DFN+fluid compressibility not using the correct reference volume
Affects | Status | Importance | Assigned to | Milestone | |
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Yade |
New
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Undecided
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Unassigned |
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)
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*
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:/
description: | updated |
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=scalingFacto r*(Vtetrahedron -Vspheres) with scalingFactor= rockPorosity/ granularAssembl yPorosity. Is that what you meant?
Luc