Self-propelled particles are autonomous agents that convert a certain amount of internal energy into motion. When a group of these particles passes through a constriction, unwanted intermittent behavior may appear. This phenomenon, which can lead to a complete arrest of the flow, has been observed in various systems: pedestrians, animals, bacteria, granular material, etc. [1,2,3]. It has been postulated that the properties of these intermittencies depend on the relative size between the particles and the opening, the random component in the motion of the particles, and the pressure exerted on the opening. A feature that has been observed in these systems is that the pressure exerted depends on the type of confining geometry [4,5]. For this reason, the interplay between flow and pressure needs to be studied in detail.

The aim of this study is to characterize the flow of particles and the pressure exerted at the opening by varying the number of participating agents. To achieve this, we employed 50 vibration-driven vehicles known as Hexbug Nano [6] and constructed an enclosure with a silo-type opening where the vehicles can flow through. To measure the exerted pressure, we installed two force sensors on the walls of the opening. An overhead camera was used to capture the system's dynamics and to determine the particles' positions, orientations, and exit times.

Bibliography:

[1] Discrete element crowd model for pedestrian evacuation through an exit Lin Peng, Ma Jian, Lo Siuming.

[2] M. Delarue, J. Hartung, C. Schreck, P. Gniewek, L. Hu, S. Herminghaus, and O. Hallatschek, Self-driven jamming in growing microbial populations.

[3] G.A. Patterson, P.I. Fierens, F. Sangiuliano Jimka, P.G. König, A. Garcimartín, I. Zuriguel, L.A. Pugnaloni, and D.R. Parisi Phys. Rev. Lett. 119, 248301 – Published 13 December 2017, Clogging Transition of Vibration-Driven Vehicles Passing through Constrictions.

[4] G. Junot, G. Briand, R. Ledesma-Alonso, and O. Dauchot Phys. Rev. Lett. 119, 028002 – Published 12 July 2017, Active versus Passive Hard Disks against a Membrane: Mechanical Pressure and Instability.

[5] José M. Pastor, Angel Garcimartín, Paula A. Gago, Juan P. Peralta, César Martín-Gómez, Luis M. Ferrer, Diego Maza, Daniel R. Parisi, Luis A. Pugnaloni, and Iker Zuriguel Phys. Rev. E 92, 062817 – Published 15 December 2015, Experimental proof of faster-is-slower in systems of frictional particles flowing through constrictions

[6] Hexbug Nano. https://www.hexbug.com/nano.html.