Coupled Hydrodynamic Analysis Of Multiple Floating Bodies Comprise A Berthing Semi-submersible Supporting Platform

With the continuous development of global economy,human's demand for energy such as oil and natural gas keeps increasing.With the gradual consumption of land energy resources,people turn their attention to the resource-rich ocean.As the necessary technical equipment for the development of oil,gas and other resources,the demand for marine platforms continues to grow rapidly.Besides drilling platforms,some drilling support platforms also appear in people's vision.When the drilling support platform is working,it is berthing close to the drilling production platform.At this time,the two platforms constitute a multi-floating body system,in which the nonlinear wave performance and mutual interference make the movement of the multi-floating body system extremely complex and make it difficult to predict the movement of the system.This article selected a multi-floating body system consists of a TLP production platform and a semi-submersible tender support drilling unit and a multi-floating body system consists of a semi-submersible drilling unit and semi-submersible tender support drilling unit as research objects where the systems applied to South-East Asian Sea and the U.K.North Sea respectively,we analyzed the two platforms and the system respectively,and three-dimensional potential flow theory in frequency domain calculation,time-domain simulation,model test and other research methods were utilized comprehensively to calculate and to analyze the system movement in different sea conditions,and the results were converted to the relative motion of gangway which was required by the project.Then the wave conditions were extrapolated and the motion of the system was simulated when the wave height changes.For the two single platforms,the hydrodynamic calculation was carried out in the frequency domain using the three-dimensional potential flow theory,and the results were compared with the experimental results to ensure the accuracy of the numerical model.Then the multi-floating system consisting of two types of platforms was calculated in frequency domain after the berthing distance was set,and the hydrodynamic results were compared with two single platforms,and it was found that the hydrodynamic parameters changed in some degrees of freedom.Through the calculation of frequency domain,the accuracy of the numerical model was confirmed,and the existence of hydrodynamic interference was preliminarily determined.On this basis,a time-domain simulation model was established within the time-domain scope,and the hydrodynamic parameters calculated in the frequency domain were imported into the time-domain model by technical operations.Through the iteration of the motion equation of the system,the motion situation at each moment was simulated,and then the movement time history of the system was converted to the project target gangway.By comparing with the results of model test,the non-negligible hydrodynamic interference was directly shown from the relative motion of gangway.Finally,the model test was carried out to check the movement of single platform and multi-floating body system,and it verified the accuracy and reliability of numerical calculation,provided experimental guarantee for practical projects,and laid a foundation for subsequent projects.On the basis of the above,improve the wave conditions by one level and two levels,then time domain simulation was carried out again.Through numerical simulation,it was concluded that the motion at the gangway was not linearly related to the wave height.At the same time,the larger wave height condition was used to judge that under the condition of typical TLP wave,the connected hawser breaking condition of multifloating body system precede the collision condition,and the hawser strength should be considered in the actual project.Subsequently,the multi-floating body corresponding to the north sea area was studied in the frequency domain,where RAO and other parameters were calculated,and the short-term motion prediction was carried out.The preparation work of frequency domain numerical calculation before time domain analysis and model test was completed,and it was found that the significant values of motion responses of the supporting platform was larger than that of the production platform.