drag coefficient dependence on time

newminde · January 23, 2013, 05:44

Hay.
I''m modeling Transient laminar flow around cylinder. A question is how to get data where will be current time and drag coefficient.
For example Let the Reynolds number be 500.
And I'm doing these steps: Solutions->Monitors->create->Drag. Unfortunately in the text file I only get the last time step and drag coefficient, but I need all time steps and CD.
Also I'm traying Calculation activites->Solution animation->every time step->Monitor->create drag monitor.
That action also write only the last step.
Please help.

Yanlong Li · January 23, 2013, 08:54

I think you should use UDF.

newminde · January 23, 2013, 11:08

It's ridiculous, but I have two times done that I'm seeking to do, but now I can't understand where is a problem that I can't get previous results.
Anyone else have similar problem?

Yanlong Li · January 23, 2013, 11:40

那你问你妹啊，傻逼！

newminde · January 24, 2013, 05:24

Any sugestions?

Yanlong Li · January 24, 2013, 07:24

还问，问你妹啊，傻逼！

Bollonga · January 24, 2013, 07:39

You can get monitors time history automatically. As you said, Solution/Monitors/cd. Be sure tocheck the "write" box, select a boundary and type a file name. That should solve your problem.

newminde · January 24, 2013, 08:29

I have done these steps exactly several times, but the results are the same I get only the last time step and CD.
Flow is TRANSIENT.
I thing that this problem is related to calculation activities.
Some other opininions.

Bollonga · January 24, 2013, 11:26

Have you tried to open the cd-history file? I open it in matlab, all information should be there.

newminde · January 24, 2013, 11:48

I open the cd-history.txt with notepad is it any diference i'll open in matlab.
You have succeeded , that all time steps and Cd were saved?

Bollonga · January 24, 2013, 12:03

Notepad should work. Mmmmh, what's your timestep and how often do you save a .dat file?

newminde · January 24, 2013, 16:54

I changing time steps, for example time step size 0.1 s, number of time steps 100, max iterations 30, but the point is that I always get the last time step and the CD.
how often do you save, how to do that.
Can you tell me all your actions, maybe I have missed something, but it hard to believe.
Thanks for a help.

Bollonga · January 24, 2013, 17:05

In calculation activities you can say when you want to save your .dat files. If you are doing 100 timesteps, you can save every 10 timesteps. Maybe you haven't saved any .dat files and cd-history.txt is not being updated. Give it a try.

newminde · January 24, 2013, 17:17

Now I understand that you mean, I have already done that thing, but still it dosn't work as I want.
It's interesting how it works for you.
What else can be important?
What I missed .
Thanks a lot

newminde · January 24, 2013, 17:21

Have you anything done with solution animations?
You have just created drag monitor and marked write ?

Bollonga · January 24, 2013, 17:49

No. I just set the case to transient, choose a model, set boundary conditions, initialize from inlet (most of the cases I do), set the solvers, set calculation activities, solve. Pass me your case file and I can have a look at it.

newminde · January 28, 2013, 03:33

I have found a solution.
So if you have transient model and you want to get Cd every time step yoo should do these steps.
1) Choose model
2) Set boundary conditions
3) Reference values(Compute from inlet)
4) Choose Solution methods
5) Solution Initialization press initialize and dont choose anything in the field compute from
6) Calculation Activities/Solution animations/create/time step/define/Display type monitor/ statistics choose only delta time/ create drag monitor/ choose write/ ok ok ok
7) Come back to solution initialization choose compute from inlet and initialize
8) Do calculations

January 23, 2013, 05:44	drag coefficient dependence on time	#1
newminde New Member Mindaugas Join Date: Jun 2012 Posts: 25 Rep Power: 14	Hay. I''m modeling Transient laminar flow around cylinder. A question is how to get data where will be current time and drag coefficient. For example Let the Reynolds number be 500. And I'm doing these steps: Solutions->Monitors->create->Drag. Unfortunately in the text file I only get the last time step and drag coefficient, but I need all time steps and CD. Also I'm traying Calculation activites->Solution animation->every time step->Monitor->create drag monitor. That action also write only the last step. Please help.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
drag coefficient in ansys fluent 12.0	krishna	FLUENT	19	April 12, 2018 01:49
Extrusion with OpenFoam problem No. Iterations 0	Lord Kelvin	OpenFOAM Running, Solving & CFD	8	March 28, 2016 12:08
plot over time	fferroni	OpenFOAM Post-Processing	7	June 8, 2012 08:56
Post Processing Drag Coefficient	squanto773	OpenFOAM Post-Processing	1	March 7, 2012 10:43
Upgraded from Karmic Koala 9.10 to Lucid Lynx10.04.3	bookie56	OpenFOAM Installation	8	August 13, 2011 05:03

January 23, 2013, 08:54		#2
Yanlong Li Member Yanlong Li Join Date: Jan 2013 Location: BeiJing Posts: 47 Rep Power: 13	I think you should use UDF.

January 23, 2013, 11:08		#3
newminde New Member Mindaugas Join Date: Jun 2012 Posts: 25 Rep Power: 14	It's ridiculous, but I have two times done that I'm seeking to do, but now I can't understand where is a problem that I can't get previous results. Anyone else have similar problem?

January 23, 2013, 11:40		#4
Yanlong Li Member Yanlong Li Join Date: Jan 2013 Location: BeiJing Posts: 47 Rep Power: 13	那你问你妹啊，傻逼！

January 24, 2013, 05:24		#5
newminde New Member Mindaugas Join Date: Jun 2012 Posts: 25 Rep Power: 14	Any sugestions?

January 24, 2013, 07:24		#6
Yanlong Li Member Yanlong Li Join Date: Jan 2013 Location: BeiJing Posts: 47 Rep Power: 13	还问，问你妹啊，傻逼！

January 24, 2013, 07:39		#7
Bollonga Senior Member Francisco Join Date: Mar 2012 Location: Spain Posts: 273 Rep Power: 15	You can get monitors time history automatically. As you said, Solution/Monitors/cd. Be sure tocheck the "write" box, select a boundary and type a file name. That should solve your problem.

January 24, 2013, 08:29		#8
newminde New Member Mindaugas Join Date: Jun 2012 Posts: 25 Rep Power: 14	I have done these steps exactly several times, but the results are the same I get only the last time step and CD. Flow is TRANSIENT. I thing that this problem is related to calculation activities. Some other opininions.

January 24, 2013, 11:26		#9
Bollonga Senior Member Francisco Join Date: Mar 2012 Location: Spain Posts: 273 Rep Power: 15	Have you tried to open the cd-history file? I open it in matlab, all information should be there.

January 24, 2013, 11:48		#10
newminde New Member Mindaugas Join Date: Jun 2012 Posts: 25 Rep Power: 14	I open the cd-history.txt with notepad is it any diference i'll open in matlab. You have succeeded , that all time steps and Cd were saved?

January 24, 2013, 12:03		#11
Bollonga Senior Member Francisco Join Date: Mar 2012 Location: Spain Posts: 273 Rep Power: 15	Notepad should work. Mmmmh, what's your timestep and how often do you save a .dat file?

January 24, 2013, 16:54		#12
newminde New Member Mindaugas Join Date: Jun 2012 Posts: 25 Rep Power: 14	I changing time steps, for example time step size 0.1 s, number of time steps 100, max iterations 30, but the point is that I always get the last time step and the CD. how often do you save, how to do that. Can you tell me all your actions, maybe I have missed something, but it hard to believe. Thanks for a help.

January 24, 2013, 17:05		#13
Bollonga Senior Member Francisco Join Date: Mar 2012 Location: Spain Posts: 273 Rep Power: 15	In calculation activities you can say when you want to save your .dat files. If you are doing 100 timesteps, you can save every 10 timesteps. Maybe you haven't saved any .dat files and cd-history.txt is not being updated. Give it a try.

January 24, 2013, 17:17		#14
newminde New Member Mindaugas Join Date: Jun 2012 Posts: 25 Rep Power: 14	Now I understand that you mean, I have already done that thing, but still it dosn't work as I want. It's interesting how it works for you. What else can be important? What I missed . Thanks a lot

January 24, 2013, 17:21		#15
newminde New Member Mindaugas Join Date: Jun 2012 Posts: 25 Rep Power: 14	Have you anything done with solution animations? You have just created drag monitor and marked write ?

January 24, 2013, 17:49		#16
Bollonga Senior Member Francisco Join Date: Mar 2012 Location: Spain Posts: 273 Rep Power: 15	No. I just set the case to transient, choose a model, set boundary conditions, initialize from inlet (most of the cases I do), set the solvers, set calculation activities, solve. Pass me your case file and I can have a look at it.

January 28, 2013, 03:33		#17
newminde New Member Mindaugas Join Date: Jun 2012 Posts: 25 Rep Power: 14	I have found a solution. So if you have transient model and you want to get Cd every time step yoo should do these steps. 1) Choose model 2) Set boundary conditions 3) Reference values(Compute from inlet) 4) Choose Solution methods 5) Solution Initialization press initialize and dont choose anything in the field compute from 6) Calculation Activities/Solution animations/create/time step/define/Display type monitor/ statistics choose only delta time/ create drag monitor/ choose write/ ok ok ok 7) Come back to solution initialization choose compute from inlet and initialize 8) Do calculations