Showing papers on "Magnetorheological fluid published in 2003"

Design and Experimental Evaluation of a Magnetorheological Brake

Abstract: A new magnetorheological (MR) brake prototype was designed, fabricated and tested. Firstly, the rheological properties of MR fluids, in particular the dynamic yield stress, were experimentally investigated based on a Bingham plastic model. The working principles of the MR brake were then analysed and discussed. The equations for transmitted torque were derived and used to evaluate the disc-shaped MR brake. This was followed by an analysis of an electromagnet using the finite element method. Following the manufacturing and fabrication of a brake prototype, the mechanical performance of the MR brake was experimentally evaluated with a specially designed test rig. The effects of magnetic field and rotary speed on the transmitted torque were addressed, and an amplifying factor was introduced to evaluate the brake performance. It was found that brake torque increased steadily with the increment of magnetic field or rotary speed. The amplifying factor showed an increasing trend with the magnetic field but a decreasing trend with rotary speed.

Shear properties of a magnetorheological elastomer

Abstract: This paper presents an experiment testing the damped free vibration of a system composed of a magnetorheological elastomer and a mass. The goal of this experiment was to obtain the dependence of the natural frequency and the damping ratio of the structure on the applied magnetic field. The shear properties, including the shear storage modulus and the damping factor, were therefore determined. The experimental results revealed that the shear storage modulus could reach a value of 60% of the zero-field modulus and was dominated by the magnetic field, but the change in the damping factor could be neglected. Furthermore, when the field was moderate and saturation did not occur, the shear storage modulus increased proportionally with the applied field. This interesting phenomenon was analysed, and it is suggested that the subquadratic field dependence, which arises from the saturation of the magnetization near the poles of closely spaced pairs of spheres, must be taken into consideration.

Semi-active control of structures incorporated with magnetorheological dampers using neural networks

Abstract: Semi-active control of buildings and structures with magnetorheological (MR) dampers for earthquake hazard mitigation represents a relatively new research area. In this paper, the Bingham model of MR damper is introduced, and the formula relating the yielding shear stress and the control current of MR dampers is put forward that matches the experimental data. Then an on-line real-time control method for semi-active control of structures with MR dampers is proposed. This method considers the time-delay problem of semi-active control, which can solve distortion of the responses of structures. Finally, through a numerical example of a three-storey reinforced concrete structure, a comparison is made between controlled structure and uncontrolled structure. The calculated results show that MR dampers can reduce the seismic responses of structures effectively. Moreover, the on-line real-time control method is compared with the traditional elastoplastic time-history analysis method, and the efficacy of the on-line real-time control method is demonstrated. In addition, the Levenberg–Marquardt algorithm is used to train the on-line control neural network, and studies show that the algorithm has a very fast convergence rate.

Control of seismically excited cable-stayed bridge employing magnetorheological fluid dampers

Abstract: This paper examines the ASCE first generation benchmark problem for a seismically excited cable-stayed bridge, and proposes a new semiactive control strategy focusing on inclusion of effects of control-structure interaction. The subject of the ASCE benchmark problem is a cable-stayed bridge in Cape Girardeau, Missouri, for which construction is expected to be completed in 2003. The goal of the benchmark study is to provide a \Itestbed\N structure on which researchers can systematically compare and evaluate the relative merits of proposed structural protection for cable stayed-bridges. In this paper, magnetorheological (MR) fluid dampers, which belong to the class of controllable fluid dampers, are proposed for use in a control strategy for protecting the bridge. A clipped-optimal control algorithm, shown to perform well in previous studies involving MR fluid dampers, is employed. A comprehensive study of the adequacy of various types of dynamic models for MR fluid dampers, such as a Bingham model, a Bouc-Wen model, and a modified Bouc-Wen model, is provided. In contrast to previous studies, models considered in this study are based on experimental data for a full-scale MR fluid damper. Because the MR fluid damper is a controllable energy-dissipation device that cannot add mechanical energy to the structural system, the proposed control strategy is fail-safe in that bounded-input, bounded-output stability of the controlled structure is guaranteed. Numerical simulation results considering several historical earthquakes scaled to various magnitudes show that the proposed semiactive control strategy using MR fluid dampers is the promising one of the applicable control methods to reduce seismic responses of cable-stayed bridges.

Semiactive Vibration Control of Train Suspension Systems via Magnetorheological Dampers

Abstract: This paper is aimed to show the feasibility for improving the ride quality of railway vehicles with semiactive secondary suspension systems using magnetorheological (MR) dampers. A nine degree-of-freedom railway vehicle model, which includes a car body, two trucks and four wheelsets, is proposed to cope with vertical, pitch and roll motions of the car body and trucks. The governing equations of the railway vehicle suspension systems integrated with MR dampers are developed. To illustrate the feasibility and effectiveness of the controlled MR dampers on railway vehicle suspension systems, the LQG control law using the acceleration feedback is adopted as the system controller, in which the state variables are estimated from the measurable accelerations with the Kalman estimator. In order to make the MR dampers track the optimal damping forces, a damper controller to command the voltage to the current drivers for the MR dampers is proposed. The acceleration responses of the car body of the train vehicle with semiactive secondary suspension system integrated with MR dampers are evaluated under random and periodical track irregularities. This semiactive controlled system is also compared to the conventional passive suspension system using viscous dampers without MR dampers, and the secondary suspension system integrated with MR dampers in passive on and passive off modes. The simulation results show that the vibration control of the train suspension system with semiactive controlled MR dampers is feasible and effective.

Vibration Control of a Landing Gear System Featuring Electrorheological/Magnetorheological Fluids

Abstract: The feasibility and effectiveness of electrorheological (ER) and magnetorheological (MR) fluid-based landing gear systems on attenuating dynamic load and vibration due to the landing impact are demonstrated. First, the theoretical model for ER/MR shock struts, which are the main components of the landing gear system,is developed based on experimental data. The analysis of a telescopic-type landing gear system using the ER/MR shock struts is theoretically constructed, and its governing equation is derived. A sliding mode controller, designed to be robust against parameter variations and external disturbances, is formulated, and controlled performance of the simulated ER/MR landing gear system is theoretically evaluated during touchdown of the aircraft.

Semi-active control of automotive suspension systems with magneto-rheological dampers

Abstract: This paper is aimed to develop semi-active control for automotive suspension systems with magneto-rheological (MR) fluid dampers. A two degree-of-freedom quarter car model is considered. A mathematical model of MR fluid damper is adopted. In this study, there are two nested controllers including system controller and damper controller. For the system controller, a model-reference sliding mode controller is developed for considering loading uncertainty to result in a robust control system. In order to choose a good reference model, the single-degree-of-freedom skyhook system is analysed. For the damper controller, the continuous-state control is used to track the actual damping force to the desired damping force. The transmissibilities of the MR suspension system are investigated. The performances of the MR suspension systems are evaluated by computer simulation with bump and random excitations. The effectiveness of the MR suspension system is also demonstrated via hardware-in-the-loop simulation (HILS) with sinusoidal excitation.

Modeling of a Magnetorheological Actuator Including Magnetic Hysteresis

Abstract: Magnetorheological (MR) actuators provide controlled torque through control of an applied magnetic field. Therefore knowledge of the relationship between the applied current and output torque is required. This paper presents a new nonlinear modeling of MR actuators considering magnetic hysteresis to determine the torque-current nonlinear relationship. Equations for transmitted torque are derived according to mechanical shear configurations of the MR actuator. Hodgdon's hysteresis model is used to capture the characteristics of hysteresis nonlinearity in the MR actuators. An MR actuator test setup has been constructed using a commercial MR brake to evaluate the proposed model. The measured torque shows hysteresis effects as the current increases and decreases. Using Hodgdon's hysteresis model of the magnetic circuit and Bingham model of the MR fluid, a novel nonlinear model of the MR actuator is obtained as a torque estimator for practical torque control purpose. The validity of the theoretical results is ...

Rheological study of the stabilization of magnetizable colloidal suspensions by addition of silica nanoparticles

Abstract: An experimental investigation is described on the stability of magnetorheological fluids (MRFs) consisting of iron suspensions in silicone oil with a thixotropic agent (silica nanoparticles) as stabilizer. The rheological properties were investigated using a commercial rheometer with a parallel-plate measuring cell. Several kinds of experiments were performed in steady-state, oscillatory, and transient regimes. The effects of the volume fraction of magnetic particles, the concentration of silica, magnetic flux density, B, and waiting time after preshear on the rheology of the MRFs were considered. Steady-state measurements demonstrated that our systems only display plastic behavior, for which a yield stress, σy, is appreciable, for the highest iron concentrations and/or magnetic fields. The yield stress was found to be independent of the magnetic flux density when the concentration of silica particles was large enough (> ∼20 g/L). This is a manifestation of the entrapment of iron particles in the silica gel. The adhesion of silica on iron particles by acid-base (proton donation) reactions between both colloids in apolar media is also investigated as another mechanism that hinders the aggregation among iron particles under the external field action. For the same reasons, σy ceased to scale as B2, or to increase with iron volume fraction, for such a threshold silica concentration. Oscillometric determinations were performed at a frequency of 1 Hz, and the complex viscosity was found to increase with B due to structure formation as a result of magnetic particle–particle interactions. In agreement with steady-state results, if the concentration of silica is sufficiently large, the complex viscosity reaches high values, but independent of magnetic flux density. Creep-recovery experiments are particularly sensitive to MRF stability, because the interplay between iron and silica concentrations, magnetic flux density, and waiting time after preshear, led to a broad range of behaviors, ranging from liquid-like to almost elastic solid.An experimental investigation is described on the stability of magnetorheological fluids (MRFs) consisting of iron suspensions in silicone oil with a thixotropic agent (silica nanoparticles) as stabilizer. The rheological properties were investigated using a commercial rheometer with a parallel-plate measuring cell. Several kinds of experiments were performed in steady-state, oscillatory, and transient regimes. The effects of the volume fraction of magnetic particles, the concentration of silica, magnetic flux density, B, and waiting time after preshear on the rheology of the MRFs were considered. Steady-state measurements demonstrated that our systems only display plastic behavior, for which a yield stress, σy, is appreciable, for the highest iron concentrations and/or magnetic fields. The yield stress was found to be independent of the magnetic flux density when the concentration of silica particles was large enough (> ∼20 g/L). This is a manifestation of the entrapment of iron particles in the silica g...

Chain model of a magnetorheological suspension in a rotating field

Abstract: We develop an athermal chain model for magnetorheological suspensions in rotating magnetic fields This model is based on a balance of hydrodynamic and magnetostatic forces and focuses on the mechanical stability of chains Using a linear approximation of the chain shape, we compute the orientation and size of a critical chain in a rotating magnetic field as a function of the Mason number Mn, which is the ratio of dipolar to hydrodynamic forces between two particles in contact The critical chain length is found to scale with the inverse square root of Mn, and its orientation relative to the instantaneous field is independent of Mn The actual nonlinear shape of a chain in a rotating field is then computed self-consistently Finally, the effect of local fields on the dipolar interaction force is considered, leading to predictions for the chain shape and orientation that depend rather strongly on the magnetic permeability of the particles A principal finding is the possibility of brittle or ductile chain fracture, depending on the permeability of the particles Single-chain simulations confirm this prediction, as do experimental measurements

Magnetorheological Damper System

Abstract: A magnetorheological damper system comprising a reservoir in communication with a damper. The damper comprises a damper cylinder defining a damper chamber, wherein the damper chamber contains a magnetorheological fluid and a movable damper piston. The damper piston comprises at least two coil windings on the outer surface of the damper piston, wherein the damper piston is capable of generating a magnetic field between the damper piston and a wall of the damper cylinder. The reservoir comprises a reservoir cylinder defining a passageway, wherein the reservoir includes a magnetorheological electromagnet capable of generating a magnetic field between the magnetorheological piston and a wall of the passageway. The combination of the an MR reservoir and MR damper leads to a damping system capable of damping a wide range of extreme forces.

Finite Element Analysis and Simulation Evaluation of a Magnetorheological Valve

Abstract: This paper presents an optimised design of a high-efficiency magnetorheological (MR) valve using finite element analysis. The MR valve is composed of a core, a wound coil, and a cylinder-shaped flux return. The core and flux return form the annulus through which the MR fluid flows. The effects of magnetic field formation mechanism and MR effect formation mechanism on the MR valve performance are investigated. Analytical results of the magnetic flux density in the valve indicate that the saturation in the magnetic flux may be in the core, the flux return, or the valve length. To prevent the saturation as well as to minimise the valve weight, the dimensions of the valve are optimally determined using finite element analysis. In addition, this analysis is coupled with the typical Bingham plastic analysis to predict the MR valve performance.

Nonlinear viscoelastic properties of MR fluids under large-amplitude-oscillatory-shear

Abstract: Nonlinear viscoelastic properties of the MR fluid, MRF-132LD, under large-amplitude oscillatory shear were investigated. This was accomplished by carrying out the experiments under the amplitude sweep mode and the frequency sweep mode, using a rheometer with parallel-plate geometry. Investigations under the influence of various magnetic field strength and temperatures were also conducted. MR fluids behave as nonlinear viscoelastic or viscoplastic materials when they are subjected to large-amplitude shear, where the storage modulus decreases rapidly with increasing strain amplitude. Hence, MR fluid behaviour ranges from predominantly elastic at small strain amplitudes to viscous at high strain amplitudes. Large-amplitude oscillatory shear measurements with frequency sweep mode reveal that the storage modulus is independent of oscillation frequency and approaches plateau values at low frequencies. With increasing frequency, the storage modulus shows a decreasing trend before increasing again. This trend may be explained by micro-structural variation. In addition, the storage modulus increases gradually with increasing field strength but it shows a slightly decreasing trend with temperature.

Experimental analysis of magnetorheological dampers for structural control

Abstract: The possibility of reducing structural response under strong external excitations such as earthquakes and wind storms via control systems is attracting the interest of a large number of researchers. In the field of civil structures, control systems based on semi-active devices seem to be close to feasible implementation. Semi-active devices are typically passive elements capable of self-adjusting their own mechanical properties according to the instantaneous response of the hosting structure and, therefore, they can be considered as smart devices. Even though dampers based on magnetorheological fluids are considered very effective in practical implementations, the literature examining their properties from the structural control point of view is still quite limited. This paper aims to show the potential of such devices and to describe their properties from this special perspective. These properties include manufacturing issues, powering, range of variability of the mechanical parameters, their dependence on the feed current and overall response time.

Magnetorheological fluid compositions and prosthetic knees utilizing same

Abstract: The present invention relates in one embodiment to magnetorheological fluids utilized in prosthetic joints in general and, in particular, to magnetorheological fluids utilized in controllable braking systems for prosthetic knee joints. Preferred magnetorheological fluids of the present invention comprises polarizable iron particles, a carrier fluid, and optionally an additive. Preferred additives include, but are not limited to functionalized carrier fluids as well as derivatized fluoropolymers. Preferred carrier fluids include, but are not limited, to perfluorinated polyethers.

Active hydrostatic bearing with magnetorheological fluid

Abstract: Special bearings based on magnetic fluids are well known in literature. These bearings use the magnetic pressure inside a ferrofluid that is exposed to a magnetic field. The biggest disadvantage of this principle is the small load that can be supported. In one reference [B. M. Berkovsky, V. F. Medvedev, and M. S. Krakov, Magnetic Fluids, Engineering Applications (Oxford University Press, Oxford, 1993)], the specific load is specified as 1 N cm−2. To support heavy loads very large support areas are needed. We will present a completely different concept for bearings with magnetorheological fluids. Hydrostatic bearings get their load bearing capacity from the hydrostatic pressure produced by an external pump and should not be confused with hydrodynamic bearings presented in another reference [R. Patzwald, M. S. thesis, Institute fur Werkzeugmaschinen und Fabrikbetrieb, Technische Universitat, Berlin (2001)]. The main disadvantage of hydrostatic bearings is that the bearing gap varies with the payload. Conven...

Vibration control of a passenger vehicle featuring magnetorheological engine mounts

Abstract: This paper proposes a semiactive controllable magnetorheological (MR) engine mount for vibration control of a passenger vehicle. A mixed-mode type MR engine mount is devised and incorporated with a full-vehicle model. The governing equations of the model are derived by considering engine excitation force, and a semi-active skyhook controller is designed to attenuate unwanted vibrations. The controller is then implemented through a hardware-in-the-loop simulation (HILS), and control responses such as acceleration at the driver's position are evaluated in time and frequency domains.

Modeling of MR damper with hysteresis for adaptive vibration control

Abstract: This paper is concerned with structural vibration control using a semi-active magnetorheological (MR) damper. A simple mathematical model of MR damper is proposed to express its hysteresis effect of dynamic friction characteristics. The model can predict the damping force based on the inputs of velocity, internal state and input voltage to the MR damper. The model can also he used to obtain an inverse dynamic model to analytically determine the necessary input voltage so that the desirable damper force could be added to the structure in an adaptive manner. In conjunction with the LQG control which gives the desired target damping force, the total adaptive algorithm can work effectively even if the MR damper has uncertainty and changeability, which is validated in numerical simulations.

Seismic Control of Civil Structures Utilizing Semi–Active MR Braces

Abstract: This paper presents the feasibility and effectiveness of magnetorheological (MR) braces in earthquake hazard mitigation. In doing so, a nondimensional variable, β, which is the ratio of the yield force of the MR damper to forcing input (the product of a characteristic mass of the building and the seismic acceleration) is used to design the MR damper preventing the locked damper motion that may worsen seismic response of the building. From this theoretical analysis, the activation gap of the damper as an important design parameter to prevent the locked damper motion is chosen. Based on this analysis, the MR damper is fabricated by modifying the commercial MR damper of Lord Corporation, SD-1000-1. Then, a three-story building with MR braces is constructed and its dynamic equation is theoretically derived. In order to investigate semi-active control methods to MR braces, three different control algorithms are formulated and evaluated both numerically and experimentally. The results show that control of the building with semi-actively controlled MR braces is very effective.

Fluid damper having continuously variable damping response

Abstract: An improved damping apparatus that utilizes a fluid having a viscosity that may be varied by the application of an electromagnetic field, such as a magnetorheological fluid or an electrorheological fluid, to provide the damping response. The damping apparatus includes a linear to rotary conversion mechanism which comprises a translatable member that is adapted for linear translation in a forward and a reverse direction and a rotatable member comprising a rotatable shaft that is rotatably coupled to the translatable member; wherein translation of the translatable member in one of the forward or the reverse directions produces a forward or a reverse rotation of the rotatable member and shaft, respectively. The damping apparatus also includes a damping mechanism which comprises a hub that is fixed to the shaft, a means for generating a variable electromagnetic field in response to an applied electrical signal that may be continuously varied in response to an input signal that is representative of a desired damping force and a fluid having a viscosity that may be continuously varied by application of the electromagnetic field that is in touching contact with the hub. Application of the variable electromagnetic field to the fluid produces changes in the viscosity of the fluid that in turn provides variable resistance to rotation of the hub and resistance to translation of the translatable member, thereby providing a damping apparatus with a continuously variable damping response.

Dynamic behavior of a magnetorheological elastomer under uniaxial deformation: I. Experiment

Abstract: This paper presents an experiment testing the accelerations of a system composed of a magnetorheological elastomer (MRE) and a cuprous mass under displacement excitation. The goal of this paper is to explain the experiment and to present the experimental results (the hysteresis loops). The method of extracting field-dependent material properties of the MRE from the results and further analysis will be presented in a subsequent paper. The experimental results reveal that the mechanical behavior is nonlinear and the field-dependent behavior of the MRE is associated with the applied frequency. (The frequency domain is divided into three ranges according to the field-dependent characteristics of the MRE.) In the low frequency range, the mechanical properties of the MRE change slightly with the applied magnetic field; in the moderate frequency range, the field-dependent properties appear and they are highly nonlinear; in the high frequency range, the field-dependent properties deviate from those of the moderate frequency range, which causes the circled area of the hysteresis loops in the two measured acceleration domains to decrease with the applied magnetic field. To explain the characteristics in the low frequency range, ABAQUS code is used to calculate the zero-field property of the MRE and a point-dipole model is employed to model the field-dependent property approximately.

Analysis of parametric models of MR linear damper

Abstract: This work deals with the analysis of parametric models of a MR linear damper, which suit various rheological structures of the MR fluid. The MR fluid structure and properties, damper description and parametric damper models which are connected in various ways with the actual behaviour of the MR fluid are presented. Based on computer simulations, the effectiveness of the models under predicted MR linear damper behaviour is shown. The values of the parametric models used in the simulations were determined in an identification experiment.

A magnetorheological semi-active isolator to reduce noise and vibration transmissibility in automobiles

Abstract: The demand for low cost, quiet operation, and increased operator comfort in automobiles and other applications is requiring that new techniques be developed for noise and vibration isolation. One a...

Modelling the hysteretic characteristics of a magnetorheological fluid damper

Abstract: A generalized model is proposed to characterize the biviscous hysteretic force characteristics of a magnetorheological (MR) fluid damper using symmetric and asymmetric sigmoid functions on the basis of a fundamental force generation mechanism, observed qualitative trends and measured data under a wide range of control and excitation conditions. Extensive laboratory measurements were performed to characterize the hysteretic force properties of an MR damper under a wide range of magnitudes of control current and excitation conditions (frequency and stroke). The global model is realized upon formulation and integration of component functions describing the preyield hysteresis, saturated hysteresis loop, linear rise and current-induced rise. The validity of the proposed model is demonstrated by comparing the simulation results with measured data in terms of hysteretic forcedisplacement and force-velocity characteristics under a wide range of test conditions. The results revealed reasonably good agreem...