| Mooring system is an important part of offshore floating production system.Compared with traditional catenary mooring system,taut mooring system using lighter polyester cable as mooring material has more obvious advantages and has a broader application prospect in deep-water offshore oil and gas development.At the same time,as the "lifeline" of underwater production system,umbilical cable is difficult and risky to lay and install in the complex marine environment.Based on Orca Flex,this paper makes an in-depth analysis and research on the taut mooring of semi-submersible platform and the laying and installation of deep-water umbilical.The main research contents include the following aspects:1.Based on the three-dimensional potential flow theory,the hydrodynamic model of the semi-submersible platform is established through SESAM,and the hydrodynamic parameters such as added mass and damping coefficient,RAOs and wave force of the semi-submersible platform are calculated.On this basis,the taut mooring system model of semi-submersible platform is built according to the initial design parameters of mooring system.Then,the time-domain coupled dynamic analysis method is used to study the motion response of the platform and the tension characteristics of the mooring lines under storm condition.It is found that the mooring scheme has a large optimization space.2.The influence of different design parameters such as the fairlead position of the platform,the size and inclination of pretension,the included angle between mooring lines and the number of mooring lines on the mooring performance are analyzed,and a set of mooring optimization scheme is obtained.The platform’s motion and tension of mooring lines with taut mooring system and those with catenary mooring system are compared and analyzed.The result shows that compared with catenary mooring,taut mooring has better mooring performance in both intact and broken states,which can provide reference for the design and selection of mooring system.3.Combined with the characteristics of umbilical system composition and the requirements of laying and installation equipment,the umbilical laying and installation scheme is formulated,and the whole operation process(First End Deck handling,First End Pull-in,Normal Laying,Second End Deployment)is described in detail.Then six key steps are pointed out,so as to pave the way for further analysis and research.4.Taking a main dynamic umbilical from SEMI to SDU as the research object,the static analysis of the whole laying and installation process is carried out,and it is determined that the installation ship and laying equipment have the ability of deep-water construction.Through further dynamic analysis of six key steps,the maximum allowable seastate of offshore construction operation is obtained.Finally,the effects of different wave parameters(incident angle,Hs and Tp)and different layback on laying and installation are studied through sensitivity analysis,which provides theoretical support for the development of deep-water oil and gas field development projects in the South China Sea. |
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