The Design Method Of A New Type Of Mooring System And The Analysis Of Its Hydrodynamic Performance

With the development of oil and gas, offshore structure has great potential. At the sametime, offshore structure gradually moved to deepwater. Main section of ocean engineering issemi-submersible platform, we must consider the motion response in sea conditionextremely which fully embodies the importance of mooring system. There are many ways todescribe mooring system, which can control the displacement of offshore structure. But wemust design the best type to control the response motion of heave. For drilling operationheave motion is a limiting factor. The reason is that the vertical motion of the risers has tobe compensated and there are limits to how much the motion can be compensated. Inconclusion, the design of new mooring system which based on origin type to control theheave motion of offshore structure. It will be better to work efficiency as possible.This paper introduced the method of time domain analysis which was used to simulatesemi-submersible platform and mooring system. This paper mainly considered the responsemotion of offshore structure and hydrodynamic performance of mooring system that wascontrolled by new type mooring system in the same environment condition. On this basis,further study on different wave direction and a mooring line break is carried out in thispaper as well. There are twelve connectors underwater631.5m, it is decisive that the shape,the net buoyancy and the physical properties of connectors to the motion response ofoffshore structure. Therefore, this paper aimed at the target to optimize the design ofconnector. However, the transportation of connectors is key to install the new type mooringsystem. Numerical simulation for the process of lifting heavy objects is required. We mustconsider coupling hydrodynamic in the multi-body system of lifting. The main work of thispaper can be concluded as follows:(1) Analysis of hydrodynamic characteristics of a deepwater drilling semi-submersibleplatform and its mooring system. Numerical simulation mainly divided into the frequencydomain and time domain. According to3D potential flow theory, the first step isfrequency-domain calculation of the semi-submersible in different condition, to obtain theadded mass and damping coefficient, as well as response amplitude operators of motions invarious frequency and wave direction. After that, considering different typical wavedirections, time-domain coupled analyses of the semi-submersible and its mooring systemare carried out in operating condition, to obtain motion responses in6degree of freedomand top tension of mooring system. Meanwhile, study on an extreme condition that onemooring line is broken, which will be useful to explore the changes in the aspects of kinematic and kinetic characteristics of deepwater semi-submersible drilling platform andmooring system.(2) There is a design concept of new type mooring system in the deepwater drillingsemi-submersible platform system. For the development of ocean engineering, it is better tocontrol more conducive to offshore drilling operation. That suggested the compared resultswith the traditional taut mooring system to show every advantages and disadvantages. Thatreveals the new type of mooring system can reduce the offset of offshore structure, increasethe horizontal stiffness and vertical stiffness which can further improve the operatingcondition.(3) Multi-body mooring system is adapted to deepwater semi-submersible platform,significant hydrodynamic interactions occur when bodies are located in close proximity onthe ocean surface. This situation exists in many application of practical importance, whichrequires rational engineering analyses. SIMO software described all the bodies, theconnection among bodies and the application of tension leg. We can debug the location ofeach body to achieve the static equilibrium location, then to calculate the motion responsefor full time domain coupling analysis.(4) Connector is more important part of multi-body structure, we must increase thesafety in the process of lifting. Numerical simulation for installation of multi-body is neededto consider the motion response of hook, slings and object, focus on the friction when theobject leaved the deck to make the motion of pendulum in the certain range. At the sametime, the vessel takes advantage of dynamic positioning system, focus on the propulsion ofthrusters.