压电智能结构的实验研究

在复合材料表层铺设压电元件，利用压电元件能够实现力学量和电学量之间相互转化的独特性能，可将其用作传感器和驱动器，赋予材料和结构传感及动作的能力。本研究的压电材料采用锆钛酸铅压电陶瓷，基体材料采用玻璃纤维－环氧树脂复合材料，与外部信号采集和控制系统结合，构成了智能结构实验系统。本文对这一系统的损伤诊断和损伤主动控制功能进行了实验研究。该结构一方面可对冲击、过载等可能造成损伤的原因进行监测，并诊断裂缝、连接松动等损伤的产生和位置，另一方面还可自适应地驱动结构中的压电驱动器，改善结构应力状态，防止损伤的扩展。     

基于Huffman最优二叉树支持向量机的舱音记录器背景信号识别

飞行器舱音记录器(CVR)记录的舱音信号,通常是语音声、警告声、开关按钮声和背景噪声等混合而成.目前国内对该类信号的分析和辨别主要是计算机译码后利用人耳进行辨听,存在不易准确分辨各种独立声音信号的缺点.针对舱音信号是一种非平稳性的时频信号,提出了基于多尺度最优小波包基的CVR背景信号特征提取算法,将10种典型信号进行小波包分解,以分解得到的子带能量作为信号初始特征,再根据类间最大距离准则选取最优小波包基,从而确定待识别信号最具有代表性的特征向量,最后基于Huffman最优二叉树支持向量机进行CVR背景信号分类.仿真实验结果表明,该方法的平均识别率为94.62%,可以应用于CVR背景声音信号的自动识别.     

湍动能模拟内部声激励的计算研究

为了研究襟翼表面的声激励对多段翼型升力特性的影响机理,利用湍动能假设进行数值计算研究。以湍动能的量值、雷诺数以及襟翼与主翼的搭接量为参数,研究上述参数的变化对升力特性的影响,得到的结果与实验值符合良好。在多段翼型缝道处加入湍动能的影响规律是：（1）在升力特性线性段减少了升力系数,在失速点附近可以推迟分离,提高升力系数;（2）当雷诺数增加时,湍动能对升力系数的影响量减小;（3）在搭接量为零时,湍动能的影响最大。上述规律与在缝道处加入声学激励的影响规律一致,表明采用注入湍动能来类比声学激励有一定的应用价值。     

Nonlinear quantum ion acoustic shock wave dynamics with exchange-correlation effects

The dynamics of linear and nonlinear electrostatic shock excitations is studied in homogeneous, unmagnetized, unbounded and dissipative quantum plasma consisting of electrons and ions. The dissipation in the system is taken into account by incorporating the ion kinematic viscosity. The system is modelled using the quantum hydrodynamic equations in which the electrons are significantly affected by the quantum forces, viz., the quantum statistical pressure, the quantum Bohm potential and electron exchange-correlations due to electron spin. In the weakly nonlinear limit, using reductive perturbation method deformed Korteweg-de Vries Burgers’s (KdVB) equation, which elegantly combines the effects of nonlinearity, dispersion and dissipation is derived. It is found that the present model predicts the existence of both nonlinear oscillatory and monotonic shock structures. The temporal evolution, stability and phase-space dynamics of nonlinear ion acoustic shocks are investigated numerically to elucidate the effects of quantum diffraction, electron exchange correlation and ion kinematic viscosity.     

Efficient prediction of ground noise from helicopters and parametric studies based on acoustic mapping

Based on the acoustic mapping, a prediction model for the ground noise radiated from an in-flight helicopter is established. For the enhancement of calculation efficiency, a high-efficiency second-level acoustic radiation model capable of taking the influence of atmosphere absorption on noise into account is first developed by the combination of the point-source idea and the rotor noise radiation characteristics. The comparison between the present model and the direct computation method of noise is done and the high efficiency of the model is validated. Rotor free-wake analysis method and Ffowcs Williams-Hawkings (FW-H) equation are applied to the aerodynamics and noise prediction in the present model. Secondly, a database of noise spheres with the characteristic parameters of advance ratio and tip-path-plane angle is established by the helicopter trim model together with a parametric modeling approach. Furthermore, based on acoustic mapping, a method of rapid simulation for the ground noise radiated from an in-flight helicopter is developed. The noise footprint for AH-1 rotor is then calculated and the influence of some parameters including advance ratio and flight path angle on ground noise is deeply analyzed using the developed model. The results suggest that with the increase of advance ratio and flight path angle, the peak noise levels on the ground first increase and then decrease, in the meantime, the maximum Sound Exposure Level (SEL) noise on the ground shifts toward the advancing side of rotor. Besides, through the analysis of the effects of longitudinal forces on miss-distance and rotor Blade-Vortex Interaction (BVI) noise in descent flight, some meaningful results for reducing the BVI noise on the ground are obtained.     

突变截面燃烧室声腔纵向振荡频率规律分析

将药柱贴壁浇注的固体火箭发动机燃烧室简化为中间管型药两端容腔的形式,建立了突变截面H型声腔的物理模型,求解了此种声腔纵向振频的理论解和有限元解,以对称声腔与非对称声腔为对象,分析了一些关键几何尺寸对纵向声振频率变化的影响规律.计算结果表明,声振频率受装药长度与燃烧室长度的比值、装药内外径比值以及药柱浇注位置的共同影响.从合理的装药装填率考虑,初始振荡频率小于圆柱型声腔的振频,并随燃面退移连续增大.      

加筋板中超高速撞击声发射源定位方法

加筋板是航天器上的常用结构。为研制基于声发射技术的在轨感知系统,需要研究加筋板中声发射波传播规律及撞击源定位方法。文章测定了断铅信号在加筋板中的传播速度,对沿不同方向传播的波速进行了比较;通过有限元仿真,研究了筋体几何尺寸对板中声发射信号传播规律的影响。试验与仿真的结果表明:筋体对信号压缩波波速影响较小,但会造成信号第一幅值的衰减,在传感器布局设计时需要考虑到该因素。将加筋板中声发射信号传播速度取为沿不同方向传播波速的平均值,可将源定位问题转化成求取函数最小值的优化问题,在加筋板上对断铅波源和超高速撞击波源进行定位效果较好。     

基于机电阻抗方法的连接接头螺钉松动损伤识别研究

飞机在飞行过程中,机翼蒙皮的螺钉在反复载荷的作用下会发生松动、甚至脱落损伤,对飞机的飞行安全埋下隐患。及时发现此类损伤并采取有效措施可以提高飞机的安全性。针对此类损伤,设计了硬铝合金板连接接头的螺钉松动损伤模式,应用机电阻抗的试验方法对其进行了识别研究。试验结果表明：当选择恰当的频率范围时,随着螺钉松动损伤程度的增加,压电片与结构组成系统的RMSD（Root Mean Square Deviation）指标增加,两者表现出单调函数关系,应用RMSD损伤指标可以识别螺钉松动损伤程度,且对小的损伤更加敏感。     

宽频声传播计算中多自由度时域阻抗边界条件的适定性

旨在验证一种多自由度时域阻抗边界条件在宽频声传播问题中的适用性与精度.选用NASA(美国国家航空航天局)流管实验数据进行数值校核;采用高精度计算气动声学方法数值求解线化欧拉方程.计算结果与实验数据及单频结果均吻合很好,表明了该多自由度时域阻抗边界条件具备精确处理宽频声传播问题的能力.