Research On Dynamic Response Of A Triangular Tension Leg Platform Considering Second Order Wave Forces

With the running out of terrestrial energy and significant increasement of human’s demand for energy,the world develops deepwater oil and gas as a key of economic development.Under this international situation,our country also promotes development of energy to deepwater and ultra deepwater areas.Therefore,research of types of new deep-sea platform has earned close attention from scholars all over the world.At present,famine of key technology of deepwater platform’s designing and analysis makes it difficult for China to develop and use the oil and gas in the South China Sea effectively.Thus,it has important economic and political significance to investigate new types of deepwater platform for development of oil and gas in the South China Sea.Tension leg platform（TLP）has attracted comprehensive attention in concepts selecting of platform technologies of drilling and production for its good performances and abilities to resist the hostile environment condition.This paper is based on the project of key technology researching on designing,construction and application of the triangular multi-functional tension leg platform,taking the triangular tension leg platform designing model in the project to study.The hydrodynamic characteristics of a triangular tension leg platform are studied using numerical prediction method.The main research contents are as follows:1.Based on potential theory and radiation-diffraction theory,the numerical calculation method of 1^st and 2^nd order wave forces is studied,and the 1^st order wave exciting forces and response amplitude operators（RAOs）are verified.2.Transfer functions of 1^st order wave exciting forces,wave drift forces,2^nd order differential frequency forces,2^nd order sum frequency forces and 2^nd order motion in different wave incident angles are researched.Besides RAOs of platform motion in six degree of freedom are predicted and analyzed.In the frequency domain analysis,the stiffness of tendons is considered.The drag term in Morison equation is linearly approximated,and the free surface model is built for full quadratic transfer function（QTF）matrix calculation.3.Full coupled system,including platform,tendons and risers,is established for numerical prediction in time domain.Influence of combination of wind,wave and current,incident angles,randomness of sea state on coupled system characteristics are investigated,and then influence caused by 2^nd order differential frequency forces and sum frequency forces on response of platform motion and tendon tension are analyzed.4.Responses of platform motion and tendon tension are numerically predicted and checked under different working conditions of real sea state.Moreover,the transient response and tension are compared and discussed which associated with one tendon disconnection at the top or the bottom.