Publications
Mass movement and Geophysical hazards
Illustration of the process for gradually developed mudflow event.
Mass movements are one specific kind of flow that occurs naturally on the Earth's surface (and over the surface of any other planet :-) ). They are characterized by the movement of solid material (sediments) due to the action of gravity. They usually are defined as function of the sediments and the interstitial fluid. Debris flow, mudflow, hyper-concentrated flow, ice avalanche, magma flow, lahar flow, are all examples of a mass movement.
In this area of expertise, I focus my projects on understanding the natural phenomenon and adapting the mathematical and numerical models to predict properties of naturally occurring flows.
I've been doing research to study aspects of sediment transport under special conditions for runoff flows. Also, I've been exploiting mathematical models to assess their capabilities to represent debris and mud flows. Those models usually employ a macroscopic rheological constitutive law, function the sediment concentration. See, for example, our last case-study on a monitored debris-flow event.
An interesting perspective of this work is related to climate changing. As we are able to develop more accurate and representative models, we can identify the controlling parameters, and even find variations of patterns that extrapolate our earthly lifetime. This kind of study is interdisciplinary and must be developed in partnership with physicists and geomorphologists.
Hydrodynamic Instabilities in Shearing Flows
At this specific subject, I'm interested in understanding the interaction between two different layers of flowing fluids. This kind of study is interesting because it helps us understand the fundamental principles of turbulence development.
Roll waves are the phenomenon that attracts me the most. Although I'm also intrigued and started doing research on Kelvin-Helmholtz instabilities.
Examples of free surface instabilities in free-surface flows can be seen in the figure. To the left, from up to bottom: tidal bore (also known as mascaret in French, or pororoca in Portuguese) at Vayres, Gironde, France, in a photo from Jacques Dassie personal website; roll waves on clean water turbulent flow at Turner Reservoir, San Diego County, California, USA, on February 24, 2005, from personal website of Victor Miguel Ponce; free-surface instabilities in a complex non-Newtonian fluid (Chanson et al., 2006). To the right: roll waves in a concrete channel in Lions Bay, B.C., from the professional website of Prof. Neil Balmforth, from the University of British Columbia.
Here you can see a personal video I made when working in my past Laboratory LH2, at FEIS-Unesp, as a record of the work we've done there. This experimental setup was designed and instrumented by me with the help of my colleagues. It is still operational nowadays, but with better instruments to perform measurements. Roll waves can be produced for laminar flows of Newtonian or non-Newtonian fluids, at any desired frequency.
Don't forget to mute the video up if you are not a fan of Kings of Leon. ;-)
In the present days, I work on CFD (using OpenFOAM) to explore characteristics of roll waves phenomena and validate mathematical models that could be capable to rapidly predict the properties of such dynamic phenomenon. In the figure to the right, we can see the influence of non-Newtonian properties of the flow in the wave properties. This is crucial for stakeholders to develop assertive safety projects whenever dealing with natural phenomena where those waves could appear.
Photometry and Imaging Techniques
Sometimes, due to the characteristic size of laminar flows (runoff, film flows, porous media, etc.), it becomes difficult to assess flow properties without disturbing them considerably. In this way, photometry and imaging techniques are powerful tools to measure and quantify flow fields without probing them with a blunt body. Light can be manipulated in the experiment and be used to quantify interface displacement, velocity fields, streamlines, recirculation zones, and many others. Currently, I'm working to assemble a team here in UFRGS, together with partners from all around the world, to be specialized in such kind of technique. We aim to measure and quantify properties using techniques such as Particle Imaging Velocimetry, Particle Tracking Velocimetry, Light Absorption Technique, Boundary Tracking, among others.
Light absorption technique can be employed for detecting the interface movement at a low scale, with good precision.
Sand-trap device for measuring sediment transport in runoff flows through PTV technique.
For a runoff flow, (free-surface turbulent flow with small height), we can obtain the RMS-values for the velocity fluctuations using PIV technique, for example.