The rise and sink dependence on the shape of a horizontally wiggling intruder

TL;DR

This study explores how the shape and oscillation parameters of a horizontally moving intruder affect its vertical motion in granular media, using DEM simulations and a cavity-based model to predict rise and sink behaviors.

Contribution

It introduces a cavity-based empirical model linking intruder shape and oscillation dynamics to vertical motion in granular media, supported by DEM simulations.

Findings

Vertical velocity depends on oscillation amplitude, frequency, and shape.

Maximum rise occurs when cavity filling time matches half the oscillation period.

A minimum amplitude exists below which the intruder's vertical position remains unchanged.

Abstract

We investigate the effect of shape and orientation for a horizontally oscillating intruder on its vertical dynamics in a granular medium via Discrete Element Method (DEM) simulations. Five distinct intruder shapes were considered in this study: a disk (OS1), a square (OS2), two rectangles with aspect ratio > 1 (OS3) and < 1 (OS4) respectively, and an equilateral triangle (OS5). The vertical velocity of the oscillating object was observed to be a function of amplitude and frequency (f) (inverse of time period (T)) of oscillation, and the shape of the object. The dynamics of the motion are modelled with the help of a cavity based model which can empirically produce the regimes observed by incorporating the free fall of the particles filling the cavity.The cavity based model assumes that there is a point on the surface of each oscillating object unique to its shape that any grain crossing it will irreversibly reach the bottom of the cavity. This leads to the creation of bed of particles at the bottom of the cavity which increases intruder's elevation as it oscillates, leading to its vertical rise in the granular medium. When an intruder oscillates much faster than the falling rate of the grains, the intruder cannot rise up and thus sinks due to energy provided by the oscillation to the bottom layer. On the contrary, if the intruder oscillates too slow, the cavity gets completely filled much before it returns. The maximum rise rate is thus observed at the oscillation time period where the cavity filling time is equal to the half time period of oscillation. In addition, we observed a minimum amplitude (Amin) below which the vertical position of the IO remains unaltered for various T. We have also presented the time-averaged pressure P, velocity V, and area fraction {\phi} fields around the intruder shapes.