A new generation of so-called “floating” offshore wind turbines are being developed in France, Europe and the world. These wind turbines will soon have reached technological maturity to be installed in farms with several dozen units. In order to reduce the costs of installation, geotechnical investigations and also maintaining these anchors; the anchors sharing seems to be a very promising lead. In such a mesh of floating wind turbines, each wind turbine is anchored to the seabed by 3 mooring lines and each anchor could hold three lines holding three different wind turbines in directions 120 degrees apart. Thus, the number of anchors required for a wind farm could be reduced by more than half.
The problem is that the multi-directionality of anchor loading has not yet been studied very carefully in offshore geotechnical engineering. Indeed, until now, studies (but also design standards) have come from oil&gas practice that has never required fields of floating structures. In addition, for security reasons, the anchor lines of platforms or FPSOs are tripled (or even quadrupled) in order to anticipate a possible failure of lines.
Scientific advances and innovation
In this MUTANC-GEOTECH project, the Gustave Eiffel University, the University of Nantes and France Energies Marines propose to study the problems of soil-anchor interactions related to one-way multidirectional and cyclical loads. At the geotechnical centrifuge of the Gustave Eiffel University, one-way loading tests, multidirectional and cyclical, will be performed on small-scale models. The advantage of placing these small-scale models in a macro-gravity field is to generate on this model the same stress state that is applied to the prototype in real size. Thus, a model reduced to the 1/100th subjected to a macro-gravity field of 100×g (100 times The Earth’s gravity) behaves like the prototype. These centrifuge tests will serve to calibrate a numerical model of the soil-anchor system that will be developed at the University of Nantes. Once this numerical model obtained, it will be used to study the temporal behaviour of the ground-anchor system in the presence of the actual stochastic loading that has been determined in the coupled France Energies Marines MUTANC project.
Expected technical and economic impact
The project therefore targets:
- the development of the new loading system validated by centrifuge tests;
- a centrifuge test campaign producing results feeding the numerical model;
- a numerical model taking into account the cyclic behavior of the soil.
Via this objective of studying the “geotechnical” feasibility of pooling anchors in floating wind turbine farms, the aim is to significantly reduce the number of anchors on an EMR field and therefore the cost of installation and geotechnical investigations but also maintenance of such farms.
Key project milestones
- September 2021 - Start of the project
- Aujust 2024 - End of the project