The DSMC Method

Description

More than fifty years have now elapsed since the writing of the first paperon the Direct Simulation Monte Carlo, or DSMC, method. The early DSMCprocedures were justifiably regarded with some suspicion and, by modemstandards, computers were extremely slow and expensive .The earlydevelopments were described in the first monograph written by the author.The title was Molecular Gas Dynamics and it was published by OxfordUniversity Press in 1 976. Given the general lack of acceptance of the DSMCmethod at that time, the DSMC method was presented in a somewhat tentativemanner and appeared only in the later chapters. By the time that the secondmonograph Molecular Gas Dynamics and the Direct Simulation of Gas Flowsappeared in 1 994, the DSMC procedures were sounder and morecomprehensive, computers were incomparably faster and, most importantly,the method had become widely accepted. At the same time, the description ofthe DSMC method was again confmed to the latter half of the book. Thebackground material associated with the words "molecular gas dynamics" hasnot changed greatly over the past two decades, but almost all the DSMCprocedures have been either revised or superseded. The writing of this bookhas been motivated by the need to document these developments.The background material has been reduced to cover only the results thatare necessary to support the description of the DSMC procedures . The 1 994monograph was concerned with alternative methods and the derivation of thebackground equations . This affected the order of presentation of the keyresults that are required for DSMC . This book is not concerned with thederivation of standard equations and the priority is to present them in a formthat makes them easily accessible to the user. While this has simplified thetask of writing the book, the recent proliferation of DSMC papers that presentalternative procedures makes it difficult to assess them all in order todetermine the optimum set of procedures. This book is largely based on theprocedures that are currently employed by the author, but they are underconstant review and will be changed when alternative procedures are found tobe preferable.The DSMC results that are presented in this book have been made eitherwith the open source computer code DSMC that forms part of the book or withthe DS2V program that is now being made available as source code . It isintended that the scope of the DSMC program will be extended in futureversions of the book to the extent that it will eventually become an easilyapplied universal parallel code with capabilities that go beyond those of thewidely used DS2V/3V codes that have, for some years, been freely downloadableas executables from www.gab.com.au. The extension of DSMC to two and threedimensional flows, together with programs for data file production andgraphical post-processing will be added in Versions 2 and 3 . It is intended thatVersion 4 will address parallel processing.