LNG vessel mooring safety analysis

LNG ship is a special ship for transporting liquefied natural gas at low temperature of 163℃, which is a kind of "super refrigerated car at sea" and has been described as the "crown jewel" of the world shipbuilding industry. At present, the cargo delivery of LNG international trade is mainly realized by LNG carriers between LNG exporting stations and LNG receiving stations, and LNG ships must be safely moored at LNG terminals before loading at LNG exporting stations or discharging at LNG receiving stations; therefore, it is urgent to conduct in-depth research on the mooring safety of LNG ships.

Mooring safety analysis studies of LNG vessels are usually conducted using OPTIMOOR software simulations, which is a computer software for ship mooring safety analysis studies and is widely used in the industry to audit and confirm the integrity of ship mooring arrangements. The mooring safety analysis of LNG vessels is also based on this software, where standard environmental constraints and LNG terminal layout parameters are inputted to derive values of vessel cable tension, quay bollards, bollard hooks and rubber fenders under various conditions based on this terminal, and compare these values with their design allowable values to determine whether the vessel can be safely moored.

To make the berth of the receiving terminal compatible with as many LNG vessels as possible, the following optimization measures can be taken: (1) Select the LNG vessel type with smooth parallel midbody to berth at the LNG terminal as far as possible. Generally speaking, the parallel midbody of a thin-film LNG vessel is much straighter than that of a spherical LNG vessel, and the safety mooring factor of a thin-film LNG vessel is higher for the same terminal. (2) On the premise of meeting the structural safety of the receiving terminal, the rubber fenders should be modified, the center distance of the rubber fenders should be shortened, and the base elevation of the rubber fenders should be increased. (3) In the design stage of LNG receiving terminal, the spacing between berthing piers should be as small as possible and the elevation of berthing piers should be as large as possible to ensure the reasonable spacing and elevation of rubber fenders.

Figure 1: OPTIMOOR Modeling Layout