Investigation on Vortex Induced Vibration Characteristics of Three-dimensional Marine Riser Considering Cross and Inline Flows Coupling Effect

Abstract

ABSTRACT Marine risers typically experience nonlinear vibration failure problems caused by the ocean vortex excitation force. To resolve this, the Hamilton variational principle is applied to establish a vortex-induced vibration (VIV) model for a flexible riser. A wake oscillator model is employed to simulate the vortex-induced forces of cross flow (CF) and inline flow (IL) and their coupling, considering the effect of top tension and internal flow on the riser. The VIV model is solved by combining the Newmark–β and Runge–Kutta methods and then verified by comparing the calculation results of the proposed vibration model with data in published literature. Based on the foregoing, the effects of uniform flow, top tension, and shear flow on the VIV behaviour of risers with a large aspect ratio are systematically investigated. Moreover, the VIV characteristics are identified. First, the results demonstrate that, when the top tension is 10 t, the IL vibration is 0.73 Hz and the CF vibration is 0.36 Hz, which shows that the IL vibration is twice as high as the CF vibration. Moreover, the amplitude of the latter is between 7 and 21 times that of the former, which are respectively 0.018 and 0.12 m. Second, the shear velocity and top tension also have considerable influence on the IL vibration under shear flow. Third, the CF vibration has a frequency-locking effect under shear flow and uniform flow conditions. The IL vibration exhibits a frequency-locking effect under uniform flow and a multifrequency effect under shear flow. The study led to the formulation of a theoretical method for safety evaluation and a practical approach for effectively improving the service life of marine risers.