Controllable Vibration Damper Using Magnetorheological Fluid.

In this paper the authors consider the problem of optimising the design of a magneto-rheological (MR) damper for controlling the lateral vibrations of a modern rail vehicle. It is shown how, using generalised test data, the primary control variable (i.e. the applied magnetic field) can be related to the desired force-velocity envelope of the MR damper. Optimisation of the damper design is then considered, taking account of the damper dimensions and available space envelope, the dynamics (due to compressibility and inertia) of the MR fluid and the configuration of the magnetic circuit. Using data from a commercially available MR fluid, it is shown how a controllable damper can be designed to improve upon the specification for a conventional lateral railcar damper. With zero applied magnetic field the MR damper is shown to be capable of providing a fail-safe minimum value of damping. Increasing the magnetic field provides a maximum equivalent damping level in excess of that available from a conventional hydraulic damper. Over the frequency range from 1 to 10 Hz it is suggested that dynamic effects would not cause significant degradation of performance. Furthermore, for the MR fluid considered, the electrical power consumption would be unlikely to exceed 100 watts.

Magnetorheological fluid dampers are attractive candidates for augmentation of lag mode damping in helicopter rotors, where additional damping is required to avert instabilities only during specific flight conditions. Magnetorheological (MR) fluids change properties dramatically with application of a magnetic field. This active damping component presents an advantage over passive elastomeric and fluid-elastomeric dampers. An extensive comparative study of fluid-elastomeric and MR dampers is presented. The study was conducted with four (a pair each) 1/6th Froude scale dampers. The MR dampers were tested with the magnetic field turned off (OFF condition) and with the magnetic field turned on (ON condition). The dampers were rested individually and in pairs, under different preloads, and under single and dual frequency excitation conditions. The fluid-elastomeric and MR (OFF) damper behavior was linear, while the MR (ON) behavior was nonlinear with the stiffness and damping varying with the displacement amplitude. Under dual frequency conditions, the MR dampers (ON condition) showed a significant degradation in damping and stiffness as the dual frequency excitation was increased. The MR (OFF) dampers showed no change in properties. The fluid-elastomeric dampers showed a mild degradation in stiffness and damping under dual frequency excitation conditions. The MR (ON) damper hysteresis was modeled using a nonlinear viscoelastic plastic model. The model captures the nonlinear behavior accurately. Using the single frequency parameters, the dual frequency hysteresis behavior was predicted, and it correlates well with experimental data.

Vibration isolation methods that vary damping and stiffness have demonstrated excellent authority over system vibration, thus, potentially making them attractive for many applications. However, conventional devices for controlling variable stiffness are typically complicated and difficult to implement in most applications. To address this issue, a new method is proposed that requires two magnetorheological (MR) fluid dampers placed in series. With this configuration, variable damping and stiffness vibration control is simultaneously achieved by varying a small current to the MR dampers. This paper presents a theoretical and experimental analysis of a two degree-of-freedom system that is controlled by the MR dampers. Five different control schemes involving the variable damping and stiffness are explored. The time and frequency responses of the two degree-of-freedom system to a random input show that combined variable damping and stiffness control provides the best vibration isolation over a frequency range spanning the system’s two structural vibration modes. The experimental results agree well with the theoretical analysis.

To explore the addressed issue of closed-loop vibration control using semi-active magneto-rheological (MR) fluid damper, an innovative control algorithm based on feedback of acceleration response at several points along stay cable for active/semi-active control of stay cables is firstly proposed in the present paper. Theoretical analysis, laboratory investigation, and in-situ tests are conducted in this study to verify the proposed control algorithm. Moreover, this paper presents the negative stiffness characteristic of the combined stay cable/semi-active MR damper system. These investigations indicate that the semi-active MR damper can achieve much better mitigation efficacy than the other passive MR dampers and the proposed control algorithm is proved to be practical. The effect of the negative stiffness on response reduction is demonstrated by the improved energy dissipation ability of the damper due to the enhanced displacement of the stay cable at the location attached with the damper. Introduction In the past few decades, many control methods have been proposed and some have been implemented to mitigate the unaccepted stay cable vibration (Johnson, 2003). At present, semi-active dampers have been proven to be effective in many applications and can potentially achieve performance levels that are almost the same as comparable active devices. For stay cables vibration control incorporated with semi-active dampers, most of the existing control strategies are based on full-state feedback of generalized coordinates. However, the generalized displacements and velocities of the stay cable cannot be measured directly. Since accelerometers can readily provide reliable and inexpensive measurements of the stay cable accelerations at strategic points on a stay cable, development of control method based on acceleration feedback at limited locations along stay cable is an ideal solution to solve the addressed practical problem. Moreover, even though the characteristic of negative stiffness of active control of stay cable vibration has been observed by some researchers(Johnson, 2003), the effects of negative stiffness on the stay cable vibration control using active/semi-active dampers 2 has not been fully researched in the present literatures. In this paper, a control algorithm based on feedback of acceleration response at several points for active and semi-active control of mass-distributed dynamic systems, e.g. stay cables is firstly proposed. Using the proposed control algorithm, the vibration control for the stay cable model attached with one MR damper and a series of field tests are carried out to investigate the control efficacy achieved by different control strategies. These investigations address that the semi-active MR damper can achieve much better mitigation efficacy than other passive MR dampers and the proposed control algorithm is proved to be practicable and available. Moreover, the effect of the negative stiffness provided by semi-active MR dampers on response reduction of cables is theoretically and numerically demonstrated by the improved energy dissipation ability of the damper due to the enhanced displacement of the cable at the location attached with the damper. Control Algorithm Based on Acceleration Feedback at Several Locations Governing equation of the combined stay cable/MR damper system shown in Figure 1 is given as (Irvine, 1981) ) ( ) ( ) , ( ) , ( ) , ( ) , ( d s x x t u t x f t x v c t x v T t x v m − + = + ′ ′ − δ & & & (1) with the boundary conditions v(0,t)=v(l,t)=0 for all t .where v(x,t) is the transverse deflection of the cable, l is the length of the cable, T is the cable tension, m and c are the cable mass and viscous damping per unit length, respectively, xd is the distance of the installed MR damper position from the left end, us(t) is the transverse control force provided by the MR damper at location x= xd, f(x,t) is the distributed load along the cable. δ(.) is the Dirac delta function. Figure1. Combined stay cable/MR damper system The transverse deflection could be approximated using a finite series ) ( ) ( ) , ( ∑ = = r j j j x t q t x v 1 φ (2) where the φj(x) is a set of shape modal functions and continuous with piecewise continuous slope to satisfy the geometric boundary conditionsφj(0)= φj(l)=0. Utilizing the approximate series solution and a standard Galerkin approach, the motion equation of the cable-MR damper system in matrix form is written as ) ( ) ( f Kq q C q M q t u x s d φ + = + + & & & (3)

A semi-active magneto-rheological (MR) damper was experimentally investigated and compared to an original equipment manufacturer (OEM) damper for a passenger vehicle, by using a quarter car models. A full-scale two-degree-of-freedom quarter car experimental set-up was constructed to study the vehicle suspension. On-off skyhook controller and Fuzzy-Lyapunov skyhook controller (FLSC) were employed to control the input current for MR damper so as to achieve the desired damping force. Tests were done to evaluate the ability of MR damper for controlling vehicle vibration. Test results show that the semi-active MR vehicle suspension vibration control system is feasible. In comparison with OEM damper, on-off and FLSC controlled MR dampers can effectively reduce the acceleration of vehicle sprung mass by about 15% and 24%, respectively.

The current research work is directed to study and improve vehicle behavior during crashes. Hence, a crash-pitch controller integrated with Magneto-Rheological (MR) dampers implemented in both vehicle suspension system and front-end structure is designed and studied. The methodology of the work is based on modeling the vehicle dynamical attitude as a half-car mathematical model that is developed with 3 degrees of freedom (DOF), longitudinal, bounce, and pitch. The model is constructed to study the vehicle’s dynamic response in a full-frontal collision against a fixed barrier. Additionally, a fuzzy logic controller is developed to integrate the suspension MR dampers with another set of MR dampers implemented within the vehicle’s front-end structure. Four different vehicle cases were discussed and compared within the simulation results of the developed model. Moreover, the four mentioned cases can be clarified as first free-rolling, second replacing the vehicle’s conventional dampers with MR dampers, third implemented MR dampers within the vehicle’s front-end structure, finally the fourth case through the integration of MR dampers implemented within both front-end structure and suspension system. Hence, the fourth case was implemented through the augmentation of simultaneous crash-pitch controllers. The simulation results showed a noticeable improvement in the front-end structure deformation as it had been reduced. Moreover, the vehicle’s body attitudes had also been improved where pitch angle had been reduced as well as its settling time. Also, pitch acceleration had been reduced which benefits human body exposure.

A promising solution for semi-active vibration control of different dynamic systems is to use magnetorheological (MR) dampers. In the present study, the investigation focuses on developing a novel single and multi-coil self-powered magnetorheological (MR) damper system using electromagnetic induction (EMI) for seismic mitigation. The conventional MR dampers, which rely on external power sources, can be unreliable and impractical in earthquake-prone locations. Thus, the EMI device connected to the MR damper can be used as an effective and alternative power source for the MR damper, results in a self-powered system. The proposed energy-harvesting system is an MR damper placed above the top of the piston. The coil is wound around the piston, and the outer casing with a ferrite magnet is fixed. As the mechanical energy of the piston is converted into electrical energy, its self-tuning capacity is a perfect fit for structural vibration control applications. The MR damper is subjected to cyclic and time-history loading. At a maximum amplitude of 15 mm, the damper generated 1767.8 N for cyclic loading and -1780 N for earthquake loading, the El Centro earthquake 1940 is considered for the study. By placing EMI, the mechanical energy is converted into electrical energy and powers the damper to avoid external power. The experimental results showcase enhanced damping forces and adaptability, thereby establishing it as an innovative and effective it can be alternative to conventional MR dampers for vibration control in future

This paper presents the procedure used for design, fabrication, testing, and numerical modeling of a magnetorheological (MR) damper that is to be applied for vibration control in a 70-ton railcar. MR dampers are semiactive vibration control devices whose damping characteristics can be modified in real time by varying an applied current. Design parameters for the MR damper are estimated from those exhibited by a linear viscous damper that exerts the necessary force required to limit vertical vibrations of the rail truck within acceptable limits. An MR damper is fabricated by modifying the piston of a standard hydraulic damper to function as a solenoid. The assembled MR damper is tested in a uniaxial testing machine by subjecting it to sinusoidal and random displacements while simultaneously varying the current flowing in the solenoid. A variable magnetic field is applied to the MR fluid that fills the damper cavity and the resisting force exerted by the damper is recorded. Data collected in the laboratory are used to train a fuzzy model of the MR damper that characterizes its behavior. Results indicate that a fuzzy model of the MR damper can predict its behavior with a sufficient degree of accuracy while requiring minimal computational time.

Due to low power consumption and fast response, magnetorheological (MR) dampers are widely used in various engineering applications. To enhance the performances, efforts have been made to increase the field dependent force with the same power consumption. However, the fluid viscous force is also increased significantly, which is undesirable in practical use. To tackle this problem, the focus of this paper is to design and test a new MR damper with micro-grooves for performance enhancement. First, the detailed design of the proposed MR damper is provided. A prototype of the new MR damper is fabricated. Silicon steel circular rings with thickness of 0.25 mm are installed around the damper piston to form two-layer micro-grooves. Experimental results of the two MR dampers without and with micro-grooves are then compared. The advantages of MR damper with micro-grooves over the one without micro-grooves are validated. The damping force and controllable force range of MR damper with micro-grooves are larger than the one without micro-grooves. When designing MR damper, making micro-grooves can also decrease the increment of fluid viscous force while keeping the same increase of field dependent force. With micro-grooves, the field dependent force is increased by 92.7% with the same power consumption, while the fluid viscous force is increased by 43%.

Magnetorheological (MR) dampers are a new generation of adjustable dampers that can generate large resistive forces against motion with low power. This feature is a unique characteristic that idealizes them for many applications including haptics. A haptic interface system is developed that includes a magnetorheological (MR) damper on the master side and a linear DC motor on the slave side. In this system, the slave motion follows the master and the force experienced by the slave is reflected to the master. The major challenge in this arrangement is control of the MR damper to create the desired resistive force. This paper investigates the different strategies for controlling the MR damper. In haptics, rather than the perfect tracking of a desired force, it is more convenient to generate a force in the master that is ‘similar’ to the actual force sensed by the slave. In addition, in many applications of MR dampers such as suspension systems, seismic response reduction, etc., perfect tracking is unneeded. Considering all of these factors, this paper proposes the concept of ‘similarity’ between the desired force and the resistive force of the MR damper. ‘Similarity’ means whenever the desired force is large, the resistive force should also be large, and whenever the desired force is small, the resistive force should then be small. Based on this concept, three controllers are applied and tested in both open loop and closed loop schemes: a gain controller, a fuzzy logic controller, and a lookup table controller. The results of these controllers are evaluated and compared to each other with respect to smaller time delays and smaller and smoother control inputs. In the absence of major differences in the results, the closed loop gain controller appeared to be a suitable choice for control because of its simple scheme and its ease of application.

Seat suspension is an important system to the ride comfort experience of a commercial vehicle's driver and passengers. The usage of magnetorheological (MR) dampers in seat suspension systems has been shown to offer a momentous enhancement regarding to the ride comfort. In the majority, research work on seat MR dampers has been emphasized on the control implementation but most of them were not quite appropriate for the semi-active and nonlinear hysteretic nature of the MR damper. This paper introduces a deeply investigation into the application of a semi-active MR damper for a truck seat suspension, enabling more efficient control algorithm. The proposed control system consists of a system controller that calculates the desired damper force using a fuzzy logic control (FLC) algorithm, and a signum function damper controller that provides an approximation of the command voltage required to track the desired damping force. A mathematical model and the equations of motion of a two degree-of-freedom semi-active seat suspension with an MR damper are derived and simulated using Matlab/Simulink software. The proposed semi-active MR seat suspension is compared to passive and uncontrolled seat suspensions for prescribed base displacements. These inputs are representative of the vibration of the body mass of a passive quarter-vehicle suspension under bump and random-profile road excitation. Seat travel distance and driver body acceleration are assessed as system performance criteria through bump and random road excitations, in order to quantify the efficiency of the proposed semi-active control technique. The simulated results indicate that the proposed FLC of the semi-active MR seat suspension provides a significant enhancement in ride comfort.

Magnetorheological (MR) damper is one of the most promising smart devices for dissipating seismic energy and reducing structural vibrations. The MR dampers with multiple coils are widely adopted to enhance the output damping forces and seismic performance. In order to study the dynamic characteristics of multicoil MR dampers from a micro to macro viewpoint, a three-coil MR damper was designed and manufactured in this paper. The performance tests of the three-coil MR damper under different excitation currents, displacement amplitudes, frequencies, and coil combinations were conducted. Assuming that the distance between two adjacent ferromagnetic particles meets chi-square distribution, the two-column micromodel for the MR fluid was modified by introducing a distribution parameter. The modified MR fluid micromodel was verified by comparing the damping forces calculated by this model with experimental data. Combining the modified micromodel for the MR fluid and the double-sigmoid model for MR dampers, a mathematical model for the three-coil MR damper was proposed. The microstructure-based sigmoid model considers the effects of yield shear stress of the MR fluid and internal magnetic induction intensity on the damping force. The comparison of the proposed model and the performance test data shows that the microstructure-based sigmoid model can finely describe the dynamic characteristics and magnetic saturation properties of the three-coil MR damper under different excitation currents and loading conditions, which provides a good basis for control strategies and dynamic analysis of structures with multicoil MR dampers.

This paper examines the effect of an electromagnetically optimized magnetorheological (MR) damper for vehicle suspension on vibration control performance. In order to achieve this goal, a cylindrical MR damper that satisfies design specifications for a middle-sized commercial passenger vehicle is designed using an optimization methodology. The optimization problem is to find the optimal geometric dimensions of the electromagnetic circuit for the MR damper in order to maximize the damping force. A first-order optimization method using commercial finite element method (FEM) software is adopted for the constrained optimization algorithm. After manufacturing the MR damper with optimally obtained design parameters, its field-dependent characteristics are experimentally evaluated. The effect of the optimal MR damper on suspension control is then investigated using a quarter-vehicle test facility. Control performances such as vertical acceleration, suspension travel, and power consumption are evaluated and compared between the initial and optimal dampers. In addition, vibration control performances of the optimal MR damper are experimentally evaluated under bump and random road conditions and presented in both time and frequency domains.

This study presents hysteresis modelling and damping force control of the frictionless magnetorheological (MR) damper for semiconductor manufacturing stage. The vibration sources of the semiconductor stage can be classified as two. The one is environmental vibration from the floor, and the other is transient vibration occurred from the stage moving. The transient vibration has serious adverse effect to the process because the vibration scale is quite larger than other vibrations. Therefore, in this research, the semi-active MR damper which can control the transient vibration is devised. In addition, the stage needs to be isolated from tiny vibration to achieve high grade vibration level. At the high frequency range, MR damper acts like a rigid body if the dry friction exists. So the tiny vibration is transferred to the stage directly. Therefore, a dry friction of the MR damper must be removed. In order to achieve this goal, a frictionless MR damper is originally designed. After then, a designed MR damper is manufactured and it's damping force characteristics and hysteresis behaviors are evaluated by experiment. The biviscous hysteresis model of MR damper is formulated and its accuracies are evaluated. Finally, damping force control performances using the hysteresis model is experimentally evaluated.

CHARACTERIZATION OF RHEOLOGICAL PROPERTIES OF NOVEL MAGNETORHEOLOGICAL FLUIDS