基于波叠加法的近场声全息空间分辨率增强方法

提出一种基于波叠加法的近场声全息空间分辨率增强方法. 该方法在波叠加法的基础上,利用全息面声压信号求得布置在全息面附近的虚源面上的简单源源强,再根据求得的简单源源强实现对全息面声压的插值,进而利用插值后的全息面声压数据进行重建. 该方法可以提高近场声全息重建图像的空间分辨率,减少测量工作量,简化测量过程. 通过仿真对影响插值结果的参数进行了分析,给出了合理的选取范围;通过仿真和实验研究验证了该方法的有效性. 关键词： 波叠加法 近场声全息 空间分辨率     

全息声压场的加权范数外推方法

全息声压外推是Patch近场声全息技术的关键步骤.本文提出了全息声压的加权范数外推方法,该方法首先通过实测声压数据的功率谱信息构造频域加权范数,然后通过极小化频域加权范数实现全息声压外推.由于外推过程中同时利用了声压信号的波数域带宽和波数谱形状信息,因此其外推结果优于传统带限外推方法.数值仿真结果表明,该方法无论在外推精度还是计算效率上都明显优于经典的全息声压波数域外推方法.刚性箱体上的声激励固支板声压外推实验进一步验证了该方法的有效性和实用性. 关键词： 近场声全息 全息声压外推 加权范数     

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.     

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     

基于分布源边界点法的局部近场声全息技术

为了克服基于分布源边界点法的近场声全息技术在小全息孔径条件下造成的重建误差问题,提出了基于分布源边界点法的局部近场声全息技术.该技术运用分布源边界点法,采用测得的较小全息面上的声压数据来外推较大全息面上的声压数据,然后用外推的数据进行全息重建.仿真和实验结果验证了采用该技术在小全息孔径条件下进行声源局部重建的有效性.     

联合波叠加法的全息理论与实验研究

当空间声场中同时存在多个相干声源时，运用常规近场声全息方法无法重建每个相干声源表面的声学信息，当然也无法预测每个声源单独产生的空间声场，相干声场的全息重建与预测已成为全息技术推广应用过程中亟待解决的问题.在提出联合波叠加法并将其应用于空间声场变换的基础上，对其进行了实验研究.通过对实际相干声场的全息重建与预测，验证了常规波叠加法在相干声场重建中的局限性、联合波叠加法在相干声场全息重建与预测过程的可行性和准确性，还研究了Tikhonov正则化方法在抑制声学逆问题的非适定性中的有效性和滤波系数的选择原则的可行性，以提高全息重建与预测的精度. 关键词： 近场声全息 联合波叠加 相干声场 Tikhonov正则化     

空间声场全息重建的波叠加方法研究

提出了基于波叠加法的近场声场全息技术，并将其用于任意形状物体的声辐射分析.在声辐射计算问题中，边界元法是通过离散边界面上的声学和位置变量来实现，而波叠加方法则通过叠加辐射体内部若干个简单源产生的声场来完成.因而，基于波叠加法的声全息就不存在边界面上的参数插值和奇异积分等问题，而这些问题是基于边界元法的声全息所固有的.与基于边界元法的声全息相比较，基于波叠加法的声全息在原理上更易于理解，在计算机上更容易实现.实验结果表明：该种全息技术在重建声场时，具有令人满意的重建精度. 关键词： 声全息 逆问题 波叠加方法 正则化方法     

基于支持向量回归的patch近场声全息研究

为了解决patch近场声全息中全息数据外推问题,提出一种基于支持向量回归的一步式patch近场声全息技术。该方法首先把初始全息面上的数据当成训练样本进行学习,构造出回归函数,然后利用回归函数实现全息数据外推,最后基于统计最优近场声全息进行重建。数值仿真和实验研究的结果表明:在各个分析频率下,该方法都可以实现小孔径全息面的近场外推。从近场声全息重建结果看,即使初始全息数据受到噪声干扰,该方法也是一种有效的patch近场声全息技术。     

声场分离技术及其在近场声全息中的应用

提出空间声场分离技术，突破了近场声全息（NAH）的应用局限.它们的局限在于全息面一侧的声场必须是自由声场，即要求所有的声源必须位于另一侧.利用波数域内的波场外推理论及声压的标量叠加原理，建立起声场分离技术的双全息面实现方法，利用波数域内的Euler公式及粒子振速的矢量叠加原理，建立起该技术的单全息面实现方法.该技术的一个突出优点是在具有背景噪声的全息测量情况下, 可以消除背景噪声对全息变换结果的影响.理论的推导表明该技术方法的正确性，而仿真算例和实验则显示该技术的可行性和有效性. 关键词： 声全息 波数域 声场分离 背景噪声     

统计最优平面近场声全息原理与声场分离技术

测量孔径尺寸的有限性，在基于空间傅里叶变换的平面近场声全息中会带来窗效应和卷绕误差. 为了克服窗效应和卷绕误差，引入了统计最优平面近场声全息技术. 运用声场叠加原理，证明了统计最优平面近场声全息的理论公式.通过在空间波数域限定kx,ky的取值范围，并离散其确定的空间波数面的途径，提出了一种确定波数矢量的方法.为了克服常规统计最优平面近场声全息技术的应用局限性——全息面一侧的声场必须为自由声场，提出了适用于统计最优平面近场声全息的、基于双全息面测量的空间声场分离技术. 通过实验和数值仿真对理论推导的正确性进行了验证. 关键词： 统计最优 平面近场声全息 波数矢量 声场分离     

Partial field decomposition of multi-source cyclostationary sound field

The cyclostationary sound field is a kind of special non-stationary field which has obvious modulation phenomena. Conventional planar near-field acoustic holography (PNAH) technique cannot exactly reflect its modulation characteristics. If the cyclic spectral density (CSD) instead of the complex sound pressure is adopted as the reconstruction variable, the modulating wave and carrier wave components of the cyclostationary sound field can be extracted effectively. A new technique called cyclostationary PNAH utilizing the CSD is proposed in this paper. Based on this technique, the problem of partial field decomposition by singular value decomposition (SVD) of multiple incoherent cyclostationary sound sources is researched. The results of numerical simulation and experiments show that the CPNAH technique and SVD decomposition method are effective.     

The radiation impedance and the energy partition among wave fields generated by a normal force strip radiator on isotropic solid surface

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波叠加法在结构辐射声功率计算中的应用

描述了用波叠加法来计算任意形状辐射体的辐射声功率的方法。该方法在给定辐射体表面的振动速度后就可求解辐射源的强度,进而求解辐射体表面声功率。文中以脉动球源的辐射问题为列,讨论了波叠加法在应用过程中对单元、节点数目以及单元形状的敏感性。通过将该方法计算结果与解析结果进行对比表明,运用此方法在保证较高精度的前提下能明显减少计算所需的单元节点数,从而节省时间提高计算效率。     

Vibration analysis and sound field characteristics of a tubular ultrasonic radiator

A sort of tubular ultrasonic radiator used in ultrasonic liquid processing is studied. The frequency equation of the tubular radiator is derived, and its radiated sound field in cylindrical reactor is calculated using finite element method and recorded by means of aluminum foil erosion. The results indicate that sound field of tubular ultrasonic radiator in cylindrical reactor appears standing waves along both its radial direction and axial direction, and amplitudes of standing waves decrease gradually along its radial direction, and the numbers of standing waves along its axial direction are equal to the axial wave numbers of tubular radiator. The experimental results are in good agreement with calculated results.     

Wave coagulation of a polydisperse gas suspension in the technology of gasification and Cryostatting of liquefied natural gas

We analyze the flow of a polydisperse suspension of methane droplets in a plane channel with simultaneous coagulation of disperse fraction particles under the action of the wave field generated in the carrier medium—gaseous methane—by oscillating parts of the channel walls. The frequency of in-phase oscillations of the walls is equal to the fundamental frequency for the transverse cross section of the channel filled with gaseous methane. In the vicinity of the radiator, a standing wave of the velocity field forms in the direction transverse to the flow and the intensity of coagulation of particles from different fractions upon their collisions increases due to mutual displacement. We describe the evolution of the dispersiveness of a vapor-droplet flow under the action of the wave field of a standing wave whose front moves transversely to the flow.     

Nearfield acoustic holography in a moving medium based on particle velocity input using nonsingular propagator

Nearfield acoustic holography in a moving medium is a technique which is typically suitable for sound sources identification in a flow.In the process of sound field reconstruction,sound pressure is usually used as the input,but it may contain considerable background noise due to the interactions between microphones and flow moving at a high velocity.To avoid this problem,particle velocity is an alternative input,which can be obtained by using laser Doppler velocimetry in a non-intrusive way.However,there is a singular problem in the conventional propagator relating the particle velocity to the pressure,and it could lead to significant errors or even false results.In view of this,in this paper,nonsingular propagators are deduced to realize accurate reconstruction in both cases that the hologram is parallel to and perpendicular to the flow direction.The advantages of the proposed method are analyzed,and simulations are conducted to verify the validation.The results show that the method can overcome the singular problem effectively,and the reconstruction errors are at a low level for different flow velocities,frequencies,and signal-to-noise ratios.     

Effect of acoustic field parameters on arc acoustic binding during ultrasonic wave-assisted arc welding

As a newly developed arc welding method, power ultrasound has been successfully introduced into arc and weld pool during ultrasonic wave-assisted arc welding process. The advanced process for molten metals can be realized by utilizing additional ultrasonic field. Under the action of the acoustic wave, the plasma arc as weld heat source is regulated and its characteristics make an obvious change. Compared with the conventional arc, the ultrasonic wave-assisted arc plasma is bound significantly and becomes brighter. To reveal the dependence of the acoustic binding force on acoustic field parameters, a two-dimensional acoustic field model for ultrasonic wave-assisted arc welding device is established. The influences of the radiator height, the central pore radius, the radiator radius, and curvature radius or depth of concave radiator surface are discussed using the boundary element method. Then the authors analyze the resonant mode by this relationship curve between acoustic radiation power and radiator height. Furthermore, the best acoustic binding ability is obtained by optimizing the geometric parameters of acoustic radiator. In addition, three concave radiator surfaces including spherical cap surface, paraboloid of revolution, and rotating single curved surface are investigated systematically. Finally, both the calculation and experiment suggest that, to obtain the best acoustic binding ability, the ultrasonic wave-assisted arc welding setup should be operated under the first resonant mode using a radiator with a spherical cap surface, a small central pore, a large section radius and an appropriate curvature radius.