声波多普勒效应演示实验

利用声波多普勒效应导致声强变化的特性,设计了声波多普勒效应实验装置,该装置将声音信号转变成电信号,并用信号大器进行放大,驱动发光二极管发光演示了声波的多普勒效应.     

Leak noise propagation and attenuation in submerged plastic water pipes

Detection of water leaks in buried distribution pipes using acoustic methods is common practice in many countries. Correlation techniques are widely used in leak detection, and these have been extremely effective when attempting to locate leaks in metal pipes. However, a number of difficulties have been highlighted when trying to determine the position of leaks in plastic pipes. Of particular interest here is what happens to the leak noise when the pipe passes through an expanse of water, such as across a river or lake.In this paper, the low-frequency acoustic propagation and attenuation characteristics of a submerged plastic water pipe are investigated experimentally in the laboratory, supported by predictions from a theoretical model. It is found that, whilst the signal attenuation for a submerged pipe is increased relative to that for a similar in-vacuo pipe, energy does not, in fact, radiate into the water; furthermore, the attenuation is small compared with that for a pipe buried in soil.     

Numerical simulation of the nonlinear ultrasonic pressure wave propagation in a cavitating bubbly liquid inside a sonochemical reactor

We investigate the acoustic wave propagation in bubbly liquid inside a pilot sonochemical reactor which aims to produce antibacterial medical textile fabrics by coating the textile with ZnO or CuO nanoparticles. Computational models on acoustic propagation are developed in order to aid the design procedures. The acoustic pressure wave propagation in the sonoreactor is simulated by solving the Helmholtz equation using a meshless numerical method. The paper implements both the state-of-the-art linear model and a nonlinear wave propagation model recently introduced by Louisnard (2012), and presents a novel iterative solution procedure for the nonlinear propagation model which can be implemented using any numerical method and/or programming tool. Comparative results regarding both the linear and the nonlinear wave propagation are shown. Effects of bubble size distribution and bubble volume fraction on the acoustic wave propagation are discussed in detail. The simulations demonstrate that the nonlinear model successfully captures the realistic spatial distribution of the cavitation zones and the associated acoustic pressure amplitudes.     

声波在含气泡液体中传播特性及产热效应*

该文对含气泡液体中的声波方程采用线性分析方法,研究了超声波在含气泡液体中的传播特性以及产热效应。当声波在含气泡液体中传播时,气泡的存在会影响声波的传播,在声波频率接近气泡共振频率的频段内,声信号在液体中传播时剧烈衰减,而在声波频率远远高于或低于气泡共振频率时,声波的传播基本不受影响。在接近气泡共振的频段内,声波耗散的能量最终转化为热能。同时液体中的气泡会在声波驱动下径向振动并辐射声波,伴随气泡壁在液体中的粘滞振动,热量随之产生。结果表明,两种产热机制分别在不同频段起主导作用。     

Sound velocity and attenuation in bubbly gels measured by transmission experiments

Measurements of the phase velocity and attenuation of sound in concentrated samples of bubbly gels are presented. Hair gel was used as a matrix material to obtain well characterized distributions of bubbles. Ultrasonic measurements were conducted over a large range of frequencies, including the resonance frequencies of the bubbles. Surprisingly good agreement with Foldy's prediction was found, even for monodisperse samples at resonance frequencies, up to volume fraction of 1%. Beyond this concentration, the effects of high-order multiple scattering were observed. These results support the feasability of ultrasonic techniques to investigate the size distribution of bubbles in a weak gel or liquid.     

Spatial attenuation of different sound field components in a water layer and shallow-water sediments

The paper presents the results of an experimental study of spatial attenuation of low-frequency vector-scalar sound fields in shallow water. The experiments employed a towed pneumatic cannon and spatially separated four-component vector-scalar receiver modules. Narrowband analysis of received signals made it possible to estimate the attenuation coefficients of the first three modes in the frequency of range of 26–182 Hz and calculate the frequency dependences of the sound absorption coefficients in the upper part of bottom sediments. We analyze the experimental and calculated (using acoustic calibration of the waveguide) laws of the drop in sound pressure and orthogonal vector projections of the oscillation velocity. It is shown that the vertical projection of the oscillation velocity vector decreases significantly faster than the sound pressure field.     

Frustration and sound attenuation in structural glasses

Three classes of harmonic disorder systems (Lennard-Jones-like glasses, percolators above threshold, and spring disordered lattices) have been numerically investigated in order to clarify the effect of different types of disorder on the mechanism of high frequency sound attenuation. We introduce the concept of frustration in structural glasses as a measure of the internal stress, and find a strong correlation between the degree of frustration and the exponent alpha that characterizes the momentum dependence of the sound attenuation gamma(Q) approximately Qalpha. In particular, alpha decreases from approximately d+1 in low-frustration systems (where d is the spectral dimension) to approximately 2 for high-frustration systems such as the realistic glasses examined.     

Refraction and reflection of sound at the boundary of a bubbly liquid

Reflection and refraction of acoustic waves at the interface between pure water and bubbly water are investigated for the case of oblique incidence. From an analysis of analytic solutions, it is concluded that, for a wave incident on the interface from the side of a bubbly liquid, a critical angle of incidence, which depends on the frequency and the parameters of the disperse system, exists, so that, at angles of incidence exceeding the critical one, the wave is totally reflected from the interface.

     

Liquid water fade margin requirements for infrared and millimeter wave runway imaging sensors in fog

Liquid water content and particle size distribution at each ten meters in the vertical for a deep advection fog and a shallow radiation fog are analyzed to determine the liquid water loss at millimeter and infrared wavelengths. The liquid water fade margin is calculated along a three degree glideslope in each fog from the current height above the runway to the touchdown point. Millimeter wave fade margin requirements are calculated from the vertical distribution of bulk liquid water content and infrared fade margin requirements are predicted from the vertical distribution of dropsize. Fog dropsize distributions for both fog layers are well fitted to a gamma distribution with a median drop diameter of approximately 9 microns. Millimeter wave imaging sensors operating in a shallow radiation fog are shown to require less than 1 dB of one-way liquid water fade margin. In the deep advection fog, one-way liquid water fade margin requirements at 8.6 mm, 6.8 mm, and 3.2 mm are predicted to be 1, 2, and 6.7 dB respectively. In comparison, the one-way liquid water fade margin requirements at near, middle, and far infrared wavelengths are two orders of magnitude greater than at millimeter wavelengths and indicate the fog layers are opaque to infrared imaging sensors even near the touchdown point. The specific attenuations predicted in the two fogs are consistent with previously reported values.     

Ice nucleation of water droplet containing solid particles under weak ultrasonic vibration

Water with small volume (a few microlitres or less) often maintains its liquid state even at temperatures much lower than 0 °C. In this study, we examine the onset of ice nucleation in micro-sized water droplets with immersed solid particles under weak ultrasonic vibrations. The experimental results show that ice nucleation inside the water droplets can be successfully induced at relatively high temperatures. The experimental observations indicate that the nucleation sites are commonly encountered in the region between the particle and the substrate. A numerical study is conducted to gain insight into the possible underlying phenomenon for ice nucleation in such systems. The simulation results show that the collapse of cavitation bubbles in the crevice at the particle surface is structure sensitive with the hemisphere-shape crevice generating pressures as high as 1.63 GPa, which is theoretically suitable for inducing ice nucleation.     

气泡幕的声透射损失和对水中壳体减振的实验研究

通过不同放气孔径和不同放气压差所形成的气泡幕的透声实验,获得了含气浓度在大范围内变化的气泡幕透声损失与频率关系的实验资料。在气泡幕对浮于水中壳体振动的影响的实验中,得到了气泡幕对壳体振动有明显抑制作用的实验结果。     

Low-frequency sound absorption and attenuation in marine medium

Original experimental data are analyzed on the low-frequency sound attenuation in the Mediterranean, Black, and Baltic Seas, Sea of Japan, and the north-western region of the Pacific Ocean. In these regions, waters significantly differ in their temperatures and salinities. The analysis is aimed at obtaining an expression for calculating the low-frequency absorption coefficient in sea water. The analysis uses the previously published data on the measured (by the temperature discontinuity method) low-frequency relaxation times associated with boron present in sea water. The dependence of the absorption on the pH value (which was revealed in the 1970s) and the experimental data on sound absorption at frequencies higher than 5–10 kHz are also taken into account. As a result of the analysis based on the assumption that low-frequency relaxation takes place, an expression is proposed that relates the low-frequency absorption to the temperature, salinity, and pH value and equally well describes the experimental frequency dependences of attenuation for the four regions at hand (except for the Baltic Sea). Increased attenuation coefficients are noticed for shallow seas and deep-water regions where waters are influenced by intense currents, strait zones, and zones of mixing waters of different origin, i.e., for the ocean areas where, in addition to the attenuation, sound scattering by inhomogeneities of the marine medium and sound energy leakage into the sea floor are significant.     

Nonlinear and linear wave phenomena in narrow pipes

Phenomena arising in the course of wave propagation in narrow pipes are considered. For nonlinear waves described by the generalized Webster equation, a simplified nonlinear equation is obtained that allows for low-frequency geometric dispersion causing an asymmetric distortion of the periodic wave profile, which qualitatively resembles the distortion of a nonlinear wave in a diffracted beam. Tunneling of a wave through a pipe constriction is investigated. Possible applications of the phenomenon are discussed, and its relation to the problems of quantum mechanics because of the similarity of the basic equations of the Klein-Gordon and Schrödinger types is pointed out. The importance of studying the tunneling of nonlinear waves and broadband signals is indicated.     

Two-dimensional mechanisms of interaction between ultrasound and sound in bubbly liquids: Interaction equations

The interaction of long (sound) and short (ultrasound) waves propagating in a rarefied monodisperse mixture of a weakly compressible liquid with gas bubbles is considered. Using the multiscale method, the Davey-Stewartson system of equations is derived as a model of two-dimensional interaction. It is shown that, for some values of parameters, this system is reduced to an integrable form (the Davey-Stewartson I equations) and has localized solutions in the form of dromions (exponentially decaying waves of the short-wave envelope). One of the most important properties of dromions is their ability to move according to the law that governs the variations of the boundary conditions set at infinity for the long wave. It is suggested that these solutions be used for controlling the effects of ultrasound on bubbly liquids.     

Calculation of shock wave propagation in water containing reactive gas bubbles

The entry of a shock wave from air into water containing reactive gas (stoichiometric acetylene–oxygen mixture) bubbles uniformly distributed over the volume of the liquid has been numerically investigated using equations describing two-phase compressible viscous reactive flow. It has been demonstrated that a steady-state supersonic self-sustaining reaction front with rapid and complete fuel burnout in the leading shock wave can propagate in this bubbly medium. This reaction front can be treated as a detonation-like front or “bubble detonation.” The calculated and measured velocities of the bubble detonation wave have been compared at initial gas volume fraction of 2 to 6%. The observed and calculated data are in satisfactory qualitative and quantitative agreement. The structure of the bubble detonation wave has been numerically studied. In this wave, the gas volume fraction behind the leading front is approximately 3–4 times higher than in the pressure wave that propagates in water with air bubbles when the other initial conditions are the same. The bubble detonation wave can form after the penetration of the shock wave to a small depth (~300 mm) into the column of the bubbly medium. The model suggested here can be used to find optimum conditions for maximizing the efficiency of momentum transfer from the pressure wave to the bubbly medium in promising hydrojet pulse detonation engines.