基于声能量密度的自适应主动结构声控制研究

目前,基于自适应滤波的噪声主动控制系统目标有:声势能控制、均方声压控制、声能量密度控制,声势能和均方声压控制忽略了声场动能,使得某处声势能的降低的同时动能增加,以至于封闭声场的总能量增加,产生控制溢出.以矩形封闭空间结构振动-声耦合系统的为研究对象,采用力控方式,建立了以声能量密度最小为控制目标的自适应主动结构声控制系统(ASAC).在应用模态叠加法建立低频声传递函数基础上,分别对腔体弹性壁单频激励振动噪声、有限带宽随机激励振动噪声进行了控制仿真研究.仿真结果表明,基于声能量密度的主动控制比基于均方声压的主动控制降噪效果明显,并使控制后封闭空间声场较为均匀,对溢出问题有明显的改善.此外,还研究了平面上传感器位置变化对降噪效果的影响.     

有源振动噪声控制技术在潜艇中的应用研究

阐述了有源振动噪声控制技术中控制器、作动器和传感器三大关键技术的研究进展,基于有源结构声控制已逐步成为未来主动噪声控制的一个重要的发展方向,主要介绍了振动主动控制方面的研究进展.从振动主动控制和噪声主动控制两个方面,介绍了振动噪声主动控制技术在舰船减振降噪中的应用现状,针对潜艇声隐身设计中被动振动噪声控制措施存在的不足及主动控制技术的发展现状,探讨了振动噪声主动控制技术在空间和有效载荷有限的潜艇中的应用前景,列举了未来潜艇声隐身设计中振动噪声主动控制技术可能的应用场合,以期为提高我国潜艇的隐身性能提供一定的借鉴作用.指出其对于提高潜艇的声隐身性能的重要意义.     

有限长圆柱壳结构水下声辐射有源控制实验

以水下有限长圆柱壳为对象,实验研究水下结构声辐射有源控制。实验中通过引入次级力源,以单个或两个误差点处的声压最小为目标函数,分析次级激振器和误差传感器布放（位置和数目）以及激励频率对控制效果的影响。结果表明：有源控制能够有效控制水下圆柱壳线谱噪声;增加次级激振器和误差传感器的数目,能够增大降噪区域;有源控制在3 000 Hz高频处对壳体噪声控制依然有效。有源控制能够对多线谱信号激励壳体辐射噪声产生抑制作用。     

基于输出预估自抗扰策略的加筋壁板结构多模态振动主动控制

针对加筋壁板结构中存在的模型难以精确确定和多模态外界干扰等问题,基于加速度传感器,提出了一种不依赖结构精确数学模型的多模态线性自抗扰振动主动控制(Linear Active Disturbance Rejection Control)策略。由于加速度传感器和压电驱动器的异位配置不可避免地使得整个控制系统存在时延。为解决该问题,利用Smith预估器的原理,引入输出预估器来补偿时延,这样设计的自抗扰振动主动控制器能够很好地解决时延对结构振动性能的影响。基于dSPACE实时仿真平台、利用加速度传感器、压电片驱动器,设计并建立四面固支压电加筋壁板结构实验系统,对提出的控制方法进行试验比较研究。最后的试验结果表明,采用提出的具有输出预估功能的自抗扰振动控制器,能够快速有效地抑制结构的多模态振动。     

基于神经网络的柔性结构振动主动控制研究

提出了采用压电元件作为传感器和驱动器 ,基于神经网络技术的柔性结构主动振动控制方法。阐述了神经网络控制的基本原理 ,导出了控制算法 ,并介绍了控制系统构成 ,最后对柔性梁在正弦和伪随机信号激励下的振动进行了主动控制实验 ,实验结果验证了本文所述方法的有效性     

主、被动噪声控制实验研究

传统的吸、隔声等被动噪声控制方法,适用于中、高频噪声的控制;主动噪声控制是利用声波的相消性干涉来达到降噪的目的,能够有效降低500Hz以下的低频噪声。针对各自的不足,提出了结合使用二者控制噪声的方法,在传统消声结构的基础上附加采用多通道FXLMS算法的主动消声系统。该装置充分发挥主、被动控制的长处,使用被动方法控制中、高频噪声,采用主动控制抵消低频声。实验结果表明主、被动噪声控制方法扩展了降噪频带范围,改善了降噪效果,是可行和有效的。     

振动主动控制中传感器与作动器参数的优化设计

本文分析了文献[5]中方法的不足,提出了梁式结构振动主动控制中同时优化系统极点和传感器/作动器位置的联合优化设计法,指出传感器/作动器最优位置不仅与受控结构的模态频率和振型有关,还与系统的极点位置有关.对于最低阶模态频率较低(小于1.0 rad/s)的受控结构的主动控制系统不宜采用加速度传感器.     

结构主动控制的一体化多目标优化研究

基于Pareto多目标遗传算法提出了结构主动控制系统的一体化多目标优化设计方法,对作动器位置与主动控制器进行同步优化设计.外界激励采用平稳过滤白噪声来模拟,在状态空间下通过求解Lyapunov方程,得到结构响应和主动控制力的均方值.主动控制器采用LQG控制算法来进行设计.以结构位移和加速度均方值最大值与相应无控响应均方值的最大值之比,以及所需控制力均方值之和作为多目标同步优化的目标函数.优化过程还考虑了结构与激励参数对优化结果的影响.最后以某6层平面框架有限元模型为例进行了计算机仿真分析,结果表明所提出的主动控制系统多目标一体化优化方法简单,高效,实用,具有较好的普适性.     

结构抗震主动控制实验研究

运用智能材料对结构进行抗震主动控制是一个前沿课题,但是目前大多局限于单个构件或者理论推导上,由于建筑结构的复杂性和离散性,进行相关的实验研究是必要的,本文结合一三层智能结构主动控制实验,进行了主动杆件设计,优化以及基于模态的控制;研究表明,主动控制效果与结构参数和布置位置关系密切,而与地震波无关;通过控制作用,结构各层的位移和加速度特别是响应剧烈的峰值得到了很大程度的抑制;主动控制时,基于遗传算法的优化可以高效的实现全局优化,而避免陷入局部优化.     

主、被动噪声控制的实验研究

传统的吸、隔声等被动噪声控制方法,适用于中、高频噪声的控制;主动噪声控制是利用声波的相消性干涉来达到降噪的目的,能够有效降低500 Hz以下的低频噪声。针对各自的不足,提出结合使用二者控制噪声的方法,在传统消声结构的基础上附加采用多通道FXLMS算法的主动消声系统。该装置充分发挥主、被动控制的长处,使用被动方法控制中、高频噪声,采用主动控制抵消低频声。实验结果表明主、被动噪声控制方法扩展降噪频带范围,改善降噪效果,是可行和有效的。     

Dynamic structural transition

The phenomenon of dynamic structural transition is discussed. Its main characteristics and dependences are noted together with various effects and applications. Pis’ma Zh. Tekh. Fiz. 25, 81–86 (January 12, 1999)     

Bi-directional evolutionary structural optimization for strut-and-tie modelling of three-dimensional structural concrete

This article presents a method for the automatic generation of optimal strut-and-tie models in reinforced concrete structures using a bi-directional evolutionary structural optimization method. The methodology presented is developed for compliance minimization relying on the Abaqus finite element software package. The proposed approach deals with the generation of truss-like designs in a three-dimensional environment, addressing the design of corbels and joints as well as bridge piers and pile caps. Several three-dimensional examples are provided to show the capabilities of the proposed framework in finding optimal strut-and-tie models in reinforced concrete structures and verifying its efficiency to cope with torsional actions. Several issues relating to the use of the topology optimization for strut-and-tie modelling of structural concrete, such as chequerboard patterns, mesh-dependency and multiple load cases, are studied. In the last example, a design procedure for detailing and dimensioning of the strut-and-tie models is given according to the American Concrete Institute (ACI) 318-08 provisions.     

Hygrothermal effects on structural stiffness and structural damping of laminated composites

In this paper the hygrothermal effects on structural stiffness and damping of laminated composites are investigated. Since the hygrothermal influence on properties of composite materials is primarily matrix dominated, we first determine experimentally the effects of temperature and moisture on the storage modulus, Poisson's ratio and material damping of the epoxy matrix. With the experimentally determined properties of the epoxy material, we then determine the complex moduli (E _L ^* ,E _T ^* ,G _LT ^* andv _LT ^* ) of unidirectional glass-epoxy and graphite-epoxy composites. The structural stiffness (extensional and flexural) and damping of symmetric angle-ply laminates of glass-epoxy and graphite-epoxy are then investigated both analytically and experimentally for temperatues of 20° C and 80° C, respectively. Three moisture contents which are the dry, saturated and a non-uniform moisture gradient states corresponding to each temperature case are considered. Numerical and limited experimental results show that the effects of moisture on the real part ofA ₁₁ ^* ,A ₆₆ ^* ,D ₁₁ ^* andD ₆₆ ^* at room temperature, 20° C, are negligible for all the considered cases. But as temperature increases, the moisture and temperature combined influence induces significant changes in the complex stiffnessA ₁₁ ^* A ₆₆ ^* ,D ₁₁ ^* , andD ₆₆ ^* especially for the matrix dominated terms.     

Analysis of structural responses of bridges based on long-term structural health monitoring

Structural health monitoring system (SHMS) has been increasingly used for the maintenance of vehicle bridges nowadays. In this paper, a centralized SHMS is developed to monitor multiple bridges. The structural responses of two vehicle bridges in China, including the deformation of main components, creep and shrinkage of concrete, and strain caused by the temperature are estimated and analyzed based on the long-term monitored data. A numerical simulation has been carried out to investigate the deformation of the bridges, as well as the strain and stress on the specific sections. The results show a good agreement with the measured data. Wavelet analysis method has been introduced to investigate the characteristics in time and frequency domain, where the strain components caused by the season temperature variation, daily thermal effects, and random traffic loads can be clearly distinguished as the signals at four levels.     

Singularity in structural optimization

Singularity conditions that arise during structural optimization can seriously degrade the performance of the optimizer. The singularities are intrinsic to the formulation of the structural optimization problem and are not associated with the method of analysis. Certain conditions that give rise to singularities in linear elastic structures have been identified in earlier papers, along with a proposition to alleviate the consequences of their presence.^1-3 These singularities were global in nature, encompassing the entire structure. Further examination revealed more complex sets of conditions in which singularities occur. Some of these singularities are local in nature, being associated with only a segment of the structure. Moreover, the likelihood that one of these local singularities may arise during an optimization procedure can be much greater than that of the global singularity identified earlier. This paper provides examples of these additional forms of singularities. It gives a framework in which these singularities can be recognized. In particular, the singularities can be identified by examination of the stress-displacement relations along with the compatibility conditions and/or the displacement-stress relations derived in the integrated force method of structural analysis. Methods for the elimination of the effects of these singularities are suggested and numerical illustrations are given.