Christian,
We better move this discussion back to yade-dev.
The fluid force Ff[i] = p*A[i] is already included if you read
O.forces.f[wallId]. As soon as PFV comes before TriaxController, you
don't have to compute it again.
You mean PFV must be defined before TSC in O.engines to get wall-fluid
interaction automatically? Or do you mean the force is already
calculated, but it does not act on the wall?
If PFV is before TSC in engines it is automatic, yes.
The problem is in the definition of kn, not in the definition of dF.
Currently kn is the stiffness of the solid phase. It should be the
cumulated stiffness of both phases.
What is the cumulated stiffness of both phases? kn + k_fluid?
The stiffness should reflect the stress-strain relation in uniaxial
undrained deformation.
Should be Young+k_fluid/porosity I think, but it is not required to be
absolutely exact (e.g. assuming porosity=0.3 is good enough).
If the fluid is incompressible the cumulated stiffness becomes infinite,
which is consistent since an undrained test with incompressible fluid is
a ill-posed problem.
You could test this idea by using a user defined stiffness in order to
see if you can stabilise the engine by defining a higher stiffness.
If so, TSC could automatically search a PFV engine in O.engines, and if
found it would use pfv.bulkModulus to update the stiffness.
Fine, but I still have a problem in understanding what a fluid
stiffness is. How can I update the stiffness from bulk modulus? Is it
kn += K/A? Then what is A?
Fluid stiffness is the inverse of fluid compressibility. ;)
PFV.bulkModulus is the stiffness. Maybe not very well named, since bulk
is more commonly used for solids or mixtures.
Cheers
Bruno
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