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.     

Development of a laboratory test device for electrorheological fluids in hydrostatic lubrication

Electrorheological (ER) fluids exhibit changes in their rheological behaviour in the presence of an external electric field. Research and development activities related to ER fluids and their applications have increased dramatically during the last few decades. If commercialised, ER fluids could have a significant impact on hydraulic equipment, and be utilised in the automotive, marine, aerospace, robotics, and machinery industries. The objective of the present study is to demonstrate the feasibility of using ER fluids to produce ‘smart’ lubricants that can control friction and wear of sliding components. The ER lubricant effect is demonstrated using a unique test machine that utilises hydrostatic lubrication. It is found that the friction torque increases by as much as 30% when a voltage of 2000 V is applied to an ER fluid in the newly developed test machine.     

Development of electrorheological chip and conducting polymer-based sensor

This paper presents the development of an integrated sensor using two types of smart materials: electrorheological (ER) fluids and conducting polymers (CPs). The developed ER chip worked as an actuator, and it was driven by different voltages and control frequencies. When the four electrodes are controlled synchronously, the diaphragm acts as a vibrator whose frequency can be adjusted in accordance with the frequency of the electrical signals. The response signals of the CP sensor were recorded, and its properties were analyzed. Experimental results show that the amplitude decreases monotonically when the frequency increases, owing to the time delay in the pressure buildup in the ER chip. However, the displacement fluctuation of the diaphragm below 20Hz can be detected clearly even if the value is very low. When the vibration frequency is larger than 20Hz, the CP sensor can hardly detect the displacement fluctuation. Thus, the upper limit frequency that the CP sensor can detect is about 20Hz. The practical applications of this microdevice are also discussed.     

圆盘式电流变离合器的动态特性

研究圆盘式电流变传动机构的动态特性，利用神经网络进行系统识别，并采用NI虚拟仪器对机构进行检测和控制，分析输出转矩与所加电场的关系，推动电流变流体传动机构的应用。     

Wear testing and specification of hydraulic fluid in industrial applications

The aim of this paper was to investigate the possibilities to use a model test to simulate the wear between cylinder bore and piston in a radial piston hydraulic motor. The tests were performed in a reciprocating test rig where the contact geometry is of the cylinder–plate type. The influence of different types of commercially available hydraulic fluids on wear protection and friction was studied. From the study, it was concluded that the use of water glycols can cause increased wear in hydraulic motors operating in low speed applications. It was also seen that the FZG test alone appears not to be enough as a hydraulic fluid wear test, at least not in the tribological conditions present in the performed wear test.     

基于仿真的粘滞阻尼系数对刚体接触力影响的分析

针对机械系统动力学仿真分析软件ADAMS中的多接触求解困难问题,基于粘滞阻尼理论来研究多接触求解,以及接触参数的设置对结果的影响,通过理论与实践相结合,分析了在多接触问题求解过程中最大阻尼系数Cmax对系统的多接触仿真分析结果的影响,为多接触问题的研究提供了一些理论基础与实践经验,且对此问题的进一步研究具有一定的参考与借鉴作用。     

Analysis of a radial magnetic fluid seal and a radical bearing lubricated with a magnetic fluid

This paper discusses the effects of viscous pumping in a magnetic fluid seal under a rotating load. The Reynolds' equation is presented for the seal based on magnetic fluid mechanics. Expressions are given for obtaining pressures in the seal, and eccentricities of the rotating shaft because of viscous pumping and seal pressures. Numerical calculations are carried out for some sample problems and for the effect of the strength of the magnetic flux on the fluid pressure. Also, eccentricities of the shaft in the seal and the seal pressures are clarified.     

Self-organizing maps for surveying lubrication within squeeze film dampers

Self-organizing maps (SOMs) represent a well-known neural network technique particularly suited to classification tasks. Here, it is adopted to monitor the lubricating conditions within squeeze film dampers for rotor support and was aimed, in particular, at identifying the aspect of the pressure waves within the oil film. Pressure distribution is indeed significantly influenced by a number of factors, which affect damper operation. Results from past research in the field make it possible to infer that the pattern of pressure signals taken in the oil film represents a valuable source of information as regards the lubricating conditions within the damper. Surveillance procedures in the operation of turbomachinery could benefit from prompt detection of possible, unwanted changes in the characteristics of lubrication, for example, when modeling bearing operations within model-based schemes. In this paper, SOM capabilities are first evaluated, dealing separately with theoretically simulated data. The subsequent tests adopted theoretical data as a reference for identifying experimental conditions. Further tests were carried out to map experimental data. Despite constraints consisting in the damper motion being imposed during the theoretical and experimental tests, the results confirmed the potential of the method and encourage further tests in conditions which are closer to real operation.     

Sleeve dampers for externally pressurised gas journal bearings

An approximate small eccentricity analysis is presented, for finding the threshold of fractional speed whirl instability of an unloaded double plane admission hybrid gas journal bearing supported by a non-rotating externally pressurised gas journal bearing sleeve damper. A line source is assumed at the feeding planes to the gas film with flow and load correction factors to account for the discreteness of the feed holes (details of these factors are presented in a related publication). The results show that, by careful selection of the design parameters, it is possible almost to remove fractional speed whirl instability from the bearing arrangement. Some practical designs of sleeve dampers are also presented.     

Tribological behavior of frictional seismic dampers of pendulum type

Frictional pendulum bearings have universal properties that can meet various requirements at service of buildings, bridges, and industrial constructions. The formulas for the average dimensionless wear rate and friction coefficient of the bearings are obtained. The use of the bearings as seismic dampers of shell drilling rigs is described and characteristics of the frictional pendulum bearings are given.     

Tribological properties of fluid phase phospholipid bilayers

Our recent studies showed that solid phase phospholipid bilayers play an important role in joint lubrication mechanism. We investigate the tribological properties of fluid phase bilayers depending on various experimental parameters. Bilayers containing a fluorescent lipid with a large head-group and surfaces covered with only one bilayer poorly lubricate meaning that the slip plane during shear is located in the thin aqueous layer between the bilayers. Lubrication and resistance to normal and tangential stresses are greatly improved in buffered saline solution. Bilayers prepared by vesicle fusion method improve the tribological properties of even very rough substrates by smoothing their topographical defects.     

利用电流变液双电极复合结构改变切削系统特性的研究

针对轴类工件切削颤振的特点 ,对所设计的一种电流变液双电极复合结构切削颤振抑制装置 ,通过静加载实验和激振实验分别对其静态和动态特性进行了实验研究和理论分析 ,证明这种结构可以用于车削颤振抑制     

应用电流变技术的变速器设计

设计一种运用电流变液的变速器，分析了变速器的工作原理、结构特点，研究电流变变速器主要结构参数与输入输出转矩的关系，获得影响传动系统性能的主要因素，使进一步的结构优化设计成为可能。     

Fast vision-based wave height measurement for dynamic characterization of tuned liquid column dampers

In this study, a novel and rapid vision-based sensing strategy is developed exclusively for dynamic wave height measurement of tuned liquid column dampers (TLCDs). The image processing algorithm of the vision-based sensing method simply counts white pixels in a binary image and thus expedites the vision-based wave height measurement. In addition to the experimental achievement, a practical methodology of dynamic characterization for the TLCDs is proposed combining linearized equations for the TLCDs and experimental data measured. An experimental characterization of dynamic behaviors and damping properties of the TLCDs is undertaken utilizing the vision-based sensing developed.     

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。     

Experimental determination of the stiffness and damping coefficients of fluid film bearings by means of step forces

A method of identifying bearing dynamic coefficients by means of step forces is described. Obtaining an accurate fast Fourier transform of the rapidly varying step function is difficult since the limitations of real time analysis by minicomputer make truncation necessary. This paper therefore proposes a feasible approach to direct analysis of the spectrum of the step function and introduces its application to measure the stiffness and damping coefficients of journal bearings. The approach followed is to use a step exciting force on the test bearings. By using the proposed direct spectrum analysis method, the transfer functions of the bearing systems and eventually the dynamic coefficients of the journal bearings can be derived.     

Numerical and Compact Model of Metal Mesh Foil Bearings

Metal mesh foil bearings (MMFBs) are novel gas foil bearings with lower manufacturing costs and higher inherent material energy dissipation ability than traditional bump-type foil bearings. To improve the design guidelines of MMFBs and predict bearing performance, a compact theoretical model is presented by considering the metal mesh substructure as assembled springs and dry friction joints. The proposed analytical model considers the effects of several factors such as relative density, wire diameter, geometrical size, and radial interference of the metal mesh substructure. The predicted stiffness coefficients, which take the dry friction effect into account, show strong nonlinear characteristics with the increasing displacement and have a significant difference between the loading and unloading process. A series of static load tests are conducted to verify the theoretical model of MMFBs. The hysteresis loops of static load versus bearing deflection with respect to the different relative densities predicted by this model are demonstrated by experimental data. The minimum film thickness, journal eccentricity, and attitude angle with respect to different relative densities, rotational speeds, and applied loads are presented and analyzed. The predicted results of the dynamic force coefficients show that the equivalent viscous damping coefficient and relative density have significant effects on bearing dynamic performance. Furthermore, the influence of radial thickness, wire diameter, and radial interference on bearing static and dynamic performance is discussed.     

A critical evaluation of film thickness‐derived pressure–viscosity coefficients

A single parameter, the pressure–viscosity coefficient, α, quantifies the pressure dependence of the viscosity of the liquid in elastohydrodynamic lubrication (EHL). Most published values of α have not been obtained from measurements of viscosity as a function of pressure. Rather, these effective pressure–viscosity coefficients have been derived from the measurement of the EHL film thickness, a more difficult procedure. In this article, five well‐characterized liquids that should be Newtonian in the EHL inlet are identified for which film‐derived coefficients have been reported. These coefficients are compared with coefficients derived from published viscosity correlations and new viscosity measurements. The film‐derived coefficients are found to not be an accurate representation of the piezoviscous response. The procedure of deriving a pressure–viscosity coefficient from a film thickness measurement does not offer an alternative to the simpler and easier viscometer measurement. Copyright © 2014 John Wiley & Sons, Ltd.     

电流变技术在机械工程中的应用展望

电流变技术是机电控制领域的一门新兴学科 ,尤其是它在机电转换过程中表现出的智能化控制特征 ,更具有巨大的潜在应用前景。本文简略回顾了电流变技术及其发展 ,以几个实际的例子介绍了目前设计的各类电流变元器件 ,展望了电流变技术在机械工程领域的应用前景。