Hi Tri Dat,
try modifiying the velocity computation to evaluate the velocity in each
element center. Maybe this velocity is better in your case.
If it ensured mass conservation with particle tracking, I'm not sure.
BTW, you are not restricted to the box-method on 2d-3d grids. The
cellcentered FV just needs a bit more treatment on the bifurcation to
ensure mass conservation and pressure continuity which you get for free
with the box method.
Best wishes
Timo
On 20.10.2016 16:45, NGO Tri Dat wrote:
Hi Timo,
I also saw the comments which indicate that the velocity computation
only works for cubes.
Indeed, when I was using Dumux 2.7, I was unable to get velocity field
for simplex meshes, it worked only for cubes.
Now, I am using Dumux 2.9 and it allows me to export velocity output
for both simplex and cube meshes but it leads to weird results for
simplex meshes.
Nevertheless, for the purpose of the calculation of effective
permeabilities and particle tracking, I still need right velocities.
Furthermore, considering that I am working on 2d-in-3d non-manifold
triangle meshes using Foamgrid, the box-method must be used.
Do you have any idea?
Best wishes,
Tri Dat
*De :*Timo Koch [mailto:timo.k...@iws.uni-stuttgart.de]
*Envoyé :* jeudi 20 octobre 2016 16:11
*À :* DuMuX User Forum; NGO Tri Dat
*Objet :* Re: [DuMuX] Wrong velocity field on simplex mesh
Hi Tri Dat,
I checked the velocity computation. There is a comment that says that
it only works for cubes. That being
said, we could compute element velocities by evaluating the pressure
gradient at element center using the P1 ansatz functions.
This is probably not done right now because we currently allow
discontinuous permeabilities per sub-control-volume. So this is why
the current approach uses a weighting of the scv velocities. Which
results as you saw in weird velocities. I don't know if the element
center approach results in better velocities especially when looking
at discontinuous param multi-phase simulation. @all Someone
else might know more than me.
So the problem that you have with both cell- and vertex centered FV is
that your only primary variable is the pressure. So computing the
velocity field is a post-processing step and generally the pressure
gradients are not approximated everywhere in the domain because we
compute fluxes, so you can't just evaluate the velocities everywhere
you want. If you look at 1p cell-centered FV with triangles you also
get weird velocity values.
There might be smarter ways to reconstruct the velocity fields than
currently implemented but they
are going to be more complicated / time consuming.
Do you need good velocities for e.g. particle tracking?
Best wishes
Timo
On 20.10.2016 15:08, NGO Tri Dat wrote:
Hi Dumuxers,
I have just done a simple test of 1p model with a pressure
gradient along X-axis on cube and simplex meshes and using
implicit box method.
The simulation parameters:
-Permeability K = 1E-11 (m^2)
-Viscosity of the fluid : mu = 1E-3 (Pa.s)
-Pressure gradient: delta_P = 1E+8 (Pa)
-delta_X = 3 (m)
The velocity along X-axis should be v = K/mu * div p = 1/3 (m/s)
The attached image shows the pressure and velocity field obtained
by Dumux.
Unfortunately, the velocity field on two meshes are quite
different. Concretely, the simulation result on cube mesh is
similar to the theoretical one, but not the test on simplex mesh.
I wonder if there is a bug in the calculation of velocity on
simplex meshes in Dumux.
Could you please check it and confirm me?
Kind regards,
Tri Dat
PS: I also send you the used *.hh/input/mesh files
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__________________________
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