Showing papers on "Magnetorheological fluid published in 1998"

An experimental study of MR dampers for seismic protection

Abstract: In this paper, the efficacy of magnetorheological (MR) dampers for seismic response reduction is examined. To investigate the performance of the MR damper, a series of experiments was conducted in which the MR damper is used in conjunction with a recently developed clipped-optimal control strategy to control a three-story test structure subjected to a one-dimensional ground excitation. The ability of the MR damper to reduce both peak responses, in a series of earthquake tests, and rms responses, in a series of broadband excitation tests, is shown. Additionally, because semi-active control systems are nonlinear, a variety of disturbance amplitudes are considered to investigate the performance of this control system over a variety of loading conditions. For each case, the results for three clipped-optimal control designs are presented and compared to the performance of two passive systems. The results indicate that the MR damper is quite effective for structural response reduction over a wide class of seismic excitations.

Properties and applications of commercial magnetorheological fluids

Abstract: The rheological and magnetic properties of several commercial magnetorheological (MR) fluids are presented and discussed. These fluids are compared using appropriate figures of merit based on conventional design paradigms. Some contemporary applications of MR fluids are discussed. These applications illustrate how various material properties may be balanced to provide optimal performance.

Nondimensional analysis of semi-active electrorheological and magnetorheological dampers using approximate parallel plate models

Abstract: We develop nonlinear quasi-steady electrorheological (ER) and magnetorheological (MR) damper models using an idealized Bingham plastic shear flow mechanism. Dampers with cylindrical geometry are investigated, where damping forces are developed in an annular bypass via Couette (shear mode), Poiseuille (flow mode) flow, or combined Couette and Poiseiulle flow (mixed mode). Models are based on parallel plate or rectangular duct geometry, and are compared to our prior 1D axisymmetric models. Three nondimensional groups are introduced for damper analysis, namely, the Bingham number, , the nondimensional plug thickness, , and the area coefficient defined as the ratio of the piston head area, , to the cross-sectional area of the annular bypass, . The approximate parallel plate analysis compares well with the 1D axisymmetric analysis when the Bingham number is small, or , or the nondimensional plug thickness is small, . Damper performance is characterized in terms of the damping coefficient, which is the ratio of the equivalent viscous damping constant, , to the Newtonian viscous damping constant, C. In shear mode, the damping coefficient is a linear function of the Bingham number. In flow mode, the damping coefficient is a function of the nondimensional plug thickness only. For the mixed mode damper, the damping coefficient reduces to that for the flow mode case when the area coefficient is large. The quasi-steady damping coefficient versus nondimensional plug thickness diagram is experimentally validated using measured 10 Hz hysteresis cycles for a electrorheological mixed mode damper.

Idealized Hysteresis Modeling of Electrorheological and Magnetorheological Dampers

Abstract: The hysteresis behavior of a linear stroke magnetorheological damper is characterized for sinusoidal displacement excitation at 2.0 Hz (nominal). Four different modeling perspectives are discussed for purposes of system identification procedures, including: (1) equivalent viscous damping, (2) nonlinear Bingham plastic model, (3) nonlinear biviscous model, and (4) nonlinear hysteretic biviscous model. By progressively adding model parameters with which to better represent pre-yield damper behavior, the force vs. velocity hysteresis model is substantially improved. The three nonlinear models represent the force vs. displacement hysteresis behavior nearly equally well. Thus, any of the three nonlinear damper models could be used equally successfully if only a prediction of energy dissipation or damping were of interest. The nonlinear hysteretic biviscous model provides the best representation of force vs. velocity hysteresis of the four models examined here.

Behavior of Magnetorheological Fluids

Abstract: In the absence of an applied magnetic field, magnetorheological (MR) fluids typically behave as nearly ideal Newtonian liquids. The application of a magnetic field induces magnetic dipole and multipole moments on each particle. The anisotropic magnetic forces between pairs of particles promote the head-to-tail alignment of the moments and draws the particles into proximity. These attractive interparticle forces lead to the formation of chains, columns, or more complicated networks of particles aligned with the direction of the magnetic field. When these structures are deformed mechanically, magnetic restoring forces tend to oppose the deformation. Substantial field-dependent enhancements of the rheological properties of these materials result, as demonstrated in Figure 1.The myriad potential applications of MR and electrorheological (ER) fluids provide considerable motivation for research on these materials. The availability of fluids with yield stresses or apparent viscosities that are controllable over many orders of magnitude by applied fields enables the construction of electromechanical devices that are engaged and controlled by electrical signals and that require few or no moving parts. Potential automotive applications include electrically engaged clutches for vehicle powertrains and engine accessories as well as semiactive shock absorbers that can adapt in real time to changing road conditions. Semiactive dampers for rotorcraft control surfaces are among the potential aerospace applications. The critical need to mitigate the structural vibrations of large structures has led to the construction of large, high-force MR-fluid-based dampers. A promising application in manufacturing processes is the computer-aided polishing of precision optics in which abrasive particles are suspended in an MR fluid so that the polishing rate is determined in part by the strength of an applied magnetic field.

Neural Network Modeling of a Magnetorheological Damper

Abstract: The magnetorheological (MR) damper is a newly developed semiactive control device that possesses unique advantages such as low power requirement and adequately fast response rate. The device has been previously tested in a laboratory to determine its dynamic properties and characterized by a system of nonlinear differential equations. This paper presents an alternative representation of the damper in terms of a multilayer perceptron neural network. A neural network model with 6 input neurons, one output neuron and twelve neurons in the hidden layer is used to simulate the dynamic behavior of the MR damper. Training of the model is done by a Gauss-Newton based Levenberg-Marquardt method using data generated from the numerical simulation of the nonlinear differential equations. An optimal brain surgeon strategy is adopted to prune the weights and optimize the neural networks. An optimal neural network is presented that satisfactorily represents dynamic behavior of the MR damper.

Two-way magnetorheological fluid valve assembly and devices utilizing same

Abstract: A controllable valve assembly (18) applicable in Magnetorheological (MR) fluid devices (20), such as MR mounts and MR dampers. The valve assembly (18) includes a valve body (32) having a magnetic circuit (40) contained therein which carries magnetic flux ζ, a controllable passageway (42) within the magnetic circuit (40), a MR (magnetically controlled) fluid (44) including soft-magnetic particles in a liquid carrier contained in the controllable passageway (42), a magnetic flux generator, such as a wound wire coil (46), generating magnetic flux ζ which is directed through the MR fluid (44) in the controllable passageway (42) thereby generating 'rheology' changes causing restriction in flow of MR fluid (44) therethrough. In one aspect, a one-way check valve (34) is operative with a passive passageway (36) which is arranged in parallel relationship to the controllable passageway (42) provides 'asymmetric' damping across the controllable valve (18) creating higher pressure differentials in a first direction and a lower in a second direction without 'rapidly switching' the current to the coil (46). In another aspect, 'asymmetric' damping is provided by a 'changeable gap' formed by a moveable wall portion of the controllable passageway (42). In a third aspect, a first controllable passageway provides controllable flow in a first direction and a second controllable passageway provides controllable flow in a second direction, thereby provide 'asymmetry'. In a fourth aspect, 'asymmetry' is provided by a 'variable magnetic short' which changes magnetic circuit reluctance dependent on flow direction.

Adjustable valve and vibration dampers utilizing same

Abstract: An adjustable valve including a passageway, a field responsive fluid within the passageway, and fluid flow adjustment through the passageway. The valve is preferably used in a vibration damper. One damper includes a body, a piston, first and second chambers, a damping valve, a piston rod, an auxiliary chamber, a passageway interconnecting to the auxiliary chamber, a field responsive fluid, a field responsive fluid valve for controlling flow to the auxiliary chamber, and pressurization means. Preferably included is a cavity partition having field responsive fluid disposed on one side and non-field responsive fluid disposed on the other. This allows a reduction of MR fluid allowing use of lighter-weight, less-expensive, hydraulic fluids for flow through the piston's damping valve. In another aspect, the damper includes mechanical adjustment means for manually adjusting the damping level. Adjustment is accomplished by a moveable permanent magnet, moveable pole piece, moveable pole-and-magnet assembly, or magnetic shunt. Manual adjustment may include a knob, lever, or cable actuation. Alternately, magnetic flux is provided by an electromagnet. The valve and damper finds utility in any suspension system where a damper body is attached to a frame component, such as a bicycle frame, and the piston rod is attached to a suspension component, such as a bicycle's swingarm.

Passive magnetorheological fluid device with excursion dependent characteristic

Abstract: A magnetorheological fluid device which exhibits excursion (stroke or rotation) dependent resistance (force or torque) which is obtained passively. Linear and rotary embodiments are described. The devices described herein include various ways for passively varying magnetic circuit reluctance to accomplish the stroke or rotation dependent characteristic. The devices include a first component with an internal cavity, a second component received in the cavity and moveable relative to the first component, a working zone created between the first and second component, a magnetorheological fluid contained therein, at least one permanent magnet for producing a magnetic field, a magnetic circuit for directing a magnetic flux created by the permanent magnet toward the magnetorheological fluid in the working zone, and passively varying a magnetic circuit reluctance (such as by changing a thickness of a magnetic return, by changing a gap thickness, by changing the material reluctance, by interacting multiple magnetic fields, or combinations thereof) as a function of excursion. This changes the magnetic field strength acting upon the MR fluid in the working zone and produces a force/torque which varies as a function of excursion (x or θ).

The Materials Science of Field-Responsive Fluids

Abstract: Scientists and engineers are most familiar with single-crystal or polycrystalline field-responsive or “smart” materials with responses typically occurring while the materials remain in the solid state. This issue of MRS Bulletin focuses on another class of field-responsive materials that exhibits a rapid, reversible, and tunable transition from a liquidlike, free-flowing state to a solidlike state upon the application of an external field. These materials demonstrate dramatic changes in their rheological behavior in response to an externally applied electric or magnetic field and are known as electrorheological (ER) fluids or magnetorheological (MR) fluids, respectively. They are often described as Bingham plastics, and exhibit a strong field-dependent shear modulus and a yield stress that must be overcome to initiate gross material deformation or flow. Prototypical ER fluids consist of linear dielectric particles (such as silica, titania, and zeolites) dispersed in nonconductive liquids such as silicone oils. Homogeneous liquid-crystalline (LC) polymerbased ER fluids have also been recently reported. MR fluids are based on ferromagnetic or ferrimagnetic, magnetically nonlinear particles (e.g., iron, nickel, cobalt, and ceramic ferrites) dispersed in organic or “aqueous liquids. Unlike ER and MR fluids, ferrofluids (or magnetic fluids), which are stable dispersions of nanosized superparamagnetic particulates (~5–10 nm) of such materials as iron oxide, do not develop a yield stress on application of a magnetic field. Applications of ferrofluids are primarily in the area of sealing devices (see Rosensweig for more information). Since ferrofluids are well-known and have been extensively discussed elsewhere in the literature, they will not be treated in detail here.

Magnetorheological transmission clutch

Abstract: A magnetorheological clutch for controllable torque transmission includes a housing defining a cavity with a rotary input element carrying at least one input clutch plate extending radially in the cavity A rotary output element carrying at least one output clutch plate extends radially into the cavity adjacent the input clutch plate with a gap defined between the input clutch plate and the output clutch plate A core formed of magnetically permeable material has a pair of side plates extending radially across the housing A coil effective to establish an electromagnetic field is carried against the core Magnetorheological fluid is carried in the cavity within the gap and is responsive to the electromagnetic field that is established by the coil through the core so that torque is transferred from the input clutch plate to the output clutch plate through the magnetorheological fluid A series of radially extending cooling fins are positioned in the cavity, radially inside the input clutch plate and the output clutch plate so that generated heat is dissipated through the cooling fins by exposure to a circulating coolant fluid flowing about the cooling fins that enters and exits the cavity through a coolant flow path Heat expansion of the magnetorheological fluid is accommodated by a thermal expansion chamber

Controllable cab suspension

Abstract: A controllable secondary suspension system (20) for vehicle cabs (18) and the like which flexibly suspends and controls movement of the vehicle's cab (22) relative to the vehicle's frame (24). The system (20) includes at least one flexible support (26), which are preferably two spaced apart air springs flexibly suspending the cab (22) relative to the frame (24), at least one controllable fluid damper, and preferably two spaced-apart controllable fluid dampers, such as Magnetorheological (MR) fluid dampers (28, 28'), interconnected between the cab (22) and the frame (24). In one aspect, the system (20) may include at least one sensor, such as a relative position sensor (30), for providing relative vibration information between the cab (22) and the frame (24), and a controller (36) for processing the relative vibration information to determine current to be supplied to the controllable fluid damper (28) to control the degree of damping thereof. Signals from additional sensors, such as a speed sensor (32), steering angle sensor (34), brake sensor (46), throttle position sensor (48), and vertical and lateral acceleration sensors (40, 44) may be used to enhance control. Roll, pitch, lurch and ride may be simultaneously or independently controlled.

Helicopter Blade Response and Aeromechanical Stability with a Magnetorheological Fluid Based Lag Damper

Abstract: This paper explores the feasibility of using Magnetorheological (MR) fluid-based dampers for lag damping augmentation in helicopters. An MR damper model is integrated with a rotor aeromechanical model. Two different control schemes are presented-namely the On-Off scheme and the Feedback Linearization scheme. In the On-Off scheme, two criteria are used to obtain equivalent linear damping for the nonlinear MR damper as a function of the size of perturbation and the applied field. The Feedback Linearization scheme uses a feedback controller to linearize the force output of the MR damper. The two control schemes are compared for lag transient response in ground resonance and their ability to reduce periodic damper loads in forward flight. It is shown that an MR damper of a size comparable to an elastomeric damper can provide sufficient damping for ground resonance stabilization and can significantly reduce periodic damper loads with ajudicious choice of operation scheme.

Proactive shock absorption and vibration isolation

Abstract: Disclosed are methods and apparatuses for varying stiffness and/or damping characteristics of a vibration isolation system based on the machine's control signal which indicates the motion status of at least one movable component of a machine supported by the vibration isolation system. The motion status of the movable component can be monitored via parameters such as the electrical power being injected into the motor of the movable component. More stiffness and/or damping are provided to absorb shocks generated while the movable component accelerates or decelerates and less stiffness and/or damping are provided while the movable component moves at a nominally constant speed or stands still. The stiffness and/or damping characteristics of a vibration isolation system are varied by controlling one or more of the following: 1) the gas flow rate between two gas chambers, 2) the strength of a magnetic field applied to a magnetorheological fluid or ferrofluid, and 3) the strength of an electric field applied to an electrorheological fluid.

Ground States of Magnetorheological Fluids

Abstract: Through energy minimization and stability argument, we find the ground states of the magnetorheological fluids to consist of magnetic particles arranged in a body centered tetragonal structure inside spheroidal clusters. The width D of the clusters varies with the length L as D , Ln, where n ­ 0.62 for magnetically saturated particles. In the case of magnetically unsaturated particles, the power law variation is divided into two segments, with n ­ 0.4 in the first segment and n ­ 0.62 in the large L limit. Our results offer a theoretical framework for the resolution of conflicting experimental observations, with the demagnetization field being the crucial physical consideration. [S0031-9007(98)06941-5]

Magnetorheological suspension-based finishing technology

Abstract: In magnetorheological finishing (MRF) the mechanical energy for material removal is generated by the hydrodynamic flow of a magnetorheological (MR) polishing suspension through a converging gap that is formed by a workpiece surface and a moving rigid wall. In addition to causing material removal, MRF also reduces the surface micro roughness of optical materials to ≤ 10 a rms. Shape errors are corrected to a fraction of a wavelength of light and subsurface damage is removed. A theoretical analysis of MRF, based on Bingham lubrication theory, illustrates that the formation of a core attached to the moving wall results in dramatically high stress on the workpiece surface. A correlation between the shear stress on the workpiece surface and materials removal is obtained.

Particle dynamics in magnetorheological suspensions using diffusing-wave spectroscopy

Abstract: Magnetorheological suspensions acquire dipole moments in an external magnetic field. Suspensions of these dipolar particles rapidly aggregate to form long chains. We use diffusing-wave spectroscopy (DWS) and density-matched superparamagnetic emulsion droplets to probe the short-wavelength motion of the chains. The measured particle displacements are independent of the magnitude of the dipolar interactions at short times, but characterized by a constrained, subdiffusive motion at long times that slows as the dipolar interactions are increased. Our observations show good qualitative agreement with Brownian dynamics simulations of dipolar chains.

Stabilized magnetorheological fluid compositions

Abstract: Magnetorheological fluids containing carbonyl iron particles with surface hydroxyl groups and high specific surface area in combination with nonpolar vehicles such as polyalphaolefins and glycol esters can be formulated to resist particle separation under high separation force applications. When the nonpolar vehicle having a suitably high molecular weight is used, the fluids may be used at working temperatures of the order of 200° C.

Shock absorber using electrorheological or magnetorheological fluid for industrial machine or automobile

Abstract: The shock absorber has a cylinder housing (2) divided into 2 pressure spaces, filled with an electrorheological or magnetorheological fluid via an axially sliding piston (3a), incorporating a bypass channel (29) for coupling the pressure spaces.

Clutch with electrorheological or magnetorheological liquid pushed through an electrode or magnet gap by means of a surface acting as a piston

Abstract: This invention relates to a controllable clutch based on electrorheological or magnetorheological liquids, in which the transmission of force or the transmission of torque is achieved in that an electrorheological or magnetorheological liquid is pushed through an electrode gap or magnet gap of the clutch by means of a surface acting as a piston.

Experimental Evaluation of Semiactive Magneto-Rheological Suspensions for Passenger Vehicles

Abstract: Mechanical Engineering This study experimentally evaluates the dynamic response of a single vehicle suspension incorporating a magneto-rheological (MR) damper. A full-scale two-degree-of-freedom (2DOF) quarter-car test apparatus has been constructed at the Advanced Vehicle Dynamics Lab at Virginia Tech to evaluate the response of a vehicle suspension under the different control schemes of skyhook, groundhook, and hybrid semiactive control. The quarter-car apparatus was constructed using materials from 80/20 Incorporated and a hydraulic actuation system from MTS. A dSPACE AutoBox was used both for controlling the MR dampers and acquiring data. The first task was to understand the baseline dynamic response of the quarter-car system with only a passive damper. Next, the passive damper was replaced with a controllable MR damper. The control schemes of skyhook, groundhook, and hybrid semiactive control were applied to the MR damper. The physical response of the quarter-car with the different control schemes was then compared to the analytical prediction for the response, with favorable results. The response of the quarter-car with the semiactive damper was also compared to the response of the quarter-car with a passive damper, and the resulting limitations of passive damping are discussed. Finally, the practical implications of this study are shown in a discussion of the physical implementation of the MR dampers in the Virginia Tech FutureCar, a full-size Chevrolet Lumina. Although the actual skyhook, groundhook, and hybrid semiactive control schemes were not implemented on the vehicle, the results were promising and generated several recommendations for future research. iii Acknowledgments I would like to thank my advisor, Dr. Mehdi Ahmadian, for his help and encouragement throughout graduate studies in the Mechanical Engineering Department. I would also like to thank Drs. Douglas Nelson and William Saunders for serving on my graduate committee. I also would like to thank Lord Corporation and Koni Incorporated for donating the time and technical expertise to supply the Advanced Vehicle Dynamics Lab at Virginia Tech with the hardware used for this study. The generous donations by PCB Piezotronics Incorporated, Texas Instruments Incorporated, and the 80/20 Corporation, which made possible the many tests that were required for this study, are greatly appreciated. Finally I would like to thank my wife, Sarah, my mother and stepfather, Carol Paré and Robert Beaudette, my sister, Kim, and G for all their love and support during the time I have spent at Virginia Tech. Introduction The purpose of this chapter is to provide …

Magnetorheological Throttle Valve in Passive Damping Systems

Abstract: The present paper considers the efficiency of modelling experimental pressure-flowrate characteristics of an MR throttle valve by a technique, according to which hydraulic resistance coefficient of a valve is determined as a function of Reynolds and Hedstrom numbers. In predictions, an MR fluid is characterised by density, out-of-field viscosity and yield stress. It is shown that the hydraulic characteristics of a valve predicted by Hedstrom's technique are fit to the experimental ones over the entire range of magnetic field and MR fluid flowrate. The procedure for prediction of valve parameters that allows a damper design to be optimised is presented.

Magnetorheological Suspension-Based High Precision Finishing Technology (MRF)

Abstract: In MRF the mechanical energy for material removal is generated by the hydrodynamic flow of a magnetorheological (MR) polishing suspension throughout a preset converging gap formed by the workpiece surface and a moving rigid wall. MRF reduces the surface microroughness of optical materials to < 10 A. Shape errors are corrected to a fraction of a wavelength of light and subsurface damage is removed.

Optical characteristics of electrorheological and electromagnetorheological fluids

Abstract: The optical character of electrorheological (ER) and electro- magnetorheological (EMR) fluids under the influence of an external field are investigated It is found that the transmission of ER fluids could be adjusted through selecting the proper electric field and suspension con- centration The IR spectral transmissions of ER fluids increase with an applied electric field The maximum transmittance for low-concentration fluid changed from 4% to 23% It is also observed that the window of transmission does not change with fluid consistency and external electric field We find that the scattering patterns of ER fluids consist of the many bright and dark bands as a scattering grating The widths of bright bands increase with increasing electric field The scattering pattern of EMR fluids under electric and magnetic fields superimposed in the perpen- dicular is also observed These phenomena provide new mechanics for the design of tunable optical devices and will have direct industrial ap- plication © 1998 Society of Photo-Optical Instrumentation Engineers (S0091-3286(98)01605-5)

Characterization of semiactive magnetorheological helicopter lag mode dampers

Abstract: Magnetorheological fluid dampers are attractive candidates for augmentation of lag mode damping in helicopter rotors, where additional damping is required to avert instabilities only during specific flight conditions. Magnetorheological (MR) fluids change properties dramatically with application of a magnetic field. This active damping component presents an advantage over passive elastomeric and fluid-elastomeric dampers. An extensive comparative study of fluid-elastomeric and MR dampers is presented. The study was conducted with four (a pair each) 1/6th Froude scale dampers. The MR dampers were tested with the magnetic field turned off (OFF condition) and with the magnetic field turned on (ON condition). The dampers were rested individually and in pairs, under different preloads, and under single and dual frequency excitation conditions. The fluid-elastomeric and MR (OFF) damper behavior was linear, while the MR (ON) behavior was nonlinear with the stiffness and damping varying with the displacement amplitude. Under dual frequency conditions, the MR dampers (ON condition) showed a significant degradation in damping and stiffness as the dual frequency excitation was increased. The MR (OFF) dampers showed no change in properties. The fluid-elastomeric dampers showed a mild degradation in stiffness and damping under dual frequency excitation conditions. The MR (ON) damper hysteresis was modeled using a nonlinear viscoelastic plastic model. The model captures the nonlinear behavior accurately. Using the single frequency parameters, the dual frequency hysteresis behavior was predicted, and it correlates well with experimental data.

Estimation and Control Related Issues in Smart Material Structures and Fluids

Abstract: : We discuss issues related to modeling of nonlinearities and hysteresis arising in a class of magnetorheological-based smart elastomers. The dynamic models intended for use in parameter estimation and control problems are presented in the context of simple elongation of a filled rubber-line rod. Theoretical computational and experimental results are given.