轴向覆盖磁约束阻尼条对悬臂壳非轴对称振动的影响

应用Rayleigh-Ritz方法建立了局部磁约束阻尼壳的振动分析模型.选取约束层的横向振动模态和面内振动模态作假设模态,形成横向位移和面内位移.调查了不同约束阻尼层配置下,轴向覆盖磁约束阻尼条对悬臂壳非轴对称振动模态(m=1,n=1)损耗因子的影响.研究表明:当阻尼层远离该模态的节线(θ=±π/2),磁约束阻尼处理的阻尼改进效果越明显.阻尼层设置在θ=0,π处,该模态的损耗因子最大,MCLD处理的阻尼改进效果也最显著,损耗因子提高约40%.可以通过改变阻尼层的长度及宽度可增加损耗因子,但随二者的增加,磁约束处理对阻尼的改进作用减小.     

恒定磁场中简支圆柱壳的磁弹性振动分析

依据电磁场方程及相应的电磁本构关系,给出了作用于圆柱壳体上的电磁力及力矩表达式.在此基础上,分别推得了纵向和横向磁场中圆柱壳体的磁弹性轴对称振动方程.针对两端简支约束条件,通过位移函数的设定,得到了相应的有阻尼振动微分方程.通过算例,给出了系统衰减振动的响应曲线图和相图,分析了磁感应强度和壳体厚度对系统振幅衰减速度的影响.结果表明,通过改变磁感应强度可以达到控制系统振动的目的.     

主动约束层阻尼梁有限元建模与动态特性研究

基于弹性、粘弹性和压电材料的本构关系,利用Hamilton原理,推导了主动约束层阻尼梁的有限元动力学模型．结合压电材料的机电耦合特性,采用自感电压的位移反馈,研究了主动约束层阻尼梁的闭环控制特性．求解了主动约束层阻尼简支梁的动态特性如固有频率、模态损耗因子及频率响应特性等．对被动控制、主动控制和主被动混合控制的控制效果进行了分析比较．研究了粘弹性层与约束层厚度等参数对减振控制效果的影响．     

剪切模量对梁的磁橡胶约束阻尼特性的影响

基于周期耗能相等的原理,将磁橡胶约束阻尼悬臂梁(MRLD)与传统的约束阻尼悬臂梁(CLD)等价,计算MRLD的模态损耗因子,研究了阻尼层剪切模量Gv对MRLD梁阻尼特性的影响.研究表明,在给定激励位移下,当Gv较小时,MRLD与CLD的阻尼一样.增加Gv引起阻尼层滑移,在Gv增加的开始阶段,MRLD表现出比CLD更好的阻尼特性,但进一步提高Gv,MRLD的阻尼性能开始降低并将低于CLD.此外,增加位移激励,使MRLD的阻尼大于CLD阻尼的有效剪切模量Gv的区域向剪切模量小的方向移动;所对应最大阻尼的剪切模量Gvopt也如此.     

扁锥面单层网壳的非线性动力学特性

用拟壳法建立了正三角形网格三向扁锥面单层网壳的轴对称非线性动力学基本方程．通过分离变量函数法,用Galerkin法得到了一个含二次、三次的非线性微分方程．为了研究混沌运动,对一类非线性动力系统的自由振动方程进行了求解,给出了单层扁锥面网壳非线性自由振动微分方程的准确解．通过求Melnikov函数,给出了发生混沌运动的临界条件．数字仿真证实了混沌运动的存在．     

激励电流对超磁致伸缩换能器动态特性的影响

本文研究了不同激励电流脉冲宽度对超磁致伸缩换能器输出位移动态特性的影响。利用有限元分析软件ANSYS建立了超磁致伸缩换能器的二维轴对称有限元模型。通过压磁-压电比拟法,对不同激励电流脉冲宽度下不同发射头质量的超磁致伸缩换能器输出位移动态特性进行了模拟研究。结果表明:激励电流脉冲宽度大小不仅直接决定超磁致伸缩换能器瞬态输出位移的大小,而且决定超磁致伸缩换能器的最佳工作状态。此研究结果为超磁致伸缩换能器的优化与应用奠定了基础。     

基础位移激励下碳纤维矩形索网的非线性振动

研究碳纤维材料矩形单层索网在基础位移激励下的非线性振动问题,是索网抗震防震设计的基础．在考虑温度变化的基础上,建立了碳纤维矩形索网在基础位移激励下的非线性振动方程,采用Galerkin原理及KBM法求得了碳纤维材料矩形单层索网非线性振动的近似解．在把碳纤维索网与钢丝索网比较的基础上,讨论分析了温度、位移激励、振幅、阻尼等因素对矩形单层索网非线性振动的影响,得到了碳纤维索网振动特性优于钢丝索网振动特性的结论．     

嵌入多层黏弹性胶膜复合材料阻尼工字梁的多目标设计优化

针对嵌入多层黏弹性胶膜的复合材料阻尼工字梁,传统的混合单元法在进行结构动态分析与设计优化时存在很大困难的问题,采用基于离散层理论的多层梁单元建模分析复合材料阻尼工字梁.通过对正交各向异性铺层和腹板进行等效处理的方法,对工字梁凸缘嵌入单层阻尼层模型进行参数化分析;分别对嵌入多层或单层阻尼层的模型建立多目标优化模型,优化目标为模态损耗因子和固有频率最大化,设计变量为阻尼层层数（厚度）及其嵌入位置;应用多目标遗传算法进行优化求解.结果表明：基于离散层理论的阻尼梁单元计算精度好且易于优化,对于嵌入单层较厚阻尼和嵌入多层较薄阻尼的复合材料工字梁,获得的阻尼效果与动刚度损失基本相当,但对于高阻尼的方案,前者比后者的动刚度损失更大.     

Fe-Ga磁致伸缩位移传感器驱动电流位置调整与回波速度校正

通过对传统Fe￣Ga磁致伸缩位移传感器驱动脉冲电流输入端位置的改进,降低了驱动脉冲电流噪声对检测线圈输出电压的影响,并使检测线圈输出电压信噪比由15.5 dB提高至23.7 dB。基于应力波无阻尼反射原理提出一种新的回波速度校正法,确立了回波速度与波导丝长度、应力波传播时间、反射波传播时间的数学关系,并给出此表达式适用的驱动脉冲电流频率范围。制作了样机,通过实验验证了此方法最大位移测量误差减小到原来的1/5,为Fe￣Ga磁致伸缩位移传感器输出性能研究提供了理论依据。     

轴向运动粘弹性夹层梁的横向振动

研究了小扰度下轴向匀速运动粘弹性夹层梁的振动模态和固有频率.基于Kelvin粘弹性本构方程,建立了轴向运动粘弹性夹层梁横向振动控制方程.分别采用Galerkin截断和复模态分析方法,研究两端简支的粘弹性夹层梁的固有频率和模态函数,讨论了轴向运动速度、夹心层与约束层厚度比、初始轴力等参数对夹层梁固有频率、临界速度及稳定性的影响.     

变速旋转圆柱薄壳动力稳定性研究

本文开展了变速旋转圆柱薄壳动力稳定性研究.基于Donnell薄壳理论建立同时考虑变转速和周期 轴向力的圆柱壳体振动微分方程;采用多尺度方法,推导系统主参数不稳定区和组合不稳定区边界的解析 表达式;分别探讨仅考虑周期轴向力、仅考虑变转速以及同时考虑两种时变因素时,系统主参数不稳定区和 组合不稳定区的变化规律;通过与文献结果以及数值结果的对比,验证了解析结果的准确性.     

A finite element formulation for composite laminates with smart constrained layer damping

A composite laminate with active constrained-layer damping treatment is studied. The interface element for viscoelastic damping layers has been developed based on the relative displacements between composite plates and piezoelectric constraining layers. As an example, the problem of forced oscillations of the laminated composite structure with a smart constrained damping treatment is solved and the vibration response of the composite plate with smart damping layers is calculated using the presently developed procedure.     

采用复合磁电换能器的振动能量采集器研究

采用Teffenol-D/PZT/Terfenol-D复合磁电换能器,设计了一种新型振动能量采集器.采集器由悬臂梁、磁电换能器和永磁体三部分组成,环境振动引起换能器与永磁体相对运动,使得作用到换能器的磁场变化,变化的磁场引起Tedenol-D产生应变,应变传递到PZT得到电输出.采用等效磁荷理论分析了影响换能器与永磁体相对运动的磁场力;并用林滋泰德-庞加莱法分析了永磁体的非线性运动情况.实验结果表明,在振动激励频率为33 Hz,加速度为0.5 gn时,输出电压峰峰值45.1 V,输出功率112.1μW.     

格栅夹层板抑振性能研究

为了有效降低铺板与圆柱壳体耦合结构中因铺板振动而引起的壳体振动,提出了以格栅夹层板作为一种铺板结构.以格栅夹层板安装于带有端板的圆柱壳体上作为研究模型,采用有限元软件对格栅夹层板的抑振性能展开了仿真分析,讨论了格栅结构参数对其抑振效果的影响,并实验验证了格栅夹层板的抑振效果.仿真和实验结果一致表明：格栅夹层板能有效降低圆柱壳体的振动响应,尤其是在中高频段抑振效果显著；格栅的结构参数对抑振效果影响规律比较复杂,格栅夹层的上层面板采用阻尼较大的材料利于提高其抑振效果.     

主动约束层阻尼圆柱壳的环向占优模态控制

基于作者最近对主动约束层阻尼（ACLD）圆柱壳的建模研究基础,通过数值算例进一步研究了电压分布方式对ACLD圆柱壳减振效果的影响,重点放在控制方式以及驱动电压的施加方案上.大量的数值计算表明,在多种外激励下的ACLD圆柱壳,采用环向占优模态控制方案,具有最佳的振动抑制效果,进而提出了环向占优模态控制策略的概念.     

Active vibration control of smart piezoelectric beams: Comparison of classical and optimal feedback control strategies

This paper presents a numerical study concerning the active vibration control of smart piezoelectric beams. A comparison between the classical control strategies, constant gain and amplitude velocity feedback, and optimal control strategies, linear quadratic regulator (LQR) and linear quadratic Gaussian (LQG) controller, is performed in order to investigate their effectiveness to suppress vibrations in beams with piezoelectric patches acting as sensors or actuators. A one-dimensional finite element of a three-layered smart beam with two piezoelectric surface layers and metallic core is utilized. A partial layerwise theory, with three discrete layers, and a fully coupled electro-mechanical theory is considered. The finite element model equations of motion and electric charge equilibrium are presented and recast into a state variable representation in terms of the physical modes of the beam. The analyzed case studies concern the vibration reduction of a cantilever aluminum beam with a collocated asymmetric piezoelectric sensor/actuator pair bonded on the surface. The transverse displacement time history, for an initial displacement field and white noise force disturbance, and point receptance at the free end are evaluated with the open- and closed-loop classical and optimal control systems. The case studies allow the comparison of their performances demonstrating some of their advantages and disadvantages.     

A new energy harvester using a cross-ply cylindrical membrane shell integrated with PVDF layers

In this paper, we proposed a smart cylindrical membrane shell panel (SCMSP) model for vibration-based energy harvester. The SCMSP is made of an orthotropic elastic core covered by outer PVDF layers with transverse polarization vector. Electrodynamics governing equations of motion are derived by applying extended Hamilton’s principle. The governing equations are based on Donnell’s linear thin shell theory. The SCMSP displacement fields are expanded by means of double Fourier series satisfying immovable edges with free rotation boundary conditions and coupled system of linear partial differential equations are obtained. The discretized linear ordinary differential equations of motion are obtained using Galerkin method. The output power is taken as an indicating criterion for the generator. A parametric study for MEMS applications is conducted to predict the power generated due to radial harmonic ambient vibration. Optimal resistance value is also obtained for the particular electrode distribution that gives maximum output power. A low vibration amplitude (5?Pa), and a low-frequency (471.79?Hz) vibration source is targeted for the resonance operation, in which the output power of 0.4111?μW and peak-to-peak voltage of 0.2952?V are predicted.     

Optimal design of a dynamic absorber using polymer-laminated steel sheets

An optimal design of dynamic absorber was made in this study by using polymer-laminated steel sheets consisting of two steel sheets bounded with a polymeric layer. Based on the optimally turned and damped dynamic vibration absorber derived by Den Hartog [1], the thickness of constraining layers and interlayer could be obtained by employing the RKU model. In approaching the optimal loss factor of the laminates, this design problem has been formulated as a nonlinear constrained minimization problem, and solved through the usage of an interior penalty function method. Also, the characteristics of a dynamic absorber were discussed, with its design having a more effective vibration damping capability on a vibration system.     

Effect of boundary conditions on natural frequencies for rotating composite cylindrical shells with orthogonal stiffeners

The effect of the boundary conditions on the natural frequencies for rotating composite cylindrical shells with the orthogonal stiffeners is investigated using Love’s shell theory and the discrete stiffener theory. The frequency equation is derived using the Rayleigh–Ritz procedure based on the energy method. The considered boundary conditions are four sets, namely: (1) clamped–clamped; (2) clamped–simply supported; (3) clamped–sliding; and (4) clamped–free. The beam modal function is used for the axial vibration mode and the trigonometric functions are used for the circumferential vibration mode. The composite shells are stiffened with uniform intervals and the stiffeners have the same material. By comparison with the previously published analytical results for the rotating composite shell without stiffeners and the orthogonally stiffened isotropic cylindrical shells, it is shown that natural frequencies can be determined with adequate precision.