The drag coefficients may be determined by first noting that the equations presented here reduce to those of Berryman and Wang  in the low frequency limit by merely neglecting the inertial terms. What is required to make the direct identification of the coefficients is a pair of coupled equations for the two increments of fluid content and . These quantities are related to the displacements by and .
The pertinent equations from Berryman and Wang  are
.^(1).^(2) = k^(11) & k^(12) k^(21) & k^(22) p_,ii^(1) p_,ii^(2) , where is the shear viscosity of the fluid, and the ks are permeabilities including possible cross-coupling terms. We can extract the terms we need from (finaleom), and then take the divergence to obtain
b_12+b_23 & - b_23 - b_23 & b_13+b_23 (B<>U^(1) - B<>u) (B<>U^(2) - B<>u) = - p_,ii^(1) p_,ii^(2) . Comparing these two sets of equations and solving for the b coefficients, we find
b_12 = ^(1)(k^(22)-k^(21)) k^(11)k^(22)-k^(12)k^(21),
b_12 = ^(2)(k^(11)-k^(12)) k^(11)k^(22)-k^(12)k^(21), and
b_23 = ^(1)k^(21) k^(11)k^(22)-k^(12)k^(21) = ^(2)k^(12) k^(11)k^(22)-k^(12)k^(21). For many applications it will be adequate to assume that the cross-coupling vanishes. In this situation, b23 = 0,
b_12 = ^(1)k^(11) and
b_13 = ^(2)k^(22), which also provides a simple interpretation of these coefficients in terms of the porosities and diagonal permeabilities.
This completes the identification of the inertial and drag coefficients introduced in the previous section.