基于小波变换的海杂波分布特性分析

提出了用小波变换对海杂波分布进行统计分析,利用小波多分辨分析估计海杂波的概率密度函数,通过拟合识别分布并求取参数,改变以往先假定海杂波分布识别的方法,克服了因为噪声的存在直接由海杂波数据估计分布参数不准确的缺点。通过适当地调整小波多分辨分析的阈值,可以获得更逼真的海杂波概率密度函数,适应各种海况下的海杂波分析。     

基于希尔伯特-黄与小波变换的压气机失速信号分析方法

针对多级跨声速压气机失速过程壁面静压测量数据,分别采用希尔伯特-黄变换(HHT)和小波分析方法进行时频分析。相比于小波分析方法,HHT时频图中失速过程的频率特征变化更为明显,且利用HHT图中失速发生后的特征频率可判断出失速团的旋转速度。结合方差分析,进一步探索了获取失速先兆信号的可行性。结果表明,两种方法均可用于压气机失速先兆预测,其中HHT方法能够提供更高层次的分解信号,得到的失速先兆更为提前。     

基于小波变换的高超声速边界层动态图像分析

利用小波变换技术,研究高超声速下动态尖锥周期俯仰摆动的边界层转捩图像。通过基于二维小波变换的图像消噪和图像增强算法,优化动态实验图像,根据小波变换图像的奇异性提取沿时间历程变化的尖锥边界线和边界层图像,得到尖锥的俯仰摆动周期和迎角变化范围。结果显示边界层厚度的变化周期与尖锥的俯仰摆动周期存在相位差,随着迎角增大,背风面转捩点向尖锥前缘移动。实验结果表明,基于小波变换的图像处理技术不仅能够作为高超声速尖锥实验流动显示进行定性观察,还可以实现对高超声速边界层转捩实验的精确观测和定量分析,成为一种重要的量化和自动化的实验技术和分析手段。     

基于小波包变换的模拟电路电源电流故障诊断

针对模拟电路故障诊断这一难点,运用基于IDDT技术的故障诊断方法,即利用小波包变换提取电源电流各频率成分的能量,作为神经网络的输入特征矢量进行故障诊断。仿真结果表明,该方法可以快速高效地进行模拟电路故障诊断与定位。     

转子故障的连续小波尺度谱特征提取新方法

引入图像分析方法,提出了直接从转子故障信号连续小波尺度谱中提取图像纹理特征的新方法.首先,通过转子故障模拟实验台采集了不平衡、不对中、碰摩及油膜涡动等典型故障信号;然后,分析了故障信号尺度谱的差别及所提取出的数字特征对故障的敏感性;最后用结构自适应集成神经网络进行了智能诊断实验,结果表明了本文所提出的尺度谱数字特征对转子故障诊断的有效性.      

Bernoulli-Euler梁振动的人工神经元网络控制方法

分析了Bernoulli-Euler梁的振动特性,从控制系统的角度得出梁振动控制系统的传递函数,并采用人工神经元网络的方法对其进行控制,辨识器及控制器均采用非线性神经元网络, 最后用matlab对振动控制系统进行仿真。     

Adaptive distributed observer design for containment control of heterogeneous discrete-time swarm systems

This paper develops both adaptive distributed dynamic state feedback control law and adaptive distributed measurement output feedback control law for heterogeneous discrete-time swarm systems with multiple leaders. The convex hull formed by the leaders and the system matrix of leaders is estimated via an adaptive distributed containment observer. Such estimations will feed the followers so that every follower can update the system matrix of the corresponding adaptive distributed containment obse...     

基于独立任务的分布式容错调度算法

主副版本法是常见的容错方法,将每个任务的主版本和副版本分配到两个不同的处理机上执行,只要任务的主版本分配到一个处理机,则对应的副版本可以在另一个处理机上重叠执行.笔者研究了分布式控制系统中,基于主副版本容错算法的副版本可以在执行时间上重叠来调度分配独立的任务,该容错算法以副版本执行时间重叠部分的最小化为复制代价,通过仿真实验与集中式调度和分布式调度算法进行对比分析.     

分布式电推进飞机动力系统评估优化方法

以电推进飞机的动力系统作为研究对象,开展了以下研究工作：采用电力系统潮流计算方法,分析了采用高压直流供电体制的分布式电推进飞机电气系统,模拟了其在稳定运行状态与断路故障状态下的能量流动关系,同时分析了直流电压等级对电气系统的影响。搭建了完整的分布式电推进飞机动力系统仿真模型,依据基于时间和基于高度的飞行剖面,对比分析了纯电推进与涡轮电推进架构在推进功率、推进效率与航程3个评价指标上的优劣。建立了动力系统典型部件的参数化模型,并使用符号规划算法对建立的参数化模型进行了优化计算,比较了传统涡轮推进与涡轮电推进架构下动力系统质量与燃油消耗率间的优化权衡关系。研究结果为分布式电推进飞机混合动力系统的设计提供了有价值的正向设计方法。     

Detection of polyphase pulse compression waveforms using the radon-ambiguity transform

The recently developed Radon-ambiguity transform (RAT) detects unknown linear frequency modulated (LFM) signals by computing line integrals through the origin of the signal's ambiguity function (AF) magnitude. It is shown that this method also detects the step LFM and frequency-derived polyphase pulse compression waveforms with varying performance degradation. Simulations are provided to estimate the detection loss relative to the LFM.     

On the free-vibration of rotating composite beams using a higher-order shear formulation

The free vibration behavior of rotating blades modeled as laminated composite, hollow (single celled) boxed beams is investigated. To this end, geometrically nonlinear structural model incorporating a number of non- classical effects such as anisotropy, heterogeneity, transverse shear flexibility, and warping inhibition is developed. Centrifugal and Coriolis force field effects are also considered in the formulation. However, Coriolis effect is discarded during the solution process. It is assumed that in-plane cross-sectional distortion is negligible. In contrast to the existing structural blade models, the traction free boundary conditions on the external surfaces of the beam are identically satisfied. The linearized dynamical equations and numerical results addressing the problem of the free vibration are supplied. Results obtained for the present higher-order shearable model are compared with those of the existing first-order shearable and the non-shearable structural models. Tailoring studies using the present model reveal an enhancement of eigenfrequency characteristics.     

Performance investigation of intercooler operating in wet condition using distributed parameter model

The performance of a marine gas turbine intercooler operating in wet condition was evaluated.The intercooler was a cross-flow plate-fin heat exchanger that used air and pure water as its working fluids at the hot and cold sides,respectively.The heat transfer performance and the water vapor condensation were investigated for a relative humidity of the inlet air that reached 100% during warship cruise.The condensation of the water vapors increased the hot side outlet temperature by a certain amount,which could in turn influence the performance of the compressor downstream.The condensate film thickness and the void fraction were calculated based on an annular two-phase flow model.It is found that water vapor condensation in hot flow channel increases the outlet temperature with a maximum value of 7.3℃ in the case of 100% relative humidity.The calculated liquid film thickness reaches a maximum value of 4μm,which indicates negligible thermal resistance to heat transfer.The results of liquid film thicknesses also provide a qualitative prediction of the diameter distribution of the condensate water droplets.     

基于小波神经网络的无叶扩压器失速分析

用来自不同文献的实验数据作为样本,对小波神经网络进行训练,并利用训练好的神经网络研究叶轮和扩压器几何尺寸对无叶扩压器失速的影响.计算分析结果表明:几何尺寸对于宽、窄扩压器失速的影响表现不同,这也证明了不同宽度的扩压器的确存在不同的失速机理.文章的结果,对无叶扩压器的设计具有一定的借鉴意义.      

不确定广义系统的鲁棒稳定性分析

本文通过矩阵测度，范数，以及Lyapunov方法研究了具有仿射型时不变香变不确定广义系统的鲁棒稳定性问题，得到了不确定广义系统具有无脉冲鲁棒容许的充分条件。并给出数值算例。     

The benefits of using ATE systems in the testing of printed circuitboards

An industry-based pragmatic review is provided of the economic and product-quality consequences of automatic test equipment (ATE) usage in printed circuit board testing. The company selection process, the nature of the industrial participants, and the data collection process are described. The benefits obtained by users are identified. It is demonstrated that the use of ATE systems does result in definable economic and quality-level benefits     

小波网络在某型航空发动机故障诊断中的应用

分析了用小波网络替代神经网络进行模型辨识的优点,在误差反向传播算法(Error back prop-agation)的基础上,结合小波分析理论,设计了一种小波网络算法.通过对某型航空发动机的仿真实验,小波网络能够及时准确地预测出发动机的输出.同时利用小波变换对残差的分析可以有效地检测出系统所发生的故障.      

Integration of onboard information-control systems using the vertical coordination principle

A principle of onboard information-control system integration on the basis of the coordinating control synthesis is proposed; the synthesis provides for transfer of state variable vector in the specified set of information-computing and control subsystems into the required region in one control step.     

High-velocity impact responses of 2618 aluminum plates for engine containment systems under combined actions of projectile form and oblique angle

Ballistic impact tests were carried out with examined projectiles of the Ti-6Al-4V titanium alloy to investigate the impact response of the 2618 aluminum plates at a nominal velocity of 210 m/s. The influence of projectile forms and oblique angles on damage formation was particularly discussed by applying different loading conditions such as multiple projectile forms and oblique angles. Additionally, the numerical simulation method was employed to provide further insight into the characteristics of damage and target responses. The Johnson-Cook(J-C)constitutive model with revised failure parameters was used to support the simulations to assess target responses and characteristics of the damage created from different impact conditions. Results show that there is a significant transition in the deformation mode as changes of the projectile form are applied. Moreover, the cracks on the back of the 2618 aluminum alloy plates impacted by the solid plate projectile and the hollow blade projectile tend to locate at different positions, which are supposed to be influenced by local bending and stretching. The work in this paper may provide guidance for the design of fan blade containment systems.     

Studies of polar current systems using the IMS Scandinavian magnetometer array

As a contribution to the International Magnetospheric Study (IMS, 1976–1979) a two-dimensional array of 42 temporary magnetometer stations was run in Scandinavia, supplementary to the permanent observatories and concentrated in the northern part of the region. This effort aimed at the time-dependent (periods above about 100 s) determination of the two-dimensional structure of substorm-related magnetic fields at the Earth's surface with highest reasonable spatial resolution (about 100 km, corresponding to the height of the ionosphere) near the footpoints of field-aligned electric currents that couple the disturbed magnetosphere to the ionosphere at auroral latitudes. It has been of particular advantage for cooperative studies that not only simultaneous data were available from all-sky cameras, riometers, balloons, rockets, and satellites, but also from the STARE radar facility yielding colocated two-dimensional ionospheric electric field distributions. In many cases it therefore was possible to infer the three-dimensional regional structure of substorm-related ionospheric current systems. The first part of this review outlines the basic relationships and methods that have been used or have been developed for such studies. The second short part presents typical equivalent current patterns observed by the magnetometer array in the course of substorms. Finally we review main results of studies that have been based on the magnetometer array observations and on additional data, omitting studies on geomagnetic pulsations. These studies contributed to a clarification of the nature of auroral electrojets including the Harang discontinuity and of ionospheric current systems related to auroral features such as the break-up at midnight, the westward traveling surge, eastward drifting omega bands, and spirals.