Abstract
The vortex induced vibrations of a pipeline close to seabed is investigated in this dissertation numerically. Firstly, a novel wake oscillator model is extended from the classic Van der Pol equation by introducing an additional nonlinear term and two empirical coefficients to account explicitly for the effects of the gap ratio and mass ratio. Then, the model parameters are calibrated against available experimental data following that the proposed model is validated. The results show that the numerical results seem to match the experimental data broadly and the model is fairly robust.Moreover, to further understand the proposed model, the analytical solutions are obtained and analysed. To get the analytical solutions, the primary resonance is mainly investigated and the amplitude-frequency equations are derived, then the analytical solutions are compared with the numerical solutions of the full model. It is found that the analytical solutions with regard to the primary resonance can capture the essential vibration behaviour of VIV. It is found that the structure damping can restrain vibration amplitude of the cylinder but has little effect on the resonance range, while the mass ratio can suppress both the vibration amplitudes and resonance ranges.
The VIV of a pipeline close to sea bed is also investigated based on Euler–Bernoulli beam theory and a newly developed wake oscillator model. Using Finite Element Method, the models are calculated numerically. It is observed that the maximum value of vibration amplitude of pipeline at midspan increases and the resonance ranges get wider with the increase of gap ratio in the range of 1 ≤ e/D < 5 opposite in the range of e/D < 1. Besides, the resonance ranges tend to shift towards smaller reduced velocities as e/D increase in the range of e/D < 1.
| Date of Award | 2016 |
|---|---|
| Original language | English |
| Sponsors | China Scholarship Council |
| Supervisor | Ping Dong (Supervisor) |