Object-Oriented/Data-Oriented Design of a Direct Simulation MonteCarlo Algorithm

摘要

National Aeronautics and Space Administration has been investing in the development of a new code, the Multiphysics Algorithm with Particles, to incorporate recent developments in direct simulation MonteCarlo algorithms and improve physical realism, time to solution, and expand the range of usefulness of National Aeronautics and Space Administration direct simulation MonteCarlo codes (in both velocity space and altitude). The Multiphysics Algorithm with Particles is an object-oriented/data-oriented code written in C++. Object-oriented codes are likely the most flexible and efficient approach for the development of new algorithms and physics modules due to their inherent modularity. However, computational efficiency is an equally critical component of software design that must be considered, which is why data-oriented design becomes important. The focus of the development of the Multiphysics Algorithm with Particles thus far has been on the creation of efficient particle data structures, the inclusion of gas models, and the ability to dynamically adapt a simulation. Future work will focus on more efficient grid structures and parallel computing strategies. The new software is evaluated in the current study with regard to 1)software design and extensibility, 2)accuracy of solution, and 3)efficiency of solution. For each category, comparisons will be made against legacy software to identify the relative merits of each software package. For software design and extensibility, the details of the Software Engineering Plan for the Multiphysics Algorithm with Particles will be presented. For accuracy of solution, comparisons will be made to test cases from the literature. Speed comparisons are made between the Multiphysics Algorithm with Particles and the current production direct simulation MonteCarlo code at National Aeronautics and Space Administration, the direct simulation MonteCarlo Analysis Code, for both serial and parallel implementations. More importantly, though, are the automated grid, time step, and surface temperature adaptation algorithms included in the Multiphysics Algorithm with Particles. The user can now specify the simulation initial conditions and begin the solution one time, and the Multiphysics Algorithm with Particles automatically adapts the solution and determines when the final solution has been reached.