Performance tests and microstructure‐based sigmoid model for a three‐coil magnetorheological damper

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 was a kind of smart instrument, and it was very suitable for the semi-active control. In this research, a large-scale MR damper working in the shear mode of the MR fluid was developed to enhance the mechanical properties of the shear wall. The influence of MR damper on the mechanical properties of the shear walls, such as stiffness, strength, ductility, and the energy dissipation capacity, had been researched. Firstly, both the model of MR damper and shear wall were established to optimize the properties of the MR damper and shear wall. Then, three different concrete shear walls were fabricated, which were reinforced by carbon fiber-reinforced polymer (CFRP) bars (W-1), CFRP bars and MR dampers (W-2), and steel strands and MR dampers (W-3), respectively. The mechanical properties of the specimens were experimentally researched and analyzed. The experimental results showed that the ductility, the ability to bear external loads, stiffness, and energy dissipation capacity of the shear walls could be enhanced by the MR damper simultaneously. Compared with W-1, the ductility, the ability to bear external loads, ultimate deformation, and energy-dissipation capacity of W-2 increased by 4.1%, 26.8%, 83.9%, and 35.8%, respectively. The residual deformation of the three shear walls was almost the same. The results indicated that the MR damper could enhance the mechanical properties of the shear walls and had no influence on the self-centering capacity of the shear walls at the same time.

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.

Most magnetorheological (MR) fluid dampers are designed as fixed-pole valve mode devices, where the MR fluid is forced to flow through a magnetically active annular gap. This forced flow generates the damping force, which can be continuously regulated by controlling the strength of the applied magnetic field. Because the size of the annular gap is usually very small relative to the radii of the annulus, the flow of the MR fluid through this annulus is usually approximated by the flow of fluid through two infinitely wide parallel plates. This approximation, which is widely used in designing and modeling of MR dampers, is satisfactory for many engineering purposes. However, the model does not represent accurately the physical processes and, therefore, expressions that correctly describe the physical behavior are highly desirable. In this paper, a mathematical model based on the flow of MR fluids through an annular gap is developed. Central to the model is the solution for the flow of any fluid model with a yield stress (of which MR fluid is an example) through the annular gap inside the damper. The physical parameters of a MR damper designed and fabricated at the University of Manchester are used to evaluate the performance of the damper and to compare with the corresponding predictions of the parallel plate model. Simulation results incorporating the effects of fluid compressibility are presented, and it is shown that this model can describe the major characteristics of such a device—nonlinear, asymmetric, and hysteretic behaviors—successfully.

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)

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.

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%.

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.

To advance the state of the art of physical-principle-enhanced hybrid artificial neural network (ANN) modeling, network configurations with parallel modules (PMNN) reflecting the structural information of the physical principles have been developed (Cao, 2001). In this paper, the PMNN configuration is applied to develop a scalable and invertible dynamic magneto-rheological (MR) fluid damper model. To advance the state of the art and address issues of the current ANN-based MR damper models found in the open literature, two ANN-based MR damper models are developed in this study. The first one is a conventional first-principle-enhanced hybrid neural network model (defined as the baseline model in the current study) that improves upon the previous ANN-based MR damper models by introducing feedback loops to represent the dynamic behaviors of the MR damper. A PMNN-based MR damper model is then derived to further improve the control-input-output scalability and realize the invertible model concept. “Input-output scalability” refers to the model's capability to accurately estimate the system response with input profiles significantly different from the training data. “Invertible model” means that the resultant forward model can be directly transformed into an inverse model through a simple algebraic operation. The network training/testing results indicate that while both models provide satisfactory performance, the PMNN model outperforms the baseline model by showing superior control-input-output scalability. The candidacy of PMNN as a control-oriented actuator modeling tool is further strengthened by the fact that it is invertible, in other words, the inverse model with desired force as input and the control signal—voltage as output can be easily established by algebraically manipulating the forward model. This study indicates that PMNN, as a scalable and invertible dynamic modeling tool, is feasible for developing system-design-oriented models of vibration control purposes.

This paper investigates how magnetorheological (MR) damper parameters affect the dynamic response of a full-vehicle suspension system in much detail. The constitutive mechanical model and characteristics of MR damper are firstly obtained and analyzed, which preferably describes the physical parametric features of MR damper. To simplify the impact analysis model, a full-vehicle control model with the PID decoupling controller based on the inverse model for MR damper is established. In line with the above developed full-vehicle model, the impact analysis of input current on the suspension dynamic responses is obtained by updating the equivalent damping coefficient of MR damper. The effect of MR damper parameters on the dynamic responses is investigated based on the RMS of the percentage-based slope, and its wear effect caused by the friction loss in practical application is also discussed. The experimental results show that the piston diameter and cylinder inner diameter have greater influence on the dynamic responses than other influence parameters include the coil turns, effective piston length and piston rod diameter. In contrast, the apparent viscosity of MR fluids has little influence on the dynamic responses. In addition, the MR semi-active suspension has better stability than the passive suspension when parameter perturbation occurs in the suspension system. It is necessary to ensure that MR damper has the suitable maximum output damping force and large enough dynamic range simultaneously.

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.

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 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

On marine vessels, delicate instruments such as navigation radars are normally mounted on ship masts. However the vibrations at the top of mast where the radar is mounted often cause serious deterioration in radar-tracking resolution. The most serious problem is caused by the rotational vibrations at the top of mast that may be due to wind loading, inertial loading from ship rolling and base excitations induced by the running propeller. This paper presents a method of semi-active vibration control using magneto-rheological (MR) dampers to reduce the rotational vibration of the mast. In the study, the classical optimal control algorithm, the independent modal space control algorithm and the double input - single output fuzzy control algorithm are employed for the vibration control. As the phenomenological model of an MR damper is highly nonlinear, which is difficult to analyse, a back- propagation neural network is trained to emulate the inverse dynamic characteristics of the MR damper in the analysis. The trained neural network gives the required voltage for each MR damper based on the displacement, velocity and control force of the MR damper quickly. Numerical simulations show that the proposed control methods can effectively suppress the rotational vibrations at the top of mast.