An Analysis of Source Tilting and Sub-cell Opacity Sampling for IMC

Wollaeger, Ryan T.¹  Urbatsch, Todd J.¹  Wollaber, Allan B.¹  Densmore, Jeffery D.¹ 

[1] Los Alamos National Laboratory

关键词: Mathematics & Computing(97);    Nuclear Physics & Radiation Physics(73);    LTE;    OPACITY;    RADIANT HEAT TRANSFER;    RADIATIONS;    SAMPLING;    SCATTERING;    TRANSPORT;    WAVE PROPAGATION;    MONTE CARLO METHOD;   

DOI  :  10.2172/1047094
RP-ID  :  LA-UR-12-23258
PID  :  OSTI ID: 1047094
Others  :  TRN: US1203969

美国|英语

来源: SciTech Connect

【 摘 要 】

Implicit Monte Carlo (IMC) is a stochastic method for solving the radiative transfer equations for multiphysics application with the material in local thermodynamic equilibrium. The IMC method employs a fictitious scattering term that is computed from an implicit discretization of the material temperature equation. Unfortunately, the original histogram representation of the temperature and opacity with respect to the spatial domain leads to nonphysically fast propagation of radiation waves through optically thick material. In the past, heuristic source tilting schemes have been used to mitigate the numerical teleportation error of the radiation particles in IMC that cause this overly rapid radiation wave propagation. While improving the material temperature profile throughout the time duration, these tilting schemes alone do not generally alleviate the teleportation error to suitable levels. Another means of potentially reducing teleportation error in IMC is implementing continuous sub-cell opacities based on sub-cell temperature profiles. We present here an analysis of source tilting and continuous sub-cell opacity sampling applied to various discretizations of the temperature equation. Through this analysis, we demonstrate that applying both heuristics does not necessarily yield more accurate results if the discretization of the material equation is inconsistent with the Monte Carlo sub-cell transport.