Dynamic bending/torsion and output power of S-shaped piezoelectric energy harvesters

This paper studies the dynamic electromechanical response of S-shaped piezoelectric energy harvesters both numerically and experimentally. The resonant frequency and output voltage of the harvesters excited by bending/torsion vibration were analyzed by three dimensional finite element method. The resonant frequency and output voltage were also measured, and a comparison was made between analysis and experiment. The effects of waviness ratio, proof mass and load resistance on the dynamic electromechanical fields and output power were then discussed in detail.     

Factors affecting the performance of piezoelectric bending actuators for advanced applications: an overview

The behaviors of piezoelectric bending actuators both in static and dynamic conditions driven by a high electric field were investigated and are summarized in this paper. In the static condition, the polarization and the displacement were measured and analyzed. It was found that the displacement hysteresis loop is the superposition of displacement loop induced by each layer of the actuator. The shape variation of the hysteresis loop is affected by the actuator configuration, i.e., the arrangement of electric field and poling direction. When the poling direction is parallel to an even electric field, such as parallel bimorph, the domain turns to switch at the exact coercive field of the piezoelectric material. However, when the poling direction is antiparallel to the electric field, such as series bimorph, the effect of electric field redistribution will take place during the domain reorientation, which reduces the actual electric field in the electric field–poling direction antiparallel layer, therefore prohibiting further domain reorientation. As a result, the series bimorph is noted to be more resistant to domain reorientation than the parallel bimorph. In the dynamic condition, the functions and relations of vibration velocity, heat generation, stress, and frequency were examined both theoretically and experimentally. It was found that the stress effect dominates at low frequency. At low frequency the failure mode of the actuator is often the physical fracture of the material. However, at high frequency, the failure modes mainly resulted from heat generation, unstable operation, depoling, and domain reorientation of the actuators. The vibration velocity will also decrease accordingly at the high frequency range due to more losses and heat generation.     

有限元在粘弹性细棒动力学参数反演中的应用

粘弹性材料具有良好的阻尼性能,在工程振动与噪声处理上的应用非常广泛。利用粘弹性材料进行阻尼结构设计并预测其动力学特性,需要知道准确的动力学参数。回顾粘弹性材料动力学参数测试的经典方法,并着重介绍共振法测试技术。研究共振法测试中细棒的动力学响应与动力学参数间的关系,在此基础上,基于共振法测试数据和有限元仿真,提出一种反演粘弹性材料动力学参数的新方法。首先根据幅值比反演出损耗因子,再根据共振频率反演出储能模量。通过具体算例验证可知,反演得出的动力学参数的相对误差均在4 % 以内,该反演方法不仅结果收敛、准确可靠且反演速度快,为在连续频率范围内的动力学参数反演奠定基础。     

基础位移激励下包装系统的非线性振动分析

包装系统的振动特性是研究其共振频率和振动过程中所受动态载荷的基础.用三次多项式函数表征包装系统非线性弹性力,建立了基础位移激励下包装系统的非线性动力学方程,分别用谐波平衡法和直接数值积分法研究了其非线性动力响应特征,得出了频响函数和幅频曲线,并揭示了忽略包装系统弹性力的非线性会导致振动分析的显著误差.分析理论和方法为预测包装系统共振频率以及振动过程中受到的动态载荷提供技术基础.     

微振动输送中圆盘型压电振子的动力学分析

目的研究压电陶瓷振动给料器的双晶片压电振子,求出其力学表达式,为振动给料器的双压电晶片的优化设计奠定理论基础。方法以螺旋式压电振动给料器的圆盘型压电振子为例,对圆盘型压电双晶片进行动力学分析,建立振动模型及动力学方程,对激振力进行求解。结果运用Rayleigh-Ritz法推导出在简支边界条件下,双压电晶片振子的弯曲振动的共振频率以及激振力表达式,得出最大误差出现在160 V处,理论计算与实验验证数据的误差为10%左右,有限元分析与实验验证数据的误差为5%左右。结论通过实验可以看出在实际应用中,要综合考虑其电压输入与压电陶瓷层的变形程度,选择最佳的电能输入,才能使压电双晶片获得最大的激励位移。     

一种采用激振器激励的扬声器振动部件共振频率测量方法及系统

提出了一种采用激振器激励方式的扬声器振动部件共振频率测量方法及系统。采用激振器作为激励被测部件振动的激励源,并通过加速度传感器实时检测夹具的振动加速度（包括幅度和相位）,以确保被夹具夹持住的被测部件在测量频率范围内上下平稳振动;通过激光位移传感器测量被测部件在不同频率点振动时的振动位移,可得到被测部件振动的频率响应（被测部件振动加速度和夹具振动加速度的比值的频率响应）;根据该频率响应进行计算最后可得到被测部件的共振频率。实验结果表明,实测频率响应的曲线与理论分析相一致,测量结果的可重复性和准确性良好,可测量的振动部件的种类和范围更广。     

磁流变阻尼器对斜拉索减振效果的试验研究

采用磁流变阻尼器作为被动控制器件，以钱江三桥南岸154m长的斜拉索为试验对象．通过阶跃激励的方法获得斜拉索振动的自由衰减信号。对采集到的信号进行小波分解、希尔伯特变换识别系统的等效阻尼比。据此来判断磁流变阻尼器在施加不同电压情况下对索前三阶模态振动的减振效果，并与油阻尼器的制振效果进行比较。试验结果表明磁流变阻尼器作为被动控制器件时制振效果明显，优于油阻尼器且控制的频域范围要比油阻尼器的广；当供电失效时也可满足索减振的要求。索的各阶共振峰频率在安装MR阻尼器后发生稍许漂移。     

Development of a Vibration Device for Grinding with Microvibration

This study aimed to develop a device to facilitate grinding experiments with microvibration for analyzing the vibration effect on surface finish of ground surfaces. A microvibration device was designed and fabricated. It can be used to provide microvibration to the workpiece vertically and/or horizontally during grinding. The relationship of the driving voltage, vibration displacement, and frequency was established. The vibration displacement of the device developed is proportional to the driving voltage amplitude for both vibration directions. The vibration frequency and displacement can be adjusted during the grinding process. Grinding experiments were carried out to compare the surface finish of silicon samples ground with and without microvibration. The results verified that microvibration of the workpiece along a certain direction during grinding can affect the surface finish of the ground workpiece.     

一种准零刚度车载隔振系统的设计与试验研究

针对车辆行驶工况环境以及振动频率,研制了一种空间占比小、安装方便的准零刚度(quasi-zero-stiffness,QZS)车载隔振系统。将垂向弹簧与两个对称的负刚度结构并联,负刚度机构用于刚度校正,通过静力学特性分析,初步确定了系统在平衡位置具有准零刚度的参数条件,在推导中引入了加工误差系数,分析了加工误差系数对系统准零刚度的影响机理。建立了系统非线性动力学方程,采用平均法求解了系统在车体简谐位移激励下的动力学响应,分析了系统参数和激励幅值对位移传递率的影响。在此基础上,设计制作了准零刚度隔振系统,进行了不同激励幅值、激励频率下的测试,得到了实测的位移传递率幅频响应曲线,并与理论计算结果进行了比较。另外,还通过TruckSim/Simulink联合仿真进行了车载随机激励工况仿真分析。研究表明,试验与理论结果吻合较好,验证了准零刚度隔振系统理论建模和分析方法的正确性。准零刚度的起始隔振频率在1.4 Hz左右,优于线性系统的起始隔振频率2.9 Hz。与车体相应相比,隔振后的位移响应均方根值降低80%以上,加速度均方根值降低90%左右,且稳态时准零刚度隔振系统的稳定性较好,具有良好的隔振性能。     

Investigation on Axial Displacement Fault Mechanism Based on Dynamic Characteristic Coefficients Identification of Tilting-Pad Thrust Bearing

To prevent the thrust bearing damage faults, the thrust bearing pad temperature and the static axial displacement variation are usually monitored and cared about, but axial vibration caused by axial dynamic excitation can also result in the severe rubbing. An electric oil pump system with overflow valve is designed on a similar industrial centrifugal compressor test-rig to apply the axial low-frequency excitation from 3 to 7 Hz, and the axial and radial vibration response amplitudes are analyzed. Then, the stiffness and damping coefficients of tilting-pad thrust bearing (TPTB) are identified by instrumental variable filter (IVF) algorithm to reveal the mechanism of TPTB dynamic characteristics affecting axial vibration. Finally, a fault case about surge and the rubbing of thrust bearing is studied. Compared with axial vibration, radial vibration does not directly correlate to axial excitation, and the axial frequency spectrum is an effective method to diagnose axial displacement faults; the static axial load, the dynamic excitation amplitude and the excitation frequency all exert influence on thrust bearing dynamic characteristics and axial vibration response. The research results can guide the design of thrust bearings and help to diagnose the axial displacement faults, while the test device and method can be used to measure the static and dynamic characteristics of thrust bearings.     

预压缩气垫包装系统静力及动力学特性研究

目的 以柱形气垫包装系统为研究对象,建立静力及动力学模型,对静态压缩、自由振动和基础激励受迫振动特性进行研究。方法 建立气柱压缩力数学模型,并通过试验、仿真验证模型,通过建立预压缩柱形气垫包装系统力学模型,研究静力及动力学特性。结果 预压缩量和充气压力越大,包装系统固有频率越高。在包装对象宽度定值约束下,选取多个小直径气柱,固有频率更高,且薄膜应力更小。在基础激励下,包装系统固有频率处存在共振峰值,对高频域气垫表现出了较好的减振特性。结论 所建立的静力压缩模型与试验、仿真结果较吻合,所建立的动力学模型合理,结果准确。     

Development of piezoelectric monomorph actuator using electrophoretic deposition

In the present work, investigation of the functional property of piezoelectric graded monomorph actuator systems is presented. The functional graded actuators were fabricated by electrophoretic deposition (EPD) using pure PZT and doped PZT materials. Actuators developed have shown gradual gradient variation in microstructure. It is noted that the trend in microstructural gradient does not represent similar trend in piezoelectric property gradient. The displacement of microstructural graded and both piezoelectric and microstructural graded actuators were measured in the static condition. The latter was also measured under dynamic condition. The results show that the proper gradient distribution of the piezoelectric properties is important to improve the electromechanical performance of the actuator.     

激励对柔性结构上设备振动传递率的影响

对机载仪器设备进行振动控制是提高其精度和寿命的重要手段。发动机、其它设备或者外部环境振动通过机体结构传递到机载设备。从这一实际出发,将机体结构建模为弹性梁,认为外部激励直接作用于梁结构,并通过隔振器传递到机载设备。运用子结构导纳法建立基础-隔振器-刚体系统动力学模型,推导出由基础结构通过隔振器传递到机器设备的速度传递率表达式,分析速度传递率随激励频率和激励施加位置变化规律,并通过试验进行验证。结果表明,基础梁的横向共振是导致传递率增大的主要原因;相对于基础梁非对称激励能激发更多基础结构弯曲共振模态;高频激励会引起隔振器纵向与弯曲共振产生驻波效应;推导出公式在100 Hz~1 000 Hz之间能够比较准确地反映传递率的变化。     

温度变化对悬索非线性内共振响应特性影响

悬索是一类典型的同时包含平方和立方非线性的柔性结构,其模态间极易发生各种形式的内共振。以悬索同时发生主共振和2∶1内共振为例,探究温度变化对悬索非线性内共振响应特性的影响。通过引入张力改变系数,建立了均匀温度场中悬索面内非线性运动微分方程;利用Galerkin法和多尺度法分别得到激励作用在高阶和低阶模态时,系统极坐标和直角坐标形式的平均方程;通过绘制共振响应时的激励响应幅值曲线、幅频响应曲线、动态解、时程曲线、相位图、频率谱以及庞加莱截面,定性和定量地描述了温度变化影响下的内共振响应特性。数值算例表明:频率会明显改变悬索模态频率,影响系统内共振响应,温度上升时,内共振更容易发生在Irvine参数较小的悬索;无论激励直接作用在高阶还是低阶模态,共振响应幅值随温度上升而增加,反之则减小;直接激发的模态响应幅值与因内共振激发的响应幅值受温度变化影响的敏感程度存在明显区别;温度变化对动态分岔(霍普和倍周期分岔)影响要比对静态分岔(鞍结点和叉形分岔)明显得多;动态分岔随着温度上升,向更小激励幅值和频率方向移动;系统的动态解和周期运动与温度变化密切相关,受温度影响,系统可能呈现出截然不同的周期运动。此外对比理论分析解和直接数值积分解,结果表明两者吻合较好。     

基于超弹性、分数导数和摩擦模型的碳黑填充橡胶隔振器动态建模

碳黑填充橡胶隔振器（以下简称＂橡胶隔振器＂）的动态特性与预载、激振频率和激振振幅相关。实验测试了一橡胶隔振器的动态特性,建立了基于超弹性、分数导数和摩擦模型的橡胶隔振器动态特性的非线性模型,其中超弹性模型用于描述橡胶隔振器的弹性,分数导数模型用于表征橡胶隔振器动态特性的激振频率相关性,摩擦模型用于表征橡胶隔振器动态特性与激振振幅相关的特性,文中论述了建模方法和参数辨识方法。有限元分析获得橡胶隔振器的静态力-位移曲线,利用测试得到的橡胶隔振器在大振幅、低频激励下的力-位移关系,拟合得到橡胶隔振器动态模型中摩擦模型的参数,利用测试得到的橡胶隔振器在小振幅、高频激励下的力-位移关系,拟合得到橡胶隔振器动态模型中分数导数模型的参数。利用建立的模型和拟合得到的参数计算分析了橡胶隔振器动态特性的振幅相关性、频率相关性和预载相关性,并与实验结果进行了对比分析。分析结果表明,建立的模型可以较好的描述橡胶隔振器的动态特性。     

钻柱纵向和扭转振动分析

介绍钻柱的振动状态和产生振动的原因。针对钻柱的纵向振动,分别建立了力激励法和位移激励法的数学模型;计算结果表明,力激励法与位移激励法求得的消振转速相反,即力激励法的消振转速恰恰是位移激励法的共振转速,反之亦然;传统多以力激励为边界条件来研究钻柱纵向振动的频率响应,并指导现场消振作业的,这样给出的最佳消振转速,恰恰是共振转速;在钻井作业中,钻头的纵向跳动比纵向受力的变化要稳定得多,钻柱的动负荷比动位移重要得多,应该用位移激励法研究钻柱的纵向振动问题。针对钻柱的扭转振动问题,分别建立了扭矩激励法和转角激励法的钻柱扭转振动数学模型;证明用转角激励法来研究钻柱的扭转振动更符合实际。     

静电梳驱动RF MEMS滤波器动力学分析

静电梳驱动硅微机械滤波器在RF通信领域有重要应用。从振动力学的角度,对硅微机械滤波器的力电耦合动态特性进行分析。分析结果表明:硅微机械滤波器输出电压V_o(t)与梳状振子振动速度成正比。谐振状态下,静电力包含直流分量和倍频分量。直流偏置电压V_p可消除系统倍频振动,为后续检测电路设计提供便利。     

可调频悬臂梁式动力吸振器多频减振研究

手持打磨工具振动大,存在多个振动峰,且不同工况振动峰对应的频率不同.动力吸振器是控制窄带振动峰的有效方法,传统的"弹簧—质量"形式动力吸振器频率不易调节,且不能同时对多个频率进行动力吸振.为适应实际工程应用,以频率可调、可多频减振为目标,首先从结构阻抗角度阐述动力吸振器减振原理,然后设计一种适用于手持打磨工具的频率可调...     

旋转超声内圆磨削砂轮变幅器的设计与试验研究

砂轮变幅器是旋转超声内圆磨削谐振系统的关键部件,其设计质量直接影响超声磨削的工艺效果。但目前内圆磨削砂轮变幅器缺乏较为完善的理论分析模型。为提高砂轮变幅器理论分析模型的通用性,基于非谐振设计理论建立了纵向谐振砂轮变幅器的理论分析模型,并利用砂轮变幅器各振动单元间的力、位移连续条件与边界条件推导了其频率方程。然后,针对频率方程进行编程求解,并通过ANSYS有限元仿真分析进行验证。最后,加工制作了纵向谐振砂轮变幅器,并开展阻抗特性分析试验、超声谐振试验和振动位移测量试验,分析了其谐振特性。试验结果表明,所研制的砂轮变幅器的谐振试验频率与理论设计频率一致,其输出端振动位移的试验值与仿真值的相对误差为7.83%,符合旋转超声内圆磨削的要求,验证了理论分析模型求解的正确性。研究结果为旋转超声内圆磨削砂轮变幅器的设计提供了便捷且有效的方法。     

Toward a multifrequency quasi‐static Ritz vector method for frequency‐dependent acoustic system application

Computational issues concerning the calculation of acoustic responses of a complex finite element (FE) model for various noise and vibration inputs have become prevalent. Such a model requires a significant amount of computation time because of repeated inversions of dynamic stiffness matrices. Thus, even state‐of‐the‐art computer hardware and software often face limitations where a model order reduction (MOR) scheme can help. The established MOR schemes such as Ritz vector or quasi‐static Ritz vector methods are efficient for general engineering systems, but these MOR methods become inaccurate for frequency response analyses in some acoustic systems with frequency‐dependent mass and stiffness matrices and force vectors (hereinafter frequency‐dependent acoustic systems). To cope with the inaccurate prediction by these methods for frequency‐dependent acoustic systems, this research presents and applies the multifrequency quasi‐static Ritz vector method. Unlike the Ritz vector or quasi‐static Ritz vector methods, the present multifrequency quasi‐static Ritz vector method employs direct Krylov subspace bases without an orthonormal procedure at multiple center frequencies. In comparison with the existing MOR scheme, a significant gain in computational efficiency is achieved, as well as enhanced accuracy. A comparison of these methods based on criteria such as efficiency, accuracy, and reliability was also conducted. Copyright © 2011 John Wiley & Sons, Ltd.