Inserting Darcy’s law (Equation 7-22) into the continuity equation produces the generalized governing equation
Insert the definition of fluid compressibility χf = (1/ρ)(∂ρ/∂p) to the right-hand side and rearrange to arrive at
In this equation, S is the storage coefficient (SI unit: 1/Pa), which can be interpreted as the weighted compressibility of the porous material and the fluid. The storage
S can be an expression involving results from a solid-deformation equation or an expression involving temperatures and concentrations from other analyses. The Darcy’s Law interface implements
Equation 7-26 in the
Porous Medium node, which explicitly includes different storage models to choose from, such as
linearized storage which defines S (SI unit: 1/Pa) using the compressibility of fluids
χf and of the porous matrix
χp: