衛星推進器引致污染及衝擊影響分析軟體發展

Abstract

直接蒙地卡羅模擬法( Direct Simulation Monte Carlo)至今已被公認為研究過渡流體的最佳模擬工具。此方法最大的優點是可以直接應用微觀物理模型模擬來模擬氣流場，其應用包含太空推進器、控制衛星的噴流及相關高真空度的應用等等。因此稀薄氣體理論(high Knudsen number)的應用在現今的科學及工業上的發展是非常重要的。然而直接蒙地卡羅模擬法在過去並無受到應有的重視，主要的原因是由於計算時間過長。故發展具變時步方法以及動態負載的直接蒙地卡羅法可大量減少模擬的計算時間。本計畫的目標，便是發展一套直接模擬蒙地卡羅(DSMC)法於叢集式電腦，來分析推進次系統推進器的噴流引致污染及衝擊影響的模擬分析軟體。計劃期間共計二年。簡述於下：第一年，計劃發展三維直接蒙地卡羅模擬法程式，結合變時步方法(variable time-step method)及平行計算之動態負載平衡(Dynamic Load Balancing)技巧來縮短計算時間。並利用此程式計算中華衛星三號之推進器噴流引致污染及衝擊情形。第二年，利用發展完成的直接蒙地卡羅模擬法程式發展一套便利的輸入資料圖形界面、科學視算後處理、平行化處理，以應用於叢集式電腦系統上。終端使用者只需輸入所需資料，便可進行數值模擬，並經由顯示器觀察正在進行的分析狀況。同時，協助太空計畫室建立一套可執行第一年發展的直接蒙地卡羅法程式之叢集式電腦系統(12-node)。最後並將負責訓練相關工程師使用該套完整分析軟體。

It is well recognized that DSMC is the most efficient method to study the gas flows in transitional flow regime. The major advantage of this method is that it can easily incorporate the particle nature of physics, which is crucial in several research disciplines, including the spacecraft reentry, the plume impingement from control thrusters on satellite, and the relative applications of high vacuum, to name a few. Each of these distinct applications of high Knudsen number flows is now of practical scientific and engineering importance. However, application of the DSMC method is limited due to its prohibitively high computational cost in the near-continuum flow regime. Thus, to develop a DSMC code combining variable-time step (VTS) method and dynamic load balancing (DLB) in parallel implementation can save huge amount of computational time. The objectives of this project are to develop an accurate and efficient DSMC code and to apply to the analysis of the plume impingement on spacecraft on PC cluster system. The proposed research is planned for a 2-year period. They are briefly described as follows: In the first year, it is proposed to develop a 3-D parallel direct simulation Monte Carlo code using variable-time step method and dynamic load balancing technique to reduce the computational time dramatically. ROCSat-3 will then be used as an example model to demonstrate its capability in analyzing the plume impingement on spacecraft.In the second year, it is proposed to integrate a simulation system including a preprocessor for input data, DSMC code and a postprocessor for visualization the results. At the same time, we will help NSPO to set up a 12-node PC cluster system. Finally, we will implement the developed software on the PC cluster system and train the engineers to use the analysis tool to analyze plume impingement on spacecraft.