Seminar - Steve Cochard (University of British Columbia, Canada) - Avalanches of fluid in the laboratory
Monday 23 February 2009, 12.00 noon - 1.00 pm
PNR Tutorial Room T315
The objective of this work was to increase our understanding of gravity-driven geophysical ﬂows by developping 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 pro jector was developed. The camera records how regular patterns pro jected 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 pro jected 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.
Steve graduated in mechanical engineering from l'Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland in 2000.
Before starting his PhD, he had been working for five years in civil engineering companies as an aero-thermodynamics engineer:
First, he joined for one year the Research and Technology Department of SNCF (French National Railway Company) in Paris, France as a consultant on the implementation of solutions to problems related to the complex and hazardous side-wind eﬀect of the new TGV line Paris-Marseille.
Second, he joined the Tunnel Ventilation Group at Electrowatt Infra AG in Zürich, Switzerland. He was a project leader for the development and improvement of ventilation systems on several existing tunnels or tunnel projects in particular in case of fire.
He started his PhD at the Environmental Hydraulic Laboratory at EPFL in 2004 on the dynamics of free-surface flows on steep slopes, with the objective of modeling natural hazards induced by water such as mudflows and avalanches.
He is now a Postdoc at the University of British Columbia, Canada, where he is still working on the dynamic of of free-surface flows on steep slopes.