[sharonyue]

Thanks Mostafa，

BTW, do you know that if the surface tension is important in this viscoelasticInterFoam?

[adambarfi]

Originally Posted by sharonyue

Thanks Mostafa，

BTW, do you know that if the surface tension is important in this viscoelasticInterFoam?

sorry, I didn't hear about viscoelasticInterFoam before!!!! but for multiphase flows the surface tension is necessary.

[sharonyue]

Okay, back to the UEqn. I mean the code implanted in 1.6ext is:

fvc::div(tau_, "div(tau)")
      - fvc::laplacian(etaP(), U)
      + fvm::laplacian(etaP() + etaS(), U)

Why dont we just use:

fvc::div(tau_, "div(tau)")
      + fvm::laplacian(etaS(), U)

[JuHyun]

Hello Foamers,

i'm korean student, Want you to help me.

Perhaps it may be a very easy question.

i'm using the viscoelasticFluidFOAM multi-phase flow simulation tries.

but, this file. I did different from the content of the file.

'transportProperties' is the file I was using.

phase1
{
transportModel HerschelBulkley;
nu nu [ 0 2 -1 0 0 0 0 ] 3e-4;
rho rho [1 -3 0 0 0 0 0] 1000;

HerschelBulkleyCoeffs
{
nu0 nu0 [0 2 -1 0 0 0 0] 0.006;
tau0 tau0 [0 2 -2 0 0 0 0] 0.025031;
k k [0 2 -1 0 0 0 0] 3e-4;
n n [0 0 0 0 0 0 0] 1;
}
}
phase2
{
transportModel Newtonian;
nu nu [0 2 -1 0 0 0 0] 1.46e-05;
rho rho [1 -3 0 0 0 0 0] 1.225;
}

refPhase phase2;

sigma sigma [1 0 -2 0 0 0 0] 0.066;


but, the viscoelasticFluidFOAM in transportProperties without using viscoelasticProerties[Giesekus] is used.

I Have used a lot of different ways. but Always viscoelasticProperties in the error appeared.

viscoelasticProperties

rheology
{

type multiMode;

models
(
first
{
type Giesekus;
rho rho [1 -3 0 0 0 0 0] 803.87097;
etaS etaS [1 -1 -1 0 0 0 0] 0.002;
etaP etaP [1 -1 -1 0 0 0 0] 0.04;
lambda lambda [0 0 1 0 0 0 0] 0.6855;
alpha alpha [0 0 0 0 0 0 0] 0.5;
}

second
{
type Giesekus;
rho rho [1 -3 0 0 0 0 0] 803.87097;
etaS etaS [1 -1 -1 0 0 0 0] 0.002;
etaP etaP [1 -1 -1 0 0 0 0] 0.2324;
lambda lambda [0 0 1 0 0 0 0] 0.1396;
alpha alpha [0 0 0 0 0 0 0] 0.2;
}

third
{
type Giesekus;
rho rho [1 -3 0 0 0 0 0] 803.87097;
etaS etaS [1 -1 -1 0 0 0 0] 0.002;
etaP etaP [1 -1 -1 0 0 0 0] 0.5664;
lambda lambda [0 0 1 0 0 0 0] 0.0389;
alpha alpha [0 0 0 0 0 0 0] 0.3;
}

fourth
{
type Giesekus;
rho rho [1 -3 0 0 0 0 0] 803.87097;
etaS etaS [1 -1 -1 0 0 0 0] 0.002;
etaP etaP [1 -1 -1 0 0 0 0] 0.5850;
lambda lambda [0 0 1 0 0 0 0] 0.0059;
alpha alpha [0 0 0 0 0 0 0] 0.2;
}

);
}

If you change this file, do let me know how, please

JuHyun.

[sharonyue]

Originally Posted by JuHyun

Hello Foamers,

i'm korean student, Want you to help me.

Perhaps it may be a very easy question.

i'm using the viscoelasticFluidFOAM multi-phase flow simulation tries.

but, this file. I did different from the content of the file.

'transportProperties' is the file I was using.

phase1
{
transportModel HerschelBulkley;
nu nu [ 0 2 -1 0 0 0 0 ] 3e-4;
rho rho [1 -3 0 0 0 0 0] 1000;

HerschelBulkleyCoeffs
{
nu0 nu0 [0 2 -1 0 0 0 0] 0.006;
tau0 tau0 [0 2 -2 0 0 0 0] 0.025031;
k k [0 2 -1 0 0 0 0] 3e-4;
n n [0 0 0 0 0 0 0] 1;
}
}
phase2
{
transportModel Newtonian;
nu nu [0 2 -1 0 0 0 0] 1.46e-05;
rho rho [1 -3 0 0 0 0 0] 1.225;
}

refPhase phase2;

sigma sigma [1 0 -2 0 0 0 0] 0.066;


but, the viscoelasticFluidFOAM in transportProperties without using viscoelasticProerties[Giesekus] is used.

I Have used a lot of different ways. but Always viscoelasticProperties in the error appeared.

viscoelasticProperties

rheology
{

type multiMode;

models
(
first
{
type Giesekus;
rho rho [1 -3 0 0 0 0 0] 803.87097;
etaS etaS [1 -1 -1 0 0 0 0] 0.002;
etaP etaP [1 -1 -1 0 0 0 0] 0.04;
lambda lambda [0 0 1 0 0 0 0] 0.6855;
alpha alpha [0 0 0 0 0 0 0] 0.5;
}

second
{
type Giesekus;
rho rho [1 -3 0 0 0 0 0] 803.87097;
etaS etaS [1 -1 -1 0 0 0 0] 0.002;
etaP etaP [1 -1 -1 0 0 0 0] 0.2324;
lambda lambda [0 0 1 0 0 0 0] 0.1396;
alpha alpha [0 0 0 0 0 0 0] 0.2;
}

third
{
type Giesekus;
rho rho [1 -3 0 0 0 0 0] 803.87097;
etaS etaS [1 -1 -1 0 0 0 0] 0.002;
etaP etaP [1 -1 -1 0 0 0 0] 0.5664;
lambda lambda [0 0 1 0 0 0 0] 0.0389;
alpha alpha [0 0 0 0 0 0 0] 0.3;
}

fourth
{
type Giesekus;
rho rho [1 -3 0 0 0 0 0] 803.87097;
etaS etaS [1 -1 -1 0 0 0 0] 0.002;
etaP etaP [1 -1 -1 0 0 0 0] 0.5850;
lambda lambda [0 0 1 0 0 0 0] 0.0059;
alpha alpha [0 0 0 0 0 0 0] 0.2;
}

);
}

If you change this file, do let me know how, please

JuHyun.

Hello,

I think it cannot simulate two-phase cases. You have to code your own solver using VOF of two-fluid model.

[JuHyun]

Originally Posted by sharonyue

Hello,

I think it cannot simulate two-phase cases. You have to code your own solver using VOF of two-fluid model.

I understand, I'll try it.

Thank you.

[sur4j]

Hello,

I would like to simulate a polymer manufacturing process known as curing of rubber, this is a process where rubber is heated resulting in viscosity changes as the molecules react and form bonds (cross-link). When the rubber is initially heated its viscosity decreases and at a certain time starts to flow, some time after this the viscosity starts to increase (cross-linking occurs) up till the point it is solid rubber.

Can I use this solver to simulate this process or will I need a alternative method of simulation? I would appreciate any help at all with this. Thank you.

[heliana60]

Originally Posted by amin144

Hi dear FOAMers

I have basic questions, maybe very amateur questions.
1)What is tau in models like Giesekus? It's total stress or extra stress?

2)If I want calculate wall stress, can I use the utility "wallShearStress" or this give me only Newtonian part of stress?

3)what is best way to calculate eta and shear rate and plot diagram of them according to each other?


Best regards,
Amin

Hi Amin,

I am new to openFoam and using the viscoelasticFluidFoam solver. Could you calculate the total stress as Jovani told you to? or you found maybe another way? I was confused by the "tau" this solver uses because aparently it doesn't take into account the solvent stress. is that true?

Could you also calculate the shear rate?

heliana

[NickolasPl]

Hello everyone,

I have a question regarding the viscoelasticFluidFoam. I understand that in the viscoelastic models (e.g. LPTT) the user must prescribe the BCs for "tau"". My question is if the tau boundary condition corresponds to the total stress tensor (as derived from the EVSS method) or the stress contribution from the polymer.
Then if we have to set the "tau" boundary condition on a free surface (e.g. the free surfaces for planar or annular extrudate swelling) what would reflect more realistic the true extrudate swelling concerning the free surface stresses...?

This.... type fixedValue;
value uniform (0 0 0 0 0 0);

????

..or this... type zeroGradient;

????

Thanking you in advance.

Nickolas

[ali jafari]

hi every body

is there any utility that it can calculate strain tensor or velocity gradient for viscoelasticFluidFoam solver?

[desert_1250]

Originally Posted by ali jafari

hi every body

is there any utility that it can calculate strain tensor or velocity gradient for viscoelasticFluidFoam solver?

Hi
use these keywords at terminal window:
foamCalc gradU // velocity gradient contour
foamCalc stressDifferences // normal stress differences N1 & N2
foamCalc wallGradU // velocity gradient at wall boundary
foamCalc components tau // all components of stress tensor
foamCalc components U // velocity components

Best

[heliana60]

Hey Jovani!

I hope you are fine. I have some problems with the relaxation factors that are used on your solver. They always affect the steady state (it takes longer to get to steady state than it should be), how do you choose them? When I use 0 for U i get a more or less nice result for the evolution of velocity on time, but for pressure or tau I am kinda lost because they are always unstable. Do you know how to choose them?

sorry this is all still kinda new for me

thanks

[jovani]

Originally Posted by heliana60

Hey Jovani!

I hope you are fine. I have some problems with the relaxation factors that are used on your solver. They always affect the steady state (it takes longer to get to steady state than it should be), how do you choose them? When I use 0 for U i get a more or less nice result for the evolution of velocity on time, but for pressure or tau I am kinda lost because they are always unstable. Do you know how to choose them?

sorry this is all still kinda new for me

thanks

Hello Heliana,

I've never heard about a "magic" rule to choose an optimal relaxation factor, it depends on each case and can be changed along the simulation time. On the other hand, "0" makes not sense, take a look on section -- 4.5.2 Solution under-relaxation, http://www.openfoam.org/docs/user/fvSolution.php -- reproduced bellow. Small relaxation factor values increase the time to reach the steady-state solution but can improve numeric robustness.

Best regards,
Jovani

"4.5.2 Solution under-relaxation
A second sub-dictionary of fvSolution that is often used in OpenFOAM is relaxationFactors which controls under-relaxation, a technique used for improving stability of a computation, particularly in solving steady-state problems. Under-relaxation works by limiting the amount which a variable changes from one iteration to the next, either by modifying the solution matrix and source prior to solving for a field or by modifying the field directly. An under-relaxation factor α, 0 < α ≤ 1 specifies the amount of under-relaxation, ranging from none at all for α = 1 and increasing in strength as α → 0. The limiting case where α = 0 represents a solution which does not change at all with successive iterations. An optimum choice of α is one that is small enough to ensure stable computation but large enough to move the iterative process forward quickly; values of α as high as 0.9 can ensure stability in some cases and anything much below, say, 0.2 are prohibitively restrictive in slowing the iterative process."

[heliana60]

Hi Jovani,

Yes, I read that too. For me your solver works really good regarding the results I get in SS, but the transients are what I would like to understand more and they are very much affected by the relaxation factors I use.

When I don't use them, and go to really small time steps, I still don't get the transient I expect in comparison to analytical results I have. Actually I get "wrong" results and my transients look like a the ones for Newtonian. I am trying to implement a nonlinear Maxwell model in a pressure driven flow.

Any comment is very much welcome,

Cheers,

Heliana

[kerim]

Hi everyone!
now i have installed the openfoam 2.3 succeed, of course i download viscoelasticinterFoam files. but i do not kown how to add it in the openfoam. I think you can help me. Thanks a lot .
Have a nice day

[ovie]

Hi all:

I am having issues with the stability of the coupled VOF - ViscoelasticFluidFoam solver. The problem typically starts with very high stress values at sharp corners of the geometry. This inturn makes the MULES solver unstable and the simulation crashes. Has anyone had similar problems? I know someone mentioned this high stress problem in another thread but I dont know if the problem has been solved yet.

I have also not been able to reproduce the results in the paper published by Jovani et al for the free surface viscoelastic solver. Has anyone succeeded with this?

Thanks.

[mehdinekooee]

Hi Foamers,

I am looking for the solver "viscoelasticinterFoam". What I can find online is "viscoelasticFluidFoam". Does anyone know how or where could I find viscoelasticinterFoam ?

Thanks

[ovie]

Hi all:

I have also encountered the strange behaviour where my viscoelastic-VOF solver shows high sensibility to slight changes in geometry. Has anyone observed a similar problem? And did you manage to resolve it?

[ovie]

Originally Posted by mehdinekooee

Hi Foamers,

I am looking for the solver "viscoelasticinterFoam". What I can find online is "viscoelasticFluidFoam". Does anyone know how or where could I find viscoelasticinterFoam ?

Thanks

Hi:

I dont think the viscoelasticInterFoam solver has been made available yet. So you might want to consider building one yourself by combining the viscoelasticFluidFoam with VOF from interFoam. Its not that difficult. I have manage to build one but its having serious stability issues with high viscoelastic stresses (see my posts on top).

Regards.

[sita]

Dear all,

Recently, I upgraded to foam-extend-3.0. To test if viscoelasticFluidFoam works all right under this version, I tried to run the Oldroyd-B tutorial case. It gives an error regarding the Cholesky preconditioner ("unknown asymmetric matrix preconditioner..."). Was this preconditioner removed in foam-extend-3.0? And if so, which preconditioner is most suitable to use instead?

Thanks in advance for your help,

Regards,

Sita