柔性障碍物对甲烷空气爆炸波激励作用的实验研究

为研究柔性障碍物对甲烷空气爆炸波的激励效应,采用双向拉伸聚丙烯（biaxially oriented polypropylene, BOPP）薄膜作为柔性障碍物将管道内甲烷空气预混气体与空气隔开,对比障碍物前后火焰、激波变化,分析膜状柔性障碍物激励效应的机理。实验结果表明:这种具有一定承压能力的柔性障碍物对甲烷爆炸波产生的激励效应不可忽视,在膜片破裂前产生多次激波反射过程,可诱导湍流火焰形成,促使膜前爆炸压力提高,膜片破裂后,火焰在伴流作用下传播速度突增,并加速逐渐逼近前驱冲击波,致使膜后爆炸压力大幅提高;激励效应可使膜片前后最大爆炸压力相差5倍,火焰速度相差7倍;另外在膜片位置2.5 m后增设一道膜片,可增强这种激励效应,而增加膜片的实质是使激波火焰相互作用的次数增加。     

改进的布谷鸟算法求解考虑运输时间的分布式柔性流水车间调度问题

针对分布式制造环境下多车间调度问题特点,结合企业实际生产情况,考虑相邻工序间的运输时间,建立以最小化最大完工时间为优化目标的分布式柔性流水车间调度模型,提出一种改进布谷鸟算法用于求解该模型。算法改进包括设计了一种基于工序、车间和机器的三层编码方案;根据问题特点设计了混合种群初始化策略以提高种群质量;改进了布谷鸟搜索操作使其适用于求解该模型;设计了一种种群进化策略以提高算法收敛速度及解的质量。最后通过仿真实验,与多种算法对比,验证所提算法的有效性和优越性。     

Rodlike/flexible polyimide composite films prepared from soluble poly(amic diethyl ester) precursors: Miscibility,structure, and properties

Homogeneous precursor/precursor solutions with various compositions were obtained with appreciably high solid contents in N-methyl-2-pyrrolidone from soluble poly(amic diethyl ester) precursors of rodlike poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) and flexible poly(4,4′-oxydiphenylene biphenyltetracarboximide) (BPDA-ODA), which are hydrolytically more stable as well as more soluble than the corresponding poly(amic acid)s being equilibrated with the constituent monomers. Both optical microscopic and light scattering measurements showed that the dried precursor blend films and resultant polyimide composite films were optically transparent, regardless of compositions and process conditions. The composite films showed a single T_g behavior. However, for the composite of 30 wt % BPDA-PDA dispersed in the matrix of 70 wt % BPDA-ODA, a smectic crystalline-like aggregation of the BPDA-PDA component was detected on wide-angle x-ray diffraction patterns, indicative of microscopic phase separation between the two components. This phase separation was not detected on the optical microscopy, light scattering, and dynamic mechanical thermal analysis because of their resolution limits: Optical microscopy has a resolution of submicrometers, whereas dynamic mechanical thermal analysis and light scattering have a resolution of ca. 50 Å. Therefore, it is speculated that in the composite films BPDA-PDA and BPDA-ODA polyimide molecules have demixed on the scale of a few nanometers. The mean long periodicity, which was estimated from the small-angle x-ray scattering pattern, varied from 134 to 170 Å as the content of BPDA-ODA component increased. In addition, mechanical properties of the composite films were characterized. ©1995 John Wiley & Sons, Inc.     

Organic-Inorganic Insulating Coatings Based on Sol-Gel Technology

The approach for improving bending strength of temperature-resistant flexible ceramic electric insulating coatings prepared by sol-gel processing is considered. Starting suspensions, based on both tetraethoxysilane (TEOS)-derived modified sols and highly dispersed fillers such as Cr₂O₃, are used to deposit the coatings on metals and alloys. Some polymers and organic substances are tested as additives for improving flexibility of the ceramic coatings. The results of study of both bending strength and electrical strength of flexible hybrid organic-inorganic insulation formed on a nichrome wire are discussed. The data obtained on the chemical and phase structure of the coatings, which have been heat treated at temperatures from 95 to 1100°C, using DSC as well as X-ray scattering techniques are presented.     

Homoclinic Chaos in 2-DOF Robot Manipulators Driven by PD Controllers

The existence of Smale horseshoes in the dynamics of twodegrees of freedom (2-DOF) robot manipulators with viscous damping anddriven by classical proportional-derivative (PD) controllers is proved.The situation where an actuator failure occurs is also analyzed. Thecontrollers correspond to the classical PD and the PD with gravitycompensation. They are considered as non-Hamiltonian perturbations of anundriven 2-DOF robot; then a technique developed by Holmes and Marsden,which uses a combination of a reduction scheme and Melnikov's methodwith an energy balance argument, is applied.     

Robust inverse optimal control for flexible structures

An inverse optimal control problem is formulated to develop robust control laws for purely oscillatory systems. The optimal control solution requires output feedback with specified constraints, leading to robustness with respect to unmodeled modes and a large class of parameter variations. The robustness properties are proved directly from known properties of control laws resulting from quadratic performance indices. The control laws are useful for poorly damped flexible structures.This research was supported by the Office of Naval Research, Contract No. N00014-77-C-0247.     

Modeling a class of state-dependent routing in flexible manufacturing systems

We develop a closed queueing network model for flexible manufacturing systems (FMSs), where parts routing follows a probabilistic shortest-queue (PSQ) scheme, i.e. parts are routed to the shortest queue (or the most empty station) with the highest probability. We allow limited local buffer at each work station. We prove that with the PSQ routing, the Markovian queue-length process satisfies time reversibility and has a product-form equilibrium distribution. An algorithm is developed to compute the solutions to the model. The model can be used as a performance evaluation tool to study FMSs.     

相干光纤传象束串象性质分析

本文报道了关于相干柔软光纤传象束(FIB)串象特性的研究.提出一种采用定标的光学视频系统定量测量相干柔软光纤传象束串象率的新方法.在光纤传象束的输入端,借助高精度的光学耦合系统,使光线仅对单根光纤输入耦合,而在传象束的输出端,由CCD阵列相机对被激光纤作大面积范围的检测.并且,测量了光纤传象束的静态调制传函数(MTF),用于描述串象率对传象束传象特性的影响,比较了多种传象束样品的测量结果.     

对于具有大范围运动和非线性变形的柔性梁的有限元动力学建模

研究具有大范围运动和非线性变形的柔性梁的有限元动力学建模.采用有限元方法对梁结构进行离散,利用Lagrange方程建立系统的精确动力学方程.该方程不仅增加了新的表征纵向、横向、侧向弯曲变形,以及扭转变形的耦合项,同时包含了变形运动与大范围运动之间的相互耦合项.     

基于无源性的不确定机器人的力控制

根据无源性理论,从一个较新的角度对机器人系统的力控制问题进行了研究.一个严格无源的动态系统一般具有良好的动态特性和较强的鲁棒性.因此在力控制中采用无源化方法对力控制器进行设计.对于机器人建模的不准确性及环境的影响,本文采用在力控制回路中加入一个补偿项来补偿模型的不确定性.仿真结果表明这种控制方案使系统获得了较好的动态性能和较强的鲁棒性.