Acoustic waves in gas flows with sound speed discontinuities

2020 ◽  
Vol 469 ◽  
pp. 115154
Author(s):  
Eduard Amromin
Keyword(s):  
Acoustic Waves ◽  
Sound Speed ◽  
Gas Flows

Acoustic waves in variable sound speed profiles

2009 ◽  
Author(s):  
Andrew Peplow ◽  
Börje Nilsson ◽  
Börje Nilsson ◽  
Louis Fishman ◽  
Anders Karlsson ◽  
...  
Keyword(s):  
Acoustic Waves ◽  
Sound Speed

scholarly journals A diverse group of echogenic particles observed with a broadband, high frequency echosounder

2017 ◽  
Vol 75 (2) ◽  
pp. 471-482 ◽  
Author(s):  
Christian Briseño-Avena ◽  
Peter J S Franks ◽  
Paul L D Roberts ◽  
Jules S Jaffe
Keyword(s):  
Acoustic Waves ◽  
High Frequency ◽  
Sound Speed ◽  
Diverse Group ◽  
Marine Snow ◽  
Frequency Range ◽  
Coastal Regions ◽  
The Past ◽  
Potential Sources ◽  
Acoustic Surveys

Abstract In 1980, Holliday and Pieper stated: “Most sound scattering in the ocean volume can be traced to a biotic origin.” However, most of the bioacoustics research in the past three decades has focused on only a few groups of organisms. Targets such as small gelatinous organisms, marine snow, and phytoplankton, e.g. have been generally to be considered relatively transparent to acoustic waves due to their sizes and relatively low sound speed and density contrasts relative to seawater. However, using a broadband system (ZOOPS-O2) we found that these targets contributed significantly to acoustic returns in the 1.5–2.5 MHz frequency range. Given that phytoplankton and marine snow layers are ubiquitous features of coastal regions; this works suggests that they should be considered as potential sources of backscatter in biological acoustic surveys.

scholarly journals Towards a Wave Theory Interpretation of Time-Distance Helioseismology Data

2001 ◽  
Vol 203 ◽  
pp. 180-182
Author(s):  
A. C. Birch ◽  
A. G. Kosovichev
Keyword(s):  
Spatial Scale ◽  
Born Approximation ◽  
Acoustic Waves ◽  
Sound Speed ◽  
Large Scale ◽  
Small Scale ◽  
Ray Theory ◽  
Travel Times ◽  
Large Spatial Scale ◽  
Time Distance

Time-distance helioseismology, which measures the time for acoustic waves to travel between points on the solar surface, has been used to study small-scale three-dimensional features in the sun, for example active regions, as well as large-scale features, such as meridional flow, that are not accessible by standard global helioseismology. Traditionally, travel times have been interpreted using geometrical ray theory, which is not always a good approximation. In order to develop a wave interpretation of time-distance data we employ the first Born approximation, which takes into account finite-wavelength effects and is expected to provide more accurate inversion results. In the Born approximation, in contrast with ray theory, travel times are sensitive to perturbations to sound speed which are located off the ray path. In an example calculation of travel time perturbations due to sound speed perturbations that are functions only of depth, we see that that the Born and ray approximations agree when applied to perturbations with large spatial scale and that the ray approximation fails when applied to perturbations with small spatial scale.

scholarly journals Investigation of a sunspot complex by time-distance helioseismology

2010 ◽  
Vol 6 (S273) ◽  
pp. 320-324 ◽  
Author(s):  
A. G. Kosovichev ◽  
T. L. Duvall
Keyword(s):  
Acoustic Waves ◽  
Sound Speed ◽  
Active Regions ◽  
Magnetic Activity ◽  
Depth Range ◽  
Travel Times ◽  
Magnetic Structures ◽  
Flow Maps ◽  
Time Distance ◽  
Deep Focus

AbstractSunspot regions often form complexes of activity that may live for several solar rotations, and represent a major component of the Sun's magnetic activity. It had been suggested that the close appearance of active regions in space and time might be related to common subsurface roots, or “nests” of activity. EUV images show that the active regions are magnetically connected in the corona, but subsurface connections have not been established. We investigate the subsurface structure and dynamics of a large complex of activity, NOAA 10987-10989, observed during the SOHO/MDI Dynamics run in March-April 2008, which was a part of the Whole Heliospheric Interval (WHI) campaign. The active regions in this complex appeared in a narrow latitudinal range, probably representing a subsurface toroidal flux tube. We use the MDI full-disk Dopplergrams to measure perturbations of travel times of acoustic waves traveling to various depths by using time-distance helioseismology, and obtain sound-speed and flow maps by inversion of the travel times. The subsurface flow maps show an interesting dynamics of decaying active regions with persistent shearing flows, which may be important for driving the flaring and CME activity, observed during the WHI campaign. Our analyses, including the seismic sound-speed inversion results and the distribution of deep-focus travel-time anomalies, gave indications of diverging roots of the magnetic structures, as could be expected from Ω-loop structures. However, no clear connection in the depth range of 0-48 Mm among the three active regions in this complex of activity was detected.

Sound speed determination in V2O5single crystals using laser‐generated acoustic waves

1985 ◽  
Vol 46 (3) ◽  
pp. 256-257 ◽  
Author(s):  
Markus W. Sigrist ◽  
László Nánai
Keyword(s):  
Acoustic Waves ◽  
Sound Speed

Flow and Temperature Profile Independence of Flow Measurements Using Long Acoustic Waves

1984 ◽  
Vol 106 (1) ◽  
pp. 18-20 ◽  
Author(s):  
Baldwin Robertson
Keyword(s):  
Temperature Profile ◽  
Acoustic Waves ◽  
Sound Speed ◽  
Cutoff Frequency ◽  
Longitudinal Component ◽  
Wave Number ◽  
Cross Sectional ◽  
Flow Measurements ◽  
Local Sound ◽  
Sectional Shape

An expansion in powers of V/c is derived for the wave number of the fundamental sound mode in a flow conduit, where V is the velocity of fluid in the conduit and c is the local sound speed. Both V and c are assumed to be independent of the longitudinal coordinates and of the time, but may have arbitrary profiles. The calculation applies to frequencies well below the cutoff frequency of the conduit, which may have an arbitrary cross-sectional shape. To lowest order, the wave number depends only on the average of the longitudinal component of V and is independent of its profile.

Measuring effective stiffness of Li-ion batteries via acoustic signal processing

2020 ◽  
Vol 8 (32) ◽  
pp. 16624-16635 ◽  
Author(s):  
Wesley Chang ◽  
Robert Mohr ◽  
Andrew Kim ◽  
Abhi Raj ◽  
Greg Davies ◽  
...  
Keyword(s):  
Signal Processing ◽  
Acoustic Signal ◽  
Acoustic Waves ◽  
Sound Speed ◽  
Effective Stiffness ◽  
High Rate ◽  
Li Ion Batteries ◽  
Material Stiffness ◽  
Li Ion

Accurate signal processing of acoustic waves is utilized to measure the intrinsic material stiffness of a layered cell stack and explore relationships between battery displacement, sound speed and stiffness during high rate cycling.

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