Water Column Oscillation in Partially Immersed Vertical Tubes

Abstract

Theoretical and laboratory studies were presented for the water column oscillation in a vertical tube partially immersed in a reservoir. Three types of oscillations were studied, with the top of the tube being fully open (free oscillation), the top capped with a hose for ventilation (damped oscillation), and the top fully capped (capped oscillation). Governing equations of the oscillations were established and good estimations of the oscillatory characteristics were obtained. In the experiments, the periods of the free oscillations and the damped oscillations were close, whereas the period of the capped oscillations was shorter, which was due to the effect of the trapped air in the tube above the water column. The damped oscillation had quicker decay than the free oscillation. Due to the finite size of the reservoir used in the experiments, the recorded oscillations were the superposition of the water column movement in the vertical tube and the surface wave of the reservoir. The former dominated the oscillation at the beginning, whereas the latter became dominant in the end. By approximating the two components as sinusoidal waves, the beats in the recorded oscillations were estimated, and the results were in good agreement with the experiments.