Vibration Control of A Flexible Marine Riser System Subject to Input Dead Zone and Extraneous Disturbances

An observer-based adaptive backstepping boundary control is proposed for vibration control of flexible offshore riser systems with unknown nonlinear input dead zone and uncertain environmental disturbances.The control algorithm can update the control law online through real-time data to make the controller adapt to the environment and improve the control precision.Specifically,based on the adaptive backstepping framework,virtual control laws and Lyapunov functions are designed for each subsystem.Three direction interference observers are designed to track the timevarying boundary disturbance.On this basis,the inverse of the dead zone and linear state transformation are used to compensate for the original system and eliminate the adverse effects of the dead zone.In addition,the stability of the closed-loop system is proven by Lyapunov stability theory.All the system states are bounded,and the vibration offset of the riser converges to a small area of the initial position.Finally,four examples of flexible marine risers are simulated in MATLAB to verify the effectiveness of the proposed controller.

Prototype observation and influencing factors of environmental vibrationinduced by flood discharge

Due to a wide range of field vibration problems caused by flood discharge at the Xiangjiaba Hydropower Station, vibration characteristics and influencing factors were investigated based on prototype observation. The results indicate that field vibrations caused by flood discharge have distinctive characteristics of constancy, low frequency, small amplitude, and randomness with impact, which significantly differ from the common high-frequency vibration characteristics. Field vibrations have a main frequency of about 0.5-3.0 Hz and the characteristics of long propagation distance and large-scale impact. The vibration of a stilling basin slab runs mainly in the vertical direction. The vibration response of the guide wall perpendicular to the flow is significantly stronger than it is in other directions and decreases linearly downstream along the guide wall. The vibration response of the underground turbine floor is mainly caused by the load of unit operation. Urban environmental vibration has particular distribution characteristics and change patterns, and is greatly affected by discharge, scheduling modes, and geological conditions. Along with the increase of the height of residential buildings, vibration responses show a significant amplification effect. The horizontal and vertical vibrations of the 7th floor are, respectively, about 6 times and 1.5 times stronger than the corresponding vibrations of the 1st floor. The vibration of a large-scale chemical plant presents the combined action of flood discharge and working machines. Meanwhile, it is very difficult to reduce the low-frequency environmental vibrations. Optimization of the discharge scheduling mode is one of the effective measures of reducing the flow impact loads at present. Choosing reasonable dam sites is crucial.

Train-induced vibration on elevated railway station

Results of in-situ vibration measurement carried out at Tianjin West Elevated Railway Station which has the trains running on the station structure were reported. The main excitation source is the train passing through the station. Vibration measurements were recorded in the vertical direction of the supporting track beam, the platform and the steel truss beam of the waiting hall, as well as in the vertical, longitudinal and transverse directions of the roof arch base of the station. Acceleration time responses were obtained. The maximum value, vibration level and one-third octave band RMS spectra of the measured accelerations were studied. The propagation of vibration in different structural floors was discussed. The influence of train speed, distance to the vibration source and the type of train on the structural vibration were analyzed. Results show that the vibration level increases with the train speed, while it attenuates with the distance to the track. Furthermore, the vibration responses of different structural floors were compared, and it is noted that the vertical vibration of the bottom slab of the platform is most severe and the transverse vibration of the roof arch base is the smallest. The results provide reference on the vibration characteristics and vibration energy distribution of this type of "Train on building frame" system used as an elevated railway station.

Dynamic response analysis of train-induced vibration impact on the Probhutaratna pagoda in Beijing

Train-induced vibration exhibits a potential dynamic impact on historic buildings and especially on those with high historical and cultural value.Under the long-term reciprocating load of train vibrations,structural fatigue damage can occur,and thus,a significant problem involves effectively evaluating and mitigating vibration impact on historic buildings while developing a rail transit system.In the present study,train-induced vibration impact and dynamic behavior of Probhutaratna pagoda in the suburb of Beijing,which has a history of approximately 1000 years,was investigated.To examine the dynamic behavior of the Probhutaratna pagoda and determine the weakest position in its architectural damage under train loads,its dynamic characteristics were measured.The free vibration modes were identified based on the dynamic measurement results.Subsequently,a finite element(FE)model of the Probhutaratna pagoda was constructed and the models and train-induced structural responses were compared with measured results.Finally,the structural dynamic responses to moving train loads were analyzed in detail.The results indicate the following conclusions.(1)The dominant frequency of the ambient vibration is below 4 Hz,and the dominant frequency of the train-induced vibration is between 8 and 16 Hz.(2)The first,second,and third order natural frequencies are 1,3.25,and 6 Hz,respectively,in the west-east direction,and are 1,3.25,and 6.25 Hz,respectively,in the north-south direction.(3)The two weakest locations(A and B)of the Probhutaratna pagoda are observed at the spire bottom and west gate of the first floor.At location A,the maximum principal stress reached 243.6 N/m^2 and the corresponding maximum tensile strain reached 3.74×10^-7.

Observer-based State Feedback Control to Suppress Stick-slip Vibrations in Oil Well Drill-string

In drilling field, stick-slip vibrations of the drill-string are the main reason for the failure of the drilling system. To suppress the undesired stick-slip vibrations, an observer-based state feedback control method is proposed. The drilling system is described by a lumped parameter model including a Karnopp friction torque model. A state observer is designed to estimate the bit velocity in bottom hole and a state feedback controller is proposed to control the top drive velocity. By simulation, the performance of the control algorithm is demonstrated. Based on the control algorithm, a stick-slip vibration control system is developed. Test results show that the control system can effectively eliminate stick-slip vibrations of the drill-string and can be applied to the drilling field.

Robust Adaptive Attitude Maneuvering and Vibration Reducing Control of Flexible Spacecraft Under Input Saturation

A robust adaptive control scheme is proposed for attitude maneuver and vibration suppression of flexible spacecraft in situations where parametric uncertainties,external disturbances,unmeasured elastic vibration and input saturation constraints exist. The controller does not need the knowledge of modal variables but the estimates of modal variables provided by appropriate dynamics of the controller. The requirements to know the system parameters and the bound of the external disturbance in advance are also eliminated by adaptive updating technique. Moreover,an auxiliary design system is constructed to analyze and compensate the effect of input saturation,and the state of the auxiliary design system is applied to the procedure of control design and stability analysis. Within the framework of the Lyapunov theory,stabilization and disturbance rejection of the overall system are ensured. Finally,simulations are conducted to study the effectiveness of the proposed control scheme,and simulation results demonstrate that the precise attitude control and vibration suppression are successfully achieved.

Field monitoring of railroad embankment vibration responses in seasonally frozen regions

To investigate the vibration characteristics of a railway subgrade in different seasons, three field experiments were carried out in the seasonally frozen Daqing area of China during spring, smnmer, and winter. The vibration characteristics and attenuation rates of the subgrade induced by passing trains were investigated, and the influences of the season, train speed, train type, train load, and number of train compartments are described in this paper. The results show that： （1） near the rail track the vibration in the vertical direction was more significant than in the lateral and longitudinal directions, and as the distance from the railway track increased, the acceleration amplitudes and the attenuation rates all decreased in all three directions; （2） the acceleration amplitudes and at- tenuation rates decreased in the three different study seasons as the distance from the railway track increased, and the attenuation rates in the freezing period were the largest; and （3） the acceleration amplitude induced by a freight train was greater than that by a passenger train, and the subgrade vibration increased with increasing passenger train speeds when the number of train compart- ments was similar. These results have great significance for enhanced understanding of the characteristics of wain-induced vibra- tion embankment response in seasonally frozen regions, and provide essential field monitoring data on train-induced vibrations in order to improve the performance criteria of railroading in seasonally frozen regions.

Robust Adaptive Attitude Maneuvering and Vibration Reducing Control of Flexible Spacecraft with Prescribed Performance

A robust adaptive control scheme with prescribed performance is proposed for attitude maneuver and vibration suppression of flexible spacecraft,in which the parametric uncertainty,external disturbances and unmeasured elastic vibration are taken into account simultaneously.On the basis of the prescribed performance control(PPC)theory,the prescribed steady state and transient performance for the attitude tracking error can be guaranteed through the stabilization of the transformed system.This controller does not need the knowledge of modal variables.The absence of measurements of these variables is compensated by appropriate dynamics of the controller which supplies their estimates.The method of sliding mode differentiator is introduced to overcome the problem of explosion of complexity inherent in traditional backstepping design.In addition,the requirements of knowing the system parameters and the unknown bound of the lumped uncertainty,including external disturbance and the estimate error of sliding mode differentiator,have been eliminated by using adaptive updating technique.Within the framework of Lyapunov theory,the stability of the transformed system is obtained.Finally,numerical simulations are carried out to verify the effectiveness of the proposed control scheme.

底流消能诱发泄洪闸闸墩振动问题分析和减振措施研究

底流式泄洪闸在大流量泄洪时常伴随着闸墩剧烈振动。针对泄洪闸闸墩振动问题,以某水电站为例,基于水弹性物理模型试验和原型观测,提出改善闸墩结构和优化水库调度方案的两种减振措施。物理模型试验为研究闸墩振动提供了数据支撑,而原型观测结果验证了模型试验的可靠性。结果表明:当泄流量为5400 m^(3)/s时,通过优化水库调度,采用“低孔+表孔”联合泄洪的方式,表孔的泄流量从单独泄洪时的5400 m^(3)/s转变为联合泄洪时的低孔泄流量3481 m^(3)/s+表孔泄流量1919 m^(3)/s,表孔闸墩的振动位移标准差可从182.3μm减小到51.7μm,振动削减效果为71.6%;当表孔泄流量为10030 m^(3)/s时,通过对闸墩进行加固,闸墩的振动位移标准差可由288.8μm减小到129.6μm,振动削减效果为55.1%。

柔性机械臂干扰力观测与无模型振动控制

为了抑制柔性机械臂运动过程中的非线性振动,提出一种基于干扰力在线观测的无模型轨迹跟踪和振动抑制混合控制策略。采用拉格朗日方程和奇异摄动法对存在未知干扰的柔性机械臂进行动力学建模和解耦,将其分解为表征刚性运动的慢变子系统和表征柔性振动的快变子系统;考虑到建模的复杂性和模型参数的不确定性,采用PD控制方法实现轨迹跟踪,并提出无模型自适应控制算法以实现柔性臂杆的非线性振动控制。针对未知外界干扰可能引起的控制发散问题,提出了改进的干扰力状态观测器,用于干扰力矩的在线估计和实时补偿,有效提高无模型振动控制算法的收敛性能。仿真试验结果表明,所提算法在存在干扰力的情况下对柔性机械臂的振动抑制效果显著,且具有良好的动态性能和鲁棒性。

主动磁轴承系统建模与准谐振自抗扰振动抑制

为了建立更准确的磁轴承数学模型,优化其控制性能,对磁轴承的电磁力非线性特性和系统固有干扰源进行了分析,通过转子动力学分析建立了含干扰源的主动磁轴承径向耦合系统模型。为抑制系统的振动,提出了一种磁轴承准谐振自抗扰振动抑制方法。通过扩张状态观测器实现系统解耦,简化控制流程,提升系统抗干扰能力;在此基础上,并入准谐振控制器对正弦周期性振动进行抑制。与传统方法相比,该方法控制结构简单,所需整定参数较少。仿真与试验结果表明,所提方法可以有效降低转子位移振动幅值,系统内常见的1、3、5倍频周期性振动得到显著抑制,具有良好的振动抑制效果。

采用干扰补偿模糊整定的双柔性机械臂抑振策略

双柔性机械臂由柔性关节和变长度的柔性负载组成,会同时受到柔性、摩擦和参数时变的影响,在运动过程中,它会出现振动的现象,导致末端执行器的跟踪精度降低。本文采用基于干扰观测器的模糊整定PI策略控制双柔性机械臂伺服系统的输出转速,通过控制柔性负载的转速波动间接抑制机械臂的振动。根据假设模态法和拉格朗日原理建立了考虑变形的双柔性机械臂伺服系统的动力学方程。根据鲁棒稳定性理论设计干扰观测器中的低通滤波器,使干扰观测器同时满足控制器参数时变和受控对象参数摄动的稳定性。通过数值仿真分析和双柔性机械臂伺服系统控制实验,验证了所提方法的有效性。实验结果表明,本文提出的控制策略可以更好地消除参数时变和柔性对于输出转速的影响,提高末端执行器的控制精度。

参数跟踪鲁棒观测器的四旋翼无人机抑振设计

提出一种针对四旋翼无人机振动的参数跟踪鲁棒观测器设计方法。首先构造辅助滤波器激励出振动特性,同时调节其参数降低噪声对辅助状态变量的影响,将主动振动抑制转化为与频率有关的常值参数估计问题,避免了估计值之间的耦合和冗余参数的运算。然后设计频率参数观测器和跟踪器的级联结构准确估计振动信息。在此基础上,通过辅助变量和频率参数对振动进行重构,设计前馈补偿的控制方法实现了系统的振动抑制。所设计的观测器不仅具有较好的鲁棒性,还避免了传统跟踪器跟踪时变信号带来的相位滞后。最后通过李雅普诺夫定理对系统的性能进行了分析,仿真算例验证了该方法的有效性。

基于状态观测器的智能悬臂梁自适应SSDV半主动振动控制研究

半主动振动控制因其不需精确的结构模型就能实现较好的振动控制效果,以航天器上使用的某种轻质复合材料制作的智能悬臂梁结构件为载体,设计一种基于状态观测器的自适应SSDV半主动控制方法对其进行振动控制研究,取得了较好的控制效果,状态观测器观测值误差在1%之内,一阶振动幅值减少了75.24%。这为航天器上柔性化和低刚度的悬臂结构件的振动控制提供一种有效可行的参考方法。

南水水库高水位运行状态下泄洪洞出口弧形闸门原型观测结果分析

随着全球气候的异常变化,局部地区出现强降雨的情况时常发生,导致地区水库长时间在高水位运行。部分水库承担泄洪任务的关键金属结构弧形闸门运行时间已超过折旧年限,判断同类闸门在此极端情况下能否安全运行至关重要。本文根据南水水库出口弧形闸门原型观测试验结果,从结构应力测试、动力特性测试、振动响应测试和启闭力测试等方面对出口弧形闸门进行安全评价,得出结论:泄洪洞出口弧形闸门虽运行逾50年,且处于高水位运行状态,但由于其合理的设计结构,仍具有可靠的安全裕度和较高的经济价值。本文研究结果对已超折旧年限且运行状态发生极端变化的弧形闸门的安全性评价具有一定的参考价值。

高速铁路引起季冻区场地环境振动实测分析

为研究冬、夏两季高速铁路引起季冻区场地环境振动评价方法的适用性,文中分别于冬、夏两季在哈—齐高速铁路龙凤湿地段开展现场观测,并将数据进行时域和频域分析。结果表明随着距桥墩中心距离的增加,冬、夏两季各测点加速度时程均呈现出先急剧衰减后缓慢衰减的趋势,0~15m夏季加速度幅值要比冬季衰减的快;近轨道处冬季峰值频率为58Hz,夏季峰值频率为47Hz。研究为季冻区土场地的道路、桥梁等的选址提供参考。

直线电机高速高精运动分段式三元复合控制

针对半导体键合机XY运动平台的直线电机在高速启停运动时残余振动较大的问题,提出了一种分段式三元复合控制方法以提高直线电机的定位精度。首先,基于正弦扫频的方法建立了直线电机被控对象的高阶精确模型;其次,在直线电机的高速运动阶段采用三阶前馈控制与PID反馈控制结合的复合控制方法,实现了高动态响应;分析了高速运动状态下扰动观测器对动态性能的影响,在定位阶段引入高阶扰动观测器以抑制残余振动。实验结果表明,与传统的“前馈+反馈”复合控制方法相比,分段式三元复合控制方法在不影响直线电机动态跟踪性能的情况下,使其定位误差调整至±0.5μm所需的时间降低了89%以上,显著提高了其定位精度。

东日本大地震后某校舍抗震加固改造与效果评估实验研究

2011年东日本大地震后,校舍建筑的抗震加固变得极为迫切。针对日本某校舍建筑的抗震加固工程展开计算分析及实验研究。首先阐述既有校舍建筑的结构特征及抗震鉴定结果,提出纵向采用钢支撑框架提高强度,首层横向新设剪力墙以及增厚楼梯间楼板的加固方案。随后,利用无线振动测试系统在校舍建筑抗震加固前后进行常时微动测试实验,分别从整体与局部角度分析加固前后校舍建筑加速度响应、固有周期以及振型等参数变化。最后,对比分析有限元计算及测试结果,阐述抗震加固方法及位置对原有建筑的性能影响,验证抗震加固方法的有效性。结果表明:采用钢支撑框架的加固方法有效提高既有校舍建筑的强度,加固后加速度响应值约降低至加固前的1/3,加固方法起到提高整体强度、改善刚度分布及结构整体性作用;固有周期以及加速度响应放大倍率的变化与该校舍抗震加固方法较吻合,表明基于振动测试的研究方法能够有效评估抗震加固措施的效果。研究成果可为既有校舍建筑的抗震加固方案选取及性能评估提供参考。

船舶水润滑尾轴承异常振动自适应控制方法

为避免因船舶水润滑尾轴承异常振动导致的严重机械故障,威胁船舶运行安全,研究船舶水润滑尾轴承异常振动自适应控制方法。依据水润滑尾轴承的异常振动产生原因,设计水润滑尾轴承异常振动控制结构。利用位移传感器采集实际水润滑尾轴承转子位移信号,使用滑膜观测器观测水润滑尾轴承的不平衡扰动力,将其作为惯性主轴位置校正器的输入,得到扰动引起位移偏差的补偿量。结合水润滑尾轴承转子理想位移值,计算轴承转子位移信号偏差值,将其作为PID控制器的输入控制量,输出轴承异常振动控制量,实现其异常振动自适应控制。实验结果表明,该方法可有效控制船舶水润滑尾轴承异常振动,提高轴承的工作稳定性。

Extended-state-observer-based robust torsional vibration suppression for rolling mill main drive system with input saturation

A robust torsional vibration suppression strategy is proposed for the main drive system of the rolling mill subject to uncertainties,disturbances and input saturation.With given model information incorporated into observer design,an extended state observer that relies only on roller speed measurements is developed to estimate the system states and lumped uncertainties of the rolling mill main drive system.To handle the motor torque saturation,an auxiliary signal system with the same order as the plant is constructed.The error between the control input and plant input is taken as the input of the constructed auxiliary system,and a number of signals are generated to compensate for the effect of the motor torque saturation.Furthermore,a robust output feedback controller is introduced to obtain better transient and steady-state performance of the rolling mill main drive system and the stability of the closed-loop system is strictly proved via Lyapunov theory.Finally,comparative simulations are performed to verify the effectiveness and superiority of the proposed control strategy.