yade-dev team mailing list archive

[Luc Scholtès <lscholtes63@xxxxxxxxx>]

1) Remark about the aperture of the cracks:

"However, an obvious problem of this is that it result in a reference
equal to zero when the crack occurs, and we need to divide by this
volume..."

Currently, if the crack occurs under tensile loading, its aperture is
not null when it appears. It is actually set equal to the normal
relative displacement needed to break the bond (interparticle distance
at the moment of breakage). Your remark made me think about the physical
relevance of such model and I tend to believe that this is OK if you
imagine what is happening between two stretched out cemented grains.

2) Use of "aperture" in calculation of fluid volume:

The "aperture" used in the calculation of the local conductivity is equal to:
- mechanical aperture + residual aperture if mechanical aperture > residual aperture
- residual aperture if mechanical aperture <= residual aperture
Moreover, a facet is not tricked if mechanical aperture <= 0 and residual aperture <= 0 (e.g. for closed induced cracks). 
"aperture" should thus never be equal to zero for a tricked facet and it can be used for computing the volume of a cell associated to a tricked facet. 

3) Computation of the crack volume:

a) Currently, the local conductivity is computed considering that the
flow occurs between parallel plates with same width and length equal to
the distance between the connected cells centers. If this is still OK
for everyone, is it compatible with Robert's proposal? I feel like there
would be something wrong in the case of a facet with multiple broken
edges since the conductivity is computed considering only one of the
broken edge aperture while the crack area (and therefore the crack
volume) is computed as the sum of the broken edges surface... Should we
add (or average?) the crack dimensions for both the conductivity and the
crack area? Why don't we use directly the size of the crack available in
JCFPM as pi*min(R1,R2)^2 with R1 and R2 the particles radii?

b) We are interested in the volume of fluid contained in a cell which
might have n facets associated to a crack and 4-n facets not associated
to a crack. How do we define the fluid volume in such a case? V =
(4-n)/4*Vcell + SumOveri_0TOn Vcracki? Or do we simply consider that
Vcracki >> V and do what Robert is suggesting: V = Vcell + SumOveri_0TOn
Vcracki?

lUC

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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 may be mainly due to a crack an its opening.
  Typically V=V(tetrahedron)-opening*area-matrixPorosity.
  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

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