ABSTRACT:

The magnetorheological (MR) dampers have been used to reduce the vibration in truck seats in the auto industry, to minimize the damage to civil engineering structures due to seismic loads, and etc. Recently some researchers introduce MR dampers into the offshore industry, mainly focusing on the dynamic response control of jacket platforms and its potential application in the riser system of floating offshore platforms. In this paper, a newly proposed inverse dynamic model of MR dampers is initially applied to a one-story building under the El-Centro earthquake. This model can be employed to predict the voltage/current of MR dampers to track the optimal/desired damping force by the Linear Quadratic Regulator (LQR) method. Different weighting factors (Q, R) for LQR method are selected to study MR damper's performance, assuming that the structures are exposed to various earthquake loads. Further, the dynamic response control of a jacket platform using the 20-ton large-scale MR dampers is also investigated. Both the earthquake loads and ice loads are considered. The inversely identified evolutionary variables are estimated to study the hysteretic behavior of MR fluids.

INTRODUCTION

Jolly et al. (1999) presented and discussed the properties and applications of several commercial magnetorheological (MR) fluids. It was summarized that the formulation of MR fluids involved the optimal balancing of properties for particular application. Carlson et al. (2002) further discussed the problem of In-Use-Thickening (IUT) that MR fluids thicken progressively until they become unworkable paste after a long-term use, so the durability and life of MR fluids were found to be a significant barrier. Therefore, good MR fluids depend on the type of device, their working condition exposed to and other factors. In civil engineering, lab tests have demonstrated MR damper's effectiveness in structural control (Spencer et al., 1997; Jansen and Dyke, 2000; Yi et al., 2001).

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