Showing papers on "Magnetorheological fluid published in 2002"

“Smart” Base Isolation Strategies Employing Magnetorheological Dampers

Abstract: One of the most successful means of protecting structures against severe seismic events is base isolation. However, optimal design of base isolation systems depends on the magnitude of the design level earthquake that is considered. The features of an isolation system designed for an El Centro-type earthquake typically will not be optimal for a Northridge-type earthquake and vice versa. To be effective during a wide range of seismic events, an isolation system must be adaptable. To demonstrate the efficacy of recently proposed ''smart'' base isolation paradigms, this paper presents the results of an experimental study of a particular adaptable, or smart, base isolation system that employs magnetorheological ~MR! dampers. The experimental structure, constructed and tested at the Structural Dynamics and Control/Earthquake Engineering Laboratory at the Univ. of Notre Dame, is a base-isolated two-degree-of-freedom building model subjected to simulated ground motion. A sponge-type MR damper is installed between the base and the ground to provide controllable damping for the system. The effectiveness of the proposed smart base isolation system is demonstrated for both far-field and near-field earthquake excitations.

Magnetostrictive phenomena in magnetorheological elastomers

Abstract: A host of fascinating and useful magnetic phenomena are found in composites containing magnetizable particles in viscoelastic solids. Embedding magnetically soft iron particles in natural rubber produces a class of magnetostrictive composites sometimes termed magnetorheological (MR) elastomers. We have previously shown that these materials can exhibit viscoelastic moduli that increase substantially in an applied magnetic field. In this paper, we incorporate MR elastomers in a simple resonant structure called a tuned absorber to measure the complex dynamic shear moduli of these materials at high frequencies. We find that the fluid-induced modulus increase in MR elastomers is substantial even at kilohertz mechanical frequencies. As in previous measurements at low frequencies, the moduli are generally found to decrease with strain amplitude. We also report preliminary measurements of the relatively large elongation of these materials in applied magnetic fields.

Rheological properties of magnetorheological fluids

Abstract: The effects of dispersed phase saturation magnetization and applied magnetic fields on the rheological properties of magnetorheological (MR) fluids are described. MR fluids based on two different grades of carbonyl iron powder with different average particle size, 7–9 μm (grade A) and 2 μm (grade B), were prepared. Vibrating sample magnetometer measurements showed that the saturation magnetization values were 2.03 and 1.89 T for grades A and B, respectively. Rheological measurements were conducted for 33 and 40 vol% grade A and grade B based MR fluids with a specially built double Couette strain rate controlled rheometer at flux densities ranging from 0.2 to ~0.8 T. The yield stresses of 33 and 40 vol% grade A were 100 ± 3 and 124 ± 3 kPa, respectively at 0.8 ± 0.1 T. The yield stress values of MR fluids based on finer particles (grade B) were consistently smaller. For example, the yield stresses for 33 and 40 vol% grade B based MR fluid were 80 ± 8 and 102 ± 2 kPa, respectively at 0.8 ± 0.1 T. The yield stresses at the flux density approaching magnetic saturation in particles (B ~ 0.8T) were found to increase quadratically with the saturation magnetization (μ0Ms) of the dispersed magnetic phase. This is in good agreement with the analytical models of uniformly saturated particle chains developed by Ginder and co-workers. The results presented here show that the decrease in yield stress for finer particle based MR fluids is due to the relatively smaller magnetization of the finer particles.

What Makes a Good MR Fluid

Abstract: Experience in manufacturing magnetorheological (MR) fluids for commercial application has shown that some of the greatest barriers to commercial success are not factors or conditions normally considered in the laboratory. The present paper looks at conditions found in MR fluid devices operating in real-world applications where shear rates may exceed 10 5 s -1 and devices are called upon to operate for very long periods of time. The problem of In-Use-Thickening wherein a MR fluid subjected to long-term use progressively thickens until it eventually becomes an unworkable paste is presented. The search for a solution to this heretofore unrecognized problem delayed commercial introduction of the Lord truck seat damper system for several years. Today, good fluids are able to operate for long periods with minimum in-use-thickening.

Vibration Control of a Suspension System via a Magnetorheological Fluid Damper

Abstract: Semi-active control systems are becoming more popular because they offer both the reliability of passive systems and the versatility of active control without imposing heavy power demands. It has been found that magneto-rheological (MR) fluids can be designed to be very effective vibration control actuators. The MR fluid damper is a semi-active control device that uses MR fluids to produce a controllable damping force. The objective of this paper is to study a single-degree-of-freedom suspension system with an MR fluid damper for the purpose of vibration control. A mathematical model for the MR fluid damper is adopted. The model is compared with experimental results for a prototype damper through finding suitable model parameters. In this study, a sliding mode controller is developed by considering loading uncertainty to result in a robust control system. Two kinds of excitations are inputted in order to investigate the performance of the suspension system. The vibration responses are evaluated in both ti...

Magnetorheology: Fluids, Structures and Rheology

Abstract: Magnetorheological suspensions are complex fluids which show a transition from a liquid behavior to a solid one upon application of a magnetic field. This transition is due to the the attractive dipolar forces between the particles which have been magnetized by the applied field. The formation of a network of particles or aggregates throughout the suspension is the basic phenomena which is responsible for the strength of the solid phase. In this paper we shall give an overview on the fluids and their properties and we shall especially emphasize the interplay between magnetic forces which are responsible for the gelling of the suspension and on the other hand of hydrodynamic and thermal forces which contribute to break this gel and allow the suspension to flow. The combination of these three forces gives rise to a very rich rheology whose many aspects are still not understood.

Neural network emulation of inverse dynamics for a magnetorheological damper

Abstract: The dynamic behavior of a magnetorheological (MR) damper is well portrayed using a Bouc–Wen hysteresis model. This model estimates damper forces based on the inputs of displacement, velocity, and voltage. In some control applications, it is necessary to command the damper so that it produces desirable control forces calculated based on some optimal control algorithms. In such cases, it is beneficial to develop an inverse dynamic model that estimates the required voltage to be input to the damper so that a desirable damper force can be produced. In this study, we explore such a possibility via the neural network (NN) technique. Recurrent NN models will be constructed to emulate the inverse dynamics of the MR damper. To illustrate the use of these NN models, two control applications will be studied: one is the optimal prediction control of a single-degree-of-freedom system and the other is the linear quadratic regulator control of a multiple-degree-of-freedom system. Numerical results indicate that, using t...

H8 Control Performance of a Full-Vehicle Suspension Featuring Magnetorheological Dampers

Abstract: Summary This paper presents an investigation of the feedback control performance of a full-vehicle suspension system featuring magnetorheological (MR) dampers. A cylindrical MR damper is designed and manufactured by incorporating a Bingham model of aMR fluid which is commercially available. After evaluating the field-dependent damping characteristics of the MR damper, a full-vehicle suspension system installed with 4 independent MR dampers is constructed and its governing equations of motion which include vertical, pitch and roll motions are derived. A H 8 controller which has inherent robustness against system uncertainties is formulated by treating the sprung mass of the vehicle as uncertain parameter. This is accomplished by adopting the loop shaping design procedure. For the demonstration of a practical feasibility, control performance characteristics for vibration suppression of the proposed MR suspension system are evaluated under various road conditions through the hardware-in-the-loop simulation (...

Design of a High-Efficiency Magnetorheological Valve:

Abstract: A high efficiency design was explored for meso-scale magnetorheological (MR) valves (< 25 mm OD with an annular gap < I mm). The objective of this paper is to miniaturize the MR valve while maintaining the maximum performance of the MR effect in the valve. The main design issues in the MR valve involve the magnetic circuit and nonlinear fluid mechanics. The performance of the MR valve is limited by saturation phenomenon in the magnetic circuit and by the finite yield stress of the MR fluid. When field is applied to the magnetic circuit in the MR valve, a semisolid plug (as a result of particle chain formation) forms perpendicular to the flow direction through the valve, and a finite yield stress is developed as a function of field. The resulting plug thickness is used to control flow rate through, and pressure drop across, the MR valve. The nondimensional plug thickness is evaluated as a basis for evaluating valve efficiency. Design parameters of the MR valve are studied and an optimal performance was designed using steel (Permalloy) material in the magnetic circuit. A maximum magnetic flux density at the gap was achieved in the optimized valve design based on a constraint on the outer diameter limitation. Valve performance was verified with simulation. A flow mode bypass damper system was fabricated and was used to experimentally validate valve performance.

The Preparation of Magnetic Fluids

Abstract: In any discussion of fluids, which have magnetic properties, it is convenient to divide them into the following categories, (A) ferrofluids; (B) magnetorheological fluids; (C) dispersions of micron-sized particles of a non-magnetic material containing magnetic nano-sized particles, and (D) fluids containing paramagnetic particles

Viscoelastic Properties of Magnetorheological Elastomers in the Regime of Dynamic Deformation

Abstract: Using the original procedure of a “clamped‐free” vibrating sandwich beam the dynamic characteristics (elastic modulus and loss factor) of a number of magnetorheological elastomers have been measured. The influence of such parameters as the type of carrying matrix, the size of ferromagnetic‐filler particles, and the intensity of action by the external magnetic field has been evaluated.

Harmonic analysis of a magnetorheological damper for vibration control

Abstract: Semi-active control systems are becoming more popular because they offer both the reliability of passive systems and the versatility of active control systems without imposing heavy power demands. In particular, it has been found that magnetorheological (MR) fluids can be designed to be very effective vibration control actuators, which use MR fluids to produce controllable damping force. The objective of this paper is to study a single-degree-of-freedom (SDOF) isolation system with an MR fluid damper under harmonic excitations. A mathematical model of the MR fluid damper with experimental verification is adopted. The motion characteristics of the SDOF system with the MR damper are studied and compared with those of the system with a conventional viscous damper. The energy dissipated and equivalent damping coefficient of the MR damper in terms of input voltage, displacement amplitude and frequency are investigated. The relative displacement with respect to the base excitation is also quantified and compared with that of the conventional viscous damper through updating the equivalent damping coefficient with changing driving frequency. In addition, the transmissibility of the MR damper system with semi-active control is also discussed. The results of this study are valuable for understanding the characteristics of the MR damper to provide effective damping for the purpose of vibration isolation or suppression.

Valve and position control using magnetorheological fluids

Abstract: Magnetorheological fluids, which solidify in response to a magnetic field, offer the ability to simplify many of the valves and control systems used downhole in the search for and production of oil and gas. They lessen the need for moving parts, provide solid-state valves, and can provide a differential movement of fluid through the valves by varying the strength of the magnetic field. Combinations of permanent and electro-magnets can improve safety by providing valves that fail, when power is lost, in either an open or closed position, depending on design. A number of examples are given.

Behavior of magnetorheological fluids utilizing nanopowder iron

Abstract: Iron nanopowders for use in magnetorheological (MR) fluids were synthesized using a Microwave Plasma Synthesis technique developed at Materials Modification Inc (Fairfax VA). Transmission electron microscopy and surface area analysis measured iron particle size at 15–25 nm. The nanopowders were mixed into hydraulic oil to create nano-scale MR fluid. A micro-scale fluid was created using 45 μm iron particles as well as a hybrid fluid using a 50/50 mix of micro- and nanoparticles. All three fluids had a solids loading of 60% (w/w or weight by weight fraction). The fluids were tested in a flow mode rheometer fabricated from a modified damper using a sinusoidal input dynamometer over a speed range of 12.7 to 177.8 mm/s (0.5 to 6 in/s) and an input current range of 0 to 2 A. The yield stress and plastic viscosity of the MR fluid were characterized using a Bingham plastic model.

Development and characterization of magnetorheological polymer gels

Abstract: Magnetorheological materials have been used in many applications in recent years. To develop new materials, polyurethane and silicone polymer gels were investigated. Rheology is qualitatively controlled for each system by controlling the concentration of reactants and diluents. The resulting polymers have solid, gel, or liquid states, depending on the crosslinking and dilution. The gels were characterized through kinetic analysis. Differential scanning calorimetry (DSC) was used with analysis methods to find the kinetic properties for diluted and undiluted polyurethane systems. Heat of reaction, order of reaction, preexponential constant, and activation energy were obtained from the experimental DSC data.

Experimental investigation of creep and recovery behaviors of magnetorheological fluids

Abstract: Creep and recovery behaviors of a magnetorheological (MR) fluid under constant stress shear were investigated. This experiment was accomplished by using a rheometer with parallel-plate geometry. The applied constant stress ranges from a small value to a big one which approaches to the yield stress. The effects of magnetic field strength and the temperature on the creep behavior were addressed. The experimental results indicate that MR fluids behave as linear viscoelastic bodies at small stresses; with increasing constant stresses, nonlinear viscoelastic, viscoplastic, or purely plastic properties will dominate. Hence, MR fluid behavior ranges from predominantly elastic at small stresses to plastic at high stresses. Moreover, the creep and recovery behaviors are explained by a typically thick column structure.

A high-torque magneto-rheological fluid clutch

Abstract: This study focuses on the design and characterization of a radial double-plate magneto-rheological fluid (MRF) clutch. The clutch's torque output can be controlled by adjusting the applied magnetic field. Electromagnetic finite element analysis (FEA) is performed to design and optimize the clutch. The shear stress distribution in MRF between the plates is theoretically predicted using the magnetic flux density distribution evaluated from the FEA. The output torque of the clutch is derived by using the Bingham plastic constitutive model. The output torque values are recorded for different input velocities and applied magnetic fields, and they are compared with the theoretical results. It was demonstrated that the clutch is capable of producing high controllable torques.

An experimental study of a semiactive magneto-rheological fluid variable damper for vibration suppression of truss structures

Abstract: The purpose of this paper is to demonstrate that vibrations of a truss structure can be suppressed nicely by a magneto-rheological (MR) fluid variable damper for semiactive vibration suppression. A variable MR fluid damper was designed and fabricated for this study. The principal characteristics of an MR damper were measured in dynamic tests, and a mathematical model of the damper was proposed. To investigate if the variable damper effectively suppresses the vibration of actual truss structures, semiactive vibration suppression experiments were performed using a cantilevered ten-bay truss beam. The experimental result has shown that the vibration was suppressed nicely by the variable MR damper, and that was compared with that of an electro-rheological (ER) damper investigated in previous research. The MR damper showed a higher performance than that of the ER damper.

Performance Analysis of ER/MR Impact Damper Systems Using Herschel-Bulkley Model

Abstract: Performance analysis for electrorheological (ER) and magnetorheological (MR) fluid-based impact damper systems is evaluated on the basis of the Herschel-Bulkley shear model. Generally, ER-MR dampers have been analyzed based on the simple Bingham-plastic shear model. However, the Bingham-plastic shear model cannot well describe the behavior of the damper under conditions of high velocity and high field input. Therefore, in this study, the Herschel-Bulkley shear model, in which the constant postyield plastic viscosity in the Bingham model is replaced with a power law model dependent on shear rate, is used to assess the performance of ER-MR impact damper systems. In doing so, an ER-MR impact damper system is proposed and its governing equation of motion is derived on the basis of the Herschel-Bulkley shear model. Then, computer simulation is done to analytically evaluate characteristics of the ER-MR impact damper system under impact loads for constant current input and embedding end-stop on-off control algorithm. As an important parameter in the Herschel-Bulkley shear model, effects of the flow behavior index, n, that is the degree of shear thinning or shear thickening, on the performance of the impact damper system are shown.

Comparative Analysis of the Time Response of Electrorheological and Magnetorheological Dampers Using Nondimensional Parameters

Abstract: Electrorheological (ER) and magnetorheological (MR) fluids show similar field-dependent rheological characteristics from a bulk fluid perspective. However, the implementation of ER and MR fluids in devices may require different strategies because of the inherent properties of ER and MR fluids such as density, viscosity and the magnitude of the yield stress. Therefore, in this study, we explore the characteristics of ER and MR fluid-based systems on the basis of dynamic range and time response in order to comprehensively understand each system. In doing so, a nondimensional analysis, based on parallel plate geometry, is used to characterize the field-dependent properties of ER and MR fluid-based dampers. Experimental tests are conducted for ER and MR dampers in order to validate our analysis.

High-torque magnetorheological fluid clutch

Abstract: This study focuses on the design and characterization of a radial double-plate magneto-rheological fluid (MRF) clutch. The clutch's torque output can be controlled by adjusting the applied magnetic field. Electromagnetic finite element analysis (FEA) is performed to design and optimize the clutch. The shear stress distribution in MRF between the plates is theoretically predicted using the magnetic flux density distribution evaluated from the FEA. The output torque of the clutch is derived by using the Bingham plastic constitutive model. The output torque values are recorded for different input velocities and applied magnetic fields, and they are compared with the theoretical results. It was demonstrated that the clutch is capable of producing high controllable torques.

Normal force study in concentrated carbonyl iron magnetorheological suspensions

Abstract: The yield behavior of concentrated carbonyl iron magnetorheological fluids (MRF) is investigated measuring the normal force during shear flow in a plate–plate controlled-stress rheometer. For high enough external magnetic fields, a positive normal force is obtained below the yield point. This result is not explained using affine deformation chain models. However, the assumption of gapspanning particle chains and spheroidal aggregates of spheres predicts not only a positive normal force but also a maximum if we plot the normal force as a function of the strain, a result also found experimentally. The field dependence of the normal force suggests the existence of a threshold field, likely associated to the formation of gapspanning structures in the MRF. Another possible explanation for the maximum in the normal force lies on the phase transition from homogeneous to layered structures with cylindrical symmetry in the suspension. Steady-state and oscillometry studies show that the maximum in the normal force ...