Three-dimensional reconstruction of the oscillatory free-surfaces of a flow over antidunes: stereoscopic and velocimetric techniques

Abstract

We present imaging methods developed to characterize the oscillatory free-surface of rapid flows and apply them to torrential currents propagating over sediment antidunes. The aim is to obtain high-resolution relief maps of the free-surface topography, in order to highlight the regular spatial patterns associated with the bedforms. Two measurement principles are outlined and tested, both based on the imaging of floating tracers dispersed on the rapidly flowing surface. The first relies on direct stereoscopic measurements obtained using two cameras, while the second exploits an original velocimetric principle allowing to derive elevation from the velocity field acquired using a single camera. The measurement procedures and image analysis algorithms are introduced for the two methods, along with the physical assumptions underlying the velocimetric principle. The results of the two techniques are compared for different free-surface patterns and good correspondence is obtained. The obtained relief maps vividly depict the variety of motifs that can evolve as a result of interaction between shallow flows and loose sediment beds.

Stereoscopic and velocimetric reconstructions of the free surface topography of antidune flows

“…To permit cross-validation, the two methods are applied to the same experiments, while each relies on its own separate camera footage and data analysis pipeline. Preliminary results of the present research effort were reported in Devriendt et al (1998) and Douxchamps et al (2000).…”

Three-dimensional Voronoï imaging methods for the measurement of near-wall particulate flows

“…The second case is a mature debris flow of PVC particles featuring steep concentration and velocity gradients, and constitutes a challenging test for the particle-tracking techniques. Monocular imaging results for similar flows were presented in Capart et al (2002), while some preliminary stereo results were described in Douxchamps et al (2000) and Spinewine et al (2000).…”