Numerical investigation of hydrodynamic interactions and cable dynamics during parallel replenishment at sea

During parallel replenishment operations, the hydrodynamic interaction between the two ships is a key factor related to operational safety. In this study, a computational fluid dynamics approach is employed to investigate the coupled mechanisms of ship-to-ship hydrodynamic interaction and cable tension dynamics under Sea State 4 conditions. The analysis focuses on a supply vessel (KCS) and a receiving vessel (DTMB 5415) connected by a highline rig. Systematic numerical simulations are conducted to quantify the influences of forward speed, lateral separation, wave heading, and cable stiffness on the coupled fluid–structure response. The findings demonstrate that cable tension exhibits pronounced sensitivity to wave heading, relative vessel positioning, and cable stiffness, while showing comparatively weak dependence on small variations in low forward speeds. Increasing cable stiffness is shown to degrade the seakeeping stability of the smaller vessel and elevate the risk of cable failure, particularly in oblique seas. From an operational perspective, the results suggest that maintaining moderate forward speed and transverse spacing, and avoiding the use of excessively stiff cables, is essential to enhance safety margins during parallel replenishment operations.