Main Help → All Commands → Diffusion Calculations / MPM Boundary Conditions → ConcentrationFlux
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.
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:
(mode)
must be external
to indicate it is an external concentration flux.(face)
specifies the particle surface that is on the edge and has the flux. In 2D, imagine a box around the initial particle. Surfaces 1 to 4 are the four edges of the box in the order bottom, right, top, and left (with normals (0,-1), (1,0), (0,1), and (-1,0)). In 3D, imagine a cube around the initial particle. Surfaces 1 to 4 are same as for 2D (now with normals (0,-1,0), (1,0,0), (0,1,0), and (-1,0,0)), 5 in the bottom z surface (normal = (0,0,-1)), and 6 is the top z surface (normal = (0,0,1)).(style)
specifies the style of the applied concentration flux. The setting depends on two parameters specified by arguments (value)
and (timeOrRes)
. If either argument is not supplied, they are set to zero. The standard units are solvent flux units for (value)
and alt time units for (timeOrRes)
(but the units may change depending on the (style) setting).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:
(mode)
must be coupled
to indicate it is a coupled concentration flux.(face)
must be the boundary face (see above).(style)
must be function
.(value)
must be the function
for the the applied flux. It is entered as a user-defined function of t
and entered as quoted text. At each time step, the variable t
will be replaced by the difference between the particle concentration potential and the entered reservoir concentration potential in parameter #5. The function should evaluate to the desired flux in alt time units. The function can additionally depend on particle position (x
, y
, z
, D
, T
, R
, or Z
in length units), and/or clockwise particle rotation (q
in radians).
(timeOrRes)
is the concentration potential of the surrounding reservoir.
Note that because t
is used for particle concentration, a couple surface flux function cannot depend on time.