基于有向距离场的代数B-样条曲线重建

提出了一种以代数B-样条曲线为表达形式、基于有向距离场的隐式曲线重建方法.首先给定一个表示封闭曲线、可能带有噪音且分布不均匀的平面点云,采用移动最小平方(moving least square,简称MLS)方法对点云去噪、重采样,得到一个低噪音、分布均匀的\"线状\"点云,再通过Level Set方法建立该\"线状\"点云的离散几何距离场,最后用一个代数B-样条函数光顺拟合该离散距离场,代数函数的零点集即为重建曲线.曲线重建过程可以归结为求解线性方程组问题.这种重建方法不仅可以得到高质量的重建曲线,还可以得到曲线周围的距离场信息.同时,避免了隐式曲线重建中经常出现的多余分支问题.     

杂交型无网格有限体积法及其应用

从有限体积法基本思想出发,采用移动最小二乘近似方案实现有限体积法与无网格法的结合,从而使有限体法摆脱网格的约束,在此基础上,提出杂交型无网格有限体积法,所谓杂交是指对位移和应力都分别进行独立插值,这样可避免在子域积分过程中被积函数出现形函数的偏导数。至于应力和位移之间的协调关系则通过配点法强制实现,采用修正配点法施加本质边界条件。算例结果表明,该方法具有很高的精度和计算效率。     

MLS地面设备的检验平台位置基准测量技术研究

在MLS地面设备检验过程中,测角与测距专用测试设备解算出接收绂射天线的位置数值后,需要和接收／发射天线的位置数值的真值进行比较,得到MLS地面设备的系统误差。本文对MLS地面设备位置基准测量技术进行了研究,提出了位置真值的测量方法。     

基于XML的数据客体与安全标记绑定方法

安全标记与数据客体的绑定,是制约多级安全真正走向网络实用化的关键问题。针对这一问题,在深入分析XML的基础上,描述了XML客体安全标记及其约束规则,提出了安全标记与数据客体的绑定方法,讨论了安全标记查询、客体内容裂解等相关操作,给出了基于XML安全标记的安全通信实施机制。该绑定方法不仅能够满足多级信息系统间安全通信的需要,而且能够实施粒度更细的访问控制,提高信息客体的利用率。     

微波着舰引导设备动态校验系统设计与技术实现

微波着舰引导系统是一种高精度的舰载航空导航系统,在引导舰载机安全着舰过程中发挥着不可替代的作用。为确保微波着舰引导设备引导的精准度和运行的可靠性,必须对其开展定期或不定期的动态飞行校验工作。针对微波着舰引导设备的动态飞行校验问题,结合飞行校验基准的精度指标要求,研究提出了飞行校验系统的总体结构设计方案,重点研究了基于移动基准站实时动态载波相位差分定位(MB-RTK)的校验基准获取以及校验数据的误差处理等关键技术。通过计算机仿真和飞行实验数据,验证了校验系统设计与技术实现的可行性和有效性。研究成果对提高微波着舰引导设备的安全性与可靠性具有较好的军事应用价值和推广前景。     

MLS3626生料立磨调试期出现的问题及处理

山东泉兴水泥有限公司5000t/d熟料生产线生料磨系统配套了两台MLS3626立磨,调试初期出现了较多问题因而延长了整条生产线的调试期。文章对立磨运行中出现的13个方面的问题进行了表象描述、原因分析和处理措施介绍,通过一段时间的磨合,该MLS3626立磨事故率得以不断降低,运转率得以不断提高。     

Transient heat conduction analysis in functionally graded materials by the meshless local boundary integral equation method

Advanced computational method for transient heat conduction analysis in continuously nonhomogeneous functionally graded materials (FGM) is proposed. The method is based on the local boundary integral equations with moving least square approximation of the temperature and heat flux. The initial-boundary value problem is solved by the Laplace transform technique. Both Papoulis and Stehfest algorithms are applied for the numerical Laplace inversion to obtain the time-dependent solutions. Numerical results are presented for a finite strip and a hollow cylinder with an exponential spatial variation of material parameters.     

An analysis of the convection-diffusion problems using meshless and meshbased methods

The numerical solution of the convection-diffusion equation represents a very important issue in many numerical methods that need some artificial methods to obtain stable and accurate solutions. In this article, a meshless method based on the local Petrov-Galerkin method is applied to solve this equation. The essential boundary condition is enforced by the transformation method, and the MLS method is used for the interpolation schemes. The streamline upwind Petrov-Galerkin (SUPG) scheme is developed to employ on the present meshless method to overcome the influence of false diffusion. In order to validate the stability and accuracy of the present method, the model is used to solve two different cases and the results of the present method are compared with the results of the upwind scheme of the MLPG method and the high order upwind scheme (QUICK) of the finite volume method. The computational results show that fairly accurate solutions can be obtained for high Peclet number and the SUPG scheme can very well eliminate the influence of false diffusion.     

Mixed discrete least squares meshless method for planar elasticity problems using regular and irregular nodal distributions

A Mixed Discrete Least Square Meshless (MDLSM) method is proposed for the solution of planar elasticity problems. In this approach, the differential equations governing the planar elasticity problems are written in terms of the stresses and displacements which are approximated independently using the same shape functions. Since the resulting governing equations are of the first order, both the displacement and stress boundary conditions are of the Dirichlet-type which is easily incorporated via a penalty method. Because least squares based algorithm of MDLSM method, the proposed method does not need to be satisfied by the LBB condition. The performance of the proposed method is tested on a benchmark example from theory of elasticity namely the problem of infinite plate with a circular hole and the results are presented and compared with those of the analytical solution and the solutions obtained using the irreducible DLSM formulation. The results indicate that the proposed MDLSM method is more accurate than the DLSM method. The results show that the numerical solutions of the MDLSM method can be obtained with lower computational cost and with higher accuracy. Also its performance is marginally affected by the irregularity of the nodal distribution.