Investigation of Available Configurations for Flexible Risers in Shallow Water

Flexible risers have been used widely in recent years for floating structure in shallow and deep water. Flexible risers have various configurations and each configuration has its specific charectresitics that helps the riser to solve the problems that exist in shallow and deep water. Selecting and designing the best configuration for flexible risers in shallow water, like deep water, present many challenges, some of these challenges can be addressed: high vessel displacement compared to the water depth, minimum riser clearance with the seabed or sea surface or the vessel keel, bending radius limitation and etc. The aim of this paper is to investigate the traditional configurations like lazy wave and pliant wave and to compare them with a new configuration like weight added wave for the riser with 15 inches internal diameter in 45m water depth connected to a turret moored floating storage unit. It is concluded that the traditional configuration can not solve the sea surface clearance problem when the riser is empty condition, in this condition the weight of riser is decreased and the buoyancy force is become higher than riser weight and lift the riser up and the riser become flooded on the sea surface. To preventing the riser from flooding on the sea surface it’s needed to use configuration with added mass. Also concluded that using added mass in touch down zone (TDZ) reduces the tension in PLEM connection point about 89% . Also concluded that the minimum bending radius for weight added wave configuration is increased about 29% in compared with traditional configurations.