One of the key design parameters of Flexible Joint as the Top Termination Unit (TTU) of Steel Catenary Riser (SCR) or Steel Lazy Wave Riser (SLWR) is the maximum predicted dynamic angular motion of the flexible joint. It is important for the Flexible Joint rotation angle not to exceed the current qualification limits to reduce project risks and avoid additional cost and potentially schedule impact.
In this paper, the design rotational angle requirements for a Flexible Joint TTU of a steel lazy wave riser hosted on a Semisubmersible Floating Production Unit (FPU) in Western Australia harsh environment is investigated. Fully coupled time domain analysis is used to develop the motion time history of the FPU that is used in detailed Finite Element Analysis (FEA) of the riser to predict the riser performance and the Flexible Joint rotational angle. 10,000 year survival condition is investigated. Far, Near and Cross conditions of the riser are analyzed. Contributions of the motion components (participation factors) to the Flexible Joint rotational angle are estimated. Offset, heave and roll/pitch modes of vessel motions are considered. Percentage contributions to the Flexible Joint rotation angle from mean, low frequency and wave frequency for each component are extracted.
Numerical results are presented to illustrate the significance of each of the motion components to the Flexible Joint rotation angle. The paper concludes with recommendations on the key design considerations and optimizations of the semisubmersible hull design that should be implemented to reduce the flexible joint angle so that it remains within the qualified limits.