三维六角形粗网格中子扩散计算方法

本文介绍对于由六角形栅元组件组成的核反应堆堆芯,采用三维粗网格展开法求解中子扩散方程,推导出九点高阶近似差分方程。该方程形式上与低阶有限差分方程类似,可以采用低阶有限差分法的求解技巧求解,所建立的方法适用于两维或三维中子扩散计算,对堆芯设计和燃耗分析很有意义。     

The boundary fitted coordinate method to improve the numerical analysis of electron optical systems

This paper illustrates some of the advantages of using the boundary fitted coordinate technique in the numerical simulation of electron-optical systems. The boundary fitted coordinate technique can be used as an automatic mesh generator for the finite-element solution of field distributions, while at the same time allowing for the possibility of high order inter-polation on the mesh, typically required for the accurate plotting of electron trajectory paths. For the finite difference method of solving field distributions, the boundary fitted coordinate method can generate regular meshes, which fit curved shaped boundaries.     

新一代电力通信宽带综合传送网建网探讨

介绍了我国电力通信专用网的现状和未来发展趋势,论述了我国电力通信专用网骨干网“十五”建设目标,并就我国新一代电力通信宽带综合传送网建网问题进行了探讨。     

Time-dependent behavior of fine-grained model material in resonant column experiments

Cyclic shear experiments with saturated and dry fine-grained corundum powder, i.e. -Al₂O₃ particles, have been conducted in a resonant column device. After an increase of total pressure the shear stiffness showed a slight decrease and a subsequent increase with time. The equivalent viscous damping ratio followed an opposite trend. The increase of shear stiffness with time did not stop after the end of primary consolidation, which cannot be explained with the slight reduction of void ratio during secondary consolidation. Stiffening of grain contacts through different dissolution-precipitation mechanisms and creep at particle contacts can explain the increase of shear stiffness with time, which has also been observed in natural soils by other researchers. Smaller rates of stiffness increase of dry samples support the idea of dissolution-precipitation mechanisms in the pore water. Higher rates for samples with smaller particles show an effect of surface-to-volume ratio.The study described in this paper was sponsored by the German Research Council (DFG), Research Group FOR 371-2. The support is gratefully appreciated.We would like to thank Professor Gudehus for many interesting discussions and valuable advice.We thank the Institute of Mechanical Process Engineering and Mechanics and the Laboratory for Electron Microscopy, University of Karlsruhe, for providing the electron micrographs and the Institute for Ceramics in Mechanical Engineering for the grain size distribution.     

A fast robust algorithm for the intersection of triangulated surfaces

The use of discrete data to represent engineering structures as derivatives from intersecting components requires algorithms to perform Boolean operations between groups of triangulated surfaces. In the intersection process, an accurate and efficient method for the determination of intersection lines is a crucial step for large scale and complex surface intersections. An algorithm based on tracing the neighbours of intersecting triangles (TNOIT) is proposed to determine the intersection lines. Given the node numbers at the vertices of the triangles, the neighbour relationship is first established. A background grid is employed to limit the scope of searching for candidate triangles that may intersect. This will drastically reduce the time of geometrical checking for intersections between triangles, making the surface intersection and mesh generation a quasi-linear process with respect to the number of elements involved. In the determination of intersection between two triangles, four fundamental cases are identified and treated systematically to enhance robustness and reliability. Tracing the neighbours for the determination of intersection lines not only greatly increases the efficiency of the process, it also improves the reliability as branching and degenerated cases can all be dealt with in a consistent manner on the intersecting surfaces concerned. Five examples on a great variety of surface and mesh characteristics are given to demonstrate the effectiveness and robustness of the algorithm.     

An adaptive mesh refinement of quadrilateral finite element meshes based upon an a posteriori error estimation of quantities of interest: modal response

Modal analysis is commonly performed in a vehicle development process to assess dynamic responses of structure designs. This paper presents an adaptive quadrilateral refinement process for modal analysis of elastic shells based upon a posteriori error estimation in natural frequencies. The process provides engineers with an estimation of their modal analysis quality and an effective adaptive refinement tool for quadrilateral meshes. The effectiveness of the process is demonstrated on the eigenvalue analyses of two numerical examples, a shock tower cap and a roof structure. It shows that the solution error in the frequency of interest is effectively reduced through the adaptive refinement process, and the resulting frequency of interest converges to the solution of a very fine model.     

Improving surface meshing from discrete data by feature recognition

In this paper, we propose a method to identify, on a mesh, geometric primitives commonly used in mechanical parts (plane, sphere, cylinder, torus, cone) in order to improve the quality of the surface remeshing. We have already presented techniques to adapt an existing surface mesh based on a mesh-free technique denoted as diffuse interpolation. In this approach, a secondary local geometrical model is built from the mesh. From this model, principal curvatures are calculated and the type of surface can be determined from the computation of the curvatures. Some of the concepts presented here are original while others have been adapted from techniques used in reverse engineering. Our approach is not limited to feature recognition on meshes but has been extended to a set of points.     

A weighted mean approach to smooth parametric representation of polygon meshes

A method for representing genus-zero polygon meshes by smooth parametric surfaces is described. A surface is defined by a weighted sum of linear functions, each describing a polygon face in parametric form. Rational Gaussian blending functions that adapt to the size and shape of mesh faces are used as the weights. The proposed representation has a very high degree of continuity everywhere and provides a smoothness parameter that can be varied to produce surfaces at varying resolutions. It is shown that the representation facilitates geometry processing of meshes. The use of locally supported weight functions as an alternative to rational Gaussian weights is also discussed.     

On fault tolerance of 3-dimensional mesh networks

In this paper, the concept of k-submesh and k-submesh connectivity fault tolerance model is proposed. And the fault tolerance of 3-D mesh networks is studied under a more realistic model in which each network node has an independent failure probability. It is first observed that if the node failure probability is fixed, then the connectivity probability of 3-D mesh networks can be arbitrarily small when the network size is sufficiently large. Thus, it is practically important for multicomputer system manufacturer to determine the upper bound for node failure probability when the probability of network connectivity and the network size are given. A novel technique is developed to formally derive lower bounds on the connectivity probability for 3-D mesh networks. The study shows that 3-D mesh networks of practical size can tolerate a large number of faulty nodes thus are reliable enough for multicomputer systems. A number of advantages of 3-D mesh networks over other popular network topologies are given.