yade-dev team mailing list archive

[Bruno Chareyre <1734653@xxxxxxxxxxxxxxxxxx>]

Q1 - I think it is possible to define a relevant geometry for multiple
cracks; it is just the intersection of one tetrahedron with multiple
polygonal faces. I think the problem of multiple fracture planes
crossing one edge is very special, I would escape it on the basis that
you can't break another time something that is already broken, so 2
planes = 1 crack locally if the two planes intersect.

> Q2. [...] area should be "weighted" by the number of fractured edges

As explained before it should be enough to accumulate the conductivities from different cracks. In pseudo code:
for e in crackedEdges:
    for facet incident to e:
        facet->conductivity += trickPermeability(edge) #currently the '+=' is a '='
The triangular surface you mention also appeared in Robert's proposal. It makes sense to use it in trickPermeability().
Problems of your equation are that 1/ it assumes the four points are in the same plane, not the case in practice, they define two triangles in two different planes and 2/ it cannot be used for 3 broken edges. 
If 2 triangles are coplanar the above loops will produce your equation for 2 broken edges (it implies that the broken edges are parallel, which can only happen at a boundary of the problem).

Q3: I would say yes, but I don't really see the problem.
Except that V(tetrahedron)-V(spheres) doesn't make much sense when the spheres are just computational nodes.

Q4. How do we define matrixPorosity?
I would leave that to the user. 

Q5. No. Why would we do that? The total volume of a cell is changing and
it must be balanced by some fluid fluxes regardless of the cracks.

Bruno

-- 
You received this bug notification because you are a member of Yade
developers, which is subscribed to Yade.
https://bugs.launchpad.net/bugs/1734653

Title:
  DFN+fluid compressibility not using the correct reference volume

Status in Yade:
  New

Bug description:
  In the basic PFV scheme the incremental change of density of a pore
  fluid after a change of pore volume is dependent on dV/Vo where Vo is
  the reference pore space within a tetrahedral cell [1], i.e.
  V(tetrahedron)-V(spheres).

  In DFNFlow "V" should reflect the fact that porosity is mainly due to cracks, i.e. it is much smaller than the numerical porosity calculated between spheres.
  Typically V=opening*area+matrixPorosity*cellVolume
  Currently it is using the same formula, hence overestimating the compressibility effect (because the DEM porosity is larger than a typical rock porosity). What should be the reference "opening" in above formula is to be clarified though, it has physical as well as numerical implications. Maybe slotInitialAperture is a candidate? Let you DFN people tell what it should be.

  Note that the "dV" is less a problem because it is a difference
  (independent on the choice of the reference volume), so the
  incompressible scheme is not affected.

  Bruno

  [1]
  https://github.com/yade/trunk/blob/master/pkg/pfv/FlowEngine.ipp.in#L439

To manage notifications about this bug go to:
https://bugs.launchpad.net/yade/+bug/1734653/+subscriptions