Article

# Gridless DSMC

FOCUS Center, Physics Department, University of Michigan, 450 Church Street, Ann Arbor, MI 48109-1120, United States; Mathematics Department, Michigan State University, D304 Wells Hall, East Lansing, MI 48824-1027, United States

Journal of Computational Physics (Impact Factor: 2.14). 01/2008; DOI: 10.1016/j.jcp.2008.04.038 - [Show abstract] [Hide abstract]

**ABSTRACT:**A new particle pairing strategy is presented for the Direct Simulation Monte Carlo (DSMC) method. By combining Nearest Neighbour (NN) and Quad Tree Sort (QTS) algorithms, this modified DSMC method becomes largely independent of grid cell size. Therefore, the method possesses considerable advantages in terms of coupling with other grid-based methods in comparison to classical DSMC methods, which have to resolve the mean free path in each cell. The Green–Kubo theory is used to estimate the effects of cell size on transport coefficients. First, the Green–Kubo theory is reviewed for the calculation of the viscosity coefficient as a function of cell size in the classical DSMC method. Next, this theory is extended to the case of using the Nearest Neighbour pairing strategy. Plane Couette flow simulations are used to demonstrate the success of the new particle pairing strategy in becoming independent of the cell size.Journal of Computational Physics 08/2013; 246:28–36. · 2.14 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**The efficiency of the direct simulation Monte Carlo (DSMC) method decreases considerably if gas is not rarefied. In order to extend the application range of the DSMC method towards non-rarefied gas regimes, the computational efficiency of the DSMC method should be increased further. One of the most time consuming parts of the DSMC method is to determine which DSMC molecules are in close proximity. If this information is calculated quickly, the efficiency of the DSMC method will be increased. Although some meshless methods are proposed, mostly structured or non-structured meshes are used to obtain this information. The simplest DSMC solvers are limited with the structured meshes. In these types of solvers, molecule indexing according to the positions can be handled very fast using simple arithmetic operations. But structured meshes are geometry dependent. Complicated geometries require the use of unstructured meshes. In this case, DSMC molecules are traced cell-by-cell. Different cell-by-cell tracing techniques exist. But, these techniques require complicated trigonometric operations or search algorithms. Both techniques are computationally expensive. In this study, a hybrid mesh structure is proposed. Hybrid meshes are both less dependent on the geometry like unstructured meshes and computationally efficient like structured meshes.Journal of Physics Conference Series 02/2013; 410(1):2075-. - [Show abstract] [Hide abstract]

**ABSTRACT:**This study details a comparison of ion beam simulations with experimental data from a simplified plasma test cell in order to study and validate numerical models and environments representative of electric propulsion devices and their plumes. The simulations employ a combination of the direct simulation Monte Carlo and particle-in-cell methods representing xenon ions and atoms as macroparticles. An anisotropic collision model is implemented for momentum exchange and charge exchange interactions between atoms and ions in order to validate the post-collision scattering behaviors of dominant collision mechanisms. Cases are simulated in which the environment is either collisionless or non-electrostatic in order to prove that the collision models are the dominant source of low- and high-angle particle scattering and current collection within this environment. Additionally, isotropic cases are run in order to show the importance of anisotropy in these collision models. An analysis of beam divergence leads to better characterization of the ion beam, a parameter that requires careful analysis. Finally, suggestions based on numerical results are made to help guide the experimental design in order to better characterize the ion environment.Physics of Plasmas 03/2013; 20(3). · 2.38 Impact Factor

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