南海北部海域内波环境下声传播损失起伏统计特性

浅海内波会引起声传播能量随时间的起伏变化,进而影响水声设备的工作性能.本文利用2015年南海北部一次浅海声场起伏实验数据,对比分析了浅海线性内波和孤立子内波条件下的声传播损失统计特性.在孤立子内波条件下,声传播损失起伏明显加剧,可达11 dB,且分布明显展宽,相对于线性内波的环境,声传播损失起伏可增加5 dB.从简正波...     

Sound Transmission Loss of Panels with Resonant Elements

Various types of resonant elements that can be used for increasing the transmission loss of panels in narrow frequency bands are analyzed. The main physical phenomena determining the transmission loss of sound waves in panels with resonant elements are studied. Three main principles of increasing the transmission loss realized in panels with resonant elements are described: the principle of soft reflection, the principle of hard reflection, and the principle of compensation. The relations for estimating the transmission loss of panels with resonant elements, which model the main physical phenomena governing the propagation of sound waves, are presented.     

激光空泡溃灭及其产生的声波

强激光脉冲在水中的自聚焦传输、成丝、击穿及击穿后产生的声波,近年来成为强激光脉冲传输应用研究领域的一个热点。强激光脉冲电离产生的空泡在溃灭过程中,对周围水体产生压缩,从而在水下产生声波。在现有理论基础上,考虑空泡含气量、水的粘滞系数和水的表面张力系数对空泡运动及其产生声波的影响。给出双空泡运动方程,分析空泡间距对空泡溃灭和其产生声压关系。根据实际情况,计算不同温度情况下单空泡和双空泡运动过程及其产生的声压,并进行相互比较。计算结果表明: 水温越高,空泡运动时达到的最小半径越小,空泡振荡周期和溃灭时间延长,产生声压越高。随双空泡间距减小,空泡溃灭时达到的最小半径线性减小,而其产生的最大声压则单调增大。     

ANALYSIS AND MEASUREMENT OF SOUND TRANSMISSION THROUGH A DOUBLE-WALLED CYLINDRICAL SHELL

Sound transmission through a double-walled cylindrical shell is studied. The solution that describes the system response is obtained by combining the solutions of two different models of the system. The first model, which describes the sound transmission due to the interaction between the acoustic waves and the bending waves in the shells, is formulated by three acoustic wave equations and two shell vibration equations. The second model describes the sound transmission by one-dimensional waves propagating through the layers of the shells and the air-gap. The transmission losses calculated from the two models are combined to represent the system response in the entire frequency range. Analytical solutions are compared to corresponding measured results, which shows reasonable agreements if the extent of the simplifications used in the analytical model is considered. The effects of important design parameters such as the air-gap size and the thickness ratio are studied using analytical solutions.     

Collinear diffraction of restricted light beams by nonmonochromatic sound

The collinear diffraction of Gaussian light beams by a two-frequency sound beam is investigated theoretically. A set of equations relating the amplitudes of transmitted and diffracted waves is derived in the case of third-order nonlinearity. The distributions of light intensities along an acousto-optical cell are calculated at different ratios between the radii of the light and sound beams. The transmission curves for detuned light waves and combination components of the diffracted waves are constructed at different ratios between the radii of the light and sound beams. The changes in the dynamic range of an acousto-optical device are calculated for different diffraction efficiencies.     

Propagation of acoustic waves in a fluid-filled pipe with periodic elastic Helmholtz resonators

Helmholtz resonators are widely used to reduce noise in a fluid-filled pipe system. It is a challenge to obtain lowfrequency and broadband attenuation with a small sized cavity. In this paper, the propagation of acoustic waves in a fluid-filled pipe system with periodic elastic Helmholtz resonators is studied theoretically. The resonance frequency and sound transmission loss of one unit are analyzed to validate the correctness of simplified acoustic impedance. The band structure of infinite periodic cells and sound transmission loss of finite periodic cells are calculated by the transfer matrix method and finite element software. The effects of several parameters on band gap and sound transmission loss are probed.Further, the negative bulk modulus of periodic cells with elastic Helmholtz resonators is analyzed. Numerical results show that the acoustic propagation properties in the periodic pipe, such as low frequency, broadband sound transmission, can be improved.     

Sound radiation into air by a point source moving underwater

Based on the discovery that the majority of radiated energy of a stationary sound source in shallow water is into the air at infrasonic frequencies, the sound transmission into air from a point source moving underwater is investigated in this letter. It is found that a moving sound source can radiate more acoustic energy into the air than a stationary one and the amount of energy radiated into the air increases with the speed of the moving source. Simulations show that the sound transmission into air is dominated by the inhomogeneous waves generated by the moving source.     

Ballistic phonon transport through a Fibonacci array of acoustic nanocavities in a narrow constriction

We investigate the ballistic phonon transport through a Fibonacci array of acoustic nanocavities in a narrow constriction of a semiconductor nanowire at low temperatures. It is found that the transmission spectrum of such a system consists of quasiband gaps and narrow resonances caused by the coupling of phonon waves. Both phonon transmission and thermal conductance exhibit the similarity due to the Fibonacci sequence structure. The similarity is sensitive to the number n and parameters of nanocavities. The results are compared with those in a periodic acoustic nanocavities.     

Transmission of low-frequency internal sound through pipe walls

Transmission loss measurements are reported for long steel pipes of circular crosssection, with air inside and out, excited by internal sound. At low frequencies (wavelength greater than the pipe diameter), most of the radiated sound is accounted for by pipe bending waves. In order to approach the much higher transmission loss predicted for pure breathing motion of the pipe, bending waves must be suppressed; this has been achieved for a straight pipe by careful isolation. A sharp 90 bend in the pipe is shown to cause significant bending-wave excitation when plane waves are incident on the bend.     

Sound propagation and speech transmission in a branching underground tunnel

The characteristics of sound propagation and speech transmission along a tunnel with a "T" intersection were investigated. At receivers within sight of the sound source, low frequencies were mainly attenuated around the intersection than high frequencies. At receivers out of sight of the source, high frequencies were extensively attenuated. The overall pattern of sound attenuation along the different sections of tunnel, which was calculated by the conical beam method, agreed well with the measurements in this study. Numerical calculations of reflected and diffracted waves with minimum transmission paths in a two-dimensional plane showed that reflected waves were the primary contributors to sound fields out of sight of the source. The articulation scores measured at receivers within sight of the source were high, and most of the confusion concerned syllables that could easily be misheard, even if there were a high signal-to-noise ratio. The types of syllable confusions observed at the receivers out of sight of the source appeared to have been caused by the greater deterioration in speech signals along this part of the tunnel, especially at high frequencies. The evaluation by rapid speech transmission indices (RASTI) appeared to be overestimated at the receivers out of sight of the source. Taking into account the early decay times of impulsive sound and the calculation procedures used in RASTI, it is concluded that speech intelligibility may not have been evaluated correctly by RASTI.     

A theoretical study of passive control of duct noise using panels of varying compliance.

It is theoretically demonstrated that, in a duct, a substantial amount of sound energy can be transferred to flexural waves on a finite wall panel when the upstream portion of the panel is made to couple strongly with sound. The flexural wave then loses its energy either through radiating reflection sound waves or by internal friction. The effectiveness of the energy transfer and damping is greatly enhanced if the panel has a gradually decreasing in vacuo wave speed, which, in this study, is achieved by using a tapered membrane under tension. A high noise attenuation rate is possible with the usual viscoelastic materials such as rubber. The transmission loss has a broadband spectrum, and it offers an alternative to conventional duct lining where a smooth air passage is desired and nonacoustical considerations, such as chemical contamination or cost of operation maintenance, are important. Another advantage of the tapered panel is that, at very low frequencies, typically 5% of the first cut-on frequency of the duct, sound reflection occurs over the entire panel length. This supplements the inevitable drop in sound absorption coefficient, and a high transmission loss may still be obtained at very low frequencies.     

南中国海海域存在孤立子内波条件下的 声场统计特性*

利用南海浅海海域低频声传播起伏实验中获取的水文数据,结合二维平流模型重构出声传播路径上的动态声速场,使用蒙特卡洛方法研究了有、无孤立子内波经过声传播路径条件下的声传播损失统计特性,并与实验结果进行了对比分析。仿真和实验结果表明：当孤立子内波经过声传播路径时,声传播损失起伏剧烈;与“下发上收”相比,“下发下收”情况下传播损失的概率分布更加分散。     

矩形波导中宽带非对称声传输

目前已有的非对称性声传输模型大部分局限于二维模式,无法直接应用于三维实际系统,针对这一问题,文中研究了通过内置非对称几何结构来实现声单向传输的三维管道模型。该几何结构体内引入天然材料——氙气,利用氙气与空气两种天然气体折射率的差异以及结构的不对称,实现声波在管道中的非对称传输,即当声波正向入射时,可通过管道内结构到达另一侧;而当反向入射时,声波无法通过内置的非对称结构。理论计算结果和仿真结果表明声波在三维矩形波导管中的非对称声传输效果和结构的厚度相关:当结构厚度较薄时,可在较宽频带范围内实现声波的非对称传输。此外,该矩形波导设计具有结构简单、透明超轻等特点,为设计新型声波非对称传输器件提供了相应的理论参考。      

Sound transmission in pipes with porous walls

Pipes with porous (permeable) walls have received the attention of several authors as a noise control element in automotive intake systems; however, a closed theory of sound transmission including the effect of the coupling of the internal and external acoustic fields and the presence of mean flow does not appear to be available. The present paper proposes an integro-differential system for the propagation of plane sound waves in pipes with porous walls, and presents its general numerical solution, as well as an approximate analytical solution. The predicted effect of the coupling between the internal and external acoustic fields in a circular pipe made of reinforced woven fabric walls is shown, and the transmission loss predictions are compared with the existing experimental data in the literature.     

Observation of anomalous transmission modes in nickel at microwave frequencies

A study has been made of the transmission of energy through nickel crystals in magnetic fields up to 13 kG using incident microwave power at 9.37 GHz. The transmission spectrum has been studied as a function of temperature and magnetic field orientation relative to the sample surface. A new set of anomalous transmission modes has been observed with the field perpendicular to the sample plane; these modes cannot be explained within the framework of existing theoretical models describing the resonance excitation of sound in ferromagnetic metals by electromagnetic waves.     

Design parameters of stainless steel plates for maximizing high frequency ultrasound wave transmission

This work validated, in a higher frequency range, the theoretical predictions made by Boyle around 1930, which state that the optimal transmission of sound pressure through a metal plate occurs when the plate thickness equals a multiple of half the wavelength of the sound wave. Several reactor design parameters influencing the transmission of high frequency ultrasonic waves through a stainless steel plate were examined. The transmission properties of steel plates of various thicknesses (1–7 mm) were studied for frequencies ranging from 400 kHz to 2 MHz and at different distances between plates and transducers. It was shown that transmission of sound pressure through a steel plate showed high dependence of the thickness of the plate to the frequency of the sound wave (thickness ratio). Maximum sound pressure transmission of ∼60% of the incident pressure was observed when the ratio of the plate thickness to the applied frequency was a multiple of a half wavelength (2 MHz, 6 mm stainless steel plate). In contrast, minimal sound pressure transmission (∼10–20%) was measured for thickness ratios that were not a multiple of a half wavelength. Furthermore, the attenuation of the sound pressure in the transmission region was also investigated. As expected, it was confirmed that higher frequencies have more pronounced sound pressure attenuation than lower frequencies. The spatial distribution of the sound pressure transmitted through the plate characterized by sonochemiluminescence measurements using luminol emission, supports the validity of the pressure measurements in this study.     

On Riccati equations describing impedance relations for forward and backward excitation in the one-dimensional cochlea model

Recent experimental observations of otoacoustic emissions suggest the existence of spontaneous emitters of sound on the basilar membrane. These tend to send off waves not only in the normal direction of propagation. It is therefore significant to study the environmental conditions such an emitter finds inside the cochlea. The impedance relations seen by these emitters are described by the Riccati equation for an inhomogeneous transmission line. The results reported in this paper differ considerably for forward and backward excitation. This reflects the quite different behavior of the cochlea pertaining to waves traveling forward and backward. Because of reflections, backward waves cannot be treated with the Liouville-Green approximation.     

Sound transmission across lightweight all-metallic sandwich panels with corrugated cores

The transmission of sound through all-metallic sandwich panels with corrugated cores is investigated using the space-harmonic method. The sandwich panel is modeled as two parallel panels connected by uniformly distributed translational springs and rotational springs, with the mass of the core sheets taken as lumped mass. Based on the periodicity of the panel structure, a unit cell model is developed to provide the effective translational and rotational stiffness of the core. To check the validity of the model, it is used first to study the sound insulation properties of double-panel structures with air cavity, and the analytical predictions agree well with existing experimental data. The model is then employed to quantify the influence of sound incidence angle and the inclination angle between facesheet and core sheet on sound transmission loss （STL） across sandwich panels with corrugated cores. The results show that the inclination angle has a significant effect on STL and it is possible to avoid STL dips by altering the inclination angle. Moreover, it is found that sandwich panels with corrugated cores are more suitable for the insulation of sound waves having small incidence angles.     

Sound field structure produced by tone sources in the Kurile-Kamchatka region of the Pacific Ocean with a surface channel and wind waves

Results of the experimental studies of sound signal propagation in the continental wedge of the northwestern Pacific, near the eastern coast of the Kamchatka Peninsula, are presented. The signals are produced by highly stable tone sources. The experiments are carried out in winter, in the presence of a strong surface sound channel and intense wind waves, at frequencies of 100, 230, and 400 Hz, on a 1000-km-long path. The signal transmission is performed by continuously towing the sound sources at a depth of 50±5 m with a speed of 4.5–5 knots, for 115 hours. The decay of the sound field level with distance is studied as a function of the sea state and the frequency. The results of the experiments, including the sound field decay along the path, are compared with the calculations for different sea states.     

Utilizing vector hydrophones to achieve an active anechoic terminal in an acoustic tube

A new integrated active sound absorptive terminal using vector hydrophones is developed for the anechoic terminal of impedance tube,with which the reflected and the incident waves can be separated.The method overcomes the limitations imposed by the sensor spacing and measuring frequency range in the traditional two-hydrophone method,and can effectively expand low-frequency sound absorption band of the terminal.The effect of hydrophone sensitivity on the sound absorptive performance of the terminal is evaluated,a correction method is also provided for the reflection and transmission coefficient.The experimental results show that the absorption coefficient in the frequency band of 0.1-2 kHz is over 0.98,which agrees well with the theoretical results.