Research On Coupled Motion And Parametric Sensitivity Between Truss Spar Platform And Moonpool Water In Deep Sea

The centerwell of the Spar platform is throughout the hull, the risers and other important drilling facilities are arranged in it according to a certain manner. According to the actual need the guide plate is generally designed to be semi-closed state and the sea water can flow freely through the moonpool. If we use the top tension riser, the quality of the sea water in the moonpool is comparable with the quality of the whole platform. The fluid motion in the moonpool and its effect to the platform motion is significant?Numerical simulation and model test are used to research the Coupled Motion between Truss Spar platform and moonpoool water.Wave loads of Truss Spar in deep sea are calculated based on the linear potential theory. The mooring force of Truss Spar platform is calculated according to the classical centenary theory. And the heave stiffness of TTR risers are calculated. Based on the pressure balance equation of the bottom, The "piston" movement modal of the numerical model is established. According to the method of equivalent mechanical model "swinging" movement mode is established. And solving the equivalent force response equation of simple pendulum,the quality of the single pendulum model is obtained. The coupling dynamics equation between surge-heave-pitch of platform and moonpool water are established and calculating the effect of different opening rate of bottom plate for the movement of platform and moonpool water. And the effect of parametric Sensitivity for the movement is analyzed.According to the result,we can find the added quality and damping increase with moonpool. So the nature periods of heave and pitch increase. Heave viscous damping are different because of different opening rate of bottom plate. And viscous damping is biggest when the rate is 30%. When the wave period is near the natural period of moonpool water vertical vibration, the moonpool fluid motion can decrease hull heave motion, and the optimal area of the guide plate opening can be designed to reduce the platform hull heave motion. With the guide plate opening rate increasing, the hull heave RAO gradually appears two peaks, which respectively appear near the moonpool fluid vertical motion natural period and the hull heave natural period.The effect of moonpool for platform heave should be considered because of the partial opening in fact.The parametric Sensitivity shows that the moon pool-platform coupling quality coefficient and damping coefficient have a significant impact for the platform heave. This Research will provide reference to the structure design of platform movement and inside of the moon pool.