Variational Delaunay approach to the generation of tetrahedral finite element meshes

We describe an algorithm which generates tetrahedral decomposition of a general solid body, whose surface is given as a collection of triangular facets. The principal idea is to modify the constraints in such a way as to make them appear in an unconstrained triangulation of the vertex set à priori. The vertex set positions are randomized to guarantee existence of a unique triangulation which satisfies the Delaunay empty‐sphere property. (Algorithms for robust, parallelized construction of such triangulations are available.) In order to make the boundary of the solid appear as a collection of tetrahedral faces, we iterate two operations, edge flip and edge split with the insertion of additional vertex, until all of the boundary facets are present in the tetrahedral mesh. The outcome of the vertex insertion is another triangulation of the input surfaces, but one which is represented as a subset of the tetrahedral faces. To determine if a constraining facet is present in the unconstrained Delaunay triangulation of the current vertex set, we use the results of Rajan which re‐formulate Delaunay triangulation as a linear programming problem. Copyright © 2001 John Wiley & Sons, Ltd.     

宁夏西海固回族聚落营建关键问题的研究

在分析宁夏西海固回族聚居区文化资源的优势与物质资源不足的基础上,运用人居环境科学、民族学、人文地理学等跨学科理论架构了西海固回族传统乡村聚落营建模式的研究框架,并且从以下几方面对西海固回族聚落营建关键问题进行探讨：回族传统聚落的变迁与当代发展;回族聚落对生态理念的传承与发展;回族传统聚落规划与建筑适宜技术的现代化集成与优化．通过对以上问题的研究可知,必须挖掘与整理“民族性、地区性知识”,将其转化为科学的营建模式,为该地区的人居环境建设提供直接的参照模板,使民族传统聚落及其营建技术得以重生,才是解决该地区现阶段人居环境建设中矛盾与问题的有效途径．     

基于辅助相位优化的交替投影阵列综合算法

本文提出一种新的方向图快速综合算法.该方法基于交替投影算法（AP）,首先对目标方向图幅度进行限制,其次引入了目标方向图相位变量并对其进行优化,得到最佳目标方向图相位,最后结合临近分裂方法来求解有约束的最小二乘问题（CLMS）以获得满足要求的激励.相比于其他AP类算法只对方向图幅度进行限制的处理,本文对方向图相位的优化处理有助于提高算法的收敛速度和性能.实验结果表明,无论有无激励约束的情况下,该算法均能取得良好的优化效果,且适用于任意阵列,具有很好的推广能力.     

Robust adaptive quantized DSC of uncertain pure‐feedback nonlinear systems with time‐varying output and state constraints

In this paper, the problem of neural adaptive dynamic surface quantized control is studied the first time for a class of pure‐feedback nonlinear systems in the presence of state and output constraint and unmodeled dynamics. The considered system is under the control of a hysteretic quantized input signal. Two types of one‐to‐one nonlinear mapping are adopted to transform the pure‐feedback system with different output and state constraints into an equivalent unconstrained pure‐feedback system. By designing a novel control law based on modified dynamic surface control technique, many assumptions of the quantized system in early literary works are removed. The unmodeled dynamics is estimated by a dynamic signal and approximated based on neural networks. The stability analysis indicates that all the signals in the closed‐loop system are semiglobally uniformly ultimately bounded, and the output and all the states remain in the prescribed time‐varying or constant constraints. Two numerical examples with a coarse quantizer show that the proposed approach is effective for the considered system.     

基于力密度的交互式B样条曲面变形

由于传统曲面造型方法缺乏直观调控及难于交互的局限性,强调了基于力学平衡和力密度方法的物理造型策略,通过建立外载荷变化和节点位移等物理意义的最小化线性方程从而实现B样条曲面的自适应性变形调整。系统地给出了基于各种几何约束下通用的几何求解方法,并进一步提出了交互式目标曲线与区域曲线自由绘制的曲面整体和局部变形技术。实验结果验证了此方法的高效性。     

分布式服务质量路由预计算算法

服务质量路由作为下一代IP互联网提供服务质量(QoS)控制的一种重要方案,如何提高其可扩展性和路由性能是有待解决的难题.本文提出了基于聚类的分布式预计算算法,以具有多种QoS参数的路由表预计算为目标,引入了支持QoS参数的扩展距离向量,通过网络中各个节点的分布式协同计算,大大降低了单个路由器的计算复杂度.文章分析了优势路径及其选取策略,给出了路由计算中优势路径聚集的聚类方法,实现了QoS路由表的高效聚集压缩.实验结果进一步验证了该算法具有计算量小和QoS路由性能高的优点,在QoS度量维数和网络规模方面均具有良好的可扩展性,并对域间算法研究提供了重要依据.     

Event-triggered path tracking control with obstacle avoidance for underactuated surface vessel compliant with COLREGs-constraints: Theory and experiments

This paper addresses the path tracking problem for an underactuated surface vessel with model parametric uncertainties, in the presence of unknown ocean currents under input saturation and limited transmission resources, while guaranteeing no collision can occur with a nearby target ship (TS) in compliance with the International Regulations for Preventing Collisions at Sea (COLREGs) rules. In view of COLREGs practice, this paper proposes a strategy to address the issue of collision avoidance in the presence of an encounter situation. Based on different stages of encounter situation, a local path re-planning-based repulsive potential function technique is proposed, such that the potential force generated by a decision-making algorithm, is directly acted on the original desired trajectory deviating thus the Own Ship (OS) to take direction in compliance with the COLREG constraints. By restoring to the path-tracking framework, this paper proposes a novel navigation control algorithm with ship-to-ship collision avoidance. At the navigation level, a finite-time prescribed performance control strategy with the deployment of novel asymmetrical envelopes is proposed to prescribe path-tracking errors within user-defined constraints while reducing transient response overshoots. Furthermore, in order to enhance the tracking performance under model uncertainties and external disturbances, a radial basis function neural network (RBFNN) technique is used. We first propose a second-order neural network disturbance observer to restrain the compound disturbances which are combined with external disturbances and neural network approximation errors. Next, based on the estimated compound disturbances, an adaptive NN controller is designed via an event-triggering mechanism along with a transverse function approach and the backstepping technique. It is shown that with the proposed technique, all signals in closed-loop systems are semi-globally uniformly bounded, while the output tracking errors converge to a prescribed arbitrarily small region within a finite time. In addition, we prove via the direct Lyapunov approach, the existence of minimal inter-event time and thus Zeno-behavior is avoided. Finally, experiments are conducted to validate the effectiveness and performances of the proposed control strategy.     

Kinematic coupling-based trajectory planning for rotary crane system with double-pendulum effects and output constraints

When the payload is too large or the hook mass cannot be ignored, the double-pendulum phenomenon may happen in rotary cranes practical applications. The increase in dynamic complexity makes it more difficult to fast and accurate positioning while suppressing swing during cargo transportation. Moreover, output constraints should be considered in actual crane systems. In this paper, a novel kinematic coupling-based trajectory planning method is proposed for double-pendulum rotary cranes with the constraints on angular acceleration and velocity of the boom. The proposed trajectory consists of two parts: a positioning reference component and a swing-eliminating component. The positioning reference trajectory takes into account the physical constraints of the actuator. The swing-eliminating trajectory is designed based on the kinematic coupling relationship among the boom luffing, the hook swing and the payload swing. Lyapunov techniques and Barbalat lemma are used for stability analysis. Numerical simulation and real experiments verify the superior control performance and robustness of the proposed control method.     

具有时变通信受限非线性信息物理系统的网络化预测控制

针对具有时变通信受限的一类非线性信息物理系统,本文采用网络化预测控制策略,对于时变通信时延和数据丢失,不是使用常规的被动方式抑制,而是进行主动补偿.为了使补偿时变通信受限的方式简单、主动和通用,提出了一种新颖的网络化非线性预测控制方法.所设计的网络化非线性预测控制器能达到具有与无网络的本地闭环控制系统完全相同的期望控制...