Two-dimensional dam-break wave analysis: particle image velocimetry versus optical flow

Dam-break waves have been the focus of a number of research papers; next to analytical investigations, scaled experimental models and numerical simulations are used to determine dam-break wave propagation. Experimental models and data analysis tools are necessary to generate calibration data for numerical models. Often, particle image velocimetry (PIV) algorithms are used to calculate two-dimensional velocity fields of propagating dam-break waves. This paper deals with a visual analysis method called optical flow (OF). An experimental model was built to identify the initial stage of dam-break waves. A comparison between results using the PIV method and the OF method is given to identify flow velocities for two-dimensional dam-break waves. It can be shown that the OF method is able to predict resulting velocity profiles accurately. The mean relative error for the comparison of manually observed data and OF results is less than 6%, while for the PIV comparison an error of 11% can be calculated. Since velocity vectors are produced for all image pixels, the resulting information density is high compared to results produced by the PIV method.