The Dynamic Response Analysis Of Deep Water TTRs Induced By Platform Random Heave And Vortex

The riser is one of the most important equipments in the development of the oiland gas in deep sea. The dynamic response of riser was studied with consideringvortex vibration and random heave motion of the up floater.The differential equation of heave motion was set up with considering the floateron the irregular wave and this was the random parametric excitation of the riser. TheVan der Pol wake oscillator model was applied to calculate the time varying liftcoefficient, and the vortex induced lift was determined. Considering the vortexinduced lift and random parametric excitation, the vibration equation of riser was setup. Then the program was edited to calculate the dynamic response of the riser, andthe characteristic of the vibration was studied. The TRUSS SPAR was chosen as theup floater and the JONSWAP spectrum was chosen to calculate the wave force andthe heave motion of spar. It determined the random parametric excitation in differentsea conditions. With the shear flow and wake oscillator model, the lift coefficient andvortex induced lift were calculated. Then the dynamic response of TTR wascalculated with the program. The effect was researched when changing the riserparameters, flow and the random wave. In addition, the model of riser with two endshinged was adopted when studying the stochastic stability.The results show that the coefficient of lift and the displacement of the vibrationincreased when considering random parametric excitation and vortex-inducedvibration. And the main frequency of the vortex vibration reduced compared to noparametrical excitation. Comparing with the significant wave height, the wave periodgreatly influenced the response of the riser. It shows that the stability of the nth modeof parametrically excitation depends on the spectral density of the excitation at twicethe natural frequency associated with that mode. And the condition of the stabilitybecomes severe with the increase of N.