Sam Ocko, School of Engineering and Applied Sciences, Harvard University. Professor Eun-Ah Kim, host.

Seminar title: Feedback induced phase transitions in active porous media

Abstract: Flow through passive porous media is typically described in terms of a linear theory relating current fluxes and driving forces, in the presence of a prescribed heterogeneous permeability. However, many porous systems such as glacial drainage networks, erosional river bed networks, vascular networks, social insect swarms and animal architectures such as termite mounds are continuously remodeled by the flow and thence modify the flow, i.e. they are active. We consider a reduced-complexity model for an active porous medium where flow and resistance are coupled to each other i.e. the porous medium is modified by the flow and in turn modifies the flow. Using numerical simulations, we show that varying the form of the feedback from flow-avoiding to flow-seeking results in both channelization and wall-building transitions. A continuum model allows us to understand the qualitative features of the resulting phase diagram. The relationship between the form of the feedback and the structures formed is consistent with natural systems.