【作者】 李双；

【导师】 陈克安；

【作者基本信息】 西北工业大学 ， 水声工程， 2007， 博士

【摘要】 有源声学结构是近年来提出的一种控制结构低频声辐射的有效方案，它是智能结构在噪声控制领域中的具体应用。本论文采用模态分析方法，将传统的结构振动模态理论和新兴的声辐射模态理论结合起来，对有源声学结构的关键问题进行深入的理论和实验研究。论文完成如下工作：(1)系统地总结了结构声辐射有源控制的各种方法及特点，对有源声学结构组成及特点做了分析说明，在总结国内外研究成果的基础上，阐述了有源声学结构的研究发展历程及研究现状，指出了尚需解决的关键问题。(2)分别采用振动模态和声辐射模态方法对结构声辐射进行分析，给出了结构表面法向速度、声场声压分布以及声功率近场计算的求解方法；将振动模态和声辐射模态联合起来对结构声辐射进行分析，解决了两个问题：1)确定了结构在不同的激励频率(或振动模态)下的主导声辐射模态；2)确定了结构各个振动模态间的耦合对辐射声功率的影响。(3)建立了声-振耦合下的有源声学结构理论模型，基于“角落单极子”模型对有源声学结构的降噪机理进行了解释并给出了次级声源的布放准则；基于声辐射模态理论，结合振动模态对次级声源的布放规律进行了定量研究，得出了次级源在各种情况下的最优布放位置以及次级声源的面积、模态分布等因素对控制效果的具体影响。通过增加次级声源个数拓宽对大面积平板声辐射的降噪频带，并从振动模态角度对次级声源的布放方案进行了研究。(4)研究了适用于有源声学结构的两种近场误差传感策略：基于振速的分布式误差传感和基于离散点近场声压的误差传感，对两种传感策略的原理及实现分别进行了深入分析。提出分频段设计法解决了声辐射模态传感器设计中PVDF对形状系数的最高阶次和振动模态的最高阶次选取之间的矛盾，给出了PVDF对的中心线选取原则，在此基础上对PVDF传感器进行了优化设计。分别研究了基于结构表面声压传感和基于测量面声压传感的有源控制，针对单频和宽带辐射噪声构建不同的有源控制目标函数，给出了相应的计算有源控制效果的公式，结合实例仿真结果进行了分析说明。对比了两种传感方式下的有源控制效果，从理论与工程实现两方面讨论了两种误差传感策略的优劣及应用中需要注意的问题。(5)从不同的角度对有源声学结构的降噪机理进行深入研究。首先从声辐射模态的角度进行分析，并得出了次级声源个数与所能抵消的辐射模态之间的定量关系；然后根据初级结构和次级结构各自的“净”辐射声功率的变化，得出了初、次级结构的能量转化机制，利用结构表面声强的变化对此进行了验证；最后对控制前后声场中的声强和声压分布变化进行了计算分析，揭示了次级板的面积、布放位置及个数对降噪效果的影响。(6)采用分布式平面声源作为次级声源，对振动钢板的声辐射进行了抵消实验，验证了以往研究中的一系列关键理论结果。主要内容包括：1)次级声源的布放准则验证；2)平面声源的面积和布放位置对降噪效果的影响；3)基于近场声压的误差传感策略有效性验证，将近场测量面声功率作为有源控制目标函数的有效性验证；4)控制前后声场中声压和声强的变化规律。更多还原

【Abstract】 Active acoustic strt, cture (AAS) proposed in recent years has been viewed as anencouraging approach to actively control sound radiation from vibrating structures,which is an application of intelligent structures into the field of noise control. In thisdissertation, the key problems encountered in the implementation of such a structurehave been investigated theoretically and experimentally based on modal analysisapproach which links structural vibration modes to acoustic radiation modes. The mainresearch works done are listed as follows.(1) Active control of sound radiation from vibrating structure are summarizedsystematically, and the configuration and main features of AAS are analyzed and thekey technical problems needed to be solved are pointed out.(2) Sound radiation from vibrating structures is analyzed based on structuralvibration mode and acoustic radiation mode respectively. The approach used tocalculate the normal velocity of vibrating structure surface and sound pressure isprovide, and a near-field approach is used to obtain the sound power output of avibrating body. Then structural vibration modes and acoustic radiation modes arecombined to investigate sound radiation from a vibrating structure and two key issuesare solved: 1) the dominant radiation modes corresponding to different structuralvibration modes or frequencies are determined; 2) the effects of structural modalcoupling on the total radiated sound power are assessed quantitatively.(3)The structural-acoustic coupled model of AAS has been established. Physicalmechanisms of active control of sound radiation with AAS are investigated and therules for secondary sound sources arrangement are given. Based on structural vibrationmode and acoustic radiation mode, the laws of the arrangement optimization ofsecondary sound sources are derived for different kinds of conditions. The effects of thearea and modal distribution of secondary panel on active reduction are examined.(4)Two kinds of near-field error sensing strategies for AAS based on distributeddisplacement and near-field sound pressure have been studied. A limited number ofPVDF film pairs could be boned to the surface of the primary panel and secondarypanels for measuring the total the radiated sound power. The shape of the PVDF pairsand corresponding reduction in the radiated sound power are achieved. In designingPVDF sensors, it is difficult but important to choose the maximum order of shapecoefficients and the order of the structural modes, and to determine the location of the center line for placing the PVDF pairs. A new approach of designing PVDF pairs inpartitioned frequency band is presented to resolve the conflict in the choosing process.The optimized design approach and the criterion for determining the location of thecenter line for placing the PVDF pairs is given. Active control using structure surfacepressure and measuring plane pressure sensing is investigated respectively. Three kindof near-field pressure based active control cost functions for AAS are presented andapplied to active control of radiated single and broadband noise. Computer simulationson sound power reduction under three cost functions are conducted to show the validityof the control strategies. Active control effect from two different kinds of error sensingstrategies is compared.(5) Physical mechanism of noise reduction in AAS is investigated from severaldifferent points of view. Firstly, the physical mechanism is analyzed based on acousticradiation mode and the relationship between the radiation modes which could becancelled and the number of secondary sound sources is obtained. Secondly, under theminimization of the total sound power output, the physical mechanism is investigatedby analyzing the sound power output change of the primary and secondary structures.The results show that there are three mechanisms in active control, which are energyrestraint, energy absorption and energy un-absorption. The change of sound intensitydistribution of structure surface is calculated to validate the above conclusion. Finally,the change of sound intensity and pressure distribution is calculated and analyzed. Fornear-field sound intensity distribution, the effect of active control is revealed byamplitude restraint and direction adjusting for sound intensity.(6) Experiments for active control of sound radiation from a vibrating steel plateusing distributed planar secondary sources are conducted. The experimental resultsshow that: 1) using one planar secondary source, the sound power of (odd, odd)modescan be reduced. 2) Using two planar secondary sources, the sound power of not only(odd, odd) modes but also (odd, even) modes can be reduced. 3) The area andarrangement location of planar secondary sources have important influence on noisereduction. Using one planar secondary source, the larger the area is, the better thecontrol effect is. 4) The near field pressure based error sensing strategies are effectiveand feasible. The sound power calculated in terms of the sound pressures abovenear-field measuring plane can be used as an objective function, which is consistentwith the total radiated sound power. 5) After control, the far field pressure and intensitycan be reduced and partial acoustic energy is transferred into near field, the distributionof near field pressure and intensity are also changed distinctly.更多还原