Effect of the transient fluid-structure interaction on sound radiation from a partially submerged cylindrical pile

Abstract

A time-domain structural acoustics model of a partially submerged cylindrical pile excited by an impact force has been developed to predict underwater sound radiation for arbitrary field conditions. Radial boundary conditions are formulated using the velocity potential so pressure waveforms near the pile wall can be estimated; however, the rapid decay observed in measured waveforms is not easily predicted because radiation loading on the structure is also transient. The sudden acceleration of the wall initially results in a net flow of energy from the structure into surrounding fluids. Subsequently part of this energy radiates to the far field as a compressional wave; however, as the forced wall motion decreases and the spatial pressure gradient at the wall reverses direction, fluid accelerates back to the pile and re-excites the wall. A model for this transient fluid-structure interaction was formulated and integrated into the time-domain structural acoustics numerical model. By accounting for energy flow back into the structure, predicted pressure waveforms are in good agreement with field data. Results indicate that a significant portion of the kinetic energy remains in the near field and does not radiate sound, and that temporal characteristics of the impact force may influence far field sound radiation.