One of the major expense factors in offshore wind farm development is turbine foundations and their installation – especially as the farms move into deeper water further offshore. GRAVITAS Offshore Ltd., UK, – a company specialised in concrete foundations – has developed an innovative concept of a self-installing concrete gravity foundation, which will significantly reduce costs while increasing flexibility. DHI assisted GRAVITAS in getting their concept ready for the market by putting it to test at our test facilities in Denmark.
The self-floating foundation is cast in concrete onshore and subsequently towed to the wind farm site, where it is installed by use of inexpensive tug boats only. The installation itself is made by lowering the structure through a controlled influx of water and sand/aggregate ballasting. It was DHI’s job to test and verify the towing and the self-installing phase, giving our client a clear understanding of how his structure behaves during these phases and pinpointing potential areas for improvement.
With video equipment and a motion detection system installed during the tests, it was detected how many towing vessels were required during various sea states (wind, waves and currents). Hence, the behaviour of the concrete gravity foundation during the self-installing phases was investigated. Moreover, the tests served to better understanding and optimising the installation procedures during various sea conditions.
The model tests allowed GRAVITAS to confirm the feasibility of the concept and to validate their numerical models, thereby bringing their innovative concept to the next level.
The new foundation on its way. © Gravitas Offshore Ltd.
Testing GRAVITAS’ concrete gravity foundation in the towing and installation phase in combined wind, waves and current at DHI’s facilities.