Characteristic Analysis Of The The Gap Resonance In The Offloading Process Of The Floating Lquid Offloading System

There are multiple coupling issues during the offloading/transfer operation of the side-by-side moored floating platform system.E.g.the coupling between the wave motion,the ship motion,the sloshing inside the liquid tank and the mooring system.The highly nonlinear free surface resonance inside the gap between the side-by-side moored floating bodies is important for carrying out the coupling analysis of the system,and is highly valuable for theoretical investigation and engineering applications.In this paper,the gap resonance characters of the floating platform/transport vessel alongside moored system are deeply analyzed based on fluid dynamics theories and existing potential/viscous flow solvers.The major works of this paper are summarized as follows:(1)Firstly,numerical simulations of the two dimensional gap resonance are carried out based on the open source CFD solver OpenFOAM through programming.The relationships between the horizontal force amplitudes on the floating bodies,the viscous dissipation inside the narrow gap,and the surface elevation inside the narrow gap are investigated to obtain the change rule of horizontal force amplitudes on the floating bodies versus the incident wave frequency.Results indicate that the hydrodynamic force amplitudes obtained by the viscous solver are reasonable,the viscous effects cannot be ignored.The change tendency of the horizontal force amplitude on the weather side structure is influenced by the phase retardation of the elevation inside the gap relative to the wave phase in front of the weather side structure.While the horizontal force on the lee side square structure depends on the fluid vibrations in the gap.(2)In order to quickly and accurately capture the obvious three dimensional narrow gap resonance of the floating platform/transport vessel alongside moored operation system,the linear potential flow software AQWA is used to solve the surface elevation inside the gap and the hydrodynamic force amplitudes on the floating bodies(the floating platform and the transport vessel)under different incident wave frequencies and wave directions,and the resonance condition when the hydrodynamic force on the floating bodies are significantly amplified is obtained.Results indicate that there are multiple resonance modes for the 3D narrow gap resonance problem.The low frequency modes(within the range of wave frequency)mainly performs as standing waves transferring along the longitudinal direction of the gap.The horizontal force on the transport ship is the maximum when it is over the upstream side and the wave frequency approaches the first-order gap resonance mode.(3)In order to accurately calculate and analyze the narrow gap resonance characteristics of the operating system,based on the viscous flow solver STAR-CCM+,the horizontal force and motion characters of the transport vessel when it is over the upstream side and the wave frequency approaches the first-order gap resonance mode are investigated.Results indicate that the horizontal force on the floating bodies is highly nonlinear.As a consequence of the free surface oscillation inside the gap,when the vessel is swaying and the rolling,it will be pushed away from the floating platform,towards the wave incident direction.Furthermore,as the gap resonance frequency approaches twice the natural roll frequency,prominent coupling between the gap resonance and the second harmonic of transport vessel roll can be observed.