My name is Tess Homan. I currently work as a post-doctoral researcher at Institut Lumière Matière, Universite Claude Bernard Lyon-1 de Villeurbanne with Hélène Delanoë-Ayari, Charlotte Rivière, and Jean-Paul Rieu on the use of soft probes in MultiCellular Spheroids. On this website you will find some of the projects I worked on in the past years.
At the moment I am studying the formation and properties of a dynamic suspension. If particles are slightly heavier than the liquid, they will sediment in a granular bed. By blowing air through the bed the top particles are mixed into liquid. They will settle again, but other particles continue to be taken out of the bed. We call this equilibrium mixed state a dynamic suspension. Besides studying the properties of the mixed phase we are also interested in how bubbles rise through such a complex medium. In a hele-shaw setup we are able to visualize the bed morphology, the rising air bubbles, and the local particle fraction.
Using a smart particle we perform direct acceleration measurements of a ball impacting on sand. We find detailed dynamics that cannot be seen in the position data such as, a downward acceleration due to the cavity collapse and the influence of interstitial air on the bed compressibility.
I did my PhD under supervision of Devaraj van der Meer and Detlef Lohse in the physics of fluids group at the university of Twente, on the influence of interstitial air on the movement of fine sand. Here you can find a pdf of my thesis and the photos of the defense.
The force that needs to be exerted to push a ball into a loose granular bed is lower when there is air present inside the bed. Pressurized, trapped air in front of the ball reduces the experienced drag.
The air pressure in the volumes above and below a loose granular bed is recorded during the impact of a metal ball. Air gets trapped inside a region of compressed sand around the ball, temporarily lowering the pressure above the bed.
As soon as an object hits the side wall of a container filled with very loose sand, the sand bed collapses. The amount the bed level changes decreases when the air pressure is lower. This indicates that interstitial air has a lubricating effect on the friction between grains.
Using an X-ray tomography system it is possible to "see" what happens inside a granular bed after the impact of an object. Different analyzation techniques give a reconstruction of the air cavity, the shape of the air bubble and the density changes in the sand.
If a metal ball impacts on fine, very loose sand, the bed behaves fluid like and the ball sinks into the bed. As soon as the cavity that is created behind the ball collapses a jet is created that rises above the bed surface.
When food is getting scarce a group of the single cellular organism Dictyostelium agglomerates. During my internship at the group of Wolfgang Losert at the university of Maryland I tracked the boundary movement of a Dicty cell to find the protrusions and retractions.
During an internship in the group of Tomas Bohr at the technical university of Denmark I investigated the formation and surface flow of a rotating polygon on a water surface.
The shape of the splash that forms after the impact of a ball on sand depends on the ambient pressure. When air is present, the splash becomes more vertical due to the suction of air flowing into the cavity created behind the ball.
6 - Tess Homan, Rob Mudde, Detlef Lohse, and Devaraj van der Meer, X-ray measurements of a ball impacting on loose sand, Journal of Fluid Mechanics 777, 690-706 (2015)
5 - Sylvain Joubaud, Tess Homan, Yoann Gasteuil, Detlef Lohse, and Devaraj van der Meer, Forces encountered by a sphere during impact into sand, Physical Review E 90, 060201 (2014)
4 - Tess Homan, Christa Gjaltema, and Devaraj van der Meer, Collapsing granular beds: The role of interstitial air, Physical Review E 89, 052204 (2014)
3 - Gabriel Caballero, Kevin Kelly, Tess Homan, Joost Weijs, Devaraj van der Meer, and Detlef Lohse, Suction of splash after impact on dry quick sand, Granular Matter 14, 179-184 (2012)
2 - Meghan Driscoll, Colin McCann, Rael Kopace, Tess Homan, John Fourkas, Carole Parent, and Wolfgang Losert, Cell shape dynamics: From waves to migration, PLoS Computational Biology 8, e1002392 (2012)
1 - Raymond Bergmann, Laust Tophoj, Tess Homan, Pascal Hersen, Anders Andersen, and Tomas Bohr, Polygon formation and surface flow on a rotating fluid surface, Journal of Fluid Mechanics 679, 415-431 (2011)