一种电流变液体减振器的结构研究

电流变液体是指在电场作用下其流变性质能迅速发生变化的一类流体,基于这一原理我们分析了电流变流体的力学性能,针对电流变减振器的结构,论述了该电流变减振器模型的工作原理,建立电流变减振器阻尼特性计算的数学模型并进行仿真分析,对构成阻尼力特性影响的主要参数进行了研究。研究表明:电流变液体减振器的机械结构对充分体现电流变效应的功能,实现振动的有效控制起着重要作用。     

AFFECTION OF ER FLUID ON STIFFNESS OF VIBRATION SYSTEM

On the application of an electric field, the mechanical properties of ER(Electro-rheological) fluid are very complex. The damping force of ER fluid is linear without electric field and is nonlinear when an electric field is applied. By increasing the strength of the electric field, the behavior of ER fluid changes from linear viscous to nonlinear viscoelastic-plastic. External electric fluid changes natural behavior of system with ER fluid besides the mechanical properties of ER fluid. The affect of ER fluid on the stiffness of nonlinear vibration system with ER dampers is analyzed by iterative perturbation method. The results show that the stiffness of structure would be increased with growing of the strength of the electric field.     

电流变夹层梁的动力稳定性分析

将电流变液等效为线性粘弹性材料，并假定在小变形情况下其储能模量和损耗因子与加在它上面的电场成正比，利用Hamilton原理和有限元方法建立电流变夹层梁的动力学方程。分析不同外加电场和厚度比情况下，电流变夹层梁的振动特性及动力稳定性。通过对单频轴向激励作用下电流变夹层悬臂梁的仿真计算显示，外加电场的增大能提高电流变夹层梁的刚度和阻尼损耗，减少不稳定区域的大小，而电流变层厚度的增加将使梁的固有频率降低，但提高了梁的稳定范围。表明合理设计电流变夹层梁可以有效抑制振动，提高系统的稳定性。     

Application of ER gel with variable friction surface to the clamp system of aerostatic slider

An electro-rheological fluid (ERF) is a functional fluid whose viscoelastic properties vary according to the intensity of the applied electric field. ERFs are mixtures of nonconductive silicone oil and inorganic/organic composite electro-rheological particles. The properties of ERFs have been exploited to control the performance of machine elements. ERFs have been applied to machine elements such as variable dampers and clutches. However, ERFs have disadvantages, namely the sedimentation of ER particles and the requirement of a seal mechanism. The sedimentation of ER particles reduces the ER effects and results in low stability of ER devices. In order to suppress the sedimentation, and thereby improve the performance of ERF devices, a new functional material called the gel-structured ERF (ERG) is developed, whose basic properties are analyzed in this study. The ER particles are suspended in the gel component, and thus will not precipitate out. This suppresses the decrease in the ER effect caused by precipitation. The ERG developed shows a large shear stress variation in response to the applied electric field. This high performance of ERG originates in a mechanism different from the ER effects of ERF. In order to elucidate the mechanism in ERG, the behavior of ER particles was observed under an electric field. The results show that the contact conditions at the interface between electrode and ERG change rapidly in response to the applied electric field, which result in a variation in shear force. On the basis of the results of a preliminary analysis, ERG was applied to the precision clamp system of an aerostatic slider, and its performance was assessed experimentally.     

Controllable high speed journal bearings, lubricated with electro-rheological fluids. An analytical and experimental approach

The problem of journal bearings control is of great importance in mechanical engineering. A very recent method for doing this is the creation of ‘smart' journal bearings using electro-rheological (ER) fluids. If such a fluid is used to lubricate a journal bearing system, it is expected that the imposition of an electric field between the rotor and the stator will cause an alteration in the dynamic properties of the journal bearing. In this paper an experiment in a high speed journal bearing (16 000 to 35 000 s⁻¹), with small radial clearance is presented. The alternation of the attitude locus (eccentricity and attitude angle) and the stiffness coefficients in a loaded journal bearing lubricated with ER fluid is investigated and presented. The Reynolds equation is solved using the finite element method in order to get the dynamic characteristics of the ER bearings vs the electric field and to simulate its dynamic behavior. The Bingham plastic model of non-Newtonian fluid flow behavior is used to described the ER lubricant. The accuracy of the algorithm is obtained by comparing the results published by previous investigators and the experimental data described in this paper. It is concluded that ER fluids can be used to create ‘smart' journal bearings. and vibration controllers can be constructed to control the dynamics and stability of the ER fluid lubricated bearings.     

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.     

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。     

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.     

气体对磁流体动力学传感器影响机理的探讨

由于气体和导电流体性质上的差异,导电流体中气体的存在将对磁流体动力学(MHD)传感器的输出特性产生影响。基于电磁感应理论和两相流理论,文章推导并建立了导电流体中含气体的MHD传感器VOF模型。通过ANSYS Fluent对含气体的MHD传感器输出特性进行仿真分析,同时搭建试验平台对不同气体含量MHD传感器进行试验验证。结果表明,导电流体中的气泡在低频时容易被拉伸撕裂成小气泡并随着角振动分散,同时使得流体环流场和电场产生偏移和畸变,角振动频率越低,此现象越明显;当导电流体中不含气体时角振动频率和幅值、重力加速度及偏心等外部因素对MHD传感器的输出特性无影响;当导电流体中含有气体时,MHD传感器的输出特性畸变等随气体含量、重力加速度和偏心的增大而增大,随角振动频率和幅值的增大而减小。文章研究成果能够为MHD传感器导电流体灌装工艺控制提供指导,有助于MHD传感器精度和稳定性的提升。     

电流变减振器用于铣床振动控制的试验研究

试验研究了电流变减振器在铣床颤振控制中的应用。试验发现，电流变减振器的刚度及阻尼随外加电场强度的增加而增大，主振系统的振幅随电场强度的增加而减小。试验表明电流变减振器具有控振效果明显、结构简单的特点。只要场强选取适当，采用电流变减振装置可以控制铣床刀杆系统的颤振。     

Effects of electric field on hydrodynamic characteristics of finite-length ER journal bearings

A numerical analysis is performed on the hydrodynamic characteristics of electrorheological (ER) fluid flows in journal bearings based on computational fluid dynamics (CFD) techniques. The bearing has a finite-length and operates under incompressible laminar flow with steady conditions. The analysis is based on the numerical solution of full three-dimensional Navier–Stokes equations. The applied electric field is imposed partially along a contractive section of the journal bearings and the modified Bingham plastic model is used to describe the behavior of ER fluid. The results presented are obtained by using finite-volume-methods and solved by the semi-implicit method for pressure-linked equations (SIMPLE) algorithm. In this study, cavitation effects are also considered by using the viscosity modeling. The results have shown that the influences of ER effects, caused by the applied electric field, on the journal bearing characteristics are significant and not negligible. Compared with the Newtonian lubricant case, the effects of the ER effects provide an enhancement in the load-carrying capacity, but do have little effects on the attitude angle. The quantitative effects on load-carrying capacity are more pronounced for journal bearings operating at higher values of eccentricity ratio or lower rotary speed.     

应用电流变材料改变镗杆动态特性的研究

为保证镗削加工切削稳定性,基于电流变材料设计一种智能型镗杆。该镗杆可通过调节施加于电流变材料上的电场强度来改变整个镗杆的动态特性,并借以抑制切削颤振。采用 端部激振方法研究镗杆在不同激振频率和不同电场强度下的动态特性。实验结果表明,在不同的电场强度和振动频率下,电流变材料表现出来的振动特性差异明显,使镗杆的支撑刚度和结构阻尼特性发生显著的变化。     

Determination of the Bingham parameters of an electrorheological fluid in an axial flow concentric-cylinder rheometer

Electrorheological (ER) fluids are fluids that undergo changes in their rheological properties in the presence of an applied electrical field. The change in the flow properties with an applied electrical field has led to their being investigated for use as ‘smart’ lubricants. The Bingham model is currently used to describe the behaviour of these fluids. In this work, the Bingham model parameters of a commercially available ER fluid are obtained using an axial flow concentric-cylinder rheometer. Two methods are used to determine these parameters. One is the Weissenberg (—Rabinowitsch) method applied to thin annular slits, to obtain corrected stress—strain rate information. The other method involves directly fitting the velocity—pressure curve data to the axial flow rate equation of a Bingham fluid through concentric cylinders. The results obtained by these two methods differ by as much as 49.4 and 63.5% for the yield stress and viscosity, respectively. It is observed for this ER fluid that the yield stress increases according to a power law relationship with the applied electrical field. The viscosity appears to decrease linearly with an increase in the applied electrical field.     

A study on the control characteristics of ER valve-FHA system and durability test

In this paper, making the best use of the features of the electro-rheological (ER) valve, a two-port pressure control valve using ER fluids is proposed and manufactured. The ER-Valve characteristics are evaluated by changing the intensity of the electric field and the number of electrode. As only with electrical signal change to the ER-Valve in which ER fluid flowing, ER fluid flow is controlled, so development of simple ER-Valves have been tried. The ER-Valves and pressure drop check method are considered to be applied to the fluid power industry. Using the manufactured pressure control valve, a one-link manipulator with FHA (Flexible Hydraulic Actuator) is driven. As a result, it is experimentally confirmed that the pressure control valve using ER fluids is applicable to use in driving actuator. If it applies characteristics of the ER fluids, it will be able to apply in the control system for the ER Valve which occurs from industrial controller. After having durability test, shear stress increased regularly because of starch particles crushed by pump and particle size that was almost the same. Moreover, Ra of copper electrode increased about 1.56 times rather than before those of performing durability test, and Rz increased about 2.2 times.     

一种新型的ER液体剪切性能测试装置

ＥＲ液体是一种在电场作用下可改变其剪切粘性的液体、本文介绍了一种可用来考察其剪切特性的装置，利用该装置不仅可分析ＥＲ液体的力矩传递特性与电场强度、剪切速率、电极间距离等因素的关系，并且稍加改进还可利用它来考察ＥＲ液体对外电场的响应时间。这对高性能ＥＲ液体的研制及其实际的工程应用都是非常必要的、最后通过对由硅油－硅胶组成液体的剪切试验，验证了该装置的有效性。     

STUDY ON ELECTRORHEOLOGICAL FLUID DAMPER FOR APPLICATION IN MACHINING CHATTER CONTROL

The electrorheological fluid(ERF)is a kind of intelligent material with bright prospects for industry applications, which has viscoelastic characteristic: under the applied electric field. The dynamic model of a milling system with an ERF damper is established, and the chatter suppression mechanism of the ER effect is discussed theoretically. Both the theoretical study and the experimental investigation show that the additional damping and additioaal stiffness produced by the ERF increase with the rise in the strength of electric field E, but their influence on the cutting stability is different. Only when both additional damping and additional stiffress cooperate, the milling chatter can be suppressed quickly and effectively. In additional, an ERF dumper used on the arbor of horizontal spindle milling machine is developed, and a series of milling shatter control experiments are performed. The experimental results show that the milling chatter can be suppressed effectively by using the ER damper.     

电流变液在工程中的应用

电流变液是一种在电场下暧时从液态变为类固态的智能材料。由于它能在瞬时改变材料的力学性能，增加了其表观粘度和强度，又具有可逆性，因而在工业上极具应用前景。本文主要论述了国内外电流变液研究在工程中的应用前景和发展趋向。     

电流变材料在结构振动控制中的非线性特性及理论模型

半主动振动控制结合了主动和被动控制的优点,得到了广泛的应用。一种采用电流变材料在线实时改变支撑条件的镗杆被设计用来对切削颤振实现半主动控制。通过试验发现当电流变材料处于屈服前后临界状态时,其在系统中相当于一参数可控的干摩擦阻尼器,致使镗杆的动态特性表现出明显的非线性。根据试验结果对含有电流变材料的镗杆建立了数学模型,从理论上对电流变材料在结构振动中处于屈服前后临界状态的条件和动态特性进行了分析。     

Use of a generalized beam/spring element to analyze natural vibration of rail track and its application

This paper describes the formulation of a generalized beam/spring track element to obtain the natural vibration characteristics of a railway track modeled as a periodic elastically coupled beam system on a Winkler foundation. The rail/tie beams are described by either the Timoshenko beam theory or the Bernoulli-Euler beam theory. The rail beam is assumed to be discretely coupled to the cross-track ties through the coupling spring elements at the periodic rail/tie intersections. The generalized beam/spring element consists of a rail span beam segment, two adjacent tie beams, the coupling spring elements and the ultimate foundation stiffness. The entire track/beam system is then discretized into an assembly of periodic structural units. An equivalent frequency-dependent spring coefficient representing the resilient, flexural and inertial characteristics of the track substructure unit is formulated to establish the dynamic stiffness matrix of the generalized element. The eigenvalue problem of the track/beam system is solved by employing a comprehensive and efficient numerical routine. Solutions are provided for the natural frequencies of the track and the mode shapes of the rail/tie beams under transversely (cross-track) symmetric vibration. The natural vibration results are used to obtain the dynamic receptance response of a typical field track and to compare them with an existing model and field experimental data.     

Vibration control of a structure using Magneto-Rheological grease damper

This paper describes an application study of Magneto-Rheological (MR) grease damper to a structure with three stories. MR fluid is known as one of successful smart materials whose rheological properties can be varied by magnetic field strength, and has been applied to various kinds of device such as dampers, clutches, engine mounts, etc. However, ferromagnetic particles dispersed in MR fluid settle out of the suspension after a certain interval due to the density difference between the particles and their career fluid. To overcome this defect, we have developed a new type of controllable working fluid using grease as the career of magnetic particles. Network of thickener in grease is expected to hold the magnetic particles and prevent them from settled down. No or little sedimentation was observed in MR grease whose characteristics could be controlled by the magnetic field strength. MR grease was introduced into a cylindrical damper and its performance was studied. As a result, it was confirmed that the damping force of MR grease damper could be controlled by the applied electric current to the coil in the cylinder of damper. Furthermore, vibration response of a three-story model structure equipped with MR grease damper was investigated experimentally, and it was shown that MR grease damper worked effectively as a semi-active damper.