Coordinateurs du projet
Context
A new generation of offshore wind turbines known as “floating” turbines is currently being developed in France, Europe, and around the world. These wind turbines will soon reach technological maturity and be ready for installation in fields comprising several dozen units. In order to reduce the cost of installation and geotechnical investigations, as well as the maintenance of the anchors for these floating structures, shared anchoring appears to be a very promising avenue.
In such a network of floating wind turbines, each turbine is anchored to the seabed by three anchor lines, and each anchor could hold three lines retaining three different turbines in 120° directions. This could reduce the number of anchors required for a wind farm by more than half.
The problem is that sharing an anchor induces a highly multidirectional load on the anchor, which has yet to be studied in depth in offshore geotechnics. Until now, studies (and design standards) have been based on oil industry practices, which have never required floating structures involving the use of shared anchors. Furthermore, for safety reasons, the mooring lines of oil platforms or FPSOs are tripled (or even quadrupled) in order to anticipate the possible breakage of certain lines.
Scientific breakthroughs and innovation
In this MUTANC-GEOTECH project, Gustave Eiffel University, the University of Nantes, and France Energies Marines propose to study soil-anchor interaction problems related to multidirectional and cyclic tensile loads. At Gustave Eiffel University’s geotechnical centrifuge, tests involving multidirectional and cyclic tensile anchor loads will be carried out on scale models. The advantage of placing these scale models in a macro-gravity field is that it generates the same stress conditions on the model as those applied to the full-scale prototype. Thus, a 1/100th scale model subjected to a macro-gravity field of 100×g (100 times Earth’s gravity) behaves like the full-scale system. These centrifuge tests will be used to calibrate a digital model of the ground-anchor system developed at the University of Nantes as part of the same project. Once this digital model has been developed, it will be used to study the temporal behavior of the ground-anchor system in the presence of the actual stochastic loading determined in the FEM’s MUTANC project.
Expected technical and economic impact
The MUTANC-GEOTECH project therefore targets:
- the development of a new loading system validated by centrifuge tests;
- a series of centrifuge tests producing results that feed into the digital model;
- a digital model that takes into account the cyclic behavior of the soil.
Through this objective of studying the “geotechnical” feasibility of sharing anchors in floating wind farm fields, the aim is to significantly reduce the number of anchors in an MRE field and thus the cost of installation and geotechnical investigations, as well as the maintenance of such fields.