Author(s): Kojiro Tani, Ichiro Fujita, Hideto Yoshimura
Linked Author(s): Kojiro Tani
Keywords: Water surface deformation, sampling Moir� technique, Space-Time Image Velocimetry (STIV), image analysis
Abstract: The characteristics of water surface deformation is subject to various causes such as the sub-surface turbulence structure but detailed examination of the free-surface dynamics has not been fully understood yet. In order to examine the water surface features in a laboratory scale flow, a sampling moir� method was used to capture the two-dimensional deformation at a high sampling rate. The target flow is a shallow open- channel flow roughened by density packed glass marbles. For the shallow flow with a depth one and a half times the marble diameter, time-dependent water surface features were captured by varying the Froude number. The instantaneous water surface profiles were analyzed as a form of the space-time image expression to examine the advection feature of the surface pattern. Subsequently, in order to clarify the spatial and temporal behavior of water surface fluctuations, the frequency wavenumber spectra were calculated. According to the results, the effect of dispersive gravity waves travelling on the water surface is greater than non-dispersive waves advected by the turbulence in the hydraulic condition where the rough wall effects directly influence the free-surface dynamics. In addition, the intensity of water surface fluctuation is found to increase with the squared value of the Froude number, which can be estimated from a theoretical consideration
Year: 2017