[idrees khan]

Dear former's


please any one could guide me How to use Non-Dimensional equations(see screenshot of equ's) in OpenForm(foam-extend-4.0).


regards
Idrees

[alexeym]

Hi,

What kind of guidance do you need? Equations in OpenFOAM are written in dimensioned form, so you have to rewrite you equations to learn what solver to use, what models to use, etc.

Right now it seems that you need

1. buoyantBoussinesqPimpleFoam solver.
2. Arrhenius viscosity model.
3. solidificationMeltingSource fvOption.

Guess, lambda in your case is thermal conductivity, so you will have to implement additional source terms to have temperature-dependent thermal diffusivity.

Just for your future posts (if you want to get answers without employing Skype):
- Nobody want to decrypt your screen-shots. Post your equations using MATH tags.
- Usually people answer questions, not vague guidance requests.
- There are a number of OpenFOAM users, limit yourself with foam-extend 4.0 is to reduce number of people, who can answer you.
- Search. I do not think, you are the first, who wants to solve dimensionless equations with OpenFOAM.

[idrees khan]

Hi Dear Nancy,
I'm going to solve a paper(having viscoelastic Model more specifically having momentum,temperature,Oldroyd-B model) in openFaom,which is basically solved in Matlab using Finite difference Method.


so difinitly i will have to use ViscoelasticFluidFoam solver which is basically for isothermal case so far in foam-extend.4.0 version,so i'll have to add Temperature equation

to viscoelasticFluidFoam solver as given in the paper.


so to compare the results with the paper,as it is solved in dimensionless form i would like to use the dimensionless governing equations(screenshot given) in openFaom (if I'm not wrong).
so kindly i need guidance for that,where i should need to make the changes?,as openFoam is strictly dimensioned.


regards
idrees khan

[idrees khan]

Originally Posted by alexeym

Hi,

What kind of guidance do you need? Equations in OpenFOAM are written in dimensioned form, so you have to rewrite you equations to learn what solver to use, what models to use, etc.

Right now it seems that you need

1. buoyantBoussinesqPimpleFoam solver.
2. Arrhenius viscosity model.
3. solidificationMeltingSource fvOption.

Guess, lambda in your case is thermal conductivity, so you will have to implement additional source terms to have temperature-dependent thermal diffusivity.

Just for your future posts (if you want to get answers without employing Skype):
- Nobody want to decrypt your screen-shots. Post your equations using MATH tags.
- Usually people answer questions, not vague guidance requests.
- There are a number of OpenFOAM users, limit yourself with foam-extend 4.0 is to reduce number of people, who can answer you.
- Search. I do not think, you are the first, who wants to solve dimensionless equations with OpenFOAM.

Dear Alexey,
Sorry I'm new don't know how to write equations using MATH tags, but let me write the equation's without that. the stress equation(using Oldroyd-B model) for isothermal case is like so,




// Stress transport equation
fvSymmTensorMatrix tauEqn
(
fvm::ddt(tau_)
+ fvm::div(phi(), tau_)
==

etaP/lambda*twoD
+ twoSymm(C)
- fvm::Sp(1/lambda, tau_)
);

tauEqn.relax();
tauEqn.solve();
}




But for non-isothermal case in the stress equation



//- WLF to update viscosities for temperature dependence
volScalarField lambda = Foam::exp( -C11_*(T - To_) / (C21_ + T - To_) )*lambda_;
volScalarField etaP = Foam::exp( -C11_*(T - To_) / (C21_ + T - To_) )*etaP_;

volScalarField muS = Foam::exp( -C11_*(T - To_) / (C21_ + T - To_) )*etaS_;





there is a term (lambda*tua_*D(log(T)/Dt where Lambda is relaxation time which also depends upon temperature i.e as define above ) means multiplication of relaxation time lambda(T) tau_ and material derivative of log(T) please have a look of screenshot)



my question is how to define in openFoam term lambda*tua_*D(log(T)/Dt rest of the equation is same as given above.


if define it like



// material derivative term of log(T) in multiplication with tau_
fvc::ddt(tau_/lambda,logT) +fvc::div(phi()*tau_,logT/lambda)



which is wrong beacause this: fvc::div(phi()*tau_,logT), phi is a surface field that are multiplying a volumetric field,I'm getting erorr's while compiling



if define like so

// material derivative term of log(T) in multiplication with tau_
tau_*fvc::ddt(1/lambda,logT) + tau_*fvc::div(phi(),logT/lambda)



But I'm not sure although it compile successfully by running "wmake libso"





what i'm thinking just like we define material derivative in momentum eqaution i.e DU/Dt which is wrtten in openFaom

fvm::ddt(U) +fvm:phi ,U) here U is a variable to whom we are taking the derivative.



regards
idrees