Large-scale MR fluid dampers: modeling and dynamic performance considerations

Abstract

The magnetorheological (MR) damper is one of the most promising new devices for structural vibration reduction. Because of its mechanical simplicity, high dynamic range, low power requirements, large force capacity and robustness, this device has been shown to mesh well with application demands and constraints to offer an attractive means of protecting civil infrastructure systems against severe earthquake and wind loading. In this paper, an overview of the essential features and advantages of MR materials and devices is given. This is followed by the derivation of a quasi-static axisymmetric model of MR dampers, which is then compared with both a simple parallel-plate model and experimental results. While useful for device design, it is found that these models are not sufficient to describe the dynamic behavior of MR dampers. Dynamic response time is an important characteristic for determining the performance of MR dampers in practical civil engineering applications. This paper also discusses issues affecting the dynamic performance of MR dampers, and a mechanical model based on the Bouc–Wen hysteresis model is developed. Approaches and algorithms to optimize the dynamic response are investigated, and experimental verification is provided.

Introduction

Over the past several decades, much attention has been given to the use of active control in civil engineering structures for earthquake hazard mitigation. These types of control systems are often called protective systems and offer the advantage of being able to dynamically modify the response of a structure in order to increase its safety and reliability. Although we are now at the point where active control systems have been designed and installed in full-scale structures, the engineering community has yet to fully embrace this technology. This lack of acceptance stems, in part, from questions of cost effectiveness, reliability, power requirements, etc.

In contrast, passive control devices, including base isolation, metallic yield dampers, friction dampers, viscoelastic dampers, viscous fluid dampers, tuned mass dampers and tuned liquid dampers, are well understood and are an accepted means for mitigating the effects of dynamic loadings [1]. However, passive devices have the limitation of not being capable of adapting to varying usage patterns and loading conditions.

An alternative approach—offering the reliability of passive devices, yet maintaining the versatility and adaptability of fully active systems—is found in semi-active control devices. According to the presently accepted definition, a semi-active control device is one which cannot input energy into the system being controlled [2]. Examples of such devices include electrorheological [3], [4], [5], [6], [7] and magnetorheological fluid dampers [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], variable orifice dampers [21], [22], [23], [24], [25], friction controllable isolators and dampers [26], [27], [28], [29], [30], [31], and variable stiffness devices [32], [33], [34], [35], [36], [37]. In contrast to active control devices, semi-active control devices do not have the potential to destabilize the structure (in the bounded input-bounded output sense), and most require little power to operate. Recent studies indicate that semi-active dampers can achieve the majority of the performance of fully active systems [10], [12], [13], [17], [38], [39], [40], thus allowing for the possibility of effective response reduction during both moderate and strong seismic activities. For these reasons, significant efforts have been devoted to the development and implementation of semi-active devices.

This paper presents results for the large-scale development of a specific class of semi-active control devices, magnetorheological (MR) dampers, for civil engineering applications. These devices overcome many of the expenses and technical difficulties associated with semi-active devices previously considered.