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ConcentrationFlux Command

The ConcentrationFlux command applies concentration or transport fluxes to surfaces near particles (which are expected to be on the surface) in MPM calculations. It applies a flux to all particles within the shape for a ParticleBC block.

ConcentrationFlux (mode),(face),(style),(value),<(timeOrRes)>,<(phaseStyle)>

where the parameters depend on the type of concentration or transport flux being applied. The two types of flux boundary conditions, which depend on (mode), are as follows.

Externally Applied Flux

This condition applies a surface concentration or transport flux (in solvent flux units or transport flux with units given below) for transport flux per unit area. A positive value is flux into the material while a negative value is flux out of the material. The parameters are:

Coupled Flux

This version calculates the concentration or transport flux (in solvent flux units or transport flux with units given below) from a function of the difference between the particle concentration potential or transport value and an entered bath value. The parameters are:

Use the optional (phaseStyle) parameter to set flux for other transport tasks. The options and their flux units are:

  1. "solvent" or "moisture" (or 1) - Using this option reverts to command with the (phaseStyle) parameter
  2. "fracture" (or 3) - generally not used; would change flux units to (energy units)/(length units)2.
  3. "battery" (or 4) - generally not used.
  4. "conduction" (or 5) - set flux in units Coulombs/((time units)-(length units)2). For Legacy units (which are mm-g-sec), the flux is in A/mm2.

Transport flux options other than "solvent" cannot use the (style) = "silent" option. When specifying (phaseStyle), the (value) and (timeOrRes) parameters are required for alignment; they can entered as 0 if not otherwise needed.

Notes

  1. All calculated concentrations are done using a concentration potential, which is required to be nonnegative (and can optional by limite to interval [0,1]). Thus the output flux may differ from specified boundary condition fluxes.
  2. Given an applied concentration flux of J, the expected concentration gradient normal to the surface with applied flux will be J/(ρ D) where D is diffusion constant (this calculation is assuming isotropic materials). In simulation output, however, the resulting concentration gradient may differ whenever the concentration is near either 0 or the saturation concentration.