温度梯度场中梁的形变控制研究

5介绍了一种新型的压电作动器—层叠式压电作动器,并使用这种作动器对温度场中的梁进行了形状控制研究。根据哈密顿原理,得到了粘贴有层叠式压电作动器的梁结构的控制方程,进行了数值仿真,并且用Comsol软件进行了模拟,两者的结果基本一致。对压电作动器的控制电压进行了优化,得到了最优控制电压。由于层叠式压电作动器的控制力与压电片的层数成二次函数关系,当控制电压恒定时,层叠式压电作动器的控制力随着压电器层数的增加而迅速减小。使用层叠式压电作动器可以在比其他作动器更小的电压下取得更好的控制效果。通过与普通压电作动器的比较,可以发现层叠式压电作动器可以有效地降低作动器的施加电压,而且可以显著增强控制效果。这种形状控制方法为应用层叠式压电作动器进行薄壁结构的形状控制提供了理论基础。     

基于音圈作动器的大型柔性结构振动主动控制

大型环形柔性结构作为卫星天线的典型结构,由于其显著增大的天线口径有效提高了通信精确度,而使重量仅微小增加,已经成为大口径卫星天线的主流结构。同时它具有固有频率极低、阻尼弱、刚度小等缺点,低频、长时间的模态响应很容易被激起。因此,大型环形柔性结构的振动控制变得尤为重要。针对大型环形柔性结构振动问题,提出一种基于激光位移传感器、音圈作动器和PD-fuzzy控制算法的振动主动控制方法。其中,激光位移传感器能够测量的最小位移为0.01 mm,音圈作动器输出位移和力,基于激光位移传感器的反馈信号运用PD-fuzzy控制算法控制音圈作动器。建立大型环形柔性结构的有限元模型并分析其特性,同时构建试验验证系统。结果表明,该振动主动控制方法性能良好,能够控制大型环形柔性结构的超低频振动,而不会产生附加刚度。     

基于内点法和拉格朗日乘子法的混合试验冗余作动器控制方法

土木工程结构试验中,作动器使用数量多于所要控制的自由度数量时会产生冗余作动器控制问题。为此,提出基于内点法和拉格朗日乘子法的冗余作动器控制方法,给出作动器系统能力可行域的求解方法,该冗余作动器控制方法在控制方程中以三参量的形式考虑了单台作动器的出力范围。以MATLAB为平台计算了作动器能力可行域和冗余作动器出力值,结果表明,当试件位移命令在作动器能力可行域内,该方法可以实现良好的加载控制精度;当位移在作动器能力可行域外,该方法可以保证试验的安全性。基于Simulink搭建控制平台,分析冗余系统和非冗余系统的工作状态;最后以双层双向虚拟混合试验为例,验证了所提冗余控制方法的精度和可行性。     

考虑作动器联接方式的结构形状控制优化

以压电材料梁式作动器控制复合材料层合板形状的设计问题为对象,研究有限个独立控制参数条件下的形状最优控制问题。研究了作动器与信号发生器(独立控制参数)联接关系的参数化描述方式,建立了作动器联接方式与控制参数协同设计的问题提法;针对优化问题中离散变量(联接方式描述参数)和连续变量(控制参数)共存的特点,建立了遗传算法和线性最小二乘(Linear Least Square,LLS)方法相结合的求解策略和方法;在响应分析所采用的有限元模型中,采用粘结层单元描述本体结构与作动器之间的连接。复合材料层合板形状控制设计的实例,验证了该文中建立的问题提法、优化模型和求解策略的有效性。     

频率可调惯性作动器的设计与试验研究

提出用电感-负电阻分流电路来调节惯性作动器的固有频率,使惯性作动器可作为频率可调动力吸振器使用。分析了电感-负电阻电磁分流阻尼的理论模型,随后通过理论和试验分析了惯性作动器固有频率与分流电路参数的关系。以悬臂梁为控制对象,对所设计的可调惯性作动器控制效果进行试验研究。试验结果表明：在保证分流电路系统稳定的前提下,惯性作动器的固有频率随着电感值的降低而增加,惯性作动器的固有频率可以从原来的46.25 Hz调节至111.3 Hz。当惯性作动器固有频率与悬臂梁的固有频率相吻合时,在该固有频率附近悬臂梁的振动幅值降低90%。由此验证了所提出的通过电磁分流电路可以调节惯性作动器固有频率,在不改变惯性作动器物理结构的基础上,使其固有频率能跟踪受控结构的外干扰力频率,就可以充分发挥惯性作动器的吸振能力,最大限度地抑制结构振动。     

振动控制中压电作动器非线性的补偿方法研究

在周期振动的自适应控制中,压电作动器的非线性特性会产生高次谐波,激发高阶模态振动。为抑制压电作动器的高次谐波激励,同时结合自适应振动控制的特点,提出一种新的作动器非线性补偿方法。该方法将作动器的非线性与结构的动态特性部分融合,用正交多项式从输入输出信号中拟合静态非线性及其逆变换,计算过程简单,数值稳定性高。在控制通道中,通过逆变换对控制信号进行预处理,使得补偿后的输入输出具有线性系统的特征,而输入输出之间的相位差完全由自适应算法进行补偿。实验结果表明,所给出的补偿方法能够抑制高次谐波,并改善了振动控制效果。     

智能桁架结构最优振动控制与作动器优化配置

研究了智能桁架结构最优振动控制和作动器的优化配置问题。首先采用有限元方法,根据Hamilton原理推导了智能桁架结构的机电耦合动力学方程,根据线性二次型最优控制理论,推导了结构振动控制的数学模型,通过最小化性能泛函,求解黎卡提矩阵代数方程确定了最优控制输入。然后通过对最优控制性能指标函数的修正,得到了与初始状态无关的性能指标,以修正的性能指标为目标函数,应用模拟退火算法对作动器位置进行了优化配置。最后给出了空间智能桁架结构振动控制算例验证建模过程和算法。算例结果表明,通过最优振动控制可以使结构振动快速衰减,达到振动抑制的效果,而且通过模拟退火算法可以确定最佳的作动器布置方式。     

主动隔振作动器刚度放大与控制误差分析

研究了主动隔振系统中作动器的刚度放大与控制误差问题。主动隔振系统中作动器的刚度应与其负载刚度相匹配,如果负载较大或者作动器刚度较小,可以利用作动器与小刚度弹簧串联的方式放大输出刚度。分析了控制器的输出误差均匀分布时主动隔振系统的隔振性能,分析表明,对作动器刚度放大时,需要同时提高控制器的相对精度与作动器的行程才能保证原有的隔振效果,作动器的输出刚度与控制器相对精度、作动器的输出行程两参数具有等效性与替代性。这为设计主动隔振系统时控制器与作动器在更广阔的范围内选择提供了依据。     

有源控制解耦中压电作动器位置优化

研究基于声辐射模态理论进行有源控制解耦中压电作动器的位置优化问题。以往的研究得出：只要四组作动器满足某种对称形式布置,就可以实现声辐射模态的有源控制解耦,但是满足对称性布置的四组作动器位置有无数个。在主动控制中,压电作动器的位置如何布置一直是个难题。论文以输入控制功率最小化为目标,对四组压电作动器的位置进行了优化。     

基于可控性柱面网壳结构主动控制作动器布置的优化研究

利用磁致伸缩材料的磁控特性制作的作动器可以对结构进行主动控制。首先分析了这种作动器的工作原理和设计方法,并通过实验对其进行了输出性能测试。接着在对作动器进行动力学建模的基础上,推导出整个柱面网壳结构的作动控制方程,同时基于作动效率,提出了不依赖于控制方法的位置优化准则,并且在综合考虑控制效果系数、硬件成本和系统复杂性等因素的基础上,初步确定了作动器的数量,然后采用遗传算法,对作动器的布置位置进行了优化。最后利用LQR主动控制算法,对一柱面网壳模型结构进行了主动控制分析。结果表明,通过优化布置的作动器能够有效地减小结构的动力反应,是一种较好的主动控制方法。此外,主动控制模拟结果也验证了应用遗传算法优化此类问题的优越性和可靠性。     

Shape control of smart composite plate with non-rectangular piezoelectric actuators

Quasi-static shape control of a smart structure may be achieved through optimizing the applied electric fields, loci, shapes and sizes of piezoelectric actuators attached to the structure. In this paper, a finite element analysis (FEA) software has been developed for analyzing static deformation of smart composite plate structures with non-rectangular shaped PZT patches as actuators. The mechanical deformation of the smart composite plate is modeled using a 3rd order plate theory, while the electric field is simulated based on a layer-wise theory. The finite element formulation is verified by comparing with experimentally measured deformation. Numerical results are obtained for the optimum values of the electric field in the PZT actuators to achieve the desired shape using the linear least square (LLS) method. The numerical results demonstrate the influence of the shapes of actuators.     

A buildup voltage distribution (BVD) algorithm for shape control of smart plate structures

 An intuitive approach for the determination of voltage distribution in the application to shape control of smart structures using piezoelectric actuators is presented here. The algorithm called the Buildup Voltage Distribution (BVD) is based on an iterative approach inspired by a combination of existing iterative techniques. The mathematical model of the smart structure is based on a High Order Displacement (HOD) field coupled with a Layerwise Linear electric potential. The current shape control work will make use of the Finite Element (FE) formulation based on the above mentioned mathematical model. The development of the BVD algorithm makes no linearity assumption between displacement and voltage and hence can be applied to non-linear mathematical models. The algorithm will then be compared with two well-known algorithms. In addition, a patch insensitivity index is defined to identify the most and least effective locations for piezoelectric actuators. Received: 15 July 1999     

Design of reconfigurable antennas based on an L-shaped slot and PIN diodes for compact wireless devices

A basic antenna structure to design pattern and pattern/frequency reconfigurable antennas is proposed. The structure consists of an L-shaped slot, PIN diodes, lumped capacitors and bias networks. The PIN diodes and the lumped capacitors located at specific positions are used to create short circuits across the slot. By carefully controlling these diodes, the induced current distribution around the slot can be changed, resulting in different antenna radiation patterns. Thus, a pattern reconfigurable antenna can be achieved. The proposed structure is then extended to design frequency/pattern reconfigurable antennas by introducing varactor diodes. Two compact reconfigurable antennas based on the proposed structure are designed and implemented to prove the design concepts. The experiment results fully demonstrated the performances of the proposed designs. Owing to the compact size and ease on manufacture, the proposed structure can be a promising solution in compact wireless devices such as smart phones and notebook computers.     

压电曲壳单元及其形状控制

板壳结构作为航空、航天工程中的主要工作元件,要承受多种环境荷载,而对形状变化非常敏感的机翼、天线等结构,有必要进行形状控制。推导了空间压电曲壳单元的有限元方程,采用约束方程法连接压电曲壳和主体结构,建立了整体结构的有限元分析模型,并基于等效应变原则验证了模型的正确性。在此基础上,利用最小二乘法对结构进行了形状控制,得到压电驱动器上电压的最优分布。算例表明:该文模型能提高计算精度和速度,达到形状控制的要求。     

Optimal design in vibration control of adaptive structures using a simulated annealing algorithm

Advanced reinforced composite structures incorporating piezoelectric sensors and actuators are increasingly becoming important due to the development of smart structures. These structures offer potential benefits in a wide range of engineering applications such as vibration and noise suppression, shape control and precision positioning. This paper presents a finite element formulation based on the classical laminated plate theory for laminated structures with integrated piezoelectric layers or patches, acting as sensors and actuators. The finite element model is a single layer triangular nonconforming plate/shell element with 18 degrees of freedom for the generalized displacements, and one additional electrical potential degree of freedom for each surface bonded piezoelectric element layer or patch. The control is initialized through a previous optimization of the core of the laminated structure, in order to minimize the vibration amplitude and maximize the first natural frequency. Also the optimization of the patches position is performed to maximize the piezoelectric actuators efficiency. The simulated annealing algorithm is used for these purposes. To achieve a mechanism of active control of the structure dynamic response, a feedback control algorithm is used, coupling the sensor and active piezoelectric layers or patches, and to calculate the dynamic response of the laminated structures the Newmark method is considered. The model is applied in the optimization of an illustrative adaptive laminated plate case. The influence of the position and number of piezoelectric patches, as well as the control gain, are investigated and the results are presented and discussed.     

A gradientless technique for optimal distribution of piezoelectric material for structural control

Application of smart piezoelectric materials in structural control is gaining momentum. Optimum placement and actuation of the smart material is an aspect of paramount importance in such structures. In this paper, we present an iterative technique to optimize the shape of piezoelectric actuators in order to achieve the desired shape of the structure. A C₀‐continuous eight‐node plate finite element with five degrees of freedom is employed. A gradientless shape design procedure based on the residual voltages is developed. It aims at minimizing the quadratic measure of the global displacement residual error between the desired and the current structural configuration. The actuators gradually adapt to a shape that is most efficient in resisting the external excitation. The present technique can be well suited for any static and time‐varying excitation. In vibration control it is often necessary to create modal sensors and actuators in order to observe or excite some specific modes. Such modal sensors and actuators alleviate spillover problems and thus they avoid exhaustive signal processing. Several numerical examples for static as well as dynamic cases are presented to demonstrate the efficacy of the present technique. Copyright © 2003 John Wiley & Sons, Ltd.     

含SMA和PZT二元驱动器的智能复合材料结构形状控制

基于有限元素法求解嵌入SMA和PZT作为联合变形驱动器的板壳型智能结构的变形,采用优化方法将最小化目标变形和实际变形差作为目标函数,确定各个驱动器的驱动电压或控制温度以实现自适应结构的任意变形控制,并考虑到了控制电压和结构温度的限制。算例结果列举了联合控制同单独PZT或SMA控制方式的控制效果对比。      

On chip plasmonic monopole nano-antennas and circuits

Analogues of many radio frequency (RF) antenna designs such as the half-wave dipole and Yagi-Uda have been successfully adapted to the optical frequency regime, opening the door for important advances in biosensing, photodetection, and emitter control. Examples of monopole antennas, however, are conspicuously rare given the element's extensive use in RF applications. Monopole antennas are attractive as they represent an easy to engineer, compact geometry and are well isolated from interference due the ground plane. Typically, however, the need to orient the antenna element perpendicular to a semi-infinite ground plane requires a three-dimensional structure and is incompatible with chip-based fabrication techniques. We propose and demonstrate here for the first time that monopole antenna elements can be fashioned out of single element nanoparticles fabricated in conventional planar geometries by using a small nanorod as a wire reflector. The structure offers a compact geometry and the reflector element provides a measure of isolation analogous to the RF counterpart. This isolation persists in the conductive coupling regime, allowing multiple monopoles to be combined into a single nanoparticle, yet still operate independently. This contrasts with several previous studies that observed dramatic variations in the spectral response of conductively coupled particles. We are able to account for these effects by modeling the system using circuit equations from standard RF antenna theory. Our model accurately describes this behavior as well as the detailed resonance tuning of the structure. As a specific practical application, the monopole resonances are precisely tuned to desired protein absorption bands, thereby enhancing their spectroscopic signatures. Furthermore, the accurate modeling of conductive coupling and demonstrated electronic isolation should be of general interest to the design of complex plasmonic circuits incorporating multiple antennas and other current carrying elements.     

Smart soft composite actuator with shape retention capability using embedded fusible alloy structures

This work presents a new kind of shape memory alloy (SMA) based composite actuators that can retain its shape in multiple configurations without continuous energy consumption by changing locally between a high-stiffness and a low-stiffness state. This was accomplished by embedding fusible alloy (FA) material, Ni-chrome (Ni–Cr) wires and SMA wires in a smart soft composite (SSC) structure. The soft morphing capability of SMA-based SSC structures allows the actuator to produce a smooth continuous deformation. The stiffness variation of the actuator was accomplished by melting the embedded FA structures using Ni–Cr wires embedded in the FA structure. First, the design and manufacturing method of the actuator are described. Then, the stiffness of the structure in the low and high-stiffness states of the actuator were measured for different applied currents and heating durations of the FA structure and results show that the highest stiffness of the actuator is more than eight times that of its lowest stiffness. The different shape retention capability of the actuator were tested using actuators with one or two segments and these were compared with a numerical model.