电流变液夹层梁结构动态特性及阻尼特性研究

着重讨论剪切型电流变液夹层梁。在简单介绍一下ＲＫＵ模型的同时，重新详尽地推导Ｍ＆Ｍ模型及其求解，探讨剪切型电流变液夹层梁在不同边界及不同外加电场情况时的结构动态特性及阻尼特性。     

含智能流变材料铝合金夹层板结构的动力学特性研究

通过对一种含电流变液铝合金夹层板智能结构的动力学实验与仿真，分析和研究该结构在外电场作用下的动力特性变化。实验发现，利用外部控制条件(电场强度)的变化，可以改变结构的固有特性，如自然频率、结构阻尼等，可实现对结构的主动控制。数值分析时采用粘弹性材料等效处理方法模拟电流变材料，计算得到的结构振动特性与实验结果吻合较好。实验与仿真计算结果均表明，随着电场强度的增大，结构固有频率也随之出现上升，且增幅与场强有关；同时，电流变材料对结构振动所产生的阻尼效应不仅受外加电场影响，还与外加激励频率有关，响应控制实验结果说明电流变材料对结构在固有频率附近所产生响应的控制效果要更为明显一些。     

电流变阻尼器支承的转子系统不平稳振动测试

对采用一种剪切型电流变阻尼器作为支承的刚性转子系统进行振动测试,对比分析了电流变阻尼器外加电场电压不同时转子振动的特点。在适当的电压条件下可使转子振动明显减低。研究了转子振动控制过程中由于电场电压切换所造成的转子不平稳振动的时频变化规律。在稳定运行过程中,由于电压突变使转子振动产生波动．而转速均匀升降会对这种不平稳振动起到一定的镇定作用。     

电流变液夹层梁滑模振动控制的研究

采用Rayleigh-Ritz方法推导电流变夹层梁的动力学方程，在夹层梁动力分析的基础上，基于滑模控制理论，设计电流变夹层梁的主动控制的控制器。研究确定性系统和不确定性系统控制率生成。数值仿真的结果表明这些控制策略是十分有效的和现实可行的。     

光纤传感网络用于电磁流变结构的特性测试与工程控制

讨论了一种先由多个光纤传感器协同工作判断电流变材料振动模式,由计算机控制改变外加电场,进而控制结构振动的方法。     

局部磁场作用下磁流变弹性体夹层梁振动特性研究

设计和制备了中间层为含铁磁颗粒质量比为80%的磁流变弹性体材料,上下表面层为铝合金的磁流变弹性体夹层梁。在局部磁场作用下搭建了磁流变弹性体夹层梁悬臂状态下的振动响应特性测试实验台。实验结果表明,通过在夹层梁水平方向移动永久磁铁,即局部外加磁场由夹层梁的固定端向自由端移动时,其一阶振动频率有逐步减小的趋势。同时,通过沿夹层梁垂直方向移动永久磁铁改变磁场强度的大小,此时夹层梁的一阶振动频率在外加磁场强增大时也呈减小趋势。两组实验均表明在局部磁场控制下能有规律地改变磁流变弹性体夹层梁的一阶振动频率。根据这种变化规律有望设计出频率变化范围更宽的移频装置。     

电流变液技术在液压控制系统中的应用

电流变液是一种流变特性可受外加电场控制的智能材料,该文阐述了电流变液材料的组成、特性和作用机理,介绍了电流变液技术在液压控制系统中的应用.     

电流变液机理及其研究现状

电流变液是一种在外加电场作用下表观粘度发生显著变化的液体，近年来，作为一种智能流体引起研究人员的广泛重视，本文阐述了电流变液的组成，作用机理，影响流变的因素及其在工程中的应用，介绍了电流变液在国内外的研究现状，并在此基础上提出了几个值得重视的问题。     

电流变液及电流变液联轴器的实验研究

本文用沸石和硅油配制的电流变液，在圆筒式电流变液联轴器上测试了在有无电场作用下扭矩的传递能力。另外，调节外加电场得到在不同输入速度下联轴器的输出转速。实验表明，在确定负载和输入转速下，可以通过调节直流电场控制联轴器的输出转速，这为传动系统的无级调速提供了一种新的简便的手段。     

电流变液在结构振动抑制中的应用研究

根据结构抑振的应用要求,研制出了几种零场粘度低、有场粘度变化梯度大的电流变液,并设计制作了电流变液静态屈服应力测试仪,测试出了所研制的电流变液的静态屈服性能随电场强度和液体组份比变化的曲线。利用自制的电流变液,对含电流变液的夹层板振动进行了单模态抑制,由此得出电流变液对振动机理在于：一方面通过电流变阻尼效应降低结构振动响应的幅值,特别是共振峰的幅值;另一方面通过电流变刚度效应使结构的有效刚度增加,结构的共振点发生移动,从而使结构在共振频率激励下的振幅大大降低。对本文的夹层板模型,在３ｋＶ／ｍ ｍ 的电场强度下,第三阶模态的响应幅值降低了９０％ 。     

An experimental and analytical investigation of the dynamic characteristics of a flexible sandwich plate filled with electrorheological fluid

This paper investigates the dynamic characteristics of a sandwich plate embedded with an electrorheological (ER) fluid. A laser holographic interference experiment and modal testing were conducted to identify natural frequencies, modal damping and shapes of the composite structure, under different electric fields applied to the fluid domain. Moreover, the influence of the ER effect on the structural dynamic responses were recorded. It was found that both of the damping and natural frequencies of the sandwich plate increase monotonously with an increasing electric field; while, at the same time, the resonant peaks of the frequency response and the amplitudes of dynamic responses decrease. Furthermore, based on the special properties of the ER fluid, a discrete dynamic model of the sandwich plate containing ER fluids was developed and validated. The numerical simulation verifies the effect of the ER material on the structure, and the calculated dynamic parameters show the coincident changes with the experimental results.     

Dynamics of geometrically exact sandwich structures

A finite element formulation of a recent theory for geometrically exact multilayer beams, applicable to one-dimensional plates, is presented here. The beam can take any arbitrary initial position in the two-dimensional space. Each layer of the beam can have different material properties with no restriction on the stiffness, mass distribution and layer thickness, thus allowing for the modeling of ideals sandwich structures. Finite rotation and shear deformation are accommodated for in each layer. The continuity of the displacements across the layer interfaces is exactly enforced; the deformed cross section is thus continuous, piecewise-linear. Extensive numerical examples including harmonic response of sandwich structures with three identical layers, with comparison to single-layer beams, and the response of ideal sandwich beams to impact forces are presented to illustrate the applicability and versatility of the proposed formulation.     

Flexural vibration analysis of a sandwich beam specimen with a partially inserted viscoelastic layer

The flexural vibration characteristics of a sandwich beam system with a partially inserted viscoelastic layer were quantitatively studied using the finite element analysis in combination with the sine-sweep experiment. Asymmetric mode shapes of the flexural vibration were visualized by holographic interferometry, which agreed with those obtained by the finite element simulation. Effects of the length and the thickness of the partial viscoelastic layer on the system loss factor (η_s) and resonant frequency (f_r) were significantly large for both the symmetric and asymmetric modes of the beam system.     

Complex moduli of electrorheological material under oscillatory shear

The electrorheological (ER) material embedded in the sandwich structure is subjected to oscillating shear as the structure is in vibration. According to this shear deformation mechanism, a testing apparatus with ER material filled in a fixture consisting of parallel plates is built in this study. With the controlled relative displacement between the parallel plates, the complex moduli, loss factor, and the dissipated energy of the ER material under oscillating shear are measured. The effects of the electric field strength, strain amplitude, and frequency on these dynamic properties are investigated. It is found that the constitutive model proposed in the previous work accurately describes the characteristics of the ER material under this loading condition.     

Vibration characteristics of hollow cantilevered beams containing an electro-rheological fluid

Electro-rheological (ER) fluids undergo a phase change when subjected to an external electric field, and this phase change typically manifests itself as a many-order-of-magnitude change in the rheological behavior. This phenomenon permits the global stiffness and energy-dissipation properties of the beam structures to be tuned in order to synthesize the desired vibration characteristics. This paper reports on a proof-of-concept experimental investigation focused on evaluating the vibration properties of hollow cantilevered beams filled with an ER fluid and, consequently, deriving an empirical model for predicting field-dependent vibration characteristics. A hydrous-based ER fluid consisting of corn starch and silicone oil is employed. From the observation of modal characteristics, the beams are considered to be uniform viscoelastic materials and are modeled as a viscously-damped harmonic oscillator. Natural frequency, damping ratio and elastic modulus are evaluated with respect to the electric field and compared among three different beams: two types of different volume fraction of ER fluid and one type of different particle concentration of ER fluid by weight. Transient and forced vibration responses are examined in the time domain to demonstrate the validity of the proposed empirical model.     

变截面智能压电梁的动态特性研究

建立变截面智能压电梁的动态模型,分析表面粘贴压电元件的均质梁的固有频率。在分析时考虑坟电元件、粘贴层、梁的剪切变形和转动惯量。研究表明,压电元件的刚度和惯量对梁的频率影响很大,变截面智能压电梁的一除非 固有频率总是高于等截面梁的固有频率。粘结层剪切 对一阶频率影响较 剪切变 转动惯量时,对梁的高阶频率影响较大。考虑梁的惊动国惯量和剪切谱形时,智能阶梯梁的频率比没有时的要低。     

Large deflections of metallic sandwich and monolithic beams under locally impulsive loading

A rigid-perfectly plastic model is adopted to predict the dynamic response of fully clamped sandwich and monolithic beams subjected to localized impulse. Large deflection effect is incorporated in analysis by considering interaction between plastic bending and stretching. Based on the principle of energy equilibrium, a membrane factor for metallic sandwich beams with nonuniform cross-section thickness is derived to consider the effect of axial force induced by large deflection. Then, the dynamic response solution is obtained for the large deflection of metallic sandwich beams subjected to localized impulse. In addition, tighter ‘bounds’ of the solutions for sandwich beams are derived by using the inscribed and circumscribed squares of a new yield criterion including the core effect. As a degenerated limit case, solution for the large deflection response of solid monolithic beams is also obtained. The present solutions are in good agreement with finite element (FE) results and lie in the ‘bounds’ of the solutions. It is demonstrated that the axial (membrane) force associated with stretching plays an important role in the dynamic response of large deflections; in comparison with small deflection solutions, the axial (membrane) forces substantially stiffen the metallic sandwich and monolithic beams.     

Anwendung balkenförmiger schwingungstilger für biegeschwingungssysteme

Tuned viscoelastic dampers, comprising a mass connected through a viscoelastic link to a vibrating structure, have been considered from many points of view. For effective operation, the resonant frequency of such a damper must be made somewhat lower than the undamped resonant frequency of the structure. If the resonant frequency of the structure is low, some difficulty is encountered in constructing a good tuned damper system. In such a damper system the viscoelastic materials must be both soft and strong enough to give the necessary tuning frequencies without the damper being too heavy. For this reason a damper, based on a different principle for lateral vibrating structures is described in this paper. The main vibrating system is a clamped-free beam. The damper is also a clamped-free beam which is accomodated in an opening of the main system. The damper beam can vibrate freely in this opening and creates a new degree of freedom in the total system. The different equations for the lateral vibrations of the main and of the damper beam can be formulated according to the classical Bernoulli - Euler theory. For theoretical analysis, the system has been simplified. The main beam has partially constant rectangular sections. The auxiliary beam has a constant rectangular section. The total system has four different parts with constant sections. Structural damping of both beams has also been considered by a complex modulus of elasticity. For vibrations in a normal mode, the Euler - Bernoulli equation can be formulated as an ordinary differential equation. A general solution for each beam section is a sum of trigonometric and hyperbolic functions. The coefficients in the general expressions can be determined from the 16 boundary conditions of the beam damper system. The equations for the forced vibrations of the main beam, which can be excited by a prescribed motion at some point in the system or by a harmonic force are written in matrix notation:

$\text{|A| · |X| = |B|}$

The components of the matrix |A| are functions of the dimensionless frequency parameter and the geometric and the dynamic properties of the system. The matrix |B| contains the exciting functions, and the matrix |X| contains the unknown coefficients of the general solutions. For the solution of matrix |X| the Wilkinson method is used. The computed examples show, for a given beam-damper system, the amplitude of the vibration of the main beam as a function of frequency; the effect of tuning on the natural frequencies of the main beam; the effect of damping on the amplitudes of the main beam; the effect of the mass ratio MDamper/MBeam on the natural frequencies and resonant amplitudes of the main system; and the effect of the attaching point of the damper on the natural frequencies and resonant amplitudes of the main beam.     

Forced transverse vibration of composite sandwich beam with magnetorheological elastomer core

We studied, experimentally and numerically, the vibrational response of a magnetorheological elastomer sandwich beam, clampedfree, delimited by two skins aluminum 7075T6, first subjected to a variable magnetic field perpendicular to the skin of the beam, and second to a harmonic excitation by magnetic force applied at the free end. Our main objective was to predict the effect of the intensity of the current flowing through a coil on several dynamic factors. The maximum amplitude of resonance and the variation of the loss factor as a function of structural stiffness are adjusted simultaneously by the application of different magnetic fields. The results of both methods are compared.