Theoretical investigation of the effects of the cushion on reducing underwater noise from offshore pile driving

Offshore pile driving noise has gained increasing attention due to its adverse influence on marine animals. Two models are established to investigate the influence of the cushion on the underwater noise from pile driving. A one-dimensional nonlinear finite difference model is developed to compute the impact force and the soil penetration. The radiated sound pressure is predicted by the second model based on a semi-analytical variational formulation. For the examined pile, a proper cushion can significantly dampen the high-frequency impact force and reduce the peak of the sound pressure. It is found that there exists a stiffness range within which the decline of the cushion stiffness effectively reduces the single sound exposure level but hardly increases the required hammer blows to achieve a certain penetration depth. (C) 2016 Acoustical Society of America.