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Old   August 6, 2009, 08:22
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Hello,
I have one question regarding forces utility.
I would like to monitor the forces on 3 bodies BUT separately.
I'd like to have 3 monitorings. (I have a system and 3 different pistons --> 3 different patches)
Is it possible?
Thanx a lot
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Old   August 7, 2009, 08:09
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ok I just needed to add other forces functions...

forces_1
{
type forces;
functionObjectLibs ("libforces.so");
patches (A);
rhoInf 870;
CofR (0 0 0);
}
forces_2
{
type forces;
functionObjectLibs ("libforces.so");
patches (B);
rhoInf 870;
CofR (0 0 0);
}
forces_3
{
type forces;
functionObjectLibs ("libforces.so");
patches (C);
rhoInf 870;
CofR (0 0 0);
}
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Old   August 28, 2009, 13:02
Default OF1.6 forces error
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Hi, I'm using OpenFOAM 1.6 and trying to calculate the forces on an airfoil. I have the following lines at the end of my controlDict file:

functions
(
forces
{
type forces;
functionObjectLibs ("libforces.so");
patches (patch6);
rhoInf 1.225;
CofR (0.15 0 0);
}
);

This is the error I get:

keyword outputControl is undefined in dictionary "::functions::forces"

Please help.
Thanks.
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Old   August 28, 2009, 14:28
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It works after adding the following lines :

outputControl timeStep;
outputInterval 1;

Last edited by nomad; August 28, 2009 at 15:47.
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Old   September 1, 2009, 03:21
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Hi.

Great thread, but I struggle a bit with getting forces out.

What I can do: I can get tutorial nacaAirfoil to work (with sonicFoam) - this tutorial already has force-output setup in controlDict. Works great.

What I can't do: If I try to add the force-output stuff from the above-mentioned sonicFoam-tutorial, into the simpleFoam tutorial airfoil2D, I get errors:

--> 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.

this seems to be something obvious (?) as velocities etc. would certainly be great to have available if OF is to compute forces and I am sure they are in there somewhere :-)

Help would be appreciated, thanks!

/Mads
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Old   September 1, 2009, 16:51
Default incorrect forces on symmetric airfoil
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Hi,
I'm trying to calculate forces on a symmetric airfoil. I've set lref to the chord length and Aref to the reference area based on the span (these have been converted from imperial to metric units). I also have two separate patches, one for the top surface and one for the lower surface.
However, i get high Cl values (which should be zero) and Cd values that don't really make sense. here's my last time step:

Time = 2

DILUPBiCG: Solving for Ux, Initial residual = 0.0209504, Final residual = 2.13957e-07, No Iterations 9
DILUPBiCG: Solving for Uy, Initial residual = 0.0586488, Final residual = 3.39781e-07, No Iterations 9
DILUPBiCG: Solving for Uz, Initial residual = 0.0873523, Final residual = 4.68623e-07, No Iterations 9
DICPCG: Solving for p, Initial residual = 0.213432, Final residual = 9.62741e-10, No Iterations 296
DICPCG: Solving for p, Initial residual = 0.368842, Final residual = 9.65877e-10, No Iterations 284
DICPCG: Solving for p, Initial residual = 0.118823, Final residual = 9.0931e-10, No Iterations 278
DICPCG: Solving for p, Initial residual = 0.0732968, Final residual = 9.25933e-10, No Iterations 258
time step continuity errors : sum local = 6.07097e-11, global = 5.91392e-19, cumulative = 2.59606e-18
smoothSolver: Solving for nuTilda, Initial residual = 0.0120958, Final residual = 0.00101485, No Iterations 2
ExecutionTime = 23.62 s ClockTime = 31 s

forces output:
forces(pressure, viscous)((-8026.46 0 0) (11.1053 -7.92581 -8.84242))
moment(pressure, viscous)((0 -10186.1 112963) (974.88 -3443.99 426.025))

forces output:
forces(pressure, viscous)((-1910.11 0 0) (1.60656 0.792914 21.378))
moment(pressure, viscous)((0 -2420.21 -39146.1) (-301.654 -1457.53 38.3032))

forceCoeffs output:
Cd = -1308.63
Cl = -1.29401
Cm = 0

forceCoeffs output:
Cd = -12267.4
Cl = 5.09667
Cm = -0

End


Any help would be highly appreciated.
Thanks.
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Old   September 2, 2009, 01:19
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Hi Nomad.

I am running OF-1.6.x and am trying to get this to work with simpleFoam and pisoFoam - what solver/version are you running (so I can verify that this will work under simpleFoam/pisoFoam)?


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Old   September 2, 2009, 14:22
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Hey,
I'm running OpenFOAM 1.6. The flow looks reasonable around a symmetric airfoil, but Cl and Cd values are just wrong. Also, solutions don't converge for angled airfoils (5 degrees). I'm running at low Re numbers, although I have turbulence turned on.
I'm guessing my mesh is just crappy, I use NGSolve and gmsh to generate and refine tet meshes.
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Old   September 3, 2009, 02:47
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Okay, so you are running simpleFoam or pisoFoam? I'm just trying to narrow down my problem - and if you can get forces out under simple/pisoFoam, I guess I should be able to do so also.

With regards to your problem, just from the top of my head: tet-cells and forces on walls easily result in wrong results, as you also imply. If your lift is y-directed then your y-forces obviously should be zero (for flow parallel to your symmetric airfoil). It seems that your y-pressure-forces indeed are zero, but the viscous ones aren't - this emphasises our suspicion that there is some unfortunate resolution of the cells adjacent to the wall. Maybe you could insert some prism-layers? Or better yet (given this simple, yet hard-to-solve, geometry): go completely hex.


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Old   September 3, 2009, 20:42
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I'm using SimpleFoam, here's my controlDict file:

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 1.6 |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

application simpleFoam;

startFrom startTime;

startTime 0;

stopAt endTime;

endTime 0.05;

deltaT 0.001;

writeControl timeStep;

writeInterval 1;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression uncompressed;

timeFormat general;

timePrecision 6;

runTimeModifiable yes;

functions
{
forces_1
{
type forces;
functionObjectLibs ("libforces.so");
log yes;
outputControl timeStep;
outputInterval 1;
patches (patch6);
rhoInf 1.225;
CofR (0 0 0);
}

forces_2
{
type forces;
functionObjectLibs ("libforces.so");
log yes;
outputControl timeStep;
outputInterval 1;
patches (patch7);
rhoInf 1.225;
CofR (0 0 0);
}

forceCoeffs_1
{
type forceCoeffs;
functionObjectLibs ("libforces.so");
log yes;
outputControl timeStep;
outputInterval 1;
patches (patch6);
rhoInf 1.225;
CofR (0 0 0);
liftDir (0 1 0);
dragDir (1 0 0);
pitchAxis (0 0 0);
magUInf 50;
lRef 1;
Aref 0.1;
}

forceCoeffs_2
{
type forceCoeffs;
functionObjectLibs ("libforces.so");
log yes;
outputControl timeStep;
outputInterval 1;
patches (patch7);
rhoInf 1.225;
CofR (0 0 0);
liftDir (0 1 0);
dragDir (1 0 0);
pitchAxis (0 0 0);
magUInf 50;
lRef 1;
Aref 0.1;
writePrecision 3;
}
};



Also, I'm using NGSolve and gmsh and I'm not sure they do tets, hex, or prisms in the same mesh. You can pick either and then refine it near the walls.
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Old   September 4, 2009, 02:30
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Thannks nomad.

Just to wrap up on my question. This thread provides the answer. If you are running OpenFOAM-1.6, as I am, the entry

rhoName rhoInf;

is needed in the forces section of the controlDict.

/Mads
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Old   September 6, 2009, 04:51
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please could you tell me! What is
magUInf 55.5;
lRef 0.6;
Aref 1;

Tanks
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Old   September 6, 2009, 05:51
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magUInf 55.5 - freestream velocity
lRef 0.6 - chord length of airfoil or diameter of cylinder
Aref 1 - surface area, or chord*span
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Old   September 6, 2009, 07:07
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Thank you nomad!

please I would like to monitor the friction forces ( X- Direction: Vector(1,0,0) in case "Flow Around a Cylinder 2D".

Any help would be highly appreciated.
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Old   September 7, 2009, 07:45
Default forcesCoeffs
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Thank you nomad!
I used the source code from aboveto monitor the forcesCoffs and I can understand why the drag should be so higher and the lift negative (output below).

I set it as follow:

CofR (0.08 0.055 0);// Cylinder-origin
liftDir (0 1 0);
dragDir (1 0 0);
pitchAxis (0 0.08 0);// Axis across the Cylinder
magUInf 2;// equal =Inlet_Velocity=2m/s
lRef 1;

output

Time = 1.0172
Courant Number mean: 0.000625676 max: 0.0181103
DILUPBiCG: Solving for Ux, Initial residual = 9.29756e-05, Final residual = 1.43061e-11, No
Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.000133566, Final residual = 3.20209e-11, No
Iterations 1
DICPCG: Solving for p, Initial residual = 0.00116615, Final residual = 9.66575e-07, No Iterations
50
DICPCG: Solving for p, Initial residual = 2.41027e-05, Final residual = 9.31728e-07, No Iterations
6
DICPCG: Solving for p, Initial residual = 1.72683e-06, Final residual = 6.66295e-07, No Iterations
1
DICPCG: Solving for p, Initial residual = 6.8258e-07, Final residual = 6.8258e-07, No Iterations 0
time step continuity errors : sum local = 1.55452e-14, global = -8.96216e-16, cumulative =
1.36155e-14
DICPCG: Solving for p, Initial residual = 8.42778e-07, Final residual = 8.42778e-07, No Iterations
0
DICPCG: Solving for p, Initial residual = 8.42778e-07, Final residual = 8.42778e-07, No Iterations
0
DICPCG: Solving for p, Initial residual = 8.42778e-07, Final residual = 8.42778e-07, No Iterations
0
DICPCG: Solving for p, Initial residual = 8.42778e-07, Final residual = 8.42778e-07, No Iterations
0 time step continuity errors :
sum local =
1.91935e-14, global =
-
8.9659e-16, cumulative =
1.27189e-14
ExecutionTime = 117.44 s ClockTime = 120 s
forces output:
forces(pressure, viscous)((1.66969 -1.40143 -1.61795e-19) (0.384086 -0.000228929
-2.21498e-22))
moment(pressure, viscous)((3.67135e-19 1.16523e-17 -111.911) (-9.2515e-22 1.8447e-20
0.000382369))
forceCoeffs output:
Cd = 83.8275
Cl = -57.2107
Cm = 0

I would like to no what i did Wrong!
Could someone please help me! It is very important
Thanks
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Old   September 7, 2009, 15:37
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Hi Nomad,

Let me give my two cents:

- At a first glance, your problem seems like it has not converged yet. The residuals are still high;

Quote:
Originally Posted by nomad View Post
...
Time = 2

DILUPBiCG: Solving for Ux, Initial residual = 0.0209504, Final residual = 2.13957e-07, No Iterations 9
DILUPBiCG: Solving for Uy, Initial residual = 0.0586488, Final residual = 3.39781e-07, No Iterations 9
DILUPBiCG: Solving for Uz, Initial residual = 0.0873523, Final residual = 4.68623e-07, No Iterations 9
DICPCG: Solving for p, Initial residual = 0.213432, Final residual = 9.62741e-10, No Iterations 296
DICPCG: Solving for p, Initial residual = 0.368842, Final residual = 9.65877e-10, No Iterations 284
DICPCG: Solving for p, Initial residual = 0.118823, Final residual = 9.0931e-10, No Iterations 278
DICPCG: Solving for p, Initial residual = 0.0732968, Final residual = 9.25933e-10, No Iterations 258
time step continuity errors : sum local = 6.07097e-11, global = 5.91392e-19, cumulative = 2.59606e-18
smoothSolver: Solving for nuTilda, Initial residual = 0.0120958, Final residual = 0.00101485, No Iterations 2
ExecutionTime = 23.62 s ClockTime = 31 s

...
- As you said, the patches are separated, and if you sum the vectors

Quote:
Originally Posted by nomad View Post
...

forces output:
forces(pressure, viscous)((-8026.46 0 0) (11.1053 -7.92581 -8.84242))
moment(pressure, viscous)((0 -10186.1 112963) (974.88 -3443.99 426.025))

forces output:
forces(pressure, viscous)((-1910.11 0 0) (1.60656 0.792914 21.378))
moment(pressure, viscous)((0 -2420.21 -39146.1) (-301.654 -1457.53 38.3032))

...
The sum of the pressure forces in the x direction are non zero (drag force), and the sum (of the pressure forces) in the y direction is zero.

The non zero sum of the viscous forces are apparently due to the non converged solution (boundary layer not yet solved). Try to follow the results until they don't change in a small range.

Hope that helps.

Best Regards,

Paulo Rocha.
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Old   September 8, 2009, 04:30
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Thank you Paulo!

I have followed the results until they don't change in a small range and post it here.
The forces Coefficient are still so high! (I need Help)

Time = 2.4164
Courant Number mean: 0.000625962 max: 0.018118
DILUPBiCG: Solving for Ux, Initial residual = 8.58266e-05, Final residual = 5.68787e-12, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.000135717, Final residual = 1.58934e-11, No Iterations 1
DICPCG: Solving for p, Initial residual = 0.000318544, Final residual = 2.92359e-06, No Iterations 10
DICPCG: Solving for p, Initial residual = 6.1916e-06, Final residual = 9.84286e-07, No Iterations 47
DICPCG: Solving for p, Initial residual = 1.54247e-06, Final residual = 7.8343e-07, No Iterations 1
DICPCG: Solving for p, Initial residual = 7.89665e-07, Final residual = 7.89665e-07, No Iterations 0
time step continuity errors : sum local = 8.41203e-15, global = 1.5953e-15, cumulative = -1.07022e-10
DICPCG: Solving for p, Initial residual = 8.12457e-07, Final residual = 8.12457e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 8.12457e-07, Final residual = 8.12457e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 8.12457e-07, Final residual = 8.12457e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 8.12457e-07, Final residual = 8.12457e-07, No Iterations 0
time step continuity errors : sum local = 8.65482e-15, global = 1.59517e-15, cumulative = -1.0702e-10
ExecutionTime = 25803.5 s ClockTime = 77443 s
forces output:
forces(pressure, viscous)((3.36771 -0.00561273 9.48494e-20) (0.365782 -2.56185e-05 -1.76796e-22))
moment(pressure, viscous)((3.44194e-19 -8.53456e-18 -0.263345) (-8.875e-22 1.48343e-20 0.0157597))
forceCoeffs output:
Cd = 152.388
Cl = -0.230137
Cm = -1.91412e-17
Time = 2.4166
Courant Number mean: 0.000625962 max: 0.0181183
DILUPBiCG: Solving for Ux, Initial residual = 8.58272e-05, Final residual = 5.68766e-12, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.000135717, Final residual = 1.5893e-11, No Iterations 1
DICPCG: Solving for p, Initial residual = 0.000307771, Final residual = 3.04239e-06, No Iterations 14
DICPCG: Solving for p, Initial residual = 5.71835e-06, Final residual = 9.44935e-07, No Iterations 174
DICPCG: Solving for p, Initial residual = 1.83437e-06, Final residual = 8.73055e-07, No Iterations 1
DICPCG: Solving for p, Initial residual = 8.84112e-07, Final residual = 8.84112e-07, No Iterations 0
time step continuity errors : sum local = 9.41649e-15, global = -2.7658e-16, cumulative = -1.0702e-10
DICPCG: Solving for p, Initial residual = 8.94637e-07, Final residual = 8.94637e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 8.94637e-07, Final residual = 8.94637e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 8.94637e-07, Final residual = 8.94637e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 8.94637e-07, Final residual = 8.94637e-07, No Iterations 0
time step continuity errors : sum local = 9.5286e-15, global = -2.7731e-16, cumulative = -1.07021e-10
ExecutionTime = 25806.4 s ClockTime = 77452 s
forces output:
forces(pressure, viscous)((3.37787 -0.0101397 9.47906e-20) (0.365779 -2.56295e-05 -1.76913e-22))
moment(pressure, viscous)((3.4472e-19 -8.52938e-18 -0.624579) (-8.87876e-22 1.48437e-20 0.0157587))
forceCoeffs output:
Cd = 152.802
Cl = -0.41491
Cm = -1.91296e-17
Time = 2.4168
Courant Number mean: 0.000625962 max: 0.0181186
DILUPBiCG: Solving for Ux, Initial residual = 8.58271e-05, Final residual = 5.68736e-12, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.000135717, Final residual = 1.58931e-11, No Iterations 1
DICPCG: Solving for p, Initial residual = 0.000308555, Final residual = 2.98446e-06, No Iterations 6
DICPCG: Solving for p, Initial residual = 5.6599e-06, Final residual = 9.87842e-07, No Iterations 193
DICPCG: Solving for p, Initial residual = 1.97131e-06, Final residual = 8.93472e-07, No Iterations 1
DICPCG: Solving for p, Initial residual = 9.0792e-07, Final residual = 9.0792e-07, No Iterations 0
time step continuity errors : sum local = 9.67148e-15, global = -1.15687e-16, cumulative = -1.07021e-10
DICPCG: Solving for p, Initial residual = 9.19959e-07, Final residual = 9.19959e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 9.19959e-07, Final residual = 9.19959e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 9.19959e-07, Final residual = 9.19959e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 9.19959e-07, Final residual = 9.19959e-07, No Iterations 0
time step continuity errors : sum local = 9.79972e-15, global = -1.14472e-16, cumulative = -1.07021e-10
ExecutionTime = 25809.3 s ClockTime = 77462 s
forces output:
forces(pressure, viscous)((3.36459 -0.00234243 9.49148e-20) (0.365777 -2.56403e-05 -1.76832e-22))
moment(pressure, viscous)((3.41853e-19 -8.54044e-18 -0.00215479) (-8.87561e-22 1.48373e-20
0.0157578))
forceCoeffs output:
Cd = 152.26
Cl = -0.0966561
Cm = -1.91544e-17
Time = 2.417
Courant Number mean: 0.000625962 max: 0.018119
DILUPBiCG: Solving for Ux, Initial residual = 8.58282e-05, Final residual = 5.68722e-12, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.000135717, Final residual = 1.58931e-11, No Iterations 1
DICPCG: Solving for p, Initial residual = 0.000315884, Final residual = 2.95918e-06, No Iterations 8
DICPCG: Solving for p, Initial residual = 6.17492e-06, Final residual = 9.82022e-07, No Iterations 76
DICPCG: Solving for p, Initial residual = 1.57902e-06, Final residual = 7.6317e-07, No Iterations 1
DICPCG: Solving for p, Initial residual = 7.70554e-07, Final residual = 7.70554e-07, No Iterations 0
time step continuity errors : sum local = 8.20779e-15, global = 9.71976e-16, cumulative = -1.0702e-10
DICPCG: Solving for p, Initial residual = 7.8575e-07, Final residual = 7.8575e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 7.8575e-07, Final residual = 7.8575e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 7.8575e-07, Final residual = 7.8575e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 7.8575e-07, Final residual = 7.8575e-07, No Iterations 0
time step continuity errors : sum local = 8.36965e-15, global = 9.71832e-16, cumulative = -1.07019e-10
ExecutionTime = 25811 s ClockTime = 77468 s
forces output:
forces(pressure, viscous)((3.37494 -0.0119856 9.47646e-20) (0.365774 -2.56513e-05 -1.76846e-22))
moment(pressure, viscous)((3.43041e-19 -8.5271e-18 -0.772271) (-8.87594e-22 1.48385e-20 0.0157568))
forceCoeffs output:
Cd = 152.682
Cl = -0.490257
Cm = -1.91245e-17
Time = 2.4172
Courant Number mean: 0.000625962 max: 0.0181193
DILUPBiCG: Solving for Ux, Initial residual = 8.58281e-05, Final residual = 5.68692e-12, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.000135718, Final residual = 1.58931e-11, No Iterations 1
DICPCG: Solving for p, Initial residual = 0.000308469, Final residual = 2.89403e-06, No Iterations 6
DICPCG: Solving for p, Initial residual = 5.61796e-06, Final residual = 9.72727e-07, No Iterations 52
DICPCG: Solving for p, Initial residual = 1.42823e-06, Final residual = 6.66354e-07, No Iterations 1
DICPCG: Solving for p, Initial residual = 6.7216e-07, Final residual = 6.7216e-07, No Iterations 0
time step continuity errors : sum local = 7.1595e-15, global = 1.21748e-15, cumulative = -1.07018e-10
DICPCG: Solving for p, Initial residual = 6.85686e-07, Final residual = 6.85686e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 6.85686e-07, Final residual = 6.85686e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 6.85686e-07, Final residual = 6.85686e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 6.85686e-07, Final residual = 6.85686e-07, No Iterations 0
time step continuity errors : sum local = 7.30358e-15, global = 1.21697e-15, cumulative = -1.07017e-10
ExecutionTime = 25812.6 s ClockTime = 77472 s
forces output:
forces(pressure, viscous)((3.37343 -0.00605809 9.48554e-20) (0.365771 -2.56622e-05 -1.76854e-22))
moment(pressure, viscous)((3.41449e-19 -8.5356e-18 -0.298624) (-8.87587e-22 1.48391e-20 0.0157559))
forceCoeffs output:
Cd = 152.621
Cl = -0.248316
Cm = -1.91435e-17
Time = 2.4174
Courant Number mean: 0.000625962 max: 0.0181196
DILUPBiCG: Solving for Ux, Initial residual = 8.58283e-05, Final residual = 5.68666e-12, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.000135718, Final residual = 1.58931e-11, No Iterations 1
DICPCG: Solving for p, Initial residual = 0.000310674, Final residual = 2.96383e-06, No Iterations 6
DICPCG: Solving for p, Initial residual = 5.80902e-06, Final residual = 9.64652e-07, No Iterations 179
DICPCG: Solving for p, Initial residual = 1.91265e-06, Final residual = 8.68626e-07, No Iterations 1
DICPCG: Solving for p, Initial residual = 8.80374e-07, Final residual = 8.80374e-07, No Iterations 0
time step continuity errors : sum local = 9.37581e-15, global = 7.32662e-17, cumulative = -1.07017e-10
DICPCG: Solving for p, Initial residual = 8.93729e-07, Final residual = 8.93729e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 8.93729e-07, Final residual = 8.93729e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 8.93729e-07, Final residual = 8.93729e-07, No Iterations 0
DICPCG: Solving for p, Initial residual = 8.93729e-07, Final residual = 8.93729e-07, No Iterations 0
time step continuity errors : sum local = 9.51804e-15, global = 7.31233e-17, cumulative = -1.07016e-10
ExecutionTime = 25815.3 s ClockTime = 77481 s
forces output:
forces(pressure, viscous)((3.36891 -0.00403213 9.48363e-20) (0.365769 -2.56731e-05 -1.7698e-22))
moment(pressure, viscous)((3.40287e-19 -8.53412e-18 -0.136958) (-8.8798e-22 1.48492e-20 0.0157549))
forceCoeffs output:
Cd = 152.436
Cl = -0.165625

Why are the focesCoefficient still so high?

please could someone help me? It´s very important.

Last edited by ronaldo; September 9, 2009 at 04:56.
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Old   November 11, 2009, 09:02
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  #138
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Milos Stanic
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Location: Novi Sad, Serbia
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Hello to everyone!

I'm using simpleFoam in OF 1.6 for some ship hull calculations and I really need either drag coeffs or forces. I tried following the instructions from this thread, but no success. I noticed that most of people here are using this forceCoeffs for airfoils (compressible flow?), so what should I change in order to get the forces for simpleFoam solver?

When I try to start my simulation it finishes up like this:

student@CFD:~/OpenFOAM/Projekti/cilindar$ simpleFoam >log

keyword outputControl is undefined in dictionary "::functions::forces"

file: ::functions::forces from line 52 to line 56.

From function dictionary::lookupEntry(const word&, bool, bool) const
in file db/dictionary/dictionary.C at line 388.

FOAM exiting


Thnx a million!
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Old   November 11, 2009, 10:44
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P.A.
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Hi milos,

try something like this:

functions
(
forces
{
type forces;
functionObjectLibs ("libforces.so");
//outputControl outputTime;
outputControl timeStep;
outputInterval 1;
patches (SHIP);
rhoInf 1025;
CofR (0 0 0);
}
);

Good luck!

Pascal.
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Old   November 12, 2009, 05:00
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Milos Stanic
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It worked Pascal, simulation has started normally. Thanks a lot! However, there are few more details that I would like to know.

1. - How do I plot the forces? Gnuplot command doesn't work...

3. - What are the units (I see in the .dat file that the numbers are way too huge to be Newtons)?

2. - Fundamentally, where's the catch?

Thanks once more.

Milos

Last edited by milos; November 12, 2009 at 07:50.
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