A jig stratifies grains by density using a pulsating water column. Each grain falls at its terminal velocity: drag balances buoyant weight, ½ ρw Cd (πd²/4) v² = (π/6) d³ (ρp − ρw) g, with the Schiller-Naumann drag law Cd = 24/Re (1 + 0.15 Re0.687) (floored at the Newton value 0.44). The solver bisects for v for every grain.

In the bed, a grain moves at dy/dt = uw(t) − vt h, where uw is the water velocity of the pulsation (sinusoidal, peak U0 = 2π f A) and h = (1 − φ)4.65 is the Richardson-Zaki hindered-settling factor. The bed is compact on the suction stroke (φ = 0.52) and dilated on the lift (φ falls to 0.22), so light grains are lifted and heavy ones are not. Grains of different density settle equally fast when d1/d2 = √((ρ2 − ρw)/(ρ1 − ρw)) (Stokes regime) or d1/d2 = (ρ2 − ρw)/(ρ1 − ρw) (Newton regime), which is why feed is sized before jigging.

Simplifications: eight independent 1D columns, no lateral mixing, no suction through the screen, sinusoidal pulsation. Densities: scheelite 6100, quartz 2650 kg/m3. Educational model.