Characterization of the Dynamic Loads Between Spar Top-Tensioned Riser Buoyancy Cans and Hull: Horn Mountain Field Data Measurements and Predictions

Abstract

The Buoyancy Can Riser Tensioner (BCRT) systems are designed to provide tension to Top-Tensioned Risers (TTRs). BCRT systems do not transfer the riser weight to the floater and they minimize the interaction between the floating platform and the riser system. For deepwater field developments, this attractive feature allows efficient design of the floaters as well as the riser systems. Although, the vertical riser load is not transferred to the hull, the BCRT system makes lateral contact with the hull at several locations. During the past 3 years, analytical models have been developed to characterize mechanics of the contact between two large floating bodies (buoyancy can and hull) and compliant guide hardware has been developed. Placement of a compliant guide between the hull and the BCRT has become the current practice for design of Spar floaters. The initial development of the analytical models and the compliant guide hardware coincided with the Horn Mountain project. The project team placed extensive instrumentation on the hull and compliant guides with a vision to confirm robustness of the guides and to calibrate analytical models used during the design phase. This paper presents a summary of the data collected on the performance of the Spar hull, compliant guides, and the riser systems for storms up to 25 ft of significant wave height. Analytical methods and predictions are presented to characterize the dynamic interaction between the BCRT system and Spar hull.

Review of Composite Marine Risers for Deep-Water Applications: Design, Development and Mechanics

“…However, composite applications in composite risers have transiting barriers and are thus seen as an enabling technology [65,119]. Composites are currently used in different components such as accumulator vessels, composite tethers, flexible risers, tensioners, buoyancy cans and the topside of platforms as well as on flow-lines, spoolable tubings, spoolable pipes, buoyancy modules and buoyancy floats [5,55,83,[200][201][202][203][204][205]. However, their application in risers has been limited to prototype production and drilling risers to date, despite that they may significantly reduce the weight of deep-water operational systems [93,94,[105][106][107][108][109][110].…”

“…As a result, increasing depth has a two-fold influence on a riser's weight and, as a result, the top tension required. According to research, the size of TLPs increases at a considerably faster pace as their top tension increases [200][201][202], limiting the number of risers that can be used or the depth to which they can be used [206][207][208][209][210]. Based on the present capabilities, the maximum depth to which a steel riser can be deployed cheaply depends on the available platforms.…”

“…However, the CPR tube, its stress joint, steel tension joint and other standard joints face global functional and environmental conditions [98,[143][144][145][146]266]. The effects of functional loadings have also been studied in comparative studies presented on both steel and composite risers, including vortex-induced vibrations (VIVs) and resonances on the CPR [11,55,[199][200][201][202]246]. Generally, it was discovered that as the water depth increases, the tension force diminishes, and the maximum tension force is reached.…”

“…Generally, it was discovered that as the water depth increases, the tension force diminishes, and the maximum tension force is reached. The stress joint at the bottom bears the brunt of the bending moment, followed by the joints across the surface of the sea, called the mean water level (MWL), displaying larger bending moments than those in the riser string's midsection [98,101,[200][201][202][203]. However, when it was compared to an all-steel riser, the axial stress and bending were significantly reduced along a composite riser's full length, comprising tension, standard and stress because of its smaller total weight, it had fewer joints.…”