# Inertial drag in granular media

## TL;DR

This paper investigates how acceleration affects drag force on objects in granular media, revealing regimes where inertial effects dominate and proposing a model to describe these forces based on grain mobilisation.

## Contribution

It introduces an elasto-inertial drag force model that captures the effects of acceleration on drag in granular materials, highlighting differences from steady loading conditions.

## Key findings

- Inertial regime where acceleration enhances drag
- Identification of rate-independent and inertial regimes
- Development of a physical model based on grain mobilisation

## Abstract

Like in liquids, objects moving in granular materials experience a drag force. We investigate here whether and how the object acceleration affect this drag force. The study is based on simulations of a canonical drag test, which involves vertically uplifting a plate through a granular packing with a prescribed acceleration pattern. Depending on the plate size, plate depth and acceleration pattern, results evidence a rate-independent regime and an inertial regime where the object acceleration strongly enhances the drag force. We introduce an elasto-inertial drag force model that captures the measured drag forces in these two regimes. The model is based on observed physical processes including a gradual, elasto-inertial mobilisation of grains located above the plate. These results and analysis point out fundamental differences between mobility in granular materials upon steady and unsteady loadings.