Background
From a safety point of view, the probability of a vessel colliding during an avoidance maneuver by another vessel or drifting due to a propulsion failure can be considered to be significant.
On the other hand, digital simulations of ship collisions against fixed wind turbines such as jacket (Le Sourne, 2015) or monopile (Bela, 2017) and floating (Echeverry, 2019) wind turbines have clearly shown that for certain scenarios perfectly realistic, an impact at relatively low speed can lead to the collapse of the wind turbine on the deck of the ship. The consequences can be significant: loss of human life, perforation of the ship’s tanks causing pollution or even an explosion in the case of an LNG carrier, damage to the impacted wind turbines, rupture of the anchor lines leading to the drift of the platform and a collision of this one against other wind turbines in the park.
Scientific advances and innovation
The objective of the ColFOWT project is to develop and validate a fast and reliable collision analysis tool, specific for floating offshore wind turbines, based on analytical formulations (super elements derived from plastic limit analysis) coupled with a large rotational floating structure movement solver.
Expected technical and economic impact
By including the action of the mooring lines on the platform rigid body movements during and after the collision, the tool developed in ColFOWT will allow design offices to assess, at pre design stage, the consequences of a collision in term of ship and wind turbine damage. Thanks to its rapidity, the ColFOWT tool will also allow both the classification societies and the traffic regulatory authorities to simulate all the scenarios requested for a complete risk analysis. Situations that may be dangerous for the wind farm or/and for the different ships navigating in the vicinity will thus be identified.
Key project milestones
- October 2019 - Kick-Off of the project
- September 2022 - Closure of the project
Results
In a first step, Finite Element Analysis of the collision of an Offshore Supply Vessel against a Spar Floating Offshore Wind Turbine allowed to identify the main damage mechanisms as well has the significance of hydrodynamic effects. A deep study of the energy balance also allowed to highlight some limitations of Ls-Dyna / MCOL package.
In a second step, analytical models based on plastic limit analysis have been developed to assess the resistant force related to the different successive deformation modes. These models have been successively confronted to numerical results for high impact energies. However, it has been shown that the elastic contribution remains significant and must be considered when the impact energy is low or moderate.
In parallel, the impact response of a reinforced concrete slab has been simulated and several behavior laws implemented in Ls-Dyna have been confronted to documented experimental tests. Existing analytical models able to assess the slab resistant force have also been studied. Then, an analytical model based on closed-form expressions have been developed and successfully confronted to experimental results extracted from the literature.
Finally, the future experimental campaign (to be held at the end of this year) where reinforced concrete beams will be impacted has been prepared.
Publications and papers published
Publications:
- Echeverry, S., Márquez, L., Rigo, P., Le Sourne, H. (2020) Numerical crashworthiness analysis of a spar floating offshore wind turbine impacted by a ship. Developments in the Collision and Grounding of Ships and Offshore Structures, Proceedings of the 8th International Conference on Collision and Grounding of Ships and Offshore Structures (ICCGS) 004(2004), 85–95, 2020.
- Le Sourne, H. The super-element method for ship collision and grounding fast analysis, Keynote Lecture, Proceedings of the 5th International Conference on Ships and Offshore Structures (ICSOS), Glasgow, Sept. 2020.
- Ladeira, I., Le Sourne, H., Echeverry, S., Rigo, P. Assessment of the energy balance gap for ship-FOWT collision simulations with LS-DYNA/MCOL. Proceedings of the 8th International Conference on Marines Structures (MARSTRUCT), Trondheim, June 2021.
- Marquez, L.., Rigo, P. Le Sourne, H. Ship Collision Events Against Reinforced Concrete Offshore Structures. Proceedings of the 8th International Conference on Marines Structures (MARSTRUCT), Trondheim, June 2021.