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

TL;DR

This study uses boundary integral simulations to explore the complex interactions between toroidal bubbles and cylindrical surfaces, revealing different collapse patterns and their effects on pressure wave spectra relevant to geophysical exploration.

Contribution

It provides new physical insights into bubble-cylinder interactions and identifies three distinct bubble collapse patterns through extensive simulations.

Findings

Identified three bubble collapse patterns: upward jetting, annular jet, and weak/no jet.

Analyzed effects of cylinder radius, initial pressure, and Froude number on oscillation and pressure waves.

Discussed impact of cylinder on pressure wave spectrum for airgun applications.

Abstract

During the operation of a seismic airgun source, a certain amount of compressed high-pressure 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 bubble-airgun-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.