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The harmonic steady-state responses of an MR seat isolator, designed and fabricated at the University of Maryland for the driver/commander seat of the Expeditionary Fighting Vehicle (EFV), are measured over a temperature range from 100°C to 1000°C, and the damper behavior is characterized using a variant of the nonlinear Bingham plastic model. The effect of damper self-heating on the model parameters is investigated and the trends with temperature variation are presented. Numerical simulations are carried out to investigate seat isolation performance across a broad frequency spectrum as temperature and payload vary. Conclusions are drawn about the performance robustness to temperature variations of the semi-active skyhook control algorithm typically utilized in vibration isolation problems.

This paper presents a new type of jetting dispenser driven by a ring type piezoelectric actuator. By operating at very high frequencies, the dispenser is expected to provide very small dispensing dot size of low viscous adhesives (viscosity of 50cp to 500cp) at high dispensing flow rate in semiconductor packaging processes. After describing the mechanism and operational principle of the dispenser, a mathematical model of the system is derived by considering behaviors of the piezostack, the actuating spring, the dispensing needle and the adhesive fluid dynamics. In the modeling, a lumped parameter method is applied to model the adhesive whose rheological property is approximately expressed by Bingham model. The governing equation of the whole dispenser is then derived by integrating the structural model with the fluid model. Based on the proposed model, the dispenser is designed and manufactured. Subsequently, the dispensing performances such as dot size and dispensing flow rate are investigated using the proposed model and then validated by experiment.

Structure design and parameters selection are crucial steps in developing magnetorheological fluid (MRF) damper for vehicle semi-active suspension system. Most traditional methods for deciding structure parameters by experiential expressions are unilateral and imprecise. In this paper, a multiobjective evolutionary optimization approach will be used to solve the optimization design problem. Based on Bingham fluid models, a structure design for MRF damper with shearing valve mode is completed for vehicle suspension. To reduce the dynamic response time and to enlarge the range the controllable damping force are taken as the optimization objectives. Three crucial parameters, including gap width, effective axial pole length and coil turns number are taken as optimization variables, a hybrid evolutionary algorithm combining particle swarm optimization (PSO) and crossover is employed to search for the Pareto solutions, According to the optimized results, a new type MRF damper design is accomplished for a pickup truck suspension system. The proposed method and analysis present a beneficial reference for MRF damper design.

Magnetorheological (MR) fluids are suspensions of micron sized ferromagnetic particles dispersed in varying proportions of a variety of non-ferromagnetic fluids. MR fluids exhibit rapid, reversible and significant changes in their rheological (mechanical) properties while subjected to an external magnetic field. In this paper, a double-plate magneto-rheological fluid (MRF) clutch with controllable torque output have been designed. Electromagnetic finite element analysis is used to optimize the design of the clutch. The geometric constraints and the magnetic properties of materials are controlling parameters in the optimization process which is used to determine the design parameters of the MRF clutch in order to let the magnetic field in the MRF domain is as higher as possible. Meanwhile, the theoretical torque output has also been calculated for a given input electric current by using the Bingham plastic constitutive model.

This paper presents force-feedback control performance of a haptic device using a controllable electrorheological (ER) fluid. A spherical type of joint is devised and its torque characteristic is analyzed by considering Bingham property of ER fluid. In order to embody a human organ into virtual space, a volumetric deformable object is adopted. The virtual object is then mathematically formulated by the shape retaining chain linked (S-chain) model. After evaluating reflection force, computational time, and compatibility with real time control, the virtual environment with the ER haptic device is established by incorporating reflection force and desired position originated from an organ and master, respectively. In order to achieve force trajectories at the haptic device in which the force comes from the virtual space, a sliding mode controller (SMC) is formulated and experimentally realized. Tracking control performances for various operating conditions are presented in time domain, and their tracking errors are evaluated.

The Magnetic, yield and rheological properties of the Magnetorheological (MR) fluids are discussed. Based on the microstructure of a magnetic chain a theoretical model was developed to analyze the effect of the applied magnetic field on the yield stress of the MR fluids. A bingham model was used to describe the rheological characteristics of the MR fluids subject to an applied magnetic field. The results show that the MR fluid exhibits super paramagnetic behavior. The yield stress increases as the applied magnetic field increases. The MR fluids can be used in clutch, valve, and damper devices because the yield stress of these fluids can be continuously adjusted by the applied magnetic field.

The primary objective of this study is to estimate the parameters of constitutive models characterizing the rheological properties of ferrous and cobalt nanoparticle-based magnetorheological fluids. Constant shear rate rheometer measurements were carried out using suspensions of nanometer sized particles in hydraulic oil. These measurements yielded shear stress vs. shear rate as a function of applied magnetic field. The MR fluid was characterized using both Bingham-Plastic and Herschel-Bulkley constitutive models. Both these models have two regimes: a rigid pre-yield behavior for shear stress less than a field-dependant yield stress, and viscous behavior for higher shear rates. While the Bingham-Plastic model assumes linear post-yield behavior, the Herschel-Bulkley model uses a power law dependent on the dynamic yield shear stress, a consistency parameter and a flow behavior index. Determination of the model parameters is a complex problem due to the non-linearity of the model and the large amount of scatter in the experimentally observed data. Usual gradient-based numerical methods are not sufficient to determine the characteristic values. In order to estimate the rheological parameters, we have used a genetic algorithm and carried out global optimization. The obtained results provide a good fit to the experimental data.

This study focuses on the design and characterization of a multi-plate magneto-rheological fluid (MRF) limited slip differential (LSD) clutch. Three-dimensional electromagnetic finite element analyzes are performed to optimize the MRF LSD clutch design. The torque transfer capacity of the clutch is predicted utilizing Bingham-Plastic constitutive model of the MRF. The MRF LSD clutch is tested at different velocities and applied magnetic fields. The clutch heating is also examined under different operating conditions to determine the thermal effects on the torque transfer performance of the multi-plate clutch.

Many efforts to understand the response of magnetorheological (MR) fluid dampers have been undertaken in the past several years. Such components are of great interest for use in automotive suspension and safety systems, as well as in aerospace and civil applications. Physically sensible models that contain realistic descriptions of fluid flow would be of great utility in optimizing the performance of these dampers. While simple models based on the familiar Bingham plastic MR fluid constitutive relation capture many of the key features of the steady-state damper response, including the existence of a magnetic-field-dependent 'yield force' and the reduction of the damping coefficient at high velocities, such models do not describe the more complex velocity dependence and dynamic response of the force observed in real dampers. Unfortunately, experimental data on viscometric flows of MR fluids at the high shear rates encountered in MR dampers are scarce. Moreover, a number of sophisticated damper models are available, but many use mathematical constructs that are not easily understood in terms of physical phenomena. Motivated by these challenges, we have measured the response of two automotive MR shock absorbers and developed a lumped-parameter model to describe their dynamic response. Using the parameters provided by this model, we have also compared the measured damper response with that predicted by simple models of magnetic flux and fluid flow in these components.

A key aspect of application of electrorheological (ER) and magnetorheological (MR) fluids is the characterization of rheological properties. For this purpose, two rotational viscometers are theoretically analyzed. One is a rotational coaxial cylinder viscometer, and the second is a rotational parallel disk viscometer. A key goal is to determine the shear stress and shear rate of ER/MR fluids for both viscometers from the torque and angular velocity data. To do this, the equations between shear stress and torque as well as shear rate and angular velocity are derived on the basis of the Bingham-plastic, biviscous, and Herschel-Bulkley constitutive models. For simplicity in mathematical form, the Bingham-plastic model is used to describe the flow behavior of ER/MR fluids. The biviscous model characterized by static and dynamic yield stresses is used to capture the preyield behavior. The preyield region where the local shear stress is smaller than the static yield stress has much larger viscosity than the postyield region. In order to account for the shear thinning or thickening in postyield region, the Herschel-Bulkley constitutive model is used in this study. The shear stress for a rotational coaxial cylinder viscometer can be calculated directly from measured torque. However, three approximation methods are applied to determine the shear rate. For rotational parallel disk viscometers, the shear rate and shear stress can be obtained directly from the torque and angular velocity data. In order to comprehensively understand the flow behavior of ER/MR fluids with respect to the constitutive models, the nondimensional analyses are undertaken in this study.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A 400kN magnetorheological damper (MR damper) for a real base-isolated building was developed and its dynamic characteristics were verified by experimental tests. The MR damper has 950mm (+/-475mm) stroke and by-pass flow potion. A new type of Magneorheological fluid is also developed in order to apply to the MR damper. MR fluid had a property of the settlement of particles in dampers. Authors developed a new MR fluid, which keeps the particles in the fluid adequately enough for usual use of MR damper. Analytical model was discussed in this paper. The force by the bingham visco-plastic model was compared with the results of experimental tests. It was found that this analytical model is useful to predict the capacity of the MR damper.

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.

This paper theoretically presents Bingham characteristics of ER (electrorheological)/MR (magnetorheological) fluids with respect to different rotational viscometers through comparative analysis. For doing so, two different types of rotational viscometers are introduced and configured for ER/MR fluids; one is a rotational coaxial cylinder viscometer and the other is a rotational parallel disk viscometer. In order to determine the shear stress and shear rate of fluids tested in both viscometers, the fundamental equations between shear stress and torque as well as shear rate and angular velocity are derived on the basis of the biviscous constitutive model. The biviscous model is characterized by a yield stress: when the shear stress is less than this yield stress, the preyield viscosity is relatively large compared to the postyield viscosity when shear stress is greater than the yield stress. For rotational coaxial cylinder viscometers, the shear stress can be calculated directly from the measured torque. However, for the determination of the shear rate, some strategies are required. In this study, different methods of determining the shear rate are developed and their accuracy is assessed. In the case of rotational parallel disk viscometers, the calculation of the shear rate is straightforward from angular velocity measurements, but the shear stress requires a relatively complicated calculation. In this study, for simplicity, the shear stress is approximated and the error of this approximation is evaluated with respect to important rotational parallel disk viscometer geometry. Finally, the Bingham characteristics of ER/MR fluids at two different rotational viscometers are theoretically presented and compared in the shear stress vs. shear rate response.

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 strength of the yield stress. Therefore, in this study, we explore the dynamic performance ranges and time response characteristics of ER and MR fluid-based systems in order to comprehensively understand each system. So far, quasi-steady fluid flow model has been widely used in the performance evaluation of ER and MR fluid-based systems. However, the quasi-steady fluid flow model can predict the dynamic performance range of the system, but does not give any information about time response characteristics of the system. Moreover, research on comparative analysis between ER and MR fluid-based systems is considerably rare. Therefore, in this study, comparative analysis for the characteristics of ER and MR fluid-based systems is undertaken based on considering the time response phenomena. For doing so, a set of nondimensional analysis based on parallel plate geometry to characterize the field-dependent properties of ER and MR fluid-based systems is developed and experimental test for ER and MR dampers are done in order to evaluate the validity of the analysis.

Magnetorheological (MR) fluids are characterized by dynamic yield stress with the application of a magnetic field. The Bingham plastic model has proven useful in modeling MR fluid properties, as in flow mode dampers. However, certain MR fluids can exhibit shear thinning behavior, wherein the fluid's apparent plastic viscosity decreases at high strain rates. The Bingham plastic model does not account for such behavior, resulting in over-prediction of equivalent viscous damping. This paper proposes a Bingham biplastic model to account for shear thinning or shear thickening. This approach assumes a bilinear post-yield viscosity, with a critical strain rate specifying the region of high strain rate flow. Furthermore, the model introduces non-dimensional terms to account for the additional parameters associated with shear thinning and thickening. A comparison is made between Bingham plastic and Bingham biplastic force responses to sinusoidal input, and equivalent viscous damping is examined with respect to nondimensional parameters.

This work presents a theoretical model for the damping force of a magneto-rheological fluid (MRF) shock absorber of an off-road motorcycle. The Bingham plastic model and a 3D electromagnetic finite-element analysis are employed to develop a theoretical model to estimate the damping force of a MRF shock absorber. The mode is based on the physical parameters of the device as well as the properties of the fluid, making a valuable tool in shock absorber design for a particular application. By comparing the theoretical and experimental results, it is demonstrated that the model accurately predicts the damping force.

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).

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.

This paper presents the development and evaluation of a controllable, semi-active magneto-rheological fluid (MRF) shock absorber for a High Mobility Multi-purpose Wheeled Vehicle (HMMWV). The University of Nevada, Reno (UNR) MRF damper is tailored for structures and ground vehicles that undergo a wide range of dynamic loading. It also has the capability for unique rebound and compression characteristics. The new MRF shock absorber emulates the original equipment manufacturer (OEM) shock absorber behavior in passive mode, and provides a wide controllable damping force range. A theoretical study is performed to evaluate the UNR MRF shock absorber. The Bingham plastic theory is employed to model the nonlinear behavior of the MR fluid. A fluid-mechanics-based theoretical model along with a three-dimensional finite element electromagnetic analysis is utilized to predict the MRF damper performance. The theoretical results are compared with experimental data and are demonstrated to be in excellent agreement.

The hysteresis behavior of a linear stroke magnetorheological damper is characterized for several magnetic fields and sinusoidal excitations over a nominal operational frequency range of 1.0 - 3.0 Hz. The behavior of the damper is inadequately modeled using the equivalent viscous damping and the complex modulus. Therefore, four different non-linear modeling perspectives are discussed for purposes of system identification procedures, including: (1) nonlinear Bingham plastic model, (2) nonlinear biviscous model, (3) nonlinear hysteretic biviscous model, and (4) nonlinear viscoelastic plastic model. The first three nonlinear models are piecewise continuous in velocity. The fourth model is piecewise smooth in velocity. The parameters for each model are identified from an identification set of experimental data, these parameters are then used to reconstruct the force vs. displacement and the force vs. velocity hysteresis cycles for the respective model. Model performance is evaluated by calculating equivalent viscous damping and force time history errors between the model fit and the experimental data. In addition to the identification study, a validation study was done. Model parameters were calculated for offset values of current and frequency. These intermediate parameters were used to calculate hysteresis cycles which were compared with a second set of experimental data, a validation data set. The results from both identification and validation studies of the MR damper behavior are presented in this paper, including calculated damping and force time history errors.

This study presents a theoretical analysis of heat generation and dissipation of field-controllable magneto-rheological fluid (MRF) shock absorbers. Since MRF dampers are energy- dissipating devices, the issues of heat generation and dissipation are important in predicting their performance. A theoretical model is developed based on Bingham plastic model to estimate temperature history of the MRF dampers. The governing equation includes the MRF viscosity as a function of the temperature. The numerical solutions are compared with experimental results in order to validate the accuracy of the model, and excellent agreements are obtained.

Our primary objective is to correlate damping predictions from a quasi-steady Bingham plastic damper analysis with experimentally measured steady state damping levels for a magnetorheological (MR) fluid damper. We seek to characterize damper properties of yield force and post-yield damping, and relate the damper parameters to effective MR fluid properties of dynamic yield stress and plastic viscosity. This characterization is done as a function of applied field and frequency. The damper was mounted in a mechanical scotch-yoke type damper dynamometer. The damper shaft was displaced sinusoidally with 1 inch of stroke and the resulting steady state force was measured as a function of applied current and frequency. The resulting force vs. displacement and force vs. velocity data is used to characterize the damper. The nonlinear hysteretic biviscous model is used to identify four physical parameters of the MR damper from the force vs. velocity diagram due to sinusoidal input displacements: pre-yield damping, post-yield damping, yield force, and zero-force velocity intercept. The post- yield damping and the yield force are used to calculate effective MR fluid properties of plastic viscosity and dynamics yield stress, respectively, from the damper data. Using the effective dynamic yield stress and the effective plastic viscosity, the Bingham plastic model is used to predict the damping, and these predictions are correlated with measurements from the force vs. displacement hysteresis cycle. The damping coefficient is the ratio of the damping with the field ON, to the Newtonian damping associated with the plastic viscosity. The resulting damping coefficient vs. nondimensional plug thickness diagram successfully predicts the damping behavior of the MR damper.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This study seeks to validate a predictive damper analysis, based on an idealized Bingham plastic shear flow mechanism, which incorporates leakage effects in an electrorheological (ER) damper. The ER bypass damper operates by a piston head pushing ER fluid out of a hydraulic cylinder and through an ER fluid bypass. The pressure to force ER fluid through the bypass produces the majority of the device's damping. The ER bypass is composed of an annulus formed from two concentric aluminum tubes. The application of a voltage potential between the aluminum tubes creates an electric field in the annulus that increases the yield stress of the ER fluid. The yield stress modifies the velocity profile of the fluid in the annulus and augments the damping coefficient of the device. The ER fluid damper contains a controlled amount of leakage around the piston head. The leakage allows ER fluid to flow from one side of the piston head to the opposite side without passing through the ER bypass. In this analysis, the leakage damping coefficient with incorporated leakage effects, predict the amount of energy dissipated for a complete cycle of the piston rod. Measured force verses displacement cycles for multiple frequencies and electric fields validate the ability of the non-dimensional groups and the leakage damping coefficient to predict the damping levels for an ER bypass damper with leakage.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The hysteresis behavior of a linear stroke magnetorheological damper is characterized for sinusoidal displacement excitation at 2.0 Hz (nominal). First, we characterize the linearized MR damper behavior using equivalent viscous damping and complex stiffness. Four different nonlinear modeling perspectives are then discussed for purposes of system identification procedures, including: (1) nonlinear Bingham plastic model, (2) nonlinear biviscous model, (3) nonlinear hysteretic biviscous model, and (4) nonlinear viscoelastic-plastic model. The first three nonlinear models are piecewise continuous in velocity. The fourth model is piecewise smooth in velocity. By adding progressively more model parameters with which to better represent preyield damper behavior, the force vs. velocity hysteresis model is substantially improved. Of the three nonlinear piecewise continuous models, the nonlinear hysteretic biviscous model provides the best representation of force vs. velocity hysteresis. The nonlinear viscoelastic plastic model is superior for purposes of simulation to the hysteretic biviscous model because it is piecewise smooth in velocity, with a smooth transition from preyield to postyield behaviors. The nonlinear models represent the force vs. displacement hysteresis behavior nearly equally well, although the nonlinear viscoelastic-plastic is quantifiably superior. Thus, any of the nonlinear damper models could be used equally successfully if only a prediction of energy dissipation or damping were of interest.

We experimentally validate nonlinear quasi-steady electrorheological (ER) and magnetorheological (MR) damper models, using an idealized Bingham plastic shear flow mechanism, for the flow mode of damper operation. An electrorheological valve or bypass damper was designed, and fabricated using predominantly commercial off-the-shelf hydraulic components. Both the hydraulic cylinder and the bypass duct have cylindrical geometry, and damping forces are developed in the annular bypass via Poiseuille (flow mode) flow. Damper models assume parallel plate geometry. Three nondimensional groups are used for damper analysis, namely, the Bingham number, Bi, the nondimensional plug thickness, (delta) , and the area coefficient defined as the ratio of the piston head area, A(rho ), to the cross-sectional area of the annular bypass, Ad. In the flow mode case, the damping coefficient, which is defined as the ratio of equivalent viscous damping of the Bingham plastic material, Ceq, to the Newtonian viscous damping, C, is a function of the nondimensional plug thickness only. The damper was tested using a mechanical damper dynamometer for sinusoidal stroke of 2 inches, over a range of frequencies below 0.63 Hz. The damping coefficient vs. nondimensional plug thickness diagram was experimentally validated using these data over a range of damper shaft velocities and applied electric field. Because the behaviors of ER and MR fluid are qualitatively similar, these ER damper modeling results may be extended to analysis of flow mode MR dampers.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper presents the modeling and experimental testing of a magnetorheological (MR) fluid damper. The damper consists of a main cylinder and piston rod that pushes MR fluid through a very small clearance between the piston and the sidewalls of the cylinder. Magnetic coils are wrapped outside the cylinder to create the magnetic field. The damper model is developed based on parallel plate analysis by using both Newtonian and Bingham shear flow mechanisms. Empirical data was used to find the required parameter for a Bingham model that is the dynamic yield stress. These empirical data show the shear stress vs. shear strain at different values of magnetic flux density (B). The dynamic yield stress of MR fluid is a function of magnetic field. Finally, the model is validated through experimental testing of the damper.

A numerical study of electrorheological (ER) dampers is presented. Two models, the Newtonian and the Bingham plastic models are used to characterize the ER fluid behavior. Damping performance of two damper configurations, the Moving Electrode and the Fixed Electrode configurations, is studied. The effects of electrode gap sizes, the field strength and the ER fluid model used are quantified. The study provides a basis for design of ER-fluid based dampers.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.