Numerical And Experimental Studies On Motions And Mooring Characteristics Of A Tension Leg Platform In The Water Depth Of 1500m

Tension Leg Platform(TLP) is one of the mostly widely used platforms in deepwater oil and gas exploitation. Because of its small heave motion, wide range of applicable depth, strong ability to resist negative sea conditions, and excellent cost performance. TLP is suitable for the south China sea and has a bright future. The exploration for deepwater oil and gas in the south China sea has began, so it's of much important practical significance to make relevant studies on TLP.This paper makes numerical analysis on a TLP operating in water depth of 1500m and studies its hydrodynamic performance. Based on the 3D potential theory, frequency-domain calculation of platform is carried out. Hydrodynamic parameters including mass and damping coefficients, transfer functions of wave drift forces, 1st order wave exciting forces and 2nd order differential frequency forces in different wave incident angles, and RAOs of platform motions in 6 degree of freedom were obtained. Furthermore, time-domain calculation is carried out according to the theory in conversion between frequency-domain and time-domain. Coupled analysis of the platform and mooring system is implemented to forecast the motion responses under different sea conditions. The hydrodynamic performance of TLP was discussed as well.The model test is performed in deepwater experiment pool. The comparison between experimental and numerical results shows that surge and sway mainly perform low-frequency response; Heave motion shows much low-frequency characteristic rather than wave-frequency; Roll and pitch motion mainly present wave-frequency and high-frequency characteristic, and their motion amplitude obtained from experiments are higher than the numerical ones, which indicates that there are some shortcoming in numerical calculation for high-frequency motion; Besides, the yaw motion cannot be ignored . The numerical results of yaw motion is small under wave direction of 180 deg and 225 deg because of central symmetry. However, more obvious yaw motion is observed in experiment. This is due to the asymmetry of stiffness error among tension legs and implies that yaw motion is sensitive to environment and its own system conditions.In addition, this paper does some researchs on the mooring system. A kind of simple and direct numerical method for static characteristic is raised according to the particularity of TLP's mooring system. It couples horizontal and vertical offset by integrating equation of static equilibrium. The calculated data is in consistent with the experimental data.Finally, two groups of regular waves experiment are designed to further confirm motion mechanism for TLP , and the effect of wavelength and wave height on motion response is studied by controlling variables.