Results are presented of a comparison between the observed behaviour of two model flexible riser systems subject to environmental loads and simulated floating production system vessel motion, and the behaviour predicted using a flexible riser computer modelling program. Significant results are the validation of the modelling program over a range of environmental conditions and the establishment of representative drag coefficients for sections of riser with distributed bluff-faced buoyancy modules. The need for an improved understanding of the drag characteristics for such systems is identified.
This paper presents the results of a comparison between the observed behaviour of two model-scale flexible riser systems subject to environmental loads and simulated floating production system (FPS) vessel motion, and the behaviour predicted using C\ state-of-the-art flexible riser computer modelling program. The study was instigated by BP as a result of experiences gained on the concept design studies for a floating production, storage and offloading unit for BP's 23/26a North Sea field in 85m water depth. The development plan intended the use of a bow-moored tanker with turret and flexible risers. Originally thought to be an impractical concept for this water depth at the 20 year return storm condition, through extensive use of a computer modelling program for flexible risers and refinement of flexible riser design the concept was deemed feasible. Further work of an investigative nature, out with the main project, was thus undertaken. The primary objective of the work was to examine in detail the accuracy and modeling capabilities of the program. A secondary objective was to compare the behaviour of the two different riser systems under identical imposed loadings. Lightweight pipes were specifically chosen for the study since they were representative of elastomeric flexible pipe constructions and because they would ensure large deflections under hydrodynamic loading.
