Two Dimensional Numerical Simulation Of Forced Oscillating Circular Cylinder

With the exploration of marine oil and gas resources moving to the deepwater,various kinds of offshore platforms which have the good adaptability to the deep water environment have been used widely.Risers are the most important and necessary components no matter what kind of platforms are used.The studies of dynamic responds of risers have always been the hot spot in offshore engineering for a long time.But until now,most research activities are focused on self-excited vibrations.Compared with self-excited vibration, forced oscillation of circular cylinder need to be paid more attentions both in experimental and numerical study,considering it can provide more information of energy transfer and the relationship between vortex sheeding and vibrations.In this thesis,computational studies of sinusoidal forced oscillation of circular cylinder are performed.Based on the Navier-Stokes equations,k-ωturbulent model,finite element method and arbitrary Lagragian-Eulerian method a hybrid numerical model is developed. The numerical simulations are conducted both at low Reynolds number(Re=100,Re=200) and subcritical Reynolds numbers(Re=10000).The study is focused on the aspects such as time histories of forces,Variation of forces with the frequencies,lock-in regions and vortex characteristics in wake regions.The relationship between fluid force and oscillating frequency is discussed.The lock-in regions are concluded in different oscillating amplitudes using FFT spectral analysis and compared well with availiable experimental data.The 2S,2P and P+S wake modes are also modeled successfully using the present numerical model.It shows that the present two-dimensional model is able to predict the elementary characteristics of VIV,but a three-dimensional viscous numerical model is necessary for the accurate numerical solution VIV in quantity.