Breathing Phenomena in Driven, Confined, Granular Chains

We consider a tapered granular alignment where the spherical grains progressively shrink in radius by a factor $q$. The system has a hard wall at one end and a piston at the other. We assume that the piston can be used to impart a force $F$ (time- dependent or otherwise) to an edge grain in the system. Extensive particle dynamics simulations and theoretical analysis reveal that such a system could revert back and forth between an oversqueezed state and a dilated state - i.e., ``breathe." The breathing is strongly dependent on the driving. When driven with a constant force, we show that $TF^ {1/6}$ is a constant for fixed $q$. More complex dynamics including nonlinear-resonance is observed when $F=F(t)$. The talk shall discuss the observed dynamical responses of the system.