On the effect of internal flow on vibrating catenary risers in three dimensions

The complete 3D nonlinear dynamic problem of extensible, catenary risers conveying fluid is considered. For describing the dynamics of the system, the Newtonian derivation procedure is followed. The velocity field inside the pipe is formulated using potential theory. The hydrodynamic effects are taken into consideration through the nonlinear drag forces and the added inertia due to the hydrodynamic mass. Following the Newtonian derivation, the dynamics of the pipe element and the fluid element are considered separately and the final governing set is derived by combining the equations of inertia equilibrium. The study focuses specifically on the effect of the inner flow to the global dynamics of the riser. This task is accomplished using both time and frequency domain solution techniques. The former apply to the complete nonlinear system and the latter to the reduced linearized set. The effect of the inner flow is assessed based on numerical predictions which were obtained after extensive numerical computations and eventually some very interesting conclusions are drawn.