An original algorithm was developed for ray tracing across unstructured 3D grid. The resulting set of rays provides the base for the grid-characteristic computation of radiative energy transfer in the high temperature plasma simulations using MPI parallel technique and grid decomposition. The algorithm is implemented as a C++ code and incorporated in 3D magneto hydrodynamic (MHD) Eulerian code. Accurate rational calculations using integers of unlimited range are applied for the intersection of rays with grid elements. Tracing of different rays within a single MPI process is carried out in parallel with the use of OpenMP threads. Acceleration and scalability of the implemented algorithms were investigated including a comparison with other solvers within MHD code. The developed algorithm enables accounting the anisotropy of the radiation field in complex multiscale 3D MHD simulations. Proposed applications are the following: 1) postprocessing the results of 3D simulations (numerical pinhole imaging, estimation of the radiation output in a given direction); 2) modeling the propagation of the laser radiation; 3) calculating the thermal radiation field on the basis of quasi-diffusion model (improvement of the Eddington factor for the diffusion approximation).
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