网格划分对叉排管束摩擦阻力系数的影响

应用流体计算软件FLUENT,对受限空间内烟气冲刷叉排管束(横竖均为5排,间距比均为1.25)的流动进行了数值模拟研究,主要研究了三角形和四边形非结构化网格及四边形结构化网格划分对流场流动摩擦阻力系数f的影响。结果表明:结构化网格相对于非结构化网格,虽然建模时间较长,但网格生成速度快,计算耗时短,易收敛且精度高;对于同类型网格,网格边界层底层厚度及圆周节点数的选取均对模拟结果存在较大影响。     

一种曲边三角形区域中的三角形网格自动生成方法

有限元数值计算时,常需用到三角形单元。在一曲边三角形区域中,本文提出了一种新的三角形网格自动生成方法,可在二维、三维空间内对板、壳等结构进行网格划分和网格疏密调节。算例表明本文的网格生成方法是方便、有效的。并避免了R.HABER等人的方法所产生的计算机数据溢出现象。     

多天线-散射体结构矩量法分析的自动网格划分方法

针对多天线-散射体(散射体可看作是由三角形面和四边形平面围成的几何体)结构,提出了一种基于矩量法的散射面自动网格划分方法。该方法通过三次网格划分得到符合矩量法分析要求的三角形面元、四边形面元。首先对散射体各表面按无天线连接并遵循面积条件进行递归二分,得到符合面积要求的面元,这就是第1次网格划分;接着分4种情况对连接有天线的有关面元进行再一次划分,得到线面结合点在中心的正方形面元以及若干三角形、四边形面元,这就是第2次网格划分;最后对狭长的面元进行第3次网格划分,得到质量较好的面元。多项工程应用表明,该网格划分方法稳定、可靠、速度快、适应性强。     

全自动自适应四边形有限元网格生成/再生成方法与软件AUTOMESH-2D/PC

独立提出并研究开发了一种密度控制和区域分解相结合的四边形网格自动生成方法,简称区域分解法.以区域分解法为基础,自主开发了商品化网格自动生成/再生成软件AUTOMESH,并已经在中国版权保护中心进行了软件著作权登记.介绍区域分解法和软件AUTOMESH,并给出多个划分实例.     

三角网格模型上的四边形曲线网生成新方法

四边形网格划分是组合曲面建模技术的首要条件。针对海量流形三角网格数据,提出了基于网格简化技术与调和映射算法的四边形网格生成新方法--映射法。该方法采用基于顶点删除的网格简化技术对三角网格模型进行简化,进而借助调和映射算法将简化网格映射到二维平面上进行四边形划分,并将所获得的平面四边形节点数据逆映射回物理域,采用短程线边界形式最终得到适于组合曲面建模的空间四边形拓扑。该方法简单、实用,运行速度较快,实际的算例也验证了方法的有效性与可行性。     

一种平面区域四边形网格生成方法

基于分层发散的思想,详尽地阐述了有限元法前处理中的网格生成方法;介绍了分层发散的网格生成中的布点、点的存贮、网格的划分、四边形单元质量判断及局部调整等内容,并给出了实例.     

高精度自适应的四边形网格重建

提出了海量数据点集的四边形网格重建算法。首先根据精度要求简化数据点,按一定规则连接相邻的简化数据点生成多边形网格,对网格中高斯曲率较大的顶点进行局部细分提高其精度,然后对多边形网格进行整体细分使其全部转化为四边形网格,最后分裂度较大的顶点对其进行优化。实验结果表明,算法对拓扑结构较为复杂的海量数据点集的四边形网格重建是行之有效的。     

NURBS曲面的四边形网格的分割与逼近

介绍了一个用于对NURBS曲面进行四边形网格的分割与逼近的算法。该算法采用二叉树递归分割的方法分割和逼近曲面，所分割的四边形除了在高度方向和曲面边界处满足给定精度外，同时在四边形四条边界满足给定的切矢精度。实例测试结果表明，用本文所述算法生成的四边形网格具有网格逼近原曲面、网格四边形接近于规则四边形等特点。     

任意形状区域的自动布点技术

针对存在多种介质材料、断层、裂纹、孔洞、开挖区域等不连续面或多连通区域情况的复杂平面区域,提出了一种自动布点算法及此算法的优化方法,该算法对不规则区域适应能力强,无需人工干预,且兼具有实现简单,耗时少等特点。这些自动布置的离散结点可直接用于无网格数值计算,也可以进一步生成有限元分析所需的三角形和四边形网格。     

一种新型球面等积六边形网格系统生成算法

分析了构建球面等积网格系统的基本原理和常用剖分方法的特点,提出了在二十面体展开图上对顶点和面统一编码的研究思路,将两个相邻三角面合并为一个四边形并建立坐标系描述孔径为4的新型递归剖分网格,最后借助施奈德等积多面体投影将平面网格映射到球面,得到了将孔径为4的等积六边形剖分产生的球面网格系统ISEA4H-3.实验结果表明,用这种算法生成的ISEA4H-3网格的几何属性优于现有球面六边形网格,更适用于海量空间信息管理,具有较强的应用价值.     

Q‐Morph: an indirect approach to advancing front quad meshing

Q‐Morph is a new algorithm for generating all‐quadrilateral meshes on bounded three‐dimensional surfaces. After first triangulating the surface, the triangles are systematically transformed to create an all‐quadrilateral mesh. An advancing front algorithm determines the sequence of triangle transformations. Quadrilaterals are formed by using existing edges in the triangulation, by inserting additional nodes, or by performing local transformations to the triangles. A method typically used for recovering the boundary of a Delaunay mesh is used on interior triangles to recover quadrilateral edges. Any number of triangles may be merged to form a single quadrilateral. Topological clean‐up and smoothing are used to improve final element quality. Q‐Morph generates well‐aligned rows of quadrilaterals parallel to the boundary of the domain while maintaining a limited number of irregular internal nodes. The proposed method also offers the advantage of avoiding expensive intersection calculations commonly associated with advancing front procedures. A series of examples of Q‐Morph meshes are also presented to demonstrate the versatility of the proposed method. Copyright © 1999 John Wiley & Sons, Ltd.     

Automatic generation of anisotropic quadrilateral meshes on three‐dimensional surfaces using metric specifications

A new algorithm for constructing full quadrilateral anisotropic meshes on 3D surfaces is proposed in this paper. The proposed method is based on the advancing front and the systemic merging techniques. Full quadrilateral meshes are constructed by systemically converting triangular elements in the background meshes into quadrilateral elements.By using the metric specifications to describe the element characteristics, the proposed algorithm is applicable to convert both isotropic and anisotropic triangular meshes into full quadrilateral meshes. Special techniques for generating anisotropic quadrilaterals such as new selection criteria of base segment for merging, new approaches for the modifications of the background mesh and construction of quadrilateral elements, are investigated and proposed in this study. Since the final quadrilateral mesh is constructed from a background triangular mesh and the merging procedure is carried out in the parametric space, the mesh generator is robust and no expensive geometrical computation that is commonly associated with direct quadrilateral mesh generation schemes is needed. Copyright © 2002 John Wiley & Sons, Ltd.     

An indirect approach for automatic generation of quadrilateral meshes with arbitrary line constraints

A new approach to the automatic generation of a quadrilateral mesh with arbitrary line constraints is proposed in this paper. It is an indirect all‐quad mesh generation and presented in the following steps: (1) discretizing the constrained lines within the domain; (2) converting the above domain to a triangular mesh together with the line constraints; (3) transforming the generated triangular mesh with line constraints to an all‐quad mesh through performing an advancing front algorithm from the line constraints, which enables the construction of quadrilaterals layer by layer, and roughly keeps the feature of the initial triangular mesh; (4) optimizing the topology of the quadrilateral mesh to reduce the number of irregular nodes; (5) smoothing the generated mesh toward high‐quality all‐quad mesh generation. Finally, a few application examples are given to demonstrate the reliability and usefulness of the proposed algorithm. Copyright © 2011 John Wiley & Sons, Ltd.     

Meshing curved wire‐frame models through energy minimization and packing of ellipses

In the initial phase of structural part design, wire‐frame models are sometimes used to represent the shapes of curved surfaces. Finite Element Analysis (FEA) of a curved surface requires a well shaped, graded mesh that smoothly interpolates the wire frame. This paper describes an algorithm that generates such a triangular mesh from a wire‐frame model in the following two steps: (1) construct a triangulated surface by minimizing the strain energy of the thin‐plate‐bending model, and (2) generate a mesh by the bubble meshing method on the projected plane and project it back onto the triangulated surface. Since the mesh elements are distorted by the projection, the algorithm generates an anisotropic mesh on the projected plane so that an isotropic mesh results from the final projection back onto the surface. Extensions of the technique to anisotropic meshing and quadrilateral meshing are also discussed. The algorithm can generate a well‐shaped, well‐graded mesh on a smooth curved surface. Copyright © 1999 John Wiley & Sons, Ltd.     

Automatic conversion of triangular finite element meshes to quadrilateral elements

A method is presented for the fully automatic conversion of a general finite element mesh containing triangular elements into a mesh composed of exclusively quadrilateral elements. The initial mesh may be constructed of entirely triangular elements or may consist of a mixture of triangular and quadrilateral elements. The technique used employs heuristic procedures and criteria to selectively combine adjacent triangular elements into quadrilaterals based on preestablished criteria for element quality. Additional procedures are included to eliminate isolated triangles. The methods operates completely without user intervention once the nodal co-ordinates and element connectivity of the original mesh are supplied.     

Automatic generation of transitional meshes

Advances in commercial computer‐aided design software have made finite element analysis with three‐dimensional solid finite elements routinely available. Since these analyses usually confine themselves to those geometrical objects for which particular CAD systems can produce finite element meshes, expanding the capability of analyses becomes an issue of expanding the capability of generating meshes. This paper presents a method for stitching together two three‐dimensional meshes with diverse elements that can include tetrahedral, pentahedral and hexahedral solid finite elements. The stitching produces a mesh that coincides with the edges which already exist on the portion of boundaries that will be joined. Moreover, the transitional mesh does not introduce new edges on these boundaries. Since the boundaries of the regions to be stitched together can have a mixture of triangles and quadrilaterals, tetrahedral and pyramidal elements provide the transitional elements required to honor these constraints. On these boundaries a pyramidal element shares its base face with the quadrilateral faces of hexahedra and pentahedra. Tetrahedral elements share a face with the triangles on the boundary. Tetrahedra populate the remaining interior of the transitional region. Copyright © 2001 John Wiley & Sons, Ltd.     

A new automatic adaptive 3D solid mesh generation scheme for thin‐walled structures

A new algorithm to generate three‐dimensional (3D) mesh for thin‐walled structures is proposed. In the proposed algorithm, the mesh generation procedure is divided into two distinct phases. In the first phase, a surface mesh generator is employed to generate a surface mesh for the mid‐surface of the thin‐walled structure. The surface mesh generator used will control the element size properties of the final mesh along the surface direction. In the second phase, specially designed algorithms are used to convert the surface mesh to a 3D solid mesh by extrusion in the surface normal direction of the surface. The extrusion procedure will control the refinement levels of the final mesh along the surface normal direction. If the input surface mesh is a pure quadrilateral mesh and refinement level in the surface normal direction is uniform along the whole surface, all hex‐meshes will be produced. Otherwise, the final 3D meshes generated will eventually consist of four types of solid elements, namely, tetrahedron, prism, pyramid and hexahedron. The presented algorithm is highly flexible in the sense that, in the first phase, any existing surface mesh generator can be employed while in the second phase, the extrusion procedure can accept either a triangular or a quadrilateral or even a mixed mesh as input and there is virtually no constraint on the grading of the input mesh. In addition, the extrusion procedure development is able to handle structural joints formed by the intersections of different surfaces. Numerical experiments indicate that the present algorithm is applicable to most practical situations and well‐shaped elements are generated. Copyright © 2004 John Wiley & Sons, Ltd.     

Quadrilateral approaches for accurate free mesh method

This paper presents the formulation of free mesh method and two approaches of the method by incorporating quadrilateral elements. The approaches do not have any difference with the original free mesh method in their fundamental algorithms, wherein local system equations with triangular elements are created nodewise to create the global system equations, and their implementation is therefore very easy. The first approach creates quadrilateral elements inside every triangular element, whilst quadrilateral elements are generated outside every triangular element in the second approach. The results of numerical examples indicate that the approaches improve the accuracy of free mesh method, further opening the possibility for more improvement using an accurate quadrilateral element. Copyright © 2000 John Wiley & Sons, Ltd.