Abstract
Risers are indispensable components of offshore platform systems that connect the wellhead at the sea bottom and to the platform at the sea surface and are normally made of high grade steel. Nowadays, fiber reinforced polymer (FRP) composite has been recognized as an attractive alternative riser material. Similarly to steel risers, FRP composite risers are also vulnerable to vortex induced vibration (VIV), and the effects of the composite makeup of these risers on VIV are the subject of the present investigation. Three risers (the tailored design composite riser, the composite riser with orthogonal reinforcements and the steel riser), three current velocities (0.36 m/s, 1.22 m/s and 2.13 m/s) and three water depths (12.5 m, 25 m and 37.5 m) are considered. In total, 9 study cases using orthogonal array (OA) sampling are investigated to study the risers’ VIV characteristics. The computational fluid dynamics (CFD) simulations with coupled fluid–structure interaction (FSI) are used to obtain the risers’ natural frequencies, global displacements, global stresses and the stress distributions in each composite lamina. The effect of 5 parameters (Etension, Ebending, L/Douter, tension force and current velocity) on the VIV amplitude in a cross flow direction of the risers is analyzed using Grey relational analysis (GRA) and the Grey relational grade of these parameters are: r 05 ( Velocity ) > r 03 ( L / D outer ) > r 04 ( Tension Force ) > r 01 ( E t e n s i o n ) > r 02 ( E b e n d i n g ) .
Highlights
Risers are a critical component of offshore platform systems, and over 80% of offshore oil and gas accidents are related to the failure of these risers
The thicknesses for risers 1, 2 and 3 were 30.5 mm, 39.5 mm and 25 mm, respectively. Both fiber reinforced polymer (FRP) composite risers, 1 and 2 (45.7 kg/m and 59.6 kg/m, respectively) achieved significant weight saving compared to the steel riser (169 kg/m) and the FRP composite riser 1 even led to a 23.3% weight reduction to the conventional FRP composite riser 2 [4]
The study of vortex induced vibration of composite risers and steel riser is presented in this paper
Summary
Risers are a critical component of offshore platform systems, and over 80% of offshore oil and gas accidents are related to the failure of these risers. In 2016, the UK national composites center announced that in the few years, the composite riser reinforced by carbon and S2 glass fibers would be tested for practical engineering In addition to these joint industry projects, which focused mainly on the concept of feasibility and mechanical tests, the responses and performance under environmental and functional loads of composite risers were studied. For the global response of composite risers, the maximum bending moment occurs on the bottom, followed by the joints at the sea surface and the tension force decreases with an increasing water depth in general [13,14,15,16,17,18] These are much smaller than those in metal risers due to the lower overall weight and tension force required [15,16]. When a variable sequence has the highest Grey relational grade, it is the most important one [30]
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