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research-article

Fatigue damage study of helical wires in catenary unbonded flexible riser near touchdown point

[+] Author and Article Information
Kunpeng Wang

School of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, Jiangsu, China
jstuwk@sina.com

Chunyan Ji

School of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, Jiangsu, China
jichunyan_just@163.com

Hongxiang Xue

State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
hongxiangxue@163.com

Wenyong Tang

State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
wytang_sjtu@163.com

1Corresponding author.

ASME doi:10.1115/1.4036675 History: Received June 22, 2016; Revised April 20, 2017

Abstract

This study presents an analytical model of flexible riser, and implements it into finite element software ABAQUS to investigate the fatigue damage of helical wires near touchdown point. In the analytical model, the interlayer contact pressure is simulated by setting up springs between adjacent interlayers. The spring stiffness is iteratively updated based on the interlayer penetration and separation conditions in the axisymmetric analysis. During the bending behavior, the axial stress of helical wire along the circumferential direction is traced to determine whether the axial force overcomes the interlayer friction force and thus lead to sliding. Based on the experimental data in the literature, the model is verified. The present study implements this model into ABAQUS to carry out the global analysis of the catenary flexible riser. In the global analysis the riser-seabed interaction is simulated by using a hysteretic seabed model in the literature. The effect of the seabed stiffness and interlayer friction on the fatigue damage of helical wire near touchdown point is parametrically studied, and the results indicate that these two aspects significantly affect the helical wire fatigue damage, and the sliding of helical wires should be taken into account in the global analysis for accurate prediction of fatigue damage. Meanwhile, different from the steel catenary riser, high seabed stiffness may not correspond to high fatigue damage of helical wires.

Copyright (c) 2017 by ASME
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