Research into Scour Pits
Offshore wind farms use different types of foundations depending on the site conditions. The most commonly used foundation types are monopiles, gravity-based structures and jacket foundations. In collaboration with Leo van Rijn, WaterProof investigated the expected dimensions of scour pits around offshore wind turbine foundations. The study combined physical scale experiments carried out in WaterProof’s flow and sediment basin with numerical modelling.
- Client: Leo van Rijn
- Location: Lelystad, Basin WaterProof
The three main types of foundations used for offshore wind turbines are applied under different conditions:
- Monopiles are the most commonly used foundation type in shallow water with a sandy seabed and migrating sand waves.
- Gravity-based structures are more suitable for shallow waters (up to approximately 30 m) with a sandy or rocky seabed.
- Jacket foundations are often used in waters up to approximately 50 m deep.
Flow around these structures can cause a scour pit to form around the foundation. In severe cases, scour can compromise the stability of a structure, potentially causing it to tilt or even collapse. To gain a better understanding of scour development and determine the expected dimensions of scour pits, WaterProof and Leo van Rijn conducted a dedicated study.
Scour Pit Experiments and Modelling
To investigate the dimensions of scour pits, a series of experiments was carried out in WaterProof’s basin. The basin contains a large rectangular test section where experiments can be performed under controlled and constant flow conditions.
During the first series of experiments, flow velocity, flow direction and turbulence around monopiles, gravity-based structures and jacket foundations were measured on a fixed bed. In addition to measurements at different locations within the test section, vertical flow velocity profiles were also measured.
In the second series of experiments, the different structures were placed on a sandy bed, and the dimensions of the developing scour pits were measured at different time intervals. The data obtained from the scale experiments were subsequently used in 1D and 2D numerical models to calculate scour pit dimensions under full-scale conditions.
The knowledge gained from this study can be used in new construction projects in flowing water to predict whether scour will develop around a structure. If scour is expected, the dimensions of the scour pit can be estimated, allowing appropriate measures to be taken to protect the structure.
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Research into Scour Pits
Offshore wind farms use different types of foundations depending on the site conditions. The most commonly used foundation types are monopiles, gravity-based structures and jacket foundations. In collaboration with Leo van Rijn, WaterProof investigated the expected dimensions of scour pits around offshore wind turbine foundations. The study combined physical scale experiments carried out in WaterProof’s flow and sediment basin with numerical modelling.
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Export cables are used to connect offshore wind farms to onshore substations, from where the electricity is fed into the national power grid. Electromagnetic fields (EMF) are generated around buried export cables as a result of the electrical current flowing through them. These EMF may potentially affect marine life. The magnitude of these fields and their potential impact are still largely unknown. We therefore work with several partners on different measurement and research projects to better understand and assess these effects. Research into the potential relationship between EMF and harbour porpoise presence within the Borssele offshore wind farm is one example.
