Pressure Fluctuation On Structures:Experimental Data Analysis

Abstract

Pressure fluctuations have been recorded on the upstream face of a sill with the presence of a hydraulic jump. Pressures have been investigated through 12 different flow configurations and in 9 vertical points on the central axis of the sill. The maximum-recorded value depends both on the sampling frequency and on the experiment duration: that leads to the question of which pressure value has to be considered to design the structures. Different models of structures have been adopted. A comparison with natural frequencies of such structures is carried out, after performing a scale transformation of both pressures and frequencies using the Froude similitude, according to different authors. Natural frequencies of the simpler structures have been computed, while they have been taken from literature for complex structures. Then a spectral analysis has been carried out on the recorded data. Results show that in general there is little difference between the design carried out with the average-recorded and the spectra-analysis pressure values. Pressure fluctuations might produce a stronger excitation when the natural frequency of the structure is abnormally low. Instead, there are no problems when the structure is a baffle or a sill. An experimental formula is also suggested in order to assess design forces on this kind of structure.