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ConcentrationFlux Command

The ConcentrationFlux command applies concentration 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)>

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

Externally Applied Concentration Flux

This condition applies a surface flux in units of kg/(m^2-sec) for transport rate of substance 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 Concentration Flux

This version calculates the concentration flux from a function of the difference between the particle concentration potential and an entered bath concentration potential. The parameters are:

Note that because t is used for particle concentration, a couple surface flux function cannot depend on time.

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.