“…Under our modeling assumptions, the settling velocity, U, of the sphere is given by the balance of Stokes' drag (neglecting permeability effects 14 ) and buoyancy, 2013) where ρ e (z) is the ambient fluid density, z = Z(t) is the sphere center depth, and V is the sphere volume. The mass of the sphere, M sph (t), is dependent on the porosity of the sphere P and solid density ρ s , M sph (t) = P Vρ s + P M fl (t) , where P = (1 − P).…”