On using degenerated solid shell elements in adaptive refinement analysis

Three different degenerated shell elements are studied in an adaptive refinement procedure for the solution of shell problems. The stress recovery procedure expressed in a convective patch co‐ordinate system is used for the construction of continuous smoothed stress fields for the a posteriori error estimation. The performance of the stress recovery procedure, the error estimator and the adaptive refinement strategy are tested by solving three benchmark shell problems. It is found that when adaptive refinement is used, the adverse effects of boundary layers and stress singularities are eliminated and all the elements tested are able to achieve their optimal convergence rates. It is also found that the accuracy of the shell elements increases with the number of polynomial terms included in the stress and strain approximations. In addition, if complete Lagrangian polynomial terms are used, the element will be less sensitive to shape distortion than the one in which only complete polynomial terms are employed. Copyright © 1999 John Wiley & Sons, Ltd.     

On the discrete core of quadrilateral mesh refinement

We present a new approach to quadrilateral mesh refinement, which reduces the problem to its structural core. The resulting problem formulation belongs to a class of discrete problems, network‐flow problems, which has been thoroughly investigated and is well understood. The network‐flow model is flexible enough to allow the simultaneous incorporation of various aspects such as the control of angles and aspect ratios, local density control, and templates (meshing primitives) for the internal refinement of mesh elements. We show that many different variants of the general quadrilateral mesh‐refinement problem are covered. In particular, we present a novel strategy, which provably finds a conformal refinement unless there is none. Copyright © 1999 John Wiley & Sons, Ltd.     

Acceleration radiosity solutions through the use of hemisphere-base formfactor calculation

In this paper, we propose a novel formfactor calculation algorithm for acceleration radiosity solutions in complex environments. Our basic algorithm is an improved version of Spencer's (S.N. Spencer, ‘The hemisphere radiosity method: a tale of two algorithms’, in Photorealism in Computer Graphics, Spencer, 1992, pp. 127–135) and Van Wyk's (G.C. Van Wyk Jr., ‘A geometry-based insolution model for computer-aided design,’ Ph.D. Thesis, The University of Michigan, 1998.) methods, which fail to remove hidden surfaces for relatively large patches and cause large discretization errors in formfactors. We also demonstrate that our technique is superior to the hemi-cube method in terms of the computation time. Moreover, we parallelize our approach on a parallel computer with shared memory, and obtain a high performance with our radiosity rendering system. Our method divides a hemisphere-base into regions, and assigns a region to each processor. The approach can be applied to geometrical data generated by CAD systems, and is evaluated in terms of the computation time, the visual effects, and the parallelization performance. © 1998 John Wiley & Sons, Ltd     

一种基于域内的访问控制策略提炼模型及其实现

以CERNET的管理为应用背景,从分析策略管理系统的关键技术和难点问题入手,提出了一种新的策略提炼模型。其原理是利用ACL的特性,将不同策略语言表示的策略映射到ACL,再分发给不同的网络设备运行。该方案简化了传统策略提炼过程中复杂的转换逻辑问题,使基于域内的安全和访问控制管理完全实现自动化。     

大庆原油基础油研制新一代高档汽油机油

根据大庆原油基础油的特性（粘度指数高,倾点高,低温性能差,抗氧化性能稍差）,采用改善常减压切割、改进精制工艺技术,提高基础油主要性能,研制出质量符合ＡＰＩＳＪ／ＩＬＳＡＣＧＦ２的汽油机油。     

Spray Formed Al MMCs via In‐situ Reactions

Reactive spray atomization and deposition processing is currently being studied as an approach for the in‐situ synthesis of Al metal matrix composites (MMCs). In the present paper, the latest developments in this field are reviewed, with an emphasis on in‐situ reaction kinetics, grain size refinement and mechanisms, and superplastic forming behavior; and future work is also discussed.     

三维有限元网格自动生成典型方法与发展方向

经过对大量三维有限元网格自动生成算法文献的分析,对典型的三维有限元网格自动生成算法进行了归纳总结,同时总结了目前常用的网格优化方法,最后简述了三维有限元网格自动生成算法的发展趋势。     

Automatic adaptive refinement for plate bending problems using Reissner–Mindlin plate bending elements

The influence of the presence of singular points and boundary layers associated with the edge effects in a Reissner–Mindlin (RM) plate in the design of an optimal mesh for a finite element solution is studied, and methods for controlling the discretization error of the solution are suggested. An effective adaptive refinement strategy for the solution of plate bending problems based on the RM plate bending model is developed. This two-stage adaptive strategy is designed to control both the total and the shear error norms of a plate in which both singular points and boundary layers are present. A series of three different order assumed strain RM plate bending elements has been used in the adaptive refinement procedure. The locations of optimal sampling points and the effect of element shape distortions on the theoretical convergence rate of these elements are given and discussed. Numerical experiments show that the suggested refinement procedure is effective and that optimally refined meshes can be generated. It is also found that all the plate bending elements used can attain their full convergence rates regardless of the presence of singular points and boundary layers inside the problem domain. Boundary layer effects are well captured in all the examples tested and the use of a second stage of refinement to control the shear error is justified. In addition, tests on the Zienkiewicz–Zhu error estimator show that their performances are satisfactory. Finally, tests of the relative effectiveness of the plate bending elements used have also been made and it is found that while the higher order cubic element is the most accurate element tested, the quadratic element tested is the most efficient one in terms of CPU time used. © 1998 John Wiley & Sons, Ltd.     

TiAl合金片层组织的形成与细化工艺及其机理研究

利用金相显微镜、扫描和透射电镜等仪器表征了TiAl合金的片层组织及结构特征,研究了Ti-48Al at%合金片层组织的形成机制和片层组织细化工艺及其机理。结果表明,Ti-48Al合金单级热处理能够得到全片层组织,平均晶粒尺寸约150μm,片层间距约1.30μm。其形成过程是:γ相在α相晶内(0001)面上通过全位错分解成核,通过不全位错滑移、层错区扩展而长大。循环热处理和双温热处理均能将片层晶粒尺寸细化到30μm,片层间距0.90μm,前者的细化机理为相变重结晶细化了α相晶粒,后者细化片层组织的关键在于低温段(α2+γ)两相区热处理形成细小的双态组织。     

戈尔膜过滤器成功应用于盐水精制

介绍山东滨化集团有限公司将戈尔膜过滤器应用于盐水精制工艺改造的成功实例,说明该工艺的应用将有力推动我国氯碱行业的发展.