In this paper, we revisit the point-in-polyhedron problem. After reviewing previous work, we develop further insight into the problem. We then claim that, for a given testing point and a three-dimensional polyhedron, a single determining triangle can be found which suffices to determine whether the point is inside or outside the polyhedron.This work can be considered to be an extension and implementation of Horn's work, which inspired us to propose a theorem for obtaining determining triangles. Building upon this theorem, algorithms are then presented, implemented, and tested. The results show that although our code has the same asymptotic time efficiency as commonly used octree-based ray crossing methods, in practice it is usually several times and sometimes more than ten times faster, while other costs such as preprocessing time and memory requirements remain the same.The ideas proposed in this paper are simple and general. They thus extend naturally to multi-material models, i.e., polyhedrons subdivided into smaller regions by internal boundaries. (C) 2010 Elsevier Ltd. All rights reserved.

In this paper, a modified projection method is combined with a self-adaptive time step procedure to develop numerical scheme for large eddy simulation (LES) of low Ma number turbulent reactive flows. The projection method introduced by Chorin is modified in this study to satisfy the simulation requirement of low Ma number reactive flow. The time step in this computation is automatically determined according to the time scales of both chemical reaction and turbulent fluctuations. This enables the simulation to capture detailed flow structures with less computational time. Numerical simulation of methane-air jet flames is carried out as an example to validate the developed numerical scheme. The mechanism of a simplified 4-step chemical kinetics is applied for the methane-air reaction. The dynamic model is adopted for the turbulent motion of sub-grid scale (SGS). The dynamic similarity model is used as the SGS model for the reaction rate. The LES results satisfactorily depict the ignition process of the turbulent jet flames and illustrate lucid and detailed coherent structures of the fully developed turbulent reactive jet flow. The LES results also exhibit the mechanism and characteristics of local extinction. The method developed in this study provides an effective way to capture more flow details with less computational time. In addition the method also helps one to investigate the mechanism of ignition and local extinction in jet flames. Copyright (C) 2008 John Wiley & Sons, Ltd.

本文研究了球形颗粒填充复合材料的有效比热问题,考虑了基体和夹杂之间非完好黏结界面的影响,给出了有效比热的近似解析表达式。分别针对界面应力模型(ISM)和线弹簧模型(LSM)两种界面本构关系,对代表性体积单元(RVE)施加特定的位移或应力与温度的边界条件组合,并基于所构造的均匀变形场,以及多相多组分复合材料的Helmholtz自由能表达式,导出了包含界面影响的球形粒子填充的有效比热近似解析表达式。

本文研究考虑温度情况下基体和夹杂之间表/界面效应对复合材料有效性质的影响。由于表/界面效应的存在,即使在没有外力作用和温度改变的自然状态下,材料内部也会诱导产生一个弹性场,对复合材料有效性质的计算应该以此自然状态为参考构形算起。本文在相关文献基础上把表面能密度的表达式扩展到包含温度项的情形,由此推导出的表/界面本构关系以及界面的Young-Laplace方程中也引入了温度项。本文把界面和夹杂的整体作为一种"等效夹杂",通过计算其Helmholtz自由能,进而求出其体积模量、热膨胀系数和比热。把该"等效夹杂"的性质替换单一夹杂的性质应用到一般的细观力学方法中,就可以得到计及表/界面效应的热弹性复...

作为一个研究小组,北京大学力学与空天技术系的SAP84小组在袁明武教授的领导下,近三十年来一直从事工程结构分析软件的研究,并在结构计算中独立发展了若干高效的算法。本文试图初步总结本小组近几年发展的几个算法——施工模拟、偶然偏心、振型积分、多点线性约束等在工程软件中的实现方案。

<正>各类颗粒或纤维填充复合材料中,通常采用线弹簧模型模拟复合位移在界面两侧的不连续,并通过放松罚函数模拟弹簧变形直至达到临界值断裂来模拟界面的逐渐脱胶的过程。但是当界面两侧的材料性质相差较大时,上述方法容易由于物理参数差异大造

In this paper, we revisit the point-in-polyhedron problem. After reviewing previous work, we develop further insight into the problem. We then claim that, for a given testing point and a three-dimensional polyhedron, a single determining triangle can be found which suffices to determine whether the point is inside or outside the polyhedron.This work can be considered to be an extension and implementation of Horn's work, which inspired us to propose a theorem for obtaining determining triangles. Building upon this theorem, algorithms are then presented, implemented, and tested. The results show that although our code has the same asymptotic time efficiency as commonly used octree-based ray crossing methods, in practice it is usually several times and sometimes more than ten times faster, while other costs such as preprocessing time and memory requirements remain the same.The ideas proposed in this paper are simple and general. They thus extend naturally to multi-material models, i.e., polyhedrons subdivided into smaller regions by internal boundaries. (C) 2010 Elsevier Ltd. All rights reserved.

In this paper, a modified projection method is combined with a self-adaptive time step procedure to develop numerical scheme for large eddy simulation (LES) of low Ma number turbulent reactive flows. The projection method introduced by Chorin is modified in this study to satisfy the simulation requirement of low Ma number reactive flow. The time step in this computation is automatically determined according to the time scales of both chemical reaction and turbulent fluctuations. This enables the simulation to capture detailed flow structures with less computational time. Numerical simulation of methane-air jet flames is carried out as an example to validate the developed numerical scheme. The mechanism of a simplified 4-step chemical kinetics is applied for the methane-air reaction. The dynamic model is adopted for the turbulent motion of sub-grid scale (SGS). The dynamic similarity model is used as the SGS model for the reaction rate. The LES results satisfactorily depict the ignition process of the turbulent jet flames and illustrate lucid and detailed coherent structures of the fully developed turbulent reactive jet flow. The LES results also exhibit the mechanism and characteristics of local extinction. The method developed in this study provides an effective way to capture more flow details with less computational time. In addition the method also helps one to investigate the mechanism of ignition and local extinction in jet flames. Copyright (C) 2008 John Wiley & Sons, Ltd.