ABSTRACT
The way moves are performed deserves some special considerations. Since we are dealing with three speeds that are not simple multiples of the smallest one, we have introduced a real-valued accumulator for the displacement of each grain.At every cycle of move, the grain speed is added to this accumulator. Once it surpasses the unity, the grain is allowed to move and the accumulator is returned to zero. It is also borrowed when the direction of movement changes. In order to add gravity, we introduce a time accumulator. At every cycle of moves, only particles without a neighbor below can add to this accumulator. When it reaches one, a minimal velocity is added in the gravity direction. This procedure can be use to simulate a vertically-vibrating sandbox at different values of the dimensionless acceleration = A(2π)2/g, with A the oscillation amplitude, f the frequency and g the gravity acceleration, just by changing the fixed amount that is added by gravity at each cycle of moves.
