正交平面织物球面成型渔网模型的几何分析

为了从理论上表征平面正交织物球面成型后的几何特征, 提出基于坐标变换求解渔网模型的新方法, 确定单层正交平面织物在球面上铺覆成型后的网格位置、 织物剪切变形和纱线弯曲变形。依据弧长不变条件确定方形织物完全包覆球面后的对称面上的网格位置和局部坐标系下中间网格的位置, 利用坐标变换获得中间网格在整体坐标系成型球面上的坐标位置; 根据变形前后的网格形状确定织物面内剪切变形和两个方向纱线的弯曲曲率, 为织物的球面成型性评价提供几何参数。通过实例证明了当网格尺寸远小于球体半径时铺覆变形程度与网格 尺寸无关, 也与球体半径无关。铺覆后织物的剪切变形和纱线弯曲变形分布只与织物在球面上的球坐标位置有关。     

基于黎曼度量参数曲面四边形网格生成方法及UG实现

论文给出了基于黎曼度量的参数曲面网格生成的改进铺砖算法。阐述了曲面自身的黎曼度量,并且运用黎曼度量计算二维参数域上单元节点的位置,从而使映射到三维物理空间的四边形网格形状良好。文中对原有铺砖法相交处理进行了改进,在运用铺砖法的同时调用UG-NX强大的二次开发库函数获取相应的信息,直接在UG-NX模型的表面生成四边形网格。算例表明,该法能在曲面上生成质量好的网格。     

船用封闭曲面铺放成型过程中的断纱控制轨迹规划算法

自动铺放技术作为一种先进的复合材料成型技术，广泛适用于加工形状复杂的复合材料构件。本研究以压辊压实量、角度偏差以及曲率半径作为评价指标，通过对不同轨迹规划算法进行对比，选取适用于船用封闭曲面的轨迹规划算法。以重叠因子为约束条件对轨迹进行满覆性分析，提出一套适用于复杂曲面的增减纱算法，实现重叠与间隙的均匀分布。基于船用封闭曲面结构提出分区轨迹优化算法，降低了断纱数量。最后在封闭曲面上进行仿真与实验分析，验证算法的正确性。     

预成形体渗透率预测及剪切变形的影响

准确预测预成型体渗透率对复合材料液态成型工艺过程仿真有重要意义,铺覆过程中织物发生的剪切变形对局部渗透率有很大影响。本工作考虑纱线的可渗透性,对织物单胞内的树脂流动建立了统一的流动控制方程,同时建立了逼真的正交单胞几何模型,基于Adams-Bashforth差分格式和Chorin投影法构造了数值求解树脂流动控制方程的高分辨率TVD格式,利用达西定律预测了单胞的渗透率,算例表明该算法预测值与实验值有较好的吻合,验证了算法的准确性。在正交单胞渗透率求解的基础上,采用贴体坐标法完成了单胞剪切变形后流动控制方程从物理域到计算域的转换,进而实现了剪切单胞渗透率的数值预测,考察了单胞主渗透率比与剪切角的关系,通过与文献中数据对比证明了该剪切单胞渗透率预测算法的合理性。     

铺层角度偏差对曲面复合材料结构固化变形的影响分析

本文阐述了铺层角度偏差对某变厚度曲面结构复合材料固化变形的影响。对铺层角度偏差的来源进行了归纳,采用考虑热膨胀和固化收缩的固化变形计算模型,对该变厚度的复合材料曲面层合板结构的固化变形进行了计算,计算结果与试验结果较为吻合,表明了计算模型的准确性。采用均匀试验设计方法,得到了该曲面结构铺层角度偏差在5°以内变化时的实验方案,对实验设计的计算结果进行了回归分析,结果显示,对于该曲面复合材料结构,总体上铺层角度偏差对固化变形的影响不大,相对的,-45°的铺层偏差对固化变形的影响较大,90°的铺层偏差对固化变形的影响较小。     

分布式传感器网络中基于条件后验克拉美-罗下界的被动声目标跟踪局部节点选择算法

针对分布式传感器网络下的被动声目标跟踪问题,提出了一种基于条件后验克拉美罗下界（Conditional Posterior Cramér-Rao Lower Bounds,CPCRLB）的局部传感器节点选择算法,基于被动声探测背景下的纯方位量测数据,采用粒子滤波器推导得到了CPCRLB的近似解析表达式,进而在该CPCRLB的基础上定义了节点效用贡献作为节点选择准则,结合分布式传感器网络的特点提出了一种局部节点选择方法,节点无需知道全网传感器节点的信息,而是仅利用局部节点信息来决定下一时刻节点的活动状态,从而在实现自治节点选择的同时大大减少网络通信量。通过仿真结果表明,该算法在跟踪精度、能量消耗和计算复杂度方面都表现出较好的性能。     

基于点位移约束的NURBS曲面变形研究

NURBS曲面变形涉及控制网格、控制点、权因子或一些物理参数等复杂计算,变形不够直观.应用Cao En曲面模型和合成函数对NURBS曲面提出一种新的变形方法,将变形后的曲面表示成NURBS原始曲面和位移函数的合成曲面.曲面变形与控制网格无关,关键点位置可随意选取,直接通过点的位移约束得到可控制的变形结果.实验证明该方法计算简单,变形操作简便直观,适用于曲面的交互设计.     

基于非对称往返测距的海洋无线传感网络节点定位算法

提出一种新的基于非对称往返测距的海洋无线传感网络节点定位(LMARR)算法,该算法利用节点间非对称的接收与发送测距信息的时间差,推算出节点间海水声速以及未知节点与其邻居参考节点之间的距离,将三维距离信息转换成二维,运用最小二乘法完成定位计算。与SWN和ARTL算法相比较,仿真结果表明:LMARR算法能有效地提高节点定位的精度,特别是在深度为20～120m海水声速持续变化的区域,定位精度比SWN算法提高了20%,比ARTL算法提高了33%;此外,LMARR算法还具有较高的稳定性。     

阶梯型对接层合板复合材料力学性能的试验研究

为了确定采用2D机织物叠层方式制备复杂曲面结构复合材料制件过程中的增强织物对接缝间隔长度与其拉伸、弯曲性能的关系,基于对称铺层顺序[0°/0°/+45°/90°/-45°/90°]S,制备了连续铺层和对接间隔长度分别为4,8,12mm的四种环氧树脂基玻璃纤维2D机织物叠层结构RTM复合材料层合板试件,测定了2D玻璃纤维机织物层合板复合材料的拉伸和弯曲强度。试验结果表明,连续铺层的抗拉强度大约为357MPa,与对接铺层相比,其强度要高出35%左右,当对接间隔长度大于8mm时,拉伸应力不再随对接间隔长度的增加而变大,其拉伸强度基本保持在220MPa左右。另外,对接铺层的试验试件基本都在接口处断裂,这是由对接缝处应力集中造成的。由此实验结果可为复杂曲面结构复合材料提供一定的数据参考,使材料性能达到最优设计。     

静电致动圆形微泵膜片的变形计算

针对静电驱动微泵（micropump）多能量域系统仿真中存在计算量大的问题,基于弹性力学小挠度变形理论和微机电系统中的静电驱动理论,建立了静电力驱动下圆形微泵膜片（membrane）的变形曲面方程,采用伽辽金加权残值法得到膜片变形和泵腔容积变化的半解析式,结果显示膜片的变形和泵的容积变化与驱动电压的平方成正比．采用本文公式建立微泵系统宏模型（macromodel）或集中参数模型,有助于提高微泵系统仿真的计算效率．     

The draping of woven fabric preforms and prepregs for production of polymer composite components

Drape trials were conducted on a simple shape and a number of aircraft parts. Predictions from computer drape simulation using the pin-jointed net model were compared with draping test results. The pin-jointed net model was evaluated. Yarn slippage, and how it is affected by the material properties and part geometry, were investigated. The criteria for optimal draping, and the means of manipulation of the drape simulation are discussed. The different methods of draping constraint are compared and their most useful applications are indicated. Some useful guidance for the application of drape simulation is given.     

基于核映射稀疏表示分类的轴承故障诊断

针对传统稀疏表示分类算法在低维空间分类精度难以保证问题,论文提出了基于核映射的稀疏表示分类算法。采用核映射方法获得了低维样本在高维空间的坐标,改善了样本间的线性可分度;在此基础上,利用稀疏表示分类算法获得样本在高维空间上的稀疏解。经滚动轴承故障分类实验验证：新算法对核参数具有较高的鲁棒性;可明显提高分类精度。     

Approximate analysis of forming forces in woven preforms

In this paper, an approximate analysis has been developed for rapid computation of forming forces. The orientation of yarns in a deformed woven fabric on a surface is obtained using a differential geometry based draping algorithm. The fabric is assumed to behave like a membrane with very small strain along the principal yarn directions. This assumption allows computation of the tension along the yarns and the pressure on the surface. This methodology can also identify areas of wrinkling, which is a function of shear stiffness and applied forces.     

Contact search strategies for FEM simulation of the blow molding process

In this paper, the efficiency and accuracy of contact search algorithms for the blow molding simulation were discussed. In order to increase the efficiency of the contact search, we proposed and implemented three kinds of global search algorithms and compared them with two existing methods in terms of both formulation and CPU time. The proposed sorted moving box method was finally proved to be the most efficient one, without loss of stability. To increase the accuracy, a contact–tolerance–adjustable local search algorithm was also proposed. Successful simulation of the stretch blow molding process was given as an example. Copyright © 2000 John Wiley & Sons, Ltd.     

多运动平台红外场景仿真

为了能对多运动平台条件下的红外信息处理算法进行验证与评估,进行了多运动平台红外场景仿真的研究与实现。首先,回顾了现有的红外场景仿真方法,指出其主要针对单平台条件设计。接着,分析了目标模型,提出了目标辐射模型和目标群运动模型。然后,在分析多运动平台红外信息处理算法特点基础上,提出了基于虚拟观测平台的成像观测模型,并据此得到了多运动平台红外场景仿真的基本流程。最后,对提出的场景产生方法进行了仿真验证。仿真结果表明:提出的多运动平台红外场景仿真方法,能够满足多运动平台协同条件下的红外信息处理算法的验证与评估的需求。     

MCMC algorithms for Subset Simulation

Subset Simulation is an adaptive simulation method that efficiently solves structural reliability problems with many random variables. The method requires sampling from conditional distributions, which is achieved through Markov Chain Monte Carlo (MCMC) algorithms. This paper discusses different MCMC algorithms proposed for Subset Simulation and introduces a novel approach for MCMC sampling in the standard normal space. Two variants of the algorithm are proposed: a basic variant, which is simpler than existing algorithms with equal accuracy and efficiency, and a more efficient variant with adaptive scaling. It is demonstrated that the proposed algorithm improves the accuracy of Subset Simulation, without the need for additional model evaluations.     

相移干涉三维形貌纳米检测及算法研究

基于相移干涉理论设计并实现了微平面三维形貌测试系统，针对三维形貌检测解包裹过程中出现的问题，改进了现有的残差点判断法，能够更加准确、快速地确定残差点的存在．对相位解包裹算法进行了系统研究．分析了干涉图中残差对相位解包裹的影响，提出了一种基于二阶导数的区域增长解包裹算法．在实际测量中，最终结果得到了明显的改善，证明了该方法的有效性，提高了系统精度、采用此算法，系统的纵向测量误差小于2nm．     

Algorithms for draping fabrics on doubly-curved surfaces

Three algorithms for draping biaxially woven fabrics on arbitrarily curved surfaces are presented and compared for numerical accuracy and computational expense. The first one minimizes the elastic energy in each fabric cell, while the two others are based on placing a net of interlocked and inextensible fibres on the surface along geodesic lines. A benchmark shows that the minimum energy technique performs the best and is also the most promising for further optimization in terms of numerical quadrature formulae.     

Collaborative Filtering for Massive Datasets Based on Bayesian Networks

This paper proposes a collaborative filtering method for massive datasets that is based on Bayesian networks. We first compare the prediction accuracy of four scoring-based learning Bayesian networks algorithms (AIC, MDL, UPSM, and BDeu) and two conditional-independence-based (Cl-based) learning Bayesian networks algorithms (MWST, and Polytree-MWST) using actual massive datasets. The results show that (1) for large networks, the scoring-based algorithms have lower prediction accuracy than the CI-based algorithms and (2) when the scoring-based algorithms use a greedy search to learn a large network, algorithms which make a lot of arcs tend to have less prediction accuracy than those that make fewer arcs. Next, we propose a learning algorithm based on MWST for collaborative filtering of massive datasets. The proposed algorithm employs a traditional data mining technique, the “a priori” algorithm, to quickly calculate the amount of mutual information, which is needed in MWST, from massive datasets. We compare the original MWST algorithm and the proposed algorithm on actual data, and the comparison shows the effectiveness of the proposed algorithm.