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Viscoelastic Fluid Flows using OpenFOAM The solver viscoelasticFluidFoam 

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March 18, 2014, 11:07 

#341 
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Hrvoje Jasak
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It runs fine here, the last change was
commit 6b50e03f4417291ba2c9184244d37e2630ef2dae Author: Henrik Rusche <h.rusche@wikkigmbh.de> Date: Thu Dec 12 00:41:18 2013 +0100 Below is the fvSolution file: /** C++ **\  =========    \\ / F ield  foamextend: Open Source CFD   \\ / O peration  Version: 3.0   \\ / A nd  Web: http://www.extendproject.de   \\/ M anipulation   \**/ FoamFile { version 2.0; format ascii; class dictionary; object fvSolution; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // solvers { p { solver PCG; preconditioner Cholesky; tolerance 1e07; relTol 0; minIter 0; maxIter 800; } U { solver BiCGStab; preconditioner ILU0; tolerance 1e6; relTol 0; minIter 0; maxIter 1000; } tau { solver BiCGStab; preconditioner ILU0; tolerance 1e6; relTol 0; minIter 0; maxIter 1000; }; } PISO { nCorrectors 2; nNonOrthogonalCorrectors 0; pRefCell 0; pRefValue 0; } relaxationFactors { p 0.3; U 0.5; tau 0.3; } // ************************************************** *********************** //
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March 18, 2014, 11:33 

#342 
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Sita Drost
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Thanks for the information. How can I check what my last change was?


April 1, 2014, 03:38 

#343 
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Sita Drost
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OK, I give up: last Thursday I installed foamextend3.0 from source, tested it on the OldroydB tutorial, AND IT WORKED!!! No problems with finding the Cholesky preconditioner or anything.
So today I tried to run a case of my own, but now suddenly foam seems to have forgotten everything it knew previously and it gives the same error I got earlier, about Cholesky being an unknown preconditioner. WHY?? I didn't change anything, as far as I know. Anyone? 

May 13, 2014, 10:46 

#344  
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litao
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Quote:
> FOAM FATAL IO ERROR: Unknown asymmetric matrix preconditioner Cholesky Valid asymmetric matrix preconditioners are : 7 ( AMG none GAMG diagonal SymGaussSeidel ILU0 DILU ) file: /home/yxiong/FileOfYxiong/projectile/system/fvSolution::solvers::U from line 82 to line 90. From function lduPreconditioner::New ( const lduMatrix& matrix, const FieldField<Field, scalar>& coupleBouCoeffs, const FieldField<Field, scalar>& coupleIntCoeffs, const lduInterfaceFieldPtrsList& interfaces, const dictionary& dict ) in file matrices/lduMatrix/lduMatrix/lduMatrixPreconditioner.C at line 141. FOAM exiting sita,did you have solved your problem?tell me,thank you! 

May 13, 2014, 11:01 

#345 
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Hrvoje Jasak
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Just change the name from Cholesky to ILU0.
Hrvoje
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May 13, 2014, 21:18 

#346 
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litao
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May 14, 2014, 00:54 

#347 
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Sita Drost
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Sorry, no, I haven't found a solution yet, maybe the Cholesky preconditioner just disappeared? Although some time ago I saw a post by Hvorje Jasak, who didn't have problems with Cholesky. I switched to using PAMG instead of Cholesky, that works.


May 21, 2014, 05:45 
divTau

#348 
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I suppose the divergence of (tau_p + tau_s) should be returned for the momentum equation. However in the viscoelastic foam, it is
fvc::div(tau_/rho_, "div(tau)")  fvc::laplacian(etaPEff/rho_, U, "laplacian(etaPEff,U)") + fvm::laplacian( (etaPEff + etaS_)/rho_, U, "laplacian(etaPEff+etaS,U)") It is not identical to div(tau_/rho_ + tau_s), isn't it? 

May 21, 2014, 12:25 

#349 
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Hrvoje Jasak
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I am sorry: did you read the paper describing the methodology?
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May 21, 2014, 17:39 

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May 22, 2014, 01:29 

#351 
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Hrvoje Jasak
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Apologies: paper.
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May 22, 2014, 04:24 

#352 
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May 22, 2014, 05:01 

#353 
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Hrvoje Jasak
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Usually when I work on something in FOAM, there are papers published with the methodology, numerics and validation results.
Try googling Favero Jasak viscoelastic, or http://scholar.google.co.uk/scholar?...ed=0CCUQgQMwAA Does this help? Hrv
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May 22, 2014, 05:19 

#354  
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Cheers, Hrv. No luck. Anyway, I suppose that divTau is the key for the viscoleastic solver no matter what model it is. Anyone dig this part?
Quote:


May 22, 2014, 06:59 
Convection term in viscoelasticFluidFoam solver

#355 
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Heliana Cardenas
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Hi Hrvoje,
I am using a model similar to the White MetznerLarson model in the visco solver, I want to study shear thinning. I am studying starup flow in a 2D channel. The model looks like this: fvSymmTensorMatrix tauEqn ( fvm::ddt(tau_) + fvm::div(phi(), tau_) == etaP_/lambda_*twoD + twoSymm(C)  fvm::Sp(1/lambdaM, tau_) ); where: lambdaM = (lambda_*gammaC_/(gammaC_+lambda_*sqrt(0.5)*mag(twoD))) In few words, the relaxation time is in function of the shear rate (my gammaC_ is 0.1) When I do this, the centerline velocity acts like if it was a almost a newtonian fluid, and it doesn't reach the steady state (analytical results). I checked also the nonNewtonian and Newtonian stress on time at a quarter of the channel and it is like \tau_ doesn't "change" anymore with time, though the newtonianStress does. I am attaching here the plot of the nonNewtonian and Newtonian shear stress at quarter of the channel vs time, so you can see how it actually goes. If I actually remove the convective term (I was just trying to see what was affecting the costitutive equation), my results reach steady state. How can this convective term affect my model, so when I use it it doesnt reach steady state like expected? Thanks, Heliana 

July 23, 2014, 04:35 
FENE model parameters

#356 
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Sita Drost
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Dear Jovani,
In your FENEP and FENECR models, the values of etaS and etaP should be specified. What do these parameters mean physically? My first guess would be that etaS + etaP = eta_eff (i.e. effective viscosity of the solution = solvent viscosity + polymer contribution), but in the FENECR code, you use an eta_eff that's defined as eta_eff = etaP. So, is etaP then the viscosity of the polymer solution? Thanks in advance for helping me out, Sita 

July 31, 2014, 01:21 

#357 
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Ron
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How to calculate drag coefficient on a cylinder for viscoelastic fluid?


July 31, 2014, 03:11 

#358  
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Sita Drost
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Quote:
Maybe this helps? Viscoelastic flow past a cylinder: drag coefficient. Nhan PhanThien & HuaShu Dou (1999). Computer Methods in Applied Mechanics and Engineering, 180 (34), pp. 243266. Good luck, Sita 

July 31, 2014, 04:20 

#359 
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Ron
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Thank you Sita for the same.
Do you know how would I implement the drag coefficient equation for these fluids in OpenFOAM? 

July 31, 2014, 07:10 

#360 
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Ron
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Anyone?
Any idea for the above post on implementation of drag coefficients for viscoelastic fluids? 

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