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-   -   Error Message Determining Forces in OpenFOAM 1.7 (http://www.cfd-online.com/Forums/openfoam/79377-error-message-determining-forces-openfoam-1-7-a.html)

Greg Givogue August 22, 2010 12:22

Error Message Determining Forces in OpenFOAM 1.7
 
Hi,

I'm an OpenFOAM beginner trying to determine the forces on a patch from the motorBike tutorial. This tutorial closely resembles a problem I'm going to try to model and thus I thought modifying this problem one step at a time would be the safest route. I've scoured this forum and have found many helpful hints. This is what I've added to the ControlDict file;

functions //added code from http://www.cfd-online.com/Forums/ope...nts-cl-cd.html // should produce a forces.dat folder in the project folder
(
forces
{
type forces;
functionObjectLibs ("libforces.so"); //Lib to load
patches (motorBike_windshield:002%2); // change to your patch name and for multiple patches seperate patch names by a space
//pName p;// added next three lines because of sonicFoam example controlDict, however no change in error message
//UName U;
//log true;
rhoInf 1.225; //Reference density for fluid - changed to SL air from 1.204
CofR (0 0 0); //Origin for moment calculations
outputControl timeStep;
outputInterval 100;
}

forceCoeffs
{
type forceCoeffs;
functionObjectLibs ("libforces.so");
patches (motorBike_windshield:002%2); //change to your patch name
//pName p;// added next three lines because of sonicFoam example controlDict
//UName U;
//log true;
rhoInf 1.225;
CofR (0 0 0);
liftDir (0 1 0);
dragDir (1 0 0);
pitchAxis (0 0 0);
magUInf 20; // changed from 0.1
lRef 1;
Aref 1;
outputControl timeStep;
outputInterval 100;
}
);

This is the error message I get in log.SimpleFoam;
Starting time loop

--> FOAM Warning :
From function void forces::read(const dictionary& dict)
in file forces/forces.C at line 277
Could not find U, p or rho in database.
De-activating forces.

I've tried looking at other tutorials that use functions, however, I can't spot how they're set-up any differently... and I don't really understand what the error message is telling me from forces.c. I think I'm missing something simple in the initialization of the problem... Thanks in advance for your help!

aloeven August 23, 2010 11:01

Just add:

rhoName rhoInf;

It can be that you have to uncomment:

pName p;
Uname U;

Greg Givogue August 23, 2010 12:48

Thanks Alex! I'm away from my computer but I'll give it a shot later tonight and I'll let you know how I make out. I hope it's something that simple.

Thanks again for the help! Greg

Greg Givogue August 23, 2010 18:03

Yep that did it. Thanks.


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