Showing papers on "Magnetorheological fluid published in 2006"

Development of an adaptive tuned vibration absorber with magnetorheological elastomer

Abstract: In this technical note we develop an adaptive tuned vibration absorber (ATVA) based on the unique characteristics of magnetorheological elastomers (MREs), whose modulus can be controlled by an applied magnetic field. The MRE used in the developed ATVA was prepared by curing a mixture of 704 silicon rubber, carbonyl iron particles and a small amount of silicone oil under a magnetic field. The ATVA works in shear mode and consists of an oscillator, smart spring elements with MREs, a magnet conductor and two coils. Natural frequencies of the ATVA under different magnetic fields were both theoretically analyzed and experimentally evaluated by employing a beam structure with two ends supported. The experimental results demonstrated that the natural frequency of the ATVA can be tuned from 55 to 82 Hz. The relative frequency change is as high as 147%. Furthermore, the absorption capacity of the developed ATVA can achieve as high as 60 dB, which was also experimentally justified.

A novel hysteretic model for magnetorheological fluid dampers and parameter identification using particle swarm optimization

Abstract: Non-linear hysteresis is a complicated phenomenon associated with magnetorheological (MR) fluid dampers. A new model for MR dampers is proposed in this paper. For this, computationally-tractable algebraic expressions are suggested here in contrast to the commonly-used Bouc–Wen model, which involves internal dynamics represented by a non-linear differential equation. In addition, the model parameters can be explicitly related to the hysteretic phenomenon. To identify the model parameters, a particle swarm optimization (PSO) algorithm is employed using experimental force–velocity data obtained from various operating conditions. In our algorithm, it is possible to relax the need for a priori knowledge on the parameters and to reduce the algorithmic complexity. Here, the PSO algorithm is enhanced by introducing a termination criterion, based on the statistical hypothesis testing to guarantee a user-specified confidence level in stopping the algorithm. Parameter identification results are included to demonstrate the accuracy of the model and the effectiveness of the identification process.

Bidisperse magnetorheological fluids using Fe particles at nanometer and micron scale

Abstract: Conventional magnetorheological (MR) fluids are suspensions of micron-sized particles in a hydraulic or silicone oil carrier fluid. Recently, research has been conducted on the advantages of using bidisperse fluids, which are mixtures of two different powder sizes in the MR suspension. The MR fluids investigated here use a mixture of conventional micron- sized particles and nanometer-sized particles. The settling rate of such bidisperse fluids using nanometer-sized particles is reduced because the nanoparticles fill pores created between the larger particles, thereby reducing fluid transport during creeping flow. This reduction in the settling rate comes at a cost of a reduction in the maximum yield stress that can be manifested by such an MR fluid at its saturation magnetization. There is a measurable and predictable variation in rheological properties as the weight percent (wt%) of the nanometer-sized particles is increased relative to the weight percent (wt%) of micron-sized particles, while maintaining a constant solids loading in the MR fluid samples. All bidisperse fluids tested in this study have a solids loading of 60 wt% of iron (Fe) particles. This study investigates the effect of increasing the wt% of 30 nm (nominal) Fe particles relative to 30mm (nominal) Fe particles on rheological characteristics, such as yield stress and postyield viscosity. The goal of this study is to find an optimal composition of the bidisperse fluid that provides the best combination of high yield stress and low settling rate based on empirical measurements. The applicability of the Bingham-plastic rheological model to the measured flow curves of these MR fluids is also presented.

Dynamic Modeling of Magnetorheological Damper Behaviors

Abstract: Based on theoretical analysis and experiments, this article proposes a new model for a magnetorheological (MR) damper. The proposed model with a smooth and concise form can interpret the bi-viscous and hysteretic behaviors of the MR damper very well. The parameters in the model have definite physical meanings. The bi-viscous and hysteretic behaviors can be characterized by two parameters � 0 and A3. The proposed model makes it convenient to study the effects of the bi-viscous and hysteretic behaviors on the performance of a system with a MR damper. As one application of the model, a vibration isolation system with a MR damper is investigated, and the effects of bi-viscous and hysteretic behaviors on system performances are studied by numerical methods and theoretical analysis.

A comprehensive analysis of the response time of MR dampers

Abstract: The primary purpose of this paper is to provide a comprehensive review on the response time of magnetorheological (MR) dampers. Rapid response time is desired for all real-time control applications. In reviewing the literature, a detailed description of the response time of semi-active dampers is seldom given. Furthermore, the methods of computing the response time are not discussed in detail. The authors intend to develop a method for the definition and the experimental determination of the response time of MR dampers. Furthermore, parameters affecting the response time of MR dampers are investigated. Specifically, the effect of operating current, piston velocity, and system compliance are addressed. Because the response time is often limited, not by the response of the fluid itself, but by the limitations of the driving electronics and the inductance of the electromagnet, the response time of the driving electronics is considered as well. The authors define the response time as the time required to transition from the initial state to 95% of the final state. Using a triangle wave to maintain constant velocity across the damper, various operating currents ranging from 0.5 to 2 A were applied and the resulting force was recorded. The results show that, for a given velocity, the response time decreases as the operating current increases. Results for the driving electronics show the opposite trend: as current increases, response time increases. To evaluate the effect of piston velocity on response time, velocities ranging from 0.1 to 4 in s−1 were tested. The results show that the response time decreases exponentially as the velocity increases, converging on some final value. Further analysis revealed that this result is an artifact of the compliance in the system. To confirm this, a series of tests was conducted in which the compliance of the system was artificially altered. The results of the compliance study indicate that compliance has a significant effect on the response time of the damper.

A new dynamic hysteresis model for magnetorheological dampers

Abstract: Semi-actively controlled magnetorheological (MR) fluid dampers offer rapid variation in damping properties in a reliable fail-safe manner using very low power requirements. Their characteristics make them ideal for semi-active control in structures and vehicle applications in order to efficiently suppress vibration. To take advantage of their exceptional characteristics, a high fidelity model is required for control design and analysis. Perfect understanding of the dynamic characteristics of such dampers is necessary when implementing MR struts in applications. Different models have been proposed to simulate the hysteresis phenomenon of MR dampers. The Bouc–Wen model has been extensively used to simulate the hysteresis behavior of MR dampers. However, considerable differences still exist between the simulation and experimental results. Moreover, the characteristic parameters in the traditional Bouc–Wen model are not functions of the frequency, amplitude and current excitations; therefore, the estimated parameters can characterize the behavior of the tested MR damper under specific excitation conditions and must be re-evaluated if a different combination of excitation parameters is desired. This can be extremely cumbersome and computationally expensive. In this work, a new hysteresis model based on the Bouc–Wen model has been developed to better characterize the hysteresis phenomenon of the MR damper. The proposed model incorporates the frequency, amplitude and current excitation as variables and thus enables us to predict efficiently and accurately the hysteresis force for changing excitation conditions. The proposed modified Bouc–Wen model has been validated against the experimental results through graphical and quantitative analysis in time, displacement and velocity domains and an excellent correlation has been found.

A review of the state of the art in magnetorheological fluid technologies - Part I: MR fluid and MR fluid models

Abstract: This paper presents a review of the state of the art in magnetorheological technology. As magnetorheological fluids continue to gain attention, the research and development of these fluids must keep pace. Since their invention in 1948, MR fluid development has made significant advancements. Throughout this time, MR fluids have been faced with many challenges and today, after many years of development, MR fluid formulations appear to have overcome many of these challenges. The fluids have proven to be commercially viable and well suited for many applications. The intent of this study is to provide a review of the state of the art in MR fluid technologies. To limit the scope, this study will focus on three common concerns associated with MR fluids; namely the strength of the fluid (i.e., the achievable yield stress), the stability of the fluid, and the durability of the fluid. When considering the use of a MR fluid in a particular application, it is these three areas that fall under the greatest scrutiny. The literature is rich in works devoted to addressing these concerns. Furthermore, with the great success of MR fluids and MR fluid devices, a number of the models used to describe the behavior of the fluid are also reviewed; specifically, works related to the visco-plastic modeling of MR fluids are reviewed. Models used to describe the physics behind the formation of the field induced yield stress are also reviewed.

Sedimentation and redispersion phenomena in iron-based magnetorheological fluids

Abstract: In this work, the effect of three different additives (oleic acid, aluminum stearate, and silica nanoparticles) on the aggregation, sedimentation, and redispersibility of concentrated iron-based magnetorheological fluids was investigated. With this aim, the sedimentation behavior was analyzed using an electromagnetic induction method, which is suitable for studying the sedimentation of opaque magnetic suspensions. The redispersibility was studied, in a quantitative way, by means of rheological measurements, both in the presence and in the absence of external magnetic field. For this purpose, samples were subjected to a constant shear stress at different moments (steps) of the settling process. The time evolution of the corresponding shear rate was measured at each step. Interestingly, it was found that although the addition of oleic acid or aluminum stearate does not avoid particle settling, the redispersibility of the suspensions is considerably enhanced. On the contrary, silica nanoparticles behave as a...

Review of magnetorheological (MR) fluids and its applications in vibration control

Abstract: Magnetorheological (MR) fluids are now well established as one of the leading materials for use in controllable structures and systems. Commercial application of MR fluids in various fields, particularly in the vibration control, has grown rapidly over the past few years. In this paper, properties of magnetorheological (MR) fluids, its applications in suspensions of vehicles, suspension of trains, high buildings cable-stayed bridges have been discussed. The scope of MR fluids in future, problems and some suggestions are also presented. Finally, effectiveness of MR fluids in vibration control of marine diesel engine through experiment is briefly discussed by the author.

Semi-active Vibration Control Schemes for Suspension Systems Using Magnetorheological Dampers

Abstract: Three semi-active control methods are investigated for use in a suspension system using a commer- cial magnetorheological damper. The three control methods are the limited relative displacement method, the modified skyhook method, and the modified Rakheja-Sankar method. The method of averaging has been adopted to provide an analytical platform for analyzing the performance of the different control methods. The analytical results are verified using numerical simulation, and further are used to assess the efficiency of dif- ferent control methods. An experimental test bed has been developed to examine the three control methods under sinusoidal and random excitations. Both analytical and experimental results confirm that the Rakheja- Sankar control and modified skyhook control methods significantly reduce the root-mean-square response of both the acceleration and relative displacement of the sprung mass, while the limited relative displacement controller can only control the relative displacement of the suspension system.

Hood lift mechanisms utilizing active materials and methods of use

Abstract: A hood lift mechanism for reversibly increasing the energy absorption capability at appropriate force levels of a vehicle hood includes a vehicle hood; an active material in operative communication with the vehicle hood, wherein the active material comprises a shape memory alloy, a ferromagnetic shape memory alloy, a shape memory polymer, a magnetorheological fluid, an electroactive polymer, a magnetorheological elastomer, an electrorheological fluid, a piezoelectric material, an ionic polymer metal composite, or combinations comprising at least one of the foregoing active materials; and an activation device in operative communication with the active material, wherein the activation device is operable to selectively apply an activation signal to the active material and effect a reversible change in a property of the active material, wherein the reversible change results in an increased clearance distance between the vehicle hood and an underlying component.

Magnetorheology for suspensions of solid particles dispersed in ferrofluids

Abstract: In this work, the magnetorheological properties of suspensions of micron-sized iron particles dispersed in magnetite ferrofluids were studied. With this aim, the flow properties of the suspensions in the steady-state regime were investigated using a commercial magnetorheometer with a parallel-plate measuring cell. The effect of both magnetite and iron concentration on the magnitude of the yield stress was studied for a broad range of magnetic fields. In addition, the experimental values of the yield stress were compared with the predictions from the chain model. With this purpose the values of the yield stress were obtained by means of finite element calculations. Interestingly, it was found that the experimental yield stress increases with the concentration of magnetite nanoparticles in the ferrofluid. Unfortunately, this behaviour is not obtained from calculations based on the chain model, which predict just the opposite trend.

Properties and application of magnetorheological fluids

Abstract: Materials AbstrAct Purpose: This paper presents basic properties of the magnetorheological fluids (MR) and their development in recent years. A variety of still growing practical applications in mechanical devices are presented. Design/methodology/approach: The theoretical research results of the properties and applications obtained in the past decades and progressed in recent years are reviewed. Findings: It is very clearly and well understood from the presented paper that replacement of the traditional devices with active, smart system better adapted to the environment stimulus are necessary. Many of them will include MR fluids as active component. Research limitations/implications: MR fluids with excellent properties can be applied in various fields of civil engineering, safety engineering, transportation and life science. They offer an outstanding capability of active control of mechanical properties. Practical implications: A very useful material for the engineers engaged in the design of brakes, dampers, clutches and shock absorbers systems. Originality/value: This article describes an up-to-date MR materials development and their application in civil engineering. The advantage of the smart systems over nowadays solutions becomes the direction of the researches and designing of 21st century devices.

Study of magnetorheological fluids at high shear rates

Abstract: The tunable rheological properties of magnetorheological (MR) materials at high shear rates are studied using a piston-driven flow-mode-type rheometer. The proposed method provides measurement of the apparent viscosity and yield stress of MR fluids for a shear rate range of 50 to 40,000 s−1. The rheological properties of a commercial MR fluid, as well as a newly developed MR polymeric gel, and a ferrofluid-based MR fluid are investigated. The results for apparent viscosity and dynamic and static shear stresses under different applied magnetic fields are reported.

Active/semi-active suspension control using magnetorheological actuators

Abstract: Magnetorheological dampers, which are semi-active devices that use MR fluids to produce controllable forces, can be used as smart actuators to reduce the vibrations of mechanical systems. The advantage of these actuators is the low power input requirements and the high output force they produce. An analytical study is performed in this article to examine the effectiveness of this type of actuator in suppressing the vibrations of a passenger car suspension system. A half-car model including passenger dynamics subjected to road disturbance is used. Two MR dampers attached to the front and back axles are used as actuators. An optimal control scheme is used to control the overall suspension system such that the vibrations of the passenger seats as well as the chassis of the car are greatly reduced or eliminated. The simulation results show that properly controlled MR dampers are effective means for vibration suppression for passenger cars.

Study on MR Semi-active Suspension System and its Road Testing

Abstract: A magnetorheological (MR) damper model is established and linearized based on theory analyses and real testing. Since the mathematical model of the suspension system is nonlinear and complicated, a model-free fuzzy control algorithm is employed to design a controller for achieving vibration isolation. As a pilot study, two MR dampers are used to replace the passive ones of the front half-car. A quarter-car fuzzy intelligent controller is employed to control the two MR independent suspension systems, respectively. The performance of the MR suspension system is evaluated by road testing. The test results indicate that the vibration of the vehicle body and unsprung mass are both reduced significantly.

Design of a novel magneto-rheological squeeze-film damper

Abstract: Magneto-rheological (MR) fluids react to magnetic fields undergoing changes in their mechanical characteristics, viscosity in particular. After an analytical and numerical study, an MR squeeze-film damper has been designed and set up on a reduced scale rotor test-rig. Numerical simulations were carried out in order to evaluate the dynamic behaviour of the damped rotor as a function of the current supplied to the adjustable device. A linear model that depicts the main characteristics of the system has been developed as a useful tool in damper and control design. By testing different fluids, an optimal fluid has been singled out. Tests conducted on the selected fluid show that it is possible to have the optimum conditions for each steady rotational speed.

Cable Vibration Control using Magnetorheological Dampers

Abstract: As the world's first implementation of magnetorheological (MR) smart damping technique in bridge structures, a total of 312 semi-active MR dampers (RD-1005, Lord Corporation) have recently been installed for rain-wind-induced cable vibration control on the cable-stayed Dongting Lake Bridge, China. This project has undergone several stages of in situ experiments and tests: (i) modal tests of undamped cables, (ii) forced vibration tests of MR-damped trial cables, (iii) monitoring of MR-damped and undamped cable responses under rain-wind excitations, (iv) comparative tests using different damper setups, (v) full installation, and (vi) field measurements and real-time control tests after the installation. After outlining the above six stages of the whole project and addressing the experience and lessons learned from both open-loop control and closed-loop control practices, this study focuses on the design considerations of implementing MR dampers for cable vibration control, taking into account the effects of the damper stiffness, damper mass, stiffness of damper support, nonlinearity of the damper, and sag and inclination of the cable. The research efforts make it possible to develop elaborate MR dampers specific for application to bridge stay cables.

Investigating the magnetorheological effect at high flow velocities

Abstract: The objective of this work is to investigate the magnetorheological (MR) effect at high flow velocities. A slit-flow rheometer has been built which allows for high speed testing of MR fluid under varying field strengths. The gap size of the rheometer was chosen to achieve high fluid velocity and high shear rates. With a 1 mm gap size, fluid velocities range from 1 to 37 m s−1 with resulting shear rates ranging from 0.07 × 105 to 2.5 × 105 s−1. In order to evaluate the performance of the fluid, the force required to drive the fluid through the flow channel is measured and force–velocity characteristics are generated. From the force–velocity curves, the apparent viscosity is found. The apparent viscosity is used to calculate the yield stress for several magnetic field strengths. Two MR valve lengths are considered (25.4 and 6.35 mm). At each velocity the yield stress is found using the closed form solution for the non-dimensional yield stress. Fluid dwell time is introduced as the amount of time the fluid spends in the presence of a magnetic field. For the range of velocities considered, fluid dwell times range from 12.4 to 0.18 ms. A reduction in apparent yield stress is observed as dwell time decreases. Results indicate that the MR fluid can achieve 63.2% of the expected yield stress for dwell times greater than 0.6 ms.

Design and Modeling of a Magnetorheological Valve with Both Annular and Radial Flow Paths

Abstract: In this article, an MR valve possessing simultaneously annular fluid flow resistance channels and radial fluid flow resistance channels is designed, and its structure and working principle are described. In addition, a mathematical model for the MR valve with both annular and radial flow paths is developed and the simulation is carried out to evaluate the newly developed MR valve. The simulation results based on the proposed model indicate that the efficiency of the MR valve with circular disk-type fluid resistance channels is superior to that with annular fluid resistance channels under the same magnetic flux density and outer radius of the valve. Furthermore, the results also show that the efficiency of the MR valve can be improved significantly with two types of fluid flow resistance gaps, viz. annular fluid flow resistance gaps and circular disk-type fluid flow resistance gaps simultaneously.

Experimental Verification of Smart Cable Damping

Abstract: Stay cables, such as are used in cable-stayed bridges, are prone to vibration due to their low inherent damping characteristics. Transversely attached passive viscous dampers have been implemented in many bridges to dampen such vibration. However, only minimal damping can be added if the attachment point is close to the bridge deck. For longer bridge cables, the relative attachment point becomes increasingly smaller, and passive damping may become insufficient. A recent analytical study by the authors demonstrated that “smart” semiactive damping can provide increased supplemental damping. This paper experimentally verifies a smart damping control strategy employing H2 ∕linear quadratic Gaussian (LQG) clipped optimal control using only force and displacement measurements at the damper for an inclined flat-sag cable. A shear mode magnetorheological fluid damper is attached to a 12.65 m inclined flat-sag steel cable to reduce cable vibration. Cable response is seen to be substantially reduced by the smart da...

Parameter optimization and analysis of a vehicle suspension system controlled by magnetorheological fluid dampers

Abstract: This paper presents the parameter optimization and simulation analysis of a new type of vehicle suspension system controlled by recently developed magnetorheological fluid dampers. First, the differential equations of motion for a vehicle suspension system considering two degrees of freedom corresponding to vertical vibration and rocking vibration are formulated. Then, the non-controlled and optimally controlled response of the suspension system under six sets of measured road surface excitation is simulated, which shows the effectiveness of full-state feedback LQR control for the vibration suppression of the suspension system. Furthermore, the influence of the control algorithm parameters is analyzed, and the results show that active control can be fully realized by semi-active control technology, due to the intrinsic variable damping behavior of LQR control. Finally, the simulation of semi-active magnetorheological fluid damper control using a limited optimal Hrovat control algorithm is carried out, and the results are compared with LQR control results. The numerical results show that using magnetorheological fluid dampers to replace active actuators in vibration control of vehicle suspension system is quite feasible. Copyright © 2005 John Wiley & Sons, Ltd.