Modelling and Global Analysis of Submerged Loading System in Deep Waters
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- Institutt for marin teknikk 
Framo Engineering has replaced tanker loading unit (TLU) by a Framo submerged loading (FSL) system at Draugen, with 257m water depth, in summer 2012. In recent years a lot of activities of oil and gas companies including drilling and exporting of oil and gas have been performed in deep and ultra deep waters. The increasing water depth also means that it is necessary to develop the riser technology to access these depths. The main purpose of this master thesis was the development of the existing FSL system and considering the feasibility of the system for operating in deep water (1000m).The first challenging step of this master thesis was to modify the existing FSL system RIFLEX model for deep water. It included modification of the existing steel riser, the buoyancy tank, the loading hose and the pick-up system. Based on DNV-OS-F201 standard, the thickness of steel riser was selected to resist internal and external overpressure as well as the other design criteria mentioned in DNV standard. The buoyancy tank length was changed in order to provide the required top tension as well as a reasonable offset. The loading hose length was increased as the system offset as well as tanker offset in 1000m water depth and harsh environment is much larger than in the Draugen with 257m water depth and moderate environment. After creating the preliminary submerged loading system model, the global analysis of the deep water submerged loading system was conducted in SIMA. Subsequently, the sensitivity studies with respect to different parameters were performed in order to ensure that the theoretical models and numerical approximations represent the real physical behaviour of the submerged loading system model. Finally, based on the obtained results in previous analyses, the deep water submerged loading system was modified and the global analysis results were presented in this report. It must be noted that this design procedure is an iterative process. Therefore, in order to present the final submerged loading system model, fatigue and VIV analyses of the system must be executed that are out of scope of this master thesis.The modified submerged loading system model sustained lower axial tension and bending moment when the buoyancy tank length decreases to 18.6m and also the buoyancy tank diameter increases to 7.5m compared to the preliminary model when the buoyancy tank had 42.6m length and 5m diameter.Moreover, Catchwheel system was proposed as the pick-up system for the deep water submerged loading system. Although, the Catchwheel system has to be designed and verified in more details, it is a simple and well-performed system which can be easily replaced and repaired because it is located close to the sea surface.Finally, it was concluded that the submerged loading system is feasible for 1000m water depth. However, more verification as well as fatigue and VIV analyses of the presented system are necessary to obtain the final submerged loading system model.