通过PVDF阵列设计阶梯梁的模态传感器

以两端固支阶梯梁为例,通过高分子压电薄膜(Poly Vinyli Dene Fluoride,PVDF)传感器阵列测量其模态坐标。在该阶梯梁表面均匀黏贴一组相同形状的矩形PVDF薄膜,首先通过实验方法直接测得该阶梯梁的曲率模态,然后把曲率模态作为这组PVDF输出信号的加权因数,从而得到所需的模态坐标。实验结果表明,这种传感器设计方法是可行的,并且PVDF阵列式模态传感器具有在不均匀梁结构表面布置方便,能准确、方便的测出实验曲率模态,不受激励力位置影响,滤波效果好等优点。     

通过PVDF阵列测量阶梯梁体积位移的实验

以阶梯梁为例,通过一组阵列式压电薄膜(Polyvinylidene fluoride,PVDF)测量阶梯梁的体积位移。在梁表面均匀布置一组相同形状的矩形PVDF阵列,通过测量PVDF与激励力之间的频率响应函数,然后利用伪逆方法结合截断奇异值法(The truncated singular value decomposition,TSVD)设计这组PVDF阵列的加权系数,从而得到阶梯梁体积位移。实验结果表明,该方法能够准确测量到阶梯梁的体积位移,具有不需计算结构模态、附加质量小、与激励力位置无关等优点。     

通过实验模态分析设计阵列式压电模态传感器

提出一种新的基于实验模态分析的阵列式压电模态传感器设计方法。首先利用PVDF阵列进行实验模态分析得到结构的曲率模态,然后直接将曲率模态振型函数在相应测量点的幅值作为加权系数,对结构进行模态滤波,得到各阶模态坐标,并加以实验验证。研究发现,利用该方法设计阵列式压电模态传感器是可行的,而且该方法不需要进行复杂的数值计算,操作简单,模态滤波效果良好,可以很容易推广到二维复杂结构,具有较好的工程应用前景。     

通过阵列传感器获取固定板声辐射模态伴随系数

以固定支撑板为例,提出一种阵列式压电式传感器的设计方法测量前三阶声辐射模态幅值.在振动板表面布置一组形状相同的矩形PVDF(Polyvinylidene fluoride聚偏氟乙烯)薄膜作为传感器,根据所需要的声辐射模态伴随系数,通过对PVDF传感器阵列输出信号设计的加权系数,使PVDF传感器阵列输出信号为相应的声辐射模态伴随系数.结果表明这种PVDF传感器阵列设计与外激励力性质(如激励力类型、频率以及位置)无关,而且适用任意边界条件板结构.     

PVDF压电薄膜测量脉动压力可行性研究

PVDF压电薄膜是一种新型的高分子聚合物型传感器材料,具有高的压电常数,质量轻、柔性好、加工性能好、频率响应宽、对高频激励实用性强等优点,该文利用PVDF薄膜的压电特性设计了一种传感器,通过对传感器测试发现,在测量压力范围内,PVDF压电薄膜传感器具有良好的线性度、较高的灵敏度、较宽的频域响应、较低的迟滞性误差和重复性误差,并且温度对传感器的灵敏度影响较大,实际测试时需考虑温度的影响,激励测试表明PVDF压电薄膜传感器满足测量脉动压力的需求。     

基于分布式压电传感器的结构表面体积速度测量实验研究

以简支矩形薄板为研究对象,首先在波数域内对结构振动体积速度与辐射声功率的关系进行分析,推导出反映结构模态对体积速度贡献规律的数学表达式.在此基础上,结合PVDF压电薄膜的电荷输出方程,利用三角函数的正交性,给出一种新方法来设计体积速度传感器,并针对具体模型进行了结构体积速度测量实验研究.结果表明,所设计的分布式体积速度传感器具有较好的传感精度,进而说明了方法的正确性.同时还发现PVDF压电薄膜制作工艺与粘贴位置的偏差对其传感精度在一定频带内有较大影响,并且对不同位置激励下传感的影响程度不同.     

层合板结构声辐射模态传感器分析与测量

利用压电高分子材料聚偏氟乙烯(Polyvinylidene fluoride,PVDF)设计一种阵列式传感器来测量复合材料层合板结构的声辐射模态幅值。以声辐射模态传感器设计理论作为基础,进一步分析了声辐射模态传感器的测量精度影响因素,即粘贴位置和粘贴方向等。利用了声辐射模态传感器对层合板结构的固有频率、声辐射模态幅值以及声功率的进行测试分析。并对实验数据与理论仿真结果进行了分析。     

振动固定板结构体积位移的获取

在低频时控制振动板结构的体积位移是降低结构总声功率的一种有效策略.提出一种阵列式压电式传感器的设计方法测量固定板体积位移.通过对PVDF传感器阵列输出信号设计的加权系数,使PVDF传感器阵列输出信号为相应结构体积位移.结果表明这种阵列式PVDF传感器的加权系数与施加在振动板表面的外激励力性质(如激励力类型、位置等)无关.并且分析了影响阵列式PVDF传感器的各种因素及其适应性.     

对体积位移传感器的研讨

以不同边界条件的振动梁为例,提出通过分部积分方法设计特定形状的PVDF薄膜测量体积位移。这种分部积分方法得到的PVDF传感器形状不但与外激励力的性质（如激励力类型、位置以及频率等）无关,而且不需要振动梁的模态信息。研究表明,可以把振动梁的边界条件分为两类,即一端固定一端任意和两端位移为零,对于每一类边界条件可以用一种特定形状PVDF传感器测量其体积位移。     

对体积位移传感器的讨论

以不同边界条件的振动梁为例,本文提出通过分部积分方法设计特定形状的PVDF薄膜测量体积位移。这种分部积分方法得到的PVDF传感器形状不但与外激励力的性质（如激励力类型、位置以及频率等）无关,而且不需要振动梁的模态信息。研究表明,可以把振动梁的边界条件分为两类,即一端固定一端任意和两端位移为零,对于每一类边界条件可以用一种特定形状PVDF传感器测量其体积位移。     

移动荷载激励下基于平均曲率模态的简支梁局部损伤识别

该文采用缺口平滑拟合技术,利用移动荷载激励下结构的响应数据,通过分析梁式结构的平均曲率模态,对结构进行局部损伤定位。该方法不需要损伤前的桥梁激振数据,受信号噪音影响较小,并且可用于多移动荷载同时激励的情况,实践性和可操作性大大提高。首先分析在质量-弹簧-阻尼体系的移动荷载激励下简支梁的动力响应,通过Newmark-β时域积分算法分析沿时间平均处理后的简支梁振动位移模态,验证了基频模态在移动荷载激励下简支梁位移响应中的支配作用,在理论上解释了平均信号处理的意义。其后,利用ANSYS生死单元技术进行质量-弹簧-阻尼体系的移动荷载仿真,构造出三角函数拟合曲线的形式用于损伤识别。数值实验取得了良好的识别效果,表明该方法在多点损伤、多移动荷载、噪音影响等情况下均具有良好的灵敏性。该文为正常通车条件下桥梁的损伤识别研究提供了一种新思路。     

通过模态滤波实现阵列式传感器系统的故障诊断

基于结构振动响应特性利用改进的模态滤波方法对阵列式传感器系统进行故障诊断。在梁结构表面均匀布置一组加速度计,利用模态振型对该系统的输出信号进行重构,将重构信号与实际信号之间的曲率误差作为敏感参数,对系统中的模拟故障传感器进行检测与识别,并加以实验验证。数值计算和实验结果表明:改进的模态滤波方法不仅可以直接有效地对传感器系统进行实时故障监测,而且该方法与外界激励力位置无关,具有良好的工程应用前景。     

基于Bessel和Meijer-G函数的楔形和锥形悬臂梁振动分析

基于欧拉-伯努利梁理论,利用Lagrange法建立了楔形和锥形截面梁在外激作用下的非线性微分方程。提出了一种基于Bessel函数和Meijer-G函数线性组合的无需迭代及近似截断的振型函数,且该振型函数不依赖于楔形和锥形变截面梁的弯曲振动的运动方程是否为标准的Bessel形式,该方法能快速求解线性基频和模态函数。随后将该方法得到的模态函数代入变截面悬臂梁非线性振动的控制方程中,得到了常微分方程的弯曲非线性系数及惯性非线性系数,最后利用多尺度法研究主共振下的幅频响应。结果表明,该方法得到的线性基频及非线性幅频响应曲线与已有文献结果高度吻合,充分验证了用该方法求解的振型函数具有很高的精确性,该方法可为楔形或锥形变截面悬臂梁模态函数解析解提供新思路。     

Evaluation of crack locations in beam using artificial neural network-based modified curvature damage index

Although the frequency response-curvature methodology is commonly used to detect irregularities in mechanical and civil structures, the artificial neural network-based frequency response-curvature damage index method may have good efficacy in the detection and localization of structural damages. By utilizing experimental data sets, a novel method is proposed to pinpoint a saw-cut damage location and the degree of damage in beam models. Using a dynamic data logger, the frequency response function of a beam model is obtained for altering damage levels at different positions. As frequency response data contains environmental and operational noise, the accuracy of obtained results may get reduced. To improve the accuracy by reducing the noise effect, the experimentally obtained frequency response data is trained through an artificial neural network. Using central difference approximation, the sets of trained modal data are utilized to determine the improved mode shape curvature. The curvature damage index is then obtained by using the improved mode shape curvature for different damaged scenarios to ultimately identify structural damages.     

Phase-matched air ultrasonic transducers using corrugated PVDF filmwith half wavelength depth

A new type of large area PVDF film air transducer is proposed. The transducer features a high power output and a sharp beam angle. Conventionally known curved length mode resonators with two clamps at both ends have a resonance frequency determined by the curvature. In the present work, PVDF was formed into alternating concave and convex multiple curved sections, eliminating clamps, i.e., a periodic corrugation structure using a single PVDF film. Each convex and concave section has a common resonance frequency. A common excitation voltage induces vibration for each section, and the vibration direction is normal to the film surface. The vibration phase of convex section is shifted 180 degrees from the concave section. These waves add constructively to form a strong acoustic beam when corrugation height is approximately one-half of the wavelength. The corrugation height controls propagation path difference, canceling excitation phase difference. The design principle based on a uniform vibration mode is presented. Experimental investigations using 8.8×2.5-, 10×5-, and 20×20-cm² transducers are presented. Side lobes unique to this corrugation structure have been observed. A theoretical analysis of the side lobes is also presented. According to the theory, choosing the corrugation height appropriately will reduce side lobes to -15 dB with regard to the main lobe, and the observed side lobe height agreed with the theoretical result     

Experimental Investigation of Notch-Type Damage Identification with a Curvature-Based Method by Using a Continuously Scanning Laser Doppler Vibrometer System

This paper experimentally investigates a notch-type damage identification methodology for beams by using a continuously scanning laser Doppler vibrometer (CSLDV) system. Velocity response of a beam along a scan line under sinusoidal excitation is measured by the CSLDV system and an operating deflection shape (ODS) of the beam is obtained by the demodulation method from velocity response. The ODS of an associated undamaged beam is obtained by using a polynomial with a proper order to fit the ODS from the demodulation method. The curvature of an ODS (CODS) can be calculated with a high quality due to a dense measurement grid of the ODS. A curvature damage index (CDI) is proposed to identify a notch with a length of 1 mm along a beam and a depth of 0.9 mm under different excitation frequencies. The CDI uses differences between CODSs associated with ODSs that are obtained by the demodulation method and the polynomial fit; an auxiliary CDI obtained by averaging CDIs at different excitation frequencies is defined to further assist identification of damage. An averaging technique is applied to velocity response of the beam to reduce measurement noise. Effects of the number of averages on ODSs, CODSs, and CDIs are investigated. Four scan lines with an equal length of 151 mm and different locations with respect to the notch are used to investigate reliability of the proposed methodology. Finally, a whole scan line with a length of 555 mm along the beam is applied and the notch is successfully identified near regions with consistently high values of CDIs at different excitation frequencies; it can also be identified with the auxiliary CDI by a prominent peak at the location of the notch.     

基于摄动法的多条裂纹欧拉梁特征模态分析

基于摄动理论推导了带多条开口裂纹的欧拉梁的特征模态参数的理论计算公式。采用最直接的方式将梁开口裂纹模拟成梁微段内的横截面折减并用δ函数表达了带开口裂纹的梁沿轴线的截面惯矩和线质量等物理参数。基于此,建立了裂纹梁动力微分方程,并采用一阶摄动理论推导得到了梁的模态频率和振型计算公式。简支梁及悬臂梁算例研究表明,该方法具有很好的精度,与有限元模拟结果及实验结果都能很好地吻合。并采用此方法分析了裂纹深度和位置对带多条开口裂纹梁的特征模态参数的影响。结果表明,裂纹对各阶模态频率虽然影响有限,但其引起的各阶频率变化有着明显的模式,可用于结构损伤定位;裂纹对模态振型影响不明显,但对模态曲率影响比较大,可用于结构损伤位置和程度的诊断。     

多变量AR建模方法在工作模态参数辨识中的应用

对于一些大型工程结构,有时很难甚至无法测量结构的输入信号,只能利用实测的响应数据进行工作模态识别.针对这一实际工程情况,首先利用工况下结构的响应数据作相关分析,继而对相关分析后得到的多组数据构造多变量自回归(AR)模型,依据逐步最小二乘法和准则函数优化思想确定模型阶次和估计模型参数,并由模型参数矩阵的特征值分解确定结构的工作模态参数,最后利用TH6350大型镗铣加工中心主轴系统进行试验验证,结果对比表明,这种方法不仅能够有效提取结构动态特性参数,而且还能提供有关激励和结构振型的信息.