配置点谱方法求解推进剂供应管路瞬变流动

基于一维管道瞬变流理论和数值谱方法,给出了求解推进剂供应系统管路内液体瞬变流控制方程的Chebyshev配置点谱方法,通过将“超谱粘性项”引入控制方程,有效地消除了由于解的间断或大梯度变化引起的数值振荡.以一段两端分别连接贮箱和阀门的等截面圆直管为例,利用该方法对阀门关闭后管道内水击现象进行了计算,给出了相应的水击压力仿真结果,并分别与采用特征线法和有限元法求解的结果进行了分析比较,论证了Chebyshev配置点谱方法求解推进剂供应管路内流体瞬变流的可行性.     

深空通信中继下行链路特性研究及仿真分析

在深空通信中,由于信号传输距离遥远,功率受限的下行链路信号衰减巨大。为解决上述问题,分析地球大气层和外层自由空间的传输特性差异,提出以地球同步轨道卫星为中继站的下行链路的构想,根据每一段链路特性的不同选择载波频率。仿真结果表明,中继链路可以提高信号传输的信噪比、增大信道容量、降低误码率,提高了深空通信下行链路的可靠性。     

推进剂管路充填过程的数值模拟

基于一维管路瞬变流理论,利用特征线有限差分法,建立了推进剂供应系统管路充填过程的数学模型.利用坐标变换方法,将管路内液体与时间相关的求解区域变换为求解较方便的固定求解区域,很好地处理了模型的移动边界问题.对由贮箱、隔离阀、管道组成的系统充填过程进行了仿真计算,并将计算结果与传统的采用特征线方法获得的结果进行对比分析,验证了方法的有效性.进一步研究了最大压力峰值的影响因素,结果表明:增多初始气体压力、减小贮箱压力、增多多变指数可有效减小最大压力峰值.      

RDX-CMDB推进剂燃烧性能的调节

调节燃速和降低压力指数是RDX-CMDB推进剂性能改善的技术关键之一.用同一种有机铅、铜盐催化剂对实测比冲为2000～2200N·s/kg的四种双基及RDX-CMDB推进剂进行试验研究表明:铅-铜-炭黑三种燃烧催化剂组合使用也可在RDX-CMDB无烟推进剂中获得良好的平台或麦沙效应.这里炭黑的加入起了关键作用,可用燃烧催化的铅-碳理论作进一步的解释.所述的铅、铜催化剂与四种碳黑搭配,可使所研究的四种推进剂燃速在14～29mm/s范围内调节.     

Fuzzy robust nonlinear control approach for electro-hydraulic flight motion simulator

A fuzzy robust nonlinear controller for hydraulic rotary actuators in flight motion simulators is proposed. Compared with other three-order models of hydraulic rotary actuators, the proposed controller based on first-order nonlinear model is more easily applied in practice, whose control law is relatively simple. It not only does not need high-order derivative of desired command,but also does not require the feedback signals of velocity, acceleration and jerk of hydraulic rotary actuators. Another advantage is that it does not rely on any information of friction, inertia force and external disturbing force/torque, which are always difficult to resolve in flight motion simulators. Due to the special composite vane seals of rectangular cross-section and goalpost shape used in hydraulic rotary actuators, the leakage model is more complicated than that of traditional linear hydraulic cylinders. Adaptive multi-input single-output(MISO) fuzzy compensators are introduced to estimate nonlinear uncertain functions about leakage and bulk modulus. Meanwhile, the decomposition of the uncertainties is used to reduce the total number of fuzzy rules. Different from other adaptive fuzzy compensators, a discontinuous projection mapping is employed to guarantee the estimation process to be bounded. Furthermore, with a sufficient number of fuzzy rules, the controller theoretically can guarantee asymptotic tracking performance in the presence of the above uncertainties, which is very important for high-accuracy tracking control of flight motion simulators.Comparative experimental results demonstrate the effectiveness of the proposed algorithm, which can guarantee transient performance and better final accurate tracking in the presence of uncertain nonlinearities and parametric uncertainties.     

PR方程推算氮气/灭火剂蒸气等熵指数

氮气(N2)/灭火剂蒸气组成的混合气体的容积等熵指数和温度等熵指数随充填压力和温度的变化关系是影响机载灭火系统灭火剂释放过程的重要因素。基于PR(Peng Robinson)方程和范德瓦尔混合规则,编制了N2/灭火剂混合气体的容积等熵指数和温度等熵指数的计算程序,计算了三组混合气体N2/HFC227ea、N2/CF3I和N2/CF3Br充填压力分别为42MPa和25MPa,初始温度为293K时等熵指数随温度的变化曲线。结果表明:它们的容积等熵指数和温度等熵指数随着温度的升高而逐渐下降,呈近似线性关系。在相同温度下,充填压力为42MPa时的三组混合物的容积等熵指数和温度等熵指数均高于充填压力25MPa时的结果。在相同的充填压力和温度下,N2/CF3I的等熵指数最大,其次为N2/HFC227ea和N2/CF3Br的最小。      

碳纤维表面特性对防热材料烧蚀性能影响的研究

为了提高碳／酚醛防热材料的烧蚀性能，着重对碳纤维的表面特性进行了分析研究。结果表明，碳纤维的表面状态对防热材料烧蚀性能有很大的影响，其中主要的影响因素是纤维的捻度和浆料。为了改善材料在高状态试验条件下的烧蚀性能，降低纤维的捻度和上浆量是必需的。     

顾客满意指数的结构方程模型与应用

分析了经典的顾客满意指数的结构关系模型的基本原理;结合企业顾客满意指数测评的实际案例,给出了结合偏最小二乘回归(PLS)方法的顾客满意指数测评的线性结构关系(LISREL)路径分析的实施途径。此外,还通过控制某些中间变量的作用,研究了原因变量对结果变量影响作用分解的一般模式。     

Optimal assimilation for ionospheric weather – Theoretical aspect

Observation, specification and prediction of ionospheric weather are the key scientific pursuits of space physicists, which largely based on an optimal assimilation system. The optimal assimilation system, or commonly called data assimilation system, consists of dynamic process, observation system and optimal estimation procedure. We attempt to give a complete framework in this paper under which the data assimilation procedure carries through. We discuss some crucial issues of data assimilation as follows: modeling a dynamic system for ionospheric weather; state estimation for static or steady system in sense of optimization and likelihood; state and its uncertainty estimation for dynamic process. Meanwhile we also discuss briefly the observability of an observation system; system parameter identification. Some data assimilation procedures existed at present are reviewed in the framework of this paper. As an example, a second order dynamic system is discussed in more detail to illustrate the specific optimal assimilation procedure, ranging from modeling the system, state and its uncertainty calculation, to the quantitatively integration of dynamic law, measurement to significantly reduce the estimation error. The analysis shows that the optimal assimilation model, with mathematical core of optimal estimation, differs from the theoretical, empirical and semi-empirical models in assimilating measured data, being constrained by physical law and being optimized respectively. The data assimilation technique, due to its optimization and integration feature, could obtain better accurate results than those obtained by dynamic process, measurement or their statistical analysis alone. The model based on optimal assimilation meets well with the criterion of the model or algorithm assessment by ‘space weather metrics’. More attention for optimal assimilation procedure creation should be paid to transition matrix finding, which is usually not easy for practical space weather system. High performance computing hardware and software studies should be promoted further so as to meet the requirement of large storage and extensive computation in the optimal estimation. The discussion in this paper is appropriate for the static or steady state or transition process of dynamic system. Many phenomena in space environment are unstable and chaos. So space environment study should include and integrate these two branches of learning. This revised version was published online in August 2006 with corrections to the Cover Date.     

原位钛基复合材料中TiB的生成热力学及动力学

采用自蔓延高温合成（SHS）、感应熔炼和熔模精铸相结合的方法，利用Ti—B—Al体系制备出了原位自生TiB增强的钛基复合材料。借助XRD、SEM和TEM分析了复合材料的物相和增强体的形态。结果表明：在复合材料中只存在TiB增强体和Ti，无TiAl3杂质相形成，TiB增强体呈柱状短纤维，这与其B27晶体结构有关，且增强体／基体界面清洁无杂质污染，并从热力学和动力学两方面论述了在Ti—B—Al体系中制备TiB增强体的生成机制：在Ti-B—Al体系中，Al首先受热熔化使得Ti和B相继溶解于Al液中；Ti与Al之间先行发生化学反应形成Ti—Al金属间化合物，放出的热量进一步引发了溶解于液相中的B和Ti产生高温自蔓延形成Ti—B化合物。以热力学理论分析，应最终形成TiB2，但实际上由于动力学影响，最终形成了TiB。