Faisal Balarabe Usman Haladu Garba and Musa Alhaji Ibrahim

Keywords: Viscoplastic surges, complex topographies, Rheology, Natural hazards, Fringe projection technique, Numerical simulation, Experiment

Abstract

This paper presents an experimental study of a dam break configuration in which free surface of a viscoplastic fluid deposited on a complex 3D topography was tracked and measured. Due to the coexistence in the flows of fluid and solid zones, whose respective boundaries are unknown, simulating the propagation and deposition of free-surface viscoplastic surges remains challenging especially when the topography is complex. The main goal of this study is to perform a well-controlled laboratory experiment which could lead to the recovery of local height of the material deposited on the free surface of the topography through monitoring the propagation of the surges. When the viscoplastic material is deposited on the topography after it reaches an arrested state, an innovative stereoscopy technique (fringe projection) was used. The fringe projection technique is applied to collect the raw data in form of images for further processing. This technique has been commonly used to generate 3D surface information. It simply consists of a video projector projecting a sinusoidal fringe pattern on a surface and a camera-taking image of the surface for further post-procession. The data collected from the experiment was post[1]treated sequentially as follows; shadow masking, phase shifting, phase unwrapping, filtering and determination of the actual phase signal using Python codes. The actual height of the topography was accurately recovered when two reference surfaces were considered (i.e., the reference plate and the naked topography). In each case, the material is deposited on the topography and their height profiles were plotted. This method allowed us to accurately compute and compare the local height profiles. The two profiles were found to be completely superimposed which turns out that the agreement between these two ways of computing the deposits is excellent. Furthermore, when the experimental height profile has been examined critically, a deviation of 2-2.3mm and 0.48mm were recorded on the upper and lower part of the topography respectively.