A concept to reduce vibrations in steel catenary risers by the use of viscoelastic materials

Abstract

One of the most important issues in steel riser systems is the VIV phenomenon (Vortex Induced Vibration). VIV may induce high levels of structural vibrations and stresses what eventually lead to considerable fatigue damage and reduction in structural lifetime. The use of suppression devices is a feasible solution to tackle this problem. Nevertheless, their disadvantage is the increase in drag coefficient; moreover, it is very expensive. This work proposes and investigates a concept aimed at suppressing vibrations in steel catenary risers by the use of viscoelastic sandwich layers and it is based on three steps. The first one considers the calibration of a viscoelastic constitutive model based on complex shear modulus measurements in a controlled experimental environment. The second one is a model validation scheme applied on the calibrated model provided by the first step and it is based on experimental data obtained out of a 1.6m long tubular sandwich structure. The third step assesses the effectiveness of viscoelastic sandwich layers using a small scale model of a steel catenary riser installed in P18 platform which is in operation in Campos Basin, Brazil. The results are quite compelling due to the great increase of damping that was observed.