Influence of the seabed conditions on the near-and far-field propagation of noise in impact piling

The prediction of underwater noise and the assessment of the influencing factors on noise transmission are significant for the control and mitigation of the noise generated by offshore pile driving. This paper presents a coupled two-step approach for modelling the underwater noise from offshore pile driving, with the focus being placed on examining the influence of the seabed conditions on the near- and far-field sound propagation. The complete model consists of a near-source module and a far from source module. The near-source module captures the coupled vibroacoustic behaviour of the pile and its surrounding fluid and layered soil media. With the input obtained from near-source module, the far-from-source module propagates the sound field at larger distances. The two modules are coupled by applying the boundary integral method. A parametric study is performed to investigate the influence of the seabed properties on the noise levels and the energy distribution at various horizontal distances from the pile. An energy flux analysis is performed by examining the total energy radiated through the cylindrical surface at target distances from the pile. As waves propagate away from the pile, the through-depth distribution of the energy in both seawater and sediment alters. The results indicate the characteristics of noise transmission and energy distribution with respect to different soil conditions; an analysis which is key to the development of effective noise mitigation strategies.