Dynamic three-dimensional displacement analysis of small-scale granular flows by fringe projection and digital image correlation

Abstract

In this work, we present experimental results that show the feasibility of measuring three-dimensional displacement in models of dry granular avalanches. For this purpose, we have used a technique that is capable to measure simultaneously the three involved mutually perpendicular components of displacement on the free surface of the granular flow. The approach comprises two simultaneously used optical techniques: fringe projection, FP, and digital image correlation, DIC; the first technique yields the out-of-plane component of displacement, and the second one, the two in-plane components. Combination of both techniques is achieved by color encoding, which consists in using different color illumination sources for the two optical techniques, in conjunction with a camera recording in RGB. The resulting combination is robust since the illumination sources are non-coherent between them, avoiding any optical interference. This contribution shows the potentiality of the method to analyze dynamic events, by presenting temporal full-field sequences of displacement of small-scale granular flows down an inclined plane, at camera speeds up to 2000 fps. These types of measurements are valuable for validation of physical and numerical models related with the analysis of the dynamic behavior of granular flows in the earth. Because these phenomena, which include rock avalanches, debris avalanches, debris flows, and pyroclastic density currents, are among the most dangerous natural hazards in mountainous and volcanic areas, the possibility to foresee their behavior in a more precise way is extremely important in order to elaborate more rigorous physical models and improve the predictive capacity of the simulation software.