Study On Mechanical Properties Of Offshore Platform Derrick Considering Corrosion Damage

Offshore derrick is an important part of offshore platform,and its safety performance is of great significance in the overall structure of the platform.In this paper,the mechanical properties of the derrick structure under multidimensional ocean environment are studied by establishing a platform-derrick overall structure model.The main research contents and results are as follows:Firstly,using the finite element method,the single derrick model and the platform derrick numerical model are established,and the static analysis and modal analysis are carried out respectively.Through comparison and analysis,it is proved that the necessity of the analysis of the mechanical properties of the offshore derrick by the platform and the holistic model of the derrick is verified.The accuracy and rationality of the numerical model are verified by measurement.On this basis,the "small scale" entity unit is adopted in two local locations of the joint and the bottom of the derrick,and the multi scale model is established,in which the MPC method is used to connect the cross scale,and the stress gradient distribution and the stress concentration position of the local position are analyzed.At the same time,4 different degrees of corrosion damage are analyzed,and the influence of damage on the structure performance of the platform is obtained.Based on the above model,the performance of derrick structure under sea wind environment is studied.On the basis of the study on the characteristics and analysis methods of the sea wind load,this paper makes a specific analysis on the normal operation and the two operating conditions of the storm self storage,focusing on the two different wind directions on the front and back,and obtains the mechanical characteristics of the structure,the influence of the damage on the structure and the distribution of the stress distribution of the local small scale.The performance of derrick structure under wave environment is studied.The Morison wave theory is used to simulate the wave load of the structure.According to the principle of similarity ratio,it is applied to the structure of the platform.The mechanical characteristics of the structure,the influence of the damage to the structure and the distribution of the stress in the local small scale are obtained by analyzing the working conditions of two kinds of sea waves.The performance of derrick structure under seismic loading is studied.By using the time history analysis method,the three-dimensional Tianjin wave is selected as the excitation,the transient dynamic analysis of the platform structure is carried out,the mechanical characteristics and the displacement response of the structure are obtained.At the same time,the seismic response of the corrosion damage structures of different degrees is analyzed,and the corresponding change rules are found.The above analysis will provide reference for subsequent safety evaluation of offshore platform derrick.