[P-PS02] Regolith Science

[PPS02-01] Brazil-Nut Effect in a sloped bottom box

*Nithin Nallani¹, Devang Khakhar², Ishan Sharma¹ (1.Indian Institute of Technology Kanpur, 2.Indian Institute of Technology Bombay)

Keywords:Brazil Nut Effect, Segregation, Boulders, Itokawa, impact induced seismic vibrations

We study the Brazil-Nut Effect in a vertically vibrated box with a sloped base connecting two flat regions at different elevations (see image). Boulders are placed at random positions inside the box, filled to a certain depth with grains. Bed depth above the two flat portions of the base differs, forming deep and shallow regions. On vertical vibration of the box, boulders move horizontally towards the shallow region. The instantaneous velocity field of the grains is periodic, with a time period four times the period of oscillation of the box. This velocity field in the deep region is two-dimensional, i.e. there is no variation of the velocity field in the Y direction, and the velocity component along the Y direction is zero. However, the velocity field is three-dimensional in the shallow region. The XY projection of the velocity field in the shallow region is either converging or diverging towards a set of vertical axes.

Time averaging the overall velocity field reveals a pair of circulation loops of different sizes. The larger circulation loop carries boulders from the deep region to the shallow region. The boulders get stuck in the shallow region, leading to net migration towards it. Our study may help explain the formation of smooth areas, such as the Muses Sea, on the asteroid Itokawa, which is subjected to multiple impact-induced seismic vibrations throughout its life.