高分辨率全球非结构网格生成实践

球面质心Voronoi网格(SCVT)是一种高质量的非结构网格,被国内外知名地球系统模式所采用。国际上,已有开源项目Message Passing Interface SCVT(MPI-SCVT)实现了并行的SCVT生成。然而,尽管MPI-SCVT可以很好地适用于一般分辨率网格的生成,当所需网格的分辨率非常高时,MPI-SCVT的使用会出现多个问题,包括初始网格点质量差、大数据MPI通信、外部库调用以及I/O问题。对于这些问题,提出了一整套解决方案。实践表明,应用此方案可以顺利完成全球1.9 km分辨率网格的生成,且到达相同精度时所需迭代步数显著减少,节约了计算时间。     

非结构粘性直角网格物面相贯线修正

非结构粘性直角网格通过对内面进行光顺、投影及分层加密等方法,在内面与物面间生成了粘性层网格,解决了直角网格在计算粘性流场时遇到的难题。但在光顺和投影之后,物形可能发生改变,从而丧失了某些原来物体具有的特征,对流场计算产生影响。提出了物面相贯线修正方法,在投影之后对各投影点的位置进行修正,解决了物面变形的问题,并通过生成DLR-F4等复杂外形的网格,对此方法进行验证。     

复杂外形三维非结构粘性直角网格的生成

在保证非结构网格逻辑关系不变的条件下,采用光顺、投影、分层加密的方法,解决直角网格物面不贴体的难点,建立三维非结构贴体直角网格生成系统,以适应粘性流场和湍流的计算,同时对自适应网格的流场计算进行研究。对航空航天领域几类复杂外形飞行器进行了三维非结构贴体直角网格的生成。     

非结构网格布点方法研究进展

用有限元方法求解偏微分方程初边值问题首先要离散求解区域,即网格生成,并且网格质量的好坏直接影响着有限元解的收敛性和精度,所以关于网格生成有很多学者从各自的领域出发做了大量的研究工作。论文关注于非结构网格点的布置方法,对已有的具有代表性的布点方法的研究进展进行了分类综述。     

非结构化四边形网格生成新算法

改进了一类基于递归区域分解过程的四边形网格生成算法。引入一套健壮的网格模板,为子域的网格剖分提供统一的处理方案,不再限制最终子域为4节点、6节点或8节点子域,提高了算法的时空效率。结合新的子域网格生成过程和自动区域分解算法,利用背景网格和网格源控制分解线上点的布置,得到一个全自动的非结构化四边形网格生成算法。最后通过网格及数值模拟实例验证了算法性能和实用性。     

解析二维非结构网格生成方法及其应用

提出弱区域指示函数描述流场形状并证明了其存在和不唯一性;利用该函数基于Delaunay方法依据流场尺度生成二维非结构网格。其中,边界引力有效解决了流场边界恢复和内嵌边界问题,弹簧振子和正三角形趋进技术有效改善网格质量。最后,弹簧振子随着弱区域指示函数的演变与监测函数的指导成功应用到自适应网格生成。     

基于非结构网格的Gas-Kinetic方法

为解决带有复杂几何边界条件的高速流体计算问题,提出基于非结构网格的Gas-Kinetic方法.对于二维非结构网格,以三角形网格作为计算单元,形成在该网格控制单元中物理量导数求解的新方法.通过物理量导数得到在控制体积元边界上的通量,然后用每个计算时间步中求出的边界通量和控制体积元中的物理量,求出下一计算时间步所需的新物理量,依次进行计算直到计算结果收敛为止.采用NACA0012翼型进行数值计算验证,结果表明该方法简单高效,适用于低速和高速流体的计算.     

有限元网格生成方法发展综述

在参阅和分析大量有关文献的基础上，对现有的各种有限元网格生成方法进行了总结，特别是对当前广泛使用的Ｄｅｌａｕｎａｙ三角化，推进波前法和八叉树方法等，从理论到具体的算法程序实现等各个方面都作了详尽的剖析，分析了各种方法的优缺点。为深入研究开发全自动、自适应有限元网格生成软件提供了有益的参考。     

非结构网格并行计算预处理方法研究

非结构网格预处理方法是非结构网格CFD并行计算的关键技术之一。提出基于缓冲数据结构的快速搜索算法来建立全局网格单元邻接关系图,算法复杂度低,能够显著降低非结构网格预处理的存储需求;在提高核心计算访存命中率方面,提出网格单元重排序算法,该算法能够提高核心计算效率,并通用于各种非结构网格问题。实验结果表明,在用于大网格量的复杂计算区域时该非结构网格预处理技术仍能得到较理想的结果。     

基于GPU的加锁并行化非结构网格生成方法研究

非结构网格的生成在时间和内存上有一定的缺陷,这里提出了一种新的方法,命名为GPU-PDMG,是基于CUDA架构的GPU并行非结构网格生成技术。该技术结合了GPU的高速并行计算能力与Delaunay三角化的优点,在英伟达GPU模块下采用CUDA程序模型,开发出了加锁并行区划分技术,通过对NACA0012翼型、多段翼型等算例进行测试,分析此方法的加速比和效率,对其计算性能展开评估。实验结果表明,GPU-PDMG优于现存在的CPU算法的速度,在保证网格质量的同时,提高了效率。     

Automatic mesh generation on a regular background grid

This paper presents and automatic mesh generation procedure on a 2D domain based on a regular background grid.The idea is to devise a robust mesh generation scheme with equal emphasis on quality and efficiency,Instead of using a traditional regular rectangular grid,a mesh of equilateral triangles is employed to ensure triangular element of the best quality will be preserved in the interior of the domain.As for the boundary,it is to be generated by a node/segment insertion process.Nodes are inserted into the background mesh one by one following the sequence of the domain boundary.The local strcture of the mesh is modified based on the Delaunay criterion with the introduction of each node.Those boundary segments.which are not produced in the phase of node insertion,will be recovered through a systematic element swap produced in the phase of node insertion will be recovered through a systematic element swap process.Two theorems will be presented and proved to set up the theoretical basic of the boundary recovery part.Examples will be presented to demonstrate the robustness and the quality of the mesh generated by the proposed technique.     

Fully automatic and fast mesh size specification for unstructured mesh generation

A fully automatic surface mesh generation system is presented in this paper. The automation is achieved by an automatic determination of a consistent mesh size distribution, which is based on geometry rasterisation. The user specifies a minimal and maximal allowed mesh size, and a maximal allowed curvature angle for the complete geometry, or, rather, parts of it. Now, these local curvature and local characteristic lengths of the geometry are computed, which determine the local mesh size. These local mesh sizes are stored and smoothed in a Cartesian background mesh. Afterwards, the triangulation is generated by an advancing front triangulator: the local resolution of the surface triangulation is determined by the mesh sizes stored in the Cartesian background mesh. The object-oriented design and implementation is described. The complete system is very fast due to an efficient parallelisation based on MPI for computer systems with distributed memory.     

A comparison of GPU strategies for unstructured mesh physics

There have been few efforts to date to write physics algorithms for general unstructured meshes (meshes composed of arbitrary polygons/polyhedra) on graphics processing units (GPUs). Typical strategies for GPU memory management, such as double‐buffering and coalescing memory accesses, are difficult to apply to the irregular memory storage patterns of unstructured meshes. This paper presents results from an initial GPU version of a typical unstructured mesh kernel. Three different memory management strategies are described and implemented. Timing results for all three strategies are presented, in some cases showing speedups of over 20 times compared with the original CPU code.Copyright © 2012 John Wiley & Sons, Ltd.     

Parallel generation of unstructured surface grids

In this paper, a new grid generation system is presented for the parallel generation of unstructured triangular surface grids. The object-oriented design and implementation of the system, the internal components and the parallel meshing process itself are described. Initially in a rasterisation stage, the geometry to be meshed is analysed and a smooth distribution of local element sizes in 3-D space is set up automatically and stored in a Cartesian mesh. This background mesh is used by the advancing front surface mesher as spacing definition for the triangle generation. Both the rasterisation and the meshing are MPI-parallelised. The underlying principles and strategies will be outlined together with the advantages and limitations of the approach. The paper will be concluded with examples demonstrating the capabilities of the presented approach.

Intelligent finite element mesh generation

A knowledge-based and automatic finite element mesh generator (INTELMESH) for two-dimensional linear elasticity problems is presented. Unlike other approaches, the proposed technique incorporates the information about the object geometry as well as the boundary and loading conditions to generate an a priori finite element mesh which is more refined around the critical regions of the problem domain. INTELMESH uses a blackboard architecture expert system and the new concept of substracting to locate the critical regions in the domain and to assign priority and mesh size to them. This involves the decomposition of the original structure into substructures (or primitives) for which an initial and approximate analysis can be performed by using analytical solutions and heuristics. It then uses the concept of wave propagation to generate graded nodes in the whole domain with proper density distribution. INTELMESH is fully automatic and allows the user to define the problem domain with minimum amount of input such as object geometry and boundary and loading conditions. Once nodes have been generated for the entire domain, they are automatically connected to form well-shaped triangular elements ensuring the Delaunay property. Several examples are presented and discussed. When incorporated into and compared with the traditional approach to the adaptive finite element analysis, it is expected that the proposed approach, which starts the process with near optimal initial meshes, will be more accurate and efficient.     

基于非结构网格的飞行器多体分离数值模拟

针对基于非结构网格方法的飞行器多体分离数值模拟中的局部网格重构问题,提出了一种基于单元相邻关系的重构区域构造方法。首先,根据单元半径比检查网格质量并标记重构单元;其次,通过网格单元的相邻关系对重构区域进行扩展;最后,通过标记非二边流形边的周围单元保证重构区域边界定义满足二边流形准则。基于该方法的某分离物投放数值实验中,成功进行了16次网格局部重构操作,重构后总体网格单元半径比的平均值达到0.71以上。计算结果和风洞实验数据的比较分析表明,数值实验精确地计算出分离物的运动轨迹和运动姿态,验证了非结构动网格重构过程的有效性。     

基于非结构化三角网格的海洋流场可视化

针对二维流场可视化均是基于结构化网格流场数据的情况,提出一种基于非结构化三角网格的海洋流场可视化策略：使用流线表达流场,流线可视化的主要挑战是种子点放置问题,即流线的初始点,制定了非结构化三角网格下基于特征引导的种子点放置策略,合理放置流线初始点以利于表达流场特征;设计了基于网格密度的层次聚类算法,引入网格密度属性对流线进行聚类并基于聚类质心进行流线放置,在保留了FVCOM 模式数据的多密度性前提下提高了流线可视化效果。实验表明,该方法可以有效地保留流场特征,并且借助 FVCOM 模式的边界拟合性能在海湾、河道等地区取得良好的可视化效果;在此基础上,基于 Cesium引擎开发了基于流线聚类数据的动态流场可视化应用,其是 FVCOM 模式数据首次应用于动态粒子流场的一次尝试,并且具有较好的可视化效果。