Analysis On Hydrodynamic Interactions Between Side-by-side FLNG And LNGC Under Different Wave Directions

As the first choice for developing stranded and marginal gas fields,Floating Liquefied Natural Gas(FLNG)system has its broad application prospects and advantages in the future.The pattern of gas field development with FLNG and LNGC greatly decreases the costs of pipeline transportation,and is far from populated areas to ensure safety and avoid pollution.Nevertheless,the cryogenic nature of liquefied natural gas(LNG)determines a small distance between FLNG and LNGC with a side-by-side configuration in offloading operation.The hydrodynamic interactions of the side-by-side floaters under unexpected weather conditions,in particular occasional oblique waves,might induce high risks and challenges in engineering applications.Thus,it is necessary to implement an accurate prediction of side-by-side vessel motions to ensure safe operability.In this article,hydrodynamic analysis of the side-by-side FLNG and LNGC system was carried out both numerical and experimentally,under oblique and head waves,to provide guidance for engineering practice.The major content of this paper includes:1.Calibrate the side-by-side numerical model through model tests and validate its effectiveness with experimental results.Then,based on the decay test results,the influence on roll damping induced by multi-body hydrodynamic interactions and different restriction patterns are further investigated.2.The damping lid method is adopted to modify the traditional potential flow model,in order to accurately calculate and analyze the resonance of gap free surface.The free surface elevations in the gap region are obtained through model tests to provide reference for lid damping selection.Gap wave elevations are then calculated to analyze the influence of different wave headings and frequencies on gap water resonance modes.3.Based on the well-tuned lid damping coefficient,hydrodynamic performances ofthe multi-body system is calculated and analyzed.First-order hydrodynamic coefficients obtained from frequency-domain calculation are used to investigate the interactions between adjacent vessels.Motion RAOs under various wave headings are achieved and compared with experimental results to study the influence of wave headings on the couplings between different modes and the hydrodynamic shielding effects.Lastly,mean drift forces of both vessels are discussed under various wave headings.4.The time-domain simulation program has been developed based on the frequency-domain results.A novel scheme is proposed to solve the divergence of time-domain calculation.Relative motions of FLNG and LNGC are calculated with the program to analyze the influence of wave headings in terms of the amplitude and phase shift.Further,high-frequency resonance of relative motions is studied considering the resonance mode of gap free surface.