Effects of Flow Conditions on the Response and Fatigue of a Suspended Gooseneck Riser Under Complex Ocean Currents

In the secondary adjustment project of Area 12389 in the Penglai 19-3 Oilfield, local seabed scouring has led to a suspended condition at the bottom gooseneck section of the platform riser. The loss of support from structures such as sandbags makes it highly susceptible to local buckling, structural fracture, and fatigue damage. This study aims to employ numerical simulation techniques to conduct in-place strength analysis and fatigue analysis based on the gooseneck suspended issue, thereby systematically evaluating the fatigue strength performance and potential failure risks of typical offshore platform risers in the Bohai Sea. The research is based on a previously developed and validated fluid–structure interaction numerical model for riser vortex-induced vibration (VIV) using the ANCF-VDP method. It systematically analyzes the VIV response and fatigue damage distribution of water injection risers under various inflow angles and inflow velocities. The results indicate that regarding the influence of inflow angle, the riser structure is highly sensitive to the flow direction. Under a 90° side-flow condition, the horizontal section is prone to significant transverse VIV response, leading to stress concentration and accelerated fatigue damage. Peak stress is primarily distributed at the gooseneck section and structural bends, constituting key areas of fatigue risk. Nevertheless, the annual fatigue damage under all inflow angle conditions meets the design life requirements. Variations in inflow angle within the 0°–90° range have an insignificant impact on the riser stress state, indicating a substantial safety margin for the structure. The riser strength varies nonlinearly with inflow velocity, but the UC values remain far less than 1 across all cases, indicating a considerable safety margin under dynamic loads. This study systematically reveals the environmental load response mechanisms, fatigue damage evolution laws, and strength characteristics of suspended gooseneck risers. It provides an important scientific basis and technical support for subsequent riser design optimization, operation and maintenance strategy formulation, and risk control.