Recent Developments in Theories of Wave Generation

We simulate the generation of acoustic and tsunami waves generated by submarine landslides using the linear model developed in [1]. The model is able to reproduce both acoustic and surface gravity waves generated by a moving source (e.g. earthquake, landslide) in a vertically stratified ocean.There are only a few studies that focus on the generation of acoustic waves by submarine landslides. In [2], the combined analysis of field data and simulations underline the presence of an interference pattern in the acoustic waves' spectrogram. The interference pattern has a time-varying bandwidth, which is a signature of the submarine landslide dynamics. In a previous work [3], we used the model developed in [1] to reproduce the interference pattern for a static source. Here we use the same model to simulate a submarine landslide in the 2D case. The simulations reproduce the time-varying bandwidth. They are then used to study the influence of two parameters on the acoustic spectrograms, namely landslide velocity and topography. Different velocity profiles available in the literature [4] are tested. For the topography, we use as reference the 2D case simulated in [1]. We also provide illustrations for the tsunami generation by the landslide. [1] Dubois J, Imperiale S, Mangeney A, Bouchut F, Sainte-Marie J. Acoustic and gravity waves in the ocean: a new derivation of a linear model from the compressible Euler equation. Journal of Fluid Mechanics. 2023;970:A28. doi:10.1017/jfm.2023.595[2] Caplan-Auerbach, J., Dziak, R. P., Bohnenstiehl, D. R., Chadwick, W. W., and Lau, T.-K. (2014), Hydroacoustic investigation of submarine landslides at West Mata volcano, Lau Basin, Geophys. Res. Lett.,  41,  5927– 5934, doi:10.1002/2014GL060964.[3] Dubois, J., Imperiale, S., Mangeney, A., and Sainte-Marie, J.: Simulation of the hydro-acoustic and gravity waves generated by a landslide, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15937, https://doi.org/10.5194/egusphere-egu23-15937, 2023. [4] Farin, M., Mangeney, A., de Rosny, J., Toussaint, R., & Trinh, P.-T. (2019). Relations between the characteristics of granular column collapses and resultant high-frequency seismic signals. Journal of Geophysical Research: Earth Surface, 124, 2987–3021. https://doi.org/10.1029/2019JF005258

The generation of acoustic-gravity waves by meteorological heat sources in the troposphere and the propagation of these waves to the heights of the upper atmosphere are studied theoretically. Equations that describe separately the generation and propagation of acoustic and gravity waves by a local heat source are derived. The heat source of the waves is divided into partial sources of gravity and acoustic waves (AWs). The power of these partial sources is estimated and it is shown that the power of the sources differs by about a factor of two, regardless of the shape, size, and frequency of the heat source. It is shown that in the case of heat sources of the waves, the generation of gravity waves cannot occur without the corresponding generation of AWs: these waves are generated only in pairs. The splitting of the problem of waves from a heat source into problems of waves from gravity and acoustic sources is illustrated by the direct modeling of these waves. The application of the obtained results to the problem of parametrization of acoustic-gravity waves in general circulation and climate models is discussed.

There is a one academic year theoretical acoustics course for postgraduate students in the Department of Acoustic Science and Engineering of Nanjing University. The course introduces the physical principles and mathematical methods for acoustics in fluids, and the main objective is to deepen understanding of acoustical principle for postgraduate students in the field of acoustics following their undergraduate fundamental acoustics course. The contents include acoustic waves in ideal fluids, acoustic radiation in infinite space, acoustic scattering and diffractions, propagation and radiation of acoustic waves in dust, acoustic fields in enclosed space, acoustic waves in dissipative fluids, acoustic waves in layered fluid, acoustic waves in moving fluids, propagation of acoustic waves with finite amplitude, and effects generated by acoustic waves with finite amplitude. More details can be found in the book title “Principle of Acoustics in Fluids” published by Science Press in China in 2012.

The measurement of quality in auditorium acoustics by subjective scaling methods—A review of developments in theory and practice

In this paper a review of the recent developments in the theory of a slowly oscillating low aspect ratio, pointed wing at sonic speed is presented, using the concepts of the parabolic method, the equivalence rule and a iteration method to approximately incorporate the thickness effect in the analysis.

Techniques of scanning acoustic microscopy generally rely on local variations of such solid state parameters influencing generation or propagation of acoustic waves. Depending on the manner of impressing acoustic waves into the sample various methods are distinguished. In conventional scanning acoustic microscopy ultrasound is generated by a lens-transducer arrangement outside the sample and focussed onto or below its surface. Changes in the propagation of this ultrasound wave, like absorption and reflexion or temporal propagation delays, enable analysis of the mechanical or elastic response. At very high frequencies and with additional time-resolving detection techniques applications of this technique to surface analysis become possible. Other scanning acoustic microscopes imply the generation of sound or ultrasound directly within the sample itself due to the impact of temporarily modulated particle or photon beams. These are presently laser, electron, or ion beams. With these methods the acoustic signal as detected by a transducer attached to the sample is on principle affected by propagation properties, too, but it is dominated by local changes of the generation process for the acoustic wave, mainly because the frequency ranges used presently are associated with very long acoustic wavelengths. Depending on the physical nature of the primary probe used many sound generation mechanisms are given resulting in a large amount of different applications. By adjusting the probe parameters in a suitable manner the sound generation process can be confined to the direct vicinity of the specimen surface, which makes this technique feasible for surface characterization. The principles of the various techniques are described, and their usability for surface analysis is discussed.

We investigate the excitation and propagation of acoustic waves in polycrystalline aluminum nitride films along the directions parallel and normal to the c-axis. Longitudinal and transverse propagations are assessed through the frequency response of surface acoustic wave and bulk acoustic wave devices fabricated on films of different crystal qualities. The crystalline properties significantly affect the electromechanical coupling factors and acoustic properties of the piezoelectric layers. The presence of misoriented grains produces an overall decrease of the piezoelectric activity, degrading more severely the excitation and propagation of waves traveling transversally to the c-axis. It is suggested that the presence of such crystalline defects in c-axis-oriented films reduces the mechanical coherence between grains and hinders the transverse deformation of the film when the electric field is applied parallel to the surface.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTComments upon Recent Developments in Theory of FiltrationB. F. Ruth, R. E. Montonna, and G. H. MontillonCite this: Ind. Eng. Chem. 1931, 23, 7, 850–851Publication Date (Print):July 1, 1931Publication History Published online1 May 2002Published inissue 1 July 1931https://doi.org/10.1021/ie50259a036RIGHTS & PERMISSIONSArticle Views57Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (326 KB) Get e-Alerts

By virtue of the diffraction-free propagation of surface acoustic waves (SAWs) on a sphere, we observed multiple round-trips of as many as 100 turns. After experimental verification of the beam shapes, we proposed ball acoustooptic devices utilizing the focussing SAWs.

The purpose of this paper is the generalization of structure factor for rods by polygon section in two dimensional phononic crystals. If we use the plane wave expansion method (PWE) for the propagation of acoustic waves in 2D phononic crystals, structure factor will be an important quantity. In order to confirm the obtained relations, we have calculated the band structure for XY and Z vibration modes in 2D phononic crystals and the propagation of bulk acoustic waves (BAW) are considered. In addition, the effect of sides’ number on the band structure and the complete band gaps width are investigated. Phononic crystals studied in this paper are composites medium of a square lattice consisting of parallel nickel rods embedded in epoxy. The frequency is calculated by PWE in the condition of elastic rigidity to the solid inclusions. The results showed that, when the section of rods have 2n+2 (n is even) and 2n+1ሺn א Nሻ by increasing sides number of the rod sections, the bands of XY mode shift to lowerfrequency, the bands are smoother and the width of the band gap increases, but the band of Z mode has not changed by n variations. Moreover, when the section of rods have 2n+2 (n is odd) by increasing sides number of rod sections, the band structure of XY mode changes slightly and the width of the complete band gap is decreased. This confirms the effect of lattice symmetry on the complete band gap width. But, the band structure of Z mode has not changed.

Based on the modification of the radial pulsation equation of an individual bubble, an effective medium method (EMM) is presented for studying propagation of linear and nonlinear longitudinal acoustic waves in viscoelastic medium permeated with air bubbles. A classical theory developed previously by Gaunaurd (Gaunaurd GC and Uberall H, J. Acoust. Soc. Am., 1978; 63: 1699–1711) is employed to verify the EMM under linear approximation by comparing the dynamic (i.e. frequency-dependent) effective parameters and an excellent agreement is obtained. The propagation of longitudinal waves is hereby studied in detail. The results illustrate that the nonlinear pulsation of bubbles serves as the source of second harmonic wave and the sound energy has the tendency to be transferred to second harmonic wave. Therefore the sound attenuation and acoustic nonlinearity of the viscoelastic matrix are remarkably enhanced due to the system's resonance induced by the existence of bubbles.

A two‐dimensional nonlinear numerical model has been developed to study atmospheric coupling due to vertically propagating acoustic gravity waves (AGWs) on different planets. The model is able to simulate both acoustic and gravity waves due to inclusion of compressibility. The model also considers dissipative effects due to viscosity, conduction, and radiative damping. The hyperbolic inviscid advection equations are solved using the Lax‐Wendroff method. The parabolic diffusion terms are solved implicitly using a linear algebra‐based Direct method. The model is validated by comparing numerical solutions against analytical results for linear propagation, critical level absorption, and mountain wave generation over an isolated hill. Acoustic wave generation in Martian atmosphere due to a pressure pulse is also demonstrated. A case study of tsunami‐generated AGWs is presented for the 2004 Sumatra earthquake whereby the model is forced through tsunamigenic sea‐surface displacement. The properties of simulated AGWs closely match those derived from ionospheric sounding observations reported in literature. Another application for Martian ice cloud formation is discussed where gravity waves from topographic sources are shown to create cold pockets with temperatures below the CO2 condensation threshold. The simulated cold pockets coincide with the cloud echo observations from the Mars Orbiting Laser Altimeter aboard Mars Global Survey spacecraft.

Physical investigation of acoustic waves induced by the oscillation and collapse of the single bubble

A theoretical analysis of non‐stationary interactions of intensive laser light and a bulk acoustic wave in dielectric crystals is made. The time dependence of the source of both, light waves and acoustic wave is considered. All fundamentals kinds of acousto‐optics interactions, viz. Stokes and anti‐Stokes processes, as well as the generation of acoustic waves by “mixing” two light beams are discussed.

The present article is a theoretical study of the combined propagation of acoustic and internal waves of finite amplitude in a (horizontally, say) stratified fluid. The linear theory of small amplitude waves predicts that the two waves (i.e., the fluctuations in acoustic pressure and in vertical particle velocity or displacement) are in general coupled. The waves are decoupled whenever the typical wavenumbers are large compared with the inverse of the scale height for the stratification. Furthermore, a horizontally propagating acoustic wave with zero vertical particle displacement (or velocity), when this is possible, is always decoupled from the internal waves, according to linear theory. In a weakly nonlinear theory, however, the waves may be coupled. A time independent radiation pressure is formed within a standing, horizontally directed acoustic wave, which produces a stationary vertical displacement of the particles. Experimental evidence of this effect has been reported elsewhere [1].