The Side-by-side Mooring Mode Study Of Super Large LNG-FSRU And LNG Carrier

As a kind of floating LNG receiving terminal,LNG-FSRU(floating storage and regasification unit)has a large of advantages of low cost,short construction period and high flexibility.With the application of clean energy,it has a broad development prospect.However,for the operation of such super large liquefied natural gas ships,especially the handling and transmission operation of LNG-FSRU,When it is under strong wind and wave loads,ship motion response becomes too large,the mooring line will bear great tension,fracture accident may occur due to the lack of rope strength.Finally,it will do great damages to the ship and terminal.At present,the main mooring modes used for LNG-FSRU in the world are single point mooring system,dynamic positioning system,multi-point mooring system,etc.The most commonly used are single point mooring system(SPM)and dynamic positioning system.However,the dock multi-point mooring system and STS mooring system of LNG-FSRU are still in the initial stage of domestic and foreign research.Therefore,it is an important technical problem that the mooring motion response forecast of single point mooring,dock mooring,side by side mooring of LNG and LNG-FSRU to be solved.The study of mooring system design and multi-body coupling movement response are also important to guarantee the transportation safety of LNG-FSRU.In this paper,the hydrodynamic analysis and time domain coupling dynamic response which include LNG-FSRU single point mooring,dock mooring and external transport mooring system are carried out based on the three-dimensional potential flow theory.The LNG-FSRU hydrodynamic performance induced by slight wave is analyzed in this paper.At the same time,we get rules of the added mass,the radiation damping,and the motion response amplitude operator that change with draft and the incident angle of wave.Based on the hydrodynamic calculation results,a preliminary mooring design of 270000 cubic meters LNG-FSRU dock mooring and 350000 cubic meters LNG-FSRU soft yoke single point mooring are carried out.We calculate and analyze the dynamic response of the mooring system under the irregular wave,wind and flow.With reference to the domestic and international similar cases of large-scale ship-to-ship mooring,the LNG moored to the LNG-FSRU operation is carried out on two typical mooring modes: dock mooring and single point mooring.We adopt the combined method of normative design,theoretical analysis and numerical simulation,and establish the theory and numerical analysis model of LNG carrier and LNG-FSRU.Considering the combined operating conditions of different water depths,drafts and external ocean environment combination of wind,wave and flow,we determine the selection and layout of mooring cables,fixed and floating type fenders.Then we conduct the numerical analysis calculation about the LNG-FSRU dock mooring,LNG-FSRU soft yoke single point mooring and side by side mooring of LNG and LNG-FSRU.According to results of numerical calculation,we carry out statistic analyses about ship movement characteristics,cable tension forces and fender pressures.And then optimize mooring system layout and parameters,provide reference for mooring equipment selection.In this paper,LNG-FSRU single point mooring system,dock mooring system,side by side mooring system of LNG and LNG-FSRU are designed.Through that,the design method and calculation flow of mooring system under external marine environment are mastered.In addition,the mooring arrangement,the cable type,the fender selection and other mooring equipments are determined.Based on the mooring criterion,the maximum allowable sea condition for safe operation of LNG-FSRU is proposed.It provides reliable technical guarantee for the safe operation of FSRU,and also provides reference for the mooring design of similar type.