Comparison of numerical methods for identification of viscoelastic line spectra from static test data

Viscoelastic line spectra are identified from creep or relaxation data of static experiments with different numerical methods, which may or may not depend on additional informations, to be provided by the user, about the unknown parameters. If the least square method is applied, a non‐linear optimization problem with non‐negative constraints on the parameters has to be solved. Its solution can be achieved directly by using a gradient‐based optimization algorithm like the projected Newton method of Bertsekas. However, appropriate starting values for the unknown parameters must be chosen. The problem can be alleviated by dividing the identification task into three successive steps, based on the Tschebyscheff approximation and the quadratic optimization method by Wolfe. Alternatively, the identification task can be reduced to a quadratic optimization problem, if the user provides additional informations about the distribution of the respondance times of the spectra. The windowing‐method of Emri and Tschoegl is based on this assumption. If the line spectrum is assumed to have equally distributed spectrum lines on the logarithmic axis, the identification problem can also be solved by standard regularization techniques, like the truncated singular value decomposition or the Tikhonov regularization. The choice of qualified respondance times as additional information requires some experience with the identification task at hand. Its results may be improved after several reruns of the algorithms. Various applications of the methods to test and experimental data are given and a comparison of their performance is discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

Direct solution of ill‐posed boundary value problems by radial basis function collocation method

Numerical solution of ill‐posed boundary value problems normally requires iterative procedures. In a typical solution, the ill‐posed problem is first converted to a well‐posed one by assuming the missing boundary values. The new problem is solved by a conventional numerical technique and the solution is checked against the unused data. The problem is solved iteratively using optimization schemes until convergence is achieved. The present paper offers a different procedure. Using the radial basis function collocation method, we demonstrate that the solution of certain ill‐posed problems can be accomplished without iteration. This method not only is efficient and accurate, but also circumvents the stability problem that can exist in the iterative method. Copyright © 2005 John Wiley & Sons, Ltd.     

论计算运动学在机构理论中的作用

简述了计算运动学的发展过程，论述了计算运动学的基础理论，并利用两个实例展现了计算运动学在机构运动分析中的作用。最后以转向机构综合为例，对比传统综合方法和现代计算运动学方法的特点。结果表明：计算运动学方法在寻找所有解，精度和系统性等方面具有较大的优势。     

关于隐函数存在定理的一个推广

本文推广了非线性泛涵中的隐函数存在定量，并将此定理应用到反函数，得到反函数存在定理的推广。     

Frobenius矩阵的逆与相似化简

介绍了Frobenius矩阵的概念,讨论了Frobenius矩阵的可逆性及其它的相似化简。     

两栖仿生机器蟹行走过程运动学研究

螃蟹具有8足步行机特征，在行走过程中，每条腿都是抬起和着地两种状态交替变化，抬起的腿从躯体上看是开链机构，相当串联手臂．而同时着地的腿与躯体构成并联多闭链多自由度机构．这种行走过程，从机构学角度看就是不同分支并联机构及串联开链机构之间的不断变化的复合型机构．针对这种机构我们采用串并联综合分析的方法，提出运动学算法及计算机仿真验证方法．通过计算机仿真验证了该方法分析结果的正确性，得出了一种用于仿生机器蟹行走过程运动学研究的行之有效的分析方法．     

正则化广义逆ERT 图像重建算法的研究

提出一种正则化广义逆ERT图像重建算法，利用ERT仿真软件得到的数据进行图像重建。与常用的ERT图像重建算法进行比较，重建出的图像经过统一的门限滤波后，反投影算法、灵敏度系数算法和正则化广义逆ERT图像重建算法重建图像的CSIE平均值分别为12％，9％和6％。研究表明，正则化广义逆ERT图像重建算法重建速度快，能显著提高重建图像的质量，适合于工业过程应用。     

A Self-Tuning Evolutionary Algorithm Applied to an Inverse Partial Differential Equation

Evolutionary algorithms (EAs) are becoming increasingly popular tools for solving complex search problems. Their popularity in various problem domains has led to the introduction and development of numerous variants of two standard EA operators—crossover and mutation. Unfortunately, there are few if any effective guidelines for choosing which operators will be most effective in a given problem. In this paper, a self-tuning EA is introduced that employs several crossover and mutation operators simultaneously. The probability of using a given operator changes during the course of an evolutionary run whereby the most effective operators are selected based on which part of the search space is currently being explored. The self-tuning EA is used to solve an inverse partial differential equation—considered to be one of the more difficult problems in the realm of engineering mathematics. Results indicate that for the particular inverse partial differential equation considered, the self-tuning EA provides an effective solution methodology.     

基于足迹采样的运动编辑

针对人体两足动画提出一种基于足迹采样的运动编辑算法．足迹很好地描述了两足动画中必须满足的时空约束，通过调整足迹的位置与朝向来编辑两足动画是一种较为自然、直观的交互方式．为有效、快速地生成编辑后的动画，采用一种实时的逆向运动学算法求解两足动画中的支撑脚约束，然后使用层次B样条技术构造偏移映射完成编辑．为了便于逆向运动学算法的求解，提出基于采样的方法来计算质心轨迹．     

一种高效的逆半调算法

论文提出了一种快速的逆半调算法,在高斯低通滤波的基础上,通过带通滤波提取边界信息,并使用界限函数和中值滤波修正边界映像,最后合成逆半调结果。实验证明该算法和现有算法相比计算速度快,输出图像信噪比高。