[bowall]

Hi,

I'm new to OpenFOAM, well actually quite new to CFD as well, and has walked through some of the OpenFOAM tutorials. I'm interested in sail boat design and would like to use OpenFOAM for looking at e.g. drag of a hull. Is it possible to exchange the geometry for the hull used in e.g. the interFoam DTCHull to another geometry (i.e. use the tutorial as a template and change it according to needs)? That would be a great start to begin exploring. My idea is to design a hull using free software, starting with DelftShip Free to design a hull and then to look at the hydrodynamic aspects using OpenFOAM. Out of my head it would basically be just to exchange the geometry of the DTCHull to my geometry (and probably do some conversion from the "CAD" to "OpenFOAM World") and everything else would come out of the box from the DTCHull example. Of course I might be wrong, it has happened Before :-). Anyone who has any pointers in any direction? Links to similar discussions?

best regards,
Bo-Göran

[sheaker]

Hello.
I'm not an expert but I would like to recommend to you Salome for geometry and grid operations. If You have created geometry in another tool then try to export it to Salome for meshing.

Run Your tutorial and check in paraview for boundaries names. You will need to create groups of faces in Salome mesh module and export mesh as ideas UNV format. Then use tutorial case as a base for your simulation, set other parameters and run it.
Sounds good, doesn't work. openFoam is pretty hard software and I think hull simulation is pretty hard phenomena to start. Prepare for unexpected errors and issues.

Have a nice day.
Sheaker

[bowall]

Originally Posted by sheaker

Hello.
I'm not an expert but I would like to recommend to you Salome for geometry and grid operations. If You have created geometry in another tool then try to export it to Salome for meshing.

Run Your tutorial and check in paraview for boundaries names. You will need to create groups of faces in Salome mesh module and export mesh as ideas UNV format. Then use tutorial case as a base for your simulation, set other parameters and run it.
Sounds good, doesn't work. openFoam is pretty hard software and I think hull simulation is pretty hard phenomena to start. Prepare for unexpected errors and issues.

Have a nice day.
Sheaker

Thanks Sheaker. I will take a look at Salome for meshing, Paraview at least allowed me to display the STL format exported by DelftShip. I realized myself that I at least need to give an input to the boundary conditions, OpenFoam of course does not know where the static waterline is which of course is dependent upon weight and exact design from DelftShip. As you mention, it's probably even more sofisticated than that. But I will dig into that.

It's interesting you say that OpenFoam is hard. As a newcomer, what is hard compared to e.g. Ansys? Working with source files instead of menus? I took the EdX course in Ansys Simulations and that's the only experience I have from Ansys. Although, I have an engineering background with an emphasis in mathematical modelling and much of the theory in the Ansys course, at least the FEM part, was known before.

I think you should solve the problems you find interesting and evolve from there, calculating heat transfer from a horse approximated by a sphere you can do in school :-).

[sheaker]

In my opinion ANSYS is doing a lot of stuff for you. In openFoam you need to do everything by yourself.
For example:
In ANSYS you can just set to see residuals. In openFoam you need to write function for it:

set logscale y
set title "Residuals"
set ylabel 'Residual'
set xlabel 'Iteration'
plot "< cat log | grep 'Solving for Ux' | cut -d' ' -f9 | tr -d ','" title 'Ux' with lines,\
     "< cat log | grep 'Solving for Uy' | cut -d' ' -f9 | tr -d ','" title 'Uy' with lines,\
     "< cat log | grep 'Solving for Uz' | cut -d' ' -f9 | tr -d ','" title 'Uz' with lines,\
     "< cat log | grep 'Solving for epsilon' | cut -d' ' -f9 | tr -d ','" title 'omega' with lines,\
     "< cat log | grep 'Solving for k' | cut -d' ' -f9 | tr -d ','" title 'k' with lines,\
     "< cat log | grep 'Solving for p' | cut -d' ' -f9 | tr -d ','" title 'p' with lines
pause 1
reread

Another one:
Bad mesh in ANSYS? ANSYS can possibly deal with it automatically.
Bad mesh in openFoam? DIVERGENCE!!! You can operate with PIMPLE loop parameters and some other corrections but manually.

Another one:
You want to check drag force in ANSYS? Just calculate force in Y direction on wing.
You want to check drag force in openFoam? Function:

    forces
    {
        type            forceCoeffs;
        functionObjectLibs ( "libforces.so" );
        outputControl   timeStep;
        outputInterval  1;

        patches
        (
            wall
        );

        pName       p;
        UName       U;
        rhoName        rho;
        log         true;
        rhoInf      1.205;
        CofR        ( 0 0 0 );
        liftDir     ( 0 1 0 );
        dragDir     ( 1 0 0 );
        pitchAxis   ( 0 0 1 );
        magUInf     148.7233;
        lRef        0.6096;
        Aref        0.6096;
    }

openFoam IS very interesting software but in my opinion is hard.

Sheaker