Measurements of the 3-D scour process around a pile in an oscillating flowthrough a stereo vision approach

The knowledge of the evolution of the scour around a vertical cylinder plac ed in a sandy bed and exposed to waves is of fundamental importance in ocea nic engineering. Measurements of this phenomenon are very difficult to be p erformed due to the mandatory constraint of adopting non-invasive technique s. In this paper a novel three-dimensional measurement technique which uses a stereo vision approach has been adopted in order to dynamically recover the bottom characteristics. In particular, the sandy bottom time evolution was here observed from the flat bed initial condition until a stable config uration was attained. Moreover some morphological parameters of the scour s uch as the maximum scour depth, the extension of the eroded area and the po sition of the maximum scour toe were measured at equilibrium condition. The se quantities were estimated with art average relative accuracy of about 5% , which appears particularly appropriate if compared to the results given b y traditional measurement strategies. These latter being not particularly s uitable for dynamic analysis of bottom evolution. The experimental investig ation performed in this paper allowed co confirm some theoretical hypothese s, such as that of considering the Keulegan-Carpenter number (KC) as the ke y parameter which controls the phenomenon, to be confirmed. Moreover the ex perimental measures of the scour depth at equilibrium stage, has been compa red with the values given by the relation proposed by Sumer et al. (1992) g iving a fairly good agreement. Finally, with regards to other three-dimensi onal features such as: the eroded area, new relations with standard dimensi onless parameters have been proposed that result useful for design purposes . (C) 2001 Elsevier Science Ltd. All rights: reserved.