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.     

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.     

电流变技术在机床颤振控制中应用的研究

研究开发了一种控制机床颤振的电流变减振器。理论分析和试验结果表明,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。只要场强选取适当,采用电流变减振装置可以使铣床心轴的振幅降低50%～80%。试验在卧式升降台铣床上进行。     

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。     

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。     

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。     

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.     

一种场致流变体测试装置的研究

场致流变体是一种智能材料,在外加场强的作用下,场致流变体的黏度和刚度等力学性能发生变化。基于有阻尼受迫振动系统,设计了一个摆振式场致流变体测试装置,将流变体黏度、刚度等参数转化为测杆振幅和相位,配合数据采集及分析系统,完成不同场强下流变体黏度和刚度的测试。     

A study of misaligned electrorheological fluid lubricated hole-entry hybrid journal bearing

The present work describes a theoretical study to demonstrate the effect of the journal misalignment on the performance of an orifice compensated hole-entry hybrid journal bearing system lubricated with ER fluid. The journal misalignment has been accounted for by defining a pair of misalignment parameters sigma and delta. Continuous Bingham Model has been used to describe the behavior of ER fluid. The bearing static and dynamic characteristic parameters presented in the study indicate that the effect of journal misalignment is in general to cause a reduction in bearing dynamic characteristic parameters whereas the electric field in the ER fluid is to partially compensate this loss.     

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。     

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。     

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.     

Friction behavior of magnetorheological fluids with different material types and magnetic field strength

Magnetorheological (MR) fluid is a type of a smart material that can control its mechanical properties under a magnetic field. Iron particles in MR fluid form chain structures in the direction of an applied magnetic field, which is known as MR effect, resulting in variation of stiffness, shear modulus, damping and tribological characteristics of MR fluid. As MR effect depends on the density of particles in the fluid or the strength of a magnetic field, the experiments are conducted to evaluate the friction property under reciprocating motion by changing the types of MR fluid and the strength of a magnetic field. The material of aluminum, brass, and steel are chosen for specimen as they are the most common material in mechanical applications. The surfaces of specimen are also observed by optical microscope before and after experiments to compare the surfaces with test conditions. The comparing results show that the friction coefficient increases as the strength of a magnetic field increases in regardless of types of MR fluid or the material. Also the density of particle in MR fluid affects the friction characteristic. The results from this research can be used to improve the performance of mechanical applications using MR fluid.     

高速受电弓整体结构特性分析

受电弓整体结构分析对于改进受电弓的设计,提高受电弓的性能,具有重要意义。为保证良好的受流质量,新型高速受电弓大量采用轻型合金材料制作,这可能导致机械强度和刚度的不足。在满足强度与刚度的前提下,最大限度减小受电弓归算质量,以改善弓—网动态性能是受电弓设计的关键问题。文中结合受电弓的开发过程,建立三维仿真模型,利用有限元计算软件Ansys,进行受电弓的强度和刚度校核以及动力特性分析。研究受电弓动力特性的目的在于优化其结构,以控制其模态频率与模态振型,对受电弓的设计具有指导意义。通过对受电弓有限元分析,进行虚拟设计,首次进行高速受电弓的整体结构特性分析。     

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。     

机械设备流固耦合动力分析的有效方法

提出流固耦合动力分析的新方法。该法通过结构动力学的有限元求解方程和Newmark法,导出了新的迭代公式。流场的动压力使弹性体的动态特性变为载荷非线性问题;同时,固体位移场的变形作用使流场成为可变域流场。这些问题都可用本法得以解决。文中给出算例和工程应用实例。数值解结果表明,该法收敛速度快,效率高,克服了耦合问题的求解困难。     

On the characteristics of an ultra-low frequency nonlinear isolator using sliding beam as negative stiffness

A novel structured ultra-low frequency nonlinear passive isolator is presented. The isolator is composed of a knife-edge supported sliding beam which offers negative stiffness and a vertical mechanical spring in parallel to get quasi-zero dynamic stiffness. The static characteristics of the isolator are studied. Assuming light viscous damping, the dynamic behavior is investigated and the response under harmonic excitation is derived using a simple approximation. Frequency response curves (FRCs), which exhibit complex double jump phenomenon, are obtained by harmonic balance method (HBM). The limitation of the excitation force level is obtained. The force transmissibility is derived and compared with an equivalent linear system with the same damping ratio. The isolation performance of the nonlinear isolator is shown to outperform the linear system for providing a wider isolation region. The influence of system parameters on the transmissibility is examined and some useful guidelines are given.     

Expressions for coefficients of electrorheological fluid dampers

Useful expressions are developed for the damping coefficient of two types of viscous dampers that contain electrorheological (ER) fluids. The damping action in the first type occurs in flow between stationary parallel plates; the second type has annular flow between two stationary concentric cylinders. For ER fluid control, an electric field is applied across the gap in which the fluid flow occurs. The solution for the concentric cylinder damper is based on a thin gap approximation. These solutions may facilitate solving mechanical systems problems, using ER fluids, and demonstrate the controllability of ER dampers.     

磁流变液阻尼器-柔性转子系统振动特性与控制的再研究

对先前提出的理论分析模型进行适当改进，用新模型对支承在磁流变液阻尼器上的单盘悬臂柔性转子系统的振动特性和控制技术进行再研究。研究表明，随着磁流变液阻尼器的库仑阻尼力的增大，系统在无阻尼临界转速处振幅明显下降，但在两阶临界转速之间的一定转速区振幅增加；同时，随着库仑阻尼力的增加，阻尼器轴承处的振幅在几乎所有转速时都被减小，甚至在某些转速区间该轴承被“锁住”，而且轴承能够振动的区间越来越窄。这说明转子系统从一个弹性支承系统逐步转化为一个准刚性支承系统，阻尼器支承的有效刚度越来越大，使得一阶有阻尼临界转速逐渐提高，并逐渐接近刚支临界转速。根据这些特性，提出通过开关控制抑止转子通过两阶临界转速过程中的振动，并使转子振幅在全转速区达到最小。仿真结果表明，系统能平稳通过两阶临界转速。