Coupled-Mode Vibration of Gates with Simultaneous Over- and Underflow

Abstract

Experimental results from two-dimensional model studies of long-span shell-type gates undergoing simultaneous over- and underflow are presented. In general, shell-type gates undergo bending vibrations in both the streamwise (horizontal) and vertical directions which are coupled through hydrodynamic forces acting on both the gate crest and the upstream weir plate, usually consisting of vertical and inclined faces. In the present study, however, a two-dimensional gate model with only a vertical weir plate (i.e., no inclined weir plate) and large overflow was tested to determine the role of overflow alone in self-excitation. The resulting self-excited vibrations are characterized in terms of vibration frequency ratios, a reduced fluid-excitation coefficient, a reduced added mass and the trajectories of gate motion. Careful examination of the test results permitted a clear definition of the mechanism of coupled self-excitation due to overflow.