ABSTRACT
Vortex-induced vibration (VIV) has a serious impact on the fatigue life of a submerged floating tunnel (SFT). Both analytical method and finite element method (FEM) are used in this study to investigate the dynamic response of a single-span SFT when VIV occurs. The SFT is simplified as a simply supported Euler-Bernoulli beam in the mathematical model. A spring-mass-damper equation with a cubic nonlinear term is established to describe the dynamic motion of the structure. Fluid drag and damping force are calculated using Morison equation. And the fluid-structure interaction (FSI) is considered by introducing a van der pol-based wake oscillator. Besides of the analytical method, a non-linear FEM based on update Lagrangian method and Newmark method is also developed in this paper. The results of both methods show great consistency. It is demonstrated that FSI and structural nonlinearity have a non-negligible influence on the dynamic response of the SFT. The model with FSI will produce a wider resonance range and a higher peak mid-span response. The nonlinear terms serve as restoring forces, increasing the stiffness of the tube structure and influence the dynamic response indirectly. In designing an SFT structure, changing span length is an effective way to reduce the fatigue damage caused by VIV.
