Theoretical and experimental research on a new system of semi-active structural control with variable stiffness and damping

In this paper,a new system of semi active structural control with active variable stiffness and damping (AVSD) is suggested.This new system amplifies the structural displacement to dissipate more energy,and in turn,effectively reduces the structural response in the case of relatively small story drifts,which occur during earthquakes.A predictive instantaneous optimal control algorithm is established for a SDOF structure equipped with an AVSD system Comparative shaking table tests of a 1/4 scale single story structural model with a full scale control device have been conducted.From the experimental and analytical results,it is shown that when compared to structures without control or with the active variable stiffness control alone, the suggested system exhibits higher efficiency in controlling the structural response,requires less energy input,operates with higher reliability,and can be manufactured at a lower cost and used in a wider range of engineering applications.

Force Control Compensation Method with Variable Load Stiffness and Damping of the Hydraulic Drive Unit Force Control System

Each joint of hydraulic drive quadruped robot is driven by the hydraulic drive unit（HDU）, and the contacting between the robot foot end and the ground is complex and variable, which increases the difficulty of force control inevitably. In the recent years, although many scholars researched some control methods such as disturbance rejection control, parameter self-adaptive control, impedance control and so on, to improve the force control performance of HDU, the robustness of the force control still needs improving. Therefore, how to simulate the complex and variable load characteristics of the environment structure and how to ensure HDU having excellent force control performance with the complex and variable load characteristics are key issues to be solved in this paper. The force control system mathematic model of HDU is established by the mechanism modeling method, and the theoretical models of a novel force control compensation method and a load characteristics simulation method under different environment structures are derived, considering the dynamic characteristics of the load stiffness and the load damping under different environment structures. Then, simulation effects of the variable load stiffness and load damping under the step and sinusoidal load force are analyzed experimentally on the HDU force control performance test platform, which provides the foundation for the force control compensation experiment research. In addition, the optimized PID control parameters are designed to make the HDU have better force control performance with suitable load stiffness and load damping, under which the force control compensation method is introduced, and the robustness of the force control system with several constant load characteristics and the variable load characteristics respectively are comparatively analyzed by experiment. The research results indicate that if the load characteristics are known, the force control compensation method presented in this paper has positive compensation effects on the load characteristics variation, i.e., this method decreases the effects of the load characteristics variation on the force control performance and enhances the force control system robustness with the constant PID parameters, thereby, the online PID parameters tuning control method which is complex needs not be adopted. All the above research provides theoretical and experimental foundation for the force control method of the quadruped robot joints with high robustness.

Approximate analysis method for displacement responses of structures with active variable stiffness systems

The performance of structures with active variable stiffness (AVS) systems exhibits strong nonlinearity due to the variety with time of the stiffness of each storey unit,in which the AVS system is installed.Hence,the classical dynamic analysis method for linear structures,such as the mode-superposition method,is not applicable to structures with AVS systems.In this paper,an approximate analysis method is proposed for displacement responses of structures with AVS systems.Firstly,an equivalent relationship between single-degree-of-freedom (SDOF) structures equipped with AVS systems and so-called fictitious linear structures is established.Then,an approximate mode-superposition (AMS) method is presented for multi-degree-of-freedom (MDOF) structures equipped with AVS systems.The accuracy of this method is investigated through extensive parametrical study using different types of earthquake excitations,and some modification is made to the method. Numerical calculation results indicate that the modified AMS method is effective for estimating the maximum displacements relative to the ground and the maximum interstorey drifts of MDOF structures equipped with AVS systems.

A novel semi-active TMD with folding variable stiffness spring

An innovative variable stiffness device is proposed and investigated based on numerical simulations. The device, called a folding variable stiffness spring （FVSS）, can be widely used, especially in tuned mass dampers （TMDs） with adaptive stiffness. An important characteristic of FVSS is its capability to change the stiffness between lower and upper bounds through a small change of distance between its supports. This special feature results in lower time-lag errors and readjustment in shorter time intervals. The governing equations of the device are derived and simplified for a symmetrical FVSS with similar elements. This device is then used to control a single-degree-of-freedom （SDOF） structure as well as a multi-degree-of-freedom （MDOF） structure via a semi-active TMD. Numerical simulations are conducted to compare several control cases for these structures. To make it more realistic, a real direct current motor with its own limitations is simulated in addition to an ideal control case with no limitations and both the results are compared. It is shown that the proposed device can be effectively used to suppress undesirable vibrations of a structure and considerably improves the performance of the controller compared to a passive device.

Variable stiffness control algorithm for high-rising buildings of closely spaced frequencies based on wavelet transforms

To establish the algorithm of SAT-TMD system with the wavelet transform(WT),the modal mass participation ratio is proposed to distinguish if the high-rising structure has the characteristic of closely distributed frequencies.A time varying analytical model of high-rising structure such as TV-tower with the SAT-TMD is developed.The proposed new idea is to use WT to identify the dominant frequency of structural response in a segment time,and track its variation as a function of time to retune the SAT-TMD.The effectiveness of SAT-TMD is investigated and it is more robust to change in building stiffness and damping than that of the TMD with a fixed frequency corresponding to a fixed mode frequency of the building.It is proved that SAT-TMD is particularly effective in reducing the response even when the building stiffness is changed by ±15%;whereas the TMD loses its effectiveness under such building stiffness variations.

Seismic response of controlled structures with active multiple tuned mass dampers

Active multiple tuned mass dampers （referred to as AMTMD）, which consist of several active tuned mass dampers （ATMDs） with identical stiffness and damping coefficients but varying mass and control force, have recently been proposed to suppress undesirable oscillations of structures under ground acceleration. It has been shown that the AMTMD can remarkably improve the performance of multiple tuned mass dampers （MTMDs） and is also more effective in reducing structure oscillation than single ATMDs. Notwithstanding this, good performance of AMTMD （including a single ATMD illustrated from frequency-domain analysis） may not necessarily translate into a good seismic reduction behavior in the time-domain. To investigate these phenomena, a three-story steel structure model controlled by AMTMD with three ATMDs was implemented in SIMULINK and subjected to several historical earthquakes. Likewise, the structure under consideration was assumed to have uncertainty of stiffness, such as 4-15% of its initial stiffness, in the numerical simulations. The optimum design parameters of the AMTMD were obtained in the frequency-domain by implementing the minimization of the minimum values of the maximum dynamic magnification factors （DMF） of general structures with AMTMD. For comparison purposes, response analysis of the same structure with a single ATMD was also performed. The numerical analysis and comparison show that the AMTMD generally renders better effectiveness when compared with a single ATMD for structures subjected to historical earthquakes. In particular, the AMTMD can improve the effectiveness of a single ATMD for a structure with an uncertainty of stiffness of 4-15% of its initial stiffness.

Analysis on Dynamic Performance for Active Magnetic Bearing-Rotor System

In the application of active magnetic bearings (AMB), one of the key problems to be solved is the safety and stability in the sense of rotor dynamics. The project related to the present paper deals with the method for analyzing bearing rotor systems with high rotation speed and specially supported by active magnetic bearings, and studies its rotor dynamics performance, including calculation of the natural frequencies with their distribution characteristics, and the critical speeds of the system. One of the targets of this project is to formulate a theory and method valid for the analysis of the dynamic performance of the active magnetic bearing rotor system by combining the traditional theory and method of rotor dynamics with the analytical theory and design method based on modern control theory of the AMB system.

Dynamics Analysis of Active Variable Stiffness Vibration Isolator for Whole-Spacecraft Systems Based on Nonlinear Output Frequency Response Functions

In order to improve the harsh dynamic environment experienced by heavy rockets during different external excitations,this study presents a novel active variable stiffness vibration isolator(AVS-VI)used as the vibration isolation device to reduce excessive vibration of the whole-spacecraft isolation system.The AVS-VI is composed of horizontal stiffness spring,positive stiffness spring,parallelogram linkage mechanism,piezoelectric actuator,acceleration sensor,viscoelastic damping,and PID active controller.Based on the AVS-VI,the generalized vibration transmissibility determined by the nonlinear output frequency response functions and the energy absorption rate is applied to analyze the isolation performance of the whole-spacecraft system with AVS-VI.The AVS-VI can conduct adaptive vibration suppression with variable stiffness to the whole-spacecraft system,and the analysis results indicate that the AVS-VI is efTective in reducing the extravagant vibration of the whole-spacecraft system,where the vibration isolation is decreased up to above 65%under different acceleration excitations.Finally,different parameters of AVS-VI are considered to optimize the whole-spacecraft system based on the generalized vibration transmissibility and the energy absorption rate.

A buffering method for quadruped robots based on active impedance control

Compared with wheeled or tracked robots,legged robots exhibit advantages on agile locomotion and higher survival chance for deadly impacts. A buffering strategy is proposed for quadruped robots with non-extreme initial attitudes from the end of air-righting to the steady standing on the ground.This approach consists of landing phase,buffering phase and recovering phase. The variable stiffness control,proportional-derivative( PD) force control and foot trajectory planning are applied to the joints of quadruped robots until the end of the recovering phase. The PD parameters are tuned according to the desired performance of each phase. The above approach is verified on a virtual platform.

Research on the evolution law of dynamic performance of CR400BF EMU train based on stochastic dynamics simulation

Purpose–This paper aims to obtain the evolution law of dynamic performance of CR400BF electric multiple unit(EMU).Design/methodology/approach–Using the dynamic simulation based on field test,stiffness of rotary arm nodes and damping coefficient of anti-hunting dampers were tested.Stiffness,damping coefficient,friction coefficient,track gauge were taken as random variables,the stochastic dynamics simulation method was constructed and applied to research the evolution law with running mileage of dynamic index of CR400BF EMU.Findings–The results showed that stiffness and damping coefficient subjected to normal distribution,the mean and variance were computed and the evolution law of stiffness and damping coefficient with running mileage was obtained.Originality/value–Firstly,based on the field test we found that stiffness of rotary arm nodes and damping coefficient of anti-hunting dampers subjected to normal distribution,and the evolution law of stiffness and damping coefficient with running mileage was proposed.Secondly stiffness,damping coefficient,friction coefficient,track gauge were taken as random variables,the stochastic dynamics simulation method was constructed and applied to the research to the evolution law with running mileage of dynamic index of CR400BF EMU.

形状记忆合金弹簧隔振系统主动控制实验设计

为探索振动系统在结构和参数变化时的实验现象和实验特征,基于被动隔振实验台,设计了具有弹簧温度和激振频率自动采集功能的形状记忆合金弹簧变阻尼主动控制系统,对形状记忆合金弹簧的刚度和阻尼随温度变化的振动特性进行分析。结果表明,在不同激振频率下,形状记忆合金弹簧阻尼比随着温度的升高而增大,刚度随着温度的升高而降低。通过弹簧温度自动调节对隔振系统进行控制,从而实现形状记忆合金弹簧的变频动态减振。该研究结果可用于形状记忆合金弹簧在特定载荷下的减振特性标定。

基于变刚度的自动制孔末端执行器半主动振动控制方法研究

自动制孔机器人末端执行器在制孔过程中会产生轴向振动,甚至会引起机体颤振,导致制孔精度降低,因此提出一种变刚度半主动振动控制方法。首先在分析各参数对振动控制器绝对位移传递率影响的基础上,优化了无扰动情况下的被动系统参数,并对其振动控制效果进行了仿真;然后运用绝对位移传递率图像特征分析法,获得激励频率与位移传递率的关系,通过调节吸振器刚度,使振动控制器的位移传递率随激励频率变化保持在最佳状态;最后运用MATLAB仿真验证了该方法的可行性。

车辆半主动悬架减振支柱的刚度特性分析

为了提高车辆行驶平顺性,对半主动悬架一体化减振支柱的结构进行了优化设计,推导了双气室空气弹簧数据模型,利用MATLAB/Simulink仿真工具,对新型一体式减振支柱刚度特性进行了仿真分析,为搭建半主动悬架一体化减振车辆整车性能分析提供理论。

基于可变刚度抗蛇行减振器的车辆动力学性能研究

CRH3系列高速动车组在长期服役过程中偶有发生蛇行运动稳定性裕量不足的问题,车辆装配T60型抗蛇行减振器,在车轮磨耗末期易发生构架横向加速度报警问题,装配T70型抗蛇行减振器,则在新轮或车轮磨耗初期易发生“晃车”的问题。针对晃车和报警问题开展可变刚度抗蛇行减振器的仿真与试验研究,以满足车辆在不同轮轨接触状态下车辆的蛇行运动稳定性需求。动力学仿真表明,可变刚度抗蛇行减振器能有效兼顾解决“晃车”和“报警”问题;进一步分析可变刚度抗蛇行减振器与两种高速踏面的适应性,采用S1002CN踏面时车辆临界速度高于350 km/h,而采用LMB10踏面时仅为220 km/h,且S1002CN踏面对应的平稳性和舒适度指标都优于LMB10踏面。最后通过整车滚振台架试验对变刚度抗蛇行减振器性能进行了试验验证,结果表明该减振器可以兼顾轮轨低锥度和高锥度匹配状态,可使车辆均具有良好的动力学性能。

斜盘式恒压变量柱塞泵动态特性研究

该文针对变量泵压力控制元件对变量泵的压力输出特性进行研究,通过模拟仿真研究压力控制阀上阻尼孔尺寸和弹簧刚度的影响规律。研究结果表明阻尼孔尺寸增加,减小变量泵输出压力的稳定时间,同时增大变量泵的泄漏量,压力输出偏差也会增大;调压弹簧刚度增加导致变量泵压力响应速度降低,同时泵的输出压力偏差会有所增大。

电磁轴承支承的船舶推进轴系纵向振动变刚度控制方法研究

船舶推进轴系纵向非定常激励激发壳体结构振动和辐射噪声,严重影响航行隐蔽性。针对这一问题,结合电磁轴承支承特性主动可控优势,首先提出了一种采用电磁轴承支承的推进轴系结构,然后推导了含推力电磁轴承结构及控制参数的轴系纵向振动频率方程,最后提出了一种基于纵向激励频率的变刚度控制方法。仿真结果表明,在推力电磁轴承可变等效刚度范围内,增大控制器比例系数,可有效提高轴系一阶纵向固有频率,对高阶纵向固有频率影响不大;轴系在不同转速下工作时可以选用不同比例系数,实时调节轴系纵向振动传递特性,有效减小纵向激励向壳体传递。

基于变论域模糊控制的时变结构震动控制方法研究

针对传统工程震动控制领域控制对象均为确定结构,未考虑实际结构在地震的过程中及地震前可能会发生的刚度退化、质量降低问题,该文章以时变三层框架结构作为被控对象,在传统模糊控制算法的基础上引入变论域法,建立了基于变论域模糊控制的时变结构震动控制方法。通过在传统主模糊控制器增设伸缩因子模糊控制器,将被控对象的误差及误差变化率作为输入,伸缩因子作为输出,根据被控对象的误差及误差变化率自适应调整主模糊控制器的模糊论域。SIMULINK软件仿真结果表明,所提出的控制方法能实现模糊控制论域自适应调整,针对时变结构位移、速度、加速度的控制效果均优于传统模糊控制和ON-OFF控制算法,具有一定工程应用前景。

基于流固耦合有限元法和集总参数法模型的建模方法

传统的半主动悬置非线性较强,难以探究其动态特性。为了更好地解决其建模过程中参数识别困难的问题,根据半主动悬置的基本原理,采用一种基于流固耦合有限元法和集总参数模型的建模方法,对其运动特性进行了理论、仿真与试验研究。首先,根据悬置的基本原理构建了力学模型,在AMESim平台中建立了悬置结构集总参数模型;然后,采用流固耦合有限元法,提取了橡胶主簧、两个液室体积刚度、流体惯性系数和阻尼系数等关键参数;最后,将参数代入集总参数模型后完成了仿真,并通过搭建试验平台,验证了仿真结果的准确性;绘制了软硬模式下悬置系统的动刚度和阻尼角曲线,分析了其动态特性。试验结果表明:流固耦合-集总参数的建模方法精准度较高,仿真与试验对比后的动刚度和阻尼角最大误差分别为6.2%和7.4%,满足工程误差要求。研究结果表明:基于流固耦合有限元法和集总参数模型的方法不仅可用于分析悬置参数对动刚度和阻尼角的影响,也可为发动机悬置优化提供建模基础,节省了研发成本,提高了研发效率。

形状记忆合金改进型双凹面变曲率摩擦摆隔震支座理论分析与数值模拟研究

介绍了形状记忆合金改进型双凹面变曲率摩擦摆隔震支座(SMA-DVFPB)的基本构造,阐述了SMA-DVFPB应具备的功能。通过静力平衡原理推导了SMA-DVFPB在平面内运动时力与位移的关系式。通过ABAQUS软件对SMA拉索和隔震支座进行了模拟,分析了支座的滞回特性,并计算了理论与模拟误差。研究了不同摩擦系数、拉索横截面积对SMA-DVFPB滞回曲线、等效刚度及等效阻尼比的影响,并分析了支座的应力情况。结果表明:理论推导与数值模拟吻合较好,耗能和等效刚度误差在10%以内;SMA-DVFPB的耗能、等效刚度、等效阻尼比均随摩擦系数增大而增大;SMA-DVFPB的耗能、等效刚度随SMA拉索横截面积增大而增大,等效阻尼比随SMA拉索横截面积增大而减小;SMA-DVFPB最大应力出现在SMA拉索与支承板的连接处,设计时应充分考虑其在锚固处的应力集中情况。

磁流变动力系统变刚度变阻尼扭转吸振研究

磁流变变刚度变阻尼扭转动力吸振器(MR-VSDTVB)为实现动力传动系统扭转振动的有效半主动控制提供了思路.为此,建立了可变刚度和阻尼的汽车动力系统扭转振动动力学模型,加速工况下研究磁流变吸振器不同刚度和阻尼对系统输出响应的影响规律;进而,基于AMEsim和MATLAB/Simulink联合仿真,分析动力系统在加速工况下半主动控制对系统扭转振动的抑制效果,验证磁流变变刚度变阻尼扭转动力吸振器对动力传动系统扭转振动抑制的有效性.