Formation and Propagation of Steep Waves: An Investigative Experimental Interpretationby P. G. Manciola, Univ of Perugia, Perugia, Italy,
A. Mazzoni, Univ of Perugia, Perugia, Italy,
F. Savi, Univ of Perugia, Perugia, Italy,
Abstract: From the end of the last century, many Authors have studied experimentally the formation and the propagation of steep waves on dry flume bottom. Up to the present time, however, some aspects of this phenomenon have not been sufficiently explained. The movement of the water immediately after rapid gate opening is mainly controlled by vertical acceleration due to gravity. It follows that the gradually-varied flow hypothesis is not valid in this initial phase and the motion is two-dimensional. Moreover, the type of gate and the velocity of opening influence the flow across the section and the wave celerity. Investigative experiments were conducted in a rectangular flume with the aim of studying in detail the flow through the gate section and the celerity of propagation of the wave immediately after the lifting of the gate. The tests were conducted at the Department of Hydraulic and Environmental Engineering at the University of Pavia by removing a top hinged sluice gate which dams in different sections a flume with horizontal bottom. A series of tests was carried out by using an adverse slope base at the downstream reach of the flume. The experiments were observed through the transparent walls of the flume by using three video cameras synchronized with the gate opening device. The video images, digitized directly by the video recorder, were processed and vectorized. In the gate section, the discharge showed a clear peak immediately after opening and thereafter it stabilized at the critical-state theoretical value. Other tests were conducted imposing a wave reflecting wall at the downstream section of the flume. The mixing of flows caused by the superimposition of waves travelling in opposite directions was studied by injecting a tracer. The experimental investigations were interpreted with the aid of a mathematical model which integrates the unsteady motion equations of a gradually varied free surface flow according to a finite difference scheme.
Subject Headings: Gates (hydraulic) | Wave propagation | Flumes | Water waves | Gradually varied flow | Imaging techniques | Wave reflection | Water discharge
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