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Diffusion Command

The Diffusion command activates generalized diffusion-style calculations.

Diffusion (style),<(conc0)>,<(nolimit)>

where

When doing "solvent" diffusion, the calculations use a "concentration potential" defined as c/csat where (csat) is a "reference" (or "saturation") concentration defined in material properties. The two optional parameters apply only when modeling "solvent" diffusion:

When solvent diffusion calculations are activated, you must define diffusion constants of the materials used in the analysis. Diffusion is coupled to strains through concentration-induced expansion, but only if you enter non-zero values for concentration expansion coefficients when defining the materials.

Other diffusion options can be used with or without solvent diffusion. Their use depends on material support for their calculations and you must define any required material properties.

Notes

  1. Diffusion calculations and poroelasticity calculations both model fluid transport between particles and in fact use much of the same code. As result, they cannot be used simulataneously. An MPM simulation can only use one of them.
  2. Diffusion calculations often benefit by periodic FMPM, especially when particle concentrations oscillate with a cell.
  3. Although all initial particle concentrations and all concentration or concentration flux boundary conditions are set using concentration potential, when concentration and concentration gradients are archived, they are converted to actual weight fraction concentration results using the material's saturation concentration setting.
  4. Note that (style)=2 corresponds to poroelasticity calculations, but they should be activated instead with a poroelasticity command.
  5. The Diffusion command is only allowed for MPM analyses.