高耐热型填料改性EPDM绝热层性能研究

以三元乙丙橡胶(EPDM)为基体,中空聚酰亚胺纤维为耐热型纤维,分别从低密度高成炭、高耐热以及分子链催化成炭三方面出发,通过机械共混法制备了酚醛空心微球(HPM)、聚酰亚胺树脂(PIR)以及含不饱和双键环磷腈衍生物(CPD)复合的EPDM绝热层,并对这三种绝热层进行了硫化性能、力学性能、与金属界面粘接性能以及耐烧蚀性能...     

三维内收缩式进气道V形溢流口热流计算与分析

为了获得流场特性和热流影响规律,将高超声速进气道中带有V形的溢流口进行简化,采用数值计算和实验相结合的方法研究了简化后V形溢流口的前缘热流,对比分析了不同前缘钝化构型、不同前缘角θ以及不同倒圆半径比R/r下V形溢流口的热流分布。结果表明,和钝头体以及旋成体相比,钝化的V形溢流口受到更加严重的热载荷,流场结构也更加复杂;改变前缘角θ并不能显著降低热流,可见通过改变前缘角θ对溢流口前缘热流改善能力有限;倒圆半径比R/r对V形溢流口热流影响明显,倒圆半径比R/r6时,溢流口前缘气动受热剧烈,倒圆半径比R/r6时,热流峰值降低且随倒圆半径比R/r变化不明显。在进气道设计中应综合考虑气动性能和热防护等因素进行合理取舍。     

一种基于控制参数化的双连杆机械臂最优PID参数整定方法

考虑一类双连杆机械臂的PID控制问题,提出一种基于控制参数化的最优PID参数整定方法.首先,把系统的性能指标建模为最优控制中的连续状态不等式约束.其次,将双连杆机械臂的最优PID参数整定问题转化为含连续状态不等式约束的最优参数选择问题.然后,应用约束转录法结合局部平滑法来处理连续状态不等式约束.得到一个标准的最优参数选择问题,且这个标准问题可以用最优控制软件MISER 3.2来求解.由于是基于梯度的方法来求解问题,所以在文中推导了代价函数和经过处理后约束的梯度公式.最后,通过数值仿真验证了提出的方法的有效性.     

芯片原子钟的工作原理及其研究进展

作为导航设备的重要部件,芯片原子钟可作为战术导弹、卫星接收机、小型无人机等所用导航设备的时钟源,也可与陀螺仪和加速度计组合实现微型定位、导航与授时。介绍了相干布局囚禁(Coherent Population Trapping, CPT)现象,以及芯片原子钟的发展历程,阐述了CPT实现方案的缺点(产生极化暗态、降低原子利用率),并给出了优化方案。此外,分析了微机电系统(Micro Electro Mechanical System, MEMS)加工工艺等用于芯片原子钟制造的关键技术,并对芯片原子钟的发展趋势进行了展望。     

DGPS-based aircraft flight guidance/test system

The utilization of the GPS system for Aircraft Flight Guidance/Test (AFGT) is a research project in China. The paper describes the concepts and the technical realization of such a system, including three components: ground subsystem, on-board subsystem and data communication link using TDMA technique. The purpose of the proposed AFGT system is to calibrate and verify performance of an on-board radar. Therefore, it must meet the requirements of evaluation of radar performances in several areas: accuracy, coverage range, and others. The AFGT System's displays are separately: a Moving Colored Digital Map on which flight trajectories, waypoints, and heights of aircrafts are clearly marked; and a Polar Coordinate Figure on which the bearings, headings, and distances of aircrafts relative to the origin of the ground control center are shown. The AFGT may monitor and guide several aircrafts flying in the pointed airspace. It support airport surface surveillance and air traffic control at the terminal area. A real-time software package RTTEST, which includes tracking display software and on-flight test software for radar evaluation, has conducted simulation with satisfactory position accuracy     

高温合金中MC碳化物晶体生长的稳定性

 利用球扰动对晶体球扩散生长模型的稳定性进行分析,把球模型的球半径转化为曲率半径的概念,进而讨论高温合金中的MC八面体碳化物晶体在高温熔体中生长的稳定性,并分析出所观察到的MC碳化物八面体枝臂形态。     

Input-Filter Design for Switching Regulators

The interaction between the input filter and the control loop of switching regulators often results in detrimental effects, such as loop instability, transient response, and audio-signal-rejection rate, etc. A small-signal average model is derived to investigate these effects. Design constraints of an input-filter and switching-regulator system are formulated. An optimum low-pass and light-weight filter configuration is proposed.     

Response regimes of narrow-band stochastic excited linear oscillator coupled to nonlinear energy sink

This paper draws attention to the issue of the vibration absorption of nonlinear mechanical system coupled to nonlinear energy sink(NES) under the impact of the narrow band stochastic excitation. Firstly, based on the complex-averaging method and frequency detuning methodology,response regimes of oscillators have been researched under the linear impact of coupling a nonlinear attachment with less relativistic mass and an external sinusoidal forcing, of which results turn out that the quasi-periodicity response regime of system which occurs when the external excitation amplitude exceeds the critical values will be the precondition of the targeted energy transfer.Secondly, basing on the path integration method, vibration suppression of NES has been researched when it is affected by a main oscillator with a narrow band stochastic force in the form of trigonometric functions, of which results show that response regimes are affected by the amplitude of stochastic excitation and the disturbance strength. Finally, all these conclusions have been approved by the numerical verification and coincided with the theoretical analysis; meanwhile, after the comparing analysis with the optimal linear absorber, it turns out that the NES which is affected by the narrow band stochastic force could also suppress the vibration of system with a better effect.     

基于粒子群算法的伪卫星布站优化设计

针对伪卫星布站问题,采用粒子群智能优化算法,以导航定位中精度因子作为粒子群适应度函数,采用线性递减惯性权值策略,通过适当次数的进化与迭代,最终寻找到最优化的伪卫星布站设计方案。通过对两条竖直平面内的抛物线轨迹进行仿真验证,结果表明,基于粒子群算法的伪卫星布站优化设计方案可以减小全程精度因子,提高了伪卫星独立定位系统的定位精度。