CFD Online URL
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

Forces in OF15

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree1Likes

Reply
 
LinkBack Thread Tools Display Modes
Old   July 22, 2008, 21:10
Default Gday Sylvia, Just check all
  #21
New Member
 
Richard Jones
Join Date: Mar 2009
Location: Adelaide, South Australia, Australia
Posts: 22
Rep Power: 7
richard is on a distinguished road
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
richard is offline   Reply With Quote

Old   July 22, 2008, 21:35
Default Thanks, Richard. I had copied
  #22
sjs
New Member
 
Sylvia Smullin
Join Date: Mar 2009
Posts: 10
Rep Power: 7
sjs is on a distinguished road
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
sjs is offline   Reply With Quote

Old   July 23, 2008, 04:54
Default I had a similar problem. Make
  #23
New Member
 
Gregor Veble
Join Date: Mar 2009
Posts: 11
Rep Power: 7
gregorv is on a distinguished road
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
gregorv is offline   Reply With Quote

Old   August 5, 2008, 03:03
Default Hi, I am trying to validate t
  #24
Member
 
Ivan Lau
Join Date: Mar 2009
Location: Hong Kong
Posts: 56
Rep Power: 7
ivanwhlau is on a distinguished road
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
ivanwhlau is offline   Reply With Quote

Old   August 5, 2008, 03:39
Default Hi Ivan, Your forceCoeffs d
  #25
New Member
 
Richard Jones
Join Date: Mar 2009
Location: Adelaide, South Australia, Australia
Posts: 22
Rep Power: 7
richard is on a distinguished road
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)
richard is offline   Reply With Quote

Old   August 5, 2008, 06:25
Default Err, you have specified the re
  #26
Senior Member
 
Eugene de Villiers
Join Date: Mar 2009
Posts: 725
Rep Power: 11
eugene is on a distinguished road
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
eugene is offline   Reply With Quote

Old   August 5, 2008, 09:48
Default Hi, Eugene and Richard, Thank
  #27
Member
 
Ivan Lau
Join Date: Mar 2009
Location: Hong Kong
Posts: 56
Rep Power: 7
ivanwhlau is on a distinguished road
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
ivanwhlau is offline   Reply With Quote

Old   August 5, 2008, 10:14
Default Hi, I would assume CofR to
  #28
Member
 
Ola Widlund
Join Date: Mar 2009
Location: Sweden
Posts: 87
Rep Power: 7
olwi is on a distinguished road
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
olwi is offline   Reply With Quote

Old   August 6, 2008, 07:50
Default hi all, where is this new d
  #29
Senior Member
 
mayank gupta
Join Date: Mar 2009
Posts: 110
Rep Power: 7
mgz1985 is on a distinguished road
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
mgz1985 is offline   Reply With Quote

Old   August 6, 2008, 14:03
Default Hi Mayank, If you do it corre
  #30
Member
 
Ivan Lau
Join Date: Mar 2009
Location: Hong Kong
Posts: 56
Rep Power: 7
ivanwhlau is on a distinguished road
Hi Mayank,
If you do it correctly, you should see the "forces" and/or "forceCoeffs" folder insides case directory. [Version 1.5 only]
Ivan
ivanwhlau is offline   Reply With Quote

Old   August 6, 2008, 15:07
Default hi ivan, I can tell you wha
  #31
Senior Member
 
mayank gupta
Join Date: Mar 2009
Posts: 110
Rep Power: 7
mgz1985 is on a distinguished road
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
mgz1985 is offline   Reply With Quote

Old   August 6, 2008, 21:11
Default Hi Mayank, I think I know you
  #32
Member
 
Ivan Lau
Join Date: Mar 2009
Location: Hong Kong
Posts: 56
Rep Power: 7
ivanwhlau is on a distinguished road
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;
}
);
ivanwhlau is offline   Reply With Quote

Old   August 7, 2008, 03:57
Default Hi Ivan, I tried what u sai
  #33
Senior Member
 
mayank gupta
Join Date: Mar 2009
Posts: 110
Rep Power: 7
mgz1985 is on a distinguished road
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 is offline   Reply With Quote

Old   August 7, 2008, 03:58
Default Hi Ivan, I tried what u sai
  #34
Senior Member
 
mayank gupta
Join Date: Mar 2009
Posts: 110
Rep Power: 7
mgz1985 is on a distinguished road
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 is offline   Reply With Quote

Old   August 7, 2008, 03:59
Default Hi Ivan, I tried what u sai
  #35
Senior Member
 
mayank gupta
Join Date: Mar 2009
Posts: 110
Rep Power: 7
mgz1985 is on a distinguished road
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 is offline   Reply With Quote

Old   August 7, 2008, 04:01
Default \attach {mayank}
  #36
Senior Member
 
mayank gupta
Join Date: Mar 2009
Posts: 110
Rep Power: 7
mgz1985 is on a distinguished road
\attach {mayank}
mgz1985 is offline   Reply With Quote

Old   August 7, 2008, 04:02
Default http://www.cfd-online.com/Ope
  #37
Senior Member
 
mayank gupta
Join Date: Mar 2009
Posts: 110
Rep Power: 7
mgz1985 is on a distinguished road
controlDict
mgz1985 is offline   Reply With Quote

Old   August 7, 2008, 04:56
Default There is a typo. Should the p
  #38
Member
 
Ivan Lau
Join Date: Mar 2009
Location: Hong Kong
Posts: 56
Rep Power: 7
ivanwhlau is on a distinguished road
There is a typo. Should the patch be "fixedWall" instead of "fiexdWall"?
ivanwhlau is offline   Reply With Quote

Old   August 7, 2008, 05:53
Default hi Ivan, I corrected the ty
  #39
Senior Member
 
mayank gupta
Join Date: Mar 2009
Posts: 110
Rep Power: 7
mgz1985 is on a distinguished road
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
mgz1985 is offline   Reply With Quote

Old   August 7, 2008, 14:18
Default Well, I test your controlDict
  #40
Member
 
Ivan Lau
Join Date: Mar 2009
Location: Hong Kong
Posts: 56
Rep Power: 7
ivanwhlau is on a distinguished road
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.
ivanwhlau is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Fan type BC in OF15 hsieh OpenFOAM Running, Solving & CFD 30 November 10, 2011 08:33
Bug in patchIntegrateC OF15 anger OpenFOAM Bugs 8 May 29, 2009 05:36
CoupledFvScalarMatrix in OF15 fisher OpenFOAM Running, Solving & CFD 8 November 29, 2008 08:36
OpenFOAMdev migration to OF15 fisher OpenFOAM Installation 1 November 25, 2008 15:39
Bug or a feature of OF15 rafal OpenFOAM Bugs 5 July 25, 2008 06:25


All times are GMT -4. The time now is 11:19.