yade-dev team mailing list archive

[Luc Scholtès <lscholtes63@xxxxxxxxx>]

Hi Bruno,

If we want to compute the volume associated to a crack, we should use
directly crackAperture*crackArea as Vo in dV/Vo, no? Of course, this is
not as straightforward because a cell is not associated to a unique
crack in our scheme but still, why did you specifically propose
V(tetrahedron)-crackAperture*crackArea-matrixPorosity? "aperture"
defined in DFNFlow is the right candidate for crackAperture as it is
defined as a function of the mechanical crack opening (particle-particle
normal displacements) and hydraulic residual aperture. We should then
probably change the way it is declared (locally in a function of DFNFlow
right now).

Now, regarding the case of an pore contained in the intact rock matrix,
are you suggesting that we need to "scale down" the porosity to adapt
the scheme for rock materials? It makes sense of course but then we
would need to define a scaling factor depending on the rock type and on
the deviation of their microstructure with respect to the one of a
granular assembly (e.g. a sandstone and a shale rock). The expression
would then be something like Vo=scalingFactor*(Vtetrahedron-Vspheres)
with scalingFactor=rockPorosity/granularAssemblyPorosity. Is that what
you meant?

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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