Abstract

This paper develops a comprehensive method to make the riser vibration simulation more efficiently and closer to reality. The dynamic control equation contains the coupling vibration in both inline (IL) and crossflow (CF) directions and is solved by Matlab programs. In order to consider the fluid–structure interaction (FSI), a novel change is developed in the Wilson–θ method iteration steps, i.e., by predicting the riser body vibration velocity two steps before the current time step. A simulation case shows the vibration responses of the IL–CF coupling effects and FSI on vibration responses.

INTRODUCTION

The research object of this paper is the drilling riser system on a TLP/Spar platform. This riser is a kind of TTR. The bottom of TTR close to the mudline is a stress joint sitting above the conductor and casings, and the top is a dry wellhead and surface BOP sitting at the wellhead slot of the platform. Because the most section of the riser is submerged in sea water, it is often in a state of vibration induced by waves and currents, which may cause fatigue damage to the structures (API RP 2RD, 1998).

Riser dynamics calculation is a basic step to obtain installation operating window, weak point analysis and fatigue analysis. In commonly used commercial software, the wave–induced vibration in IL direction and the vortex–induced vibration in CF direction are generally calculated separately, and the coupling effects of the IL and CF directions are not fully considered. Engineering calculations often use fixed fluid force coefficients, and do not fully consider the effect of FSI; if FSI is fully considered, it requires to do three–dimensional CFD numerical simulation. Such calculation is complicated, time–consuming, and difficult to use in engineering.

As a key issue, for decades, scholars have repeatedly optimized the calculation method of riser dynamics, considering from different aspects, and gradually improving the calculation efficiency, the degree of closeness to the actual project, and the ease of use in an engineering design. Williams (2010) discussed the optimization of drilling riser operability envelopes for harsh environments, in which soft/hard riser hang–off configurations for storm events were assessed. Chen, Li and Zheng (2015) evaluated the impacts of top–end vessel sway on vortexinduced vibration of a submarine riser for a floating platform in deep water. Iwona, Lucyna andŁukasz (2015) analyzed the influence of vessel motion on dynamics of risers by the rigid finite element method. Fan, Li and Wang (2017) developed a method for dynamic analysis of a hang-off drilling riser considering internal solitary wave and vessel motion, in which the Wilson–θ method and the preconditioned GMRES algorithm were used. However, most literatures separately calculated the wave–induced vibration in the IL direction and the vortex–induced vibration in the CF direction, and taken fluid force coefficients as fixed values.

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