Stephan Lippert

COMPILE—A Generic Benchmark Case for Predictions of Marine Pile-Driving Noise

The prediction of underwater noise emissions from impact pile driving during near-shore and offshore construction activities and its potential effect on the marine environment has been a major field of research for several years. A number of different modeling approaches have been suggested recently to predict the radiated sound pressure at different distances and depths from a driven pile. As there are no closed-form analytical solutions for this complex class of problems and for a lack of publicly available measurement data, the need for a benchmark case arises to compare the different approaches. Such a benchmark case was set up by the Institute of Modelling and Computation, Hamburg University of Technology (Hamburg, Germany) and the Organisation for Applied Scientific Research (TNO, The Hague, The Netherlands). Research groups from all over the world, who are involved in modeling sound emissions from offshore pile driving, were invited to contribute to the first so-called COMPILE (a portmanteau combining computation, comparison, and pile) workshop in Hamburg in June 2014. In this paper, the benchmark case is presented, alongside an overview of the seven models and the associated results contributed by the research groups from six different countries. The modeling results from the workshop are discussed, exhibiting a remarkable consistency in the provided levels out to several tens of kilometers. Additionally, possible future benchmark case extensions are proposed.

On the numerical investigation of sound transmission through double-walled structures with membrane-type acoustic metamaterials

Acoustic metamaterials appear to be of great help in the design of reliable and effective noise reduction measures in the low frequency range. The current contribution is concerned with the modeling of a low-frequency noise shield, based on a double wall arrangement, which includes membrane-type acoustic metamaterials (MAMs), considered as the most promising approach when it comes especially to the tonal noise at frequencies below 300 Hz. MAMs consist of small-sized membranes loaded with a mass. Due to their robustness and relatively simple production, MAMs have been proven to decrease the sound transmission in frequency ranges, for which poro-elastic materials have a rather negligible effect. A simulation model of a double wall panel, whose acoustic cavity is furnished with layers of metamaterials, has been developed and the sound transmission loss (STL) through the structure was calculated, using the finite element method. In order to validate the modelling approach, the STL estimation from the finite element analysis was compared to experimental measurements. The achieved results indicate a noise-decreasing possibility in tunable narrow bands as well as a broadband noise reduction for frequencies less than 300 Hz without significantly adding to the panel mass.

Prediction of underwater noise and far field propagation due to pile driving for offshore wind farms

Wind energy plays a key role towards a greener and more sustainable energy generation. Due to limited onshore areas and possible negative effects on human living space, offshore wind parks become increasingly popular. However, during construction by pile driving, high levels of underwater sound emission are observed. To avoid negative effects on marine mammals and other sea life, different approaches are currently investigated to cut down the sound pressure levels, like e.g. bubble curtains or cofferdams. In order to predict the expected underwater noise both with and without sound damping measures, numerical simulation models are needed to avoid complex and costly offshore tests. Within this contribution, possible modelling strategies for the prediction of underwater noise due to pile driving are discussed. Different approaches are shown for the direct adjacencies of the pile and for the far field sound propagation. The effectivity of potential noise mitigation measures is investigated using a detailed f...

On the challenges of validating a profound pile driving noise model

When predicting underwater sound levels for offshore pile driving by using numerical simulation models, appropriate model validation becomes of major importance. In fact, different parallel transmission paths for sound emission into the water column, i.e., pile-to-water, pile-to-soil, and soil-to-water, make a validation at each of the involved interfaces necessary. As the offshore environment comes with difficult and often unpredictable conditions, measurement campaigns are very time consuming and cost intensive. Model developers have to keep in mind that even thorough planning cannot overcome practical restrictions as well as technical limits and thus require for a reasonable model balancing. The current work presents the validation approach chosen for a comprehensive pile driving noise model—consisting of a near field finite element model as well as a far field propagation model—that is used for the prediction of noise levels at offshore wind farms.

Offshore pile driving noise—Prediction through comprehensive model development

Offshore wind energy is one of the most potent among renewables and thus the worldwide number of offshore wind turbines increases rapidly. The foundations of the wind turbines are typically fastened to the seabed by impact pile driving, which comes along with a significant amount of waterborne noise. To protect the marine biosphere, the use of noise mitigation systems, like bubble curtains or cofferdams, may become necessary. In this context, the model-based prediction of underwater sound pressure levels as well as the design and optimization of effective sound mitigation measures by using numerical models is one of today’s challenges. The current work presents a modeling approach that consists of a near field finite element model and a far field propagation model. Furthermore, it has been found necessary to generate a benchmark to allow for a qualitative and quantitative comparison between the manifold modeling approaches that are currently developed at various institutes and companies.