Analysis On Pipe-laying Vessel Motion Response And Mooring System

In order to maximize the utilization of the ships,the paper mainly considers an anchor moored positioning pipeline layer whose working depth is 40 m and after it completed the Hong Kong side tonggu waterway of the submarine pipeline laying task successfully, for the purpose of reusing it in relatively deep water in the East China Sea and improving its pipelaying ability, this paper studies properties of the vessel mooring system under various loading conditions. The main research contents and principle components of the results are as followings:(1) Based on three dimensional potential theory with zero speed. The hydrodynamic characteristic of the vessel is studied, including the added mass, damping matrix, RAO of vessel motions and first order and second order wave force. Moreover the short term statistic and short term responses of the vessel motions are carried out.(2)The vessel and mooring system model is created. Properties of the whole system are analyzed, including the decaying line of the vessel motions in six degree freedom and vessel motions and the effect tension of the mooring lines are calculated in time domain.Effect of various mooring layout and mooring length is considered. The limit operated sea condition is obtained.(3)Influence of existence of roller on hydrodynamic characteristic of the vessel is studied. The tensile stress strain and bending stress strain of the pipeline effected by the vessel motions are studied, in turn,the impact of pipeline on the properties of mooring system is considered. The load condition includes the different environment directions and various length of sagbend and diverse tension of upper end of pipeline.Some main conclusions are obtained base on the research:(1)The natural period of heave,roll and pitch is 7.5s,6.3s and 11.2s respectively. The maximal short term statistic values for heave, roll and pitch are 0.28 m, 3.5deg and 0.15 deg.(2)Heave and roll and pitch motion is given priority to with the wave frequency energy,while surge,sway,yaw motion and the mooring tension is given priority to with low frequency energy. Different mooring layouts contribute to different vessel motions and mooring tensions.(3)Translational motion of the vessel has far greater influence on the stress strain of pipeline than shake motions. The pipeline also has significant reaction on mooring system and different wave directions cause various impact on the six freedom motions. The various length of sagbend and different values of the upper end of pipeline have significant impact on the surge motion and have greater influence on the tension of mooring lines.