The pressure field generated by a seismic airgun

A model-scale seismic airgun is used to investigate the behaviour and pressure field of the bubble generated at different standoffs from a steel plate and a free surface in an open top tank. The airgun is fired at 50 and 100 bar initial pressures and the field pressure, wall pressure and wall acceleration are recorded. Wavelet and Fast Fourier Transforms are used to analyse the bubble frequency. The reduction of pressure with distance from both the initial shock and first bubble collapse are presented. The hydrodynamic component of the pressure signal generated by the bubble collapses is also discussed. The trend of the bubble period for different standoffs from the free surface is compared with other data in the literature and found to be similar. The acceleration and displacement of the steel plate are presented for varying bubble standoffs, and as the plate moves in phase with the bubble, little pressure is felt from the collapse pulses. This information provides basic understanding of the dynamics of an airgun bubble when considering their application as a method of shock testing naval ships.