Experimental and numerical investigation of dynamic characteristics and safe mooring criteria of moored outfitting ships under swell conditions

Abstract

Outfitting ships are characterized by a small draft and a large wind area. As a kind of unpowered ship, when subjected to strong lateral loads, excessive sway motion could cause cable breakage, resulting in potential ship damage or casualties. In this paper, physical and numerical model experiments have been carried out to investigate the effects of swells on moored outfitting ships. The data is analyzed in time and frequency domains to discover the relationship between swells, mooring patterns, ship motions and mooring forces. Subsequently, a numerical model is developed in AQWA, and in conjunction with the physical model experiments, safe mooring criteria for outfitting ships under swell are proposed. Results show that both reducing the sea severity and increasing the number of cables is effective in reducing the risk of cable breakage. The horizontal and heave motions of outfitting ships are controlled by swell period, while the roll and pitch motions are mainly controlled by own parameters. For the cables at different locations, the bow/stern line, breast line and spring line are mainly controlled by sway/yaw motions, sway motion and surge motion, respectively. Additionally, the safe mooring criteria could be widely applied to outfitting quays to ensure the safe operation.