机械噪声源识别的混合波叠加法

提出了一种稳健声场的全息变换算法——混合波叠加法，它结合了波叠加法和Helmholtz方程最小二乘（HELS）方法的优点，用相对少量的测点数据就可重建任意形状源表面的声场。在半消声室里，运用29个传声器组成的“＋”字形平面传声器阵列，对一运转的电机进行噪声源识别，得到声源的空间声压场分布及声源位置，显示出混合波叠加法在工程实践中广泛的应用前景。     

基于遗传算法的动态优化波叠加噪声源识别方法

针对现有声全息以及波束形成等方法中重建声场的虚假声源问题,提出一种利用遗传算法搜索声源位置的波叠加噪声源识别方法。该方法通过传声器阵列测量声音信号,基于时间延迟算法进行声源面的声压预估;选取预估声压峰值点作为等效源的初始位置;根据初始识别结果确定声源位置搜索的三维空间范围,以重建传声器声压误差函数作为位置评价指标,利用遗传算法动态地优化等效声源的空间位置,并实现声场的波叠加重构。对该方法进行仿真试验,得到的识别结果中旁瓣引起的虚假声源强度下降到真实声源的10%以下。试验结果表明利用该技术重建声场时,与传统的全息和阵列技术相比,可以有效消除虚假声源以及旁瓣效应,与静态波叠加方法相比,可以取得准确的声源位置和重建声压值。     

混合波叠加法识别噪声源的理论与试验研究

针对基于边界元法的声全息中的奇异值积分和解的非惟一性难题及其基于Helmholtz方程最小二乘法（HELS）特殊函数选择计算问题，提出以一种稳健的声场的全息变换算法——混合波叠加法，此法用相对少量的测点数据就可重建任意形状源表面的声场。在对典型声源进行数值仿真并验证该技术重建空间声压场精度高、精确地识别和定位噪声源后，在半消声室里，运用29个传声器组成的“＋”字型平面传声器阵列，得到音箱声源的空间声压场分布及声源位置，显示出混合波叠加法在工程实践中广泛的应用前景。     

理想声源辐射声场的数值分析

通过声场的特性和规律分析可以识别和定位噪声源,对噪声控制以及声源的设计提供参考。数值方法是求解有源声场的重要工具,复杂的声辐射一般可分解为简单的声辐射叠加。研究了单极子、偶极子、活塞等几种理想声源辐射声场的解析解,并用有限元法计算数值解,得到相应的辐射声场,包括声压、速度、指向性等量,有限元法得到的数值结果与解析解吻合;利用有限元法计算了点声源的线性阵列与平面阵列等典型的叠加声场。对各种声源的特性和辐射声场的规律以及在工程领域中的应用进行了归纳。     

车辆主要噪声源识别方法的研究

描述了车辆车外主要噪声源的两种常用识别方法即声强法和声压法,给出了小客车车外噪声源的声强法和声压法的对比识别结果。这两种方法对比识别结果表明：在声源愈单一的情况下,声强法与声压法识别结果的相差愈小;在声源愈复杂的情况下,声强法与声压法识别结果相差愈大。     

基于单全息面三维声强测量的声场分离技术

在测量全息面三维声强和均方声压的基础上，根据平面上二维切向有功声强与复声压相位间的关系来间接获取复声压的相位，结合测得的均方声压，得到全息复声压；根据全息面上微粒法向振速的叠加原理和波数域的Euler公式，推导出基于单全息面三维声强测量的声场分离公式，将全息面两侧声源各自在全息面上产生的声压分离开来。在全息面两侧均有声源的情况下，实现噪声源的识别与定位，克服了近场声全息(NAH)和基于声强测量的宽带声全息(BAHIM)的应用局限性。数值仿真的结果证明了该技术的可行性和有效性。     

基于HELS方法的噪声诊断技术研究

基于赫姆霍兹方程最小二乘法（HELS）的噪声诊断技术,将赫姆霍兹方程应用于噪声诊断技术中,把声场中声压转化为一组线性无关的独立函数的叠加,使用最小二乘法根据已知的较少噪声信号准确高效地重建声源表面的声压。建立基于非线性优化理论的新型HELS-PSO模型进行噪声源识别和声场重建研究,在实验室中以音箱作为模拟噪声源,通过实验进行验证。实验结果验证了该算法的有效性和高效性,表明新算法的求解精度较高。     

基于矢量阵测量的振速重构近场声全息技术

近场声全息技术是一种声源识别和声场可视化技术,它通过在辐射体的近场测量声压数据可以重建和预测出整个三维空间声场的声学量.针对水中声源的振速重构问题,采用质点振速测量来进行声全息重构,推导基于振速重构的平面近场声全息技术的重建公式.利用所编制的程序进行仿真验证,采用矢量水听器进行水中全息试验,验证矢量阵应用于水中近场全息测量的可行性和准确性.试验结果表明,该技术在水中声源辐射声场的噪声源识别和定位中有着明显的优势.     

波叠加法在机械噪声故障特征提取中的应用研究

声学故障诊断中,测量到的噪声信号是现场所有声信号的混合.为提取待诊设备噪声故障特征,建立机器系统的多声源宽带相关混合声场模型,使用波叠加法重建源表面为任意形状的空间声压场分布,计算出未知声源的数目与位置.提出的算法具有计算速度快、重建精度高,能够消除其他噪声源信号的干扰,从较小的信噪比的观测信号中分离待监测源信号的功率谱,有效提取机械噪声故障特征.实验结果验证模型与算法的可行性.     

基于声全息的故障诊断方法

基于振动信号的故障诊断方法在某些场合下存在着局限性.机械噪声蕴含着丰富的设备状态信息,而且具有非接触式测量的优点,可以部分地替代振动信号,用于故障诊断.传统的噪声诊断方法主要基于频谱分析,无法反映声源位置和强度 /的变化信息,只能进行初步的故障诊断.基于此,提出一种基于声全息的故障诊断方法.该方法采用由少量传声器组成的阵列测量声压,应用波叠加法重构物体的外部声场,可以方便快速地进行声场可视化.一旦准确地重建出物体的外部声场,就可以利用这些全息场的信息进行故障诊断.通过建立基于全息图的正常状态与故障状态的模板,将机器的运行信息与这些模板对比,就可以判定机器的运行状态,从而进行故障诊断.采用由多个脉动球组成的声源模型进行了数值仿真,并在消声室内对两只音箱噪声源进行了试验研究,都准确地识别出辐射体声场状态变化,找出了故障.从而验证了该方法的正确性和实用性,为其在现场应用打下基础.     

二维动态网格压缩波束形成声源识别方法

基于平面传声器阵列测量和固定网格的传统二维压缩波束形成通过建立阵列传声器测量声压信号和假想声源网格点未知源强之间的欠定线性方程组，基于主声源通常为稀疏分布这一事实，利用稀疏促进算法求解上述方程组从而获得声源波达方向和源强的准确估计，进而准确识别声源。然而，当声源波达方向与网格点不一致、即发生基不匹配时，性能会劣化。为克服该问题，提出二维动态网格压缩波束形成声源识别方法。定义网格坐标和源强分布矢量为变量并采用对数求和罚函数构建目标函数以促进解的稀疏性；基于优化最小化框架在目标函数的基础上构造合适的替代函数以降低优化复杂度；通过梯度下降法对替代函数进行迭代优化求解，从而使网格坐标和源强分布矢量逐渐收敛至真实值附近。仿真和试验均表明，相较于传统固定网格的二维压缩波束形成，该方法能够克服基不匹配问题、获得更高的定位精度和量化精度；该方法能够适用于传声器随机分布的平面阵列，且无需先验的信噪比（噪声干扰）及声源稀疏度等信息，即使在传声器数量较少的情况下也能得到低污染高分辨率的声源成像，保证了高精度的二维波达方向估计和源强量化。     

微通道对流换热系统的流动阻力分析

针对在恶劣温度条件下工作的芯片热控制系统问题,基于由微泵、微通道、热电模块、智能控制单元、散热片以及液体管道等构成的微通道对流换热设计思想,数值仿真分析了微通道结构的速度场和压力分布,计算了系统管道、微通道等部件的沿程阻力和局部阻力,给出了换热系统的最佳工况点,确定了系统必需的微泵工作性能参数。     

On the positioning of control sources in active noise control of three-dimensional interior space

Locations of secondary sources in three-dimensional active noise control influence greatly on final control result. To find efficient secondary source sites for given primary source layout, an acoustic analysis of a three-dimensional interior space is done for low frequency ranges with low modal density. By using the boundary element method, magnitude and phase of optimum velocities of boundaries are evaluated for underdetermined system with an example of a rectangular box. Because the potential energy at mutiple field points depends on boundary velocity field, “good” sites for control sources can be determined by investigating the distribution of resultant velocity vectors. Results show a general tendency that the dipole positioning is most effective and the source should be placed at antinodes of related modes for maximum noise reduction, and this agrees with previous ones. With this method, positions of control sources for maximum noise attenuation can be determined for a variety of primary source configurations and for irregular boundary shapes.     

车辆乘坐室内低频噪声声源识别研究

提出了一种用于车内低频噪声声源识别的理论分析方法。该方法摆脱了对试验的依赖，可用于车身结构低噪声优化设计（或修改）的迭代求解过程。分别采用所提方法和相关分析法，对某型国产轿车乘坐室内驾驶员右耳位置处的低频噪声主要来源进行识别，得出了一致的结论。     

某柴油机噪声源识别及分析

根据声强法对某柴油机进行了声强测量研究,绘制出发动机的声强云图,得到了整机的噪声分布情况,确定了该机在不同工况下的主要噪声源,并对其噪声辐射特性进行了分析,为整机降噪研究奠定了良好的基础。     

Blind source separation for classification and detection of flaws in impact-echo testing

This paper presents a technique for defect detection and material classification based on blind source separation by independent component analysis (ICA) for application in impact-echo testing. The transfer functions between the impact point and the defects in the material are modelled as “sources” for blind source separation. The sensors located on the material surface measure a convolutive mixture of the contribution of each of the defects. From spectral analysis the dominant resonance frequencies, varying from homogeneous to defective material, are selected. These frequencies are processed by instantaneous ICA in order to obtain more information about the defects using bootstrap resampling to analyse the stability of the solution. Results show that source estimates fit well with the theoretical response of the material. In addition, it has been found that the number of defects can be estimated by ICA in simulations and experiments with various defective parallelepiped-shape materials of aluminium alloy series 2000.     

Probe and method for simultaneous measurements of 'true' instantaneous temperature and three velocity components in turbulent flow

In the measurement of turbulent flows the need has always existed to obtain correct instantaneous values of temperature and three components of velocity at a particular point. Many proposed lengthy approximate correction methods that attempt to account for 'nonlinear' effects (cross contamination between different quantities) in hot-wire measurements cannot be considered satisfactory. The availability of powerful digital computers for theoretical and experimental studies has placed pressure on experimentalists to develop better probes and methods. This paper attempts to answer these pressures by describing the development of a special four-wire probe and a method of processing the obtained signals. The use of four 0.625-microm-diam sensors makes the probe practically interference free. The processing method is based on the simultaneous solution of four complete nonlinear response equations for the sensors, yielding in principle exact instantaneous values of velocity components and temperature. Additional features of the processing method include: instantaneous full correction for tunnel free stream velocity and temperature fluctuations, first-order correction for dc drifts of the signals during data acquisition, subtraction of all 60-Hz related noise, and correction for streamwise displacement of sensors based on instantaneous streamwise velocity.     

Evaluation of substitution monopole models for tire noise sound synthesis

Due to the considerable efforts in engine noise reduction, tire noise has become one of the major sources of passenger car noise nowadays and the demand for accurate prediction models is high. A rolling tire is therefore experimentally characterized by means of the substitution monopole technique, suiting a general sound synthesis approach with a focus on perceived sound quality. The running tire is substituted by a monopole distribution covering the static tire. All monopoles have mutual phase relationships and a well-defined volume velocity distribution which is derived by means of the airborne source quantification technique; i.e. by combining static transfer function measurements with operating indicator pressure measurements close to the rolling tire. Models with varying numbers/locations of monopoles are discussed and the application of different regularization techniques is evaluated.     

一种水冷电抗器的散热器数值模拟

根据大容量电抗器的发热冷却原理,采用强迫水冷散热的设计方案,应用流体仿真软件Fluent对其中的水冷散热器进行了三维数值模拟。文中计算了在流体的不同初速度下,散热器内腔各处水流的速度场、压力场,以及散热器和流体的温度场。计算结果和实验所得结果基本符合,验证了数值模拟方法的合理性,为水冷散热器的结构优化提供了理论依据。     

Numerical and experimental study on flow-induced noise at blade-passing frequency in centrifugal pumps

With the increasing noise pollution, low noise optimization of centrifugal pimps has become a hot topic. However, experimental study on this problem is unacceptable for industrial applications due to unsustainable cost. A hybrid method that couples computational fluid dynamics （CFD） with computational aeroacoustic software is used to predict the flow-induced noise of pumps in order to minimize the noise of centrifugal pumps in actual projects. Under Langthjem＇s assumption that the blade surface pressure is the main flow-induced acoustic source in centrifugal pumps, the blade surface pressure pulsation is considered in terms of the acoustical sources and simulated using CFX software. The pressure pulsation and noise distribution in the near-cutoff region are examined for the blade-passing frequency （BPF） noise, and the sound pressure level （SPL） reached peaks near the cutoff that corresponded with the pressure pulsation in this region. An experiment is performed to validate this prediction. Four hydrophones are fixed to the inlet and outlet ports of the test pump to measure the flow-induced noise from the four-port model. The simulation results for the noise are analyzed and compared with the experimental results. The variation in the calculated noise with changes in the flow agreed well with the experimental results. When the flow rate was increased, the SPL first decreased and reached the minimum near the best efficient point （BEP）; it then increased when the flow rate was further increased. The numerical and experimental results confirmed that the BPF noise generated by a blade-rotating dipole roughly reflects the acoustic features of centrifugal pumps. The noise simulation method in current study has a good feasibility and suitability, which could be adopted in engineering design to predict and optimize the hydroacoustic behavior of centrifugal pumps.