Flexible pipes and risers are critical components of offshore field developments because they provide the means of transferring fluid or power between individual subsea modules and a topside floating platform. These risers are designed to carry tensile forces and accommodate floating platform motion at the sea surface by being flexible. They are consequently manufactured to possess high structural axial stiffness and relatively low structural bending stiffness. When considered in an offshore environment, these structural properties provide a very small resistance to disturbances caused by wave and current induced hydrodynamic loadings. Hence their behaviour can be said to be more mechanical rather than structural and can be predicted very efficiently using a finite difference numerical solution scheme - this scheme is particularly suited to these types of structures.

This paper presents descriptions and a practical application of efficient numerical methods for static and dynamic response analysis of flexible riser systems. The static method employs a dynamic relaxation technique coupled with kinetic damping whereas the dynamic method employs an optimised finite difference scheme incorporated with an implicit and therefore an unconditionally stable time integration algorithm. The structural behaviour of single and multiple flexible riser systems is examined and some of the problems associated with flexible risers regarding their mechanical behaviour and manufacturing materials are discussed.

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