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
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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 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
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