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- - **viscoelastic fluid abbreviations**
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viscoelastic fluid abbreviationsHello 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. |

general viscoelastic material model - OpenFOAM-1.6-extdear 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 OpenFOAM-1.6-ext. There is a general viscoelastic solver there.
It is more difficult to install the OF-ext 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 OF-ext 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 |

Dear JonThanks 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 co-relate it with the theory. Anyways, Thanks for your help. --- Regards, Tushar |

about twoSymm(L)hi again,
I dont think there is any twoSymm(L) used in the code. But if you look at the ~/OpenFOAM/OpenFOAM-2.1.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. |

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. |

shear rateHi foamers
How can i extract from my results using viscoelasticFluidFoam?shear ratetnx |

shear rateQuote:
(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 rate-of-strain tensor" like I did in Wallevik, J.E., Minimizing end-effects in the coaxial cylinders viscometer: Viscoplastic flow inside the ConTec BML Viscometer 3. J. Non-Newtonian Fluid Mech. 155 (2008) 116-123. Hope this helps cheers Jon |

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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