Characteristic Study On Vertex-Induced Motions Of Multi-Cell SPAR Platform

Oil will still be the most important energy for human beings in the coming 20 years. The peak of oil production which is predicted by many scientists is postponed by the fast development of deep water oil fields. Huge demand, consistent input and the great improvement of deep sea technology has rendered deep water oil & gas the next growing point for oil production. Spar as the newest type of platform, is specialized for the deep water oil production. However, unlike other platforms, Spar has a natural default: vortex-induced motions (VIM). Scholars and researchers have done a lot of works on formation, evolvement and maximum response. Nevertheless, there are still a lot of problems outstanding for VIM of Spar due to many reasons.State Key Laboratory of Ocean Engineering of Shanghai Jiao Tong University independently brings forward a new concept design: Cell Truss Spar (CT Spar), based on the previous 3 generations of Spar. CT Spar takes in the advantages of previous Spars. It costs relatively low but produces oil efficiently. Before it formally goes to Industry for field production, systemic study of VIM performance of CT Spar must be carried out.This thesis firstly summarizes previous studies on VIM of Spars, introduces the main control function of VIM and its main influence factors: environment parameters, general attribute of Spar Hull, mooring system, etc. The important reference factors of this research are fluid force coefficient, movement responses and flow field. Among many influence factors, current velocity, current directions and number of buoyancy cell outside the hull are selected for serial studies. This research relies on numerical simulation experiments. Turbulence model SST kωis used for CFD calculations and moving mesh method is employed to realize vortex-induced motions.CT Spar II-B is simplified into a 2D numerical model 8-CT Spar in a Cartesian coordinate system. Validation is done to test mesh. Serial experiments in 4 different directional currents and 9 different current velocities are carried out. Results of those experiments state that current direction has little influence on lift and drag coefficients, but do affect the maximum amplitudes and zero positions of lift coefficient. Velocity contour plots can match up with their corresponding fluid coefficients. This thesis designs and develops 6-CT Spar and 9-CT Spar based on 8-CT Spar. Flow fields and movement responses are studied for fixed Spar experiments and oscillating ones. X-CT Spar hereafter represents 6, 8 and 9-CT Spar. Results of numerical experiments show characteristics of flow field for fixed X-CT Spar are similar with 8-CT Spar in previous research. When X-CT Spars are in self-excited oscillation, fluid force coefficients reduce remarkably, whereas those parameters become considerably large when X-CT Spars in lock-in area. In relative high current velocity, movement responses of X-CT Spars show unstable beat phenomena. Maximum value of displacement can be achieved for X-CT Spar subjected to current in certain direction. Upon limited data, the movement responses of 8-CT Spar are largest, 6-CT Spar smallest and 9-CT Spar smallest. Velocity, vorticity contour plots, together with their corresponding time series of lift, drag coefficients and movement responses will show periodic regulations of VIM.