基于单元辐射叠加法的结构声源声场重建方法

为了提高分布式结构声源的声场重建精度,本文提出了基于单元辐射叠加法的结构声源声场重建方法.该方法首先利用声场叠加原理和结构振声传递特性,建立了结构声源表面振动与辐射声场之间的振声传递关系解析表达式,得到便于快速计算的振声传递矩阵,能够解决连续分布、相干结构噪声源的声传播模型精细化表征问题.然后利用振声传递矩阵作为传递算...     

基于目标运动的复眼式双目视觉测距法

昆虫（螳螂）复眼利用目标的动态差异实现立体视觉,具有视场大、计算简单、实时性高等特点,是立体视觉研究的新方向。为实现复眼立体视觉在机器人视觉导航中的应用,根据复眼结构以及信息处理机制,提出并研究了环形光电传感器的目标快速检测与定位方法。首先,搭建了基于60个光电二极管的等6°夹角分布式环形传感器,形成具有360°视场的环形仿生复眼;其次,建立了基于光流原理的运动目标方位角检测模型,采用傅里叶拟合法实现了方位角检测模型的优化,实现了运动目标方位角与目标距离大视野范围内的简单、快速检测。实验结果表明:1）可实现距离375 mm范围内运动速度为30 mm/s的目标方位角实时检测,测量误差在2°范围内;2）基于目标方位角检测模型,可实现双目阵列传感器在300 mm×375 mm视野重叠区域范围内、平均测量误差在10 mm范围内的立体视觉测距。基于光流的运动目标方位角检测模型可用于实现对运动目标空间位置的动态实时检测,在运动检测、视觉导航等领域具有广泛的应用前景。     

双目视觉中基于对偶四元数的三维运动估计

针对现有的三维运动估计算法在精度、效率和稳定性等综合性能上的不足,提出了一种结合双目视觉三维重建和利用对偶四元数表达运动参数的新算法。该算法以双目视觉系统为基础,采用SIFT算法进行图像特征点的提取和匹配;根据匹配关系进行三维特征点重建,以获取三维场景中运动目标的结构参数;利用对偶四元数可同时表示刚体的旋转和平移运动的特点,实现目标对象运动参数的表达和求解。通过实验将提出的算法与现有算法(包括奇异值分解法、正交分解法和单位四元数分解法)进行比较,结果表明,该算法具有更加简洁的表达形式,在保持传统算法精度和稳定性优势的基础上提高了计算效率,具有更优的综合性能。     

一种基于双目视觉技术的运动线缆空间位姿测量方法

为了测量柔性运动线缆的空间位姿,提出了一种基于双目视觉的中心线匹配法,可以对长径比较大的柔性线缆类零件的空间位姿进行光学测量。通过运动估计方法提取ROI(感兴趣区域),对ROI进行二值化处理,再通过细化算法提取区域的骨架作为中心线,结合极线约束寻找中心线上的匹配点对,重建中心线上点列并拟合空间中心线。建立了实验系统,通过实验测试表明,该方法平均测量误差为0.09mm,证明了实验方法的正确性和可行性。     

Video visualization for moving sound sources based on binoculars stereo and acoustic holography

The video visualization methods for moving sound sources are very important. The spatial positions in the sound filed measurement of moving sources arc measured by an automated method based on the binoculars stereo technique,the spatial coordinates of the surface of the moving sound source are determined automatically.The sound field of the surface of the moving source is reconstructed with a microphone array using the acoustic holography method for moving sound sources.The spatial mapping between the sound field and the video images is constructed,and also the time sequence of the sound field and the images is founded. Then,the reconstructed sound field and the real-world images are merged,and the visualized sound field video of the moving source is generated automatically.A sound field measurement system based on this method is developed,the measurement results of the moving sound source with this system indicate that the sound field video visualization is realized effectively with the proposed method,the sound sources and their changing process can be seen directly from the generated video,the identification and localization for the moving sound sources can be easier with this method.     

Application of cylindrical near-field acoustical holography to the visualization of aeroacoustic sources

The purpose of this study was to develop methods for visualizing the sound radiation from aeroacoustic sources in order to identify their source strength distribution, radiation patterns, and to quantify the performance of noise control solutions. Here, cylindrical Near-field Acoustical Holography was used for that purpose. In a practical holographic measurement of sources comprising either partially correlated or uncorrelated subsources, it is necessary to use a number of reference microphones so that the sound field on the hologram surface can be decomposed into mutually incoherent partial fields before holographic projection. In this article, procedures are described for determining the number of reference microphones required when visualizing partially correlated aeroacoustic sources; performing source nonstationarity compensation; and applying regularization. The procedures have been demonstrated by application to a ducted fan. Holographic tests were performed to visualize the sound radiation from that source in its original form. The system was then altered to investigate the effect of two modifications on the fan's sound radiation pattern: first, leaks were created in the fan and duct assembly, and second, sound absorbing material was used to line the downstream duct section. Results in all three cases are shown at the blade passing frequency and for a broadband noise component. In the absence of leakage, both components were found to exhibit a dipole-like radiation pattern. Leakage was found to have a strong influence on the directivity of the blade passing tone. The increase of the flow resistance caused by adding the acoustical lining resulted in a nearly symmetric reduction of sound radiation.     

Underwater moving noise source identification based on hybrid near-field acoustical holography

Near-field acoustical holography (NAH) is a powerful tool for identifying noise sources and visualizing acoustic field. By recording the acoustic pressures in the near-field, the acoustic quantities in the whole 3-D field can be reconstructed and predicted. However, the current theory of NAH is not applicable to tracking large scale moving noise sources. Therefore, the hybrid near-field acoustical holography is developed for reconstructing acoustic radiation, which is derived from statistically optimized ne...     

Image reconstruction of moving acoustic sound sources by temporal reference holography

The feasibility of applying temporal reference holography to detection of moving acoustic radiation sources are examined theoretically and experimentally. Temporal reference holography is proved to be used for the purpose if the width of amplitude spectrum of sound is within a certain range, because the point spread functions of temporal reference hologram coincide with amplitude spectra of sound waves used for recording them.     

Planar near-field acoustical holography in a moving medium

Near-field acoustical holography (NAH) is a well-established method to study acoustic radiation near a stationary sound source in a homogeneous, stationary medium. However, the current theory of NAH is not applicable to moving sound sources, such as automobiles and trains. In this paper, the inclusion of a moving medium (i.e., moving source and receiver) is introduced in the wave equation and a new set of equations for plannar NAH is developed. Equations are developed for the acoustic pressure, particle velocity, and intensity when mean flow is either parallel or perpendicular to the hologram plane. If the source and the measurement plane are moving at the same speed, the frequency Doppler effect is absent, but a wave number Doppler effect exists. This leads to errors when reconstructing the acoustic field both towards and away from the source using static NAH. To investigate these errors, a point source is studied analytically using planar NAH with flow in one direction. The effect of the medium moving parallel to the hologram plane is noted by a shift of the radiation circle in wave number space (k-space). A k-space Green's function and a k-space filter are developed that include the effects of the moving medium.     

运动声源的边界元声全息识别方法研究

提出了一种可实现任意形状的运动结构噪声源识别的声全息方法。通过结合移动框架技术与边界元声全息技术两种算法的特点,提出利用移动框架技术将存在多普勒效应的时域数据转换成边界元声全息所需的双平面全息数据,然后由边界元法声全息公式重构任意结构表面的声学信息,实现运动结构噪声源定位。该方法既具有移动框架技术处理运动问题的快速简便,又具有边界元方法可处理任意形状问题的特点。最后在半消声水池中,对运动速度为9.96 cm/s的带帽圆柱壳体进行了试验验证,结果表明:在低速条件下,该方法能够准确反演得到该结构的表面有功声强以及声压等声场信息,从而实现噪声源定位。由于条件有限,高速验证需进一步验证。     

基于神经网络的近场声全息方法研究

研究了用于声源识别的近场声全息方法中的声场重建算法,针对一般声场重建算法速度慢、误差大的缺点,提出了基于RBF神经网络的声场重建算法。通过仿真证明:相比较于常用的利用菲涅尔变换推导的声全息重建算法,该重建算法具有重建误差小、速度快的优点,具有较好的可行性。     

Optimisation of ground attenuation for moving sound sources

In an earlier study, Attenborough and Li [Attenborough K, Li, KM. Ground effect for A-weighted noise in the presence of turbulence and refraction. J Acoust Soc Am 102:1997;1013-22] derived a closed form analytical formula to calculate optimum ground parameters for reducing the A-weighted noise due to a stationary point source. This paper extends this earlier study by deriving an expression to calculate the sound field due to a source moving at a constant speed above a ground surface. An A-weighted mean-square sound pressure has been derived that enables one to estimate the sound exposure levels of a moving source. Numerical calculations for a realistic range of speeds show the influence of the source motion on the noise levels. Although the predicted effects on the ground attenuation are moderate, they are significant at a relatively low Mach number. In addition, the sensitivity to the atmospheric turbulence and the geometrical parameters tends to be altered by the source motion. On the other hand, it is demonstrated that the optimum ground parameters are similar for stationary and moving sources.     

运动声源识别的动态波叠加方法研究

为更好地识别运动声源并解决声源识别中的虚假声源问题,基于运动声源短时信号的Doppler频移特性, 建立运动声场的短时波叠加关系, 利用波束形成方法对声源点进行预估, 基于预估建立起多运动声源的动态叠加方程, 进一步通过波叠加方程的求解进行声源的计算, 从而创建一种可以用于运动声源识别的动态波叠加方法. 该方法可以有效识别运动声源, 将波叠加方法扩展到了运动声源测量领域, 并在不增加传声器数量以及改变阵列形式的条件下有效抑制运动声源重建中的旁瓣效应, 解决运动声源识别中的虚假声源问题. 仿真及实际运动声源的测量试验结果证明了该方法的有效性.     

Planar nearfield acoustical holography in moving fluid medium at subsonic and uniform velocity

Nearfield acoustical holography (NAH) data measured by using a microphone array attached to a high-speed aircraft or ground vehicle include significant airflow effects. For the purpose of processing the measured NAH data, an improved nearfield acoustical holography procedure is introduced that includes the effects of a fluid medium moving at a subsonic and uniform velocity. The convective wave equation along with the convective Euler's equation is used to develop the proposed NAH procedure. A mapping function between static and moving fluid medium cases is derived from the convective wave equation. Then, a conventional wave number filter designed for static fluid media is modified to be applicable to the moving fluid cases by applying the mapping function to the static wave number filter. In order to validate the proposed NAH procedure, a monopole simulation at the airflow speed of Mach=-0.6 is conducted. The reconstructed acoustic fields obtained by applying the proposed NAH procedure to the simulation data agree well with directly-calculated acoustic fields. Through an experiment with two loudspeakers performed in a wind tunnel operating at Mach=-0.12, it is shown that the proposed NAH procedure can be also used to reconstruct the sound fields radiated from the two loudspeakers.