Angle of Repose of Powders
The maximum angle of the slope that keeps stability without falling apart
when it is piled up soil (a rock piece or sand) and a powder grain body
(culm) with "the angle of repose"
Spring elements are placed from the powders center radially here and
the powders surface are modeled by uniting the tip with contact elements.
The behavior of each powders are calculated under an symmetrical motion
of walls on both sides in the opposite direction at constant speed.
