This paper present the strength analysis of COBRA riser due to hydrodynamic load in deep water environment of Sabah offshore. The risers were design under ULS design limit and analyze using LFRD method. The riser was modelled and analyze using finite element analysis via Orcaflex software with the 100 year return period of typical Sabah offshore metocean data. The analysis consist of Global strength analysis between COBRA riser and Lazy Wave riser, and also Sensitivity Case analysis between configurations of COBRA risers with different depth of sub-surface buoy from sea surface. Based on detailed Global Strength analysis result in this paper concludes that COBRA riser concept has a robust design and it is feasible for 1400 m water depth, in particular for Sabah offshore rather than Lazy Wave SCR. Sensitivity case analysis result in this paper found that the COBRA riser with deepest depth of sub-surface buoy from sea surface has a robust design, this shows that deeper depth of sub-surface buoy from sea surface gives less dynamic effect on the riser due to application of flexible jumper that able to decouple and dampen the energy from vessel due to excitation wave force and it shows that the current force decrease with deeper depth.
Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, Skudai, Johor, Malaysia
Ocean and Aerospace Research Institute, Riau, Indonesia
As Malaysia has start deep water oil exploration near offshore Sabah, more floating structures have been installed. However, less study has been conducted on FPSO with turret mooring system in Malaysia seawater especially in offshore Borneo. Even though offshore Borneo is part of South China Sea, the environmental condition is milder and its exhibit strong current from depth 50m to 150m. Hence, the present study analyzed the influence of turret location to surge, sway, heave, pitch, roll and yaw motions effect on the FPSO Kikeh operating in Kikeh Field. A simulation on FPSO Kikeh with five different turret locations in regular wave and collinear sea states have been done. From the analysis on the simulations, it is found that yaw motions become critical as turret distance from bow increases. Besides that, roll motion increases as yaw motion increases and this is due to coupling effect. Turret at bow is the best design for FPSO operating in Kikeh because it has the lowest structure excursion and lowest mooring lines tension. In addition, the environmental force exerted on the structure also low.
Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, Skudai, Johor, Malaysia
Ocean and Aerospace Research Institute, Riau, Indonesia
