Abstract
Offshore wind turbines in the vicinity of ship traffic are exposed to increased risks of ship collisions. To better understand the impact mechanism, this paper evaluates the dynamic responses of a monopile-supported wind turbine under ship impacts, using both numerical and analytical methods. The nonlinear finite element method is applied during the numerical simulations, and the wind load effects, soil conditions, and rigid and deformable ship bows are considered. The analytical approach, originally developed based on the energy method, is extended here to address the damping effects of monopile-supported wind turbines. In the case study, the impacts are studied between a 4600-ton vessel and a 5-MW offshore wind turbine. The effects are presented of the aerodynamic damping, ship impact velocity, mean wind speed, wind direction, and ship bow stiffness on the collision responses. A comparison between the numerical and analytical results shows a generally good agreement for the maximum contact force. Under an impact velocity of 1 m/s and 3 m/s, the discrepancy between the two methods is 5% and 7%, respectively. The developed engineering approaches can be used to address accidental collision problems between ships and bottom-fixed offshore wind turbines.
Highlights
Offshore wind energy is an attractive form of renewable energy resources
To obtain more accurate response evaluation of a monopilesupported offshore wind turbines (OWTs) subjected to ship impact, this paper considers the interaction between the wind loads and the motion of OWT in the dynamic analysis
The calculated natural frequencies of the lowest eigenmodes in the fore-aft and side-side directions are approximately 0.24 Hz. These results match those of the full system predicted by the HAWC2 code, which indicates that the simplified OWT model can reflect the structure dynamic behavior with a reasonable accuracy
Summary
Offshore wind energy is an attractive form of renewable energy resources. Since 1990s, the offshore wind industry has been expanding successfully. Offshore wind farms have been constructed across more than 10 European countries. Accidental events like ship collisions are not yet addressed in practice, probably due to the marginal profitability of the offshore wind energy sector and the low occurrence rate of such events. As an increasing number of offshore wind farms are located close to ship traffic routes, the risks of collisions between ships and OWTs increase [7]. Dropped objects of the damaged OWT can pose threat to ship safety. These scenarios are not fully understood because of the complex dynamic interactions between a ship and an OWT during a collision, the collision loads from ships are very important for the structural design of OWTs
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