Effective impedance spectra for predicting rough sea effects on atmospheric impulsive sounds

Boulanger, Patrice; Attenborough, Keith

doi:10.1121/1.1847872

Cited by 16 publications

(26 citation statements)

References 22 publications

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“…In the context of predicting sonic booms, the complex excess attenuation spectrum due to a line source above a boundary consisting of intersecting parabolas, which are representative of wind-driven deep water waves, has been predicted by a boundary element method (BEM) and has been used to deduce effective impedance as a function of sea state corresponding to mean wave heights between 0.25 and 7.5 m and for five incidence angles at each height. 8 The resulting predictions suggest that sea surface roughness could influence sonic boom profiles and rise times to an extent comparable to turbulence and molecular relaxation effects.…”

Section: Introductionmentioning

confidence: 99%

Laboratory studies of near-grazing impulsive sound propagating over rough water

Qin

Lukaschuk

Attenborough

2008

The Journal of the Acoustical Society of America

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Acoustic impulses due to an electrical spark source (main acoustic energy near 15kHz) have been measured after propagating near to the water surface in a shallow container resting on a vibrating platform. Control of the platform vibration enabled control of water wave amplitudes. Analysis of the results reveals systematic variations in the received acoustic waveforms as the mean trough-to-crest water wave amplitude is increased up to 7mm. The amplitudes of the peaks corresponding to specular reflections are reduced and the variability in the tails of the waveforms is increased.

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Section: Introductionmentioning

confidence: 99%

Laboratory studies of near-grazing impulsive sound propagating over rough water

Qin

Lukaschuk

Attenborough

2008

The Journal of the Acoustical Society of America

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“…In addition, deriving an effective impedance is likely to be unsuccessful when the surface undulation is too high relative to the sound frequencies of interest 20 . Agreement at sound frequencies above roughly 1 kHz becomes already difficult at sea state 4 as illustrated in Fig.…”

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confidence: 99%

“…At 10 km, the sea surface representative for sea state 4 would potentially lead to a decrease in 20 level of 10 dBA relative to sea state 3, and to more than 15 dBA relative to sea state 2.…”

Section: Figure 6]mentioning

confidence: 99%

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Airborne sound propagation over sea during offshore wind farm piling

Renterghem¹,

Botteldooren²,

Dekoninck³

2014

The Journal of the Acoustical Society of America

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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.

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“…A heuristic extension of this model to sound reflection from rough surfaces of finite impedance has given predictions in tolerable agreement with ground effect measured over rough surfaces in the laboratory and outdoors [10]. However, the real part of the effective impedance obtained from Lucas and Twersky's theory for hard rough surfaces does not have the dominant real part low frequency limit that is expected from physical considerations [11]. Measurements of complex relative sound pressure level over porous roughness on a flat hard surface have been reported [12], and effective impedance spectra have been obtained from these measurements by numerical solution of the complex admittance equation [13] obtained from the classical expression for a point source over an impedance boundary.…”

Section: Introductionmentioning

confidence: 78%

Reflection of sound from random distributions of semi-cylinders on a hard plane: models and data

Boulanger

Attenborough

Qin

et al. 2005

J. Phys. D: Appl. Phys.

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A new analytical theory for multiple scattering of cylindrical acoustic waves by an array of finite impedance semi-cylinders embedded in a smooth acoustically hard surface is derived by extending previous results for plane waves [Linton and Martin, J. Acoust. Soc. Am. 117 (6) 3413 -3423 (2005)]. Although the computational demands of the new theory increase as the number of the semi-cylinders in the arrays and/or the frequency increases, the theory offers an improvement on analytical boss theories since the latter (i) are restricted to non-deterministic (infinite) random distributions of semi-cylinders with spacing/radii small compared to the incident wavelength and (ii) are derived only for plane waves. The influence on prediction accuracy of truncation of the infinite system of equations introduced by the new theory is explored empirically. Laboratory measurements have been made over deterministic random arrays of identical varnished wooden semi-cylinders on a glass plate. The agreement between predictions and measured relative Sound Pressure Level spectra is very good both for single deterministic random distributions and for averages representing non-deterministic random distributions. The analytical theory is found to give identical results to a Boundary Element calculation but is much faster to compute.PACS numbers: 43.50.Vt, 43.28.En IntroductionSurface roughness is known to have significant influence on near-grazing sound. One approach to modeling long wavelength sound reflection from randomly rough surfaces considers scattering from idealized roughness elements or 'bosses'. Several measurements have been made of relative sound pressure level (SPL) spectra above rough surfaces, where the roughness height and spacing are small compared to the wavelengths of interest [1][2][3][4][5]. These data have been compared with predictions of models derived by Attenborough and Taherzadeh [1] from a boss theory by Tolstoy [6], [7]. It has been found necessary to adjust the impedance of the scatterers and imbedding plane to obtain good agreement between predictions based on Tolstoy's boss theory and the data. Tolstoy's effective admittance models [6], [7] predict that a surface wave is generated at grazingincidence above a hard rough boundary and that the effective admittance above a hard rough boundary is purely imaginary. However, comparison with data [2] indicates that Tolstoy-based predictions overestimate the surface wave component, especially at grazing incidence, and that it is necessary to include attenuation due to non-specular scatter to obtain a good fit with these data [4]. In other comparisons of predictions and data [5], the assumed location of the effective admittance plane has been adjusted to improve agreement with data at higher frequencies. Poor agreement between laboratory measurements of propagation over rough convex surfaces and

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Effective impedance spectra for predicting rough sea effects on atmospheric impulsive sounds

Cited by 16 publications

References 22 publications

Laboratory studies of near-grazing impulsive sound propagating over rough water

Laboratory studies of near-grazing impulsive sound propagating over rough water

Airborne sound propagation over sea during offshore wind farm piling

Reflection of sound from random distributions of semi-cylinders on a hard plane: models and data

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