Evaluation of the semi-submersible oil platform under different operational scenarios with a mooring line failure

This study presents the dynamic responses of a semi-submersible platform through a time-domain numerical simulation, during which four distinct mooring configurations were examined. During a simulated storm condition, one of the four mooring lines was severed in each scenario to assess the impact on the remaining mooring lines and the production riser. The semi-submersible platform, production riser, and position mooring lines are included in the numerical simulation. The Amirkabir semi-submersible platform, located at a depth of 713 m, was used in this study. First, stability and free decay tests were investigated at various vertical center of gravity (VCG) positions. Subsequently, the dynamic responses of the platform were analyzed under three different directions. Irregular waves, following the JONSWAP wave spectrum, were employed to simulate extreme sea conditions directed toward the platform. The mooring lines and riser responses were evaluated utilizing the potential flow-based boundary element method within the ANSYS-AQWA software in the time domain. The results indicated that the failure of mooring lines did not lead to a significant increase in riser tension, and riser displacement increased when a mooring line failed. Also, the study discusses the mooring line tensions observed under three different wave directions when one mooring line was broken.