Analysis of the interaction of acoustic waves with hard and soft corals in the near field of a source.

2010 ◽  
Vol 128 (4) ◽  
pp. 2415-2415
Author(s):  
Mardi C. Hastings
Keyword(s):  
Acoustic Waves ◽  
Near Field ◽  
Soft Corals

Near field diffraction pattern of ion acoustic waves

1977 ◽  
Vol 20 (5) ◽  
pp. 840 ◽  
Author(s):  
Thomas Christensen ◽  
Noah Hershkowitz
Keyword(s):  
Diffraction Pattern ◽  
Acoustic Waves ◽  
Near Field ◽  
Ion Acoustic Waves ◽  
Ion Acoustic

Reconfigurable Acoustic Arrays With Deployable Structure Based on a Hoberman–Miura System Synthesis

2020 ◽  
Vol 143 (6) ◽  
Author(s):  
Ningxiner Zhao ◽  
Ryan L. Harne
Keyword(s):  
Acoustic Waves ◽  
Shape Change ◽  
Near Field ◽  
Ring Structure ◽  
Wave Focusing ◽  
System Synthesis ◽  
Reconfigurable Mechanisms ◽  
Acoustic Arrays ◽  
Dimensional Shape ◽  
Low Dimensional

Abstract Curved surfaces are often used to radiate and focus acoustic waves. Yet, when tessellated into reconfigurable surfaces for sake of deployability needs, origami-inspired acoustic arrays may be challenging to hold into curved shape and may not retain flat foldability. On the other hand, deployable mechanisms such as the Hoberman ring are as low-dimensional as many origami tessellations and may maintain curved shape with ease due to ideal rigid bar compositions. This research explores an interface between a Hoberman ring and Miura-ori tessellation that maintain kinematic and geometric compatibility for sake of maintaining curved shapes for sound focusing. The Miura-ori facets are considered to vibrate like baffled pistons and generate acoustic waves that radiate from the ring structure. An analytical model is built to reveal the near field acoustic behavior of acoustic arrays resulting from a Hoberman–Miura system synthesis. Acoustic wave focusing capability is scrutinized and validated through proof-of-principle experiments. Studies reveal wave focusing phenomena distinct to this manifestation of the acoustic array and uncover design and operational influences on wave focusing effectiveness. The results encourage exploration of new interfaces between reconfigurable mechanisms and origami devices where low-dimensional shape change is desired.

Self-generation of organized waves in an impinging turbulent jet at low Mach number

1982 ◽  
Vol 117 ◽  
pp. 425-441 ◽  
Author(s):  
Donald Rockwell ◽  
Andreas Schachenmann
Keyword(s):  
Mach Number ◽  
Phase Difference ◽  
Acoustic Waves ◽  
Near Field ◽  
Turbulent Jet ◽  
Maximum Pressure ◽  
Pressure Amplitude ◽  
Axisymmetric Cavity ◽  
Low Mach Number ◽  
Oscillation Frequencies

Self-generation of highly organized waves in a nominally turbulent jet at very low Mach number can arise from its impingement upon the downstream orifice of an axisymmetric cavity, having an impingement length much shorter than the corresponding acoustic wavelength. The oscillation frequencies are compatible with the resonant modes of a long pipe located upstream of the cavity and with jet-instability frequencies based on the column mode (0·3 [siml ] SD [siml ] 0·6), as well as the near-field shear layer mode (0·016 [siml ] Sθ0 [siml ] 0·03). Moreover, the frequency of the organized wave is constant from separation to impingement; consequently vortex pairing does not occur.Within the cavity, the pressure amplitude associated with the organized wave is directly related to the phase difference between the organized velocity fluctuations at separation and impingement. Maximum pressure amplitude occurs when this phase difference, measured along the cavity (i.e. jet) centre-line, is 2nπ. Streamwise amplitude and phase distributions of the organized wave cannot be explained from purely hydrodynamic considerations; however, they can be effectively modelled by superposing contributions from hydrodynamic and acoustic waves. This aspect has important consequences for externally excited jets as well.

scholarly journals Coherent backscattering of acoustic waves in the near field

2001 ◽  
Vol 145 (3) ◽  
pp. 593-603 ◽  
Author(s):  
L. Margerin ◽  
M. Campillo ◽  
B. A. van Tiggelen
Keyword(s):  
Acoustic Waves ◽  
Near Field ◽  
Coherent Backscattering

scholarly journals Identification of an unbounded bi-periodic interface for the inverse fluid-solid interaction problem

2021 ◽  
Author(s):  
Yanli Cui ◽  
Fenglong Qu ◽  
Changkun Wei
Keyword(s):  
Acoustic Waves ◽  
Near Field ◽  
A Priori ◽  
Scattering Problem ◽  
Three Dimensional ◽  
A Priori Estimate ◽  
Countably Infinite ◽  
Fluid Solid Interaction ◽  
Interaction Problem ◽  
Scattering Of Acoustic Waves

This paper is concerned with the inverse scattering of acoustic waves by an unbounded periodic elastic medium in the three-dimensional case. A novel uniqueness theorem is proved for the inverse problem of recovering a bi-periodic interface between acoustic and elastic waves using the near-field data measured only from the acoustic side of the interface, corresponding to a countably infinite number of quasi-periodic incident acoustic waves. The proposed method depends only on a fundamental a priori estimate established for the acoustic and elastic wave fields and a new mixed-reciprocity relation established in this paper for the solutions of the fluid-solid interaction scattering problem.

scholarly journals Recent Developments and Applications of Acoustic Infrasound to Monitor Volcanic Emissions

2019 ◽  
Vol 11 (11) ◽  
pp. 1302 ◽  
Author(s):  
Silvio De Angelis ◽  
Alejandro Diaz-Moreno ◽  
Luciano Zuccarello
Keyword(s):  
Acoustic Waves ◽  
Risk Mitigation ◽  
Near Field ◽  
Source Parameters ◽  
Time History ◽  
Wave Theory ◽  
Volume Flow ◽  
Civil Aviation ◽  
Volcanic Emissions ◽  
Early Assessment

Volcanic ash is a well-known hazard to population, infrastructure, and commercial and civil aviation. Early assessment of the parameters that control the development and evolution of volcanic plumes is crucial to effective risk mitigation. Acoustic infrasound is a ground-based remote sensing technique—increasingly popular in the past two decades—that allows rapid estimates of eruption source parameters, including fluid flow velocities and volume flow rates of erupted material. The rate at which material is ejected from volcanic vents during eruptions, is one of the main inputs into models of atmospheric ash transport used to dispatch aviation warnings during eruptive crises. During explosive activity at volcanoes, the injection of hot gas-laden pyroclasts into the atmosphere generates acoustic waves that are recorded at local, regional and global scale. Within the framework of linear acoustic theory, infrasound sources can be modelled as multipole series, and acoustic pressure waveforms can be inverted to obtain the time history of volume flow at the vent. Here, we review near-field (<10 km from the vent) linear acoustic wave theory and its applications to the assessment of eruption source parameters. We evaluate recent advances in volcano infrasound modelling and inversion, and comment on the advantages and current limitations of these methods. We review published case studies from different volcanoes and show applications to new data that provide a benchmark for future acoustic infrasound studies.

Analysis of the Reflection Coefficient of Rayleigh Waves From Surface-Breaking Cracks

2000 ◽  
Author(s):  
Waled Hassan ◽  
William Veronesi
Keyword(s):  
Reflection Coefficient ◽  
Rayleigh Wave ◽  
Acoustic Waves ◽  
Near Field ◽  
Crack Depth ◽  
Wave Length ◽  
Surface Acoustic Waves ◽  
Finite Size ◽  
High Crack ◽  
Limiting Value

Abstract The interaction of surface acoustic waves with finite-size, surface-breaking, semi-circular cracks is studied theoretically, numerically, and experimentally. We focus on the behavior of the reflection coefficient of the Rayleigh wave from such cracks in both the far and near fields of the crack. It is shown that, in the near field, the reflection coefficient from such cracks is higher than the reflection coefficient measured in the far field. This is mainly due to the diverging nature of the Rayleigh wave reflected from the crack. In the high crack depth to wave length ratio, the finite element and experimental results approach the limiting value of the reflection coefficient from a 90-degree corner.

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