Abstract
Underwater vapor cavities can be generated by acoustic stimulation. When the acoustic signals from several air guns are reflected from the sea surface, the pressure drop at some locations is sufficient for cavity growth and subsequent collapse. In this paper the generation of multiple water vapor cavities and their collapses are numerically modeled and the results are validated by comparing with field data from a seismic air gun array test. In a first modeling attempt where cavity interaction is neglected, a correspondence between measured and modeled data is found. Then, this correspondence is improved by assuming that the acoustic signal generated by the other cavities changes the hydrostatic pressure surrounding each cavity. This modeling can be used to estimate the amount and strength of high frequency signals generated by typical marine air gun arrays, given that a calibration step is performed prior to the modeling.
Highlights
In the case of air gun arrays, ghost cavitation clouds can be formed because of the sudden pressure drop due to multiple reflected ghost signals from several single air guns in the array (Landrø et al, 2011, 2013). This acoustically generated cavitation is assumed to be generated by a cavitation cloud and this hypothesis was further confirmed by more dedicated experiments (Landrø et al, 2016)
We believe that the similarity between nucleation-collapse-burnout dynamics in plasmas and cavitation-expansioncollapse in fluids is more than skin-deep
We have developed a modeling scheme that incorporates the creation of water vapor cavities due to acoustic stimulation by multiple ghost reflections from air guns that are fired simultaneously when marine seismic data are acquired
Summary
Underwater man-made noise is recognized to have several adverse effects on aquatic animals and it is a worldwide problem (Southall et al, 2008; Williams et al, 2014). An active source radiates acoustic waves into the Earth and subsequently the subsurface structure is determined from measured reflected elastic waves using a large number of receivers These receivers might be hydrophones organized in long cables that are towed behind the seismic vessel, or geophones that are deployed at the seabed. To reduce the high frequencies which are due to the steep rise time of pressure signals from each individual air gun, a new air gun was designed and successfully tested (Coste et al, 2014; Gerez et al, 2015) Another mechanism is interaction between reflected ghost wave and air gun bubble which generates frequencies between 400 and 600 Hz (King et al, 2015; King, 2015). These reflections are referred to as ghost signals, and the term ghost-cavitation is used for this phenomenon
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
