Hydrodynamic Performance Analysis And Motion Control Of Deepwater Semi-submersible Drilling Unit

With the exploitation of offshore oil and gas resources gradually shifting to thedeepwater areas, floating offshore platform is used more and more widely.Semi-submersible drilling platform has become the main platform for deepwaterdrilling because of its special characteristics: the great performance of stability, thewide water depth range of operating and the strong ability of drilling. Thus, it will beof great significance to carry out comprehensive research on Semi-submersibleplatform.In this paper, the motion performance of a semi-submersible drilling platformwhich is serving the South China Sea in operating and survival conditions is studied.On this basis, some methods of controlling the platform motion response are explored,leading to some conclusions. The main work of this paper can be concluded asfollows:Firstly, the main types of the compliant platform used for ocean oil and gasexploitation, such as TLP, Spar, FPSO and semi-submersible platform, have beenintroduced, their developmental process and engineering application have beendemonstrated. Meanwhile, the studies on the semi-submersible platform have beenreviewed.Secondly, a hydrodynamic numerical model of the target platform is built basedon the AQWA-Line software to analyze the hydrodynamic parameters, such as addedmass coefficients, radiation damping coefficients and the RAOs, in the frequencydomain of the semisubmersible platform using the three-dimensional potential theory.On the basis of frequency domain analysis, coupled analysis in time domain of thesemisubmersible and its mooring system are carried out with the AQWA-Driftsoftware in both operating and survival sea conditions considering different typical wave directions, to obtain motion responses in6degree of freedom and tension ofmooring system.Lastly, the effects of different gravity center heights, drafts and heave plates onthe hydrodynamic performances of whole system are explored respectively bycomparison with the original platform. Particularly, changes of the mass, depth, areaand shape of heave plate on motion performance are discussed in detail. Conclusionsare obtained about motion control of semisubmersible platform by comparison of themotion performance of different platforms in both frequency and time domainanalysis.In this paper, the motion response of semi-submersible in regular and irregularwaves is studied. Some methods to improve the platform motion are discussed as well.Conclusions obtained in this paper will be useful in prediction of hydrodynamicperformance accurately and further design of the semi-submersible.