A NEW STOCHASTIC OPTIMAL CONTROL STRATEGY FOR HYSTERETIC MR DAMPERS

A new stochastic optimal control strategy for randomly excited quasi-integrable Hamiltonian systems using magneto-rheological (MR) dampers is proposed. The dynamic be- havior of an MR damper is characterized by the Bouc-Wen hysteretic model. The control force produced by the MR damper is separated into a passive part incorporated in the uncontrolled system and a semi-active part to be determined. The system combining the Bouc-Wen hysteretic force is converted into an equivalent non-hysteretic nonlinear stochastic control system. Then It?o stochastic di?erential equations are derived from the equivalent system by using the stochastic averaging method. A dynamical programming equation for the controlled di?usion processes is established based on the stochastic dynamical programming principle. The non-clipping nonlin- ear optimal control law is obtained for a certain performance index by minimizing the dynamical programming equation. Finally, an example is given to illustrate the application and e?ectiveness of the proposed control strategy.

Earthquake response of asymmetric building with MR damper

Plan asymmetric buildings are very susceptible to earthquake induced damage due to lateral torsional coupling, and the corners of these systems suffer heavy damage during earthquakes. Therefore, it is important to investigate the seismic behavior of an asymmetric plan building with MR dampers. In this study, the effectiveness of MR damper-based control systems has been investigated for seismic hazard mitigation of a plan asymmetric building. Furthermore, the infl uence of the building parameters and damper command voltage on the control performance is examined through parametric study. The building parameters chosen are eccentricity ratio and frequency ratio. The results show that the MR damper-based control systems are effective for plan asymmetric systems.

Intelligent technology-based control of motion and vibration using MR dampers

Due to their intrinsically nonlinear characteristics,development of control strategies that are implementable and can fully utilize the capabilities of semiactive control devices is an important and challenging task.In this study,two control strategies are proposed for protecting buildings against dynamic hazards,such as severe earthquakes and strong winds,using one of the most promising semiactive control devices,the magnetorheological (MR) damper.The first control strategy is implemented by introducing an inverse neural network (NN) model of the MR damper.These NN models provide direct estimation of the voltage that is required to produce a target control force calculated from some optimal control algorithms.The major objective of this research is to provide an effective means for implementation of the MR damper with existing control algorithms.The second control strategy involves the design of a fuzzy controller and an adaptation law.The control objective is to minimize the difference between some desirable responses and the response of the combined system by adaptively adjusting the MR damper.The use of the adaptation law eliminates the need to acquire characteristics of the combined system in advance. Because the control strategy based on the combination of the fuzzy controller and the adaptation law doesn't require a prior knowledge of the combined building-damper system,this approach provides a robust control strategy that can be used to protect nonlinear or uncertain structures subjected to random loads.

Seismic response control of a complex structure using multiple MR dampers: experimental investigation

This paper presents an experimental investigation on semi-active seismic response control of a multi- story building with a podium structure using multiple magnetorheological (MR) dampers manipulated by a logic control algorithm.The experiments are performed in three phases on a seismic simulator with a slender 12-story building model representing a multi-story building and a relatively stiff 3-story building model typifying a podium structure.The first phase of the investigation is to assess control performance of using three MR dampers to link the 3-story building to the 12-story building,in which seismic responses of the controlled two buildings are compared with those of the two buildings without any connection and with rigid connection.The second phase is to investigate reliability of the semi-active control system and robustness of the logic control algorithm when 2 out of 3 MR dampers fail and when the electricity supply to MR dampers is completely stopped.The last phase is to examine sensitivity of semi-active control performance of two buildings to change in ground excitation.The experimental results show that multiple MR dampers with the logic control algorithm can achieve a significant reduction in seismic responses of both buildings.The proposed semi-active control system is of high reliability and good robustness.

MODELLING OF A NEW TYPE MR DAMPER

Applying the rule of laminar flow in the gap between two parallel disks, thetheoretical model of a new type MR damper is established, the damping characteristic and structuralcharacteristic of the MR damper are analyzed. Experimental results show that the model can reflectthe fundamental characteristics of the disk-gap MR damper.

A Novel Shear Mode MR Damper and Its Mechanical Performance

This paper presents a linear shear mod magneto-rheological(MR) damper which can be applied to vibration control system.The proposed MR damper featured by a small amount of MR fluid,absence of a gas chamber or diaphragm and piston with helix slotted.Because of the absence of a gas chamber or diaphragm,unnecessary damping force caused by gas compression is not generated.Magnitude and damping coefficient of damping force are two important indexes to evaluate performance of MR damper.The piston with helix slotted is developed based on mechanical analysis on rheological characteristics of MR damper,and the damping performance of MR damper with helix slotted piston is investigated through performance experiments and comparison with analytical simulation.The results indicate that helix slot may increase friction coefficient on surface of the piston,and improve the maximum damping force without reducing damping coefficient of the damper.The reflux of MR fluid may be increased by adjusting helix angle suitably,which avoids the settlement of MR fluid.

Studies on structural vibration control with MR dampers using μGA

A new approach to reducing the seismic response of spatial structures with magneto-theological （MR） dampers is presented in this paper. The Genetic Algorithm with small populations （μGA） is used to optimize the control for the MR dampers to reduce structural vibration, which is difficult to achieve using classical optimal control. The advantages of μGA are the use of global properties and that fewer conditions are required to obtain the optimal function. Numerical results demonstrate the effectiveness of the proposed method in reducing the seismic response of structures.

GENERATION OF ASYMMETRIC F-v CHARACTERISTICS FOR SYMMETRIC MR DAMPERS

An asymmetric damping force generation algorithm is originally proposed to yield the asymmetric force-velocity characteristics for the symmetric magneto-rheological （MR） dampers. The command current is formulated in an asymmetric manner to excite the symmetric MR dampers by employing the “on-off” control law in response to the direction of velocity, and a smooth modulation function is developed without phase shift to suppress strong transients in the damping forces caused by the current-switching discontinuity. The effectiveness of the proposed algorithm is evaluated by analyzing the dynamic responses of a quarter-vehicle suspension system with a symmetric MR-damper by modulating the command current into the asymmetric manner. The simulation results show that the proposed algorithm could achieve a better compromise between the conflicting requirements of the asymmetric damping force ratio and the force-velocity curve smoothness, and the asymmetric damping MR-suspension design can ideally improve the road holding and ride performances of vehicle motion. The proposed algorithm can be generally incorporated with a controller synthesis to realize an intelligent vehicle suspension design with the symmetric MR dampers.

基于未知风荷载作用下拉索振动位移的拉索MR阻尼器失效破坏的原位识别方法

MR阻尼器在长期服役过程中可能由于各种因素导致阻尼器失效破坏。现有的对MR阻尼器的性能识别多为离线方法,需将阻尼器从斜拉索上拆卸下来后进行人工检测。该文提出一种基于斜拉索在未知风荷载作用下振动位移,对在役失效无模型的MR阻尼器作用力进行原位在线识别的方法。首先,建立模态坐标下斜拉索-阻尼器系统运动方程及观测方程,并进行模态截断以减少未知变量的数量。然后,将模态风荷载建模为随机游走过程并加入系统的增广状态中,并视MR阻尼器的作用力视为作用在斜拉索上的‘附加未知输入’,采用最近提出的无直接反馈的平滑最小方差无偏Bayesian滤波,对结构增广状态和MR阻尼器作用力进行识别。通过识别数值模拟的MR阻尼器三种典型的失效破坏模式,验证所提方法的有效性。

Semi-active fuzzy control of Lali Cable-Stayed Bridge using MR dampers under seismic excitation

Seismic control of cable-stayed bridges is of paramount importance due to their complex dynamic behavior,high flexibility,and low structural damping.In the present study,several semi-active Fuzzy Control Algorithms(FCAs)for vibration mitigation of Lali Cable-Stayed Bridge are devised.To demonstrate the efficiency of the algorithms,a comprehensive nonlinear 3-D model of the bridge is created using OpenSees.An efficient method for connecting MATLAB and OpenSees is devised for applying FCAs to the structural model of the bridge.Two innovative fuzzy rulebases are introduced.A total of six different fiuzzy rule-bases are utilized.The efficiency of the FCAs is evaluated in a comparative manner.The performance of fuzzy control systems is also compared with a sky-hook and a passive-on system.Moreover,the sensitivity of efficiency of control systems to the peak ground acceleration is evaluated qualitatively.In addition,the effect of time lag is also investigated.This study thoroughly examines the efficiency of the FCAs in different aspects.Therefore,the results can be regarded as a general guide to design semi-active fuzzy control systems for vibration mitigation of cable-stayed bridges.

基于MR阻尼器的大跨斜拉桥碰撞效应减震控制

研究目的:漂浮体系大跨度斜拉桥纵向约束较弱,在地震作用下其梁端会产生较大纵向位移,引起碰撞,因此需采取合适的控制措施。本文以一座大跨度公铁两用双塔斜拉桥主引桥为工程背景,针对地震作用下主引桥的碰撞问题,将MR阻尼器引入该桥,通过SIMULINK建模,采取被动、半主动和智能模糊控制等不同的控制措施,研究MR阻尼器在该斜拉桥主引桥碰撞问题中的减震控制效果,以探究最佳控制方案。研究结论:(1)通过将七种控制策略分别与无控下结构的纵向位移响应相对比,可发现半主动控制与被动控制减震效果相接近,模糊逻辑控制效果最佳;(2)从碰撞力响应可看出,七种控制策略均能使主引桥之间的碰撞次数及碰撞力峰值减小,其中半主动控制与模糊逻辑控制的减震效果要优于被动控制;(3)从阻尼器耗能可看出,模糊控制的能量输入要远远小于被动控制和半主动控制;(4)本研究结论可供类似桥梁的主引桥碰撞控制参考和借鉴。

Semi-active predictive control strategy for seismically excited structures using MRF-04K dampers

The theoretical study of a semi-active predictive control(SAPC) system with magnetorheological(MR) dampers to reduce the responses of seismically excited structures was presented.The SAPC scheme is based on a prediction model of the system response to obtain the control actions by minimizing an object function,which has a function of self-compensation for time delay occurring in real application.A double-ended shear mode combined with a valve mode MR damper,named MRF-04K damper,with the maximum force of 20 kN was designed and manufactured,and parameters of the Bouc-Wen hysteresis model were determined to portray the behavior of this damper.As an example,a 5-story building frame equipped with 2 MRF-04K dampers was presented to demonstrate the performance of the proposed SAPC scheme for addressing time delay and reducing the structural responses under different earthquakes.Comparison with the uncontrolled structure,the passive-off and passive-on cases indicates that both the peak and the norm values of structural responses are all clearly reduced,and the SAPC scheme has a better performance than the two passive cases.

Trust-region based instantaneous optimal semi-active control of long-span spatially extended structures with MRF-04K damper

In the field of civil engineering, magnetorheological fluid （MRF） damper-based semi-active control systems have received considerable attention for use in protecting structures from natural hazards such as strong earthquakes and high winds. In this paper, the MRF damper-based semi-active control system is applied to a long-span spatially extended structure and its feasibility is discussed. Meanwhile, a _trust-region method based instantaneous optimal semi-active control algorithm （TIOC） is proposed to improve the performance of the semi-active control system in a multiple damper situation. The proposed TIOC describes the control process as a bounded constraint optimization problem, in which an optimal semi- active control force vector is solved by the trust-region method in every control step to minimize the structural responses. A numerical example of a railway station roof structure installed with MRF-04K dampers is presented. First, a modified Bouc- Wen model is utilized to describe the behavior of the selected MRF-04K damper. Then, two semi-active control systems, including the well-known clipped-optimal controller and the proposed TIOC controller, are considered. Based on the characteristics of the long-span spatially extended structure, the performance of the control system is evaluated under uniform earthquake excitation and travelling-wave excitation with different apparent velocities. The simulation results indicate that the MR fluid damper-based semi-active control systems have the potential to mitigate the responses of full-scale long-span spatially extended structures under earthquake hazards. The superiority of the proposed TIOC controller is demonstrated by comparing its control effectiveness with the clipped-optimal controller for several different cases.

WPT-Based Modal Control on Distributed Structures with MRF-04K Damper

The magnetorheological (MR) fluid damper-based semiactive control systems have received considerable attention for protecting structures against natural hazards such as strong earthquakes and high winds. In this paper, a novel modal controller using wavelet packet transform (WPT) is proposed for the vibration control of distributed structures. In the proposed control system, the WPT method is utilized to decompose the acceleration measurement and select the modes containing most of the WPT energy component as the dominant modes. Then, a modal controller is designed to control the dominant modes and the optimal active control force is solved. Finally, Clipped-optimal con- trol law is adopted to determine the voltage applied to each MR damper. A Kalman-filter observer, which estimates the full controlled modal states from local accelerometer feedbacks, is designed for rendering the controller to be more applicable to distributed structures with a large number of degrees of freedom. A numerical example of a stadium roof structure installed with MRF-04K damper is presented. The effectiveness of the controller is evaluated under both Tianjin and El Centro earthquake excitations. The superior performance and adaptability of the controller for versatile loading conditions are demonstrated through the comparison with traditional truncated modal controller.

基于磁流变阻尼器的滚珠丝杠进给系统主动抑振研究

针对滚珠丝杠进给系统轴向振动影响工件的加工质量和精度保持性的问题,将磁流变阻尼器应用于机床滚珠丝杠进给系统轴向抑振。设计磁流变阻尼器,进行磁流变阻尼器阻尼特性试验,采用最小二乘法和BP神经网络对阻尼力进行了辨识。建立带有磁流变阻尼器的机床滚珠丝杠进给系统单自由度振动模型,基于Runge-Kutta法计算了系统的动态响应。通过数值计算发现:阻尼器输入电流由零逐渐增大时,系统能够快速趋向于稳定;由幅频曲线可以看出,磁流变阻尼器抑制滚珠丝杠进给系统的振动是可行的。最后试验验证了磁流变阻尼器能够很好地抑制滚珠丝杠进给系统的振动。

ER/MR智能阻尼器耦联的带裙房高层建筑结构地震反应的半主动控制

本文建立了用ＥＲ／ＭＲ智能阻尼器耦联的带裙房高层建筑结构地震反应半主动控制的设计计算方法。文中，在导出了ＥＲ／ＭＲ智能阻尼器力学模型的基础上，建立了ＥＲ／ＭＲ智能阻尼器耦联的带裙房高层建筑结构地震反应的基本方程，并根据瞬时最优主动控制的原则，提出了 ＥＲ／ＭＲ智能阻尼器耦联的带裙房高层建筑地震反应半主动控制的基于最优主动控制位移的“开关－耗能”半主动控制策略。应用本文方法对主楼２０层、裙房５层的计算结构受控地震反应的模拟计算结果表明：耦联主楼和裙房的半主动的ＥＲ／ＭＲ智能阻尼器可有效地抑制带裙房高层建筑结构地震反应的鞭梢效应．并可均匀地减小结构各层的地震反应，是一种简单、方便和有效的智能控制装置。

MR智能阻尼器对空间网壳结构的风振抑制分析

磁流变液(MR)智能阻尼器是一种新型智能材料减振装置,可用于空间网壳结构的风振抑制。以适当方式和空间网壳结构结合即形成智能材料杆件空间网壳结构。建立了智能材料杆件有限元模型,研究了磁流变阻尼器布置方式和控制策略对空间网壳结构抗风减振的影响。将MR阻尼器设置于网壳结构径向肋杆处优于设在结构环向杆件处。不同控制策略导致不同的风振控制效果。Passive-off控制策略的风振抑制效果较差;Passive-on策略对控制结构的位移响应效果较好,而对控制结构的速度响应和加速度响应效果不佳。半主动控制策略对控制结构的位移响应、速度响应和加速度响应均较理想。针对不同风荷载作用,采用相同阻尼器布置方案和控制策略,结构风振控制效果大致相同。

MR智能阻尼器试验研究及径向基网络模型

制作了 MR智能阻尼器 ,并在不同的位移 ,速度和电流输入情况下 ,对自制的 MR智能阻尼器进行了性能试验研究 ,建立了 MR智能阻尼器的径向基函数网络模型。结果表明 :神经网络模型能精确的描述阻尼器正向和逆向工作特性 ,并且对液体沉降、液体磁响应时间、蓄能器刚度等因素的影响也能很好的解决。

MR阻尼器在抑制斜拉桥拉索风雨振中的应用研究

介绍了磁流变 ( MR)智能型阻尼器的原理 ,通过在我国洞庭湖大桥拉索振动控制的试验 ,得出在安装 MR阻尼器后拉索等效模态阻尼比的优化值 ,从而可调节 MR阻尼器外接电压值实现对拉索振动的优化控制 ,为探索更有效的抑制拉索振动方法提供了科学依据 .现场实测的风雨振现象 ,也证实了

永磁调节式MR阻尼器试验研究及工程应用

设计制作了永磁调节式MR阻尼器,在专用加载试验台上对该阻尼器的力学性能进行了试验研究,分析了影响阻尼力的各种因素,对永磁式MR阻尼器和油阻尼器、橡胶阻尼器进行了拉索减振的现场对比试验研究。结果表明,所设计制作的永磁式MR阻尼器阻尼力可调范围大,比油阻尼器具有更好的温度稳定性和更大的耗能减振能力,能保证每根拉索取得最优的减振效果。该阻尼器已成功应用于长沙洪山大桥,解决了该桥严重的风致振动问题。