Research On Kinetic Characteristic Of Semi-submerged Berthing Platform

The semi-submerged berthing platform is a new kind of flexible mooring system with good property and comparatively low fabrication cost. It will be one kind of the platforms in exploiting offshore petroleum and natural gas in future. When a ship berths, the semi-submerged berthing system absorbs power through changing its berthing platform's position. So the interaction force between the ship and the berthing platform is smaller than the one in the traditional berthing mode which is through fixed dock's rubber fenders.This paper introduces the operating principle of the semi-submerged berthing platform and its characters. The mathematical model is composed of semi-submerged berthing platform motion model in waves. The boundary progressive matching method and the eigenfunction expansion method are used to obtain the semi-analytical solution of fluid velocity potential field for an isolated cylinder.Based on flexible berthing system's model experiment, we analyzed all factors influencing the boats'mooring and berthing, and we get the moving rule of the semi-submerged berthing platform.(1)Through model experiments, the natural period of sway of the semi-submerged platform in dead water is 15s which is obtained by the method of spectrum analysis. The period of common sea wave is in the scope of 7～12s. So the natural period in the direction of sway of the semi-submerged platform is out of the frequency-domain scope of the common sea wave.(2)When berthing, the displacement of the platform and the tension of mooring chains are increasing greatly as the velocity and weight of the ship are increasing. If the velocity of ship is smaller, the function of berthing platform's absorbing power won't be externalized. And the force of percussion will be larger if the velocity of ship is bigger. So the velocity of ship should be between 0.2m/s and 0.5m/s when berthing.(3)When mooring in the sea, the impact of platform fender is greatly increasing as the depth of water is rising. The displacement of the platform and the tension of mooring chains have the same tendency.(4) When mooring in the sea, mooring chain's pre-tension can increase while buoy's net buoyant force increases, as a result, the rigidity of berthing force platform will increase and the displacement will go in the scope of design. However, if the net buoyant force is too big, the mooring chain's tension will greatly increase. So the net buoyant force rational or not is the key if the flexible berthing platform will succeed.