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 root structure installed with MRF-04K damper is presented. The effectiveness of the controller is evaluated under both Tianjin and E1 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.

Modal Control of Cantilever Beam Using a Gyrostabilizer

In this paper,an experimental model of a horizontal cantilever beam with a rotating/oscillating attached to the shaker for harmonic excitation at the one end and a gyrostabilizer at the other end is built to verify the equations of the Lagrangian model.The primary focus of the study was to investigate the parameters of excitation amplitude,natural frequency,rotating mass(disk mass),and disk speed of gyro that would minimize the amplitude of the beam to identify these effects.Numerical and experimental results indicate that the angular momentum of the gyrostabilizer is the most effective parameter in the reduction of beam displacement.

Effects of Joint Controller on Analytical Modal Analysis of Rotational Flexible Manipulator

Modal analysis is a fundamental and important task for modeling and control of the flexible manipulator. However, almost all of the traditional modal analysis methods view the flexible manipulator as a pure mechanical structure and neglect feedback action of joint controller. In order to study the effects of joint controller on the modal analysis of rotational flexible manipulator, a closed-loop analytical modal analysis method is proposed. Firstly, two exact boundary constraints, namely servo feedback constraint and bending moment constraint, are derived to solve the vibration partial differential equation. It is found that the stiffness and damping gains of joint controller are both included in the boundary conditions, which lead to an unconventional secular term. Secondly, analytical algorithm based on Ritz approach is developed by using Laplace transform and complex modal approach to obtain the natural frequencies and mode shapes. And then, the numerical simulations are performed and the computational results show that joint controller has pronounced influence on the modal parameters： joint controller stiffness reduces the natural frequency, while joint controller damping makes the shape phase non-zero. Furthermore, the validity of the presented conclusion is confirmed through experimental studies. These findings are expected to improve the performance of dynamics simulation systems and model-based controllers.

Sensory Modality Matters in Attentional Control

Imagine how many times your attention is distracted by the surrounding sounds or sights irrelevant to your work or study.To maintain concentrated,you have to control yourself intentionally,which is called"attentional control"or"cognitive control"in psychology.An interesting question arises:when we successfully direct our attention away from one visual distractor,can we be immune to another

Terminal-Modality-Based Joint Call Admission Control Algorithm for Fair Radio Resource Allocation in Heterogeneous Cellular Networks

There is a problem of unfairness in allocation of radio resources among heterogeneous mobile terminals in heterogeneous wireless networks. Low-capability mobile terminals (such as single-mode terminals) suffer high call blocking probability whereas high-capability mobile terminals (such as quad-mode terminals) experience very low call blocking probability, in the same heterogeneous wireless network. This paper proposes a Terminal-Modality-Based Joint Call Admission Control (TJCAC) algorithm to reduce this problem of unfairness. The proposed TJCAC algorithm makes call admission decisions based on mobile terminal modality (capability), network load, and radio access technology (RAT) terminal support index. The objectives of the proposed TJCAC algorithm are to reduce call blocking/dropping probability, and ensure fairness in allocation of radio resources among heterogeneous mobile terminals in heterogeneous networks. An analytical model is developed to evaluate the performance of the proposed TJCAC scheme in terms of call blocking/dropping probability in a heterogeneous wireless network. The performance of the proposed TJCAC algorithm is compared with that of other JCAC algorithms. Results show that the proposed algorithm reduces call blocking/dropping probability in the networks, and ensure fairness in allocation of radio resources among heterogeneous terminals.

MODAL SYNTHESIS METHOD FOR NORM COMPUTATION OF H_∞ DECENTRALIZED CONTROL SYSTEMS (II)

When using H_∞ techniques to design decentralized controllers for large systems, the whole system is divided into subsystems, which are analysed using H_∞ control theory before being recombined. An analogy was established with substructural analysis in structural mechanics, in which H_∞ decentralized control theory corresponds to substructural modal synthesis theory so that the optimal H_∞ norm of the whole system corresponds to the fundamental vibration frequency of the whole structure. Hence, modal synthesis methodology and the extended Wittrick_Williams algorithm were transplanted from structural mechanics to compute the optimal H_∞ norm of the control system. The orthogonality and the expansion theorem of eigenfunctions of the subsystems H_∞ control are presented in part (Ⅰ) of the paper. The modal synthesis method for computation of the optimal H_∞ norm of decentralized control systems and numerical examples are presented in part (Ⅱ).

基于滤波技术的激光数控加工误差控制策略

为降低激光数控加工过程中的轨迹跟踪误差,分析了激光数控加工进给伺服系统跟踪误差和等效模型偏差形成的原因,设计了基于滤波技术的激光数控加工误差控制策略,旨在预测激光数控加工轨迹跟踪误差。通过设计的模态滤波控制器进行激光数控加工运动轨迹补偿,从而实现加工误差控制。测试结果表明,该策略能够有效获取激光数控加工轨迹的跟踪误差结果,两种加工模式均可在1 s内完成控制响应;能够有效完成激光数控加工动作补偿,双向加工轨迹跟踪误差结果均在15μm以下。

悬索桥竖弯涡振MTMD减振控制效果和参数优化研究

为研究多重调谐质量阻尼器(Multiple Tuned Mass Damper,MTMD)抑制桥梁单阶涡振的性能,建立桥梁结构-MTMD系统竖弯涡振广义单自由度动力方程,以某大跨度悬索桥为背景进行MTMD减振控制效果和参数优化分析。采用数值方法求解动力方程,获得系统在简谐涡激力下达到稳态谐振时结构的动力放大系数和MTMD对结构的附加模态阻尼比,并与单一频率调谐质量阻尼器(Single Tuned Mass Damper,STMD)的减振控制效果进行对比,然后以附加模态阻尼比为目标对MTMD进行参数优化。结果表明:MTMD比最优参数STMD拥有更宽的控制频带和更好的减振效果,经优化后的MTMD减振性能优于最优参数STMD。实际应用MTMD时,应选择较大广义质量、5~7种频率规格,并根据二者找到无量纲频率范围和各TMD阻尼比的惟一最优取值。

管道中激发L(0,2)导波的EMAT结构设计及优化

超声导波在管道中传播时具有多模态特性,导致超声导波检测的回波信号复杂难以分辨。依据EMAT激发机理和纵向超声导波的波结构特性,设计一种周期性永磁铁组以增大洛伦兹力轴向分量、减小径向分量,激励纯净的L(0,2)模态导波。研究永磁铁宽度对L(0,1)模态抑制效果的影响规律,得到控制效果较好的永磁铁宽度。结果表明:相比传统EMAT,新型EMAT对L(0,1)模态抑制效果显著,L(0,2)模态与L(0,1)模态峰值之比是传统EMAT的7.62倍。

一种基于PSO-VMD和LSTM的复杂山地风电场观测风速数据质量控制算法

复杂山地风电场普遍存在观测风速数据质量差引起风资源评估误差大、风功率预测精度低的问题。而复杂山地风速呈现较强的间隙性、波动性和非平稳性,导致常规质量控制方法无法有效提高数据质量。针对此,提出一种基于粒子群改进变分模态分解和长短期记忆网络的集成学习算法(PVL),并应用于复杂山地观测风速的质量控制以提高风速数据的质量。以广西某复杂山地风场内5基观测塔2015—2016年逐10 min风速数据为案例进行PVL应用效果检验,并与传统单站及空间回归法、反距离加权法进行对比。应用表明,PVL比传统方法具有更高的寻误率,且在异地形、多风况上具有更强的适应性。

应用变速控制力矩陀螺的航天器姿态自适应控制

为提高敏捷挠性航天器在轨连续机动的快速性和高稳定性,应用变速控制力矩陀螺(variable speed control moment gyroscopes,VSCMGs)作为姿态控制执行机构,提出了一种将观测器与自适应控制结合的姿态控制律与VSCMGs复合操纵律。考虑到机动过程中挠性模态及精确惯量不可知,采用模态观测器和转动惯量估计器对不可测的状态或参数进行辨识,辨识结果用于精确估计前馈补偿力矩,利用Lyapunov分析方法证明了闭环控制系统的稳定性。鉴于VSCMGs实际使用的力矩分配能力、避奇异能力、轮速平衡能力与末态框架角定位能力,分别设计了加权伪逆操纵律与3种对应的零运动。基于雅可比矩阵条件数提出了末态框架角的优选方法,给出了VSCMGs零运动在机动过程不同阶段的部署方案。结果表明:通过连续姿态机动数值仿真验证了所提算法的有效性;VSCMGs在连续机动过程中平滑切换模式,在不同的机动阶段实现了相应功能。模态观测值和惯量估计值在多次机动后收敛至真值附近,经过参数辨识后的控制器使航天器在机动末端更快更稳地达到指向精度要求。

深水钻井隔水管横向振动振型分析

为了分析深水钻井隔水管的横向振动固有频率和振型,综合考虑深水隔水管受到的顶部张紧力、海洋环境载荷、钻井平台漂移等作用力,借助微元法建立受力分析模型。根据连续梁理论和隔水管单元的动力学微分方程,确定其无阻尼自然振动基本方程,并进一步剖析建立隔水管横向振动固有频率微分方程和模态振型基本方程,然后进行数值求解。使用控制变量法逐步分析隔水管长度、张力比、自身材质对隔水管固有频率的影响和变化规律。通过MATLAB软件表现出不同阶数的振动振型,结果表明:控制张力比、合理选择隔水管类型能够有效提高固有频率,避免与波流力形成共振,进而保证深水钻井作业安全。此外,隔水管的振型并不是标准正弦曲线,振型会受时间的影响不断变化。

电力系统受迫振荡检测与自适应振荡抑制研究

电力系统受迫振荡的振荡频率与系统跨区域振荡模态接近,因而能够引发强烈振荡。文中提出了一种受迫振荡模态检测方法,其通过小信号分析方法得出系统在受迫扰动下对应受迫振荡模态的解析形式;同时提出一种不需要安装额外的功率振荡阻尼器的功率振荡阻尼控制策略,用于抑制受迫振荡以及跨区域振荡。通过改进的14机系统验证了文中方法的鲁棒性和优越性。仿真算例证明所提方法对于外界扰动具有较强鲁棒性,且较传统方法具有明显优越性。

一种多模态振动系统的位置控制方法

以多模态柔性系统为研究对象,针对多模态柔性系统在操作时产生振动,影响操作性能和定位精度的问题,提出了一种基于振动叠加原理和位置控制原理对柔性系统进行主动振动抑制的方法。首先利用振动叠加原理,对系统的振动进行分解,讨论了系统的振动状态与能量表达;接着以系统的振动能量为指标,给出了抑制振动的输入位移的一种选择方法;然后为保证多模态系统在减振完成后的定位精度,提出了一种位置控制方法。为了验证所提出的振动抑制方法的有效性,首先在ADAMS中建立了单输入多模态系统的模型,然后导入Simulink中进行联合仿真,讨论此振动抑制方法的有效性以及其抑制特性。仿真结果表明:所提出的方法的减振效果良好,对比传统的控制方法来说,有较高的鲁棒性,有效抑制了系统的振动并且保证了系统的定位精度。

动力学系统在亏损时的反馈控制设计

通过引入反馈控制,使亏损系统动态特性得到优化。基于广义模态理论,利用系统矩阵结构特征,讨论亏损系统增益向量的计算方法,简化计算过程。通过分析二自由度飞机机翼运动学模型数据,验证该方法的有效性。

基于阻尼器与分隔器混合措施的吊索多模态减振控制研究

吊索是悬索桥的关键传力构件,其长细比大、质量小、阻尼低,极易在动荷载作用下发生大幅振动。目前,采用索端阻尼器结合刚性分隔器的混合减振措施已被证明在悬索桥吊索减振控制中具有较好效果,但目前针对该措施的研究多局限在控制吊索的低阶及单阶模态。而某些情况下,吊索可能会出现高阶及多阶模态振动问题,超出了既有研究的适用范围。鉴于此,开展了索端阻尼器结合刚性分隔器的吊索多模态减振控制研究。首先,基于有限差分法,建立双索-阻尼器系统运动方程,并验证其准确性,得到了双索-阻尼器系统的动力特性;其次,提出双索-阻尼器系统多模态减振控制的优化目标,对分隔器和阻尼器参数进行了优化设计。结果表明,阻尼器所能提供的多阶模态阻尼效果受到分隔器的刚度和位置的影响,当分隔器安装在远离阻尼器的一端时,阻尼器能够实现更好的多模态减振效果。相较于奇数阶模态的最大阻尼比,偶数阶模态的最大阻尼比受分隔器参数的影响更为明显。

基于模态阻尼指标的空间杆系结构作动器位置优化

针对空间杆系结构作动器的位置优化问题,本文基于线性二次型最优控制理论(LQR),建立了空间杆系结构振动的主动控制系统,提出了目标控制模态的模态阻尼最大化的作动器位置优化准则.采用四角锥网架结构和Levy型索穹顶结构来验证本文方法的有效性,并在控制效果和控制能量输入两方面与常用的模态控制力方法进行了对比分析.结果表明:随着作动器数量的增加,本文方法的控制效果和控制能量输入比模态控制力方法提升更快;在作动器数量相同或控制能量输入相同时,本文方法对外界激励的控制效果优于模态控制力方法.

分散式速度反馈控制流激薄板声振响应的模态解及特性

采用模态展开法推导了湍流边界层和分散式速度反馈控制共同作用下薄板的响应和声辐射,给出了与分散式速度反馈控制增益系数、单元位置、数量和大小相关的模态阻尼的显示表达式。给定激励和参数的条件下,通过与元素法的计算结果进行对比,验证了模态展开法具有较高的计算效率和准确性。讨论了分散式速度反馈控制单元的布置方式和数量对模态阻尼的影响,以及反馈控制单元的布置方式对薄板动能、辐射声功率和模态平均辐射系数的影响。数值分析结果表明反馈控制单元的数量和布放位置对控制效果影响显著,反馈控制单元沿螺旋线布置能明显拓宽控制频带;两种反馈控制单元布置方式,在动能和辐射声功率控制较好的共振频率处,除第一阶模态外,模态平均声辐射效率随反馈增益的增大明显提高。

Dynamics of cantilever plates and its hybrid vibration control

Applying Lagrange-Germain＇s theory of elas- tic thin plates and Hamiltonian formulation, the dynamics of cantilever plates and the problem of its vibration control are studied, and a general solution is finally given. Based on Hamiltonian and Lagrangian density function, we can obtain the flexural wave equation of the plate and the relationship between the transverse and the longitudinal eigenvalues. Based on eigenfunction expansion, dispersion equations of propagation mode of cantilever plates are deduced. By satisfying the boundary conditions of cantilever plates, the natural frequencies of the cantilever plate structure can be given. Then, analytic solution of the problem in plate structure is obtained. An hybrid wave/mode control approach, which is based on both independent modal space control and wave control methods, is described and adopted to analyze the active vibration control of cantilever plates. The low-order （controlled by modal control） and the high-order （controlled by wave control） frequency response of plates are both improved. The control spillover is avoided and the robustness of the system is also improved. Finally, simulation results are analyzed and discussed.

Research on active vibration control on a piezoelectric intelligent flexible beam

The principles and methods of active vibration control on a flexible cantilever beam using piezoelectric patches as actuators is studied. Active control of the first two modes of the flexible can- tilever beam is implemented based on the independent modal control law. Experimental results show that the structural damping of the flexible cantilever beam is effectively improved and an excellent degree of vibration suppression is achieved with the active vibration control strategy.