Three-dimensional Vortex-induced Vibration Nonlinear Dynamics of A Flexible Viscoelastic Fluid-conveying Riser

In this paper, the geometric nonlinearity and hydrodynamic characteristics of a long flexible viscoelastic riser under the interaction of internal and cross-flow velocity are presented. The system governing equation is obtained by using the extended Hamilton principle. The drag and lifting coefficients of coupled and distributed van der Pol wake oscillators are established to represent hydrodynamic of ocean currents. The effects of internal flow velocity, cross-flow velocity and viscoelastic coefficient on the stresses, displacements, natural frequency and mode variation of the pipeline are theoretically investigated. The results show that the cross-flow velocity, internal velocity and viscoelastic coefficient have important impacts on the vibration amplitude and critical internal fluid velocity of the riser. Additionally, the cross-flow velocity, internal fluid velocity and viscoelastic coefficient have vital effects on the riser mode order. Therefore, choosing the appropriate viscoelastic coefficient can reduce the vibration amplitudes of the riser. These findings have important reference value for the design and control of ocean riser.