Ho-Guen Lee

Dynamic properties of an ER fluid under shear and flow modes

This paper presents the field-dependent Bingham and response characteristics of an electro-rheological(ER) fluid under shear and flow modes. Two different types of electroviscometers are designed and manufactured for the shear mode and the flow mode, respectively. An ER fluid consisting of soluble chemical starches (particles) and silicone oil is made and its field-dependent yield stress is experimentally distilled at two different temperatures using the electroviscometers. Time responses of the ER fluid to step electric fields are also evaluated under two operating modes. A single-disc type ER clutch, which is operated under the shear mode, is adopted and its measured transmitted torque is compared with the predicted ones from Bingham models obtained at two different operating modes. In addition, the field-dependent damping force of a cylindrical ER damper, which is operated under the flow mode is measured and compared with the predicted ones from Bingham models obtained under both the shear and the flow modes.

Bracing Systems for Installation of MR Dampers in a Building Structure

In this study, the effects of bracing systems for installing a magnetorheological (MR) damper in a building structure on seismic response control are analytically and experimentally investigated. The performance of the toggle brace system which enables the installed damper to generate larger effective control force due to its response amplification mechanism than a conventional brace system is evaluated. In addition, the nonlinear velocity amplification factor for the toggle brace—MR damper system and the effect of toggle configuration are considered. Analytical and experimental results show that control performance can be enhanced using the toggle brace system especially for the case in which the MR damper installed using non-amplifying brace system cannot provide sufficient response reduction.

PERFORMANCE COMPARISON OF MR DAMPERS WITH THREE DIFFERENT WORKING MODES: SHEAR, FLOW AND MIXED MODE

In this work, three different magneto-rheological(MR) dampers, which are applicable for vibration control of a multi-story structure, are devised and their performance characteristics are compared. As a first step, the schematic configurations of the shear, flow, and mixed mode MR dampers are described with design constraints. The analytical models to predict the field-dependent damping forces are derived for each type and their damping forces are evaluated. The field-dependent damping forces are compared in terms of the damping force magnitude and the mixed-mode type of MR damper is chosen as an optimal candidate for the vibration control of the multi-story structure. An appropriate size of the mixed mode MR damper is manufactured and its field-dependent damping characteristics are evaluated in time domain. In addition, the displacement vs. damping force cycles of the piston are observed at various field intensities.

Design and control of a hybrid mount featuring a magnetorheological fluid and a piezostack

In this study, a hybrid mount featuring a magnetorheological (MR) fluid and a piezostack is devised to reduce vibrations occuring in dynamic systems which are operated in a wide frequency range. An MR fluid is adopted to improve isolation performance at resonant low frequencies, whereas a piezostack actuator is adopted for performance improvement at non-resonant high frequencies. As a first step, a passive rubber part is manufactured and its dynamic characteristics are experimentally evaluated. By adopting the MR fluid and the piezostack, semi-active and active actuating mechanisms are devised and their mathematical models are derived. In particular, the magnetic circuit for MR operation is optimally designed via finite element analysis. After evaluating the dynamic characteristics of the manufactured MR device and inertial piezostack actuator, the proposed hybrid mount is then established by integrating them with the rubber part. Subsequently, a vibration control system is constructed using the proposed hybrid mount, and a sliding mode controller (SMC) is designed to attenuate the vibrations transmitted from the base excitation. Control performances of the proposed mount are experimentally evaluated in time and frequency domains.

Vibration Control of MR Suspension System Considering Damping Force Hysteresis

This paper presents vibration control performances of a commercial magnetorheological(MR) suspension via new control strategy considering hysteresis of the field-dependent damping force of MR damper. A commercial MR damper which is applicable to high class passenger vehicle is adopted and its field-dependent damping force is experimentally evaluated. Preisach hysteresis model for the MR damper is identified using experimental first order descending(FOD) curves. Then, a feed-forward compensation strategy for the MR damper is formulated and integrated with a linear quadratic regulation(LQR) feedback controller for the suspension system. Control performances of the proposed control strategy for the MR suspension is experimentally evaluated with quarter vehicle test facility.

A study on the performance estimation of semi-active suspension system considering the response time of electro-rheological fluid

This paper deals with the performance estimation of the semi-active suspension system considering the response time of electro-rheological fluid (ERF)-based damper. The Bingham characteristics and response time of ERFs are obtained experimentally. Then the ER damper is applied to the quarter car model and its performance using sky-hook control algorithm is compared to the system using conventional damper through computer simulation. As simulation results, the gain is improved above 50% but it is deteriorated rapidly with the increase of response time. So it is proved that the response time as well as the yield stress of ERFs is the dominant factor to design the semi-active suspension system using the ER damper.

Performance Analysis with Different Tire Pressure of Quarter-vehicle System Featuring MR Damper

ABSTRACT This paper presents performance analysis of a quarter-vehicle magneto-rheological(MR) suspension system with respect to different tire pressure. As a first step, MR damper is designed and manufactured based on the optimized damping force levels and mechanical dimensions required for a commercial mid-sized passenger vehicle. After experimentally evaluating dynamic characteristics of the manufactured MR damper, the quarter-vehicle MR suspension system consisting of sprung mass, spring, tire and the MR damper is constructed in order to investigate the ride comfort. After deriving the equations of the motion for the proposed quarter-vehicle MR suspension system, vertical tire stiffness with respect to different tire pressure is experimentally identified. The skyhook controller is then implemented for the realization of quarter-vehicle MR suspension system. Ride comfort characteristics such as vertical acceleration RMS and weighted RMS of sprung mass are evaluated under various road conditions.

PRELIMINARY DESIGN PROCEDURE OF MR DAMPERS FOR CONTROLLING SEISMIC RESPONSE OF BUILDING STRUCTURES

In this paper, a preliminary design procedure of magnetorheological (MR) dampers is developed for controlling building response induced by seismic excitation. Hysteretic biviscous model which is simple and can describe the hysteretic characteristics of MR damper, is used for parametric studies. The capacity of MR damper is determined as a portion of not the building weight but the lateral restoring force. A method is proposed for the optimal placement and number of MR dampers, and its effectiveness is verified by comparing it with the simplified sequential search algorithm. Numerical results indicate that capacity, number and placement can be reasonably determined using the proposed design procedure.

Preview control of vehicle suspension system featuring MR shock absorber

This paper presents control performance evaluation of optimal preview control algorithm for vehicle suspension featuring MR shock absorber. The optimal preview control algorithm has several advantages such as high control performance over that which is best for a non-preview system. In order to achieve this goal, a commercial MR shock absorber, Delphi MganerideTM, which is applicable to high class passenger vehicle, is adopted and its field-dependent damping force and dynamic responses are experimentally evaluated. Then the governing equation of motion for the full-vehicle model is established and integrated with the MR shock absorber. Subsequently, optimal controller with preview control algorithm is formulated and implemented for vibration suppression of the car body. Control performance of the preview controller is evaluated for the full-vehicle model under random road condition. In addition, the control performances depending on preview distances are evaluated.

Ride comfort characteristics with different tire pressure of passenger vehicle featuring MR damper

This paper presents ride comfort characteristics of a quarter-vehicle magneto-rheological (MR) suspension system with respect to different tire pressure. As a first step, controllable MR damper is designed and manufactured based on the optimized damping force levels and mechanical dimensions required for a commercial mid-sized passenger vehicle. After experimentally evaluating dynamic characteristics of the manufactured MR damper, the quarter-vehicle suspension system consisting of sprung mass, spring, tire and the MR damper is constructed in order to investigate the ride comfort. After deriving the equations of the motion for the proposed quarter-vehicle MR suspension system, vertical tire stiffness with respect to different tire pressure is experimentally identified. The skyhook controller is then implemented for the realization of quarter-vehicle MR suspension system. Ride comfort characteristics such as vertical acceleration RMS of sprung mass are evaluated under bump road condition and presented in time domain.