In an oscillating incompressible flow field the force per unit mass acting on a fluid particle is obtained from Newton's second law in intensive form F av + (V.V)V at m Suppose the characteristic speed and characteristic length for a given flow field are V, and L, respectively. Also suppose that is a characteristic angular frequency (rad/s) of the oscillation (Fig. 1). Define the following nondimensionalized variables. t' = wt, x* = ±‚ V*= Lʊ, and V* - Since there is no given characteristic scale for the force per unit mass acting on a fluid particle, we assign one, noting that). Namely, we let (A) = Nondimensionalize the equation of motion and identify w2L m any established (named) dimensionless parameters that may appear. Fig. 1 Fim