Measurements of time-dependent free-surface viscoplastic flows down steep slopes

The objective of this thesis was to increase our understanding of gravity-driven geophysical flows by developing a new platform to simulate avalanches of fluid in the laboratory. To simulate flow avalanches in the laboratory, we created a unique experimental setup consisting of a metallic frame supporting a reservoir, an inclined aluminum plane, and a horizontal run-out zone. At 6-m long, 1.8-m wide, and 3.5-m high, the structure is probably the largest laboratory setup of its kind in the world. In a dam-break experiment, up to 120 liters of fluid can be released from the reservoir down the 4-m long inclined plane. We precisely control initial and boundary conditions. To measure the free-surface profile, a novel imaging system consisting of a high-speed digital camera coupled to a synchronized micro-mirror projector was developed. The camera records how regular patterns projected onto the surface are deformed when the free surface moves. We developed algorithms to post-process the image data, determine the spreading rate, and generate whole-field 3-dimensional shape measurements of the free-surface profile. We compute the phase of the projected pattern, unwrap the phase, and then apply a calibration matrix to extract the flow thickness from the unwrapped phase. 56 different flow configurations, with a wide range of inclinations, were finally tested with Newtonian and viscoplastic fluids. For each test, the evolution of the free surface was recorded in 3 dimensions. Different flow regimes were observed, which depend on: the plane inclination, the setup geometry, the volume, and characteristics of the fluid. Partial agreements were found between theoretical models and our results.

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