EXPERIMENTAL AND NUMERICAL INVESTIGATION OF THE INLET EFFECT ON THE DYNAMICS OF A WATER INTAKE PIPE

A water intake pipe/riser is an important component in deep seawater utilization technologies. Regarding the issue of flow-induced vibration, the concern of instability due to the internal flow has received considerable interest. A key question, particularly in the water-aspirating pipes, is the effect of the inlet flow on the dynamics. This study experimentally investigates the internal flow and inlet effects on the dynamics of a hang-off water intake pipe under top-end excitations. The results indicate that the internal flow effect increases inline response. In particular, it suggests the existence of a bifurcation phenomenon, where the amplitude significantly increases under excitation at slightly shorter periods than the natural period. The experiments further compare different inlet shapes: bellmouth, T-shape and L-shape; however, no significant differences in their response characteristics are observed. The second part of this paper provides a discussion based on CFD simulations stressing the contribution of the contracted jet formed inside the pipe and the sink flow in the vicinity outside the inlet to the dynamics of the water intake pipes.