Zhaochun Li

Magnetic Circuit Design and Multiphysics Analysis of a Novel MR Damper for Applications under High Velocity

A novel magnetorheological (MR) damper with a multistage piston and independent input currents is designed and analyzed. The equivalent magnetic circuit model is investigated along with the relation between magnetic induction density in the working gap and input currents of the electromagnetic coils. Finite element method (FEM) is used to analyze the distribution of magnetic field through the MR fluid region. Considering the real situation, coupling equations are presented to analyze the electromagnetic-thermal-flow coupling problems. Software COMSOL is used to analyze the multiphysics, that is, electromagnetic, thermal dynamic, and fluid mechanic. A measurement index involving total damping force, dynamic range, and induction time needed for magnetic coil is put forward to evaluate the performance of the novel multistage MR damper. The simulation results show that it is promising for applications under high velocity and works better when more electromagnetic coils are applied with input currents separately. Besides, in order to reduce energy consumption, it is recommended to apply more electromagnetic coils with relative low currents based on the analysis of pressure drop along the annular gap.

Analysis and compensation methods for time delays in an impact buffer system based on magnetorheological dampers

Magnetorheological dampers have been widely studied as versatile real-time actuators for solving vibration problems in various structures and systems. However, the inherent time delay problem of magnetorheological actuators may cause performance degradation of semi-active control systems. The primary purposes of this article are to provide a comprehensive analysis on the time delay of an impact buffer system based on a magnetorheological damper and to propose compensation methods to reduce the time delay. To this end, this study evaluated the electromagnetic circuit in the magnetorheological damper and designed an advanced correcting circuit to improve the response time. The simulation results show that the proposed circuit reduces the time delay by 5 ms. Using a magnetorheological buffer system setup, its force response times were tested. The experimental results show that the electromagnetic circuit plays a significant role in the time delay and it is highly dependent on the effectiveness of the electric parts of the control hardware. Furthermore, a proportional–integral–derivative controller is able to reduce the time delay and improve the dynamic performance of the magnetorheological impact buffer system.

Experimental analysis of separately controlled multi-coils on the performance of magnetorheological absorber under impact loading

A magnetorheological absorber is capable of actively adapting any gun recoil condition by means of controlled Coulomb force. The objective of multi-coil magnetorheological absorber with individual input currents is to mitigate the peak force transferred to the buffer structure during bullet firing, and thus to increase the structural fatigue life. This article investigates various cases by applying random combinations of input currents to the magnetic coils. The impact tests were conducted by obtaining and analyzing the force, displacement, and velocity. As a reference, input currents with equivalent magnitude are considered statistically, in terms of average peak force and occurrence time. The experimental results show that separately controlled multi-coils contribute to the magnitude and occurrence time of peak force significantly. Furthermore, to reduce peak forces, a simple open-loop control strategy was proposed and validated effectively by the experimental results.

Transient multi-physics analysis of a magnetorheological shock absorber with the inverse Jiles–Atherton hysteresis model

This paper presents multi-physics modeling of an MR absorber considering the magnetic hysteresis to capture the nonlinear relationship between the applied current and the generated force under impact loading. The magnetic field, temperature field, and fluid dynamics are represented by the Maxwell equations, conjugate heat transfer equations, and Navier–Stokes equations. These fields are coupled through the apparent viscosity and the magnetic force, both of which in turn depend on the magnetic flux density and the temperature. Based on a parametric study, an inverse Jiles–Atherton hysteresis model is used and implemented for the magnetic field simulation. The temperature rise of the MR fluid in the annular gap caused by core loss (i.e. eddy current loss and hysteresis loss) and fluid motion is computed to investigate the current–force behavior. A group of impulsive tests was performed for the manufactured MR absorber with step exciting currents. The numerical and experimental results showed good agreement, which validates the effectiveness of the proposed multi-physics FEA model.

An improved polynomial dynamic model of a magnetorheological fluid damper under impact loadings

With fast response time and adjustable damping properties, magnetorheological (MR) dampers have shown their capabilities in reducing vibration of structures when subjected to impact loadings. In order to achieve the best performance of MR dampers for vibration control, a suitable semi-active control method is desired. Understanding and modeling of the dynamic behavior of MR dampers is crucial in development of control strategies. This paper presents both theoretical and experimental studies on modeling MR dampers under impact loadings. An improved polynomial model with simple form, which is easy to be solved inversely and suitable for implement in real time control, is proposed. A group of experimental tests are performed to evaluate the accuracy of the proposed model. The results show that the proposed model can well describe the relationship of damper velocity and its output force during buffering motion.

Research on Time Delay of MR Buffer System Under Impact Load

The primary purpose of this paper is to provide a comprehensive review on the time delay of impact MR buffer system. The phenomenon of time delay which occurs in most of the MR buffer systems has been given little attentions especially in the applications where little time delay is demanded. Furthermore, the methods of reducing time delay have not been discussed in detail. So, in this study, several efforts have been made to decrease or even eliminate the phenomenon of time delay. Firstly, we analyzed two kinds of power supply sources and coil winding patterns. Next, an advanced correcting circuit was designed and the parameters of transfer function were determined by experimental data. The results show that, compared with the original circuit, it only takes 5ms to achieve 95% of the final state after correction, which increases 75% immediately. Furthermore, to evaluate the effect of compensation control strategy on time delay, the adaptive Smith compensation control was adopted and tested. Using the open on-off control strategy, four operating start times of current were applied, ranging from 0 to 300ms in increments of 100ms. The results show that the original maximum time delay is more than 150ms and it can be reduced to less than 50ms by adaptive smith compensation. Further analysis illustrates that decreasing time delay improves the dynamic performance of MRD in the buffer process, such as decreased overshoot, less fluctuation etc.© 2013 ASME

Controllability analysis and testing of a novel magnetorheological absorber for field gun recoil mitigation

This paper aims to analyze the effects of combined working coils of magnetorheological (MR) absorber on the shock mitigation performance and verify the controllability of MR absorber as applied in the recoil system of a field gun. A physical scale model of the field gun is established and a long-stroke MR recoil absorber with four-stage parallel electromagnetic coils is designed to apply separate current to each stage and generate variable magnetic field distribution in the annular flow channel. Based on dynamic analysis and firing stability conditions of the field gun, ideal recoil force-stroke profiles of MR absorber at different limiting firing angles are obtained. The experimental studies are carried out on an impact test rig under different combinations of current loading: conventional unified control mode, separate control mode and timing control mode. The fullness degree index (FDI) is defined as the quantitative evaluation criterion of the controllability of MR absorber during the whole recoil motion. The results show that the force-stroke profile of the novel MR absorber can approach the ideal curve within 25 degrees of the limiting firing angle through judicious exploitation of the adjustable rheological properties of MR fluid.

Heating of Long-Stroke Magnetorheological Fluid Damper

Magnetorhelogical (MR) dampers are gradually used in military devices for shock isolation and civil structures for suppressing earthquake-induced shaking and wind-induced vibrations because of their mechanical simplicity, high dynamic range, low power requirements, large force capacity and robustness. Since MR fluid dampers are energy-dissipating device, the issues of heat generation and dissipation is important. In this study, phenomenon of viscous heating and consequent temperature increase in a long-stroke MR damper are presented. In addition, a theoretical model is developed which predicts the temperature increase in the long-stroke MR damper. This model is solved numerically and a new coupling method was proposed to analyze the electromagnetic-thermal coupling problem on the basis of the mechanism of coupled field. Aim at the high frequency of piston head moving back and forth, as well as the changing current, the simulation model is established. The results show that the temperature effect on the damping force is significant and provide a theoretical basis and calculation method for the design and analysis of long-stroke MR damper.Copyright