Magnetorheological Damper With Micro-Grooves: Design and Experiment

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)

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.

Magneto-rheological (MR) damper is a typical non-linear actuator. The nonlinear relationship between the input and the output of MR damper should be characterized accurately in order to produce a required control action supplied by MR damper. The challenges of the conventional parametric model are the time-consuming and the requirement of complex parameter identification for MR damper. In this paper, a non-parametric model of MR damper based on the adaptive neuro-fuzzy system theory is presented to overcome the drawbacks of the conventional parametric model. This non-parametric model is developed by means of two adaptive neural fuzzy sub-systems which are designed to describe the nonlinear relationship in MR damper successfully. One sub-system is used to characterize the dependence of the damping force on velocity and acceleration, the other sub-system is used to characterize the dependence of the damping force level on the control voltage. The proposed non-parametric model is identified by experimental results. Furthermore, the accuracy of the model is investigated and evaluated. The model supplies a key technical support to achieve excellent control performances for semi-active suspension systems with MR dampers in vehicle.

In this paper, a new current control algorithm has been proposed in order to control the current provided into a coil which produces a magnetic field in the MR (magneto-rheological) damper. The MR (magneto-rheological) damper is able to control a damping coefficient of the fluid through an orifice by using the MR fluid which has a characteristic of viscosity variation according to inducted current. In general, The MR CDC (continuous damping control) damper has faster response time than other ones. However, the MR damper has disadvantage of time delay according to input command due to very large inductance of internal coil. A new robust lead compensation control algorithm has been to overcome the above disadvantage of the MR damper. The proposed control algorithm is also able to provide more robust current control performance even under variation of the coil resistance induced from temperature variation.

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.

Magnetorheological (MR) dampers are used for semi-active vibration control of various dynamic systems. Existing MR dampers are usually cylinder-piston based design, which may limit the shapes and have constraints to the design of MR devices. In this paper, we propose a new MR-fluid working operation, in which MR fluids work between gear transmissions. This operation could provide more design flexibility. A prototype of the regenerative damper with MR fluids working between gear transmissions was designed, fabricated, and tested. This MR damper has the capability of power generation and velocity sensing. The feasibilities of the controllable MR damping force, power generation and velocity sensing are experimentally verified. The results of this research would be beneficial to advance the design and multiple functions of MR dampers while not limited to traditional piston-type design.

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.

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.

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.

The smart behavior of magneto-rheological (MR) fluid is used in the present work in designing, experimentally characterizing and analyzing a MR damper for automotive application using the twin-tube damper concept. A commercially available passive damper of a passenger van was tested to find the characteristic damping requirement of the vehicle. With this as reference, a twin-tube MR damper working in valve mode was designed and fabricated. The magnetic flux density induced in the fluid flow gap is maximized using Taguchi analysis and finite element method magnetics (FEMM) software. The FEMM results are validated by verifying with results obtained analytically using electromagnetic circuit theory. The MR damper filled with commercially available MR fluid was experimentally tested in damper testing machine. The results demonstrate that the force developed by the MR damper is indeed increasing with the value of the current supplied. At various frequencies of input oscillation, the energy dissipated by the MR damper in a single cycle increases significantly with current supplied. The novelty of this work is that a twin-tube MR damper working in valve mode was designed as a replacement for the passive damper used in a passenger van. The MR damper thus developed is capable of producing practical levels of damping force at actual operating frequencies and amplitudes of the passive damper in the passenger van. For further analysis, the behavior of the MR damper is modeled by using the Bouc–Wen model for hysteretic systems. A proportional–integral–derivative controller is used to track the desired damping force in time domain to demonstrate the application of the MR damper in a semi-active suspension system.

Magnetorheological (MR) dampers, renowned for their tunable mechanical properties and energy dissipation capabilities, have been widely implemented in various vibration control systems. Nonetheless, the preparation and infusion process of MR fluids inherently entails the presence of trapped air, and sealing deficiencies can cause fluid leakage during operation, thereby leading to fluid deficiency within the damper’s chamber. Fluid deficiency induces a force lag phenomenon, substantially undermining the damping performance of MR dampers, especially for multi-coil dampers where multiple steps internally restrict the trapped airflow. Existing experimental investigations and mechanical models of MR dampers inadequately consider the force lag phenomenon in fluid-deficient multi-coil MR dampers under multiple modes. Addressing this issue, this study focuses on the experimental investigation and dynamic modeling of the force lag phenomenon in multi-coil MR dampers induced by fluid deficiency. Firstly, performance tests were conducted on a tri-coil MR damper, contrasting force lag phenomenon under varied loading conditions. A dynamic mathematical model was then proposed to characterize this, comprising a series connection of nonlinear spring and hyperbolic tangent elements, in parallel with a damping component, designed to predict multi-coil MR damper behavior under fluid deficiency. Through analyzing experimentally derived force-lag curves, model parameters were determined, leading to the development of a force-lag model for multi-coil fluid-deficient MR dampers. Model calculations were compared with experimental results to verify its efficacy in depicting the altered mechanical properties of multi-coil MR dampers influenced by fluid deficiency. This research furnishes a foundational model for explaining and forecasting the damping performance of multi-coil fluid-deficient MR dampers, facilitating the expanded application of MR damping technology across diverse disciplines.

Magnetorheological (MR) damper has received a great deal of attention in the recent years. A new mechanical model---double sigmoid is proposed based on the experimental study of MR damper, and it can accurately describe the hysteresis nonlinear properties of MR damper. A 3-storey frame-shear wall structure model with an asymmetric stiffness distribution is considered, and multiple MR dampers are used to control this test structure. The simulation model of this test structure is built according to the coupled translation and torsion response, with and without MR dampers, based on Matlab/Simulink and hardware/software resources of dSPACE. Then the shaking table experiment has been carried out in Dalian University of Technology. It is found that the coupled translation and torsion response is significantly mitigated with MR dampers under different earthquake

This paper presents an optimal design of magnetorheological(MR) damper based on analytical methodology and finite element analysis. The proposed MR damper consists of MR valve and gas chamber. The MR valve is constrained in a specific volume and the optimization problem identifies geometric dimensions of the valve structure that maximize the pressure drop of the MR valve or damping force of the MR damper. In this work, the single-coil annular MR valve structure is considered. After describing the schematic configuration and operating principle of MR valve and damper, a quasi-static model is derived based on Bingham model of MR fluid. The magnetic circuit of the valve and damper is then analyzed by applying the Kirchoff' s law and magnetic flux conservation rule. Based on the quasi-static modeling and the magnetic circuit analysis, the optimization problem of the MR valve and damper is built. The optimal solution of the optimization problem of the MR valve structure constrained in a specific volume is then obtained and compared with the solution obtained from finite element method.

Magnetorheological (MR) damper is a prominent semi-active control device for earthquake response mitigation of structures. The most important topic for the intelligent MR structures is choosing the control current of MR damper quickly and accurately. The typical control strategy is on-off control strategy, while inherent time-delay and coarse control precision lie in this strategy. This article proposes a semi-active control strategy for restricting the MR structures efficiently, in which the genetic algorithm (GA) is adopted to search for the optimal feedback control gain in time-delayed dynamic equations forming a GA controller, and next optimize the control current of the MR damper accurately by a series of GA procedure. The GA strategy has the capability to effectively control the MR structure involving time delay and adjusting for controlled current of the MR damper timely and accurately. Accordingly, numerical examples are used to testify that the feedback gain optimized by GA has the capability to reduce a given objective response dramatically. In addition, a comparison between GA controller and LQR controller indicates that the proposed approach performs much better than LQR method, especially in time-delay systems. Finally, simulation results for a seismically excited structure subjected by the MR damper are presented to verify that the semi-active strategy using GA is predominant in mitigating the dynamic structure efficiently. The strategy and the results presented will also throw light on the development and control of other novel structures.

Magneto-rheological (MR) fluid technology has significantly developed during the past decades. The application of MR fluids has proliferated in various engineering fields with the development of MR fluid-based devices, especially MR fluid dampers. MR dampers are semi-active devices used for vibration reduction in many engineering applications. The MR dampers could offer an outstanding capability in semi-active vibration control due to excellent dynamical features such as fast response, low power consumption, and simple interfaces between electronic input and mechanical output. Modelling of MR damper is crucial in describing MR damper’s behaviour. It is critical to comprehend the dynamic behaviour of these devices, as nonlinear hysteresis is a rather complex phenomenon. The Modified Bouc-Wen model represents the MR damper mathematically since this model is capable of performing as precisely as the non-parametric model. The Modified Bouc-Wen model parameters are damper dependent and must be defined for further simulation studies before utilising the damper. Validation of MR damper experimentally is one of the tasks required to confirm the parametric model performance. The specified parameters are believed to be worthwhile for this MR damper’s use in further studies of real-time semi-active (SA) suspension systems. The small values of percentage difference for force (0.5-3.5%) indicate that the parameters implemented in the Modified Bouc-Wen model accurately portray the characteristics and behaviour of the MR damper.