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#1 |
New Member
Bayard Morales
Join Date: Aug 2009
Posts: 24
Rep Power: 17 ![]() |
Hi there.
I am running a gas-solid euler-euler transient simulation in Fluent 14. I am using the granular model. The transient formulation is the first order implicit. I would like to use adaptive timesteps, but I cannot select it under the Time Stepping Method scroll list. It only has the fixed time step option available. How can I do it? I have found the following info in the manual: Important: Adaptive time stepping is available only with the pressure-based and density-based implicit formulations; it cannot be used with the density-based explicit formulation. In addition, it cannot be used with the discrete phase model, second-order time integration, Euler-Euler multiphase models (Approaches to Multiphase Modeling in the Theory Guide), or user-defined scalars (User-Defined Scalar (UDS) Transport Equations). Is there any way that I can set an UDF or something to adapt the time step? Regards! |
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#2 |
Senior Member
SSL
Join Date: Oct 2012
Posts: 226
Rep Power: 14 ![]() |
You can use DEFINE_DELTAT to adapt timestep in density-based mode.
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#3 |
New Member
anonymous
Join Date: Jan 2011
Posts: 23
Rep Power: 15 ![]() |
DEFINE_DELTAT could be used irrespective of the solver.
You could write your own time step controlling mechanism. |
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#4 |
New Member
Bayard Morales
Join Date: Aug 2009
Posts: 24
Rep Power: 17 ![]() |
Hi guys - thanks for your help.
I haven't tried to do what you told me, so I may sound a little grumpy, but I have found this in the Fluent UDF manual: DEFINE_DELTAT is a general-purpose macro that you can use to control the size of the time step during the solution of a transient problem. Note that this macro can be used only if Adaptive is selected from the Time Stepping Method drop-down list in the Run Calculation task page in ANSYS FLUENT In my case, the Adaptative option is not available in the drop-down list. Did you guys go to run Euler-euler transient with adaptive? Thanks! |
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#5 |
New Member
Bayard Morales
Join Date: Aug 2009
Posts: 24
Rep Power: 17 ![]() |
[SOLVED]
In short: I cannot use UDF to change the time-step in Euler-Euler, but using the journal, I can do something similar. I have contacted the Ansys support and this was the answer. ------ If granular model does not allow for adaptive time stepping then you will not be able to use DEFINE_DELTAT. This is because the hook for this function is available only when we select adaptive time stepping. Instead of UDF, you can use a jurnal file for this purpose. A jurnal file is a file which contains commands for Fluent. In journal file, you can put text menu interface (TUI) commands which tells Fluent to do some time steps and then change the time step size. You can find more details on TUI commands in ANSYS14 help guide at this location: // User's Guide :: 2 // 3. Text User Interface (TUI) // 3.1. Text Menu System For example if you want to run the case for 5 time steps using existing timestep size and then want to change the time steps size to 2e-3 sec, here are the commands: ********************* solve dual-time-iterate 5 10 solve set time-step 2e-3 *********************** You can put these two commands in a file with extension as jou and read it in Fluent from File->read -> journal |
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#6 |
Senior Member
B_Kia
Join Date: May 2014
Location: Ir
Posts: 123
Rep Power: 12 ![]() |
hi , you can use a journal file and in that change the time step size , it is easy to make one
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Tags |
adaptive-time stepping, time step |
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