A study on X-FEM in continuum structural optimization using a level set model

In this paper, we implement the extended finite element method (X-FEM) combined with the level set method to solve structural shape and topology optimization problems. Numerical comparisons with the conventional finite element method in a fixed grid show that the X-FEM leads to more accurate results without increasing the mesh density and the degrees of freedom. Furthermore, the mesh in X-FEM is independent of the physical boundary of the design, so there is no need for remeshing during the optimization process. Numerical examples of mean compliance minimization in 2D are studied in regard to efficiency, convergence and accuracy. The results suggest that combining the X-FEM for structural analysis with the level set based boundary representation is a promising approach for continuum structural optimization.     

A survey on various computational techniques for nonlinear elliptic boundary value problems

In this paper a classification and a survey on numerical techniques for solving nonlinear (quasilinear, semilinear, superlinear, sublinear) elliptic boundary value problems between 2001 and 2006 have been presented and discussed the nature of positive solution of the various problems. The introduction of the methods and results presented by different researchers are summarized.     

Greedy algorithms for eigenvalue optimization problems in shape design of two-density inhomogeneous materials

This paper studies the eigenvalue optimization problems in the shape design of the two-density inhomogeneous materials. Two types of greedy algorithms are proposed to solve three optimization problems in finite element discretization. In the first type, the whole domain is initialized by one density. For each problem of the eigenvalue optimizations, we define a measurement of the element, which is the criterion to determine the ‘best’ element. We change the density of the ‘best’ element to the other density. Then the algorithm repeats the procedure until the area constraint is satisfied. In the second type, the algorithm begins with the density distribution satisfying the area constraint. Also, according to the measurement of the element, the algorithm finds a pair of the ‘best’ elements and exchanges their densities between each other. Furthermore, the accelerating greedy algorithms are proposed to speed up both two types. Three numerical examples are provided to illustrate the results.     

三肢体机器人足部力传感器弹性体分析

提出将传感器传递矩阵条件数和行范数两项指标综合的方法,对一种三肢体机器人的足部三维力传感器弹性体结构进行优化,使传感器在具有低传递误差的同时具有较高的灵敏度.并应用有限元法分析了弹性体各结构尺寸对传感器性能的影响,得到了弹性体在单向受力时的应力、应变分布状态及其静、动态特性,为传感器的结构设计和进一步分析提供了依据.     

基于凸规划方法的计算机辅助结构拓扑优化设计

基于SIMP密度-刚度插值模型和移动渐近线方法,推导并建立了线弹性连续体结构刚度拓扑优化设计的数学模型．对中间密度材料进行研究,得出了惩罚因子的合理取值范围,分析了棋盘格式和网格依赖性等数值计算中存在的问题,并结合一种敏度过滤技术改善了这些问题．给出文中方法的程序流程,开发出二维结构的拓扑优化系统,通过一些经典的算例,证明了文中方法的有效性．     

基于固定内存和状态管理的模型检测方法*

在研究固定内存和状态管理的基础上,提出了一种新的模型检测方法,使得在任何计算机上都能对任意规模的并发系统进行模型检测.     

An adaptive wavelet collocation method for solving optimal control of elliptic variational inequalities of the obstacle type

This paper presents a fast computational technique based on the wavelet collocation method for the numerical solution of an optimal control problem governed by elliptic variational inequalities of obstacle type. In this problem, the solution divides the domain into contact and noncontact sets. The boundary between the contact and noncontact sets is a free boundary, which is not known a priori and the solution is not smooth on it. Accordingly, a very fine grid is needed in order to obtain a solution with a reasonable accuracy. In this paper, our aim is to propose an adaptive scheme in order to generate an appropriate and economic irregular dyadic mesh for finding the optimal control and state functions. The irregular mesh will be generated such that its density around the free boundary is higher than in other places and high-resolution computations are focused on these zones. To this aim, we use an adaptive wavelet collocation method and take advantage of the fast wavelet transform of compact-supported interpolating wavelets to develop a multi-level algorithm, which generates an adaptive computational grid. Using this adaptive grid takes less CPU time than using a full regular mesh. At each step of the algorithm, the active set method is used for solving the optimality system of the obstacle problem on the adapted mesh. Finally, the numerical examples are presented to show the validity and efficiency of the technique.     

Modeling of steady state hot flow behavior of API-X70 microalloyed steel using genetic algorithm and design of experiments

API-X70 microalloyed steel is one of the most conventional materials that has been used to produce the pipelines used in oil and gas industry. This steel is produced by thermo mechanical processing (TMP). Prediction of steady state hot flow behavior of metals during TMP, for design of its forming process is of great importance. In this research, flow curves of API-X70 were obtained using hot torsion test at temperature range of 950–1150 °C and strain rates of 0.001–3 s⁻¹. Genetic algorithm (GA) was used to find parameters of steady state stress semi-empirical model in the way that minimizing the difference between experimental data and model output. The optimal combination of GA parameters were chosen by Taguchi design of experiments(DOE) method in order to increase efficiency of GA. Accuracy of developed model to predict flow stress in steady state region was evaluated through statistical methods. Results showed a good agreement between developed model and experimental data with R² = 0.99 and this model can predict steady state flow stress well.     

基于分支界限搜索的EFSM协议测试序列生成算法

针对EFSM中状态迁移不确定导致的协议一致性测试序列生成困难的问题, 提出了一种协议一致性测试序列生成算法。该算法基于互异代表系理论为每个协议状态变迁赋权值, 再基于分支界限法搜索生成的协议测试序列, 将协议一致性测试序列的生成转换为寻找最小权值状态变迁路径的问题。该算法克服了无赋权要求的宽度优先搜索的缺陷, 降低了测试序列的搜索与生成时间复杂度, 提高了测试序列生成的效率。     

广义非线性系统的极限值问题

应用单调迭代法和上下解的方法讨论了广义非线性系统的极限值问题 ,给出了解存在性的构造性证明 ,所构造的逼近序列是线性系统的解 ,因此较易实现数值计算 .并且所得结果推广了非线性微分系统的结果 .     

一种新型自解耦六维力/力矩传感器结构设计与优化

针对多维传感器广泛存在维间耦合效应,精度难以提高的问题,设计了一种具有自解耦特性的新型六维力/力矩传感器.采用有限元法对该传感器弹性体进行静力分析,研究了结构在不同工况下的应力应变分布.基于结构变形特点,对特征点位置和布片组桥方式进行了优化.同时也对结构进行了维间耦合分析,验证了该新型传感器具有耦合效应低的优点,提高了传感器的精度,具有较好的应用前景.     

A simulation-based design paradigm for complex cast components

This paper describes and exercises a new design paradigm for cast components. The methodology integrates foundry process simulation, non-destructive evaluation (NDE), stress analysis and damage tolerance simulations into the design process. Foundry process simulation is used to predict an array of porosity-related anomalies. The probability of detection of these anomalies is investigated with a radiographic inspection simulation tool (XRSIM). The likelihood that the predicted array of anomalies will lead to a failure is determined by a fatigue crack growth simulation based on the extended finite element method and therefore does not require meshing nor remeshing as the cracks grow. With this approach, the casting modeling provides initial anomaly information, the stress analysis provides a value for the critical size of an anomaly and the NDE assessment provides a detectability measure. The combination of these tools allows for accept/reject criteria to be determined at the early design stage and enables damage tolerant design philosophies. The methodology is applied to the design of a cast monolithic door used on the Boeing 757 aircraft.     

Normalized explicit finite element approximate inverse preconditioning

Normalized explicit approximate inverse matrix techniques for computing explicitly various families of normalized approximate inverses based on normalized approximate factorization procedures for solving sparse linear systems, which are derived from the finite difference and finite element discretization of partial differential equations are presented. Normalized explicit preconditioned conjugate gradient-type schemes in conjunction with normalized approximate inverse matrix techniques are presented for the efficient solution of linear and non-linear systems. Theoretical estimates on the rate of convergence and computational complexity of the normalized explicit preconditioned conjugate gradient method are also presented. Applications of the proposed methods on characteristic linear and non-linear problems are discussed and numerical results are given.     

语音变速不变调软体化处理方法

语音变速不变调亦称语音时域压扩,可以满足学习外语、报告记录、语音研究及公安侦察等需要。我们把自然辩证法基本思想及物理学基本规律应用于声波研究之中,同时假设人的听觉感受器是按一份一份地接收声波所载的信息这一方式工作的,认为声波相对于听觉也有波粒二像性。基于这些发现,我们采用基于类正弦波的微元法进行语音时域压扩,实验中达到了变速不变调的效果,而且信噪比比较高。反过来,实验结果也一定程度上支持了听觉感受器工作模型假设以及声波相对于听觉的波粒二像性。     

基于优化的量子门节点神经网络的煤与瓦斯突出预测

为了精准地预测煤与瓦斯突出风险等级,提出了一种基于子维进化的粒子群优化算法(sdPSO)和量子门节点神经网络(QGNN)的瓦斯突出风险等级预测模型sdPSO-QGNN.利用灰色关联分析(GRA)对突出影响因素进行降维处理,将筛选出的主控因素作为QGNN的输入,利用sdPSO对量子门节点神经网络参数进行优化,以提高量子门节点神经网络的全局与局部搜索能力,建立sdPSO-QGNN的瓦斯突出风险等级预测模型,实现对瓦斯突出风险的预测.实验结果表明,与BP(back propagation)神经网络、对称Alpha稳定分布的概率神经网络(SαS-PNN)、免疫粒子群算法优化的支持向量机(IPSO-SVM)、Memetic算法优化的极限学习机(Memetic-ELM)等预测模型相比,所提方法在提升模型泛化能力、提高预测精度方面效果显著.     

Sufficient conditions of deterministic implementation of finite-state automata with retention of the numbers of their states

The following three conditions for nondeterministic finite-state automata are defined: input embeddability, output embeddability, and input decomposability. Automata satisfying these conditions are called nondeterministic automata with embeddability. A method for deterministic implementation of such automata with retention of the numbers of their states is proposed. These automata correspond to block-procedural high-level programming languages. Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 55–62, May–June, 2000.