The Study Of Coupled Motion Response Of Mooring Offshore Platform Near The Reef Island With Ship Berthing

Due to the complex topography of the reef and the severe change of water depth near the shore,the transport ship is unable to be berthed beside the island which makes it difficult for large machinery and equipment to be transported to the island.This problem can be solved by using the mooring system to limit the motion of the platform to keep the stability of its position so that the transport ship can be berthed beside the platform,and then supplies can be sent to the island by the shallow draft floats barge which can back and forth between the platform and the island.However,due to the complex reef environment,the development of the dynamic response prediction technique for the floating platform and its special mooring scheme is not mature enough,and the interaction between the ship and the floating platform will lead to complex changes in the motion response of the floating platform.Therefore,the accurate prediction of the motion response of the floating platform near the island reef has an important guiding role in the security and feasibility of the floating platform and its mooring system.This paper uses software AQWA based on potential flow to analyze the hydrodynamic performance and motion responses of the floating platform and the tension of the mooring system.At the same time,the numerical results are compared with the experimental results.The major works and research achievements of this paper are as follows:The LINE module of the software AQWA is used to make frequency domain analysis on hydrodynamic force of the floating platform in order to get the added mass,radiation damping and the amplitude response operator under different wave angles,first order wave force and the two order wave force and other hydrodynamic coefficients under operation and survival conditions when the platform is in the environment of deep water or near the island reefs.FINE/Marine software is used to obtain the wind coefficient and flow coefficient at different angles under operation and survival conditions.With the application of DRIFT module of AQWA software,the numerical simulation of the motion response of the floating platform is carried out under a total of 74 kinds of working conditions when the platform is in the environment of deep water or near the island reefs to get the duration curve of six degrees of freedom motion of the platform and the calculation results of 74 kinds of working conditions are classified and analyzed according to the deepwater environment,the shallow water environment,the working condition,thesurvival condition,the wave direction,wave parameters,the wind direction,wind parameters,the flow direction and flow parameters.The results show that: the motion response of the platform near the island reef is generally reduced compared with that of deep water.When the platform is under working condition,the amount of motion of the platform and the maximum tension of the cable generally increase with the increase of the incident wave spectrum peak period and the sensible wave height.The distribution law of tension of the mooring line is affected by the wave direction and the wind direction.It is the tension value of the mooring cable instead of the distribution law of tension of the mooring line that is affected by the flow load.When the platform is under survival condition,with the increase of spectral peak period,the three degrees of freedom motion of surge,sway and yaw are reduced,the two degrees of freedom motion of heave and pitch are increased,the motion of roll is basically equal and the pulling force of the mooring system is decreased.In the residual state,the motion response of the floating platform is slightly increased except for the sway and pitch and the maximum tension of the mooring system is reduced.Not only the stress but also the tension distribution of the mooring system are affected by wind direction.It is the tension value of the mooring cable instead of the distribution law of tension of the mooring line that is affected by the flow load.The LINE module of the software AQWA is used to make frequency domain analysis on hydrodynamic force of the floating platform in order to get the added mass,radiation damping and the amplitude response operator under different wave angles,first order wave force and the two order wave force and other hydrodynamic coefficients under operation conditions when the ship docked to the platform.With the application of DRIFT module of AQWA software,the numerical simulation of the motion response of the floating platform is carried out under a total of 15 kinds of working conditions when the ship docked to the platform to get the duration curve of six degrees of freedom motion of the platform and the calculation results of 74 kinds of working conditions are classified and analyzed according to the wave direction,wave parameters,the wind direction,wind parameters,the flow direction and flow parameters.The results show that: the motion response of the platform with the ship docked is generally reduced compared with that with no ship docked.The motion response of the platform generally increases with the increase of the incident wave spectrum peak period and the sensible wave height when the ship docked to the platform.The maximum tension of platform mooring system decreases slightly when the ship docked to the platform.Due to the asymmetry of ship's head and tail,the distribution of mooring cable tension is changedby ships in some sea conditions.The pool test is carried out and the experimental datas are analyzed.The results of the numerical simulation are compared with the test results.The results show that the data results of the numerical simulation and the model test are in good agreement.