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Lean Hoek - One of the best experts on this subject based on the ideXlab platform.
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hearing frequency thresholds of harbor porpoises phocoena phocoena temporarily affected by played back Offshore Pile driving sounds
Journal of the Acoustical Society of America, 2015Co-Authors: Ronald A Kastelein, Robin Gransier, Michelle A T Marijt, Lean HoekAbstract:Harbor porpoises may suffer hearing loss when exposed to intense sounds. After exposure to playbacks of broadband Pile driving sounds for 60 min, the temporary hearing threshold shift (TTS) of a porpoise was quantified at 0.5, 1, 2, 4, 8, 16, 32, 63, and 125 kHz with a psychoacoustic technique. Details of the Pile driving sounds were as follows: pulse duration 124 ms, rate 2760 strikes/h, inter-pulse interval 1.3 s, average received single strike unweighted sound exposure level (SEL) 146 dB re 1 μPa2 s (cumulative SEL: 180 dB re 1 μPa2 s). Statistically significant TTS only occurred at 4 and 8 kHz; mean TTS (1–4 min. after sound exposure stopped) was 2.3 dB at 4 kHz, and 3.6 dB at 8 kHz; recovery occurred within 48 min. This study shows that exposure to multiple impulsive sounds with most of their energy in the low frequencies can cause reduced hearing at higher frequencies in harbor porpoises. The porpoise's hearing threshold for the frequency in the range of its echolocation signals was not affected by the Pile driving playback sounds.
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behavioral responses of a harbor porpoise phocoena phocoena to playbacks of broadband Pile driving sounds
Marine Environmental Research, 2013Co-Authors: Ronald A Kastelein, Dorianne Van Heerden, Robin Gransier, Lean HoekAbstract:The high under-water sound pressure levels (SPLs) produced during Pile driving to build Offshore wind turbines may affect harbor porpoises. To estimate the discomfort threshold of Pile driving sounds, a porpoise in a quiet pool was exposed to playbacks (46 strikes/min) at five SPLs (6 dB steps: 130–154 dB re 1 μPa). The spectrum of the impulsive sound resembled the spectrum of Pile driving sound at tens of kilometers from the Pile driving location in shallow water such as that found in the North Sea. The animal's behavior during test and baseline periods was compared. At and above a received broadband SPL of 136 dB re 1 μPa [zero-peak sound pressure level: 151 dB re 1 μPa; t90: 126 ms; sound exposure level of a single strike (SELss): 127 dB re 1 μPa2 s] the porpoise's respiration rate increased in response to the Pile driving sounds. At higher levels, he also jumped out of the water more often. Wild porpoises are expected to move tens of kilometers away from Offshore Pile driving locations; response distances will vary with context, the sounds' source level, parameters influencing sound propagation, and background noise levels.
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temporary threshold shifts and recovery in a harbor porpoise phocoena phocoena after octave band noise at 4 khz
Journal of the Acoustical Society of America, 2012Co-Authors: Ronald A Kastelein, Robin Gransier, Lean Hoek, Juul OlthuisAbstract:Safety criteria for underwater sound produced during Offshore Pile driving are needed to protect marine mammals. A harbor porpoise was exposed to fatiguing noise at 18 sound pressure level (SPL) and duration combinations. Its temporary hearing threshold shift (TTS) and hearing recovery were quantified with a psychoacoustic technique. Octave-band white noise centered at 4 kHz was the fatiguing stimulus at three mean received SPLs (124, 136, and 148 dB re 1 μPa) and at six durations (7.5, 15, 30, 60, 120, and 240 min). Approximate received sound exposure levels (SELs) varied between 151 and 190 dB re 1 μPa2 s. Hearing thresholds were determined for a narrow-band frequency-swept sine wave (3.9–4.1 kHz; 1 s) before exposure to the fatiguing noise, and at 1–4, 4–8, 8–12, 48, and 96 min after exposure. The lowest SEL (151 dB re 1 μPa2 s) which caused a significant TTS1–4 was due to exposure to an SPL of 124 dB re 1 μPa for 7.5 min. The maximum TTS1–4, induced after a 240 min exposure to 148 dB re 1 μPa, was around 15 dB at a SEL of 190 dB re 1 μPa2 s. Recovery time following TTS varied between 4 min and under 96 min, depending on the exposure level, duration, and the TTS induced.
Andrei V. Metrikine - One of the best experts on this subject based on the ideXlab platform.
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Noise reduction by the application of an air-bubble curtain in Offshore Pile driving
Journal of Sound and Vibration, 2016Co-Authors: A. Tsouvalas, Andrei V. MetrikineAbstract:Abstract Underwater noise pollution is a by-product of marine industrial operations. In particular, the noise generated when a foundation Pile is driven into the soil with an impact hammer is considered to be harmful for the aquatic species. In an attempt to reduce the ecological footprint, several noise mitigation techniques have been investigated. Among the various solutions proposed, the air-bubble curtain is often applied due to its efficacy in noise reduction. In this paper, a model is proposed for the investigation of the sound reduction during marine piling when an air-bubble curtain is placed around the Pile. The model consists of the Pile, the surrounding water and soil media, and the air-bubble curtain which is positioned at a certain distance from the Pile surface. The solution approach is semi-analytical and is based on the dynamic sub-structuring technique and the modal decomposition method. Two main results of the paper can be distinguished. First, a new model is proposed that can be used for predictions of the noise levels in a computationally efficient manner. Second, an analysis is presented of the principal mechanisms that are responsible for the noise reduction due to the application of the air-bubble curtain in marine piling. The understanding of these mechanisms turns to be crucial for the exploitation of the maximum efficiency of the system. It is shown that the principal mechanism of noise reduction depends strongly on the frequency content of the radiated sound and the characteristics of the bubbly medium. For Piles of large diameter which radiate most of the acoustic energy at relatively low frequencies, the noise reduction is mainly attributed to the mismatch of the acoustic impedances between the seawater and the bubbly layer. On the contrary, for smaller Piles and when the radiated acoustic energy is concentrated at frequencies close to, or higher than, the resonance frequency of the air bubbles, the sound absorption within the bubbly layer becomes critical.
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a three dimensional vibroacoustic model for the prediction of underwater noise from Offshore Pile driving
Journal of Sound and Vibration, 2014Co-Authors: A. Tsouvalas, Andrei V. MetrikineAbstract:Abstract Steel monoPiles are nowadays widely used as foundations for a large number of Offshore structures. The installation procedure commonly involves a Pile driving process which can last up to several hours depending upon Pile dimensions, soil conditions and input energy of the hydraulic hammer. In impact Pile driving, a hydraulic hammer delivers a series of hammer blows at the head of the Pile that drive the Pile into the sediment. Each hammer strike results in Pile vibrations that emit strong impulsive sounds into the water column which can be harmful for the marine ecosystem. With today's increasing concern regarding the environmental impact of such operations, engineering tools which will be able to provide reliable predictions of the underwater noise levels are required. In this study, a linear semi-analytical formulation of the coupled vibroacoustics of a complete Pile–water–soil interaction model is addressed. The Pile is described by a high order thin shell theory whereas both water and soil are modelled as three-dimensional continua. Results obtained with the developed model indicate that the near-field response in the water column consists mainly of pressure conical waves generated by the supersonic compressional waves in the Pile excited by the impact hammer. The soil response is dominated by shear waves with almost vertical polarization. The Scholte waves are also generated at the water–seabed interface which can produce pressure fluctuations in the water column that are particularly significant close to the sea floor. The effects of soil elasticity and Pile size are thoroughly investigated and their influence on the generated pressure levels is highlighted. The results are also compared with those ones of a similar model in which the soil is treated as an equivalent acoustic fluid. It is shown that the latter approximation can yield inaccurate results at low frequencies especially for harder soil sediments.
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a three dimensional semi analytical model for the prediction of underwater noise generated by Offshore Pile driving
2014Co-Authors: A. Tsouvalas, Andrei V. MetrikineAbstract:In this work, the problem of underwater noise generated during the Offshore installation of steel monoPiles is addressed. The monoPiles are driven into place with the help of hydraulic hammers. During installation, the underwater noise levels generated can be very high and harmful for the marine life. A linear semi-analytical model is developed which is able to represent the dynamics of the coupled vibro-acoustic system. The Pile is modelled using a high order thin shell theory whereas both water and soil are modelled as three-dimensional continua. The results indicate that the near-field response in the water column consists of pressure conical waves due to the the supersonic compressional waves in the Pile generated by the impact hammer. The soil response is dominated by vertically polarised shear waves. Scholte waves are also generated at the water-seabed interface and can produce pressure fluctuations in the water column that are particularly significant close to the sea floor.
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a semi analytical model for the prediction of underwater noise from Offshore Pile driving
Journal of Sound and Vibration, 2013Co-Authors: A. Tsouvalas, Andrei V. MetrikineAbstract:Abstract Underwater noise from Offshore Pile driving gained considerable attention in recent years mainly due to the large scale construction of Offshore wind farms. The most common foundation type of a wind turbine is a monoPile, upon which the wind tower rests. The Pile is driven into place with the help of hydraulic hammers. During the hammering of the Pile, high levels of noise are generated which are known to produce deleterious effects on both mammals and fish. In this work, a linear semi-analytical model is developed for predicting the levels of underwater noise for a wide range of system parameters. The model incorporates all major parts of the system. The hydraulic hammer is substituted by an external force, the Pile is described as a thin circular cylindrical shell, the water is modelled as a compressible fluid and the water-saturated seabed is defined by distributed springs and dashpots in all directions. The solution of the coupled vibroacoustic problem is based on the representation of the response of the complete system on the modal basis of the in vacuo shell structure. The influence that the inter-modal coupling, the choice of the soil parameters and the acoustic impedance of the seabed have on the generated noise levels is studied in the frequency domain. Strong and weak points of the present model are discussed on the basis of a comparison with a set of available experimental data. The obtained results show the capability of the model to predict the underwater noise levels both qualitatively and quantitatively.
Ronald A Kastelein - One of the best experts on this subject based on the ideXlab platform.
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hearing frequency thresholds of harbor porpoises phocoena phocoena temporarily affected by played back Offshore Pile driving sounds
Journal of the Acoustical Society of America, 2015Co-Authors: Ronald A Kastelein, Robin Gransier, Michelle A T Marijt, Lean HoekAbstract:Harbor porpoises may suffer hearing loss when exposed to intense sounds. After exposure to playbacks of broadband Pile driving sounds for 60 min, the temporary hearing threshold shift (TTS) of a porpoise was quantified at 0.5, 1, 2, 4, 8, 16, 32, 63, and 125 kHz with a psychoacoustic technique. Details of the Pile driving sounds were as follows: pulse duration 124 ms, rate 2760 strikes/h, inter-pulse interval 1.3 s, average received single strike unweighted sound exposure level (SEL) 146 dB re 1 μPa2 s (cumulative SEL: 180 dB re 1 μPa2 s). Statistically significant TTS only occurred at 4 and 8 kHz; mean TTS (1–4 min. after sound exposure stopped) was 2.3 dB at 4 kHz, and 3.6 dB at 8 kHz; recovery occurred within 48 min. This study shows that exposure to multiple impulsive sounds with most of their energy in the low frequencies can cause reduced hearing at higher frequencies in harbor porpoises. The porpoise's hearing threshold for the frequency in the range of its echolocation signals was not affected by the Pile driving playback sounds.
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behavioral responses of a harbor porpoise phocoena phocoena to playbacks of broadband Pile driving sounds
Marine Environmental Research, 2013Co-Authors: Ronald A Kastelein, Dorianne Van Heerden, Robin Gransier, Lean HoekAbstract:The high under-water sound pressure levels (SPLs) produced during Pile driving to build Offshore wind turbines may affect harbor porpoises. To estimate the discomfort threshold of Pile driving sounds, a porpoise in a quiet pool was exposed to playbacks (46 strikes/min) at five SPLs (6 dB steps: 130–154 dB re 1 μPa). The spectrum of the impulsive sound resembled the spectrum of Pile driving sound at tens of kilometers from the Pile driving location in shallow water such as that found in the North Sea. The animal's behavior during test and baseline periods was compared. At and above a received broadband SPL of 136 dB re 1 μPa [zero-peak sound pressure level: 151 dB re 1 μPa; t90: 126 ms; sound exposure level of a single strike (SELss): 127 dB re 1 μPa2 s] the porpoise's respiration rate increased in response to the Pile driving sounds. At higher levels, he also jumped out of the water more often. Wild porpoises are expected to move tens of kilometers away from Offshore Pile driving locations; response distances will vary with context, the sounds' source level, parameters influencing sound propagation, and background noise levels.
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temporary threshold shifts and recovery in a harbor porpoise phocoena phocoena after octave band noise at 4 khz
Journal of the Acoustical Society of America, 2012Co-Authors: Ronald A Kastelein, Robin Gransier, Lean Hoek, Juul OlthuisAbstract:Safety criteria for underwater sound produced during Offshore Pile driving are needed to protect marine mammals. A harbor porpoise was exposed to fatiguing noise at 18 sound pressure level (SPL) and duration combinations. Its temporary hearing threshold shift (TTS) and hearing recovery were quantified with a psychoacoustic technique. Octave-band white noise centered at 4 kHz was the fatiguing stimulus at three mean received SPLs (124, 136, and 148 dB re 1 μPa) and at six durations (7.5, 15, 30, 60, 120, and 240 min). Approximate received sound exposure levels (SELs) varied between 151 and 190 dB re 1 μPa2 s. Hearing thresholds were determined for a narrow-band frequency-swept sine wave (3.9–4.1 kHz; 1 s) before exposure to the fatiguing noise, and at 1–4, 4–8, 8–12, 48, and 96 min after exposure. The lowest SEL (151 dB re 1 μPa2 s) which caused a significant TTS1–4 was due to exposure to an SPL of 124 dB re 1 μPa for 7.5 min. The maximum TTS1–4, induced after a 240 min exposure to 148 dB re 1 μPa, was around 15 dB at a SEL of 190 dB re 1 μPa2 s. Recovery time following TTS varied between 4 min and under 96 min, depending on the exposure level, duration, and the TTS induced.
Tsouvalas A. - One of the best experts on this subject based on the ideXlab platform.
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Study of the sound escape with the use of an air bubble curtain in Offshore Pile driving
'MDPI AG', 2021Co-Authors: Peng Y., Tsouvalas A., Stampoultzoglou Tasos, Metrikine A.Abstract:Underwater noise pollution generated by Offshore Pile driving has raised serious concerns over the ecological impact on marine life. To comply with the strict governmental regulations on the threshold levels of underwater noise, bubble curtains are usually applied in practice. This paper examines the effectiveness of an air bubble curtain system in noise reduction for Offshore Pile driving. The focus is placed on the evaluation of noise transmission paths, which are essential for the effective blockage of sound propagation. A coupled two-step approach for the prediction of underwater noise is adopted, which allows us to treat the waterborne and soilborne noise transmission paths separately. The complete model consists of two modules: a noise prediction module for Offshore Pile driving aiming at the generation and propagation of the wave field and a noise reduction module for predicting the transmission loss in passing through an air bubble curtain. With the proposed model, underwater noise prognosis is examined in the following cases: (i) free-field noise prediction without the air bubble curtain, (ii) waterborne path fully blocked at the position of the air bubble curtain while the rest of the wave field is propagated at the target distance, (iii) similarly to (ii) but with a non-fully blocked waterborne path close to the seabed, and (iv) air bubble curtain modeled explicitly using an effective medium theory. The results provide a clear indication of the amount of energy that can be channeled through the seabed and through possible gaps in the water column adjacent to the seabed. The model allows for a large number of simulations and for a thorough parametric study of the noise escape when a bubble curtain is applied Offshore.Dynamics of StructuresOffshore EngineeringEngineering Structure
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A coupled modelling approach for the fast computation of underwater noise radiation from Offshore Pile driving
European Association for Structural Dynamics EASD, 2020Co-Authors: Peng Y., Tsouvalas A., Metrikine A.Abstract:This paper presents a computationally efficient modelling approach for the prediction of underwater noise radiation from Offshore Pile driving. A near-source module is adopted to capture the interaction between the Pile, fluid and soil, which is based on a previously developed semi-analytical vibro-acoustic model. This module primarily aims at modelling the sound generation and propagation in the vicinity of the monoPile. The Green's tensor for an axisymmetric ring source in a horizontally stratified acousto-elastic half-space emitting both compressional and shear waves is derived using the normal modes and branch line integrations. The boundary integral equations are then formulated based on the reciprocity theorem, which forms the mathematical basis of the far-from-source module for the propagation of the wave field at large radial distances. The complete noise prediction model comprises the two modules, which are coupled through the boundary integral formulation with the input obtained from the near-source module. Model predictions are benchmarked against measurement data from an Offshore installation campaign.Dynamics of StructuresOffshore EngineeringEngineering Structure
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Underwater Noise Emission Due to Offshore Pile Installation: A Review
'MDPI AG', 2020Co-Authors: Tsouvalas A.Abstract:The growing demand for renewable energy supply stimulates a drastic increase in the deployment rate of Offshore wind energy. Offshore wind power generators are usually supported by large foundation Piles that are driven into the seabed with hydraulic impact hammers or vibratory devices. The Pile installation process, which is key to the construction of every new wind farm, is hindered by a serious by-product: the underwater noise pollution. This paper presents a comprehensive review of the state-of-the-art computational methods to predict the underwater noise emission by the installation of foundation Piles Offshore including the available noise mitigation strategies. Future challenges in the field are identified under the prism of the ever-increasing size of wind turbines and the emerging Pile driving technologies.Dynamics of StructuresOffshore Engineerin
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Underwater Noise Emission Due to Offshore Pile Installation: A Review
'MDPI AG', 2020Co-Authors: Tsouvalas A.Abstract:The growing demand for renewable energy supply stimulates a drastic increase in the deployment rate of Offshore wind energy. Offshore wind power generators are usually supported by large foundation Piles that are driven into the seabed with hydraulic impact hammers or vibratory devices. The Pile installation process, which is key to the construction of every new wind farm, is hindered by a serious by-product: the underwater noise pollution. This paper presents a comprehensive review of the state-of-the-art computational methods to predict the underwater noise emission by the installation of foundation Piles Offshore including the available noise mitigation strategies. Future challenges in the field are identified under the prism of the ever-increasing size of wind turbines and the emerging Pile driving technologies
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Underwater noise generated by Offshore Pile driving
2015Co-Authors: Tsouvalas A.Abstract:Anthropogenic noise emission in the marine environment has always been an environmental issue of serious concern. In particular, the noise generated during the installation of foundation Piles is considered to be one of the most significant sources of underwater noise pollution. This is mainly attributed to the recent developments in the Offshore wind industry. To meet the increasing demand for energy from renewable resources, a large number of Offshore wind farms are planned to be constructed in the near future. Despite the plethora of the available foundation concepts to accommodate the tower of an Offshore wind power generator, the steel monoPile is the most widely used and economically profitable choice for wind turbines installed in shallow water depths. The installation of foundation Piles requires a tremendous amount of input energy and the development of special equipment. The Piles are usually driven into the seabed with a hydraulic impact hammer that is positioned at the head of the Pile and delivers a series of blows, forcing the Pile to gradually progress into the sediment. This process is associated with strong impulsive noise that is emitted into the underwater environment and can be detected tens of kilometres away from the construction site. The latter is considered to be harmful for the aquatic species, especially for mammals who exhibit sensitive auditory behaviour. To date, the available knowledge regarding the physics of noise generation caused by marine piling is limited. Without a proper understanding of the noise generation mechanisms, any attempt to mitigate the noise will fall short of expectation. This study aims to fill this knowledge gap. The primary goal is to shed new light on the underlying physics of the underwater noise generated by marine piling in order to help the practitioners to develop more efficient noise mitigation equipment. To reach this aim, the following objectives were set: (i) development of a vibroacoustic model that is computationally efficient and can reproduce the physical mechanisms of underwater sound generation and propagation; (ii) analysis of data collected during an experimental campaign in order to identify the main sources that contribute to the underwater noise pollution; and (iii) theoretical investigation of the effectiveness of a chosen noise mitigation technique and, if possible, generalisation of the conclusions to several other noise mitigation concepts. Regarding the first objective mentioned above, considerable effort has been placed in the development of computationally efficient models to describe the radiated sound field caused by marine piling. The models consist generally of three subsystems, i.e. the Pile, the water and the soil. The hammer is substituted by a distributed force exerted at the Pile head. A high-order thin shell theory is adopted for the description of the Pile dynamics while the seawater is modelled as a compressible fluid medium. For the soil, several approaches are considered which mark the actual differences between the various models. In the \textit{simplified model}, the soil is represented by linear springs and dashpots. In the \textit{advanced model}, the soil is modelled as a layered three-dimensional elastic continuum which is considered to be a more realistic representation of the actual environment. The solution approach adopted to describe the coupled vibroacoustic behaviour of the Pile-water-soil system is semi-analytical. It is based on the expansion of the response of the total system in terms of two complete sets of eigenmodes: the \textit{in vacuo} structural modes and the modes of the exterior domain. The modal coefficients are subsequently determined by an appropriate combination of the kinematic conditions that are imposed at the Pile-water and Pile-soil interfaces together with the use of the orthogonality relations of each set of eigenmodes. This method of solution is considered to be advantageous for several reasons: (i) the computational time is considerably reduced when compared, for example, to the finite element or the boundary element methods; (ii) different stages of the installation process can be investigated with minimum computational effort; and (iii) considerable insight is gained into the physics of noise generation and into the contribution of the various modes to the total acoustic field. The predictions of the models show that the acoustic field in the seawater consists of pressure conical waves (\textit{Mach cones}) generated by the \textit{wave packet} propagating along the Pile after the hammer impact. As the wave packet enters the soil region, both shear and compressional waves are radiated, with the former being much stronger than the latter. At later moments in time, \textit{Scholte} waves are observed along the seabed-water interface. These propagate with a velocity slightly lower than that of the shear waves in the soil medium, their energy is localized in the vicinity of the seabed-water interface, and they experience much less attenuation when compared to other propagating modes. A parametric study was also conducted in order to determine the critical parameters of the system and the way they influence the radiated sound. Among the various parameters examined, the Pile diameter and the soil properties were found to be the most influential ones in the determination of the underwater sound field. The former defines largely the frequency spectrum of the radiated sound whereas the latter the energy distribution among the various subsystems. In particular, the shear rigidity of the soil was found to be crucial for the correct estimation of the noise levels close to the seabed surface due to the energy transferred into the interface waves. The higher the shear rigidity of the seabed, the larger the penetration depth of the Scholte wave into the fluid and, consequently, the higher the noise levels close to the seabed-water interface. Soil stratification is also important but the influence is mainly governed by the properties and depth of the upper soil layer which is in direct contact with the seawater. Since the soil modelling was found to be critical for the prediction of the noise levels, the results obtained with the Pile-water-soil model were also compared with another model in which the soil was substituted by an acoustic fluid with additional dissipation to account for the energy transferred into the shear waves (\textit{fluid model}). The substitution of the soil by a modified acoustic fluid is often favoured in underwater acoustics in order to improve the computational speed. In this study we show that the acoustic approximation of the seabed can yield inaccurate results when certain conditions are not met. Additionally, it has the tendency to underestimate the noise levels especially close to the seabed level. Thus, the substitution of the soil by an acoustic medium should always be carried out with great cautiousness in applications related to marine piling, even if one is interested only in the prediction of the sound field in the seawater region. With regard to the second objective, time series data collected during a measurement campaign were analysed in the time, the frequency, and the time-frequency domains. The analysis has shown that the dynamic response of the system is blow-invariant provided that the input energy and penetration depth remain almost constant. The vibration modes with frequencies below the ring frequency of the shell structure \textit{in vacuo} were shown to be best coupled to the surrounding fluid and therefore able to radiate considerable energy into the exterior fluid domain. This observation was, in fact, verified by the model predictions. In addition, the sound levels in the near-field region showed a strong depth-dependence. Finally, the analysis of the geophone signals verified the existence of low-frequency oscillations close to the seabed level which are attributed to the Scholte waves that were predicted by the prediction models. Regarding the third objective, the final chapter of the thesis is devoted to noise mitigation. A state-of-the-art review of the available mitigation concepts is included and a final model is developed which includes an air-bubble curtain. A parametric study is conducted in order to reveal the principal mechanism of noise reduction and the optimum system configuration for a specific case. The influence of a number of parameters, i.e the volume of the air content, the thickness of the bubble curtain and the distance from the Pile surface, on the predicted sound levels, were investigated. It is found that for Piles of large diameter, the main mechanism responsible for the noise reduction is the impedance contrast between the seawater and the air-bubble medium. The dissipation effects due to resonance of the individual bubbles seem not to be important for the relatively low-frequencies associated with the sound radiation of large monoPiles. Additionally, the efficiency of the air-bubble curtain increases, the higher the air-volume content, and the larger the horizontal distance it is placed from the Pile
A. Tsouvalas - One of the best experts on this subject based on the ideXlab platform.
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Noise reduction by the application of an air-bubble curtain in Offshore Pile driving
Journal of Sound and Vibration, 2016Co-Authors: A. Tsouvalas, Andrei V. MetrikineAbstract:Abstract Underwater noise pollution is a by-product of marine industrial operations. In particular, the noise generated when a foundation Pile is driven into the soil with an impact hammer is considered to be harmful for the aquatic species. In an attempt to reduce the ecological footprint, several noise mitigation techniques have been investigated. Among the various solutions proposed, the air-bubble curtain is often applied due to its efficacy in noise reduction. In this paper, a model is proposed for the investigation of the sound reduction during marine piling when an air-bubble curtain is placed around the Pile. The model consists of the Pile, the surrounding water and soil media, and the air-bubble curtain which is positioned at a certain distance from the Pile surface. The solution approach is semi-analytical and is based on the dynamic sub-structuring technique and the modal decomposition method. Two main results of the paper can be distinguished. First, a new model is proposed that can be used for predictions of the noise levels in a computationally efficient manner. Second, an analysis is presented of the principal mechanisms that are responsible for the noise reduction due to the application of the air-bubble curtain in marine piling. The understanding of these mechanisms turns to be crucial for the exploitation of the maximum efficiency of the system. It is shown that the principal mechanism of noise reduction depends strongly on the frequency content of the radiated sound and the characteristics of the bubbly medium. For Piles of large diameter which radiate most of the acoustic energy at relatively low frequencies, the noise reduction is mainly attributed to the mismatch of the acoustic impedances between the seawater and the bubbly layer. On the contrary, for smaller Piles and when the radiated acoustic energy is concentrated at frequencies close to, or higher than, the resonance frequency of the air bubbles, the sound absorption within the bubbly layer becomes critical.
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a three dimensional vibroacoustic model for the prediction of underwater noise from Offshore Pile driving
Journal of Sound and Vibration, 2014Co-Authors: A. Tsouvalas, Andrei V. MetrikineAbstract:Abstract Steel monoPiles are nowadays widely used as foundations for a large number of Offshore structures. The installation procedure commonly involves a Pile driving process which can last up to several hours depending upon Pile dimensions, soil conditions and input energy of the hydraulic hammer. In impact Pile driving, a hydraulic hammer delivers a series of hammer blows at the head of the Pile that drive the Pile into the sediment. Each hammer strike results in Pile vibrations that emit strong impulsive sounds into the water column which can be harmful for the marine ecosystem. With today's increasing concern regarding the environmental impact of such operations, engineering tools which will be able to provide reliable predictions of the underwater noise levels are required. In this study, a linear semi-analytical formulation of the coupled vibroacoustics of a complete Pile–water–soil interaction model is addressed. The Pile is described by a high order thin shell theory whereas both water and soil are modelled as three-dimensional continua. Results obtained with the developed model indicate that the near-field response in the water column consists mainly of pressure conical waves generated by the supersonic compressional waves in the Pile excited by the impact hammer. The soil response is dominated by shear waves with almost vertical polarization. The Scholte waves are also generated at the water–seabed interface which can produce pressure fluctuations in the water column that are particularly significant close to the sea floor. The effects of soil elasticity and Pile size are thoroughly investigated and their influence on the generated pressure levels is highlighted. The results are also compared with those ones of a similar model in which the soil is treated as an equivalent acoustic fluid. It is shown that the latter approximation can yield inaccurate results at low frequencies especially for harder soil sediments.
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a three dimensional semi analytical model for the prediction of underwater noise generated by Offshore Pile driving
2014Co-Authors: A. Tsouvalas, Andrei V. MetrikineAbstract:In this work, the problem of underwater noise generated during the Offshore installation of steel monoPiles is addressed. The monoPiles are driven into place with the help of hydraulic hammers. During installation, the underwater noise levels generated can be very high and harmful for the marine life. A linear semi-analytical model is developed which is able to represent the dynamics of the coupled vibro-acoustic system. The Pile is modelled using a high order thin shell theory whereas both water and soil are modelled as three-dimensional continua. The results indicate that the near-field response in the water column consists of pressure conical waves due to the the supersonic compressional waves in the Pile generated by the impact hammer. The soil response is dominated by vertically polarised shear waves. Scholte waves are also generated at the water-seabed interface and can produce pressure fluctuations in the water column that are particularly significant close to the sea floor.
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a semi analytical model for the prediction of underwater noise from Offshore Pile driving
Journal of Sound and Vibration, 2013Co-Authors: A. Tsouvalas, Andrei V. MetrikineAbstract:Abstract Underwater noise from Offshore Pile driving gained considerable attention in recent years mainly due to the large scale construction of Offshore wind farms. The most common foundation type of a wind turbine is a monoPile, upon which the wind tower rests. The Pile is driven into place with the help of hydraulic hammers. During the hammering of the Pile, high levels of noise are generated which are known to produce deleterious effects on both mammals and fish. In this work, a linear semi-analytical model is developed for predicting the levels of underwater noise for a wide range of system parameters. The model incorporates all major parts of the system. The hydraulic hammer is substituted by an external force, the Pile is described as a thin circular cylindrical shell, the water is modelled as a compressible fluid and the water-saturated seabed is defined by distributed springs and dashpots in all directions. The solution of the coupled vibroacoustic problem is based on the representation of the response of the complete system on the modal basis of the in vacuo shell structure. The influence that the inter-modal coupling, the choice of the soil parameters and the acoustic impedance of the seabed have on the generated noise levels is studied in the frequency domain. Strong and weak points of the present model are discussed on the basis of a comparison with a set of available experimental data. The obtained results show the capability of the model to predict the underwater noise levels both qualitatively and quantitatively.
