Offshore engineering needs to face huge waves and the impact of waves on the structure, and its structural strength and safety are crucial aspects in the design of offshore engineering structures. In this paper, based on the three-dimensional potential flow theory, the theoretical model of ocean engineering structure is established by using the partial differential equation of motion in time domain, and the finite element model of semisubmersible ocean platform is constructed by combining with finite element software. The safety of the ocean engineering structure is evaluated, analyzed and calibrated on the basis of considering the environmental wave loads, current loads and wind loads. Then, based on the limit state equation of the cracked structure, the PNET method is used to calculate the failure probability of the cracked structure of the offshore engineering, and the durability assessment of the offshore engineering structure is realized in this way. In the motion response of semisubmersible offshore platform, the change trend of transverse oscillation and longitudinal oscillation motion is opposite. After the wave period increases to 30~50s, the amplitude of the vertical oscillation response tends to be about 1.5 at each wave direction angle. The response amplitude of the bow rocking motion tends to be close to zero at the wave angles of 0° and 90°. 130° is the most dangerous wave direction under the LC class sea state, and the peak tension of the mooring structure of the offshore engineering platform reaches 3252.74kN, but the safety coefficient is still higher than the threshold value of 2.58%. Solving the durability of offshore engineering structures by limit state equations can guide the inspection and repair of offshore engineering structures. Relying on the time-domain partial differential equation of motion combined with finite element software can realize the effective analysis of motion response and limit state of offshore engineering structures, which can help to improve the safety and durability of offshore engineering structures in high-pressure environment.
