None of them are related to my question .. !

I understand the question to mean that permeable constituent materials may be anisotropic (such as fiber bundles modelled as a single, larger fiber) and you wonder why GeoDict allows only isotropic permeable constitutents.

It turns out, GeoDict has the technology in place in principle.

The flow solvers in FlowDict can do a fully anisotropic Brinkman term and the gof (GeoDict Orientation File) format that lets one turn a permeability vector into any orientation in space, i.e. provide the solver with the Brinkman coefficients that one may specify per material, such as parallel and perpendicular to the direction of the fiber bundle.

But two ingredients are still missing.

First, a good idea how to make the pre-processing for anisotropic constituents available as easy as all the other pre-processing in GeoDict. Second, a sponsor who requires this feature urgently enough to raise the pressure (and funds :) for the implementation.

For fiber bundles, the orientation is straight forward when the fiber bundles are modelled, because their orientation is known at the time of creation. For scanned models (from micro CT or FIB SEM, for example), this information can be estimated with the FiberGuess and FiberFind modules. So, stay tuned, anisotropic constituents for flow simulations will become available in GeoDict at some point in the near future. 

Thanks, Andreas.

Hi Andreas,

I have a quick question regarding boundary condition on the solid pore interface in FlowDict. Is it no slip? Or some shear balance? I mean when we assume the fiber bundles to be solid, how the flow goes to zero in the solid phase?

Regards,

Ali

Dear Muhammad

The standard boundary is no-slip, as you expect. We are also working on slip flow, but that turned out to be very difficult on voxels. There, you set the component of the flow that is normal to the boundary to zero, while the tangential component may be non-zero. But in a staircase, you set alternatingly x- and y- component to zero and will not achieve significant slip unless the fow is parallel to the coordinate axis. Out approach with Lipinf Cheng and Sven Linden is to in the future use subgrid information and use a representation of the tangent direction on the voxels to get a proper implementation of slip flow.