The Study On The Parametric Vibration For Top-Tension Riser In Deep-sea

In recent years,the production and consumption of oil and other petroleum product have been rapidly increasing, which has led to the scarcity of easily retrieved offshore oil field. As a result, oil producers are motivated to go to deep sea to develop oil and gas in that severe environment, at depths of 1500 meter and more. Riser is a catheter that connected surface floating platforms and submarine equipments at the sea bed. It is one of the most important components of marine structures, but also the weakest components. The riser system has always been a hot research field of petroleum engineering due to the harsh marine environment. Currently the theory of shallow water riser is relatively mature, but the research on deep-sea riser is still at initial stage.In this paper, the basic theory of parametric vibration, the derivation of Mathieu equation and Mathieu instability domains is introduced. The pure parametric vibration of marine riser is studied to reveal the parametric resonance mechanism. Parameters of the riser and marine environment are changed to study the relationship between parametric instability domains and these parameters, determining key parameters that have great impact on parametric resonance. The vibration of riser caused by wave, current and heave excitation is studied using finite element method. At last, the parametric vibration and VIV of risers are studied.Research shows that when the heave frequency is equal to 2 times the natural frequency of riser, the first order parametric resonance occurs; the first parametrically excited instability zone is the most important part of the instability zone. Due to damping, high-order instability zones rapidly move up, so they have little importance for riser. When designing a riser, we should adjust the parameter to make the natural frequencies out of 4~12s. The parametric excitation has little influence to riser's vibration due to wave,but the depth of water is the key parameter for riser'fatigue life. The parametric excitation has great impact to VIV on both the amplitude and frequencies, especially when the parametric excitation equals 2 times the first order natural frequency.