Ice Induced Vibration Analysis Of Offshore Platform Structure Based On Cohesive Element Method

In the cold area,ice load is one of the main loads borne by offshore platforms.The ice induced vibration caused by continuous ice load also has a serious adverse impact on the structural safety of offshore platforms.Taking the jacket platform of offshore booster station as the research object,this paper simulates the process of sea ice impacting the jacket platform based on the cohesive element method,numerically analyzes the ice induced vibration effect of the offshore platform in the process of different ice velocity and ice downward collision with the sea ice,and studies the damping effect of conical anti-collision device and vibration isolation device on the ice induced vibration of the offshore platform.The main work of this paper is as follows:(1)Based on the cohesive element,the sea ice calculation model is established.The initial finite element mesh is split by python programming,and the zero thickness cohesive element is embedded on the boundary of each solid element.The feasibility of sea ice simulation by cohesive element method is further verified by comparing with the standard calculation results and the open data in uniaxial compression experiment and Hamburg ice pool experiment.(2)The finite element software ABAQUS is used to simulate the sea ice collision with the offshore platform,and the ice induced vibration of the offshore platform with different ice velocity and different ice downward is compared respectively.It is found that the maximum horizontal acceleration of the deck is directly proportional to the ice velocity.The greater the ice velocity,the greater the maximum horizontal acceleration of the deck.The time history curves of ice loads under different ice directions are calculated respectively.It is concluded that due to the geometric asymmetry of the platform structure,the jacket platform of offshore booster station has the maximum acceleration at 150 degrees and 210 degrees and the minimum acceleration at 0 degrees.The 150 degree and 210 degrees ice directions are the most dangerous ice directions of the jacket platform of booster station.(3)The damping effect of the cone angle of the anti-collision cone on the jacket platform is discussed.In the case of single cone,when the cone angle is between 30 degrees and 60 degrees,the flat ice mainly occurs bending failure,the overall ice load is small,and the ice load increases with the increase of cone angle;When the cone angle is 75 degrees,the main failure type of flat ice changes from bending failure to continuous brittle extrusion failure,the overall ice load increases greatly,and the ice force time history curve has no obvious periodic change and is continuous;When the cone angle is 90 degrees,that is,the conical anti-collision device is transformed into a vertical cylindrical structure,the flat ice almost only has continuous brittle extrusion failure,and the horizontal ice load has the maximum value under the same conditions.The ice induced vibration of the platform under different cone angles is calculated.The anti-collision cone with a cone angle of 52.5 degrees has the best vibration isolation effect,and the unit reduction rate a is proposed to measure the vibration reduction effect of the anti-collision cone under the unit cost.It is calculated that the anti-collision cone with a cone angle of 60 degrees has the highest cost performance.(4)The damping effect of vibration isolation device on jacket platform is discussed.The calculation shows that the vibration isolation layer has a good vibration reduction effect,and the vibration reduction effect decreases with the increase of ice velocity.Finally,it is calculated that the maximum acceleration of the deck is reduced by 79.9% compared with no vibration reduction measures when the vibration isolation support and anti-collision cone are added at the same time,which further shows that the combined action of vibration isolation support and anti-collision cone is a better vibration reduction measure.