Scaling Laws for Offshore Pile Driving Noise and Bathymetry Induced 3D Effects

The present thesis focuses on the investigation of the influence of bathymetry induced 3D effects on the sound levels and the derivation of simple to apply scaling laws for unmitigated as well as for mitigated pile driving scenarios. For this purpose, a hybrid pile driving noise model based on the finite element method and the Parabolic Equations (PE) is developed. The finite element model is used to derive the starting field for the computationally more efficient PE model, which is able to include horizontal diffraction and therefore allows for the investigation of bathymetry induced 3D effects. In addition, noise mitigation measures such as bubble curtains can be included in the model. The developed modelling approach is validated with measurement data from three different wind farms including unmitigated and mitigated pile driving. The location of the occurrence of bathymetry induced 3D effects is investigated with data of three real-life scenarios with dedicated water depth profiles. It is shown that sand dunes oriented in propagation direction are the main cause of 3D effects at the considered ranges. Furthermore, the influence of the sample size of the bathymetry data and the influence of uncertain acoustical parameters of the sea floor on the 3D effects are nvestigated and discussed. The modelling approach is used to derive scaling laws for the influence of the strike energy, the pile diameter, the ram weight, and the water depth on the sound exposure level and the peak sound pressure level. This is done for mitigated and unmitigated scenarios.