Nonlinear three-dimensional dynamics of a marine viscoelastic riser subjected to uniform flow

The three-dimensional nonlinear dynamic model of a long marine riser with Kelvin-Voigt viscoelasticity properties under vortex-induced vibration is proposed and investigated. The objective is to find the appropriate viscoelastic coefficients to suppress the nonlinear dynamic response of a marine riser. The pipe is placed in a uniform cross flow and geometric nonlinearities are considered. Two distributed and coupled Van der Pol wake oscillators are applied to characterize the fluctuating lift and drag coefficients, respectively. The highly nonlinear fluid-structure interaction equations are directly coupled and solved by the finite element method. Firstly, the model is validated by comparing with published experimental data and numerical simulation results. Then, modal analysis is performed to determine the impact of viscoelastic coefficients on the natural frequency for different damping values. A nonlinear dynamic analysis is carried out to determine the impacts of the viscoelastic coefficients on displacements, stresses, modal variation and phase portraits. The results show that the viscoelastic coefficients have a significant effect on the natural frequency of the studied marine riser. It is also demonstrated that appropriate viscoelastic coefficients are very important to effectively suppress the maximum displacements and stresses.