Experimental Study of Self-Excited Vibrations of a Flexible Weir due to Fluid Discharge

Abstract

This paper deals with the characteristics of unstable self-excited vibrations of a rectangular, flexible weir installed between two tanks, over which the water in the upper tank discharges into the lower one. Experiments were done for measuring vibrational strains of the weir, oscillation of the overflow water thickness, and the oscillations of the water surface in the upper and lower tanks with changing inlet velocity of water into the upper tank and water discharge height. Four unstable vibration modes were found in our experiments. The 1st unstable vibration mode was sloshing-dominated weir vibration and its vibration frequency was almost equal to the sloshing one for the lower tank. The 2nd one was a high frequency vibration of the weir unrelated to the sloshing oscillation and the 3rd one was a torsional one of the weir with a high frequency different from the 2nd one. The 4th mode was peculiar to the experimental system due mostly to the coupling between the inlet water jet and the weir The phase relations between the weir vibration and overflow water thickness were experimentally investigated.