Investigation On Dynamic Response Characteristics For Tension Leg Platforms In Internal Solitary Waves

The 21^st century is the century of ocean,deep sea oil and gas resource exploitation of the South China Sea is one of the important ways to realize the nation strategy of sea power.Deepwater floating platforms,such as tension leg platform?TLP?,will be applied in oil and gas resources exploitation of the South China Sea.Relevant data show that internal solitary wave happens frequently and spreads widely in South China Sea,and carrying huge energy in its propagation process could have destructive effects on offshore platforms.Internal solitary waves have become a severe ocean environmental phenomenon.Therefore,the influence of internal solitary waves on the hydrodynamic characteristics of TLP cannot be neglected in its design and application.For dynamic problem of a TLP in internal solitary waves,the traditional way is to simplify the tension leg as a linear spring model.However,in deep water,due to the fact that TLP will have significantly horizontal drift in a large amplitude internal solitary wave,the linear spring model will be no longer applicable and it needs to consider the nonlinear response problems of the tension legs.Considering this situation,a theory model is proposed in this thesis to simplify the structure of the tension leg as a nonlinear beam model and study on the coupled dynamic responses of the TLP with the nonlinear beam model of tension leg in an internal solitary wave.The main work of the thesis is as follows.In chapter II,a theory model of coupled dynamic responses of the TLP with the nonlinear tendon model has been proposed.Firstly,the theoretical solution of KdV,eKdV and MCC and the applicability conditions of these three internal solitary wave theories are presented.Then,based on the applicability conditions of three internal solitary wave theories,a theoretical model for analyzing the characteristics of internal solitary waves of interaction with the TLP by simplifying the tendon as a nonlinear beam is presented by using coupled motion equations of the floating body in time domain,where the dynamic loads on the platform due to internal solitary waves are calculated with Morison and Froude-Krylov formulas.At last,this chapter gives numerical method for solving the coupled motion equations of the floating body in time domain.In chapter III,numerical calculations of coupled dynamic responses of the TLP with the nonlinear tendon model in internal solitary waves have been considered.To simulate the variation characteristics of the dynamic loads,motion responses and tether tensions,torque and stress for a classical TLP?ISSC-TLP?,the observed data near Dongsha Islands are used as the characteristic parameters of internal solitary waves and the applicability conditions of internal solitary wave models and theoretical model proposed in chapter II are used as the calculation conditions.In addition,the darg and inertia coefficients in the numerical calculations are determined by related series experiment of a TLP and a cylindrical structure.This thesis presents a practical theoretical model for the dynamic response analysis of TLP in internal solitary waves.