Asymmetric propagation of low-frequency acoustic waves in a granular chain using asymmetric intruders

2019 ◽  
Vol 126 (7) ◽  
pp. 075116 ◽  
Author(s):  
Hoda Jalali ◽  
Piervincenzo Rizzo ◽  
Amir Nasrollahi
Keyword(s):  
Acoustic Waves ◽  
Low Frequency ◽  
Granular Chain

Studies on the interaction of low‐frequency acoustic signals with the ocean bottom

Geophysics ◽  
1979 ◽  
Vol 44 (12) ◽  
pp. 1922-1940 ◽  
Author(s):  
Salvatore R. Santaniello ◽  
Frederick R. DiNapoli ◽  
Robert K. Dullea ◽  
Peter D. Herstein
Keyword(s):  
Acoustic Waves ◽  
Grazing Angle ◽  
Low Frequency ◽  
Propagation Loss ◽  
Ocean Bottom ◽  
Computer Technique ◽  
Quantitative Evidence ◽  
Ocean Sediment ◽  
Wave Models ◽  
Processing Techniques

Understanding the mechanisms by which the ocean sediment redirects impinging sound back into the ocean is necessary in developing propagation models for sonar performance prediction. The Naval Underwater Systems Center (NUSC) has (1) conducted controlled, self‐calibrating acoustic measurements where the ocean bottom interacted signal is isolated in time for analysis, (2) developed deconvolution processing techniques to aid in describing the impulse response of the ocean sediment, and (3) performed modeling to study the interaction of acoustic waves at the ocean bottom. This paper presents a synopsis of studies showing the necessity of considering the refraction of sound by the ocean sediment when predicting low‐frequency propagation loss. Constructive interference between nonplanar wave sediment refracted sound and sound reflected by the ocean‐sediment interface and subbottom layering can cause negative values of bottom loss when using plane‐wave models to interpret measured data. These models cannot account for all possible acoustic arrivals at a receiver. In addition, for a given frequency and constant ocean bottom grazing angle, bottom loss can be dependent upon both processing bandwidth and source/receiver depth. Deconvolution has aided in time resolution of signals that make up the bottom‐interacted signals. Resolution of these signals aids in interpreting results. A modeling effort utilizing the Fast Field Program (a computer technique for evaluating the field integral by the fast Fourier transform) provides quantitative evidence for the necessity of accounting for the refraction of sound by subocean sediments to interpret properly low‐frequency propagation loss measurements.

LOW-FREQUENCY ACOUSTIC SCATTERING BY AN INHOMOGENEOUS MEDIUM

2005 ◽  
Vol 15 (10) ◽  
pp. 1459-1468 ◽  
Author(s):  
GEORGE VENKOV
Keyword(s):  
Refractive Index ◽  
Plane Wave ◽  
Inhomogeneous Medium ◽  
Acoustic Waves ◽  
Spherical Wave ◽  
Low Frequency ◽  
Far Field ◽  
Scattering Medium ◽  
Wave Incidence ◽  
Plane Wave Incidence

This paper deals with the scattering of time-harmonic acoustic waves by inhomogeneous medium. We study the problem to recover the near and the far field using a priori information about the refractive index and the support of inhomogeneity. The incident spherical wave is modified in such a way as to recover the plane wave incidence when the source point approaches infinity. Applying the low-frequency expansions, the scattering medium problem is reduced to a sequence of potential problems for the approximation coefficients in the presence of a monopole singularity located at the source of incidence. Complete expansions for the integral representation formula in the near field as well as for the scattering amplitude in the far field are provided. The method is applied to the case of a spherical region of inhomogeneity and a radial dependent refractive index. As the point singularity tends to infinity, the relative results recover the scattering medium problem for plane wave incidence.

scholarly journals Sub-wavelength focusing of acoustic waves in bubbly media

2017 ◽  
Vol 473 (2208) ◽  
pp. 20170469 ◽  
Author(s):  
Habib Ammari ◽  
Brian Fitzpatrick ◽  
David Gontier ◽  
Hyundae Lee ◽  
Hai Zhang
Keyword(s):  
Acoustic Waves ◽  
Wave Scattering ◽  
Low Frequency ◽  
Scattering Function ◽  
Point Scatterer ◽  
Layer Potential ◽  
Spherical Bubble ◽  
Acoustic Wave Scattering ◽  
Frequency Regime ◽  
Sub Wavelength

The purpose of this paper is to investigate acoustic wave scattering by a large number of bubbles in a liquid at frequencies near the Minnaert resonance frequency. This bubbly media has been exploited in practice to obtain super-focusing of acoustic waves. Using layer potential techniques, we derive the scattering function for a single spherical bubble excited by an incident wave in the low frequency regime. We then propose a point scatterer approximation for N bubbles, and describe several numerical simulations based on this approximation, that demonstrate the possibility of achieving super-focusing using bubbly media.

Acoustic Resonances of an Industrial Gas Turbine Combustion System

2000 ◽  
Vol 123 (4) ◽  
pp. 766-773 ◽  
Author(s):  
S. Hubbard ◽  
A. P. Dowling
Keyword(s):  
Gas Turbine ◽  
Acoustic Waves ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Nonlinear Effects ◽  
Operating Conditions ◽  
Resonant Frequencies ◽  
Bulk Mode ◽  
Acoustic Resonances ◽  
Industrial Gas Turbine

A theory is developed to describe low-frequency acoustic waves in the complicated diffuser/combustor geometry of a typical industrial gas turbine. This is applied to the RB211-DLE geometry to give predictions for the frequencies of the acoustic resonances at a range of operating conditions. The main resonant frequencies are to be found around 605 Hz (associated with the plenum) and around 461 Hz and 823 Hz (associated with the combustion chamber), as well as one at around 22 Hz (a bulk mode associated with the system as a whole). The stabilizing effects of a Helmholtz resonator, which models damping through nonlinear effects, are included, together with effects of coupled pressure waves in the fuel supply system.

Depth-integrated equation for hydro-acoustic waves with bottom damping

2015 ◽  
Vol 766 ◽  
Author(s):  
Ali Abdolali ◽  
James T. Kirby ◽  
Giorgio Bellotti
Keyword(s):  
Acoustic Waves ◽  
Large Scale ◽  
Model Equation ◽  
Low Frequency ◽  
3D Models ◽  
Sediment Layer ◽  
Sea Bed ◽  
Weakly Compressible ◽  
Acoustic Wave Generation

AbstractWe present a depth-integrated equation for the mechanics of generation, propagation and dissipation of low-frequency hydro-acoustic waves due to sudden bottom displacement in a weakly compressible ocean overlying a weakly compressible viscous sediment layer. The model is validated against a full 3D computational model. Physical properties of these waves are studied and compared with those for waves over a rigid sea bed, revealing changes in the frequency spectrum and modal peaks. The resulting model equation can be used for numerical prediction in large-scale domains, overcoming the computational difficulties of 3D models while taking into account the role of bottom dissipation on hydro-acoustic wave generation and propagation.

scholarly journals ACAT1 Benchmark of RANS-Informed Analytical Methods for Fan Broadband Noise Prediction: Part II—Influence of the Acoustic Models

Acoustics ◽  
2020 ◽  
Vol 2 (3) ◽  
pp. 617-649
Author(s):  
Sébastien Guérin ◽  
Carolin Kissner ◽  
Pascal Seeler ◽  
Ricardo Blázquez ◽  
Pedro Carrasco Laraña ◽  
...  
Keyword(s):  
Analytical Methods ◽  
Acoustic Waves ◽  
Power Spectra ◽  
Low Frequency ◽  
Broadband Noise ◽  
Experimental Results ◽  
Acoustic Analogy ◽  
Noise Sources ◽  
Acoustic Models ◽  
The Impact

A benchmark dedicated to RANS-informed analytical methods for the prediction of turbofan rotor–stator interaction broadband noise was organised within the framework of the European project TurboNoiseBB. The second part of this benchmark focuses on the impact of the acoustic models. Twelve different approaches implemented in seven different acoustic solvers are compared. Some of the methods resort to the acoustic analogy, while some use a direct approach bypassing the calculation of a source term. Due to differing application objectives, the studied methods vary in terms of complexity to represent the turbulence, to calculate the acoustic response of the stator and to model the boundary and flow conditions for the generation and propagation of the acoustic waves. This diversity of approaches constitutes the unique quality of this work. The overall agreement of the predicted sound power spectra is satisfactory. While the comparison between the models show significant deviations at low frequency, the power levels vary within an interval of ±3 dB at mid and high frequencies. The trends predicted by increasing the rotor speed are similar for almost all models. However, most predicted levels are some decibels lower than the experimental results. This comparison is not completely fair—particularly at low frequency—because of the presence of noise sources in the experimental results, which were not considered in the simulations.

Determination of wave growth from measured distribution functions and transport theory

1980 ◽  
Vol 23 (1) ◽  
pp. 91-113 ◽  
Author(s):  
C. T. Dum ◽  
E. Marsch ◽  
W. Pilipp
Keyword(s):  
Acoustic Waves ◽  
Transport Theory ◽  
Low Frequency ◽  
Distribution Functions ◽  
Ion Acoustic Waves ◽  
Wave Growth ◽  
Ion Cyclotron Waves ◽  
Precise Shape ◽  
The Magnetic Field

A stability analysis which directly uses particle distribution functions determined from experiments or transport theory, rather than model distributions, is carried out. The features of distribution functions relevant to whistlers, ion cyclotron waves, including their low-frequency extensions for propagation along the magnetic field, and to ion-acoustic waves are analyzed in detail. The dependence of wave growth on the precise shape of the distributions and the numerical feasibility of the method is demonstrated by the use of measured solar wind distributions.

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