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October 4, 2012, 02:43 
viscoelastic fluid abbreviations

#1 
Senior Member

Hello Everybody,
I am stuck with the terms: "// Twice the rate of deformation tensor volSymmTensorField twoD = twoSymm(L); // Stress transport equation fvSymmTensorMatrix tauEqn ( fvm::ddt(tau_) + fvm::div(phi(), tau_) == etaP_/lambda_*twoD + twoSymm(C)  fvm::Sp(1/lambda_, tau_) );  I do know the term, it is: rate of deformation of stress and is expressed as: 1/2 * (grad(U) + grad(U).T). Does any one know from where, I will get the OpenFOAM coding of this term "twoSymm(L)" in of OF directory? I want to see the code definition of it and from which file it is compiled in the OF.  Thanks in Advance. 

October 4, 2012, 07:21 
general viscoelastic material model  OpenFOAM1.6ext

#2 
Member
Jon Elvar Wallevik
Join Date: Nov 2010
Location: Reykjavik, ICELAND
Posts: 82
Rep Power: 12 
dear Tushar Chourushi, it appears that you want to do a general viscoleastic simulation. This is a very difficult subject, both theoretically as well as numerically and there are lot of instability issues surrounding it. My recommendation is use rather OpenFOAM1.6ext. There is a general viscoelastic solver there.
It is more difficult to install the OFext version relative to the standard OF version, so my second recommendation is use ubuntu 12.04. I just recently installed it on one of mine Ubuntu server 12.04.1 (64bit) machines without problems. My third recommendation is, use lot of time to prepare, both for the installation of OFext as well in learning on the viscoelastic solver. Just jumping into this and expecting things to go you way is most certainly a killer. Be patient in your difficult work ahead. good luck, Jon 

October 4, 2012, 07:33 
Dear Jon

#3 
Senior Member

Thanks for your suggestion, I have already installed the viscoelasticFoam on my machine. I wanted to see how the equations are written in openFOAM as compared to the constitutive equation for different models?
That too.. I was having problem with the term which I have mentioned in my earlier thread, as I was not able to corelate it with the theory. Anyways, Thanks for your help.  Regards, Tushar 

October 4, 2012, 08:27 
about twoSymm(L)

#4 
Member
Jon Elvar Wallevik
Join Date: Nov 2010
Location: Reykjavik, ICELAND
Posts: 82
Rep Power: 12 
hi again,
I dont think there is any twoSymm(L) used in the code. But if you look at the ~/OpenFOAM/OpenFOAM2.1.x/src/transportModels/incompressible/viscosityModels/viscosityModel/viscosityModel.C there is a component,... sqrt(2.0)*mag(symm(fvc::grad(U_))); ..., which calculates the shear rate. thus the rate of deformation tensor 1/2 * (grad(U) + grad(U).T) is "symm(fvc::grad(U_))" The mag(symm(fvc::grad(U_))); would be its double dot, square root. Any you can see a bit by searching for "shear rate" J. 

January 5, 2013, 00:41 

#5 
Senior Member

Thanks Jon,
Actually I wasn't talking about the available code with OpenFOAM, I was looking at the extended source code of OpenFOAM. There I found that variable, anyways thanks for your help. I got the answer while exploring the forum. 

February 25, 2014, 03:30 
shear rate

#6 
Member

Hi foamers
How can i extract shear rate from my results using viscoelasticFluidFoam? tnx 

February 25, 2014, 20:38 
shear rate

#7  
Member
Jon Elvar Wallevik
Join Date: Nov 2010
Location: Reykjavik, ICELAND
Posts: 82
Rep Power: 12 
Quote:
(1) in "createFields.H" add the following:  volScalarField shearRate ( IOobject ( "shearRate", runTime.timeName(), mesh, IOobject::NO_READ, IOobject::AUTO_WRITE ), mesh, dimensionedScalar("shearRate", dimensionSet(0,0,1,0,0,0,0), scalar(0.0)) );  (2) in viscoelasticFluidFoam.C before "runTime.write();" add the following  dimensionedScalar sqrtOfTwo("sqrtOfTwo", dimless, 1.4142135623730950488); shearRate = sqrtOfTwo*mag(symm(fvc::grad(U)));  The runTime.write(); thingi will write the shear rate automatically. One note, now I am assuming that you accept that the shear rate is "sqrtOfTwo*mag(symm(fvc::grad(U)));" It is so for incompressible fluid that comply to the Generalized Newtonian Model (GNM), e.g. Bingham viscoplastic model, power law fluid or Newtonian fluid. But viscoelasticity is not GNM. If you are in trouble, then you can just call this "Magnitude of the rateofstrain tensor" like I did in Wallevik, J.E., Minimizing endeffects in the coaxial cylinders viscometer: Viscoplastic flow inside the ConTec BML Viscometer 3. J. NonNewtonian Fluid Mech. 155 (2008) 116123. Hope this helps cheers Jon 

February 26, 2014, 01:59 

#8  
Member

Quote:
Dear Jan, I exerted and compiled the code succesefully, now i have shear rate at every time writing. thankful for your quick and valuable reply. Kind Regards/ Rasoul 

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