[ali jafari]

hi

I want to calculate first and second normal stress differences in newer OpenFoam version (2.2.0) but in this version there is not the "stressDifferences" utility and I cant find it for compiling. also this utility taken from previous version dosent compile correctly in the new one.

if you have a modified version of this utility or have other suggestion please share it with me.

special Thanks

[ali jafari]

Originally Posted by ali jafari

hi

I want to calculate first and second normal stress differences in newer OpenFoam version (2.2.0) but in this version there is not the "stressDifferences" utility and I cant find it for compiling. also this utility taken from previous version dosent compile correctly in the new one.

if you have a modified version of this utility or have other suggestion please share it with me.

special Thanks

I find it !!!!

[hcx552362]

Originally Posted by ali jafari

I find it !!!!

Hi jafari
can you give me this files, I will use it to do sth. My email address is hcx552362@163.com
Thanks a lot
best wishes

[ali jafari]

Originally Posted by hcx552362

Hi jafari
can you give me this files, I will use it to do sth. My email address is hcx552362@163.com
Thanks a lot
best wishes

I found it , it work on OF 2.2.0

[Raymond.Leoi]

I noticed that viscoelasticFoam tends to be diverged for cases with high Weissenberg number. Any way to make the solver robust?

[hjasak]

Are you sure you are doing the right thing?

We did Weissenberg number of the order of million, which is huge and 3 orders of magnitude larger than other codes, eg Polyflow.

It would be unusual to have such extreme conditions and if these are serious cases I am happy to help through support contracts.

Hrv @ Wikki

[ali jafari]

Originally Posted by Raymond.Leoi

I noticed that viscoelasticFoam tends to be diverged for cases with high Weissenberg number. Any way to make the solver robust?

hi
This can refer to the ratio of viscosity (ethaS/ethaP) .How do you define Wi number ?

[Raymond.Leoi]

It's ascertained that the viscoelasticFoam is properly set up. Couldn't imagine what scenario it is for the fluids with Wi of million. Nevertheless, it makes sense to me that the viscoelastic models are difficult to simulate at large Wi, since tau_p*(velocity gradient tensor) could grow exponentially. I wonder how you made it work even Wi goes to million?

Originally Posted by hjasak

Are you sure you are doing the right thing?

We did Weissenberg number of the order of million, which is huge and 3 orders of magnitude larger than other codes, eg Polyflow.

It would be unusual to have such extreme conditions and if these are serious cases I am happy to help through support contracts.

Hrv @ Wikki

[Raymond.Leoi]

The ratio of viscosity could be constant.

What I did is Wi=(relaxation time)*(shear rate based on the average velocity at inlet).

Originally Posted by ali jafari

hi
This can refer to the ratio of viscosity (ethaS/ethaP) .How do you define Wi number ?

[hcx552362]

Originally Posted by hjasak

Are you sure you are doing the right thing?

We did Weissenberg number of the order of million, which is huge and 3 orders of magnitude larger than other codes, eg Polyflow.

It would be unusual to have such extreme conditions and if these are serious cases I am happy to help through support contracts.

Hrv @ Wikki

Hi hjasak
Now I am using the OF. When I using the S-MDCPP model to simulate the contraction flow with the viscoelasticFluidFoam software, the result is so serious, Maybe it is not diverge. I do not hoe to solve it?
thanks

[ali jafari]

hi

I used viscoelastic utility (stressSymmComponents). but when I created a calculator filter , two scaler were appeared , tauxx and tau_XX . what's different between two scaler ?

[EricKl.]

Hello,

I'm continuing work of literature. I took an existing mesh in a monograph and would like to use it in my thesis. The author just released the code blockMesh e viscoelasticProperties
When I put the mesh in my example, squeegee the blockMesh no problem.

When I run the Parafoam to check if the mesh has a problem, the ParaView generates the following information:

--> FOAM FATAL IO ERROR: 
size 48050 is not equal to the given value of 32040

file: /home/administrador/tutorials/viscoelastic/VIFErick/Extr/0/alpha from line 17 to line 48103.

    From function Field<Type>::Field(const word& keyword, const dictionary&, const label)
    in file /home/administrador/OpenFOAM/OpenFOAM-1.6-ext/src/OpenFOAM/lnInclude/Field.C at line 237.

FOAM exiting

What can I do to fix it?

thank you

[ali jafari]

Originally Posted by EricKl.

Hello,

I'm continuing work of literature. I took an existing mesh in a monograph and would like to use it in my thesis. The author just released the code blockMesh e viscoelasticProperties
When I put the mesh in my example, squeegee the blockMesh no problem.

When I run the Parafoam to check if the mesh has a problem, the ParaView generates the following information:

--> FOAM FATAL IO ERROR: 
size 48050 is not equal to the given value of 32040

file: /home/administrador/tutorials/viscoelastic/VIFErick/Extr/0/alpha from line 17 to line 48103.

    From function Field<Type>::Field(const word& keyword, const dictionary&, const label)
    in file /home/administrador/OpenFOAM/OpenFOAM-1.6-ext/src/OpenFOAM/lnInclude/Field.C at line 237.

FOAM exiting

What can I do to fix it?

thank you

hi dear EricKl

after blockMesh please use checkMesh and check any warning and error. I think your problem refer to pre-processing.

[nimasam]

Originally Posted by ali jafari

hi dear EricKl

after blockMesh please use checkMesh and check any warning and error. I think your problem refer to pre-processing.

in general Ali suggestion is good for every simulation, but i feel you refine your mesh and your internalField is non-uniform, then you saw that error
i suggest to copy your alpha1 file from backup file if you have

cp 0/alpha1.org 0/alpha1

[ali jafari]

Originally Posted by ali jafari

hi

I used viscoelastic utility (stressSymmComponents). but when I created a calculator filter , two scaler were appeared , tauxx and tau_XX . what's different between two scaler ?

any one can not help me ?

[sharonyue]

Hi guys,

This is a piece of code in Giesekus.C

return
    (
        fvc::div(tau_/rho_, "div(tau)")
      - fvc::laplacian(etaPEff/rho_, U, "laplacian(etaPEff,U)")
      + fvm::laplacian( (etaPEff + etaS_)/rho_, U, "laplacian(etaPEff+etaS,U)")
    );

Why is it fvc instead of fvm? Thanks.

[adambarfi]

Originally Posted by sharonyue

Hi guys,

This is a piece of code in Giesekus.C

return
    (
        fvc::div(tau_/rho_, "div(tau)")
      - fvc::laplacian(etaPEff/rho_, U, "laplacian(etaPEff,U)")
      + fvm::laplacian( (etaPEff + etaS_)/rho_, U, "laplacian(etaPEff+etaS,U)")
    );

Why is it fvc instead of fvm? Thanks.

hi

Using "fvc::" will calculate the derivative using the current values. While "fvm::" will discretize the term into the matrix equation. So "fvc::" will generate a field, while "fvm::" will return matrix coefficients. Soo, if you're solving [M] [Q] = [B]

fvm:: generates coefficients for [M]
fvc:: goes in [B]

Its more or less a distinction between explicit and implicit terms.

or

Taking an other example, the UEqn from mhdFoam:

Quote:
fvVectorMatrix UEqn
(
fvm::ddt(U)
+ fvm::div(phi, U)
- fvc::div(phiB, 2.0*DBU*B)
- fvm::laplacian(nu, U)
+ fvc::grad(DBU*magSqr(B))
);
The velocity U can not be calculated analytically, only by iteration. That means it is implicitely given = fvm.

When calculating U, the field B is kept constant. If it is constant, it may be calculated/readed easily (explicitly) = fvc.

=> So whenever there is a U in the UEqn, I have to write fvm, if it is not fvc. Can someone confirm that or say it better?

more for info see the below links:
http://openfoamwiki.net/index.php/Implicit_equation
http://openfoamwiki.net/index.php/Explicit_equation

[adambarfi]

hi everybody

I have a problem with my residuals. I added the temperature with Boussinesq assumption to viscoelasticFluidFoam solver and when I ran it the 'tau' residuals are oscillating and the interesting point is that it is ahead of the rest!!!!
I've attach the residuals plot.

any body knows where is the problem?

thatks
Mostafa

[sharonyue]

Originally Posted by sharonyue

return
    (
        fvc::div(tau_/rho_, "div(tau)")
      - fvc::laplacian(etaPEff/rho_, U, "laplacian(etaPEff,U)")
      + fvm::laplacian( (etaPEff + etaS_)/rho_, U, "laplacian(etaPEff+etaS,U)")
    );

Hi Mostafa,

You can see that its

fvc::laplacian(etaPEff/rho_, U, "laplacian(etaPEff,U)")

I think its like fvm::laplacian(nu,U), but it is using fvc::laplacian(nu,U). This is where I am confused. I think laplacian term should be implicit term. Thanks in advance,.

[adambarfi]

hi sharonyue,

by Joani:

The procedure used to solve the problem of viscoelastic
fluid flow can be summarized in 4 steps for each time step:

1.
With an initial known velocity field U*, a given pressure p* and
stress tau*, the momentum equation is implicitly solved for each
component of the velocity vector resulting in U**. The pressure
gradient and the stress divergent are calculated explicitly with
values of the previous step.

2.
With the news velocity values U** it is estimated the new
pressure field p** using an equation for the pressure and makes
the correction of velocity field to satisfy the continuity equation,
resulting in U***. The PISO algorithm is used.

3.
With the corrected velocity field U*** is made the calculation of
the stress tensor field tau**  using a constitutive equation desired.

4.
For more accurate solutions to transient
flow the steps 1, 2 and
3 can be iterate in a same time step.

Also, you can get more information in follow pdf file, pages 32-60:
http://powerlab.fsb.hr/ped/kturbo/Op...cFluidFoam.pdf