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newminde January 23, 2013 05:44

drag coefficient dependence on time
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


newminde January 24, 2013 05:24

Any sugestions?

Yanlong Li January 24, 2013 07:24


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.
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

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