Coupled Motion Of Hull And Moonpool Water Of Deep Sea Spar Platform

Spar platform is one of the most important platforms of deep-sea oil and gas field.The centerwellof the Spar platform is throughout the hull, the risers and other important drilling facilities are arrangedin it according to a certain manner.Theoretically the guide plate is required all closed. However,according to the actual need the guide plate is generally designed to be semi-closed state and the seawater can flow freely through the moonpool which causes moonpool internal fluid resonance.The main works and conclusions are as follow:(1) Using SESAM software calculates the Spar platform heave hydrodynamic performance andRAOcurve When the moonpool bottom guide plate is totally open and closed. The heave results showthat when the moonpool bottom guide plate is totally closed, The moonpool seawater is treated as rigidbodyattached to the platform, we can only consider the influence of the moonpool water quality on theplatform movement mass and stiffness, when the moonpool bottom guide plate is totally opened, heaveRAO appear peak on the moonpool fuild natural period, higher heave is exhibited when thewaveperiod is near the natural period of moonpool fluid vertical vibration.(2) Considered the stiffness of TTRs and tension, the two-degree-of-freedom differential equationof coupled motion of hull heave and moonpool water vertical motion are established, and haveexperimental research on the calculation model. Test results and numerical results match, themoonpool fluid motion can decrease hull heave motion, the optimal area of the guide plate openingcan be designed to reduce the platform hull heave motion. For the large opening area of guide platethe hull heave RAO appears two peaks, the higher heave is exhibited when the wave period is near thenatural period of moonpool water vertical vibration; coupling coefficient between the platform hull andmoonpool fluid have the significant effect on the hull heave motion.(3)Assumed the guide plate all closed, on the basis of the sloshing theory of the equivalentmechanical model, the equivalent mechanical model parameters can be determined, use ANSYS as themodel building and meshing processing software; Use Galerkin finite element method to solve thecorresponding monthpool fluid sloshing natural frequencies, modal function and potential function ofdiscrete solution; Application of Matlab software established the moonpool fluid sloshing program, thecalculation model of the calculation results match the analytic solution, shows the correctness of theprogram.(4)The coupled dynamic equation of hull heave-pitch and moonpool of Spar platform isestablished by using Lagrange principle, considered the heave parametric excitation and moonpoolfluid sloshing, derive the Mathieu equation of the coupling system, use perturbation theory todetermine the harmonic vibration and1/2harmonic vibration stability boundary. The results shows that,the liquid sloshing damping significantly reduced the harmonic vibration unstable region, and for 1/2harmonic vibration unstable region the effect is not obvious. When the heave motion parameters isin the unstable region, the pitch response of the Spar platform is excessive.