Acoustically induced cavity cloud generated by air-gun arrays<b>—</b>Comparing video recordings and acoustic data to modeling

Khodabandeloo, Babak; Landrø, Martin

doi:10.1121/1.5040490

Cited by 14 publications

(11 citation statements)

References 43 publications

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“…However, since the recorded acoustic signals in this experiment were saturated in some parts, they are not appropriate to be compared with the modelled signals. Details of the photographed cavity cloud and the recorded acoustic signal is given in (Khodabandeloo and Landrø, 2018).…”

Section: Visualizing Ghost Cavity Cloudmentioning

confidence: 99%

Characterizing the acoustic properties of the cavity cloud generated close to an air-gun array as a time-dependent effective medium

Khodabandeloo

Landrø

2018

Geophysical Journal International

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A ghost cavity cloud consists of many small vapour cavities and appears above and around the airguns in the source array a few milliseconds after the source is fired. Since there are dissolved gases and stable microbubbles in natural seawater, the cavities will likely contain some amount of air in addition to water vapour. The cavity cloud exists for around 10 ms depending on the size and the configuration of the array. It is well known that with increasing volume fraction of tiny bubbles within the liquid, the sound velocity of the mixture at frequencies below the resonance frequencies of the bubbles gradually drops. Depending on the volume fraction of tiny bubbles, the sound velocity in the mixture can even drop below the sound velocity of the individual constituents. Vapour content within the bubblesor cavitiesfurther reduces the sound velocity. We do not know whether the volume fraction of the cavity cloud is high enough to significantly drop the sound velocity, nor do we know whether the far-field acoustic recording is affected even if the sound velocity within the cavity cloud drops substantially. To answer these questions, a modified k-wave − a k-space pseudo-spectral numerical method − is used. Subsequently, the simulation results are compared to recorded field data in order to estimate a potential sound velocity drop within the ghost cavity cloud. According to this comparison, we find that the reduction in sound velocity is probably less than 10 %.

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Section: Visualizing Ghost Cavity Cloudmentioning

confidence: 99%

Characterizing the acoustic properties of the cavity cloud generated close to an air-gun array as a time-dependent effective medium

Khodabandeloo

Landrø

2018

Geophysical Journal International

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“…However, for lower frequencies, we notice that the cluster signal is slightly stronger than that of the two separate guns (3.3 dB). Hopperstad et al (2012) point out that a hypercluster gives more low frequencies for the same quantity of air used. Their measurements show that the low-frequency peak changed from approximately 9 Hz for individual guns to 5 Hz for a hypercluster with the same total volume (1680 in 3 ).…”

Section: Comparing Signatures From a Singlementioning

confidence: 94%

Comparing the broadband acoustic frequency response of single, clustered, and arrays of marine air guns

Landrø

Langhammer

2020

GEOPHYSICS

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Field data acquired from a seismic vessel by a seabed hydrophone is used to analyze the broadband response (10 Hz to 62.5 kHz) for various source configurations: single air guns, clustered air guns, and a full array consisting of 30 air guns. The various parts of the acoustic signal are analyzed in detail, and it is found that a high-frequency signal arriving prior to the main peak of a single air-gun signal most likely is caused by small vapor cavities collapsing at or close to the surface of the gun. This is confirmed by high-speed photographs taken when a small air gun is fired in a water tank. When the full array is used, a second type of cavitation signal is observed: ghost cavitation caused by acoustic stimulation by the negative pressure that is backscattered from the free surface. As this ghost signal from 30 different guns arrives at a specific location in the water, cavities might be formed, and they create a high-frequency acoustic signal.

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“…The high-frequency waves (10-150 kHz) not only are useless in deepsea geophysical exploration but also disturb, injure or kill marine life [53,13]. To reduce the environmental impact, the high-frequency content should be controlled below a safety level.…”

Section: The Impact Of the Cylinder On Realistic Airgun-bubblesmentioning

confidence: 99%

“…This study aims to explore the interaction between the bubble and the airgun-body. In most of the existing works [9,10,11,12,13], the Rayleigh-Plesset equation [14,15] has been used for airgun modeling. However, the spherical symmetry assumption which underlies the Rayleigh-Plesset equation is inappropriate for airgun bubbles because the action of gravity causes highly non-spherical deformation of such large-scale bubbles [16].…”

Section: Introductionmentioning

confidence: 99%

Dynamics of a toroidal bubble on a cylinder surface with an application to geophysical exploration

Li,

Prosperetti,

van der Meer

2020

Preprint

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During the operation of a seismic airgun source, a certain amount of compressed highpressure air is released from the airgun chamber into the surrounding water, generating an expanding toroidal bubble attached to the airgun-body. The subsequent oscillations of the bubble generate low-frequency pressure waves, which are used to map the ocean subbottom, e.g., to locate oil and gas reserves. The bubble dynamic behavior and the emitted pressure waves are inevitably influenced by the airgun-body. However, the bubbleairgun-body interaction is far from well understood. This paper investigates the strong interaction between a long cylinder and an attached toroidal bubble via hundreds of boundary integral simulations, aiming to provide new physical insights for airgun-bubble dynamics. Firstly, the overall physical phenomena are discussed and three types of bubble collapse patterns are identified, namely (i) upward jetting due to gravity, (ii) annular jet toward the cylinder body and (iii) weak/no jet. Thereafter, we investigate the effects of the cylinder radius, initial bubble pressure and Froude number on the bubble oscillation period and the pressure wave induced by the bubble. At last, the impact of a cylinder on a Sercel type airgun-bubble is discussed with a particular focus on the spectrum of the pressure waves.

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Acoustically induced cavity cloud generated by air-gun arrays—Comparing video recordings and acoustic data to modeling

Cited by 14 publications

References 43 publications

Characterizing the acoustic properties of the cavity cloud generated close to an air-gun array as a time-dependent effective medium

Characterizing the acoustic properties of the cavity cloud generated close to an air-gun array as a time-dependent effective medium

Comparing the broadband acoustic frequency response of single, clustered, and arrays of marine air guns

Dynamics of a toroidal bubble on a cylinder surface with an application to geophysical exploration

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