基于近场声压传感的结构声辐射有源控制

为了解决有源声学结构中误差信息的传感问题,提出利用近场声压估算结构声辐功率的方法。首先推导了基于近场声压的声辐射功率计算公式,然后针对单频和宽带辐射噪声,提出了不同的有源控制目标函数,推粤了相应的计算有源控制效果的公式,并借助计算机仿真研究了影响有源控制效果的各种因素。最后探讨了实际条件下实现有源控制误差信息传感的各种方法。结果表明:有限阶声压辐射模态和近场均方声压都可以作为自适应声学结构的目标函数。     

基于希尔伯特变化的微小振动激光多普勒信号处理

为了实现对固体目标微小振动参数的测量,建立了微小振动的激光多普勒信号模型。采用希尔伯特数字运算,将激光多普勒振动信号的即时信号采样转化为信号的谱采样。通过频谱计算得到每个振动周期中瞬时频率的平均数,应用差值采样序列积分计算得到振动频率,最后根据振动信号频率变化与振幅的关系得到振幅。采用希尔伯特方法对实验测试结果进行处理验证,并分析了误差来源。实验结果表明：实验测量目标的振动振幅约为1.85×10-4m,转动的圆频率约为170 Hz。因此,应用希尔伯特变换方法处理测量的目标微小振动信号,获取目标运动的参数是可行的。     

基于声透镜的三维光声成像技术

基于声透镜的光声成像系统中, 由样品的光声压分布等效样品的吸收分布, 进行光声像重建, 但之前的这种等效是一种近似, 理论上并不准确. 本文阐述了声透镜三维光声成像的基本原理, 揭示了声透镜像面上光声压信号的时间分布与样品轴向吸收分布之间的关系; 提出用积分法和希尔伯特变换提取光声信号瞬时值法, 解调样品吸收系数分布并重建光声像; 实验上, 对不同样品分别用积分法和希尔伯特变换法获取样品的吸收系数, 重建光声像的横向和轴向分辨率均约为1 mm, 实现了真正的三维快速光声成像.     

结构振动和声辐射的可控性和可观性指标

结构振动和声辐射的可控性和可观性指标对有源控制系统作动器/传感器的布置具有重要意义。对结构振动和声辐射的可控性和可观性指标进行了研究,提出了基于声压输出的振动模态可观性指标,在振动模态可控性和可观性指标的基础上,结合振动模态的声辐射效率,提出了结构声辐射的可控性和可观性指标和基于声压输出的可观性指标。以板结构为例,对结构振动和声辐射的可控性和可观性指标进行了计算分析和讨论,比较了基于声压输出和基于振动响应输出的振动模态可观性,重点研究了基于声压输出的振动模态可观性和结构振动及声辐射的可观性特点,最后对指标值在结构声有源控制中输入(输出)位置选择上的应用进行了讨论和比较,通过数值仿真对指标的有效性进行了验证。     

高效半解析方法分析周期正交加筋板的振动-声辐射特性

为了对水下无穷大双周期正交加筋板结构模型在简谐面力激励下的振动响应及声辐射特性进行更为合理的理论预测与分析,建立了加筋板结构的数学模型。结合傅里叶变换、泊松迭加公式及空间波数法,将周期加筋板的振动响应及辐射声压表达为关于结构位移谐波分量的函数方程,对加筋板模型提出了高效分析求解方法并进行了谐波分量截断求解。验证了方法的正确性,并分析了结构的振动特性以及加强筋周期间距和扭矩对辐射声压的影响。结果表明,加强筋的扭转作用影响加筋板结构的振动模态频率,对于较高精度要求的工程应用,加强筋的扭转作用不能忽略。通过调节加强筋周期间距及横截面尺寸,可以降低薄板在较低频域区间的远场辐射声压。      

结构振动和声辐射的可控性和可观性指标

结构振动和声辐射的可控性和可观性指标对有源控制系统作动器/传感器的布置具有重要意义。对结构振动和声辐射的可控性和可观性指标进行了研究,提出了基于声压输出的振动模态可观性指标,在振动模态可控性和可观性指标的基础上,结合振动模态的声辐射效率,提出了结构声辐射的可控性和可观性指标和基于声压输出的可观性指标。以板结构为例,对结构振动和声辐射的可控性和可观性指标进行了计算分析和讨论,比较了基于声压输出和基于振动响应输出的振动模态可观性,重点研究了基于声压输出的振动模态可观性和结构振动及声辐射的可观性特点,最后对指标值在结构声有源控制中输入(输出)位置选择上的应用进行了讨论和比较,通过数值仿真对指标的有效性进行了验证。      

自由液面和刚性壁面对结构振动声辐射的影响

在边界元理论的基础上,建立了半无限流体域中、特别是与无限大平面接触的结构流固耦合振动方程,计算了方箱的固有频率、振动响应及声辐射,探讨了自由液面和刚性壁面对结构的固有频率、振动响应和有关声学物理量的影响,并讨论了板厚、结构阻尼、结构与无限大平面的距离等有关因素。研究结果表明:自由液面和刚性壁面对结构的固有频率、振动响应及声辐射的影响是不容忽视的。     

超分辨近场结构光盘的传统以及差分读出方法研究

利用标量衍射理论和角谱方法,针对超分辨近场结构光盘存储系统建立了简单物理模型,并提出了超分辨近场结构光盘的读出信号仿真计算方法.通过对比实际测试信号与模拟信号,证明了该读出信号计算方法的可行性.此外,针对超分辨掩膜层对不同功率入射激光响应不同的特性,分别分析了单轨道和三轨道记录符在高、低功率两束激光读出下的差分信号.数...     

适用于循环平稳声场的基于波叠加法的近场声全息技术

在原有的平面循环平稳近场声全息基础上,提出一种基于波叠加法的循环平稳近场声全息技术,可以对具有复杂表面的声源进行全息重建,重建的声源表面声压谱相关密度函数能反映出调制信号的信息.声源表面声压谱相关密度函数全息图形象地反映了调制信号在表面的强弱分布情况,可由此确定调制信号源的产生位置.仿真分析和实验验证表明,基于波叠加法的循环平稳近场声全息技术可以更准确地反映循环平稳声场的调制特性.该方法继承了波叠加法的优点,无需计算边界奇异积分,计算效率高、精度好. 关键词： 近场声全息 循环平稳信号 波叠加     

基于希尔伯特-黄变换方法的同轴粒子全息图中粒子轴向位置提取方法

在颗粒的数字全息中,传统方法应用数值再现反演计算得到颗粒的相关信息,其中再现的判焦过程中存在繁琐费时的缺点.本文提出了一种基于希尔伯特-黄变换方法的同轴粒子全息图分析方法.将粒子同轴全息图沿中心往外得到的单个粒子径向强度分布作为初始信号,根据希尔伯特-黄变换方法中的经验模态分解首先将信号分解成几个本征模态函数,通过分析第一本征模态函数的希尔伯特谱,由拉依达法则剔除部分奇异点后做最小二乘线性回归分析,得到粒子的空间位置.该方法不需要对全息图进行重建,由信号自身构建基函数,有很强的适应性.理论模拟和实验证明,该方法计算速度快,准确度高,有望应用于全息图的实时在线分析.     

压电瞬态响应在换能器声功率测量中的应用

探索一种简便的聚焦超声功率测量方法,利用压电陶瓷片直接接收超声信号,通过机电类比得到压电瞬态响应由压电片在声波作用力下引起受迫振动产生的电压响应与固有振动产生的高频衰减响应叠加而成,分析输出压电信号与换能器声功率之间的换算关系。对输出压电信号进行二次包络提取,获得表征声功率变化的电压幅度曲线,分别找出不同换能器驱动电压下包络曲线的最大峰值电压,将其平方值与声功率计所测声功率进行线性拟合,并对理论关系式中的比例系数进行标定。实验结果所得线性拟合度较高,且标定后所得声功率与声功率计所测值相对误差低于8.7%,证明了通过压电瞬态响应测量换能器声功率具有可行性。      

AN INVERSE METHOD TO COMPUTE EQUIVALENT FORCES ON A STRUCTURE BASED ON SOUND POWER MEASUREMENTS

When modelling the dynamic response of an existing structure to predict the effects of design modifications, many types of forces are difficult to characterize, e.g., those due to unsteady flows or acoustic excitation. To model the forcing function in such cases, a method is presented which solves for an equivalent forcing function based on sound power measurements. The method assumes that the equivalent forcing function may be represented with a superposition of force distributions on a mode-by-mode basis, i.e., there is one force distribution per eigenvalue with the shape of the eigenvector. The method is applied to cases where the structure is lightly damped and has low modal density. Experimental results show that the method accurately predicts the effect of design changes on the structure's radiated sound power. The accuracy of the method is sensitive to small differences between the experimental and theoretical natural frequencies and thus it is important to match the damped natural frequencies of the physical structure as accurately as possible.     

气体物理性质对近场超声悬浮特性的影响研究

在利用近场超声悬浮技术搬运晶圆的过程中,为提高近场超声悬浮力,该文研究了气体物理性质与近场超声悬浮力之间的关系。利用声辐射压理论与流体力学理论对不同气体介质下的悬浮力进行建模与求解。搭建了可测量不同气体环境中悬浮力的实验平台。实验发现氩气环境下超声悬浮力平均值相对空气环境下提升24.8%。结合实验与理论计算分析了气体密度、比热容比、声速与动力黏度对悬浮力的影响,推断气体的比热容比为影响近场超声悬浮力的主要参数。该方法为晶圆搬运的环境适用性提供了参考价值。     

一种耐静压分布反馈式光纤激光水听器探头设计

大深度工作环境下，静水压会引起分布反馈式光纤激光水听器反射中心波长漂出解调系统的复用窗口，使水听器无法解调目标声压信号；不同的静水压也会引起分布反馈式光纤激光水听器灵敏度的变化，影响光纤激光水听器阵列的一致性。基于电力声类比理论，提出带静压补偿的分布反馈式光纤激光水听器探头，建立结构的声压传递函数，分析各结构参数对传递函数的影响，为分布反馈式光纤激光水听器探头频率响应平坦化设计提供理论依据。加工制作了耐静压分布反馈式光纤激光水听器样品进行测试，在0 kHz～10 kHz频率范围内声压灵敏度波动范围不大于±2.4 dB，2.3 MPa内出射激光中心波长漂移量不大于0.06 nm，对深水光纤激光水听器的研究具有指导意义。     

金属片镶嵌微缝薄膜结构的吸声特性分析*

为了使声波在低声压级、低频带达到理想的吸收效果,本文提出了金属片镶嵌微缝薄膜结构理论模型,并分析了该模型的吸声机理。首先将该结构的力学模型看作多自由度系统,构建振动微分方程,得到了金属片镶嵌薄膜的分布位置与每段薄膜弹性系数之间的关系。并在此基础上分析了激励频率与固有频率之间的关系,得出基频对该结构吸声效果的影响。然后利用有限元软件对该结构的模态振型和声阻抗进行了分析,得到了镶嵌在微缝薄膜上的金属片与声波的耦合形式。最后通过试验对该结构的吸声特性进行了验证,结果表明:吸收峰值受镶嵌位置影响较小,平均吸声系数变化不大,一阶固有频率会受镶嵌位置的改变而改变。     

A modal test method using sound pressure transducers based on vibro-acoustic reciprocity

A modal test method that uses sound pressure transducers at fixed locations and an impact hammer roving over a test structure is developed in this work. Since sound pressure transducers are used, the current method deals with a coupled structural–acoustic system. Based on the vibro-acoustic reciprocity, the method is equivalent to one, where acoustic excitations at fixed locations are given and the resulting acceleration of the test structure is measured. The current method can eliminate mass loading due to use of accelerometers, which can destroy existence of repeated or close natural frequencies of a symmetric structure. It can also avoid effects of a nodal line of a mode and an inactive area of a local mode, and measure all the out-of-plane modes within a frequency range of interest, including global and local ones. The coupling between the structure and the acoustic field in a structural–acoustic system introduces asymmetry in the model formulation. An equivalent state space formulation is used for a damped structural–acoustic system and the associated eigenvalue problem is derived. The biorthonormality relations between the left and right eigenvectors and the relations between the structural and acoustic components in the left and right eigenvectors are proved. The frequency response functions associated with the current method are derived and their physical meanings are explained. The guidelines for using the current method, including the types of structures that are suitable for the method, the positions of the sound pressure transducers, and the orientation of the test structure relative to the transducers, are provided. Modal tests were carried out on an automotive disk brake using the traditional and current methods, where multiple accelerometers and microphones were used to measure its dynamic responses induced by impacts, respectively. The differences between the measured natural frequencies using the current method and those from the finite element model of the disk brake are less than 3 percent for the first 18 elastic modes, and the modal assurance criterion values of the associated mode shapes are all above 90 percent. The current method was also used to measure the natural frequencies, damping ratios, and mode shapes of a light circuit board.     

A study on radial directional natural frequency and damping ratio in a vehicle tire

The measurement of radial directional natural frequency and damping ratio in a vehicle tire has been studied. Natural frequencies and damping ratios in the radial direction of various tires, from passenger car tires to truck bus tires, are reported. The radial direction modal parameters of tires subjected to different levels of inflation pressure, have been determined by using a frequency response function method. To obtain the theoretical natural frequency and mode shape, the plane vibration of a tire has been modeled as though it were that of a circular beam. By using the Tielking method that is based on Hamilton’s principle, theoretical results have been determined by considering the rotational velocity, tangential and radial stiffness, radial directional velocity and tension force which is due to tire inflation pressure. The results show that experimental conditions can be considered as the parameters that shift the natural frequency and damping ratio.     

Secondary actuation and error sensing for active acoustic structure

A typical approach to active control of sound radiation or transmission from vibrating structures involves active structural acoustic control (ASAC) and active noise control (ANC), which introduce respectively force input and compacted sound source to apply on or be close to the vibrating structure. However, for the ASAC approach, arrangement for secondary force and error sensor is heavily dependent upon the properties of the primary structure and acoustical space; for the ANC approach, a large number of compacted secondary sources are required. Hence, in this paper, based on distributed secondary sound source and near-field error sensor, active acoustic structure is proposed to construct adaptive or smart structure as a versatile module or element for controlling sound radiation or transmission at low frequencies. First, a theoretical model based on a minimization of the total sound radiation from the primary and secondary panel is established, after which, taking into consideration the relationship between the vibration modes pattern and sound radiation characteristics for secondary panels, optimal arrangement for the secondary panels is examined in detail. Finally, a near-field pressure-based error sensing approach is presented, based on two kinds of object function, and active control of sound radiation is performed.     

Machinery noise predictions at the design stage using acoustic modelling

This paper presents a simple method of predicting the $\text{L}{}_{\mathrm{eq}}$ sound pressure levels in the operator's position for a machine, whilst the latter is still at the design stage. Simple acoustic models are used to estimate mean values for the transfer functions between vibrational response and sound pressure at a point. Given a force input to a structure (machine) and the subsequent vibration response, which can be calculated by finite element or other means, it provides a quick and easy method of accurately predicting overall rms sound levels. The method is applied and provided with data obtained from a full-scale industrial drop hammer. It is applicable to any machine which can be identified as a distribution of separate sound sources.     

基于声粒子分布积分的无网格声场计算方法

小尺度封闭空间内部声场的数值计算是声学设计、噪声控制等领域的关键技术。由于波动声学及几何声学方法计算频率上的限制,中频段声场计算问题一直是个难点。本文以声学无网格法为基础,提出了一种基于声粒子分布积分的无网格声场数值计算方法。文中利用声线跟踪理论计算声场中的声粒子分布,并以某个时间点上的声粒子作为蒙特卡罗法中的积分点,将其应用于无网格法中,从而获得声场中的节点声压。利用该方法对一个矩形封闭空间的中低频声场进行了计算,并与模态叠加法、商用声场计算软件、经典无网格法的结果进行了对比,证明基于声粒子分布积分的无网格声场数值计算方法在中低频段相较于传统基于网格的方法具有更高的精度。