多阶梯弯振圆盘的设计

由弯振辐射阶梯盘与纵振换能器组合而成的复合超声振动系统,因其兼具弯曲振动低声阻抗和纵振换能器高辐射效率的特点,在气介式功率超声领域有着很好的应用。阶梯圆盘的频率方程中包含特殊函数,且方程数目多,求解过程非常繁杂。以自由边界条件下的单阶梯、双阶梯弯振圆盘为例,提出在给定阶梯圆盘弯振频率﹑基底厚度以及材料参数的条件下利用数值计算方法,编程设计阶梯圆盘的方法。试验测试与理论计算相吻合。为多阶梯弯振圆盘的设计提供一种新的方法。     

纵弯转换超声振动雾化系统的雾化特性研究

提出了一种由夹心式纵向振动换能器与弯曲振动圆盘构成的纵弯转换模式的超声振动雾化系统。弯曲振动圆盘的周边与变幅杆的端部相连接,并在变幅杆纵向振动的激励下产生弯曲振动。受圆盘弯曲振动的作用,液体在圆盘的端面上实现雾化。通过理论分析和实验对这一振动雾化系统的振动特性、辐射阻抗和声场进行了研究。结果表明：该系统比传统的纵向振动雾化系统具有更高的功率输出能力,并且可以使液体雾化后具有更强的指向性和作用能量。     

基于Mindlin理论多阶梯厚圆盘弯曲振动特性研究

实际应用中为了获得大辐射声功率,通常采用多阶梯圆盘作为辐射体。从声学工程应用角度,基于Mindlin厚板理论结合连接处的连续性条件和边界条件推导了自由边界条件下的多阶梯厚弯振圆盘的弯振频率方程,利用数值计算法对多阶梯厚圆盘振动特性和频率特性进行研究,并结合有限元法进行模态分析,其结果与试验测试及理论计算基本一致;研究了各结构参数对振动频率的影响规律,结果表明各阶频率随阶梯圆盘节线半径r1的增加而增大,随阶梯圆环外半径r2的增大而减小,随圆盘高度和基底高度的增加而增加;各部分的材料对多阶梯圆盘的频率影响不同,其中材料的弹性模量影响最大,研究结果为多阶梯弯振厚圆盘和大功率弯曲振动辐射器的设计提供理论参考和频率调试依据。     

弯曲振动圆盘几何尺寸与振动特性关系的研究

对超声珩磨声学系统中弯曲振动圆盘的振动特性进行了试验研究，结果表明，振动圆盘振幅随厚度的减小而增大。并且当圆盘为薄圆盘(厚度半径比≤1/5)时，圆盘振动为弯曲振动，能够获得良好的振动效果，最大振幅可达20.5μm，存在增幅特性，同时可以看出波节圆数目和大小。当圆盘直径不变时，共振频率随圆盘厚度的减小而降低，圆盘在不同频率下被激发共振。所获得的相应最大振幅值，对弯曲振动圆盘的尺寸设计和应用具有一定的参考价值。     

简支条件下三叠片复合弯振换能器振动特性研究

采用瑞利法对简支边界条件下三叠片圆盘弯振换能器进行理论研究,并推导其谐振频率及有效机电耦合系数,通过数值计算分析了谐振频率及有效机电耦合系数随换能器各尺寸参数的变化规律,结果表明换能器结构参数对谐振频率和有效机电耦合系数有很大影响,谐振频率随换能器各尺寸参数的增大而增大,在其它尺寸一定的情况下有效机电耦合系数随着金属片厚度,都有一个最大值,也为三叠片弯曲振动换能器的进一步广泛应用提供理论支持。     

纵-扭复合模式压电超声换能器设计分析

提出了一种螺旋槽纵-扭复合模式振动压电超声换能器结构,并对其纵-扭复合模式振动进行了理论分析。重点研究了螺旋槽的尺寸对换能器频率的影响,通过模拟分析发现螺旋槽的深度对换能器的共振频率影响比较大,并得到了纵扭共振时换能器的几何尺寸。理论模拟与试验结果吻合较好。     

基于传感器对风力机塔架轴向及横向振动特征分析

采用振动测试分析系统对小型水平轴风力机塔架不同高度测点位置的轴向及横向振动信号进行测试与分析。实验结果表明,塔架非共振(以塔架一阶弯振频率作为共振的对照频率)时,塔架横向振动幅度大于轴向振动;风轮旋转基频与塔架一阶弯振固有频率接近时,塔架发生共振,塔架轴向振动幅度大于横向振动。工程应用中利用该规律,可以对小型水平轴风力机进行监控预警避免塔架共振,也可在设计阶段加强塔架横向结构,增加塔架寿命。     

新型结晶器非正弦振动系统弹性振动响应的研究

针对开发的逆平行四连杆驱动的串接式全板簧结晶器非正弦振动系统,利用集中参数法建立该系统扭振与线振相耦合的动力学模型,并推导其运动微分方程。采用谐波平衡法求出系统的弹性振动响应,时域分析结果表明,在某些工作频率下结晶器运动规律产生畸变,系统发生剧烈弹性振动。频域方面,由FFT分析得出系统发生共振是结晶器运动规律产生畸变的原因,其本质是弹性振动响应的频谱中谐波明显增多,谐波幅值大幅增加。在此基础上分析系统各类激励对弹性振动的影响,结果表明,具有多频性的内激励是系统共振的决定因素,决定了共振的频率,而外激励只影响共振峰值的大小。这些结论为该振动系统的进一步应用及结晶器非正弦振动系统的平稳性研究提供了理论依据。     

利用导波传输实现二维高频超声振动

为简化二维超声椭圆振动结构,提高刀尖振动响应精度,利用导波具备单向动态刚度特性,研制了利用导波线传导超声振动的高频二维振动装置。该装置由101.96 kHz的纵振换能器和纵-弯复合振动工具头组成,用导波线将换能器和振动工具头连接起来,通过两路激励电源输出相位差的调节,能够获得相应的二维振动轨迹,并利用有限元仿真模态分析对该装置进行结构优化,确定最优结构。对整体二维振动装置振动特性检测结果表明,振动工具头前端的刀尖能产生一个0.4 mm振幅的纵-弯复合振动。该装置可以应用于超精密切削,如航空航天、军事、电子和光学等需要高精度或难加工零部件的加工。     

复合盘压电超声换能器的径向振动频率方程

提出并研究一种复合盘压电超声换能器的径向振动特性。依据机电类比原理,建立复合系统的径向振动等效电路,并推导出其径向振动频率方程。数值计算表明,当换能器半径比一定时,对给定材料换能器径向共振频率与压电晶片直径的积为常数。此外,径向复合换能器不满足传统的“半波长”级联规律,必须进行整体设计。作为算例,给出常用材料钢、铝和钛与PZT-4复合压电超声换能器的径向共振频率常数与其半径比的拟合关系曲线。试验加工两个径向复合压电超声换能器,并测定其共振基频。结果表明,换能器谐振频率误差小于3%,能够满足工程应用需要。     

复合棒型换能器锥形前辐射头弯曲振动特性

宽频带声换能器在军用及民用上都有着广泛的应用 ,近几年来国内外都开展了一些研究工作。利用复合棒型换能器的纵向振动基频与前辐射头弯曲振动的恰当耦合 ,可展宽换能器的频带 ,前辐射头是一关键部件。本文用有限元方法计算并分析了前辐射头在水中及空气中不同边界条件下的弯曲振动特性 ,结果表明 :并非所有几何尺寸的辐射头都能激发出弯曲振动来 ,两端自由时和螺栓端固定时 ,弯曲振动基频与辐射头厚度的关系恰恰相反。     

Scattering of flexural wave in a thin plate with multiple circular inclusions by using the multipole method

The multipole method is presented to analytically solve the scattering of flexural wave by multiple circular inclusions in an infinite thin plate. The near-field dynamic moment concentration factor (DMCF) and the far-field scattering pattern are both investigated in this paper. The former has a connection with the fatigue failures and the defects in plate-like structures can be detected by the latter. Owing to the addition theorem, the multipole expansion for the multiple scattering fields can be transformed into one coordinate system centered at one circle where continuity conditions are required. In this way, a coupled infinite linear algebraic system is derived as an analytical model for an infinite thin plate with multiple circular inclusions subject to an incident flexural wave. The convergence analysis is conducted to provide the guideline of usage for the proposed method. The effects of the size and thickness of the flexible inclusion, and the central distance between inclusions on the near-field DMCF and the far-field scattering pattern are investigated in the numerical experiments. It shows that the scattering pattern correlates closely with the size and thickness of weakness, indicating the importance of the scattering pattern to detect the various defects. In addition, the DMCF of two corrosion defects is larger than that of one. Therefore, it is essential to evaluate structural safety when multiple circular defects are very close to each other. The effect of the space between the inclusions on the near-field DMCF is different from that on the far-field scattering pattern.     

固定边界阶梯圆盘的设计及其振动特性计算

利用薄板的弯曲振动理论,推出了固定边界条件下带有一个阶梯的阶梯圆盘的频率方程,提出了求解频率方程的数值计算方法,编制了计算程序,由此可计算出阶梯圆盘的半径和节线位置,设计出完整的阶梯圆盘。并用有限元仿真软件对阶梯圆盘的振型和位移分布进行了计算,两者计算结果基本吻合,为这种条件下阶梯圆盘的设计提供了方法。     

Calculation of the Bottom Signal of a Direct Transducer with a Rectangular Piezoelectric Plate

The dependence of the bottom signal of a direct transducer with a rectangular piezoelectric plate on the distance to a reflective planar plate is calculated using a two-dimensional Fourier transform. The calculations for piezoelectric plates with different aspect ratios are made using numeric integration. Results for rectangular and circular piezoelectric plates are compared.     

Calculation of DGS diagrams of a normal transducer with a rectangular piezoelectric plate

In the Kirchhoff approximation, the acoustic path of a normal transducer with a rectangular piezoelectric plate is calculated for reflectors of the type of rectangular and circular flat-bottom holes. The formula for the acoustic path can be used for constructing DGS diagrams. In limiting cases, relationships coinciding with familiar ones follow from this formula for the acoustic path. Numerical calculations of DGS diagrams of a transducer with a rectangular piezoelectric plate with different ratios of sides are performed and certain features are pointed out. Additional results of numerical calculations of a bottom signal of such a transducer performed with the relation obtained above are presented.     

基于摄动方法的受损薄板模态分析

将结构的损伤用δ函数进行表达,建立损伤条件下薄板的自由振动方程。利用一阶摄动方法给出摄动项的一般表达式,并结合δ函数的性质,求出受损薄板模态参数的解析表达式。以一个四边简支的受损薄板为数值算例,计算损伤条件下其模态参数的变化。最后分析损伤情况对模态参数的影响,为利用动力学特性对板的损伤监控和检测提供理论依据。     

On the directivity characteristic of an angle transducer in the reception mode

The acoustic path of an angle transducer is calculated in the reception mode in the geometrical-acoustics approximation. The comparison of the angles of propagation of transverse and longitudinal waves in the reception mode with the corresponding angles in the transmission mode shows their coincidence. It is established that the directivity characteristics of an angle transducer for transmission and reception are identical. The formula of the acoustic path for a flat-bottom circular reflector with different positions and orientations is obtained for the far-field zone of the angle transducer.     

Transverse vibration of a quarter of an elliptic plate with variable thickness

Rayleigh-Ritz method has been used to find the first three frequencies and mode shapes for free flexural vibration of a plate in the form of a quadrant of an ellipse with linear and quadratic thickness variations. The results for a quarter of a circular plate with uniform thickness have been obtained as a special case and comparison has been made with results already available. By taking various combinations of clamped, simply-supported and completely-free edges we get twenty-seven different cases. Tables are given for the first three frequencies for different values of parameters. Mode shapes have also been plotted in some cases. The convergence of results is indicated by working out approximations of various orders.     

Creative approach for the deflection formula according to relative length of supporting edge in a partially supported circular plate

The purpose of this investigation is to derive the maximum deflection formula of the circular plate with nonaxisymmetric boundary condition, such as chalk valves for vessel and artificial heart valves, with respect to the length ratio of supporting edge using elastic beam theory. To evaluate the deflection characteristics of this plate, we assumed the circular plate to have a cross-section that varies in the longitudinal direction, and derived the maximum deflection formula of this circular plate with a radius of ‘r’ in four boundary conditions. Then to verify the deflection formula that is derived from elastic beam theory, five different relative lengths of the supporting edge were adopted as the design parameter, and finite element analysis was carried out for each model.