Alternative Design of Flexible Jumpers for Deepwater Hybrid Riser Configurations

Abstract

Recent studies on the behavior of the simple free-hanging configuration for flexible risers have shown that, for very deepwater levels, they are reaching their technical and economic limits. Other alternative configurations are currently being investigated, including hybrid riser configurations based on flexible jumpers connected to an intermediate point closer to the free surface (usually a submerged buoy). This work focuses on the jumper issue, considering that, since it is completely suspended, its behavior may differ significantly from the behavior of a riser resting on the seabed. Therefore, the usual design procedure employed for conventional applications may not be completely adequate, and should be complemented by alternative approaches. This work considers analytical, numerical, and experimental approaches for the design of flexible jumpers. First, a comprehensive static analysis using consistent catenary concepts is developed; this results in criteria that are essential for safe design. Subsequently, a modal analysis procedure is described; this procedure considers the nonlinear behavior of the jumpers under the static component of the environmental loads, and may show the existence of resonant modes that require careful consideration. This defines the importance of damping mechanisms, and orients parametric time-domain nonlinear verifications. Finally, reduced model tests are considered, devised specifically to investigate the jumper behavior under centenary conditions. The design of the physical model and the similarity analysis of the experimental results are also presented.