Showing papers on "Magnetorheological fluid published in 2000"

Semiactive Control Strategies for MR Dampers: Comparative Study

Abstract: This paper presents the results of a study to evaluate the performance of a number of recently proposed semiactive control algorithms for use with multiple magnetorheological (MR) dampers. Various control algorithms used in recent semiactive control studies are considered including the Lyapunov controller, decentralized bang-bang controller, modulated homogeneous friction algorithm, and a clipped optimal controller. Each algorithm is formulated for use with the MR damper. Additionally, each algorithm uses measurements of the absolute acceleration and device displacements for determining the control action to ensure that the algorithms could be implemented on a physical structure. The performance of the algorithms is compared through a numerical example, and the advantages of each algorithm are discussed. The numerical example considers a six-story structure controlled with MR dampers on the lower two floors. In simulation, an El Centro earthquake is used to excite the system, and the reduction in the drif...

Vibration Control of a MR Seat Damper for Commercial Vehicles

Abstract: This paper presents vibration control of a semi-active seat suspension with a magneto-rheological (MR) fluid damper, which is applicable to commercial vehicles such as large size of trucks. A cylindrical MR seat damper is designed on the basis of the Bingham model of the MR fluid. After manufacturing the seat damper, field-dependent damping force characteristics are experimentally evaluated. A semi-active seat suspension system installed with the seat damper is then constructed and its governing equation of motion is derived. A skyhook controller to reduce vibration level at the driver’s seat is formulated and realized in a closed-loop control fashion. The control responses, such as acceleration transmissibility, are investigated in both frequency and time domains. In addition, a full-vehicle model featuring the proposed semi-active seat suspension is established and its vibration control performances are evaluated via the hardware-in-the-loop simulation (HILS).

Controllable-stiffness components based on magnetorheological elastomers

Abstract: So-called magnetorheological (MR) elastomers, comprising rubbery polymers loaded with magnetizable particles that are aligned in a magnetic field, possess dynamic stiffness and damping that can subsequently be controlled by applied fields. Tunable automotive bushings and mounts incorporating these materials and an embedded magnetic field source have been constructed. In this article, the response of these components to dynamic mechanical loading is described. They behave essentially as elastomeric springs with stiffness and damping that is increased by tens of percent with an applied electrical current. Their time of response to a change in current is less than ten milliseconds. In addition to a tunable spring or force generator, these components may also serve as deflection sensors.

Control and Response Characteristics of a Magneto-Rheological Fluid Damper for Passenger Vehicles:

Abstract: This paper presents control characteristics of a full-car suspension featuring a semi-active magnetorheological (MR) fluid damper A cylindrical MR damper is devised and its field-dependent damping force is evaluated with respect to the piston velocity After verifying that the damping force can be continuously controlled by the intensity of the magnetic field, the MR damper is applied to a full-car model The governing equations of motions, which include vertical, pitch, and roll motions are derived and incorporated with the skyhook controller Control characteristics of the full-car suspension installed with the proposed MR damper are evaluated through hardware-in-the-loop simulation (HILS), and presented in both time and frequency domains

Structure-enhanced yield stress of magnetorheological fluids

Abstract: The yield stress of magnetorheological (MR) fluids depends on the induced solid structure. Since thick columns have a yield stress much higher than a single-chain structure, we improve the yield stress of MR fluids by changing the fluid microstructure. Immediately after a magnetic field is applied, we compress the MR fluid along the field direction. Scanning electron microscopy images show that particle chains are pushed together to form thick columns. The shear force measured after the compression shows that the structure-enhanced static yield stress can reach as high as 800 kPa under a moderate magnetic field, while the same MR fluid has a yield stress of 80 kPa without compression. This improved yield stress increases with the magnetic field and compression pressure and has an upper limit well above 800 kPa. The method may also be useful for electrorheological fluids.

Testing and steady state modeling of a linear MR damper under sinusoidal loading

Abstract: A linear magnetorheological (MR) damper, supplied by Lord Corporation, was tested and modeled. Under dynamic conditions, the effects of displacement amplitude, frequency, and magnetic fields on the mechanical properties of MR damper, such as damping force, equivalent-damping capability, were experimentally studied with an INSTRON test machine. A viscoelastic-plastic model is proposed to model the MR behavior. It is shown that the damper response can be satisfactorily predicted with this model.

Fuzzy modeling of a magnetorheological damper using ANFIS

Abstract: The magnetorheological (MR) damper is a semi-active control device that has received much attention by the vibration control community. Of primary interest is its fast response to a variable control signal as well as its low power requirements. The highly nonlinear dynamic nature of this device, however, has proven to be a significant challenge for researchers who wish to characterize its behavior. Research by others has shown that a system of nonlinear differential equations can successfully be used to describe the behavior of a MR damper. The paper presents an alternative for modeling a damper in the form of a Takagi-Sugeno-Kang fuzzy inference system. An ANFIS (adaptive neuro-fuzzy inference system) is used to determine 27 nonlinear premise parameters and 96 linear consequent parameters that describe the behavior of the SD-1000 model MR damper. Data used for training and checking of the model is generated from numerical simulation of nonlinear differential equations. The resulting fuzzy inference system is shown to satisfactorily represent behavior of the magnetorheological damper while greatly reducing computational requirements. Use of the neuro-fuzzy model increases the feasibility of real time simulation.

Micromechanics of magnetorheological suspensions.

Abstract: We apply optical trapping techniques in a magnetorheological (MR) suspension, allowing us to directly measure the mechanical properties of single dipolar chains, such as the rupturing tensions and strains under tensile and lateral deformations. Our results are in excellent agreement with calculations of the rupturing tensions using a self-consistent point dipole model of the particle interaction that accounts for induction and multibody effects along the chain. Additionally, we observe the annealing of chain defects under an applied stress, such as the inclusion of neighboring particles into the chain. The micromechanical properties of single chains offers important insight into magnetorheology and electrorheology, especially the yield stress behavior.

Seismic response control of frame structures using magnetorheological/electrorheological dampers

Abstract: Semi-active control of buildings and structures for earthquake hazard mitigation represents a relatively new research area. Two optimal displacement control strategies for semi-active control of seismic response of frame structures using magnetorheological (MR) dampers or electrorheological (ER) dampers are proposed in this study. The efficacy of these displacement control strategies is compared with the optimal force control strategy. The stiffness of brace system supporting the smart damper is also taken into consideration. An extensive parameter study is carried out to find the optimal parameters of MR or ER fluids, by which the maximum reduction of seismic response may be achieved, and to assess the effects of earthquake intensity and brace stiffness on damper performance. The work on example buildings showed that the installation of the smart dampers with proper parameters and proper control strategy could significantly reduce seismic responses of structures, and the performance of the smart damper is better than that of the common brace or the passive devices. The optimal parameters of the damper and the proper control strategy could be identified through a parameter study. Copyright © 2000 John Wiley & Sons, Ltd.

Structure and dynamics of magnetorheological fluids in rotating magnetic fields

Abstract: We report on the orientation dynamics and aggregation processes of magnetorheological fluids subject to rotating magnetic fields using the technique of scattering dichroism. In the presence of stationary fields we find that the mean length of the field-induced aggregates reaches a saturation value due to finite-size effects. When a rotating field is imposed, we see the chains rotate with the magnetic field frequency (synchronous regime) but with a retarded phase angle for all the rotational frequencies applied. However, two different behaviors are found below or above a critical frequency ${f}_{c}.$ Within the first regime (low frequency values) the size of the aggregates remains almost constant, while at high frequencies this size becomes shorter due to hydrodynamic drag. Experimental results have been reproduced by a simple model considering a torque balance on the chainlike aggregates.

Magnetorheology of magnetic holes compared to magnetic particles

Abstract: We compare the rheological behavior in a shear flow of two types of suspension of magnetic particles in the presence of a magnetic field. The first suspension is made of silica particles in a ferrofluid and the second one is made of carbonyl iron particles in silicone oil. The permeability curves of these two suspensions have been measured for different volume fractions as a function of the magnetic field in order to characterize the magnetic interactions. We show for both cases the existence of two different yield stresses: one associated with the solid friction of the particles on the plates of the rheometer and the second one with the rupture of the aggregates. This second yield stress presents a maximum with the volume fraction for the suspension of magnetic holes but grows faster than linearly with the volume fraction for the suspension of carbonyl iron. These features are explained by theoretical models based, respectively, on the deformation of aggregates of macroscopic size and on ruptures between particles at the particle scale. When plotted as a function of the Mason number, the curves for different fields well collapse on the same one but the slope of this master curve on a log–log plot is quite different from the one of the Bingham law, especially for the suspension of magnetic holes. For both suspensions the exponent depends on the volume fraction.

"Smart" Isolation for Seismic Control.

Abstract: Consideration of near-source, high velocity, long-period seismic pulses, as were recorded during the Northridge and Kobe earthquakes, has taught engineers and researchers that ground motions due to such earthquakes can be difficult to accommodate. This paper discusses a base isolation system using "smart" dampers, such as magnetorheological fluid dampers, that can adapt to, and protect against, seismic excitatiorn of different characteristics. A linear, two degree-of-freedom, lumped-mass model of a base-isolated budding is used as the testbed for this study. Linear viscous dampers are shown to have an optimal damping level for several design earthquakes to achieve minimum peak accelerations. A study of a family of controllers for the smart damper is used to find an "optimal" isolation system over the suite of ground motions considered. This "optimal" system further decreases the base drift compared to the "optimal" linear viscous damper without increasing the accelerations imparted into the superstructure. The "smart" damper is shown to be a most effective alternative for a broad class of earthquakes including near-source events.

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 systems without imposing heavy power demands. It has been found that magneto-rheological (MR) fluids can be designed to be very effective vibration control actuators. MR fluid damper is a semi-active control device that uses MR fluids to produce controllable damping force. The objective of this paper is to study a single-degree-of- freedom suspension system with a MR fluid damper for the purpose of vibration control. A mathematical model of 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 time and frequency domains. Compared to the passive system, the acceleration of the sprung mass is significantly reduced for the system with a controlled MR damper. Under random excitation, the ability of the MR fluid damper to reduce both peak response and root-mean-square response is also shown.

"Smart" Isolation for Seismic Control

Abstract: Consideration of near-source, high velocity, long-period seismic pulses, as were recorded during the Northridge and Kobe earthquakes, has taught engineers and researchers that ground motions due to such earthquakes can be difficult to accommodate. This paper discusses a base isolation system using "smart" dampers, such as magnetorheological fluid dampers, that can adapt to, and protect against, seismic excitatiorn of different characteristics. A linear, two degree-of-freedom, lumped-mass model of a base-isolated budding is used as the testbed for this study. Linear viscous dampers are shown to have an optimal damping level for several design earthquakes to achieve minimum peak accelerations. A study of a family of controllers for the smart damper is used to find an "optimal" isolation system over the suite of ground motions considered. This "optimal" system further decreases the base drift compared to the "optimal" linear viscous damper without increasing the accelerations imparted into the superstructure. The "smart" damper is shown to be a most effective alternative for a broad class of earthquakes including near-source events.

The influence of particle size on the magnetorheological properties of an inverse ferrofluid

Abstract: The dependence of magnetorheological properties on particle size is studied, using a model magnetorheological fluid consisting of nonmagnetic silica particles suspended in a ferrofluid. For small particles a strong increase of magnetorheological properties with particle size was found. At a certain particle size and field strength a crossover occurs to a regime where there is only a very limited size dependence. This can be understood in terms of the length of the chains in relation to the gap size of the geometry. Crossover occurs when the average chain length becomes comparable to the gap size. The remaining size dependence may be explained by polydispersity, variations in the morphology, variations in the sterically stabilizing layer of the particles and surface roughness of the geometry.

Vibration control of an MR seat damper for commercial vehicles

Abstract: This paper presents a semi-active seat suspension with a magneto-rheological (MR) fluid damper, which is applicable to commercial vehicles such as a large size of truck. A cylindrical MR seat damper is designed and manufactured by incorporating Bingham model of MR fluid. After evaluating field-dependent damping characteristics, the controllability of the damping force is experimentally demonstrated in time domain by implementing PID controller. A semi-active seat suspension system is then constructed and its governing equation of motion is derived. A skyhook control scheme is formulated in order to reduce vibration level at the driver's seat. The controlled responses such as acceleration transmissibility are evaluated in frequency domain. In addition, performance characteristics of a full-car model installed with the proposed MR seat suspension are evaluated via hardware-in-the-loop simulation (HILS).

Force feedback devices using fluid braking

Abstract: A haptic feedback device including a fluid viscosity-controlled brake that outputs high forces to the device user at low cost while maintaining inherent safety. An interface device includes a manipulandum physically contacted by the user. A sensor senses a position of the manipulandum and outputs a sensor signal. The interface device also includes a brake including a field-controlled fluid having a viscosity that can be controlled by controlling an electric current in a coil, where a resistive force or drag on the manipulandum is controlled by controlling the fluid's viscosity. The fluid can be an electrorheological fluid controlled by an electric field or a magnetorheological fluid controlled by a magnetic field. In one preferred embodiment, the resistive force is controlled by adjusting a degree of contact of the brake with the manipulandum based on the fluid's viscosity. Disclosed embodiments include fishing devices, bicycle simulators, and control knobs.

Control and response characteristics of a magnetorheological fluid damper for passenger vehicles

Abstract: This paper presents control characteristics of a semi-active magneto-rheological (MR) fluid damper for a passenger vehicle. A cylindrical MR damper is devised and its governing equation is derived. After verifying that the damping force of the MR damper can be continuously tuned by the intensity of the magnetic field, PID controller is employed to achieve the desired damping force. The proposed MR damper is then applied to a full-car model and performance characteristics of the full-car such as vertical acceleration of the body are evaluated via hardware-in-the-loop-simulation (HILS).

Analysis of electro- and magneto-rheological flow mode dampers using Herschel-Bulkley model

Abstract: Electrorheological (ER) and magnetorheological (MR) fluid- based dampers are typically analyzed using Bingham-plastic shear flow analysis under quasi-steady fully developed flow conditions. An alternative perspective, supported by measurements reported in the literature, is to allow for post- yield shear thinning and shear thickening. To model these, the constant post-yield plastic viscosity in Bingham model can be replaced with a power law model dependent on shear strain rate that is known as the Herschel-Bulkley fluid model. Depending on the value of the flow behavior index number, varying degrees of post-yield shear thickening or thinning behavior can be analyzed. A nominal ER bypass damper is considered. Damping forces in the damper are analyzed by approximate parallel plate geometry. The impacts of flow behavior index on shear stress-strain relationship and velocity profile for variable electric field are also examined numerically. Then, analytical damping predictions of ER/MR flow mode dampers are compared using the nonlinear Bingham-plastic and nonlinear Herschel-Bulkley analyses.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Yield stress measurements of magnetorheological fluids in tubes

Abstract: A pressure-driven apparatus was used to measure the yield stress of magnetorheological (MR) fluids as a function of the applied magnetic field, the carbonyl iron particle content, and the amount of surfactant used to stabilize the MR fluid. The yield stress was measured from the pressure difference necessary to initiate flow of a MR fluid in a straight tube present in a magnetic field. Yield stress measurements were made on MR fluids that contained up to 30 vol % carbonyl iron particles, up to 14 vol % surfactant oleic acid, and the remainder 100 cS silicone oil. In the absence of an applied magnetic field, the MR fluids did not have a yield stress and behaved as Newtonian fluids. In the presence of magnetic fields up to 2.2 kG, the MR fluids had yield stresses up to 1.9 kPa. An effect of the tube size on the yield stress was observed for MR fluids above 15 vol % carbonyl iron and magnetic fields above 1.0 kG.

Stable magnetorheological fluids

Abstract: Magnetorheological fluid compositions that include a carrier fluid, magnetic-responsive particles and an organoclay. These fluids exhibit superior soft sedimentation.

Magnetorheological fluid damper

Abstract: A novel and improved magnetorheological fluid damper is provided which effectively secures a flux ring to a piston core in a manner which prevents relative axial and radial movement between the flux ring and the core throughout operation The damper includes crimp portions formed on each end of the flux ring for engaging respective end plates positioned at each end of the piston core to secure the end plates and thus the flux ring to the piston core One of the end plates may, in turn, function to maintain a piston rod in connection with the piston core Specifically, each end plate functions as a spring device by being elastically deformed during a crimping process causing the end plates to apply a spring force against the flux ring One of the end plates may also apply another spring force to the piston rod A crimping method is also provided which effectively and efficiently permits crimping in a simple manner

Durable magnetorheological fluid compositions

Abstract: A durable MR fluid formulation is described which includes mechanically hard magnetizable particles, a carrier fluid derived from a polyalphaolefin and a plasticizer, and at least one colloidal additive such as colloidal polytetrafluoroethylene or colloidal graphite. The use of these colloidal additives inhibits surface-to-surface contact and scuffing while providing reliable lubrication under boundary lubrication conditions.

Field-controllable electro- and magneto-rheological fluid dampers in flow mode using Herschel-Bulkley theory

Abstract: The Bingham plastic constitutive model has been widely used to predict the post-yield behavior of electro- and magneto- rheological fluids (ER and MR fluids). However, if these fluids experience shear thinning or shear thickening, the Bingham plastic model may not be an accurate predictor of behavior, since the post-yield plastic viscosity is assumed to be constant. In a recent study, it was theoretically and experimentally demonstrated that the Herschel-Bulkley fluid model can be successfully employed when evaluating non- Newtonian post-yield behavior of ER and MR fluids. In this paper, the Herschel-Bulkley model is employed to include a detailed analysis of ER and MR fluid dynamics through pipes and parallel plates. Simplified explicit expressions for the exact formulation are also developed. It is shown that the proposed simplified model of the Herschel-Bulkley steady flow equations for pipes and parallel plates can be used as an accurate design tool while providing a convenient and generalized mathematical form for modeling ER and MR fluids. Theoretical and experimental analyses are presented for a MR fluid damper, which is designed, developed, and tested at the University of Nevada, Reno (UNR).

Development and experiments of actuator using MR fluid

Abstract: Magnetorheological (MR) fluids are materials that respond to an applied magnetic field with a change in their rheological behavior. Though they are functionally similar to electrorheological (ER) fluids, MR fluids exhibit much higher yield strengths for applied magnetic fields than ER fluid for applied electric fields. The devices using MR fluids have an ability to provide high-torque, low-inertia, safe device and simple interface. In this study, the authors develop an actuator using MR fluid that consists of an input part, an output part and an MR-fluid clutch between them. The output part can be simply a cylinder or a disk, and thereby made extremely lightweight. In order to investigate the characteristics of the developed MR actuator, the experiments are examined.

Flexible Fixturing with Phase-Change Materials. Part 1. Experimental Study on Magnetorheological Fluids

Abstract: Flexible fixturing is an important issue in manufacturing, where a single set of fixtures are used for locating and holding a variety of workpieces. Flexible fixturing with phase-change materials involves the use of functional materials which change the status from liquid to solid under certain conditions. The workpiece is located in the liquid fixture material and held firmly when the material is changed into the solid state. Therefore, the material strength in the solid state is crucial for a successful application to production. This paper presents an experimental study of magnetorheological (MR) fluid material. With the application of a compression technique, a thick column structure is formed and enhanced. Hence, a high shear strength of the MR fluid in solid status is achieved. Experimental results are reported in this paper. Further application of this technique is under development for flexible fixturing in industrial applications.

Dynamic characteristics of magneto-rheological fluid damper

Abstract: Two kinds of Magneto-rheological fluid damper (MRF damper) have been designed and manufactured. One has a nominal capacity of 2kN and the other 20kN. A bypass flow system is adopted for both dampers and each has the same capacity of electromagnet attached to the bypass portion. The effective fluid orifice is the rectangular space and the magnetic field is applied from the outside. A test was performed by applying different magnetic fields to the orifice portion of the rectangular space. The damping force and the force- displacement loop were evaluated. The test results yielded the following: (1) Two type's of dampers functioned by using one unit of the electromagnet under an appropriate electrical current control. (2) The magnitude of the damping force depends on the input magnetic field, but it has an upper limit. (3) Without an applied magnetic field, the MRF damper exhibits viscous-like behavior, while with a magnetic field it shows friction-like behavior. A mechanical model of the damper is estimated by taking account of the force-displacement loop. It is clarified that MRF dampers provide a technology that enables effective semi-active control in real building structures.