Flexible riser global analysis for very shallow water

Abstract

Flexible risers are widely used for a range of water depths and can accommodate large floater motions when using a buoyant system. A wide range of buoyancy solutions have been developed for very shallow water (e.g. 30-50 m), shallow water (e.g. 90-110 m) and semi-deep water (e.g. 300-400 m) and in the ranges between these depths. Flexible risers can have different configurations. These different solutions have different characteristics which influence their suitability for a given situation. The pipes should not experience excessive curvature; a limiting value is given by the manufacturer. The system should avoid axial compression in the pipes and contact between the pipes and other structures. This thesis will focus on the challenges and solutions for very shallow water depths (less than 50 m). This thesis will consider the design of dynamic, flexible unbounded riser pipes connecting a subsea pipeline to an FSO turret. The following work will be presented: • Study of flexible riser technology, especially comparing different very shallow water buoyancy systems. • Methodology of design of flexible riser • Parameters effect on flexible riser design • A case study of a typical very shallow water project using dynamic flexible risers: i. Presenting relevant input data for designing the risers. ii. Static and dynamic design and analysis, taking FSO motions and hydrodynamics into account and checking against relevant design codes. Modeling and Dynamic analysis will be performed by using FE software OrcaFlex. Irregular waves are taken into account for the dynamic analysis. The wave spectra will be investigated based on location.