AN ALGORITHM FOR RADIATION MAGNETOHYDRODYNAMICS BASED ON SOLVING THE TIME-DEPENDENT TRANSFER EQUATION
AN ALGORITHM FOR RADIATION MAGNETOHYDRODYNAMICS BASED ON SOLVING THE TIME-DEPENDENT TRANSFER EQUATION
复制标题
基于求解时变传递方程的辐射磁流体动力学算法
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
S. Davis
中科院分区：
文献类型：
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作者：
Yan;J. Stone;S. Davis
我们描述了一种在光穿越时间仅略短于动力学时间的情况下求解耦合频率积分传递方程和磁流体动力学方程的新算法。传递方程在混合标架中求解，包括与速度有关的源项，精确到。采用算子分裂方法计算离散射线的比强度，沿每条射线采用迎风单调插值法更新输运项，采用隐式方法计算散射和吸收源项。输运项采用守恒差分，确保了比强度(以及能量和动量)沿每条射线守恒，从而达到舍入误差。源项隐式方法的使用确保了即使源项非常坚硬，方法也是稳定的。为了将传输方程的解耦合到 雅典娜程序中的磁流体算法中，我们对角度上的比强度进行直接求积，以计算能量源项和动量源项。我们给出了该方法的各种测试结果，如计算非LTE大气结构、平流扩散测试、线性波会聚测试和众所周知的阴影测试。我们使用辐射修正激波的新的半解析解来证明我们的算法能够准确地捕捉各向异性辐射场的影响。由于该方法使用了空间算子的显式差分，因此在并行计算机上表现出了良好的弱标度特性。
We describe a new algorithm for solving the coupled frequency-integrated transfer equation and the equations of magnetohydrodynamics in the regime that light-crossing time is only marginally shorter than dynamical timescales. The transfer equation is solved in the mixed frame, including velocity-dependent source terms accurate to . An operator split approach is used to compute the specific intensity along discrete rays, with upwind monotonic interpolation used along each ray to update the transport terms, and implicit methods used to compute the scattering and absorption source terms. Conservative differencing is used for the transport terms, which ensures the specific intensity (as well as energy and momentum) are conserved along each ray to round-off error. The use of implicit methods for the source terms ensures the method is stable even if the source terms are very stiff. To couple the solution of the transfer equation to the MHD algorithms in the Athena code, we perform direct quadrature of the specific intensity over angles to compute the energy and momentum source terms. We present the results of a variety of tests of the method, such as calculating the structure of a non-LTE atmosphere, an advective diffusion test, linear wave convergence tests, and the well-known shadow test. We use new semi-analytic solutions for radiation modified shocks to demonstrate the ability of our algorithm to capture the effects of an anisotropic radiation field accurately. Since the method uses explicit differencing of the spatial operators, it shows excellent weak scaling on parallel computers.