Stereo vision for noninvasive dynamic measurements of the scour process around a circular cylinder in an oscillating flow

Abstract

A novel three-dimensional measurement technique which uses a stereo vision approach to recover the morphological evolution of a sandy bottom around a vertical pile is presented. In particular, the bottom time evolution due to the wave action was observed from the initial flat bed condition until a stable configuration was attained. Moreover, some morphological parameters of the scour, such as the maximum scour depth, the extension of the eroded area and the position of the maximum scour toe, were measured at equilibrium condition. These quantities were estimated with an average relative accuracy of about five percent, which appears particularly appropriate if compared to the results given by traditional measurement strategies. The key parameter which controls the phenomenon is the Keulegan-Carpenter number (KC). The experimental measures of the scour depth at equilibrium stage were compared with the empirical relations proposed by Sumer et al. (1992) giving a fairly good agreement, while for other three-dimensional features, such as the eroded area, new relations with typical dimensionless parameters useful for design purposes are proposed.