三角网格曲面的球面参数化

提出了一种球面参数化三角网格曲面的方法。结合平面凸参数化和球面参数化,计算出封闭网格的切割线边界,网格边界映射到球面的凸区域边界上。然后分别参数化各子网格,最后将三角网格内部点映射到球面上。并用实例验证了此方法的可行性和有效性。     

三重三角网格细分算法研究

标准的二值细分操作会在那些特殊顶点相关联处产生极大的曲率,这个缺陷可以通过对细分操作的特征值施加一个限定的曲率频谱来消除,但会扩大对那些超出了二价的顶点的支持.三重细分方案将网格的边一分为三,上述情况不会发生.该文中,作者推广了二阶连续的四次样条的三重细分到任意的三角形.该细分算法具有有界的曲率,并且被设计成能够维持凸包的属性.     

面向四面体网格生成的曲面Delaunay三角化算法

提出了一种曲面域Delaunay三角网格的直接构造算法。该算法在曲面网格剖分的边界递归算法和限定Delaunay四面体化算法的基础上,利用曲面采样点集的空间Delaunay四面体网格来辅助曲面三角网格的生成,曲面上的三角网格根据最小空球最小准则由辅助四面体网格中选取,每个三角形都满足三维Delaunay空球准则,网格质量有保证,并且极大的方便了进一步的曲面边界限定下的Delaunay四面体化的进行。     

应用区域变换实现三角 Bezier 曲面分割

本文根据实际应用需要采用参数域变换方法对三角Ｂｅｚｉｅｒ曲面片进行分割，可简单地确定复杂分割模型下各子曲面片的控制顶点，避免了采用Ｃ－Ｔ分割带来的冗余计算和某些情况下的复杂处理过程，并且使分割算法统一。     

三角网格特征边识别的一种有效方法

三角网格特征边识别在数字几何处理和计算机辅助制造(CAM)的模具加工中都有着广泛的应用,该文指出了近年来有关网格特征边识别算法的各种弊端及原因,给出了一种鲁棒的网格特征边识别新算法.该算法以网格特征点的识别为基础,能够识别以往算法常遗漏的一些二面法向夹角比较小的网格边,增强了对C1不连续网格边的识别能力.众多数值例子支持了这个结论.     

动态隐式曲面高质量三角化

提出了一种新的动态隐式曲面的快速、高质量绘制方法。该方法首先用粒子分裂和漂移实现隐式曲面均匀采样,然后用滚球法(BPA)法对均匀采样点进行快速三角化,最后用细分法对重建网格进行细分,从而得到高质量的隐式曲面多边形化模型。对于动态变化的隐式曲面,该方法充分利用变化前后的连贯性,实现动态隐式曲面的快速绘制。     

复杂曲面五轴加工局部干涉处理技术研究

针对复杂曲面环形刀五轴数控加工中的局部干涉问题,提出了一种基于曲率匹配及网格点的干涉处理技术。首先,利用曲率匹配原则选出合理的刀具半径,以保证在切触点处沿任何方向上刀具与被加工曲面之间不会发生干涉,然后在各个切触点处通过比较刀具曲面最小主曲率与加工曲面最大主曲率确定出刀具的初始倾角。为了判断切触点邻近区域是否存在干涉问题,采用了网格点来快速自动生成检测区域及初始检测点。文中对有效检测点的筛选以及干涉的判断和处理技术分别进行了详细论述。最后,以非均匀有理B样条曲面为加工实例,对上述算法进行了测试和验证。     

网格技术及其在电力系统中的应用

随着当今世界互联网技术的不断成熟和发展,我国市场的信息化也在快速的发展,协同应用的需求也在逐渐的扩大。传统的计算机已经不能满足当前硬件的连通和网页的互连,不能够满足动态构成的个体,资源集合之间对高性能的计算、资源共享和一站式的服务需求逐步的加大。特别是在科学研究的领域当中,对于信息技术的要求越来越高,网格计算作为现代一种面向服务的体系架构,能够使各种设备在各个企业当中得以虚拟的共享、管理及其访问,使得用户能够无缝、无干扰的访问这些资源。它主要在电力系统当中的生产、管理、决策等方面有着广泛的应用前景,对于提高电网安全稳定运行具有着很大的意义。     

浅谈网格技术的现状及其应用

论述网格计算的发展概况,在科学领域的应用范围,网格服务的特点以及在未来网络市场中的发展潜力。     

边界无网格技术在噪声源识别中的应用

根据非共形面声全息对声辐射传播建模的高精确度要求,将边界无网格法引入声辐射传播建模过程中,实现对三维空间任意封闭曲面上Kirchhoff-Helmholtz边界积分方程高精度离散和求解计算。进一步研究非共形面声全息逆向重构问题的基本原理及其不适定性,采用了Landweber迭代正则化和L曲线正则化参数选取方法,从而确立有效的声场逆向重构求解方法。最后,还进行减速电机噪声源表面振动重构实验,验证研究的基于边界无网格的非共形面声全息的相关理论和方法可行。     

A study on solid modelling with surface trimming method

Abstract

This paper proposes a Surface Trimming Method based on the intersection curves between free‐form surfaces so that a complex solid model with several primitive surfaces can be constructed. These solid models will not only be used by the mechanical engineering industry to design and analyze conventional mechanical parts, but will also be used by the civil engineers to design and analyze structures of irregular shape. The scope of solid modelling application is thus enhanced.     

The effect of trimming on strain gauge accuracy

During a programme of fatigue testing welded tubular joints, similar to those in use in North Sea offshore structures, it was necessary to measure the strain as close to the weld toe as possible and also to detect crack initiation. To this end general purpose miniature foil strain gauges were used. The backings of these gauges were trimmed prior to installation to enable placing the measuring grid as close as possible to the weld toe. The investigation described was carried out to assess the accuracy of these strain gauge installations.     

Intersecting and trimming parametric meshes on finite element shells

We present an algorithm for intersecting finite element meshes defined on parametric surface patches. The intersection curves are modelled precisely and both meshes are adjusted to the newly formed borders, without unwanted reparametrizations. The algorithm is part of an interactive shell modelling program that has been used in the design of large offshore oil structures. To achieve good interactive response, we represent meshes with a topological data structure that stores its entities in spatial indexing trees instead of linear lists. These trees speed up the intersection computations required to determine points of the trimming curves; moreover, when combined with the topological information, they allow remeshing using only local queries. Copyright © 2000 John Wiley & Sons, Ltd.     

Automatic sizing functions for unstructured surface mesh generation

Accurate sizing functions are crucial for efficient generation of high‐quality meshes, but to define the sizing function is often the bottleneck in complicated mesh generation tasks because of the tedious user interaction involved. We present a novel algorithm to automatically create high‐quality sizing functions for surface mesh generation. First, the tessellation of a Computer Aided Design (CAD) model is taken as the background mesh, in which an initial sizing function is defined by considering geometrical factors and user‐specified parameters. Then, a convex nonlinear programming problem is formulated and solved efficiently to obtain a smoothed sizing function that corresponds to a mesh satisfying necessary gradient constraint conditions and containing a significantly reduced element number. Finally, this sizing function is applied in an advancing front mesher. With the aid of a walk‐through algorithm, an efficient sizing‐value query scheme is developed. Meshing experiments of some very complicated geometry models are presented to demonstrate that the proposed sizing‐function approach enables accurate and fully automatic surface mesh generation. Copyright © 2016 John Wiley & Sons, Ltd.     

Inserting a surface into an existing unstructured mesh

In this work, a new method for inserting a surface as an internal boundary into an existing unstructured tetrahedral mesh is developed. The surface is discretized by initially placing vertices on its bounding curves, defining a length scale at every location on each boundary curve based on the local underlying mesh, and equidistributing length scale along these curves between vertices. The surface is then sampled based on this boundary discretization, resulting in a surface mesh spaced in a way that is consistent with the initial mesh. The new points are then inserted into the mesh, and local refinement is performed, resulting in a final mesh containing a representation of the surface while preserving mesh quality. The advantage of this algorithm over generating a new mesh from scratch is in allowing for the majority of existing simulation data to be preserved and not have to be interpolated onto the new mesh. This algorithm is demonstrated in two and three dimensions on problems with and without intersections with existing internal boundaries. Copyright © 2015 John Wiley & Sons, Ltd.     

GradH‐Correction: guaranteed sizing gradation in multi‐patch parametric surface meshing

In this paper a new method, called GradH‐Correction, for the generation of multi‐patch parametric surface meshes with controlled sizing gradation is presented. Such gradation is obtained performing a correction on the size values located on the vertices of the background mesh used to define the control space that governs the meshing process. In the presence of a multi‐patch surface, like shells of BREP solids, the proposed algorithm manages the whole composite surface simultaneously and as a unique entity. Sizing information can spread from a patch to its adjacent ones and the resulting size gradation is independent from the surface partitioning. Theoretical considerations lead to the assertion that, given a parameter λ, after performing a GradH‐Correction of level λ over the control space, the unit mesh constructed using the corrected control space is a mesh of gradation λ in the real space (target space). This means that the length ratio of any two adjacent edges of the mesh is bounded between 1/λ and λ. Numerical results show that meshes generated from corrected control spaces are of high quality and good gradation also when the background mesh has poor quality. However, due to mesh generator imprecision and theoretical limitations, guaranteed gradation is achieved only for the sizing specifications and not for the generated mesh. Copyright © 2004 John Wiley & Sons, Ltd.     

一种曲面裁剪的快速新算法

曲面裁剪算法是曲面造型的关键算法之一。传统的裁剪算法是通过对重点和重边进行较复杂的特殊处理并基于环的两两并、交、差来实现的。本文首先提出并严格的定义了入点、出点等概念,在此基础上,提出了一种 对被裁剪曲面参数域进行快速组环的分裂、组环方法,从而实现了对曲面的快速裁剪,该算法已实现并用在ＳｕｐｅｒｍａｎＣＡＤ／ＣＡＭ曲面造型系统。     

Generation and adaptation of computational surface meshes from discrete anatomical data

Fast and accurate scanning devices are nowadays widely used in many engineering and biomedical fields. The resulting discrete data is usually directly converted into polygonal surface meshes, using ‘brute‐force’ algorithms, often resulting in meshes that may contain several millions of polygons. Simplification is therefore required in order to make storage, computation and display possible if not efficient. In this paper, we present a general scheme for mesh simplification and optimization that allows to control the geometric approximation as well as the element shape and size quality (required for numerical simulations). Several examples ranging from academic to complex biomedical geometries (organs) are presented to illustrate the efficiency and the utility of the proposed approach. Copyright © 2004 John Wiley & Sons, Ltd.     

Recovery of an arbitrary edge on an existing surface mesh using local mesh modifications

This study describes an algorithm for recovering an edge which is arbitrarily inserted onto a pre‐triangulated surface mesh. The recovery process does not rely on the parametric space of the surface mesh provided by the geometric modeller. The topological and geometrical validity of the surface mesh is preserved through the entire recovery process. The ability of inserting and recovering an arbitrary edge onto a surface mesh can be an invaluable tool for a number of meshing applications such as boundary layer mesh generation, solution adaptation, preserving the surface conformity, and possibly as a primary tool for mesh generation. The edge recovery algorithm utilizes local surface mesh modification operations of edge swapping, collapsing and splitting. The mesh modification operations are decided by the results of pure geometrical checks such as point and line projections onto faces and face‐line intersections. The accuracy of these checks on the recovery process are investigated and the substantiated precautions are devised and discussed in this study. Copyright © 2001 John Wiley & Sons, Ltd.     

双阻带红外频率选择表面的设计与分析

本文设计了工作在第二个大气窗口(3 μm～5 μm)和第三个大气窗口(8 μm～14 μm)的双频段FSS。该FSS为双屏结构,由六边形金属网格和六边形谐振环阵列组合而成。仿真结果表明,该FSS在两个大气窗口的平均透过率低于5%,且对不同角度入射的电磁波具有良好的角度稳定性。分析了结构主要尺寸参数对传输特性的影响,结果表明,调整六边形谐振环的单元尺寸能够有效调节3 μm～5 μm波段范围内-10 dB阻带的带宽,增大金属网格的单元尺寸会使得8 μm～14 μm波段范围内的阻带向长波方向移动。