基于MLS点云模型特征的提取算法

针对以往特征提取算法提取边界特征效果不理想和特征识别时间较长的问题,提出了一种改进的点云模型特征边界线提取算法.该算法以移动最小二乘法为基础,在对已有的边界特征提取方法研究的基础上,结合研究对象棱角分明的特点,提取点云模型边界特征点集,利用双向搜索方法快速生成模型的特征边界线,并对得到的特征边界线进行特征修复,从而得到较为稳定的点云模型的特征边界线.实验结果表明,该算法能快速地提取点云模型的特征边界线,为后续基于特征边界的建模节约了大量时间.     

应用WEMLS的安全数据集成模型

针对现有的安全域存在许多异构安全数据需要集成的问题,引入多级安全策略(MLS)的思想,提出一种应用扩展权值MLS策略(WEMLS)的安全数据集成模型。定义可信权值的概念,建立进程授权机制和信任计算机制。应用结果表明,该模型能使可信进程更灵活地访问客体。     

MLS‐based variable‐node elements compatible with quadratic interpolation. Part I: formulation and application for non‐matching meshes

Two‐dimensional variable‐node elements compatible with quadratic interpolation are developed using the moving least‐square (MLS) approximation. The mapping from the parental domain to the physical element domain is implicitly obtained from MLS approximation, with the shape functions and their derivatives calculated and saved only at the numerical integration points. It is shown that the present MLS‐based variable‐node elements meet the patch test if a sufficiently large number of integration points are employed for numerical integration. The cantilever problem with non‐matching meshes is chosen to check the feasibility of the present MLS‐based variable‐node elements, and the result is compared with that from the lower‐order case compatible with linear interpolation. Copyright © 2005 John Wiley & Sons, Ltd.     

The intrinsic XFEM: a method for arbitrary discontinuities without additional unknowns

A new method for treating arbitrary discontinuities in a finite element (FE) context is presented. Unlike the standard extended FE method (XFEM), no additional unknowns are introduced at the nodes whose supports are crossed by discontinuities. The method constructs an approximation space consisting of mesh‐based, enriched moving least‐squares (MLS) functions near discontinuities and standard FE shape functions elsewhere. There is only one shape function per node, and these functions are able to represent known characteristics of the solution such as discontinuities, singularities, etc. The MLS method constructs shape functions based on an intrinsic basis by minimizing a weighted error functional. Thereby, weight functions are involved, and special mesh‐based weight functions are proposed in this work. The enrichment is achieved through the intrinsic basis. The method is illustrated for linear elastic examples involving strong and weak discontinuities, and matches optimal rates of convergence even for crack‐tip applications. Copyright © 2006 John Wiley & Sons, Ltd.     

A boundary element-free method (BEFM) for three-dimensional elasticity problems

This study combines the boundary integral equation (BIE) method and improved moving least-squares (IMLS) approximation to present a direct meshless boundary integral equation method, the boundary element-free method (BEFM) for three-dimensional elasticity. Based on the improved moving least-squares approximation and the boundary integral equation for three-dimensional elasticity, the formulae of the boundary element-free method are given, and the numerical procedure is also shown. Unlike other meshless boundary integral equation methods, the BEFM is a direct numerical method in which the basic unknown quantity is the real solution of the nodal variables, and the boundary conditions can be applied directly and easily, thus giving it a greater computational precision. Three selected numerical examples are presented to demonstrate the method.Aknowledgement The work in this project was fully supported by a grant from the Research Grants Council (RGC) of the Hong Kong Special Administrative Region, China (Project No. CityU 1011/02E).The work that is described in this paper was supported by Project No. CityU 1011/02E, which was awarded by the Research Grants Council of the Hong Kong Special Administrative Region, China. The authors are grateful for the financial support.     

网络GIS技术发展探讨

网络GIS经过多年发展技术体系日趋成熟，但在网络技术、计算机技术、图像图形技术、通讯技术等相关领域的理论和技术不断进步的情况下，网络GIS又面对着新的发展机遇。本文结合几种可在网络GIS开发中应用的新技术，讨论了网络GIS的下一步发展。本文认为空间元数据共享模型、GML与SVG、互操作模型、虚拟地理环境和MLS将会是网络GIS的重点研究方向。     

On Logical Foundations of Multilevel Secure Databases

It is envisaged that the application of the multilevel security (MLS) scheme will enhance flexibility and effectiveness of authorization policies in shared enterprise databases and will replace cumbersome authorization enforcement practices through complicated view definitions on a per user basis. However, the critical problem with the current model is that the belief at a higher security level is cluttered with irrelevant or inconsistent data as no mechanism for attenuation is supported. Critics also argue that it is imperative for MLS database users to theorize about the belief of others, perhaps at different security levels, an apparatus that is currently missing and the absence of which is seriously felt.The impetus for our current research is the need to provide an adequate framework for belief reasoning in MLS databases. In this paper, we show that these concepts can be captured in a F-logic style declarative query language, called MultiLog, for MLS deductive databases for which a proof theoretic, model theoretic and fixpoint semantics exist. This development is significant from a database perspective as it now enables us to compute the semantics of MultiLog databases in a bottom-up fashion. We also define a bottom-up procedure to compute unique models of stratified MultiLog databases. Finally, we establish the equivalence of MultiLog's three logical characterizations—model theory, fixpoint theory and proof theory.     

基于ANSYS二次开发的高阶连续梁数值模拟

为解决有限元软件对高阶连续结构数值模拟的局限性问题,利用有限元软件ANSYS提供的UELMatx.F用户自定义程序,将高阶连续理论及尺度因子概念引入到ANSYS进行计算分析,实现移动最小二乘法(MLS)在有限元软件中的应用。并以高阶连续梁为例,验证了该方法的可行性。     

Self‐adaptive 3D pairwise view registration by surface‐fitting and hill‐climbing method

A self‐adaptive 3D pairwise view registration method is presented. Coarse registration of neighboring views is achieved according to their common continuous nonflat areas. These areas are calculated by local least‐square (LS) surface fitting. Then, the principle of point‐to‐surface projection is used to search for the corresponding points, where the local moving least‐square (MLS) surface is employed. Finally, multidimensional optimization based on the technique of hill‐climbing is performed to refine the coarse registration. Experimental results show that this method gives good noise immunity and requires simple computation process and very few manual interventions. Thus it is suitable for large‐scale free‐form surfaces lacking obvious geometric characteristics. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

移动最小二乘法在液压泵/马达特性曲线绘制中的应用

介绍一种新的液压泵/液压马达特性曲线(等功率曲线、等效率曲线、综合特性曲线等)的绘制方法,即利用移动最小二乘法对液压泵/马达的特性曲线进行拟合.所得到的特性曲线具有拟合精度高、通用性强等特点.最后在MATLAB中编制程序并给出了曲线绘制实例.