Validation of finite element computations for the quantitative prediction of underwater noise from impact pile driving

Observations of underwater noise from impact pile driving were made with a vertical line array. Previous studies [Reinhall and Dahl, J. Acoust. Soc. Am. 130, 1209-1216 show that the dominant underwater noise from impact driving is from the Mach wave associated with the radial expansion of the pile that propagates down the pile at supersonic speed after impact. Here precise estimates of the vertical arrival angles associated with the down-and up-going Mach wave are made via beam forming, and the energy budget of the arrival structure is quantified.

“…1 would be similar to that for phase 1, with subsequent reflections being too weak to distinguish from other noise emission processes, such as pile vibration modes of higher order. 5 …”

Section: Angles Associated With the Mach Wave Structure Of The Fieldmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Beam forming of the underwater sound field from impact pile driving

Dahl

Reinhall

2013

“…Vibrations of impacted poles lead to high immission levels in the water column and sound pulses reach very long distances 3 . Numerical models have been developed and measurements have been performed to assess underwater noise levels during piling [4][5][6][7][8] . Injury and behavioral changes in marine animals have been reported, even at large distances from the piling location [9][10][11][12] .…”

Section: Introductionmentioning

confidence: 99%

Airborne sound propagation over sea during offshore wind farm piling

Renterghem¹,

Botteldooren²,

Dekoninck³

2014

Offshore piling for wind farm construction has attracted a lot of attention in recent years due to the extremely high noise emission levels associated with such operations. While underwater noise levels were shown to be harmful for the marine biology, the propagation of airborne piling noise over sea has not been studied in detail before. In this study, detailed numerical calculations have been performed with the Green's Function Parabolic Equation (GFPE) method to estimate noise levels up to a distance of 10 km. Measured noise emission levels during piling of pinpiles for a jacket-foundation wind turbine were assessed and used together with combinations of the sea surface state and idealized vertical sound speed profiles (downwind sound propagation). Effective impedances were found and used to represent non-flat sea surfaces at low-wind sea states 2, 3, and 4. Calculations show that scattering by a rough sea surface, which decreases sound pressure levels, exceeds refractive effects, which increase sound pressure levels under downwind conditions. This suggests that the presence of wind, even when blowing downwind to potential receivers, is beneficial to increase the attenuation of piling sound over the sea. A fully flat sea surface therefore represents a worst-case scenario.

“…25 The marine sediment is traditionally described by an equivalent fluid for the modeling of underwater acoustics generated by pile driving. [26][27][28] More advanced methods for the description of unconsolidated marine sediments do exist. These can be divided into three primary groups.…”

Section: Wave Radiation Generated By Offshore Pile Drivingmentioning

confidence: 99%

“…(27) and (31),ṽ f ;z ðr; z; xÞ andṽ f ;r ðr; z; xÞ correspond to the vertical and radial velocity components of the fluid, respectively. A modal decomposition is applied both for the shell structure and the acousto-elastic waveguide.…”

Section: A Governing Equations and Modal Decompositionmentioning

confidence: 99%

The significance of the evanescent spectrum in structure-waveguide interaction problems

Tsouvalas

Dalen

Metrikine

2015

Modal decomposition is often applied in elastodynamics and acoustics for the solution of problems related to propagation of mechanical disturbances in waveguides. One of the key elements of this method is the solution of an eigenvalue problem for obtaining the roots of the dispersion equation, which signify the wavenumbers of the waves that may exist in the system. For non-dissipative media, the wavenumber spectrum consists of a finite number of real roots supplemented by infinitely many imaginary and complex ones. The former refer to the propagating modes in the medium, whereas the latter constitute the so-called evanescent spectrum. This study investigates the significance of the evanescent spectrum in structure-waveguide interaction problems. Two cases are analysed, namely, a beam in contact with a fluid layer and a cylindrical shell interacting with an acousto-elastic waveguide. The first case allows the introduction of a modal decomposition method and the establishment of appropriate criteria for the truncation of the modal expansions in a simple mathematical framework. The second case describes structure-borne wave radiation in an offshore environment during the installation of a pile with an impact hammer-a problem that has raised serious concerns in recent years due to the associated underwater noise pollution.