Modal analysis-based initial axial force recognition method for jacket platform

Jacket platform is the marine structure that anchor piles to the sea floor, among which the leg is one of the most important components of fixed marine structure. Most of the existing stress and strain monitoring methods for offshore platform ignore the existing forces in the structures caused by deck load and installation errors before the monitoring, which cannot be ignored in the subsequent monitoring and evaluation. Based on this, a method for axial force identification of marine structures is proposed in this paper. The partial differential equation of free vibration of Timoshenko beams with axial force under the influence of damping is derived. This method can accurately identify the axial force of beams without knowing the boundary conditions. The simulation results of the single beam show that this method can be used to identify the axial forces of beams with various cross sections and sizes. Then, the method is applied to the axial force identification of the legs of a four-legged jacket platform. The results show that the method can be applied to the axial force identification of the legs with the relative error (RE) of the identification results is less than 6.5%.