展向行波状Lorentz力的波数对壁湍流控制的影响

展向行波状Lorentz力可以有效调制湍流近壁流动及减少壁面摩擦阻力。为了解行波波数在壁湍流控制中的影响,并进一步揭示该方法的减阻机理,本文利用Fourier-Chebyshev谱方法,通过直接数值模拟（DNS）,对槽道湍流的展向行波状Lorentz力控制和减阻问题进行了研究,讨论了展向波数kz对近壁流动及壁面阻力的影响。结果表明,当展向行波状Lorentz力诱导的流场被用来调制固有的近壁湍流流场时,固有流场和诱导流场同时受到调制。Lorentz力的展向波数对流场调制效果具有显著影响。通过波数的选择,引进新的涡结构,可以调制条带结构的展向间距与强度,影响近壁流体的湍流猝发活动,从而调制壁面摩擦阻力的大小。     

深空环境下卫星编队飞行队形重构实时重规划

针对深空环境中卫星编队自主队形重构的机动问题,设计了队形重构过程中的实时重规划方案。在每次重规划过程中首先用Legendre伪谱法将当前时刻到终端时刻的重构问题离散化为非线性规划问题;其次,根据卫星编队飞行队形重构的特点,使用协同进化粒子群(CPSO)方法对每次重规划进行求解,该方法既避免了传统优化方法对复杂问题梯度的求解,又能在整个优化过程中保证约束条件的满足,并且能够事先为粒子群的进化提供大致方向,极大地提高了每次重规划的计算速度;最后,提出了重构过程中具体的重规划策略,以保证队形重构的顺利进行。仿真结果表明,与传统的控制方法相比,在重构过程中,该方法能够在初始给定轨迹的基础上进一步优化,可以有效降低重构过程的能量消耗,并能够避免重构过程中碰撞的发生。     

基于三轴磁强计与雷达高度计的融合导航算法

为了减小近地轨道(小于1000km)地磁导航的估计误差协方差，提高导航的可靠性和准确性，在地磁导航系统中引入雷达高度计作为一个新的测量设备，提出了一种基于三轴磁强计与雷达高度计的融合导航算法。该算法取卫星的位置和速度向量作为状态向量，建立状态方程；取卫星周围的磁场强度和卫星到星下点实际海平面距离求出的地心距，作为观测量建立观测方程；利用扩展卡尔曼滤波构成一种融合导航算法。仿真结果表明，提出的融合导航算法对轨道位置的估计误差小于20米，速度的估计误差小于1米／秒，导航算法的精度和收敛性都优于使用单一地磁导航的系统。     

MANET中多路径AODV仿真与分析

在AODV路由协议的基础上引人备份路由,旨在提高Ad Ho.网络的性能.论文首先介绍了AODV路由协议,并指出AODV路由协议的不足,然后针对这种不足在AODV路由协议加入了备份路由.最后通过NS2仿真实验,比较了AODV路由协议、M- AODV路由协议的封包到达率、端到端时延等,表明M-AODV路由协议较AODV路由协议更具优势.     

硝酸羟胺水溶液的制备及其含量分析

以复分解法制备硝酸羟胺(HAN)水溶液，用正交实验分析了反应温度、反应时间和减压蒸馏温度对反应产率的影响。确定的实验室最佳制备条件为：反应时间25min，反应温度60℃，减压蒸馏温度50℃。并比较了氧化还原滴定法与酸碱滴定法测定硝酸羟胺水溶液中硝酸羟胺含量的精度。     

星地动态双向时间同步与测距算法

针对卫星运动对星地距离和钟差测量的不利影响,提出一种基于最小二乘拟合的星地动态双向时间同步与测距算法。在建立星地可视模型基础上,仿真了MEO运动卫星与地面时间同步站之间星地距离的变化规律,分析了卫星运动对星地双向时间同步与测距的主要不利影响。该算法首先利用星地双向时间同步数据分别生成星地距离和钟差拟合多项式,然后联合求解出运动卫星误差最小的星地距离与钟差。实验结果表明了该算法的合理性和科学性,在包含仿真误差的条件下,其时间同步精度优于3ns,测距精度优于3m。将其应用到各种空天应用系统的星地时间同步与测距中,可以消除卫星运动对双向时间同步与测距的不利影响,提高时间同步与测距精度。     

Fault diagnosis based on measurement reconstruction of HPT exit pressure for turbofan engine

Aero-engine gas path health monitoring plays a critical role in Engine Health Management(EHM). To achieve unbiased estimation, traditional filtering methods have strict requirements on measurement parameters which sometimes cannot be measured in engineering. The most typical one is the High-Pressure Turbine(HPT) exit pressure, which is vital to distinguishing failure modes between different turbines. For the case of an abrupt failure occurring in a single turbine component, a model-based sensor measurement reconstruction method is proposed in this paper. First,to estimate the missing measurements, the forward algorithm and the backward algorithm are developed based on corresponding component models according to the failure hypotheses. Then,a new fault diagnosis logic is designed and the traditional nonlinear filter is improved by adding the measurement estimation module and the health parameter correction module, which uses the reconstructed measurement to complete the health parameters estimation. Simulation results show that the proposed method can well restore the desired measurement and the estimated measurement can be used in the turbofan engine gas path diagnosis. Compared with the diagnosis under the condition of missing sensors, this method can distinguish between different failure modes, quantify the variations of health parameters, and achieve good performance at multiple operating points in the flight envelope.     

Effects of yaw-roll coupling ratio on the lateral-directional departure prediction and restraint

The experimental data obtained from yaw-roll coupled wind tunnel tests are used for lateral-directional departure prediction, by linearizing the_b model to extract nominal dynamic derivatives at each coupling ratio.The prediction results are compared with those of the existing engineering methods which are based on the conventional aerodynamic derivatives.The comparison shows that the yaw-roll coupling ratio has a great influence on the departure susceptibility.The departure resistance will loss in partial region of the coupling ratio when the angle of attack is higher than a critical value.According to the stable and unstable regions of coupling ratio, a two-segment stability augmentation system with two different feedback gain matrices is obtained by pole-placement method.The two-segment stability augmentation system is used in the simulations of straight and level flight, steady turn, spin recovery and Herbst maneuver.The simulation results are also compared with the applications of a fixed-gain stability augmentation system designed by the conventional aerodynamic derivatives.When the yaw-roll coupling effects are fully considered, the two-segment stability augmentation system is more effective for departure restraint and can provide a better flying quality with less control energy.     

前置不同诱导轮的高速离心泵性能

为研究分流叶片诱导轮及变螺距诱导轮对离心泵水力性能及汽蚀性能的影响,对具有前置诱导轮的高速离心泵进行了试验和数值模拟。外特性试验表明,两种前置诱导轮对高速离心泵效率的影响均不显著,前置分流叶片诱导轮的离心泵扬程相对于前置变螺距诱导轮有显著下降。汽蚀试验表明,小流量工况下前置分流叶片诱导轮的离心泵抗汽蚀性能较优,大流量工况下前置变螺距诱导轮的离心泵抗汽蚀性能较优,其余工况下两者的抗汽蚀性能相当。仿真结果表明,大流量工况下分流叶片诱导轮扬程较低,不能满足离心轮进口能量需求,致使前置分流叶片诱导轮的离心泵汽蚀性能变差。     

空间带电粒子辐照与预应力耦合作用对功能形面薄膜结构性能影响研究

空间大尺度薄膜航天器是航天技术发展的重要方向,采用折叠展开的大面积功能形面结构是此类航天器的基本特征,为满足热控、通信、聚光、成像与能量传输等功能,结构需要通过预应力来维持形面,保证较高的形面精度和结构基频,但预应力加载对带电粒子辐照下薄膜材料性能退化存在促进作用.文章通过对薄膜材料在不同预应力工况和空间环境耦合作用下的损伤行为以及退化规律开展试验研究,建立与预应力状态、辐照注量相关的材料性能退化规律,量化研究了预应力对空间辐射环境下功能形面薄膜结构性能影响.随着薄膜力学性能的退化,形面结构基频随之有微弱的降低,且对薄膜结构平面度造成一定影响.