结构基于独立模态空间控制的神经网络控制

在对柔性结构振动的主动控制中，独立模态空间控制是一种适合于柔性结构振动控制的方法，但如果控制器选择不好就会带来观测溢出和控制溢出．神经网络控制则具有较好的泛化作用和鲁棒性，对抑制观测溢出和控制溢出具有较好的效果．本在独立模态空间控制的基础上设计了一种神经网络控制，并对柔性梁及板进行了控制的数值仿真，取得了较好的效果．     

一种逆优化设计振动控制作动器的数目和位置的方法

在建立了悬臂梁上粘贴压电陶瓷片实现振动控制的动力学方程的基础上，研究了一种逆优化设计作动器／传感器的数目和位置的方法；用压电陶瓷作为自传感器作动器，以悬臂梁的振动控制为研究对象，要求振动控制系统具有一定的模态阻尼比，并以作动器控制力最小为目标函数，优化设计作动器／传感器的数目和位置。最后通过数值算例证明了该方法的有效性。     

一种区间B样条小波平板壳单元及应用

基于二维张量积区间B样条小波,构造了一种件能良好的小波平板壳单元．在小波单元的构造过程中,用二维区间B样条小波尺度函数取代传统多项式插值,在所构造的区间B样条平面弹性单元和平面Mindlin板单元的基础上组合而成．区间B样条小波单元同时具有B样条函数数值逼近精度高和多种用于结构分析的基函数的特点．数值算例表明：与传统有限元和解析解相比,构造的小波平板壳单元具有求解精度高,单元数量和自由度少等优点．     

区间B样条小波薄壳截锥单元构造

利用区间B样条小波的尺度函数作为有限元插值函数,从轴对称壳的能量泛函出发,由变分原理导出了单元刚度矩阵和载荷列阵,构造了区间B样条小波薄壳截锥单元.区间B样条小波单元同时具有B样条函数数值逼近精度高和多种用于结构分析的变尺度基函数的特点.数值算例表明:与传统截锥单元相比,本文构造的小波单元具有求解精度高、单元数量和自由度少等优点.     

一维区间B样条小波单元的构造研究

基于区间B样条小波及小波有限元理论,提出了一种区间B样条小波有限元方法。传统有限元多项式插值被一维区间B样条小波尺度函数取代,进而构造形状函数和单元。与小波Galer-kin方法不同,本文构造的区间B样条小波单元通过转换矩阵将无明确物理意义的小波插值系数转换到物理空间。转换矩阵在小波单元构造过程中起到关键作用,为了保证求解的稳定性,转换矩阵必须非奇异。构造了以区间B样条尺度函数为插值函数的一系列一维区间B样条小波单元。数值算例表明,本文构造的区间B样条小波单元与传统有限元方法相比,在求解变截面,变载荷等问题时具有收敛快和精度高等优势;有效地丰富了小波有限元法单元库。     

非线性压电效应下压电弯曲执行器的动力分析

研究压电弯曲执行器在强电场作用下的非线性动力行为．考虑电致伸缩和电致弹性的非线性压电效应，导出了压电悬臂执行器变刚度的弯曲振动控制方程．利用非定常振动的渐近理论，讨论了弯曲压电执行器的动力特征．根据目前的非线性模型可以计算压电悬臂执行器的固有共振频率与电场的变化关系．结果表明压电执行器端头挠度谐振幅度随作用电场振幅的增大而增大，以及力学品质因数随电场振幅的增大而减少，并且与实验结果非常吻合．通过数值比较得到在电场频率随时间变化非常缓慢的情况下非定常振动问题可以近似地用定常振动来处理．     

多尺度有限差分方法求解波动方程

小波分析是多尺度分析方法，本文利用具有紧支集的正交小波变换对有限差分方程进行空间多尺度近似，提出适合于层状介质波传问题数值计算的多尺度有限差分方法，将波动方程的求解转换到小波域中进行。利用小波基的自适应性与消失矩特性，有效减少了计算量、提高了稳定性，扩大了可求解的速度范围。地球物理勘探中的数值实例显示了算法具有良好效率。     

小波分析技术在GPS数据预处理中的应用

将小波分析技术应用于数据预处理,利用小波变换对GPS位观测值进行小波分解,可将GPS观测值分解为不同的频率成分,通过一定尺度上的带通滤波器进行滤波,就可以将特定的频率成分提取出来,而将其它成分滤去,从而有效地消除或削弱多路径效应及观测噪声的影响,提高GPS数据处理的精度.并运用Matlab语言进行了编程实现,对比不同基线长度下小波变换前后的预处理精度估值可知,经小波变换后的精度估值有了一定提高,表明了该方法的有效性与可行性.     

基于小波多分辨滤波特性的结构损伤识别

小波分析作为一个很好的损伤识别工具,可以看作是传统傅立叶变换的扩展,小波变换采取了可调整的时频窗口,因此小波变换的优势是它具有了“可变焦”性能对局部信号进行多尺度的刻画。小波基的伸缩和平移系列,使小波变换可看作是一组带通滤波器。本文全面分析了小波变换多尺度带通滤波器特性以及在结构在线损伤识别中的应用。结构损伤的出现体现在结构物理参数的改变,相对应的动力响应信号将会产生局部时变特性。利用小波分析的多尺度带通滤波器在不同尺度下对结构振动信号作滤波分析。通过观察不同带宽内振动信号的时频变化来判断结构损伤的存在。     

基于小波变换的撞击流压力波动信号分析

通过小波变换对信号进行多尺度细化分析,解决了傅里叶变换不能解决的许多问题．从分析噪声和信号本身奇异点的区别入手,利用小波在时频两域突出信号局部特征能力的重要性质,即噪声信号小波变换的极大值随尺度的加大而显著减少的特点,对撞击流反应器撞击区压力波动信号进行处理分析．分析结果表明:小波变换可以较好地去除信号中的噪声;通过消噪后信号的功率谱可知,撞击流压力波动信号具有自相似的分形特征,与前期的实验研究相吻合．     

Vibration control of piezoelectric beam-type plates with geometrically nonlinear deformation

This paper presents a wavelet-based approach of deformation identification and vibration control of beam-type plates with geometrically nonlinear deflection using piezoelectric sensors and actuators. The identification is performed by transferring the nonlinear equations of identifying deflection into a system of solvable nonlinear algebraic equations in terms of the measurable electric charges and currents on piezoelectric sensors. After that, a control law of negative feedback of the identified signals of deflection and velocity is employed, and the weighted residual method is chosen to determine control voltages applied on the piezoelectric actuators. Due to that the scaling function transform is like a low-pass filter which can automatically filter out high-order signals of vibration or disturbance from the measurement and the controller employed here, this control approach does not lead to the undesired phenomenon of control instability which is generated by the spilling over of high-order signals. Finally, some numerical simulations are carried out to show the efficiency of the proposed approach.     

基于小波变换的重力变化信号处理技术研究

针对重力敏感器中所测信号的特点，提出了小波变换的多分辨率分析方法。采用了强制去噪和阈值去噪两种方法，利用Daubechies小波函数，分别针对三种典型情况进行了分析。结果表明，对于信噪比非常小的重力变化信号，阈值去噪法相对于强制去噪法来说效果并没有明显提高，第9层下重建信号的逼近误差满足性能指标。文中还讨论了加入确定性干扰的情况下微弱信号的提取情况，结果表明，加入大的确定性干扰后，为了满足设计要求，小波分解的尺度有所增加，整体的滤波效果与未加入确定性干扰的情况基本相同。     

铝板中激光Lamb波信号的模态分析与缺陷检测研究

激光激励的Lamb波信号具有较宽的频带,且包含多个模态信息。本文采用二维傅里叶变换和时频分析等信号分析技术用于检测信号中的模态成分及缺陷信息识别。首先,对200组激光Lamb波信号进行二维傅里叶变换,得到信号的频率-波数图,可识别出激光Lamb波信号中的低阶A0、S0和高阶模态,并且A0模态能量高,可用于缺陷检测。随后对有、无缺陷状态下Lamb波信号进行连续小波变换,从时频图中识别出缺陷信号的频率成分,进一步提取特定频率下的小波系数幅值信号,实现了缺陷信息的识别。结果表明,二维傅里叶变换能较好地识别激光Lamb波的模态成分,而提取出的连续小波变换系数图,能准确实现缺陷定位。     

Extended Self Similarity of Passive Scalar in Rayleigh-Bénard Convection Flow Based on Wavelet Transform

Wavetet transform was used to analyze the scaling law of temperature data utilize the method of extended self similarity, presented first by Benzi et al. , to study the scaling exponent of temperature data. The obtained results show that the inertial range is much wider than that one determined directly from the conventional structure function, and find the obtained scaling exponent agrees well with the one obtained from the temperature data in an experiment of wind tunnel. The second one was that, by extending the formula which was proposed by A. Arneodo et al. for extracting the scaling exponentζ(q) of velocity data to temperature data, a newly defined formula which is also based on wavelet transform, and can determine the scaling exponentζ(q) of temperature data was proposed.The obtained results demonstrate that by using the method which is named as WTMM ( wavelet transform maximum modulus )ζ(q) correctly can be extracted.     

Robust disturbance rejection method for uncertain system with disturbances of unknown frequencies

In this paper, we discuss a robust disturbance rejection method for dealing with disturbances of unknown frequencies. Unlike many other approaches, the method proposed here does not require the disturbance frequencies of the separate harmonics to be estimated. The current approach is based on disturbance reduction and disturbance suppression. This novel disturbance reduction controller consists of an inverse of the nominal model with an input deduction and a high gain integral term. The proposed controller can reduce both periodic and nonperiodic unknown disturbances with uncertainties in both stable and unstable systems. In addition, undesired responses caused by residual disturbances and residual modeling uncertainties are suppressed by combining the novel disturbance reduction controller with a sliding mode controller. The simulation results demonstrate that the proposed disturbance rejection method performs well under different disturbance inputs including random signals.     

Wavelet packet based damage identification of beam structures

Most of vibration-based damage detection methods require the modal properties that are obtained from measured signals through the system identification techniques. However, the modal properties such as natural frequencies and mode shapes are not such a good sensitive indication of structural damage. The wavelet packet transform (WPT) is a mathematical tool that has a special advantage over the traditional Fourier transform in analyzing non-stationary signals. It adopts redundant basis functions and hence can provide an arbitrary time-frequency resolution. In this study, a damage detection index called wavelet packet energy rate index (WPERI), is proposed for the damage detection of beam structures. The measured dynamic signals are decomposed into the wavelet packet components and the wavelet energy rate index is computed to indicate the structural damage. The proposed damage identification method is firstly illustrated with a simulated simply supported beam and the identified damage is satisfactory with assumed damage. Afterward, the method is applied to the tested steel beams with three damage scenarios in the laboratory. Despite the noise is present for real measurement data, the identified damage pattern is comparable with the tests. Both simulated and experimental studies demonstrated that the WPT-based energy rate index is a good candidate index that is sensitive to structural local damage.     

吹吸扰动对壁湍流相干结构的影响

采用热线风速仪测量受吹吸扰动的壁湍流边界层的流向速度，用傅里叶变换和子波变换研究 吹吸扰动对壁湍流能谱的影响，结果显示施加的低频扰动使边界层内层大尺度结构的能量减 少，小尺度结构的能量有所增强，远离壁面时扰动强度逐步衰减直到在外层中消失；通过VITA 法和子波变换法检测猝发事件，表明该扰动降低了猝发强度，使猝发周期延长，条件平均速 度波形的幅值降低、持续时间变短，说明扰动明显抑制了相干结构的猝发过程. 利用子波变 换可以实现湍谱分析，能有效检测猝发中的湍流结构，是一种客观的分析工具.     

Applications of wavelet Galerkin FEM to bending of plate structure

A kind of calculating method for high order differentials expanded by the wavelet scaling functions and the integral of their product used in Galerkin FEM is proposed, so that we can use the wavelet Galerkin FEM to solve boundary-value differential equations with orders higher than two. To combine this method with the Generalized Gaussian integral method in wavelet theory, we can find that this method has many merits in solving mechanical problems, such as the bending of plates and those with variable thickness. The numerical results show that this method is accurate. This project is supported by the National Natural Science Foundation of China (No. 19772014) and the National Outstanding Young Scientist Foundation of China (No. 19725207).     

基于时间响应函数的结构阻尼识别方法比较

研究了3种基于时间响应函数的结构阻尼识别方法, 包括对数衰减法、希尔 伯特方法和小波方法. 给出了3种方法的实现算法, 分析了对密集模态的识别能力. 构造仿真算例, 采用3种方法识别了5{\%}, 10{\%}和30{\%}噪声条件下的模态阻尼. 结果表明, 小波方法比对数衰减法和希尔伯特方法具有更好的噪声鲁棒性. 采用小波方法分析了润扬大桥结构健康监测系统获得的实测数据, 识别出了润扬大桥悬索桥前6阶模态参数, 第2阶和第3阶模态频率相差仅为0.015\,Hz. 研究表明, 小波方法具备噪声条件下密集模态的识别能力, 是工程中阻尼识别的优选方法.     

Determination of mode shapes using wavelet transform of free vibration data

In this article, a new method is proposed to determine the mode shapes of linear dynamic systems with proportional viscous damping excited by an impact force. The time signals of responses and a priori knowledge of the natural frequencies are required in this method. The method is particularly suitable for the wavelet techniques which can precisely estimate the natural frequencies. A previously proposed method based on a modified Morlet wavelet function with an adjusting parameter is used to identify the natural frequencies and damping ratios of system, and the mode shapes are estimated using the proposed method in this work. It is shown that the extracted mode shapes are not scaled. Therefore, mass change method is used for scaling the mode shapes. Moreover, the effect of noise on the extracted modal parameters is investigated. The validity of method is demonstrated using numerical and experimental case studies.