title: Validation of finite element computations for the quantitative prediction of underwater noise from impact pile driving.
abstract: The acoustic radiation from a pile being driven into the sediment by a sequence of hammer strikes is studied with a linear, axisymmetric, structural acoustic frequency domain finite element model. Each hammer strike results in an impulsive sound that is emitted from the pile and then propagated in the shallow water waveguide. Measurements from accelerometers mounted on the head of a test pile and from hydrophones deployed in the water are used to validate the model results. Transfer functions between the force input at the top of the anvil and field quantities, such as acceleration components in the structure or pressure in the fluid, are computed with the model. These transfer functions are validated using accelerometer or hydrophone measurements to infer the structural forcing. A modeled hammer forcing pulse is used in the successive step to produce quantitative predictions of sound exposure at the hydrophones. The comparison between the model and the measurements shows that, although several simplifying assumptions were made, useful predictions of noise levels based on linear structural acoustic models are possible. In the final part of the paper, the model is used to characterize the pile as an acoustic radiator by analyzing the flow of acoustic energy.
authors.affiliation: TNO, Acoustics and Sonar Group, P.O. Box 96864, 2509 JG, The Hague, The Netherlands. mario.zampolli@ctbto.org
authors.forename: Mario
authors.initials: M
authors.lastname: Zampolli
authors.forename: Marten J J
authors.initials: MJ
authors.lastname: Nijhof
authors.forename: Christ A F
authors.initials: CA
authors.lastname: de Jong
authors.forename: Michael A
authors.initials: MA
authors.lastname: Ainslie
authors.forename: Erwin H W
authors.initials: EH
authors.lastname: Jansen
authors.forename: Benoit A J
authors.initials: BA
authors.lastname: Quesson
mesh_terms: D061725:Accelerometry; D000162:Acoustics / Q000295:instrumentation; D003198:Computer Simulation; D004867:Equipment Design; D020342:Finite Element Analysis; D016014:Linear Models; D008962:Models, Theoretical; D009038:Motion; D009622:Noise; D009716:Numerical Analysis, Computer-Assisted; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D013018:Sound Spectrography; D013997:Time Factors; D014159:Transducers; D014867:Water
chemical_list: D014867:Water