Experimental And Numerical Analysis Of The Collision Between The Ship And The Offshore Wind Turbine

With the economic benefits of offshore wind farms being paid more attention by more countries,the possibility of collision between ships and offshore wind turbines(OWTS)is becoming higher and higher in the complex marine environment.Offshore wind turbine is a typical high-rise structure with heavy "head".The impact on the bottom may cause the deformation of the tower,and even the collapse and instability of the whole structure.Therefore,it is of great significance and urgency to study the collision between ship and offshore wind turbine.In this work,based on a 4MW monopile OWT project and corresponding international standards for the collision between ships and OWT structures,the scale model test and the nonlinear finite element method(FEM)code LS-DYNA have been both used for the investigation of the dynamic responses of the collision between ships and OWT structures with or without a proposed new crashworthy device.The complex collision effect of the contact nonlinearity,the material nonlinearity and the geometry large deformation has been taken into consideration.The main work are summarized as follows:(1)Based on the dynamics similarity,the model test system of the collision between a ship and a monopile OWT has been set up.The dynamic characteristics of the monopile OWT structure(with or without a crashworthy device)under typical ship collision cases have been experimentally investigated.The results indicate that the ship impact force on the OWT without a crashworthy device is mainly depended on the ship impact energy.The new crashworthy device with combined outer steel shell and inner rubber pad can effectively reduce the responses of the impact force and the nacelle acceleration.The open hole design of the protective device is more conducive to the plastic deformation of the outer thin-walled steel shell,and through the deformation to absorb the energy generated by the collision,which is conducive to the further optimization design of the protective device.(2)Based on the LS-DYNA code,the numerical results of the dynamic responses of the ship-OWT collision(with or without a crashworthy device)have a good agreement with the corresponding model test data,so the availability of the numerical model has been well verified.The information of the collision system energy variation,the stress contour and the plastic deformation from the numerical simulation,is helpful for better understanding the dynamic response characteristics of the ship-OWT collision.(3)The new crashworthy device with combined outer steel shell and rubber pad can take advantage of the rubber pad to prolong the ship collision contact duration,and effectively reduce the amplitude of the impact force.The outer steel shell can use its plastic deformation to absorb the ship collision energy,and protect the main OWT structure.For the same crashworthy device,its anti-impact performance gradually decreases as the increase of the ship collision energy.That’s because the structure deformation energy of the crashworthy device has its upper limit.When the ship collision energy is far over the potential structure deformation energy of the crashworthy device,the anti-impact performance of the crashworthy device will reach its limit.