DDt

iamed18 · June 12, 2012, 09:51

Quote:

Originally Posted by grtabor

Its to do with the discretisation of the

U & fvc::grad(T)

term. In the FVM we discretise this using Gauss theorem, converting it into fluxes into and out of the domain. If we discretise the term written like this then it is not guaranteed to preserve conservation of the quantity being advected (here essentially the energy); i.e. your derivative may be loosing or gaining energy. If you do some manipulation of the term to get it into the form

fvc::div(phi, T)

where phi is essentially the same as U, then when we apply Gauss we get something which preserves continuity at the _numerical_ level, rather than the mathematical level. This would be a strong conservative implementation.

Gavin

Forgive my lack of mathematical background, but is there someone that would be able to show the manipulation steps such that

$\vec{U}\cdot\nabla\vec{U}=\nabla\cdot(\phi\vec{U})$ where $\phi=\vec{U}\cdot\vec{S}_f$ ?

I've taken a few whacks at it and my lack of FVM, I think, is making me miss some obvious connection.

Many thanks to whomever is able to assist me!

Edit: Nevermind. Figured it out. Odd way, though it works.

Mohammad Jam · September 9, 2016, 03:03

Hi

How to implement .oldTime(); after writing volScalarField in chtMultiregionFoam?

When i do that it gives this error:
class Foam::PtrList<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> >’ has no member named ‘oldTime’

idrees khan · January 19, 2021, 05:10

Hi Dear Former's
I'm going to Add temperature Equation to viscoelasticFluidFoam solver.
there is material derivative term of log(T)(screenshot attached) in the constitutive equation(I.e in this case Olroyd-B)

kindly any could guide me how to erite the that term in OldoydB.C file

I write it like fvm::ddt(tau_,logT) + fvc::div(phi()*tau_,logT)

Note:change to fvc and fvm respectively but getting same error's.(scrrenshot Attached)

regards
Idrees khan

idrees khan · January 19, 2021, 05:57

Hi Dear Former's
I'm going to Add temperature Equation to viscoelasticFluidFoam solver.
there is material derivative term of log(T)(screenshot attached) in the constitutive equation(I.e in this case Olroyd-B)

kindly any could guide me how to erite the that term in OldoydB.C file

I write it like fvm::ddt(tau_,logT) + fvc::div(phi()*tau_,logT)

Note:change to fvc and fvm respectively but getting same error's.(scrrenshot Attached)

regards
Idrees khan

idrees khan · January 19, 2021, 06:04

Hi Dear Former's
I'm going to Add temperature Equation to viscoelasticFluidFoam solver.
there is material derivative term of log(T)(screenshot attached) in the constitutive equation(I.e in this case Olroyd-B)

kindly any could guide me how to erite the that term in OldoydB.C file

I write it like fvm::ddt(tau_,logT) + fvc::div(phi()*tau_,logT)

Note:change to fvc and fvm respectively but getting same error's.(scrrenshot Attached)

regards
Idrees khan

September 9, 2016, 03:03	.oldTime(); in chtMultiregionFoam	#22
Mohammad Jam Member Join Date: Oct 2015 Location: montreal- canada Posts: 46 Rep Power: 10	Hi How to implement .oldTime(); after writing volScalarField in chtMultiregionFoam? When i do that it gives this error: class Foam::PtrList<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> >’ has no member named ‘oldTime’