Groups of interacting active particles, insects, or humans can form clusters that hinder the goals of the collective; therefore, development of robust strategies for control of such clogs is essential, particularly in confined environments. Our biological and robophysical excavation experiments, supported by computational and theoretical models, reveal that digging performance can be robustly optimized within the constraints of narrow tunnels by individual idleness and retreating. Tools from the study of dense particulate ensembles elucidate how idleness reduces the frequency of flow-stopping clogs and how selective retreating reduces cluster dissolution time for the rare clusters that still occur. Our results point to strategies by which dense active matter and swarms can become task capable without sophisticated sensing, planning, and global control of the collective.

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When small particles like, flour, pollen, etc., contact an air-liquid interface, they disperse rapidly in the lateral direction. Using direct numerical simulation (DNS) we showed that the rapid dispersion is due to the fact that the capillary force pulls particles into the interface causing them to accelerate to a large velocity. The vertical motion of a particle during its adsorption causes a radially-outward lateral flow on the interface that causes nearby particles to move away. The goal of this study is to experimentally analyze the reasons for the rapid dispersion of particles when they are simultaneously adsorbed at a two-fluid interface. Specifically, we will analyze the effect of particle size on the oscillatory behavior of a single particle, as it is being trapped at an air-water interface. The diameter of a particle will be varied between 300–850 μm. Our experimental setup consists of a high speed camera with a resolution of 512×512 pixel and the recording speed up to 3000 frames per second which is connected to a 12X microscope. The camera outputs are analyzed to determine the frequency and amplitude of oscillation during adsorption. The measured amplitudes and frequencies for the micro glass spheres used in the experiment were found to be in qualitative match with the DNS results.