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-   -   Oscillating cylinder using icoFoam blowing up (https://www.cfd-online.com/Forums/openfoam-solving/80272-oscillating-cylinder-using-icofoam-blowing-up.html)

rieuk September 21, 2010 07:40
Oscillating cylinder using icoFoam blowing up
 
Hey guys I'm simulating a (2D) transversely oscillating cylinder using a non-inertial reference frame using the following modification to icoFoam:

Code:
scalar Pi = mathematicalConstant::pi;
dimensionedScalar accCt("accCt",dimensionSet(0,1,-2,0,0,0,0),-3.0*pow(2.0*Pi/3.0,2)*Foam::cos(2.0*Pi*runTime.value()/3.0));
dimensionedVector acc("acc",dimensionSet(0,1,-2,0,0,0,0), vector::zero);

acc.component(vector::Y) = accCt;

        fvVectorMatrix UEqn
        (
            fvm::ddt(U)
          + fvm::div(phi, U)
          - fvm::laplacian(nu, U)
    ==
      acc
        );


        solve(UEqn ==  - fvc::grad(p));
However the run keeps blowing up (Floating Point Exception with ridiculously high velocity magnitude) at around the same time even for very small delta T... can anyone see what's wrong with my implementation?

rieuk September 22, 2010 05:02
Hmm does my acc term need to be scaled by density of the fluid?...

ata September 22, 2010 09:22
Hi
I hope you are doing very well.
I am not sure that your solver is true. But may I ask you how implement geometry and boundary conditions?
Best regards
Good luck

Ata

rieuk September 22, 2010 09:25
What do you mean you're not sure, as in you think it's wrong? Well with velocity boundary conditions I intend to use dirichlet conditions (freestream + sinusoidal cylinder velocity component) for inlet and top/bottom and zero gradient for outlet. I'm thinking groovyBC is the only way to handle that but for now I'm just using fixedValue to see if the solver is doing what it's supposed to. Right now it's just doing crazy things like creating random vortices emanating from the boundaries...

ata September 22, 2010 09:32
no no no no
Excuse me. I do not mean your code is incorrect. At least in my knowledge.
I think may be your BCs are bad.
good luck

rieuk September 22, 2010 11:25
What's wrong with them?


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