面向大型复杂焊接结构仿真的组合式自适应四面体网格生成算法

目的 研究高质量、高效率的网格生成技术以实现大型复杂结构的焊接工艺仿真优化。方法 提出一种组合式的自适应四面体网格划分算法,即在高效生成各个零部件四面体网格的基础上,根据焊缝中心面的几何信息自动对焊缝附近网格进行细分,再缝合成高质量的大型复杂焊接结构的整体四面体网格,并集成到自主可控的商用网格划分软件Vision Mesh中。提出了摄动几何边界的方法,解决了大型复杂结构STL几何体在存在几何错误时网格难以生成的问题。提出了基于BVH树结构表达的背景网格表达方法,解决了多条焊缝同时高效、自动细分的难题,并通过“四面体分割–四面体合并–四面体翻转–点平滑优化”方法,实现了四面体网格的高质量优化。结果 算法网格效率可以达到200万个/h,生成的四面体99%以上均接近正四面体。可以由多个零部件一步组合生成大型结构的整体网格,并可对焊缝区域进行自动细分,大幅度简化了划分流程。将生成的网格导入国产焊接仿真软件InteWeld中进行测试,验证算法可用于大型复杂焊接结构整体应力变形的计算中。结论 实现了大型复杂焊接结构的高质量自适应四面体网格划分,使用简便操作得到了高质量网格,为焊接结构件工艺仿真优化...     

Achieving finite element mesh quality via optimization of the Jacobian matrix norm and associated quantities. Part I—a framework for surface mesh optimization

Structured mesh quality optimization methods are extended to optimization of unstructured triangular, quadrilateral, and mixed finite element meshes. New interpretations of well‐known nodally based objective functions are made possible using matrices and matrix norms. The matrix perspective also suggests several new objective functions. Particularly significant is the interpretation of the Oddy metric and the smoothness objective functions in terms of the condition number of the metric tensor and Jacobian matrix, respectively. Objective functions are grouped according to dimensionality to form weighted combinations. A simple unconstrained local optimum is computed using a modified Newton iteration. The optimization approach was implemented in the CUBIT mesh generation code and tested on several problems. Results were compared against several standard element‐based quality measures to demonstrate that good mesh quality can be achieved with nodally based objective functions. Published in 2000 by John Wiley & Sons, Ltd.     

桁架动力学形状优化的统一设计变量方法

研究了具有多种约束 ,特别是动力学约束 (频率约束 )作用下的平面桁架形状优化问题。提出一种将两类不同性质的设计变量 (尺寸变量、节点几何坐标变量 )变换为统一形式的无量纲设计变量的方法 ,解决了不同性质变量耦合引起的收敛困难问题 ,并拓展了设计空间。联合运用内点罚函数法、DFP法 (即变尺度法 )和一维搜索技术 (二次插值法 ) ,将约束优化问题转化为无约束序列优化问题 ,得到了满意的优化结果。算例表明本文方法对桁架形状优化的有效性 ,并显示了算法的简洁性和工程设计实用性     

三维泡泡布点方法及网格生成

本文研究如何在三维区域上生成高质量的节点集并基于节点集进行网格生成.根据区域边界的几何描述和理想间隔控制函数,先后对曲面及区域内部用泡泡布点法进行节点布置.节点布置结束后,对区域边界的节点集运用高质量点集的局部网格生成算法(BLMG)进行网格剖分,对区域内部的点集直接进行Delaunay三角剖分.通过计算节点集生成Delaunay网格单元的质量来评价区域节点集的质量.泡泡均匀分布与非均匀分布的算例均表明,该算法生成的节点具有较高的质量并且在泡泡非均匀分布时具有很好的渐进性.     

Shape optimization of bonded patch to cylindrical shell structures

Adhesive bonding has been widely used to join or repair metallic and composite structural components to achieve or restore their designated structural stiffness and strengths. However, current analysis methods and empirical databases for composite bonded patch repairs or joints are limited to flat structures, and there exists a very limited knowledge on the effect of curvature on the performance and durability of composite bonded joints and repairs. Recently, a novel finite element formulation was presented for developing adhesive elements for conducting 2.5‐D simplified stress analysis of bonded repairs to curved structures. This paper presents the work on optimal shape design of a bonded curved composite patch using the newly developed adhesive element. The Sequential Linear Programming (SLP) method is employed as the optimization algorithm in conjunction with a fully implemented mesh generation algorithm into which new features have been incorporated. The objective of shape optimization is to minimize the maximum stress in the entire adhesive layer to ensure that the bonded patch effectively works together with the parent structure in service. Several different objective functions, related to possible failure mechanisms of the adhesive layer, are proposed to optimize the shape of a bonded patch. Copyright © 2003 John Wiley & Sons, Ltd.     

Generation and optimization of tetrahedral meshes by advancing front technique

An algorithm for tetrahedron mesh generation and optimization with respect to a shape and a size criterion is presented. A well distributed set of nodes is first generated by an octree method, and the set is then triangulated. The advancing front technique is used to mesh the whole volume. Emphasis has been placed on management of the front. The method involves priority construction of enhanced quality tetrahedra. Each face is assigned to a front corresponding to the quality of the best tetrahedron which can be constructed. Elements are destroyed in the case of non-convergence. Optimization procedures make local use of the algorithm used to mesh the complete model. Industrial examples of relatively complex volumes are given, demonstrating that a high quality and optimized mesh can be obtained by the proposed method. © 1998 John Wiley & Sons, Ltd.     

Achieving finite element mesh quality via optimization of the Jacobian matrix norm and associated quantities. Part II—A framework for volume mesh optimization and the condition number of the Jacobian matrix

Three‐dimensional unstructured tetrahedral and hexahedral finite element mesh optimization is studied from a theoretical perspective and by computer experiments to determine what objective functions are most effective in attaining valid, high‐quality meshes. The approach uses matrices and matrix norms to extend the work in Part I to build suitable 3D objective functions. Because certain matrix norm identities which hold for 2×2 matrices do not hold for 3×3 matrices, significant differences arise between surface and volume mesh optimization objective functions. It is shown, for example, that the equality in two dimensions of the smoothness and condition number of the Jacobian matrix objective functions does not extend to three dimensions and further, that the equality of the Oddy and condition number of the metric tensor objective functions in two dimensions also fails to extend to three dimensions. Matrix norm identities are used to systematically construct dimensionally homogeneous groups of objective functions. The concept of an ideal minimizing matrix is introduced for both hexahedral and tetrahedral elements. Non‐dimensional objective functions having barriers are emphasized as the most logical choice for mesh optimization. The performance of a number of objective functions in improving mesh quality was assessed on a suite of realistic test problems, focusing particularly on all‐hexahedral ‘whisker‐weaved’ meshes. Performance is investigated on both structured and unstructured meshes and on both hexahedral and tetrahedral meshes. Although several objective functions are competitive, the condition number objective function is particularly attractive. The objective functions are closely related to mesh quality measures. To illustrate, it is shown that the condition number metric can be viewed as a new tetrahedral element quality measure. Published in 2000 by John Wiley & Sons, Ltd.     

颗粒流体系统Euler/Lagrange模型中自适应三角网格的生成

针对二维颗粒流体系统Euler／Lagrange模型的有限元模拟,建立了三角网格生成的自适应算法。该算法能够根据颗粒分布与颗粒大小自适应地调整网格的疏密程度,使其网格密度在系统边界附近及颗粒边缘附近较大,而在其它地方较小。与此同时,网格的光滑化也提高了网格质量, 从而为颗粒流体系统介观尺度的有限元模拟奠定了基础。     

基于遗传算法和梯度算法的桁架结构动力学形状优化

本文提出了一种基于遗传算法和梯度算法的桁架动力学形状优化方法 ,该方法综合了梯度算法的快速收敛与遗传算法的全局搜索能力。算例表明了本文方法的有效性和工程适应性。     

Mesh data structure selection for mesh generation and FEA applications

The data structure representing a mesh and the operators to create and query such a database play a crucial role in the performance of mesh generation and FE analysis applications. The design of such a database must balance the conflicting requirements of compactness and computational efficiency. In this article, 10 different mesh representations are reviewed for linear tetrahedral and hexahedral meshes. A methodology for calculating the storage and computational costs of mesh representations is presented and the 10 data structures are analysed. Also, a system for ranking different data structures based on their computational and storage costs is devised and the various mesh representations are ranked according to this measure. Copyright © 2002 John Wiley & Sons, Ltd.     

垃圾焚烧发电系统优化及综合利用技术

垃圾焚烧发电项目已逐渐成为由地方政府主导的PPP项目,随着国家能源战略的深入,依靠科技创新,加快节能减排技术研发和产业化推广已成为迫在眉睫的任务。在项目建设标准和融资要求高,垃圾处理费低和投资回收期长等多重压力下,通过对垃圾焚烧发电系统进行逐步、分项的设计优化,利用最新技术使资源得到高效深度利用,可以有效降低工程建设成本,提高项目运营经济性,实现垃圾减量化、无害化和资源化,对垃圾发电长远健康发展具有参考价值。     

基于分布式光伏发电的多目标分时电价优化策略

现有电力定价研究大多为峰谷分时定价,时段划分方式单一且大多采用传统非支配排序遗传算法-II求解多目标问题。针对这个问题,提出一种基于分布式光伏发电的多目标分时电价优化策略。建立用电量与电价响应模型,基于等效负荷进行时段划分,以负荷方差最小,等效负荷的峰谷差最小,用户满意度指数最大为目标,建立多目标非线性分布式光伏分时定价模型,并提出基于邻域搜索的多目标遗传算法求解。数值实验结果表明,供电稳定性提高了37.77%,分布式光伏发电的利用率提高了4.51%,用户满意度为74.3%;且提出的求解算法要优于常用的非支配排序遗传算法-II,表明本文提出的定价策略是有效的。     

星载可展开网状天线的网面成形与防缠绕设计

由网状反射面和可展开桁架结构构成的大型可展开网状天线是卫星通讯的有效工具。系统介绍了星载可展开网状天线的网面成形设计,并提出了几种有效的网状天线防缠绕设计方案。根据这些设计方法,利用FORTRAN语言编制了抛物面索网的网格优化程序,并成功设计制造了两种不同网格形式的缩比天线模型,进行了初步试验分析,验证了防缠绕设计的有效性,从而能够为类似的可展开网状天线设计提供重要的参考依据。     

Mesh generation and adaptivity for the solution of compressible viscous high speed flows

An implicit–explicit procedure for the solution of the compressible Navier–Stokes equations on unstructured triangular and tetrahedral meshes is outlined. A procedure for constructing continuous lines, made up of edges in the mesh, is employed and the implicit equation system is solved via line relaxation. The problem of generating, and adapting, unstructured meshes for viscous flow simulations is addressed. A number of examples are included which demonstrate the numerical performance of the proposed procedures.     

A new scheme for efficient and direct shape optimization of complex structures represented by polygonal meshes

In this paper, a new shape optimization approach is proposed to provide an efficient optimization solution of complex structures represented by polygonal meshes. Our approach consists of three main steps: (1) surface partitioning of polygonal meshes; (2) generation of shape design variables on the basis of partitioned surface patches; and (3) gradient‐based shape optimization of the structures by reducing a weighted compliance among all load cases. The main contributions of this paper include (i) that our approach can be directly applied on polygonal meshes with the reduction of design variables or decision variables by 10 to 1000 times, compared to the conventional design variable scheme of using each mesh node; (ii) our perturbation scheme is mathematically proven with respect to maintaining the smoothness of each surface patch, except on its boundary; and (iii) overall, our approach can be used to automate time‐consuming shape optimization of polygonal meshes to a greater extent. Numerical experiments have been conducted and the results indicate the effectiveness of the approach. Copyright © 2003 John Wiley & Sons, Ltd.     

Unification of parametric and implicit methods for shape sensitivity analysis and optimization with fixed mesh

Parametric and implicit methods are traditionally thought to be two irrelevant approaches in structural shape optimization. Parametric method works as a Lagrangian approach and often uses the parametric boundary representation (B‐rep) of curves/surfaces, for example, Bezier and B‐splines in combination with the conformal mesh of a finite element model, while implicit method relies upon level‐set functions, that is, implicit functions for B‐rep, and works as an Eulerian approach in combination with the fixed mesh within the scope of extended finite element method or finite cell method. The original contribution of this work is the unification of both methods. First, a new shape optimization method is proposed by combining the features of the parametric and implicit B‐reps. Shape changes of the structural boundary are governed by parametric B‐rep on the fixed mesh to maintain the merit in computer‐aided design modeling and avoid laborious remeshing. Second, analytical shape design sensitivity is formulated for the parametric B‐rep in the framework of fixed mesh of finite cell method by means of the Hamilton–Jacobi equation. Numerical examples are solved to illustrate the unified methodology. Copyright © 2016 John Wiley & Sons, Ltd.     

拖钩套筒复合冷挤压数值模拟与毛坯优化

将挤压模具视为刚体,采用有限元分析软件MARC,对拖钩套筒零件进行了冷挤压过程的数值模拟计算。根据各主要阶段等效应力及等效应变的分布,总结了挤压过程中金属材料塑性流动的规律。以最大挤压力为目标,对毛坯的尺寸进行了优化,为挤压工艺的改善提供了依据。根据计算结果,得出了挤压完成后零件所受最大主应力数值及其分布规律,为后期模具强度的研究奠定了基础。