equations of gas dynamics, shallow water equations and ideal MHD equations in one and two dimensions are presented which demonstrate the efficiency and accuracy of this numerical method in capturing the flow features.

  • An Accurate Shock Capturing Algorithm with a Relaxation System for Hyperbolic Conservation Laws
    16th AIAA Computational Fluid Dynamics Conference, 2003
    Co-Authors: S. V. Raghurama Rao, K. Balakrishna
    Abstract:

    Using the framework of a Relaxation System, which converts a non-linear conservation law into a system of linear convection equations with non-linear source terms, an accurate shock capturing algorithm is developed for the numerical simulation of hyperbolic conservation equations. The basic idea is to formulate a nite volume method with open coecients of numerical dissipation for the discrete Boltzmann equation and compare the resulting relaxed scheme with Rankine-Hugoniot Condition for xing the coecients of numerical dissipation. Since the Rankine-Hugoniot Condition is satised by the discretized scheme, the steady discontinuities are captured exactly, like Roe’s approximate Riemann solver. The features of this Accurate Shock Capturing Algorithm with a Relaxation System (ASCARS) are demonstrated by applying it to some standard bench-mark problems.

Zensho Yoshida - One of the best experts on this subject based on the ideXlab platform.

Congyao Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Standoff distance of bow shocks in galaxy clusters as proxy for Mach number
    Monthly Notices of the Royal Astronomical Society, 2018
    Co-Authors: Congyao Zhang, Eugene Churazov, William R. Forman, Christine Jones
    Abstract:

    X-ray observations of merging clusters provide many examples of bow shocks leading merging subclusters. While the Mach number of a shock can be estimated from the observed density jump using Rankine-Hugoniot Condition, it reflects only the velocity of the shock itself and is generally not equal to the velocity of the infalling subcluster dark matter halo or to the velocity of the contact discontinuity separating gaseous atmospheres of the two subclusters. Here we systematically analyze additional information that can be obtained by measuring the standoff distance, i.e. the distance between the leading edge of the shock and the contact discontinuity that drives this shock. The standoff distance is influenced by a number of additional effects, e.g. (1) the gravitational pull of the main cluster (causing acceleration/deceleration of the infalling subcluster), (2) the density and pressure gradients of the atmosphere in the main cluster, (3) the non-spherical shape of the subcluster, and (4) projection effects. The first two effects tend to bias the standoff distance in the same direction, pushing the bow shock closer to (farther away from) the subcluster during the pre- (post-)merger stages. Particularly, in the post-merger stage, the shock could be much farther away from the subcluster than predicted by a model of a body moving at a constant speed in a uniform medium. This implies that a combination of the standoff distance with measurements of the Mach number from density/temperature jumps can provide important information on the merger, e.g. differentiating between the pre- and post-merger stages.

S. Jaisankar - One of the best experts on this subject based on the ideXlab platform.

  • A central Rankine-Hugoniot solver for hyperbolic conservation laws
    Journal of Computational Physics, 2009
    Co-Authors: S. Jaisankar, S. V. Raghurama Rao
    Abstract:

    A numerical method in which the Rankine-Hugoniot Condition is enforced at the discrete level is developed. The simple format of central discretization in a finite volume method is used together with the jump Condition to develop a simple and yet accurate numerical method free of Riemann solvers and complicated flux splittings. The steady discontinuities are captured accurately by this numerical method. The basic idea is to fix the coefficient of numerical dissipation based on the Rankine-Hugoniot (jump) Condition. Several numerical examples for scalar and vector hyperbolic conservation laws representing the inviscid Burgers equation, the Euler equations of gas dynamics, shallow water equations and ideal MHD equations in one and two dimensions are presented which demonstrate the efficiency and accuracy of this numerical method in capturing the flow features.

  • Accurate Computational Algorithms For Hyperbolic Conservation Laws
    2008
    Co-Authors: S. Jaisankar
    Abstract:

    The numerics of hyperbolic conservation laws, e.g., the Euler equations of gas dynamics, shallow water equations and MHD equations, is non-trivial due to the convective terms being highly non-linear and equations being coupled. Many numerical methods have been developed to solve these equations, out of which central schemes and upwind schemes (such as Flux Vector Splitting methods, Riemann solvers, Kinetic Theory based Schemes, Relaxation Schemes etc.) are well known. The majority of the above mentioned schemes give rise to very dissipative solutions. In this thesis, we propose novel low dissipative numerical algorithms for some hyperbolic conservation laws representing fluid flows. Four different and independent numerical methods which give low diffusive solutions are developed and demonstrated. The first idea is to regulate the numerical diffusion in the existing dissipative schemes so that the smearing of solution is reduced. A diffusion regulator model is developed and used along with the existing methods, resulting in crisper shock solutions at almost no added computational cost. The diffusion regulator is a function of jump in Mach number across the interface of the finite volume and the average Mach number across the surface. The introduction of the diffusion regulator makes the diffusive parent schemes to be very accurate and the steady contact discontinuities are captured exactly. The model is demonstrated in improving the diffusive Local Lax-Friedrichs (LLF) (or Rusanov) method and a Kinetic Scheme. Even when employed together with accurate methods of Roe and Osher, improvement in solutions is demonstrated for multidimensional problems. The second method, a Central Upwind-Biased Scheme (CUBS), attempts to reorganize a central scheme such that information from irrelevant directions is largely reduced and the upwind biased information is retained. The diffusion co-efficient follows a new format unlike the use of maximum characteristic speed in the Local Lax-Friedrichs method and the scheme results in improved solutions of the flow features. The grid-aligned steady contacts are captured exactly with the reorganized format of diffusion co-efficient. The stability and positivity of the scheme are discussed and the procedure is demonstrated for its ability to capture all the features of solution for different flow problems. Another method proposed in this thesis, a Central Rankine-Hugoniot Solver, attempts to integrate more physics into the discretization procedure by enforcing a simplified Rankine-Hugoniot Condition which describes the jumps and hence resolves steady discontinuities very accurately. Three different variants of the scheme, termed as the Method of Optimal Viscosity for Enhanced Resolution of Shocks (MOVERS), based on a single wave (MOVERS-1), multiple waves (MOVERS-n) and limiter based diffusion (MOVERS-L) are presented. The scheme is demonstrated for scalar Burgers equation and systems of conservation laws like Euler equations, ideal Magneto-hydrodynamics equations and shallow water equations.…