arXiv subjects

Fu-Ling Yang

Publications and source records attributed to Fu-Ling Yang.

2 recordsLinked to original sources

arXiv2024

Digging through 2D densely-packed coarse granular media as a critical phenomenon

We create a mechanical digger able to move within 2D densely-packed granular media, in a manner intrinsically different from the existing biomimic diggers. The characteristics of our design include that the average grain size is about one tenth as large as the digger, and the area packing density {\phi} for testing is between about 0.610 and 0.762. Unlike conventional autonomous diggers that move by fluidizing the surrounding granular media with a much finer grain size, our digger uses a different mobility mechanism as coarse grains with interparticle friction are hard to be fluidized. To cope with high interparticle friction, the digger has a circular shape and singly captures granular particles near the front entrance of the recess formed by the center unit running across its body and then ejects the captured particles backwards. We validate this moving strategy in both experiments using a manual digger and the corresponding numerical simulations, and demonstrate that the moving efficiency can be enhanced by the judgement of the human operator but the effectiveness is not significantly influenced by the shape of granular particles. In addition, localized vibration is needed to degrade friction between interlocked irregular-shaped particles. Our numerical results show that the distribution of both moving distances and time intervals between consecutive ejections follow a power-law. Reducing {\phi} shrinks the spatial and temporal spans over which the power laws hold. Further, we experimentally verify this finding by demonstrating that similar power-laws are observed from an automated digger which periodically randomizes its digging direction. Finding these spatio-temporal power laws indicates that digging within a densely-packed granular environment could be a critical phenomenon.

cond-mat.soft↗

arXiv2020

Enhanced flow rate by the concentration mechanism of Tetris particles when discharged from a hopper with an obstacle

We apply a holistic 2D Tetris-like model, where particles move based on prescribed rules, to investigate the flow rate enhancement from a hopper. This phenomenon was originally reported in the literature as a feature of placing an obstacle at an optimal location near the exit of a hopper discharging athermal granular particles under gravity. We find that this phenomenon is limited to a system of sufficiently many particles. In addition to the waiting room effect, another mechanism able to explain and create the flow rate enhancement is the concentration mechanism of particles on their way to reaching the hopper exit after passing the obstacle. We elucidate the concentration mechanism by decomposing the flow rate into its constituent variables: the local area packing fraction $\phi_l^E$ and the averaged particle velocity $v_y^E$ at the hopper exit. In comparison to the case without an obstacle, our results show that an optimally placed obstacle can create a net flow rate enhancement of relatively weakly driven particles, caused by the exit-bottleneck coupling if $\phi_l^E > \phi_o^c$, where $\phi_o^c$ is a characteristic area packing fraction marking a transition from fast to slow flow regimes of Tetris particles. Utilizing the concentration mechanism by artificially guiding particles into the central sparse space under the obstacle or narrowing the hopper exit angle under the obstacle, we can create a man-made flow rate peak of relatively strongly-driven particles that initially exhibit no flow rate peak. Additionally, the enhanced flow rate can be maximized by an optimal obstacle shape, particle acceleration rate towards the hopper exit, or exit geometry of the hopper.

cond-mat.soft↗