Prediction of structure borne noise radiation and propagation from offshore impact pile driving.

摘要

This study investigates prediction of structure borne noise radiation and propagation from offshore impact pile driving in shallow water environment. Noise generated by offshore impact pile driving radiates into and propagates through the air, water, and sediment medium. Predicting noise levels around the pile structure at sea is required to estimate the effects of the noise and vibration on marine life. This study used one of the commercial FE (Finite Element) code Abaqus 6.11 to calculate harmonic and transient response of the offshore wind turbine support structure and associated acoustic pressure amplitudes due to hydraulic hammer impact on top. First of all, the study focuses on long range prediction of acoustic pressure by utilizing the results from FE model to existing parabolic equation model as its starting field. In addition to numerical approach, a simple analytic solution has been developed based on the theory of free and forced vibration of thin cylindrical shell. It is useful to calculate structural response by inputting basic pile design parameters such as length, radius and material properties instead of developing numerical models. Then the study numerically investigated effects of noise and vibration along the water - ocean bottom interface because many benthic animals live on the seabed. The ocean bottom for this study was considered as elastic medium which supports propagation of shear and interface waves in addition to compressional waves. Finally, it is important how much we can reduce the noise to protect biological damages on marine life. This study quantitatively predicted noise attenuation of air bubble curtain by putting small size air bubbles in the water column.