• Energy Research

This study aims to improve the design of scour protection around offshore wind turbine monopiles, as well as future-proofing them against the impacts of climate change. A series of large-scale experiments have been performed in the context of the European HYDRALAB-PLUS PROTEUS (Protection of offshore wind turbine monopiles against scouring) project in the Fast Flow Facility in HR Wallingford. These experiments make use of state of the art optical and acoustic measurement techniques to assess the damage of scour protections under the combined action of waves and currents. These novel PROTEUS tests focus on the study of the grading of the scour protection material as a stabilizing parameter, which has never been done under the combined action of waves and currents at a large scale. Scale effects are reduced and, thus, design risks are minimized. Moreover, the generated data will support the development of future scour protection designs and the validation of numerical models used by researchers worldwide. The testing program objectives are: (i) to compare the performance of single-layer wide-graded material used against scouring with current design practices; (ii) to verify the stability of the scour protection designs under extreme flow conditions; (iii) to provide a benchmark dataset for scour protection stability at large scale; and (iv) to investigate the scale effects on scour protection stability.

Offshore wind farms contribute significantly to contemporary renewable energy production. By installing these offshore structures, new technical design challenges arise, such as foundation optimisation. Present LCoE (Levelized Cost of Electricity) of offshore wind turbines amounts up to 170 Euro/MWh (Crown Estate, 2015), but the ambition is to reduce this by 2020 to 90 Euro/MWh (EY, 2015). Offshore wind turbine foundation costs are 20 % of the total costs in the case of a monopile (NREL, 2014). An important part of those costs is related to the foundation's scour protection. Therefore, optimisations in the design of the scour protection are indispensable.Another promising track to reduce the costs of offshore wind turbines is their lifetime extension. Recent studies (Crown Estate, 2015) show that a 5 year lifetime extension can reduce the cost per kWh by 6 %. To check the feasibility of a lifetime extension, it will be necessary to diagnose or inspect the conditions of several core parts of the turbines, notably its foundation and scour protection. Therefore, more fundamental insight into the (longer term damage) behaviour of the scour protection around the monopile is needed.Beside the interest in design optimisation and lifetime extension, the influence of climate change needs to be investigated in more detail. Climate change will increase the design storm conditions and influence the scour protection stability. Therefore, research towards a risk-based design will help to evaluate the functionality of scour protection already installed and improve the design of future scour protections adapted to climate change.Based on the above motivations, the main research objective is to establish a basic benchmark dataset on the stability of scour protection around monopile foundations to serve as a basis for model tests in other flumes in the future (rather than to carry out a traditional sensitivity study with a fine resolution for all governing parameters). To achieve the goals, scour researchers from several institutions are set to start work on a collaborative project at HR Wallingford's Fast Flow Facility (FFF) as part of PROTEUS, an EU-funded Hydralab+ project. Hydralab+ which is funded by the EU's Horizon 2020 Research and Innovation Programme brings together facilities and researchers in experimental hydraulic and hydrodynamics.The research project aims to improve the design of scour protection around offshore wind turbine monopiles, as well as future-proofing them against the impacts of climate change. PROTEUS, which stands for the 'PRotection of Offshore wind Turbine monopilEs against Scouring' will facilitate the conducting of a series of large scale experiments over a seven week period in the FFF flume at HR Wallingford's UK physical modelling facilities.Partners involved in PROTEUS are: Department of Civil Engineering at Ghent University, HR Wallingford (UK), the Ludwig-Franzius Institute for Hydraulic, Estuarine and Coastal Engineering at the University of Hannover, the Faculty of Engineering at the University of Porto, the Geotechnics division of the Belgian Department of Mobility and Public Works, and International Marine and Dredging Consultants (IMDC nv).