Attenuation of noise from impact pile driving in water using an acoustic shield
Per G. Reinhall, Peter H. Dahl and John T. Dardis
Offshore impact pile driving produces extremely high sound levels in water. Peak acoustic pressures from the pile driving operation of ~103 Pa at a range of 3000 m, ~104 Pa at a range of 60 m, and ~105 Pa at a range of 10 m have been measured. Pressures of these magnitudes can have negative effects on both fish and marine mammals. Previously, it was shown that the primary source of sound originates from radial expansion of the pile as a compression wavepropagates down the pile after each strike. As the compression wave travels it produces an acoustic field in the shape of an axisymmetric cone, or Mach cone. The field associated with this cone clearly dominates the peak pressures. In this paper, we present an evaluation of the effectiveness of attenuating pile driving noise using an acoustic shield. In order to fully evaluate the acoustic shield, we provide results from finite element modeling and simple plane waveanalysis of impact pile driving events with and without a noise shield. This effort is supported by the findings from a full-scale pile driving experiment designed to evaluate the effectiveness of thenoise shield. Finally, we will discuss methods for improving the effectiveness of the acoustic shield.
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