二维弹塑性有限元程序全自动重分

对二维弹塑性流体力学有限元计算中的非结构三角网格 ,提出了一种简单、实用的全自动网格重分方法。并在LTZ 2D程序上编制了全自动重分模块 ,重分使拉格朗日流体程序能计算包含大变形的一些问题。给出两个算例 ,圆柱体撞击 (Taylor实验 )和射流形成 ,通过网格重分数值计算结果与实验和文献结果比较 ,定性、定量均有较好的符合。     

二维自适应非结构网格DSMC并行算法研究

研究了二维自适应非结构网格DSMC并行算法实现的过程.首先提出了一类非结构网格自适应策略,有效降低了网格尺度对计算结果的影响,提高了流场的分辨率;然后基于PC-CLUSTER群机并行体系结构与消息传递库MPI并行环境,利用分区并行思想,设计了非结构网格DSMC并行算法,节约了计算时间.利用For-tran90的动态分配内存技术编制了通用计算程序;最后对过渡流域高超声绕流进行了数值模拟,计算结果初步验证了算法的可行性与有效性.     

GMRES方法在含动边界流场中的应用

以基于格心的有限体积法为基础，空间二阶精度，采用4阶Runge—Kutta，GMRES隐式方法求解基于ALE形式的Euler方程，网格单元边界处守恒量通量的计算采用了Hanel方法，对NACA0012翼型绕流及运动圆球绕流等问题进行数值模拟，取得了较好的结果．GMRES方法克服了以往隐式方法大量耗费内存的弱点，达到了计算耗时短和占用内存少的统一．     

动网格生成技术及非定常计算方法进展综述

对应用于飞行器非定常运动的数值计算方法(包括动态网格技术和相应的数值离散格式)进行了综述.根据网格拓扑结构的不同,重点论述了基于结构网格的非定常计算方法和基于非结构/混合网格的非定常计算方法,比较了各种方法的优缺点.在基于结构网格的非定常计算方法中,重点介绍了刚性运动网格技术、超限插值动态网格技术、重叠动网格技术、滑移动网格技术等动态结构网格生成方法,同时介绍了惯性系和非惯性系下的控制方程,讨论了非定常时间离散方法、动网格计算的几何守恒律等问题.在基于非结构/混合网格的非定常计算方法中,重点介绍了重叠非结构动网格技术、重构非结构动网格技术、变形非结构动网格技术以及变形/重构耦合动态混合网格技术等方法,以及相应的计算格式,包括非定常时间离散、几何守恒律计算方法、可压缩和不可压缩非定常流动的计算方法、各种加速收敛技术等.在介绍国内外进展的同时,介绍了作者在动态混合网格生成技术和相应的非定常方法方面的研究与应用工作.     

基于多块嵌套结构动网格的拦截弹防热保护罩的二维分离模拟

在末制导阶段,拦截弹上的红外热保护罩要进行分离,分离引起的气动力变化将直接影响到导弹的制导精度.采用多块嵌套结构动网格技术数值模拟了拦截导弹的热保护罩的二维分离过程.给出了在整个分离过程中,两片保护罩运动的轨迹,并且给出了各个时间步对应的压力云图.预测了由于前激波而产生的作用在导弹上气动力的振荡.跟踪了在各个时刻流场对于导弹上红外窗口的影响.     

基于Voronoi cells的二维不规则自适应网格的生成及其应用

基于Voronoi cells的数据结构和算法，给出了一种二维不规则自适应网格的生成方法，用VisualC＋＋语言在微机上开发了Windows环境下网格自动生成的可视化软件。既可以得到Voronoi cells网格，也可得到相应的Delaunay triangles网格，网格生成的实例表明，本文方法所得到的网格非常适合于多尺度系统的流动问题的计算，具有较好的应用前景。     

基于ALE方程的动网格膛口流场数值研究

基于ALE(Arbitrary Lagrangian-Eulerian Equation)方程的有限体积法,采用高精度Roe方法及结构化动网格,利用嵌入网格技术及动边界条件,对弹丸由膛内高压气体推动射出到完全飞高初始流场的整个过程进行了数值模拟.根据数值结果绘制了膛口流场密度和压力分布的时序图,形象地再现了膛口流场中初始激波、弓形激波及膛口冲击波,以及接触闻断、漩涡和剪切层等的动力学发展过程.结果基本反映了膛口流场的典型变化特征,为进一步研究真实膛口流场(如带化学反应、湍流等)奠定了基础.     

基于背景网格变形的动态网格移动方法

基于Delaunay背景网格插值技术的动态网格生成方法无需迭代计算,效率较高。但对复杂构形大幅运动的动边界问题,尤其当边界大幅转动时,背景网格极易交叉重叠。重新生成背景网格和重新定位网格节点信息不仅费时而且会导致网格质量的严重下降。本文提出改进的基于背景网格的动态网格变形方法,通过在初始Delaunay背景网格中添加辅助点,生成一层新的背景网格和新的映射关系;采用ball-vertex弹簧法驱动新背景网格的变形,进而牵动目标网格的变形。算例表明,本文提出的动态网格变形方法对所关心区域的网格具有良好保形性,边界可转动更大角度而不会出现网格交叉重叠问题,总体上提高了动态网格更新的效率和质量。     

二维自适应网格生成的改进AFT与背景网格法

在基于重生成的自适应有限元网格生成算法研究中,将推进波前法（AFT）与背景网格法结合并提出改进方法,有效地解决了网格生成和单元尺寸计算这两个关键问题。改进的AFT方法,将前沿区分为活跃前沿和非活跃前沿两类,在选取目标前沿时既考虑前沿尺寸又考虑前沿分类。改进的背景网格法,利用结构化栅格对背景网格进行管理,在栅格中直接存放背景网格中的单元,既提高了新单元尺寸的计算速度,又从数值上保证了新生成网格中单元之间尺寸合理过渡。     

一种快速稳健的并行多块结构动网格方法

为解决传统网格处理方法不能满足复杂外形在大设计空间内进行优化时对网格质量的要求的问题,提出了一种并行多块动网格方法,该方法基于初始外形的多块结构网格,根据优化过程中个体外形与初始外形拓扑结构相近的特性,利用体样条插值方法来拟合多块结构网格各块顶点的位移,得到几何外形变化后的拓扑结构,再利用无限插值方法并行地移动初始外形多块结构网格的边、面和块内的网格点,进行光顺处理后得到变形后几何外形的空间网格;该方法在保证网格质量的同时,可以极大地提高网格生成效率,本文以某翼身组合体为例结果表明,该方法在大设计空间的复杂外形设计问题中具有很强的实用性。     

Evaluation of adaptive mesh refinement and coarsening for the computation of compressible flows on unstructured meshes

The compressible gas flows of interest to aerospace applications often involve situations where shock and expansion waves are present. Decreasing the characteristic dimension of the computational cells in the vicinity of shock waves improves the quality of the computed flows. This reduction in size may be accomplished by the use of mesh adaption procedures. In this paper an analysis is presented of an adaptive mesh scheme developed for an unstructured mesh finite volume upwind computer code. This scheme is tailored to refine or coarsen the computational mesh where gradients of the flow properties are respectively high or low. The refinement and coarsening procedures are applied to the classical gas dynamic problems of the stabilization of shock waves by solid bodies. In particular, situations where oblique shock waves interact with an expansion fan and where bow shocks arise around solid bodies are considered. The effectiveness of the scheme in reducing the computational time, while increasing the solution accuracy, is assessed. It is shown that the refinement procedure alone leads to a number of computational cells which is 20% larger than when alternate passes of refinement and coarsening are used. Accordingly, a reduction of computational time of the same order of magnitude is obtained. Copyright © 2005 John Wiley & Sons, Ltd.     

A nodal Godunov method for Lagrangian shock hydrodynamics on unstructured tetrahedral grids

We present a nodal Godunov method for Lagrangian shock hydrodynamics. The method is designed to operate on three‐dimensional unstructured grids composed of tetrahedral cells. A node‐centered finite element formulation avoids mesh stiffness, and an approximate Riemann solver in the fluid reference frame ensures a stable, upwind formulation. This choice leads to a non‐zero mass flux between control volumes, even though the mesh moves at the fluid velocity, but eliminates volume errors that arise due to the difference between the fluid velocity and the contact wave speed. A monotone piecewise linear reconstruction of primitive variables is used to compute interface unknowns and recover second‐order accuracy. The scheme has been tested on a variety of standard test problems and exhibits first‐order accuracy on shock problems and second‐order accuracy on smooth flows using meshes of up to O(10⁶) tetrahedra. Copyright © 2014 John Wiley & Sons, Ltd.     

A parallel unstructured dynamic mesh adaptation algorithm for 3‐D unsteady flows

An unstructured dynamic mesh adaptation and load balancing algorithm has been developed for the efficient simulation of three‐dimensional unsteady inviscid flows on parallel machines. The numerical scheme was based on a cell‐centred finite‐volume method and the Roe's flux‐difference splitting. Second‐order accuracy was achieved in time by using an implicit Jacobi/Gauss–Seidel iteration. The resolution of time‐dependent solutions was enhanced by adopting an h‐refinement/coarsening algorithm. Parallelization and load balancing were concurrently achieved on the adaptive dynamic meshes for computational speed‐up and efficient memory redistribution. A new tree data structure for boundary faces was developed for the continuous transfer of the communication data across the parallel subdomain boundary. The parallel efficiency was validated by applying the present method to an unsteady shock‐tube problem. The flows around oscillating NACA0012 wing and F‐5 wing were also calculated for the numerical verification of the present dynamic mesh adaptation and load balancing algorithm. Copyright © 2005 John Wiley & Sons, Ltd.     

An adaptive dynamic relaxation method for quasi-static simulations using the peridynamic theory

The peridynamic theory is advantageous for problems involving damage since the peridynamic equation of motion is valid everywhere, regardless of existing discontinuities, and an external criterion is not necessary for predicting damage initiation and propagation. However, the current solution methods for the equations of peridynamics utilize explicit time integration, which poses difficulties in simulations of most experiments under quasi-static conditions. Thus, there is a need to obtain steady-state solutions in order to validate peridynamic predictions against experimental measurements. This study presents an extension of dynamic relaxation methods for obtaining steady-state solutions of nonlinear peridynamic equations.     

动力松弛方法中Rayleigh阻尼参数取值分析

论文阐述了动力松弛法计算静力问题的原理,分析了Rayleigh阻尼对计算的影响,提出了一种对质量阻尼和刚度阻尼参数取值的新方法。这种取值方法可以避免计算结果的振荡和过塑性的问题,并利用实例计算进行了对比分析,验证了本文中Rayleigh阻尼取值的合理性。     

A new TVD method for advection simulation on 2D unstructured grids

For advection schemes with flux limiters derived on one‐dimensional grids to two‐dimensional (2D) unstructured triangular ones. In this method, the variables located normal to this face are taken into more account to compute the flux, by means of defining required nodes along the line through the center point of the considered face and perpendicular to it. Besides, the new method adopts the improved total variation diminishing schemes in, which consider the face position between the two neighboring cells as well as the size differences of the related cells; therefore, it fits 2D unstructured grids well. Compared with the present flux limiting methods for 2D unstructured grids, a higher accuracy and efficiency and a good monotonicity are achieved by the new method.Copyright © 2012 John Wiley & Sons, Ltd.     

An accurate gradient and Hessian reconstruction method for cell‐centered finite volume discretizations on general unstructured grids

In this paper, a novel reconstruction of the gradient and Hessian tensors on an arbitrary unstructured grid, developed for implementation in a cell‐centered finite volume framework, is presented. The reconstruction, based on the application of Gauss' theorem, provides a fully second‐order accurate estimate of the gradient, along with a first‐order estimate of the Hessian tensor. The reconstruction is implemented through the construction of coefficient matrices for the gradient components and independent components of the Hessian tensor, resulting in a linear system for the gradient and Hessian fields, which may be solved to an arbitrary precision by employing one of the many methods available for the efficient inversion of large sparse matrices. Numerical experiments are conducted to demonstrate the accuracy, robustness, and computational efficiency of the reconstruction by comparison with other common methods. Copyright © 2009 John Wiley & Sons, Ltd.     

Anisotropic mesh adaptation: towards user‐independent,mesh‐independent and solver‐independent CFD. Part II. Structured grids

The present paper is the second article in a three‐part series on anisotropic mesh adaptation and its application to (2‐D) structured and unstructured meshes. In the first article, the theory was presented, the methodology detailed and brief examples given of the application of the method to both types of grids. The second part details the application of the mesh adaptation method to structured grids. The adaptation operations are restricted to mesh movement in order to avoid the creation of hanging nodes. Being based on a spring analogy with no restrictive orthogonality constraint, a wide grid motion is allowed. The adaptation process is first validated on analytical test cases and its high efficiency is shown on relevant transonic and supersonic benchmarks. These latter test cases are also solved on adapted unstructured grids to provide a reference for comparison studies. The third part of the series will demonstrate the capability of the methodology on 2‐D unstructured test cases. Copyright © 2002 John Wiley & Sons, Ltd.     

Discretization of transport equations on 2D Cartesian unstructured grids using data from remote cells for the convection terms

This paper presents a new finite volume discretization methodology for the solution of transport equations on locally refined or unstructured Cartesian meshes. The implementation of the cell‐face values of the dependent variables enables the employment of data from remote cells and thus the use of higher‐order differencing schemes. It also results in simple and flux‐conservative multiple‐scale stencils for the discretization of the governing equations. The latter are finally cast into a generalized form that does not depend on the local mesh structure. The performance of the numerical model is demonstrated on some classical 2D problems using various gridding techniques and a bounded second‐order upwind scheme. A stable and efficient behaviour of the algorithm is observed in all test cases. The results indicate that the combination in the present model of both local grid refinement and second‐order discretization can produce substantially more accurate solutions than each of the above techniques alone, for the same computational effort. The method is also applicable to turbulent flows and can be easily extended to three‐dimensions. Copyright © 2003 John Wiley & Sons, Ltd.