Three-dimensional vortex-induced vibration analysis of catenary-type risers under flow with different incident angles

This paper proposes a three-dimensional (3D) numerical model for the analysis of vortex-induced vibration (VIV) on catenary-type risers (CTRs). Fully considering the geometrical nonlinearities and large deformation behavior of CTR, this model is established based on the vector form intrinsic finite element (VFIFE) theory and the independence principle (i.e., consider only the flow component perpendicular to the riser axis). The riser is discretized into a finite number of particles, the motion of these particles only has to satisfy Newton's second law and the structure is in perpetual dynamic equilibrium under the combined excitation of internal and external forces on the particles. Moreover, the unsteady hydrodynamic force associated with cross-flow (CF) vibration is modeled as distributed Van der Pol wake oscillators. The model is used to predict the VIV response of the CTRs under various flow conditions (i.e., in-plane uniform flow, shear flow, and diverse angled flow), and the results show well agreement with the corresponding experimental results. Then, the CTR's VIV characteristics under diverse angled flow are further analyzed. The obtained results highlight that the incident angle of the flow has a great influence on the mode transition, frequency locking position, energy transfer, and internal forces.