Numerical And Experimental Analysis Of Motion Characteristics For Multiple Floating Body Coupled System

With the exploration and development of offshore oil and gas has been gradually marching into the deep sea,the deep-water floating platforms and the diversified combination operation mode has been increasingly applied to engineering practice.As one of the modes,the Tender Assisted Drilling(TAD)has meet the complex and various engineering needs,and has set up an efficient and economical operation ways,which has contributed a significant meaning to the exploration of the offshore petroleum and gas.When the multiple floating bodies are located with close proximity,the complex hydrodynamic interaction and the collision accident of the platforms need to be taken seriously,the motion performance of the platforms may be entirely different in the single body state and the coupled state because of the hydrodynamic interaction or the coupling force of the mooring system,thus,it is not enough to guarantee the accuracy and safety of the motion performance for a platform in the coupled system by referring to the characteristics of the platform in the single body state.In consequence,the hydrodynamic interaction research and motion performance analysis considering mooring system for multiple floating coupled system has vital practical significance.Based on the metocean conditions of West Africa Sea,the research on the motion characteristics of multiple floating coupled bodies composed of Spar platform with relatively stable performance and semisubmersible platform has been conducted.Firstly,the effect of hydrodynamic interaction on the platforms has been analyzed through the frequency domain calculation based on the three-dimensional potential flow theory,the hydrodynamic parameters,first order wave excitation force and the mean wave drift force of the two platforms in single and coupled states have been calculated.By comparison and analysis of the results,the mean wave drift force of the platforms is more sensitive to the hydrodynamic interaction,the extent of being affected is more obvious than other hydrodynamic parameters.In addition,based on the static similarity principle,the horizontal truncation project of the multiple floating body system has been designed,and the length,stiffness and mass per unit length of the mooring lines have been adjusted.The static restoring characteristics and time domain analysis of the mooring lines and the platforms have been simulated,through the analysis results,the truncated horizontal restoring force of the mooring lines coincide with it of the full-scale well,but the vertical restoring force has a certain extent of increase in truncated conditions due to the change of the top angle of the mooring lines,which lead to a result that the draft of the semi-platform changed to some degree.The model tests of the TAD multiple floating body system have been conducted,and the single body state,coupled state without connecting cables and full coupled state tests have been carried out to measure the motion performance of the platforms and tension characteristics of the mooring lines.Subsequently,to verify the reliability of the numerical results,a comparison of the simulation results and model test results have been conducted,which indicate that the surge motion of the two platforms have been affected to the hydrodynamic interaction,and the range of motion become more stable due to the nonlinear connecting cables.In addition,by comparing the tension results,the horizontal truncation design is feasible to a certain extent.