Analysis On Dynamic Characteristics Of Deepwater Platforms With Mooring Lines And Risers

Offshore structures are main tools to exploit oil and gas resources in oceans. Semi-submersible platforms have strong ability of anti-wave and wide range of operational water depths. Spar platforms have excellent motion performances and are relatively low cost. These platforms will be the primary marine engineering equipments to exploit the deep-sea resources in the South China Sea, and both of which are composed by floating vessel modeled as rigid body and flexible slender structure systems (mooring lines and marine risers), these parts interact to resist sea entironment loads.This paper deals with the coupled-dynamic characteristics of floating hulls/mooring lines/risers for deepwater Semi-submersible and Spar platforms in the time-domain under winds, random waves and currents. Chapter I reviews and summarizes recent progress in such areas briefly. Chapter II presents the numerical method for the coupled-dynamic analysis of a deepwateer floating structure with mooring lines/risers in the time domain. Then the following work has been carried out:In Chapter III, the dynamic characteristics of a Semi-submersible platform with catenary mooring lines in random waves are analyzed. The proposed method is validated by comparing with the model test results, and the motion responses of the platform and the tension characteristics of the mooring lines are analysized under the cases where one mooring line is broken.Moreover, the dynamic characteristics of a Semi-submersible platform with taut mooring lines in winds, random waves and currents are further analyzed. The effects of two kinds of risers (SCRs and TTRs) on the motion responses of the platform and the tension characteristics of the mooring lines are considered, and then dynamic characteristics of the platform with taut mooring lines and SCRs are analysized under the cases where some mooring lines are broken.In Chapter IV, the dynamic characteristics of a classic Spar in winds, random waves and currents are considered, the effects of the winds and currents on the motion responses of the platform and the tension characteristics of the mooring lines/risers are considered, and then dynamic characteristics of the platform with taut mooring lines and a TTR are analysized under the cases where some mooring lines are broken.Results show that the motion performances of the platforms will be underestimated, and the limit tensions of the mooring lines will be overestimated if the effects of risers are ignored. When some mooring lines are broken, the surge and pitch will increase significantly for the semi-submersible platform while the surge and heave will increase obviously for the Spar platform, moreover the tension will increase for taut mooring lines and decrease for slack ones greatly.