Studies on a passive electromagnetic damper

The passive electromagnetic damper has the same configuration as that of the electromagnetic bearing, but no sensors and no closed loop control are needed. Its robustness and no-contact structure are its great advantages. When the rotor vibrates, the electromagnetic field intensity in the air gap is altered, then fluctuating currents in the damper coils and eddy currents inside the surface layer of rotor are created. Damping force is caused by the fluctuating currents, while retardation torque is generated by eddy currents. The characteristics of a damper may be improved by adding an additional electrical circuit. Numerical studies showed that damping coefficient increases with increasing static current, but decreases with increasing frequency. And the damping coefficient of the improved damper at higher frequency is more evident than that of the original damper. Experimental results showed that the resonant vibration around the first critical speed was obviously suppressed by both types of passive electromagnetic damper.     

阻尼器系数对悬挂建筑结构减震效率影响研究

利用拉格朗日方程建立了核筒悬挂建筑结构体系运动方程,采用Longe-Kuta方法求解体系地震动力响应时程。实例计算结果表明,阻尼器系数对悬挂结构的减震效果具有明显影响,楼层位移沿结构高度的分布趋于均匀,且相对于普通无悬挂结构其层间位移、层位移、层速度以及层加速度大幅度减小,而且存在一个优化的阻尼器系数使得结构层间位移有最小值。     

Experimental Study on Magnetorheological Damper for Semi-Active Vibration Control of Civil Infrastructures

Magnetorheological (MR) fluid is a kind of smart material whose rheological properties can be rapidly varied in magnetic field. To make full use of the advantages of MR fluid to devices, a model of double-ended,shear-combined and valve-typed MR damper is designed and manufactured, and the dynamic properties under sinusoidal excitations are experimentally studied. The experiment results show that the maximum damping force of the MR damper at the full magnetic intensity reaches about 20 k while the maximum power required is less than 50W, which predicts that the MR damper will be a powerful measurement for semi-active vibration control of civil infrastructures.     

压路机变阻尼减振器的结构设计及仿真分析

针对振动压路机采用的橡胶减振装置存在阻尼不可调的问题,文章利用磁流变液具有快速相变和易于控制的特征,并结合压路机结构特性设计一种由磁流变和橡胶耦合而成的变阻尼减振器,通过力学计算与有限元仿真,对减振器结构设计进行校核与优化。仿真结果发现:经过结构优化的变阻尼减振器提高了控制磁场的利用率,从而提高磁流变橡胶耦合减振器的性能与品质。     

双质点摩擦滑移隔震结构非线性分析

采用小波变换方法分析了双质点摩擦滑移隔震结构时频特性,结果表明：摩擦滑移隔震结构的动力特性与其运动形态有关,隔震层摩擦系数的改变对结构频率非线性影响较小,对阻尼非线性影响较大.     

Seismic response analysis of damper-connected adjacent structures with stochastic parameters

Dynamic response analysis of damper connected adjacent multi-story structures with uncertain parameters is carried out. A formula of the multi degree of freedom （MDOF） for the structure-damper system with stochastic parameters is derived. The uncertainties of mass and stiffness are taken into consideration firstly. The ground acceleration is represented by Kanai-Tajimi filtered non-stationary process. The mean square random responses of structural displacement and story drift are chosen as the optimization objective. The variations of mean square responses of top floor displacements and bottom story drifts in neighboring structures with the damper stiffness and damping coefficient are analyzed in detail. Through the parametric study, the acquiring optimum parameters of damper are regarded as numerical results. Then, a reducing order model of the MDOF system for adjacent structures with mean parameters is presented. The explicit expressions for determining optimal parameters of Kelvin model-defined damper which is used to connect adjacent single degree of freedom （SDOF） structures subjected to a white-noise excitation are employed to achieve the appropriate damper parameters, which are called theory results. Through a comparative study, it can be found that the theory values of damper parameters are consistent with the results based on extensive parametric studies. The analytical results can be obtained by using the first natural frequencies and the total mass of the adjacent deterministic structures with mean parameters. The analytical formulas can be used to find appropriate parameters of damper between adjacent structures for engineering applications. The performance of damper is investigated on the basis of mitigations of mean square random responses of inter-story drifts, displacements and accelerations in adjacent structures. The numerical results demonstrate the robustness of coupled building control strategies.     

Optimal arrangement of viscoelastic dampers for seismic control of adjacent shear-type structures

The optimal arrangement of viscoelastic dampers (VEDs) used to link two adjacent shear-type structures under seismic excitation was investigated. A two-step optimal design method is proposed. First, optimal parameter expressions of the Kelvin model are used to calculate the optimal stiffness and damping coefficient of the VEDs. Then, using the two-step optimal design method, taking the quadratic performance index as the optimization objective, the optimal arrangement of the dampers is determined. General rules about the optimal arrangement of the VEDs were obtained. The results show that the placement of only one damper between two adjacent shear-type structures should be avoided; if more than one damper is used, they should be distributed on the top and lower floors of the structures. Optimization of the number of dampers had little effect on response reduction. The most important factor was the optimization of the placement of the dampers. Through comparative study, for buildings of equal and unequal heights, the optimal parameters of dampers from parametric studies were shown to match the theoretical results for different numbers and placements of dampers. The level of response reduction was shown to be sensitive to the damping coefficient of the dampers.     

Nonlinear dynamic response of stay cables under axial harmonic excitation

This paper proposes a new numerical simulation method for analyzing the parametric vibration of stay cables based on the theory of nonlinear dynamic response of structures under the asynchronous support excitation. The effects of important parameters related to parametric vibration of cables, i.e., characteristics of structure, excitation frequency, excitation amplitude, damping effect of the air and the viscous damping coefficient of the cables, were investigated by using the proposed method for the cables with significant length difference as examples. The analysis results show that nonlinear finite element method is a powerful technique in analyzing the parametric vibration of cables, the behavior of parametric vibration of the two cables with different Irvine parameters has similar properties, the amplitudes of parametric vibration of cables are related to the frequency and amplitude of harmonic support excitations and the effect of distributed viscous damping on parametric vibration of the cables is very small.     

Retrofit of Ressalat jacket platform （Persian Gulf） using friction damper device

A friction damper device (FDD) is used for vibration control of an existing steel jacket platform under seismic excitation. First, the damping is presented for vibration mitigation of structures located in seismically active zones. A new method for quick design of friction or yielding damping devices is presented. The effectiveness of the damping system employing such FDDs in a jacket platform is evaluated numerically. The influence of key parameters of the damping system on the vibration suppression of the offshore structure is studied in detail. To examine the vibration control effectiveness of the FDD for the jacket platform, performance of the controlled structure under the seismic forces is studied using numerical simulations. A parametric study is undertaken to discover the optimized slip load and brace area of the FDD. It is shown that the FDD is effective in mitigating the dynamic responses of the offshore platform structure.     

Signal frequency based self-tuning fuzzy controller for semi-active suspension system

A new kind of fuzzy control scheme, based on the identification of the signal's main frequency and the behavior of the ER damper, is proposed to control the semi-active suspension system. This method adjusts the fuzzy controller to achieve the best isolation effect by analyzing the main frequency's characters and inspecting the change of system parameters. The input of the fuzzy controller is the main frequency and the optimal damping ratio is the output. Simulation results indicated that the proposed control method is very effective in isolating the vibration. Project (No. 69974024) supported by the National Natural Science Foundation of China     

Signal frequency based self-tuning fuzzy controller for semi-active suspension system

INTRODUCTIONRoadvehiclesuspensiondesignhasreceivedgreatattentioninrecentyears .Theperformanceofthesuspensionsystemplaysanimportantroleinachievinggoodhandlingandridingcomfort.Practically ,thesimplestandmostcommontypesofsuspensionsarepassiveinthesensethatno…     

MATLAB/SIMULINK在包装动力学教学中的应用

以包装件跌落冲击和简谐位移激励的受迫振动为例,依据系统的运动微分方程建立MATLAB/SIMULINK仿真模型,并进行一系列实例仿真,仿真结果直观地反映出系统的动态响应以及阻尼、弹性系数、激励频率等对动态响应的影响规律。该方法使复杂的、理论性很强的包装动力学教学变得简单和可视化,促进了学生对知识的理解和掌握,提高了教学质量。     

An in-plane low-noise accelerometer fabricated with an improved process flow

We present a bulk micromachined in-plane capacitive accelerometer fabricated with an improved process flow, by etching only one-fifth of the wafer thickness at the back of the silicon while forming the bar-structure electrode for the sensing capacitor. The improved flow greatly lowers the footing effect during deep reactive ion etching （DRIE）, and increases the proof mass by 54% compared to the traditional way, resulting in both improved device quality and a higher yield rate. Acceleration in the X direction is sensed capacitively by varying the overlapped area of a differential capacitor pair, which eliminates the nonlinear behavior by fixing the parallel-plate gap. The damping coefficient of the sensing motion is low due to the slide-film damping. A large proof mass is made using DRIE, which also ensures that dimensions of the spring beams in the Y and Z directions can be made large to lower cross axis coupling and increase the pull-in voltage. The theoretical Brownian noise floor is 0.47 μg/Hz^1/2 at room temperature and atmospheric pressure. The tested frequency response of a prototype complies with the low damping design scheme. Output data for input acceleration from -1 g to 1 g are recorded by a digital multimeter and show very good linearity. The tested random bias of the prototype is 130 μg at an averaging time of around 6 s.     

阻尼器连接的毗邻建筑地震响应分析(英文)

建立阻尼器连接的毗邻建筑在地震力作用下的运动方程．在求解地震响应时,地面运动加速度被描述为一随机过程．由于结构系统的非正交阻尼性质,用虚拟激励法在频域内求解结构地震响应．通过分析得出,毗邻建筑用阻尼器连接后,结构的地震响应得到有效控制,较连接前明显改善;选择一定的阻尼器参数可得最佳的减震效果．     

A disc-type magneto-rheologic fluid damper

A disc-type magneto-rheological fluid damper operating in shear mode is proposed in this paper, which is based on the special characteristics of the magneto-rheological (MR) fluid with rapid, reversible and dramatic change in its rheological properties by the application of an external magnetic field. The magnetic field of the disc-type MR fluid damper is analysed by the finite element method; the controllability of the disc-type MR fluid damper on the dynamic behaviour of a rotor system; and the effectiveness of the disc-type MR fluid damper in controlling the vibration of a rotor system, are studied in a flexible rotor system with an over-hung disc. It is shown that the magnetic flux density of the disc-type MR fluid damper in the working areas can significantly change with the applied current in the coil; and that the dynamic behavior of the disc-type MR fluid damper can be varied by the application of an external magnetic field produced by a low voltage electromagnetic coil. The disc-type MR fluid damper can significantly change the dynamic characteristics of a rotor system, provided that the location of the disk-type MR fluid damper is carefully chosen. The disc-type MR fluid damper is a new actuator with good dynamic characteristics for rotating machinery.     

可变阻尼对汽车悬架系统振动性能影响分析

通过建立1/4悬架系统的理论数模,分析阻尼系数影响系统的幅频特性.在不同的振动频率范围内,阻尼的相应变化将改善悬架系统的输出性能.     

A disc-type magneto-rheologic fluid damper

INTRODUCTIONElectro rheological (ER ) Magneto rheologi cal(MR)fluidisakindofcontrollablefluidwhoserheologicalproperties,especiallyapparentviscosity,canbedramaticallyandreversiblyvariedinafewmillisecondsbytheapplicationofanexternalelectrical magneticfield…     

A disc-type magneto-rheologtic fluid damper

A disc-type magneto-rheological fluid damper operating in shear mode is proposed in this paper, which is based on the special characteristics of the magneto-rheological (MR) fluid with rapid, reversible and dramatic change in its rheological properties by the application of an external magnetic field. The magnetic field of the disc-type MR fluid damper is analysed by the finite element method; the controllability of the disc-type MR fluid damper on the dynamic behaviour of a rotor system; and the effectiveness of the disc-type MR fluid damper in controlling the vibration of a rotor system, are studied in a flexible rotor system with an overhung disc. it is shown that the magnetic flux density of the disc-type MR fluid damper in the working areas can significantly change with the applied current in the coil; and that the dynamic behavior of the disc-type MR fluid damper can be varied by the application of an external magnetic field produced by a low voltage electromagnetic coil. The disc-type MR fluid damper can significantly change the dynamic characteristics of a rotor system, provided that the location of the disk-type MR fluid damper is carefully chosen. The disc-type MR fluid damper is a new actuator with good dynamic characteristics for rotating machinery. Project supported partially by the EC BRITE/EURAM program under BRPR-CT97-0544 IMPACT project and State Key Laboratory of Vibration, Shock and Noise, Shanghai Jiatong University     

Left-handed materials in magnetized metallic magnetic thin films

INTRODUCTION Veselago (1968) showed that if both the permit- tivity ε and the magnetic permeability μ of a material are negative, the propagation direction of an elec- tromagnetic (EM) wave will be opposite to its energy flow direction. Such media are called left-handed materials (LHMs) since the electric field E, magnetic field H, and wave vector k in these media form a left-hand triplet of vectors, instead of a right-hand triplet observed in conventional materials. For a long time, …     

磁流变液阻尼器设计与性能测试

自动化生产中,自动检测设备的使用越来越广泛,为保证检测精度,这类设备都需要控制气动和电动振动对检测的干扰和影响．为此本文设计了MRF可控阻尼器及可调振动滑台装置,总结基于MRF力学模型和磁路设计模型,设计MRF阻尼器的经验;基于NI数字化测试系统检测MRF阻尼器控制移动滑台振动的效果．实验结果证实MRF阻尼器能快捷方便地调节阻尼、高精度控制移动滑台的振动,MRF阻尼器振动控制装置具有教学实用价值．