Evaluation of ice-induced fatigue life for a vertical offshore structure in the Bohai Sea

In China, the oil and natural gas resources of the Bohai Sea are mainly marginal oil fields. Therefore, it is necessary to build both ice-resistant and economical offshore platforms. These platforms underwent severe ice-induced vibrations during winter season, which not only can disturb the crews and endanger facilities available on the platforms, but also may evoke fatigue damage in tubular joints. Hence, it is vital to carry out a fatigue analysis for ice-resistant structures, which are built in the Bohai Sea. At the present, a holistic approach with the aim of analysis of ice-induced fatigue life is still not available for vertical offshore structures. Based on the field observations over several years in Bohai Bay, in this study, an interaction between ice and a vertical-leg jacket structure is analyzed. Then, a fatigue life assessment method is presented for sea ice conditions and structural characteristics, which would be applicable to the Bohai Sea as well. Eventually, a jacket structure in the Bohai Sea is numerically simulated using ANSYS software. Besides, a comparison regarding the fatigue damage of the jacket structure under steady-state and random vibrations is made, and the fatigue life is accordingly calculated using the total damage.