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Theory Manual Version 3.6
 Subsection 3.2.1: Linearization Up Section 3.2: Weak formulation for biphasic materials Subsection 3.2.3: Discretization 

3.2.2 Stabilization

Finite element models of deformable porous media are known to exhibit oscillations in fluid pressure caused by relatively coarse meshes near free-draining boundaries, where a boundary layer in fluid pressure normally forms during the early time response to loading. These spurious oscillations typically occur when the mesh is not able to resolve this boundary layer. Stabilization methods serve as an alternative to mesh refinement, when the latter is not feasible or practical. In FEBio we have implemented a stabilization method based on the work of Aguilar et al. [1]. Basically, this method proposes that the fluid flux be evaluated from instead of eq.(2.5.1-6), where represents the stabilization parameter. A representative value for may be evaluated from where is the element thickness on the free-draining boundary, is a representative measure of the solid matrix elastic modulus and is a representative measure of the hydraulic permeability tensor . The contribution of this form of to the virtual work expression in eq.(3.2-2) is The linearizations of are then given by
 Subsection 3.2.1: Linearization Up Section 3.2: Weak formulation for biphasic materials Subsection 3.2.3: Discretization