Enter a value or expression for the Diffusion coefficient Dc of each species in the corresponding input field. This can be a scalar value for isotropic diffusion or a tensor describing anisotropic diffusion. Select the appropriate tensor type —
Isotropic,
Diagonal, or
Symmetric that describes the diffusion transport, and then enter the values in the corresponding element (one value for each species).
This section is only available with the Advanced Physics Options selected and when the model contains a split between the material frame and the spatial frame. A split of these frames occurs when using a
Moving Mesh node or a Structural Mechanics interface like
Solid Mechanics. In such a model, the reference geometry (the material frame) differs from the deformed geometry (the spatial frame). The diffusive transport of species is solved for on the material frame, but the equation is adjusted for geometry deformations so that species conservation is achieved on the spatial frame. Use the
Diffusion model to define the frame of reference for the diffusion tensor.
Select Reference geometry based (Lagrangian) to specify the diffusion tensor in the undeformed geometry, implying that the diffusion is defined in the material frame (indicated by coordinates
X,
Y,
Z). This is the preferred setting for an anisotropic diffusion in combination with solid body translation or rotation. Also in general when the diffusion tensor components have been measured in an undeformed geometry.
Select Deformed geometry based (Eulerian) to specify the diffusion tensor in the deformed geometry. This means that the diffusion is defined in the spatial frame (indicated by coordinates
x,
y,
z). Use this setting when the diffusion tensor components have been measured in a deformed geometry.
The Advanced Physics Options is found in the
Show More Options dialog box, accessed by clicking the
Show More Options button (
).