Numerical Simulation Of Liquid Tank Sloshing Coupled Motion Of Single-point Mooring FLNG

With the increase of China’s new energy development in the South China Sea,the scope of exploitation has gradually shifted from shallow water to deep water.Pipeline transportation methods are no longer applicable.In this regard,FLNG,a large-scale LNG production and storage platform with unique advantages,has been proposed internationally.The tank sloshing phenomenon in the FLNG internal tank and the single-point mooring system make the hull motion response very complicated,so the related research has important engineering design reference value.Based on the open source platform OpenFOAM,this paper simulates and explores the tank sloshing coupled motion of a single-point moored liquid-filled FLNG in waves using the in-house developed ship and ocean hydrodynamic CFD solver naoe-FOAM-SJTU.Firstly,the accuracy of numerical wave generation of this solver is verified by making waves in an empty numerical wave tank.Then,by simulating the coupled motion problem of the simplified FLNG tank model with double liquid tanks in waves,the full flow field is solved using CFD method simultaneously.The accuracy and reliability of the solver are verified by comparing motion amplitude RAO results with experimental results.In order to investigate the sloshing coupled motion of the tank,research about the effects of wave frequency,tank filling ratio and wave height on the coupled roll motion of the liquid-filled FLNG have been done systematically.By comparing the motion response time series and the extracted moments inside and outside the liquid tank wall.It is found that whether the sloshing phenomenon intensifies the amplitude of the coupled motion of the tank,is mainly determined by the phase difference of the moment on the inner and outer wall of the liquid tank.And the amplitude increase or decrease is mainly depend on the amplitude of the moments.After that,this paper constructs a multi-tank FLNG ship model with the reference of physical experiments.And the free decay motion of the model is simulated.By comparing the numerical simulation results and physical test results of the free decay period of the FLNG model,the accuracy of the model structure and parameter configuration is verified.Then,the mesh generation method and the suitable mesh quantity for the simulation are given by the work of grid convergence verification.Referring to the results of the experiment,the amplitudes RAO of the sloshing coupled motion response of the FLNG tank under various incident wave frequencies are compared in beam and head waves.And the accuracy and reliability of the solver are verified.On this basis,by comparing the results of the empty tank cases,the effects of tank filling ratio,wave frequency and wave direction on the motion response of liquid-filled FLNG are investigated.The roll motion of FLNG in beam waves is the most sensitive to the sloshing influence.At the same time,the paper shows the flow field information inside and outside the FLNG tank,and explains the interaction between the wave and the hull.Finally,this paper implements a numerical simulation of the six degreeof-freedom motion of liquid-filled FLNG under single-point mooring.The coupled effects of mooring system,wave environment and tank sloshing on the overall motion of the hull are analyzed.By comparing the FLNG motion time series,the flow field inside and outside the tank and the mooring force before and after single-point mooring and liquid tank filling,it is found that in beam wave condition,FLNG will rotate around the mooring point under the wave load excitation.During this process,the amplitude of roll motion angle will gradually increase,which will threaten the safety of FLNG.At the same time,due to the multi-tank design of FLNG,the fluid sloshing phenomenon in tanks will be obviously reduced,thus improving the stability of the ship.The relevant results of this paper can provide reference for engineering practice.