A semi-analytical model for predicting underwater noise from operating offshore wind turbines

Underwater noise generated by operational offshore wind turbines has attracted great concern in marine acoustics and offshore engineering. Existing approaches for evaluating the sound pressure levels highly rely on empirical formulations or computationally intensive finite element models. In this study, a semi-analytical model is developed to provide a quick yet reliable tool for predicting the sound pressure levels from operating turbines. A monopile-supported turbine equipped with a gearbox is considered due to its widespread use in practice. It is carefully assumed that the gear force is the dominant excitation source according to related literature. The seawater and the seabed are modeled as three-dimensional acoustic and elastic media, respectively, while both the tower and monopile are represented using Timoshenko theory. The governing equations are solved using the Laplace transform and separation of variables methods by combining the pile-water-soil coupled interaction. Model validation is demonstrated through comparisons with published studies, including numerical simulations, field measurements, and an empirical model. These cases cover turbines of 1, 1.5, 3.6, and 6 MW, with monitoring distances ranging from 20 to 500 m from the monopile foundation. The results demonstrate that the model provides reasonable predictions of underwater noise generated by operating turbines.