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Conference programme 

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Poster session

Lead Session Chair:
Stephan Barth, Managing Director, ForWind - Center for Wind Energy Research, Germany
René Smidt Lützen Lloyd's Register Consulting, Denmark
Co-authors:
René Smidt Lützen (1) F P Benjamin Trimoreau (1) Peter Skjellerup (2) Jon Vindahl Kringelum (3) Amir Shajarati (3)
(1) Lloyd's Register Consulting, Hellerup, Denmark (2) Geocos, Rødovre, Denmark (3) DONG Energy Wind Power, Gentofte, Denmark
Poster Award Winner

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Poster
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Presenter's biography

Biographies are supplied directly by presenters at OFFSHORE 2015 and are published here unedited

Mr. Lützen is a Principal Consultant with Lloyd’s Register Consulting, specializing in acoustics and vibration. He acts as project manager for predictions, investigations, and measurements with regard to machinery noise & vibration, and underwater acoustics. As a student of Prof. Bjørnø at Technical University of Denmark he received his MSc degree in 1998 with a Thesis on underwater communication. The subsequent 16 years Mr. Lützen has worked continuously as an acoustic consultant, first with Ødegaard & Danneskiold-Samsøe, then with Grontmij, and since 2012 with Lloyd’s Register Consulting. His experience includes development of new modelling and measurement approaches.

Abstract

New method for accurate prediction of underwater noise from pile driving

Introduction

Underwater noise from pile driving can only be mitigated efficiently, both from an environmental and cost perspective, if we understand the finer details of how noise is created and its propagation into the water. To achieve this understanding, accurate models are needed. A key target is to help the industry address the environmental concerns related to these anthropogenic noise sources. A new approach combining geotechnical methods with vibro-acoustic modelling has shown promising results. DONG Energy Wind Power has together with Lloyd’s Register Consulting conducted a variety of targeted industrial research and development activities to increase knowledge within this field.

Approach

Various detailed numerical modelling approaches are currently being investigated to improve the accuracy and reliability of noise estimates. A tricky question, in general, is the interaction between foundation and soil. One example of a numerical scheme combines two well proven techniques: Wave Equation Analysis for Piling (WEAP) and vibro-acoustic Finite Element (FE) modelling. The novel WEAP-FE technique combines the strengths of both techniques. Hence, a fairly detailed model is established while maintaining computational effectiveness.

Main body of abstract

Two cases were considered in terms of comparison of full-scale measurements with WEAP-FE modelling results, and the results were very promising. This contribution presents results from the two cases. First, an experimental setup from the literature containing detailed measurement results was modelled. The numerical representation included the hammer system, the pile, and the seabed. Good agreement between model results and measurement data was found.
During the construction of the Anholt Offshore Wind Farm a comprehensive full-scale measurement campaign concerning underwater noise was carried out. As a second validation case, a detailed model was established for the Anholt case. Here, properties of certain hydraulic hammer components were determined using structural Finite Element modelling. As for the literature case, a model describing hammer system, pile, and seabed was established. In addition, the presence of the installation vessel had to be addressed, as it affected the acoustic propagation. It was found that the hammer system representation was quite accurate, and that the loss mechanisms related to pile-seabed interaction were well represented. Reflections from the asymmetric pile location relative to the installation posed certain challenges. Nevertheless, modelling results agreed with measurements within +/-2 dB in terms of overall Sound Exposure Level (SEL).


Conclusion

While not a simplistic approach, the WEAP-FE technique appears quite promising for the prediction of pile driving noise. The method allows for a detailed description of the hammer-pile-soil system and benefits from decades of geotechnical real-world experience for the soil properties. The good match between measurements and modelling results for the two presented cases demonstrates great potential of the WEAP-FE technique.


Learning objectives
This contribution shows a new technique for precise prediction of underwater noise from pile driving. It involves novel use of the classic geotechnical WEAP technique combined with vibro-acoustic Finite Element modelling. Using full-scale measurement data from a literature case and the construction of Anholt Offshore Wind Farm, in-depth validation steps are presented and concluded on. In both cases a quite satisfactory agreement between the WEAP-FE model and the measurements is demonstrated.