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Structure-Borne Noise in Offshore Piling
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.
Pascal . In The Netherlands, regulations have recently changed from the allowance of piling during specific period of the year to the adoption of specific sound level criteria . The latter are similar to those imposed in Germany, but consider additionally cumulative noise exposure levels. In the United Kingdom, a separate environmental impact assessment (EIA) is followed per project in which acoustic deterrent devices (seal scarers) are used  together with trained marine mammal observers who monitor the activity using both visual inspection of the site and passive acoustic detection devices . Similar regulations exist in several other countries and lessons learned from previously gathered experiences slowly find their way into new regulations . The majority of the regulations though do not consider in detail the frequency content of the radiated noise; an item worth further investigation in the near future .
2. Structure-Borne Noise in Offshore Piling: The Historical Development of Models
The prediction of underwater noise requires an in-depth study of the source and of the domain in which the acoustic energy is released . Underwater noise in deep oceans is well documented in the literature [68,69,70], driven partly by the need to design SOund Navigation And Ranging (sonar) systems for military applications [71,72]. On the contrary, sound propagation in shallow waters is more complicated due to multiple reflections, refractions and scattering of sound waves at the sea surface and the seabed [73,74,75,76]. The seabed plays a key role here as it is the element that contains the largest uncertainty in the characterisation of its composition [77,78,79].
Next to the challenges associated with wave propagation in shallow waters, the study of noise generated by pile driving, adds an extra complexity; the need to investigate a system composed of three interrelated domains being the seawater, the seabed and the pile, the interaction of which determines the sound source mechanism. Henceforth, a historical overview of the developments in the field of pile vibroacoustics is given, reflecting the evolution of our understanding of the physics of underwater noise emission due to pile driving.
2.1. First Generation Models: The Fluid Approximation of the Seabed
Although some early studies dealing with pile driving noise do exist [80,81,82], Reinhall and Dahl  were the first to develop a detailed numerical model focusing on the prediction of underwater noise from impact pile driving. Their approach tackles the problem in two steps: First, a finite element model (FEM) is adopted for the sound generation which includes a sufficient degree of detailing in modelling the source mechanism. Thereafter, the parabolic equation (PE) is applied for the propagation of sound at larger distances . The pile is modelled using structural elements whereas both water and soil are described as linear acoustic fluids. Perfectly Matched Layers (PML)  are employed to truncate the fluid domains in the FEM as shown in Figure 2.
Figure 2. Axisymmetric FE model of pile and water (left). Acoustic pressure surface plots showing the acoustic radiation from the pile at 3, 6, 10 and 16 ms after impact by pile hammer. The propagation direction of the wave front associated with the Mach cones produced in the water and the sediment is indicated by the arrows (right). Reprinted with permission from Reinhall, P.G., Dahl, P.H. Underwater Mach wave radiation from impact pile driving: Theory and observation. The Journal of the Acoustical Society of America 2011, 130, 1209–1216. Copyright 2011, Acoustic Society of America.
The significant result obtained from this study was the observation that the pressure field in the pile proximity is composed of Mach cones, i.e., coherent wave fronts defining alternating zones of compression and rarefaction in the seawater (Figure 2). These are generated by the supersonic compressional stress waves propagating from the pile head to the pile toe right after the hammer impact. Reverse Mach cones were also computed upon reflection of the stress waves from the pile toe. The angle of the cones is equal to sin−1(cw/cp)≈ 17.2° in the seawater and sin−1(cL/cp) ≈ 18.6° in the seabed, with cp, cw and cL being the phase speeds of compressional waves in the pile, water, and seabed, respectively. The physics involved mark essentially a moving source problem which is classical in many field of wave mechanics, i.e., supersonic jets  or trains that surpass the speed of Rayleigh waves [87,88]. In the case of pile driving, the stress wave in the pile constitutes the moving source. These observations were soon after confirmed by beam forming analysis of measured data [89,90].
The modelling approach introduced by Reinhall and Dahl  was subsequently adopted by other researchers [91,92,93,94,95,96,97], i.e., a FEM was employed for the sound generation and a propagation algorithm was applied for wave field predictions at larger distances. As an alternative to the FEM, MacGillivray [98,99,100] adopted a finite difference (FD) scheme for the near-field acoustics under the simplifying assumption of no bending energy stored in the shell surface. Depending on the degree of detailing required, the far-range propagation model can take several mathematical forms:
- normal mode (NM) representations ,
- wavenumber intergation (WI) algorithms [91,93,94],
- energy flux-based methods  and
- parabolic equation (PE) models [83,96,102,103].
Numerical models which couple the structural domain modelled by finite elements and the exterior (soil) domain modelled by means of the boundary element method also exist [104,105,106], albeit their focus is primarily placed on the soil vibrations in the pile proximity.
In contrast to the models described above, which are primarily based on numerical discretisation of the partial differential equations, semi-analytical solutions were also proposed by several authors [107,108,109,110,111,112]. The analytical model by Hall  considers a thin cylindrical shell immersed in a fluid in which semi-analytical solutions are obtained for the radiated sound pressure and particle velocity similar to Junger and Feit .
In the model by Tsouvalas and Metrikine  (Figure 3), the pile is modelled using the shell theory, the water is described as a linearised acoustic fluid and the soil is treated by distributed springs and dashpots attached to the pile surface. The shell and water responses are expressed in terms of modes and then a mode matching technique is employed to solve the coupled problem. The models by Deng et al. , Deng et al.  are similar to those in , but expand the shell response in terms of different basis functions. The advantage of the semi-analytical models is that they are computationally fast and can be used when a large number of simulations are required. The downside of this is that they are not able to achieve the same degree of detailing as in FEM.
Figure 3. Model proposed by Tsouvalas and Metrikine  to treat the pile–water–soil interaction and the generation of sound in the seawater. Inner fluid occupies the region z0≤z≤Lwhile the outer fluid domain the region z1≤z≤z2. Soil reaction to the pile is represented by distributed spring-dashpot elements attached on the pile surface at z2≤z≤L. Reprinted from Tsouvalas, A., Metrikine, A.V. A semi-analytical model for the prediction of underwater noise from offshore pile driving. Journal of Sound and Vibration 2013, 332, 3232–3257. Copyright 2013, with permission from Elsevier.
2.2. Second Generation Models: Inclusion of the Elastic Seabed
The models described in Section 2.1 constitute a significant step towards understanding the physics of underwater sound emission in impact piling. However, their main limitation is that they describe the seabed either by an acoustic medium or by spring-dashpot elements. The former approximation, albeit reasonable in many ocean acoustic applications, cannot capture all the essential physics of the problem at hand for two main reasons. First, the energy is largely released in the seabed during pile driving while the pile is partly embedded into the soil . Thus, an accurate prediction of the energy flux in the surrounding acousto-elastic region requires a detailed description of the seabed next to that of the seawater. Second, the accurate identification of the acoustic source amplitude, i.e., pile response, requires the consideration of the coupled soil–fluid–pile problem. In other words, without an accurate description of the coupled problem, the noise source mechanism cannot be identified properly.
Tsouvalas et al. [115,116,117,118] were among the first to include the elastic description of the seabed in the pile driving acoustics. In Figure 4, results of model simulations are shown for illustration of the physics of the wave radiation pattern for a typical case of an offshore pile installation scenario. Next to the pressure cones in the seawater, the response in the soil is dominated by shear waves with almost vertical polarisation because the shock waves in the pile travel at hypersonic speed compared to that of the shear waves in the soil (M=cp/cS≈27). Additionally, compressional waves exist in the seabed similar to the ones observed in the seawater. Apart from the waves travelling in the bulk of the media, Scholte waves are generated at the seabed–water interface travelling with much lower speed compared to the speed of the compressional waves. The prediction of these elastic waves was later confirmed by several authors [119,120,121,122,123], while experimental data measuring the soil response together with the pressures in the water column close to the seabed have confirmed the existence of the interface waves [124,125].
Figure 4. Evolution of the particle velocity norm in the seawater (z≥0 m) and the seabed (z<0 m) for several moments in time after the hammer impact using the model by Tsouvalas and Metrikine . In the case analysed, the pile has a diameter of 7 m and a length of 78 m and the seabed consists of a soft upper soil layer overlying a stiffer soil halfspace. The time increases from top to bottom and from left to right.
The entry is from 10.3390/en13123037
- Breton, S.P.; Moe, G. Status, plans and technologies for offshore wind turbines in Europe and North America. Renew. Energy 2009, 34, 646–654.
- Sun, X.; Huang, D.; Wu, G. The current state of offshore wind energy technology development. Energy 2012, 41, 298–312.
- Athanasia, A.; Anne-Bénédicte, G.; Jacopo, M. The offshore wind market deployment: Forecasts for 2020, 2030 and impacts on the European supply chain development. Energy Procedia 2012, 24, 2–10.
- Kaldellis, J.; Kapsali, M. Shifting towards offshore wind energy—Recent activity and future development. Energy Policy 2013, 53, 136–148.
- Perveen, R.; Kishor, N.; Mohanty, S.R. Off-shore wind farm development: Present status and challenges. Renew. Sustain. Energy Rev. 2014, 29, 780–792.
- Fried, L.; Shukla, S.; Sawyer, S. Chapter 26—Growth Trends and the Future of Wind Energy. In Wind Energy Engineering; Letcher, T.M., Ed.; Academic Press: Cambridge, MA, USA, 2017; pp. 559–586.
- Bilgili, M.; Yasar, A.; Simsek, E. Offshore wind power development in Europe and its comparison with onshore counterpart. Renew. Sustain. Energy Rev. 2011, 15, 905–915.
- Byrne, B.W.; Houlsby, G.T. Foundations for Offshore Wind Turbines. Philos. Trans. Math. Phys. Eng. Sci. 2003, 361, 2909–2930.
- Oh, K.Y.; Nam, W.; Ryu, M.S.; Kim, J.Y.; Epureanu, B.I. A review of foundations of offshore wind energy convertors: Current status and future perspectives. Renew. Sustain. Energy Rev. 2018, 88, 16–36.
- Wu, X.; Hu, Y.; Li, Y.; Yang, J.; Duan, L.; Wang, T.; Adcock, T.; Jiang, Z.; Gao, Z.; Lin, Z.; et al. Foundations of offshore wind turbines: A review. Renew. Sustain. Energy Rev. 2019, 104, 379–393.
- Lozano-Minguez, E.; Kolios, A.; Brennan, F. Multi-criteria assessment of offshore wind turbine support structures. Renew. Energy 2011, 36, 2831–2837.
- O’Kelly, B.; Arshad, M. 20—Offshore wind turbine foundations–analysis and design. In Offshore Wind Farms; Ng, C., Ran, L., Eds.; Woodhead Publishing: Cambridge, UK, 2016; pp. 589–610.
- Negro, V.; López-Gutiérrez, J.S.; Esteban, M.D.; Alberdi, P.; Imaz, M.; Serraclara, J.M. Monopiles in offshore wind: Preliminary estimate of main dimensions. Ocean Eng. 2017, 133, 253–261.
- European Wind Energy Association (EWEA). Offshore Wind in Europe—Key Trends and Statistics 2018; Technical Report; WindEurope asbl/vzw: Brussels, Belgium, 2019.
- Thomsen, K.E. Chapter Eleven—Commonly Used Installation Methods. In Offshore Wind; Thomsen, K.E., Ed.; Elsevier: Boston, MA, USA, 2012; pp. 157–184.
- Jonker, G. Vibratory Pile Driving Hammers for Pile Installations and Soil Improvement Projects. In Proceedings of the Offshore Technology Conference, Houston, TX, USA, 27–30 April 1987.
- Warrington, D. Theory and Development of Vibratory Pile-Driving Equipment. In Proceedings of the Offshore Technology Conference, Houston, TX, USA, 1–4 May 1989.
- Viking, K. Vibro-Driveability—A Field Study of Vibratory Driven Sheet Piles in Non-Cohesive Soils. Ph.D. Thesis, KTH Byggvetenskap, Stockholm, Sweden, 2002.
- Tsouvalas, A. Underwater Noise Generated by Offshore Pile Driving. Ph.D. Thesis, Delft University of Technology, Delft, The Netherlands, 2015.
- Farcas, A.; Thompson, P.M.; Merchant, N.D. Underwater noise modelling for environmental impact assessment. Environ. Impact Assess. Rev. 2016, 57, 114–122.
- Popper, A.; Hastings, M. The effects of anthropogenic sources of sound on fishes. J. Fish Biol. 2009, 75, 455–489.
- Slabbekoorn, H.; Bouton, N.; van Opzeeland, I.; Coers, A.; ten Cate, C.; Popper, A.N. A noisy spring: The impact of globally rising underwater sound levels on fish. Trends Ecol. Evol. 2010, 25, 419–427.
- Finneran, J.J. Noise-induced hearing loss in marine mammals: A review of temporary threshold shift studies from 1996 to 2015. J. Acoust. Soc. Am. 2015, 138, 1702–1726.
- Erbe, C.; Dunlop, R.; Dolman, S. Effects of anthropogenic noise on animals. In Effects of Anthropogenic Noise on Animals; Springer: New York, NY, USA, 2018; pp. 277–309.
- Bailey, H.; Senior, B.; Simmons, D.; Rusin, J.; Picken, G.; Thompson, P.M. Assessing underwater noise levels during pile-driving at an offshore windfarm and its potential effects on marine mammals. Mar. Pollution Bull. 2010, 60, 888–897.
- Brandt, M.; Diederichs, A.; Betke, K.; Nehls, G. Responses of harbour porpoises to pile driving at the Horns Rev II offshore wind farm in the Danish North Sea. Mar. Ecol. Prog. Ser. 2011, 421, 205–216.
- Tougaard, J.; Kyhn, L.A.; Amundin, M.; Wennerberg, D.; Bordin, C. Behavioral reactions of harbor porpoise to pile-driving noise. Adv. Exp. Med. Biol. 2012, 730, 277–280.
- Dähne, M.; Gilles, A.; Lucke, K.; Peschko, V.; Adler, S.; Krügel, K.; Sundermeyer, J.; Siebert, U. Effects of pile-driving on harbour porpoises ( Phocoena phocoena ) at the first offshore wind farm in Germany. Environ. Res. Lett. 2013, 8, 025002.
- Haelters, J.; Dulière, V.; Vigin, L.; Degraer, S. Towards a numerical model to simulate the observed displacement of harbour porpoises Phocoena phocoena due to pile driving in Belgian waters. Hydrobiologia 2015, 756, 105–116.
- Carstensen, J.; Henriksen, O.; Teilmann, J. Impacts of offshore wind farm construction on harbour porpoises: Acoustic monitoring of echolocation activity using porpoise detectors (T-PODs). Mar. Ecol. Prog. Ser. 2006, 321, 295–308.
- David, J. Likely sensitivity of bottlenose dolphins to pile-driving noise. Water Environ. J. 2006, 20, 48–54.
- Madsen, P.; Wahlberg, M.; Tougaard, J.; Lucke, K.; Tyack, P. Wind turbine underwater noise and marine mammals: Implications of current knowledge and data needs. Mar. Ecol. Prog. Ser. 2006, 309, 279–295.
- Herbert-Read, J.E.; Kremer, L.; Bruintjes, R.; Radford, A.N.; Ioannou, C.C. Anthropogenic noise pollution from pile-driving disrupts the structure and dynamics of fish shoals. Proc. R. Soc. B Biol. Sci. 2017, 284, 20171627.
- Hastie, G.; Merchant, N.D.; Götz, T.; Russell, D.J.F.; Thompson, P.; Janik, V.M. Effects of impulsive noise on marine mammals: Investigating range-dependent risk. Ecol. Appl. 2019, 29, e01906.
- Leunissen, E.M.; Dawson, S.M. Underwater noise levels of pile-driving in a New Zealand harbour, and the potential impacts on endangered Hector’s dolphins. Mar. Pollut. Bull. 2018, 135, 195–204.
- Kastelein, R.A.; Hoek, L.; Gransier, R.; de Jong, C.A.F. Hearing thresholds of a harbor porpoise (Phocoena phocoena) for playbacks of multiple pile driving strike sounds. J. Acoust. Soc. Am. 2013, 134, 2302–2306.
- Kastelein, R.A.; van Heerden, D.; Gransier, R.; Hoek, L. Behavioral responses of a harbor porpoise (Phocoena phocoena) to playbacks of broadband pile driving sounds. Mar. Environ. Res. 2013, 92, 206–214.
- Kastelein, R.A.; Hoek, L.; Gransier, R.; Jennings, N. Hearing thresholds of two harbor seals (Phoca vitulina) for playbacks of multiple pile driving strike sounds. J. Acoust. Soc. Am. 2013, 134, 2307–2312.
- Debusschere, E.; Hostens, K.; Adriaens, D.; Ampe, B.; Botteldooren, D.; De Boeck, G.; De Muynck, A.; Sinha, A.K.; Vandendriessche, S.; Van Hoorebeke, L.; et al. Acoustic stress responses in juvenile sea bass Dicentrarchus labrax induced by offshore pile driving. Environ. Pollut. 2016, 208, 747–757.
- Bejder, L.; Samuels, A.; Whitehead, H.; Finn, H.; Allen, S. Impact assessment research: Use and misuse of habituation, sensitisation and tolerance in describing wildlife responses to anthropogenic stimuli. Mar. Ecol. Prog. Ser. 2009, 395, 177–185.
- Teilmann, J.; Carstensen, J. Negative long term effects on harbour porpoises from a large scale offshore wind farm in the Baltic—Evidence of slow recovery. Environ. Res. Lett. 2012, 7, 045101.
- Thompson, P.M.; Hastie, G.D.; Nedwell, J.; Barham, R.; Brookes, K.L.; Cordes, L.S.; Bailey, H.; McLean, N. Framework for assessing impacts of pile-driving noise from offshore wind farm construction on a harbour seal population. Environ. Impact Assess. Rev. 2013, 43, 73–85.
- Russell, D.J.; Hastie, G.D.; Thompson, D.; Janik, V.M.; Hammond, P.S.; Scott-Hayward, L.A.; Matthiopoulos, J.; Jones, E.L.; McConnell, B.J. Avoidance of wind farms by harbour seals is limited to pile driving activities. J. Appl. Ecol. 2016, 53, 1642–1652.
- Graham, I.M.; Merchant, N.D.; Farcas, A.; Barton, T.R.; Cheney, B.; Bono, S.; Thompson, P.M. Harbour porpoise responses to pile-driving diminish over time. R. Soc. Open Sci. 2019, 6, 190335.
- Dahl, P.H.; Dall’Osto, D.R.; Farrell, D.M. The underwater sound field from vibratory pile driving. J. Acoust. Soc. Am. 2015, 137, 3544–3554.
- Tsouvalas, A.; Metrikine, A. Structure-Borne Wave Radiation by Impact and Vibratory Piling in Offshore Installations: From Sound Prediction to Auditory Damage. J. Mar. Sci. Eng. 2016, 4, 44.
- Paiva, E.G.; Salgado Kent, C.P.; Gagnon, M.M.; McCauley, R.; Finn, H. Reduced Detection of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) in an Inner Harbour Channel During Pile Driving Activities. Aquat. Mamm. 2015, 41, 455–468.
- Graham, I.M.; Pirotta, E.; Merchant, N.D.; Farcas, A.; Barton, T.R.; Cheney, B.; Hastie, G.D.; Thompson, P.M. Responses of bottlenose dolphins and harbor porpoises to impact and vibration piling noise during harbor construction. Ecosphere 2017, 8, e01793.
- Nehls, G.; Rose, A.; Diederichs, A.; Bellmann, M.; Pehlke, H. Noise Mitigation During Pile Driving Efficiently Reduces Disturbance of Marine Mammals. In Advances in Experimental Medicine and Biology; Springer: New York, NY, USA, 2016; pp. 755–762.
- Dähne, M.; Tougaard, J.; Carstensen, J.; Rose, A.; Nabe-Nielsen, J. Bubble curtains attenuate noise from offshore wind farm construction and reduce temporary habitat loss for harbour porpoises. Mar. Ecol. Prog. Ser. 2017, 580, 221–237.
- Compton, R.; Goodwin, L.; Handy, R.; Abbott, V. A critical examination of worldwide guidelines for minimising the disturbance to marine mammals during seismic surveys. Mar. Policy 2008, 32, 255–262.
- Erbe, C. International regulation of underwater noise. Acoust. Aust. 2013, 41, 12–19.
- Williams, R.; Erbe, C.; Ashe, E.; Clark, C.W. Quiet(er) marine protected areas. Mar. Pollut. Bull. 2015, 100, 154–161.
- Dolman, S.J.; Jasny, M. Evolution of Marine Noise Pollution Management. Aquat. Mamm. 2015, 41, 357–374.
- Rossington, K.; Benson, T.; Lepper, P.; Jones, D. Eco-hydro-acoustic modeling and its use as an EIA tool. Mar. Pollut. Bull. 2013, 75, 235–243.
- Werner, S. Towards a Precautionary Approach for Regulation of Noise Introduction in the Marine Environment from Pile Driving; Federal Environmental Agency: Stralsund, Germany, 2010.
- Lucke, K.; Siebert, U.; Lepper, P.A.; Blanchet, M.A. Temporary shift in masked hearing thresholds in a harbor porpoise (Phocoena phocoena) after exposure to seismic airgun stimuli. J. Acoust. Soc. Am. 2009, 125, 4060–4070.
- Ainslie, M.A. Standard for Measurement and Monitoring of Underwater Noise, Part I. Physical Quantities and Their Units; Report No. TNO-DV 2011 C235; Nederlandse Organisatie voor Toegepast-Natuurwetenschappelijk Onderzoek (TNO): Den Haag, The Netherlands, 2011.
- De Jong, C.A.F.; Ainslie, M.A.; Blacquière, G. Standard for Measurement and Monitoring of Underwater Noise, Part II: Procedures for Measuring Underwater Noise in Connection with Offshore wind Farm Licensing; Report No. TNO-DV 2011 C251; Nederlandse Organisatie voor Toegepast-Natuurwetenschappelijk Onderzoek (TNO): Den Haag, The Netherlands, 2011.
- Brandt, M.J.; Höschle, C.; Diederichs, A.; Betke, K.; Matuschek, R.; Nehls, G. Seal scarers as a tool to deter harbour porpoises from offshore construction sites. Mar. Ecol. Prog. Ser. 2013, 475, 291–302.
- Joint Nature Conservation Committee. Statutory Nature Conservation Agency Protocol for Minimising the Risk Injury to Marine Mammals from Piling Noise; JNCC: Aberdeen, UK, 2010.
- Dolman, S.; Simmonds, M. Towards best environmental practice for cetacean conservation in developing Scotland’s marine renewable energy. Mar. Policy 2010, 34, 1021–1027.
- Bailey, H.; Brookes, K.L.; Thompson, P.M. Assessing environmental impacts of offshore wind farms: Lessons learned and recommendations for the future. Aquat. Biosyst. 2014, 10, 8.
- Schaffeld, T.; Ruser, A.; Woelfing, B.; Baltzer, J.; Kristensen, J.H.; Larsson, J.; Schnitzler, J.G.; Siebert, U. The use of seal scarers as a protective mitigation measure can induce hearing impairment in harbour porpoises. J. Acoust. Soc. Am. 2019, 146, 4288–4298.
- Tougaard, J.; Dähne, M. Why is auditory frequency weighting so important in regulation of underwater noise? J. Acoust. Soc. Am. 2017, 142, EL415–EL420.
- Stöber, U.; Thomsen, F. Effect of impact pile driving noise on marine mammals: A comparison of different noise exposure criteria. J. Acoust. Soc. Am. 2019, 145, 3252–3259.