[richard]

Gday Sylvia,

Just check all the semi-colons, spaces, brackets (normal and curly) and spelling are correct. For a while I had the same problem with the forces file not appearing, there wasn't any error output.

I haven't had a chance to check the units yet, but at first glance it looks like N, Nm and dimensionless.

Cheers!
Richard

[sjs]

Thanks, Richard. I had copied syntax from an earlier post in the thread and that was wrong --- it didn't give any error messages, so it took me awhile to realize it was wrong. Everything's great now.

cheers,
Sylvia

[gregorv]

I had a similar problem. Make sure you have the entry "functions" not "functionObjects" in the controlDict file. Richard mentions this in his post, but it takes a keen eye to spot the difference, it took me a while to see the issue.

Cheers,

-Gregor

[ivanwhlau]

Hi,
I am trying to validate the force coefficient using turbFoam (2D incompressible wind flow around a square cylinder)
What is wrong with my force coefficient:
I got very large magitude (Cd = 1.27e+4), which I expect Cd = 1.6
I noted that I need to multiply this by density (1.225kg/m^3), but still.....

Here is my paramenter
forceCoeffs
{
type forceCoeffs;
functionObjectLibs ("libforces.so");
patches (building);
rhoInf 1.0;
CofR (0 0 0);
liftDir (0 1 0);
dragDir (1 0 0);
pitchAxis (0 0 0);
magUInf 1;
lRef 1.0;
Aref 1.0;
}
Btw, where can I find the explanation these function parameters?
Regards,
Ivan

[richard]

Hi Ivan,

Your forceCoeffs description looks fine.

I can't find an explanation for the function parameters either - most seem logically named, but what has me puzzled is the pitchAxis and CofR parameters..? Are they meant to be different?

The nature of the transient rans technique makes it pretty poor at resolving forces - since it is trying to average flow over a small time. But they certainly shouldn't be that bad. It's more likely to be poor convergence by the sounds of it (use foamLog and plot initial residuals over time and make sure the max Courant number stays down around 0.2 or 0.3)

[eugene]

Err, you have specified the reference area (Aref) as 1 m2 and the reference velocity (magUInf) as 1 m/s. So the result you are looking at is more like the force in Newtons times (2*rho).

Definition of terms:
rhoInf - reference density
CofR - Centre of rotation
dragDir - Direction of drag coefficient
liftDir - Direction of lift coefficient
pitchAxis - Pitching moment axis
magUinf - free stream velocity magnitude
lRef - reference length
Aref - reference area

[ivanwhlau]

Hi, Eugene and Richard,
Thanks for your comment
Richard, I tried to find information about the difference between pitchAxis and CofR. I only know pitch is related to airplane.
By the way, do you know if there is any easy way to plot/calculate pressure coefficient?
Cheers,
Ivan

[olwi]

Hi,

I would assume CofR to be a point, and pitchAxis to be a vector (presumably in the transverse direction, relative to the motion/flow). But Eugene's should be able to tell you what it does...

/Ola

[mgz1985]

hi all,

where is this new directory created after copying the patch above to controlDict. I copied at the bottom of controlDict for my case and ran icoFoam

but i do not see any new directory anywhere. can sum1 tell exactly where is this directory.

thanx all

[ivanwhlau]

Hi Mayank,
If you do it correctly, you should see the "forces" and/or "forceCoeffs" folder insides case directory. [Version 1.5 only]
Ivan

[mgz1985]

hi ivan,

I can tell you what I did

I copied the fie above posted by you.it was placed at the bottom of the controlDict file. I made the appropriate changes i.e. renamed the patch and made the change in functionObjectLibs ("libforces.so") to functionLibs ("libforces.so").

This is what I did. I did check for the semi-colons and all. There was no syntax error generated by the machine.

If it is ok, I can post my controlDict file here for your review tomorrow as I am not in my office right now.

Thanx for replying

[ivanwhlau]

Hi Mayank,
I think I know your problem....
Try the following but change your parameters:

functions // this one!
(
forces
{
type forces;
functionObjectLibs ("libforces.so"); //Lib to load
patches (building); // change to your patch name
rhoInf 1.225; //Reference density for fluid
CofR (0 0 0); //Origin for moment calculations
}
forceCoeffs
{
type forceCoeffs;
functionObjectLibs ("libforces.so");
patches (building); //change to your patch name
rhoInf 1.225;
CofR (0 0 0);
liftDir (0 1 0);
dragDir (1 0 0);
pitchAxis (0 0 0);
magUInf 11.2;
lRef 45;
Aref 45;
}
);

[mgz1985]

Hi Ivan,

I tried what u said but it does not still display the directory. If you do not mind can u please take a look at my controlDict file and tell me where is the error. I am posting it here. I copied the patch u have put above and made the changes but still.

I just want to see the directory.

/attach{text}

[mgz1985]

Hi Ivan,

I tried what u said but it does not still display the directory. If you do not mind can u please take a look at my controlDict file and tell me where is the error. I am posting it here. I copied the patch u have put above and made the changes but still.

I just want to see the directory.

/attach{ }

[mgz1985]

Hi Ivan,

I tried what u said but it does not still display the directory. If you do not mind can u please take a look at my controlDict file and tell me where is the error. I am posting it here. I copied the patch u have put above and made the changes but still.

I just want to see the directory.

\attach { }

[mgz1985]

\attach {mayank}

[mgz1985]

controlDict

[ivanwhlau]

There is a typo. Should the patch be "fixedWall" instead of "fiexdWall"?

[mgz1985]

hi Ivan,

I corrected the typo but still there is no change. Still can not get the directory in the case directory or anywhere.

Is there anychanges to be made in some other files of the software library or what

[ivanwhlau]

Well, I test your controlDict with tutorials/icoFoam. It WORKS if I only paste your "function" part at the end. Then I replace the controlDict with your controlDict. it doesn't work. You may try and compare.