Seismic control of multi-degrees-of-freedom structures by vertical mass isolation method using MR dampers

Vertical mass isolation(VMI)is one of the novel methods for the seismic control of structures.In this method,the entire structure is assumed to consist of two mass and stiffness subsystems,and an isolated layer is located among them.In this study,the magnetorheological damper in three modes:passive-off,passive-on,and semi-active mode with variable voltage between zero and 9 volts was used as an isolated layer between two subsystems.Multi-degrees-of-freedom structures with 5,10,and 15 floors in two dimensions were examined under 11 pairs of near field earthquakes.On each level,the displacement of MR dampers was taken into account.The responses of maximum displacement,maximum inter-story drift,and maximum base shear in controlled and uncontrolled buildings were compared to assess the suggested approach for seismic control of the structures.According to the results,the semi-active control method can reduce the response by more than 12%compared to the uncontrolled mode in terms of maximum displacement of the mass subsystem of the structures.This method can reduce more than 16%and 20%of the responses compared to the uncontrolled mode in terms of maximum inter-story drift and base shear of the structure,respectively.

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。

Investigation on Magnetorheological Effect of Novel Self-healing Magnetorheological Elastomers

Magnetorheological elastomers(MREs)hold significant promise in various fields such as automotive engineering,and civil engineering,where they serve as intelligent materials.Depending on the application of an external magnetic field,these materials exhibit varying magnetorheological and viscoelastic properties,including shear stress,yield stress,dynamic moduli,and damping.In this work,a new type of MRE,termed self-healing MREs(SH-MREs),has been developed by adding a novel self-healing agent into existing MREs.The dynamic modulus and loss factor of SH-MREs with different compositions have been characterized under various conditions of frequency,temperature,and strain.The results show that as the strain value increases,the loss factor also increases.Moreover,the loss factor initially increases and then decreases with increasing magnetic field strength.Although higher concentrations of ferromagnetic particles increase the loss factor,they enhance the operational range due to their better responsiveness to magnetic fields.SH-MREs demonstrate improved damping capabilities,attributed to the formation of coordination bonds between ferromagnetic particles and the self-healing agent.The stable structure increases the viscosity of MREs.The results of the regression model suggest a direct proportionality between sensitivity to the magnetic field and the ferromagnetic particle concentration.

基于MRG/CNT复合材料的磁电阻效应研究

通过在磁流变胶泥(MRG)中加入碳纳米管(CNT)组成复合材料,结合MRG的优良磁响应特性与CNT的电导特性,以复合材料作为填充材料设计实验敏感元件,建立实验表征系统对复合材料磁电阻效应的静态与动态特性开展了实验研究,并从微观层面分析了磁电阻效应机理,揭示了激励磁场影响复合材料电阻的关键因素。结果表明:复合材料处在磁工作区范围内,敏感元件的电阻值随磁场的增强而衰减,相对变化量达到了62.2%,同时表现出良好的时间稳定性;实验的动态响应输出与激励磁场的变化趋势高度一致,证明了复合材料具有良好的动态磁电阻响应特性。

Development and Application of a Power Law Constitutive Model for Eddy Current Dampers

Eddy current dampers (ECDs) have emerged as highly desirable solutions for vibration control due to theirexceptional damping performance and durability. However, the existing constitutive models present challenges tothe widespread implementation of ECD technology, and there is limited availability of finite element analysis (FEA)software capable of accurately modeling the behavior of ECDs. This study addresses these issues by developing anewconstitutivemodel that is both easily understandable and user-friendly for FEAsoftware. By utilizing numericalresults obtained from electromagnetic FEA, a novel power law constitutive model is proposed to capture thenonlinear behavior of ECDs. The effectiveness of the power law constitutive model is validated throughmechanicalproperty tests and numerical seismic analysis. Furthermore, a detailed description of the application process ofthe power law constitutive model in ANSYS FEA software is provided. To facilitate the preliminary design ofECDs, an analytical derivation of energy dissipation and parameter optimization for ECDs under harmonicmotionis performed. The results demonstrate that the power law constitutive model serves as a viable alternative forconducting dynamic analysis using FEA and optimizing parameters for ECDs.

Vibration attenuation performance of wind turbine tower using a prestressed tuned mass damper under seismic excitation

With the rapid development of large megawatt wind turbines,the operation environment of wind turbine towers(WTTs)has become increasingly complex.In particular,seismic excitation can create a resonance response and cause excessive vibration of the WTT.To investigate the vibration attenuation performance of the WTT under seismic excitations,a novel passive vibration control device,called a prestressed tuned mass damper(PS-TMD),is presented in this study.First,a mathematical model is established based on structural dynamics under seismic excitation.Then,the mathematical analytical expression of the dynamic coefficient is deduced,and the parameter design method is obtained by system tuning optimization.Next,based on a theoretical analysis and parameter design,the numerical results showed that the PS-TMD was able to effectively mitigate the resonance under the harmonic basal acceleration.Finally,the time-history analysis method is used to verify the effectiveness of the traditional pendulum tuned mass damper(PTMD)and the novel PS-TMD device,and the results indicate that the vibration attenuation performance of the PS-TMD is better than the PTMD.In addition,the PS-TMD avoids the nonlinear effect due to the large oscillation angle,and has the potential to dissipate hysteretic energy under seismic excitation.

Parameters Optimization and Performance Evaluation of the Tuned Inerter Damper for the Seismic Protection of Adjacent Building Structures

In order to improve the seismic performance of adjacent buildings,two types of tuned inerter damper(TID)damping systems for adjacent buildings are proposed,which are composed of springs,inerter devices and dampers in serial or in parallel.The dynamic equations of TID adjacent building damping systems were derived,and the H2 norm criterion was used to optimize and adjust them,so that the system had the optimum damping performance under white noise random excitation.Taking TID frequency ratio and damping ratio as optimization parameters,the optimum analytical solutions of the displacement frequency response of the undamped structure under white noise excitation were obtained.The results showed that compared with the classic TMD,TID could obtain a better damping effect in the adjacent buildings.Comparing the TIDs composed of serial or parallel,it was found that the parallel TIDs had more significant advantages in controlling the peak displacement frequency response,while the H2 norm of the displacement frequency response of the damping system under the coupling of serial TID was smaller.Taking the adjacent building composed of two ten-story frame structures as an example,the displacement and energy collection time history analysis of the adjacent building coupled with the optimum design parameter TIDs were carried out.It was found that TID had a better damping effect in the full-time range compared with the classic TMD.This paper also studied the potential power of TID in adjacent buildings,which can be converted into available power resources during earthquakes.

Adaptive Backstepping Control Design for Semi-Active Suspension of Half-Vehicle With Magnetorheological Damper

This paper investigates the problem of controlling half-vehicle semi-active suspension system involving a magnetorheological(MR)damper.This features a hysteretic behavior that is presently captured through the nonlinear Bouc-Wen model.The control objective is to regulate well the heave and the pitch motions of the chassis despite the road irregularities.The difficulty of the control problem lies in the nonlinearity of the system model,the uncertainty of some of its parameters,and the inaccessibility to measurements of the hysteresis internal state variables.Using Lyapunov control design tools,we design two observers to get online estimates of the hysteresis internal states and a stabilizing adaptive state-feedback regulator.The whole adaptive controller is formally shown to meet the desired control objectives.This theoretical result is confirmed by several simulations demonstrating the supremacy of the latter compared to the skyhook control and passive suspension.

Adaptive Control of Helicopter Ground Resonance with Magnetorheological Damper

The methodology for adaptive control of helicopter ground resonance with magnetorheological （MR） damper is presented. The adaptive inverse control method is used to control the output damping force of MR damper and the range of the damping force is given. Through the adaptive inverse control, the damping force of MR damper is fit to a desired damping force. With the background of applying MR damper to control of helicopter ground resonance, a model of loss force and an adaptive arithmetic for stabilization of the coupled rotor/fuselage system are presented. The simulation shows that the controller presented in this paper can stabilize the rotor/fuselage coupling system quickly and control the helicopter ground resonance effectively.

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.

Study on semi-active control of mega-sub controlled structure by MR damper subject to random wind loads

The recently proposed mega-sub controlled structure （MSCS）, a new type of structure associated with the design and construction of super-tall buildings, has attracted the attention of designers for use in enhancing the control effectiveness in mega-frame buildings. In this paper, a dynamic equation and method to assemble parameter matrixes for a mega-sub controlled structure under random wind loads is presented. Semi-active control using magnetorheological dampers for the MSCS under random wind loads is investigated, and is compared with a corresponding system without dampers. A parametric study of the relative stiffness ratio and relative mass ratio between the mega-frame and the substructures, as well as the additional column stiffness ratio that influences the response control effectiveness of the MSCS, is discussed. The studies reveal, for the first time, that different control mechanisms exist. The results indicate that the proposed structure employing semi-active control can offer an effective control mechanism. Guidelines for selecting parameters are provided based on the analytical study.

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。

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.

GENERALIZED ASYMMETRIC HYSTERESIS MODEL OF CONTROLLABLE MAGNETORHEOLOGICAL DAMPER FOR VEHICLE SUSPENSION ATTENUATION

A generalized model is synthesized to characterize the asymmetric hysteresisforce-velocity (F-v) properties of the magneto-rheological (MR) fluids damper. The model isrepresented as a function of the command current, excitation frequency, and displacement amplitude,based on the symmetric and asymmetric sigmoid functions. The symmetric hysteresis damping propertiesof the controllable MR-damper and properties of the conventional passive hydraulic damper can alsobe described by the proposed model. The validity of the model is verified by experiments, which showthat the results calculated from the model are consistent with the measured data. In addition, itis shown that the model applies to a wide vibration frequency range. The proposed model haspotential application in vehicle suspension design employing the symmetry MR-damper, and also indeveloping the asymmetry MR-damper especially for the vehicle suspension attenuation.

Smart Semi-active PID-ACO control strategy for tower vibration reduction in Wind Turbines with MR damper

Wind turbine technology is well known around the globe as an eco-friendly and eff ective renewable power source. However, this technology often faces reliability problems due to structural vibration. This study proposes a smart semi-active vibration control system using Magnetorheological (MR) dampers where feedback controllers are optimized with nature-inspired algorithms. Proportional integral derivative (PID) and Proportional integral (PI) controllers are designed to achieve the optimal desired force and current input for MR the damper. PID control parameters are optimized using an Ant colony optimization (ACO) algorithm. The eff ectiveness of the ACO algorithm is validated by comparing its performance with Ziegler-Nichols (Z-N) and particle swarm optimization (PSO). The placement of the MR damper on the tower is also investigated to ensure structural balance and optimal desired force from the MR damper. The simulation results show that the proposed semi-active PID-ACO control strategy can signifi cantly reduce vibration on the wind turbine tower under diff erent frequencies (i.e., 67%, 73%, 79% and 34.4% at 2 Hz, 3 Hz, 4.6 Hz and 6 Hz, respectively) and amplitudes (i.e. 50%, 58% and 67% for 50 N, 80 N, and 100 N, respectively). In this study, the simulation model is validated with an experimental study in terms of natural frequency, mode shape and uncontrolled response at the 1st mode. The proposed PID-ACO control strategy and optimal MR damper position is also implemented on a lab-scaled wind turbine tower model. The results show that the vibration reduction rate is 66% and 73% in the experimental and simulation study, respectively, at the 1st mode.

Optimizing Control for Rotor Vibration with Magnetorheological Fluid Damper

The aim of this work is to analyze and design a control system for vibration reduction in a rotor system using a shear mode magnetorheological fluid(MRF)damper.A dynamic model of the MRF damper-rotor system was built and simulated in Matlab/Simulink to analyze the rotor vibration characteristics and the vibration reduction effect of the MRF damper.Based on the numerical simulation analysis,an optimizing control strategy using pattern search method was proposed and designed.The control system was constructed on a test rotor bench and experiment validations on the effectiveness of the proposed control strategy were conducted.Experimental results show that rotor vibration caused by unbalance can be well controlled whether in resonance region(70%)or in non-resonance region(30%).An irregular vibration amplitude jump can be suppressed with the optimization strategy.Furthermore,it is found that the rapidity of transient response and efficiency of optimizing technique depend on the pattern search step.The presented strategies and control system can be extended to multi-span(more than two or three spans)rotor system.It provides a powerful technical support for the extension and application in target and control for shafting vibration.

Semi-Active Control of Wave-Induced Vibration for Offshore Platforms by Use of MR Damper

The objective of the present research is to examine the effectiveness of the lateral vibration control of wave-excited response of offshore platforms with magneto-rheological (MR) damper. In this study, the offshore platform is simplified to be a singled degree-of-freedom (SDOF) system by extracting the first vibration mode of the structure. The external 'generalized' wave force is determined with a white noise via a designed filter. A semi-active control method based on optimal control theory is proposed considering that the yield stress of the MR damper can he varied continuously within a certain range. The dynamics of SDOF structure coupled with the MR damper is investigated. Numerical simulation demonstrates that the MR damper with this control strategy can significantly reduce the maximum responses and the root-mean-square (RMS) values.

Simplified design method for shear-valve magnetorheological dampers

Based on the Bingham parallel-plate model, a simplified design method of shear-valve magnetorheological （MR） dampers is proposed considering the magnetic circuit optimization. Correspondingly, a new MR damper with a full-length effective damping path is proposed. The prototype dampers are also fabricated and studied numerically and experimentally. According to the test results, the Bingham parallel-plate model is further modified to obtain a damping force prediction model of the proposed MR dampers. This prediction model considers the magnetic saturation phenomenon. The study indicates that the proposed simplified design method is simple, effective and reliable. The maximum damping force of the proposed MR dampers with a full-length effective damping path is at least twice as large as those of conventional MR dampers. The dynamic range of damping force increases by at least 70%. The proposed damping force prediction model considers the magnetic saturation phenomenon and it can realize the actual characteristic of MR fluids. The model is able to predict the actual damping force of MR dampers precisely.

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.

Optimizing control of a two-span rotor system with magnetorheological fluid dampers

A control system aims at vibration reduction in a two-span rotor system with two shear mode magnetorheological （MRF） dampers is designed. A finite element model of the MRF damper- rotor system is built and used to analyze the rotor vibration characteristics. Based on Hooke and Jeeves algorithm and the numerical simulation analysis, an optimal appropriate controller is proposed and designed. Experimental results show that rotor vibration caused by unbalance is well controlled （ first critical speed region 37% , second critical speed region 42% ）. To reflect advantages of optimi- zing strategy presented and validate the intelligent optimization control technology, detailed experi- ments were developed on a two-span rotor-vibration-control platform. The influence on accuracy, rapidity and stability of optimizing control for rotor vibration are analyzed. It provides a powerful technical support for the extension and application in target and control for shafting vibration.