Monopiles are the most common form of foundations for offshore wind turbines. Monopile foundations support slender flexible tower and they withstand hydrodynamic and aerodynamic forces due to ocean and wind waves respectively. In order to reduce their cost, wind turbines must have a powerful generator and a minimum overall weight. This has the consequence of making the structure of the wind turbine sensitive to dynamic loading even at low frequencies.
Scientific advances and innovation
The state of the art in the behavior analysis of offshore wind turbine foundations is essentially based on methods involving the ground-foundation interaction (in this case soil-monopole in the present case of wind turbine placed on a large diameter monopile) neglecting the interaction with the tower. In addition, the analyses are usually performed in static. However, the wind turbine is subjected to hydrodynamic and aerodynamic forces due to the swell and the wind respectively and which are of dynamic nature.
The originality of this project is to carry out an analysis taking into account the dynamic nature of the waves and wind forces and considering in addition the interaction with the structure because this interaction can have a very great influence on the answer sought (displacement and rotation induced at the top of the monopile and at the top of the tower). Since the dynamic response of the system can be influenced by the variability of soil properties and the degradation of its properties during dynamic loading, both aspects will be considered in this project.
Expected technical and economic impact
The DYNA project focuses on the dynamic analysis of the soil – monopile – structure system using the finite element method and considering wave and wind loads with their dynamic and random nature.
Beforehand, a validation of the numerical results which will be obtained in the case of a static loading and a single monopile (without tower) will be carried out via experiments, the objective being to validate the numerical modelling procedure adopted to model the soil-monopile interaction.
The computational means developed will eventually allow for more reliable and economical sizing, thus reducing the conservatism of current approaches. The software developed will be use by the companies involved in the sector of marine energy.
Key project milestones
- October 2018 - Begining of the project
- October 2019 - Deterministic dynamic analysis
- April 2020 - Taking into account the uncertainty of the loads cases
- October 2020 - Taking into account soil variability
- April 2021 - Taking into account the degradation of the rigidity of the soil
- October 2021 - End of the project: Theisis defense and publications in international journals
Development of numerical tools for the analysis of wind turbine foundations that may be used by practical geotechnical engineers working in the area of offshore structures.