Timestep control via CEL?

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

 September 12, 2007, 11:45 Timestep control via CEL? #1 Claudia Guest   Posts: n/a Hi, is it possible to set the physical timestep via an expression? Or is it possible to control the timestep in any other way than manually? I would like to choose a larger timestep for example in the first 50 iterations and then a smaller one. Thanks Claudia

 September 12, 2007, 12:18 Re: Timestep control via CEL? #2 Alex Guest   Posts: n/a There are a number of ways to do this. You can use an expression if you like, or you can just give a list of timesteps. Check the documentation: CFX-Pre Users Guide -> Simulation Type -> Editing the Simulation Type -> Basic Settings Tab.

 September 12, 2007, 12:24 Re: Timestep control via CEL? #3 Claudia Guest   Posts: n/a But this is I think only for transient simulations. My simulation is steady state.

 September 12, 2007, 12:33 Re: Timestep control via CEL? #4 Robin Guest   Posts: n/a Hi Claudia, Create a 1D interpolation function of timestep in [s] vs iteration number, which is dimensionless []. You can do so in the GUI, but here is the resulting CCL object: LIBRARY: CEL: FUNCTION: myTimeStep Argument Units = [] Option = Interpolation Profile Function = Off Result Units = [s] INTERPOLATION DATA: Data Pairs = 0,0.1,50,0.1,60,0.01 Extend Max = On Extend Min = On Option = One Dimensional END END END END The above function will use a timestep of .1 for the first 50 iterations, then linearly decrease it to .01 between 50 and 60 iterations. The Extend Min and Extend Max parameters simply extend the max and min values to be used beyond the range defined in the function (if you don't enable these you'll get a failure at iteration 61 because the function would be undefined) You would then define your timestep as either: myTimeStep(aitern) or myTimeStep(citern) 'aitern' returns the Absolute Iteration Number (i.e. the number of iterations since it was first started) whereas 'citern' returns the Current Iteration Number (the number of iterations in the current run, reset to zero with each restart). Regards, Robin

 September 12, 2007, 13:36 Re: Timestep control via CEL? #5 Alex Guest   Posts: n/a It works for steady state as well.

 September 13, 2007, 08:00 Re: Timestep control via CEL? #6 Claudia Guest   Posts: n/a Thanks Robin, I will test it in the next simulation. But I think this is what I looked for. Claudia

 September 13, 2007, 14:02 Re: Timestep control via CEL? #7 HekLer Guest   Posts: n/a If you don't want to use an interpolation function you can also use the CEL step() function. For example, you could create a CEL expression like this: CEL: EXPRESSIONS: transition = 15 dt1 = 1.0 [s] dt2 = 10.0 [s] dtf = dt1*step(transition-aitern) + step(aitern-transition)*dt2 END END and then set the physical timescale to dtf. This will transition from dt1 to dt2 at the specified iteration.

 September 14, 2007, 05:00 Re: Timestep control via CEL? #8 Claudia Guest   Posts: n/a Hi HekLer, yes, I tried it a few days ago and it didn't work, but I think it was my fault. I will try it once more. Thanks! Claudia

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post vovogoal CFX 17 December 30, 2014 05:00 wolle1982 OpenFOAM Running, Solving & CFD 4 July 27, 2011 05:40 kmgraju CFX 1 May 2, 2011 02:32 Carlos AndrĂ©s CFX 8 April 29, 2007 16:38 Morten Andersen CFX 1 January 8, 2007 12:37

All times are GMT -4. The time now is 20:51.