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Viscoelastic Fluid Flows using OpenFOAM The solver viscoelasticFluidFoam 

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November 2, 2013, 11:00 

#321 
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Dongyue Li
Join Date: Jun 2012
Location: Torino, Italy
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Thanks Mostafa，
BTW, do you know that if the surface tension is important in this viscoelasticInterFoam? 

November 2, 2013, 14:46 

#322 
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November 4, 2013, 10:03 

#323 
Senior Member
Dongyue Li
Join Date: Jun 2012
Location: Torino, Italy
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Okay, back to the UEqn. I mean the code implanted in 1.6ext is:
Code:
fvc::div(tau_, "div(tau)")  fvc::laplacian(etaP(), U) + fvm::laplacian(etaP() + etaS(), U) Code:
fvc::div(tau_, "div(tau)") + fvm::laplacian(etaS(), U) 

November 14, 2013, 04:59 
viscoelasticProperties Problem

#324 
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KimJuHyun
Join Date: Nov 2013
Posts: 2
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Hello Foamers,
i'm korean student, Want you to help me. Perhaps it may be a very easy question. i'm using the viscoelasticFluidFOAM multiphase 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 ] 3e4; 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] 3e4; n n [0 0 0 0 0 0 0] 1; } } phase2 { transportModel Newtonian; nu nu [0 2 1 0 0 0 0] 1.46e05; 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. 

November 14, 2013, 05:02 

#325  
Senior Member
Dongyue Li
Join Date: Jun 2012
Location: Torino, Italy
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Quote:
I think it cannot simulate twophase cases. You have to code your own solver using VOF of twofluid model. 

November 14, 2013, 05:15 

#326 
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KimJuHyun
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November 20, 2013, 16:24 

#327 
Member
Join Date: Aug 2013
Posts: 60
Rep Power: 5 
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 (crosslink). 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 (crosslinking 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. 

December 4, 2013, 11:06 
questions??

#328  
Member
Heliana Cardenas
Join Date: Jul 2013
Posts: 30
Rep Power: 5 
Quote:
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 

January 30, 2014, 12:37 

#329 
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Nickolas P
Join Date: Oct 2010
Location: Greece
Posts: 30
Rep Power: 8 
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 

February 9, 2014, 14:02 
Strain tensor , shear rate ?!

#330 
Member
ali jafari
Join Date: Sep 2012
Posts: 50
Rep Power: 6 
hi every body
is there any utility that it can calculate strain tensor or velocity gradient for viscoelasticFluidFoam solver? 

February 9, 2014, 14:42 

#331  
Member

Quote:
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 

March 7, 2014, 08:44 

#332 
Member
Heliana Cardenas
Join Date: Jul 2013
Posts: 30
Rep Power: 5 
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 

March 13, 2014, 21:10 

#333  
Member

Quote:
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 underrelaxation, http://www.openfoam.org/docs/user/fvSolution.php  reproduced bellow. Small relaxation factor values increase the time to reach the steadystate solution but can improve numeric robustness. Best regards, Jovani "4.5.2 Solution underrelaxation A second subdictionary of fvSolution that is often used in OpenFOAM is relaxationFactors which controls underrelaxation, a technique used for improving stability of a computation, particularly in solving steadystate problems. Underrelaxation 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 underrelaxation factor α, 0 < α ≤ 1 specifies the amount of underrelaxation, 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." 

March 14, 2014, 09:10 
relaxation factors  viscoelasticFluidFoam  transients

#334 
Member
Heliana Cardenas
Join Date: Jul 2013
Posts: 30
Rep Power: 5 
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 

March 14, 2014, 12:26 
viscoelasticinterfoam help wanted

#335 
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abdikerim kurbanaliev
Join Date: Jun 2010
Location: Kyrgyzstan, Osh
Posts: 19
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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 

March 14, 2014, 15:18 
High stress values and instability of Viscoelastic Solver with VOF

#336 
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Ovie Doro
Join Date: Jul 2009
Posts: 99
Rep Power: 9 
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. 

March 14, 2014, 20:25 
Looking for "viscoelasticinterFoam"

#337 
New Member
CFDGuy
Join Date: Nov 2013
Posts: 5
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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 

March 14, 2014, 20:31 
How sensitive is the viscoelasticVOF solver to geometry?

#338 
Member
Ovie Doro
Join Date: Jul 2009
Posts: 99
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Hi all:
I have also encountered the strange behaviour where my viscoelasticVOF solver shows high sensibility to slight changes in geometry. Has anyone observed a similar problem? And did you manage to resolve it? 

March 14, 2014, 20:41 

#339  
Member
Ovie Doro
Join Date: Jul 2009
Posts: 99
Rep Power: 9 
Quote:
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. 

March 18, 2014, 06:43 
foamextend3.0 preconditioner problem

#340 
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Sita Drost
Join Date: Mar 2009
Location: Arnhem, The Netherlands
Posts: 52
Rep Power: 10 
Dear all,
Recently, I upgraded to foamextend3.0. To test if viscoelasticFluidFoam works all right under this version, I tried to run the OldroydB tutorial case. It gives an error regarding the Cholesky preconditioner ("unknown asymmetric matrix preconditioner..."). Was this preconditioner removed in foamextend3.0? And if so, which preconditioner is most suitable to use instead? Thanks in advance for your help, Regards, Sita 

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