Bilinear Fatigue Performance of Composite Marine Risers in Deep Offshore Fields Due to Vortex Induced Vibrations

Abstract Risers are an integral part of an offshore oil and gas exploration structures, and that they are prone to vortex-induced vibration (VIV). Although several studies are conducted to analyze the VIV characteristics of risers, the results of amalgamation of multiple parameters and also the relative significance of every parameter on the risers’ VIV characteristics have seldom been considered. Vortex elicited vibration is one of the main causes of the fatigue damage of the riser. In deep sea atmosphere currents sometimes vary in magnitude and direction with depth, thereby causing the likelihood of exciting multiple modes of the riser vibration because of VIV. Vortex elicited vibration analysis has been carried out of a long marine riser for different probable sea locations. To boost the understanding of deepwater environments, the behavior of a composite riser under these forces is investigated. 3D nonlinear dynamic analysis of riser is obtained in time domain using finite part software package ABAQUS/Aqua. The response histories thus obtained are utilized for fatigue safety analyses of the riser. Uncertainty modeling, particularly of crack growth parameters, is undertaken by means of the bi-linear crack growth relationship. Results concerning fatigue safety and crack size evolution are given using Monte Carlo Simulation. The bi-linear crack growth models are found to result in to higher fatigue life estimation. Sensitivity behavior pertinent to limit state adopted has also been investigated.