Analysis Of Coupled Dynamics Response For Octagonal FPSO In Tandem Offloading Operation

Rencently,mang research institutions and professors focus on new structural forms of FPSO in the marine engineering.In this thesis,the research object is octagonal FPSO,which is designed for the development of marginal oilfield in the South China Sea.It has the advatages of convenience construction,better economic,good hydrodynamic performance and so on.The tandem offloading scheme is studied for octagonal FPSO with 100 m and 300 m water depth.Research work is pioneering and significant for both theory and engineering.The floating multi-body dynamic model is set up which consists of FPSO and its mooring system,shuttle tanker,positioning tug,hawser which connected to the FPSO and the shuttle tnaker.The hydrodynamic performance of octagonal FPSO and shuttle tanker is obtained by AQWA based on the three dimensions potential theory.These parameters include added mass coefficients,radiation damping coefficients,1st order and 2nd wave load transfer function,etc.The stiffness characteristics of mooring system for octagonal FPSO is analysised using elastic segmental catenary theory.According to the elastic catenary theory,under the different water depths of FPSO mooring system train stiffness characteristics analysis with working depth 100 m and 300 m.The design criterion of connection hawser is edtablished and parameters of hawser is decided.Then coupled time domain response is performed for working condition of main offloading,adaptability for main direction of offloading,different offloading positions' influence.In order to optimize the parameters of mooring system for offloading,the sensibility analysis of hawser length,tug force is carried out.By setting a serious of guadually enhanced sea conditons,the critical offloading environmental parameter is found out by searching calculation.With the help of wave scatter diagram,the offloading time rate of every month is calculated,which has a great significance for production arrangement.The extreme sample is obtained by different time domain calculation with different seeds.Then an extreme value distribution is fitted with the sanple based on the extreme theory.The excessive surge motion can be predicted.And the collision risk between shuttle tanker and octagonal FPSO in offloading operation analysis could carried out.Some main conclusions are as follows: the response characteristics of floating multi-body system are obtained,and the influence regularity of offloading key parameters is clear.The critical environmental conditions of offloading operation are carried out for different water depths.The collision risk between octagonal FPSO and shuttle tanker is predicted.This conclusions have the great significance for the design of offloading system for octagonal FPSO.