Axial and transverse coupled vibration characteristics of deep-water riser with internal flow

The present paper investigates the axial and transverse coupled vibration law of deep-water top-tensioned riser (TTR) under the combined effects of the internal fluid flow and external wave and current loads. The paper aims to derive nonlinear vibration equations of deep-water riser, which account for the coupling of axial and transverse vibration including vortex-induced vibration, the internal fluid flow and the changes of the riser cross-sectional area caused by internal and external pressure alteration. With all factors above involved, a coupling vibration model is developed for deep-water riser. Based on the numerical model established, the influences of internal flow and the changes of internal flow velocity on the coupled vibration of deep-water riser are analyzed. In addition, parameter excited dynamic response of the riser under complex environment is also studied. The comprehensive analysis demonstrates that the internal flow can greatly change the vibration characteristics of the riser, comparing with a hollow one. The results lend support to the conclusion that the vibration of riser is not sensitive to changes of the internal flow velocity. (C) 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).