非饱和土与特殊土力学的理论与实践

对非饱和土与特殊土(包括填土、黄土、膨胀土、膨润土等)开展了持久深入的研究,取得了系统的创造性成果:在国内率先研制成非饱和土固结仪、直剪仪、渗气仪、小型三轴仪、温控三轴仪、多功能三轴仪和土工CT-三轴仪等一系列仪器设备,揭示了非饱和土与特殊土的水气运动规律、变形、强度、屈服、水量变化、细观结构演化、温度效应等许多重要力...     

动力伞8自由度动力学建模与仿真

现有文献中的翼伞建模方法多数是针对不带动力情况下的翼伞建模,不能适应动力翼伞的飞行控制。为了实现动力伞的有效控制,首先要建立合理的动力学模型。假设翼伞承载物和软翼之间具有2个自由度,分别建立软翼和承载物体坐标系下的作用力和力矩的平衡方程,通过体坐标系转换和消除翼伞内部状态量,得到有利于实现翼伞控制的8自由度非线性状态方程。仿真表明模型的飞行曲线与飞行实验的结果相一致,验证了模型的有效性。     

超音速气流中热塑性复合材料壁板的非线性热颤振特性

热塑性复合材料结构在高速流场中的颤振行为是可重复使用航天器设计中需要考虑的问题.基于Mindlin厚板理论和Von-Karman大变形理论描述热塑性复合壁板结构大变形,超音速气动力采用活塞气动理论.考虑温度引起的壁板面内热应力和热塑性材料力学性能的改变.根据虚功原理和有限元法推导建立了热塑性复合材料壁板的热颤振模型,进...     

态势生成中一种非线性运动模型的建立

探讨了在信息融合仿真试验床的态势生成部分,建立飞行实体运动模型的方法;通过保留运动学方程,简化动力学方程的方法,给出了一种常见的机动飞行方式(俯冲爬升类运动)的运动模型的计算公式;并对这种运动模型的非线性和机动性进行了分析和讨论;通过仿真,比较了几种机动目标跟踪算法对该运动模型的跟踪效果,验证了该方法的有效性。     

Algorithms for solving the conditional covering problem on paths

Consider the conditional covering problem on an undirected graph, where each node represents a site that must be covered by a facility, and facilities may only be established at these nodes. Each facility can cover all sites that lie within some common covering radius, except the site at which it is located. Although this problem is difficult to solve on general graphs, there exist special structures on which the problem is easily solvable. In this paper, we consider the special case in which the graph is a simple path. For the case in which facility location costs do not vary based on the site, we derive characteristics of the problem that lead to a linear‐time shortest path algorithm for solving the problem. When the facility location costs vary according to the site, we provide a more complex, but still polynomial‐time, dynamic programming algorithm to find the optimal solution. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005.     

On parallel machine replacement problems with general replacement cost functions and stochastic deterioration

The parallel machine replacement problem consists of finding a minimum cost replacement policy for a finite population of economically interdependent machines. In this paper, we formulate a stochastic version of the problem and analyze the structure of optimal policies under general classes of replacement cost functions. We prove that for problems with arbitrary cost functions, there can be optimal policies where a machine is replaced only if all machines in worse states are replaced (Worse Cluster Replacement Rule). We then show that, for problems with replacement cost functions exhibiting nonincreasing marginal costs, there are optimal policies such that, in any stage, machines in the same state are either all kept or all replaced (No‐Splitting Rule). We also present an example that shows that economies of scale in replacement costs do not guarantee optimal policies that satisfy the No‐Splitting Rule. These results lead to the fundamental insight that replacement decisions are driven by marginal costs, and not by economies of scale as suggested in the literature. Finally, we describe how the optimal policy structure, i.e., the No‐Splitting and Worse Cluster Replacement Rules, can be used to reduce the computational effort required to obtain optimal replacement policies. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005     

Approximating nondominated sets in continuous multiobjective optimization problems

Many important problems in Operations Research and Statistics require the computation of nondominated (or Pareto or efficient) sets. This task may be currently undertaken efficiently for discrete sets of alternatives or for continuous sets under special and fairly tight structural conditions. Under more general continuous settings, parametric characterisations of the nondominated set, for example through convex combinations of the objective functions or ε‐constrained problems, or discretizations‐based approaches, pose several problems. In this paper, the lack of a general approach to approximate the nondominated set in continuous multiobjective problems is addressed. Our simulation‐based procedure only requires to sample from the set of alternatives and check whether an alternative dominates another. Stopping rules, efficient sampling schemes, and procedures to check for dominance are proposed. A continuous approximation to the nondominated set is obtained by fitting a surface through the points of a discrete approximation, using a local (robust) regression method. Other actions like clustering and projecting points onto the frontier are required in nonconvex feasible regions and nonconnected Pareto sets. In a sense, our method may be seen as an evolutionary algorithm with a variable population size. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005.     

Optimal power control in a wireless network using a model with stochastic link coefficients

This paper addresses optimal power allocation in a wireless communication network under uncertainty. The paper introduces a framework for optimal transmit power allocation in a wireless network where both the useful and interference coefficients are random. The new approach to power control is based on a stochastic programming formulation with probabilistic SIR constraints. This allows to state the power allocation problem as a convex optimization problem assuming normally or log‐normally distributed communication link coefficients. Numerical examples illustrate the performance of the optimal stochastic power allocation. A distributed algorithm for the decentralized solution of the stochastic power allocation problem is discussed. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2005     

信息不完备群组决策问题的ANP方法

群组决策是一类重要的决策问题,信息不完备的群组决策问题,因为判断矩阵有缺损,传统的AHP不能求解.文中将评价图引入信息不完备的群组决策问题,在此基础上提出用二次规划问题解决在这种情况下的权重确定问题,最后通过ANP的超矩阵得到总排序结果.经过实例检验,证明了ANP方法的正确性与可行性.     

复杂非线性隔冲减振系统计算分析

基于结构动力学理论,提出了一种用于分析计算复杂非线性隔冲减振系统的双模型两步计算法。该方法将冲击振动分成2个阶段:冲击作用阶段和自由振动阶段。冲击作用阶段,采用两自由度模型进行响应计算,该两自由度模型可有效地解决基础冲击输入问题;自由振动阶段,采用单自由度模型进行响应计算,设备在该阶段以冲击终了时刻的速度和位移为初始条件进行振动。文中还对一个典型的复杂非线性系统的冲击过程进行了数值计算.该方法亦可用于线性隔冲减振系统的计算分析.