Transient simulation issue

stevie-tran · September 17, 2015, 09:27

I am doing a transient simulation with fluent. In the first 30s, I got a convergent solutions for each time steps. Then, I increased the time step size, I got a divergent error. I reverted to the time step size I used in the first 30s of the simulation, but I kept receiving the divergent error.

May I ask if you have any idea I can delete the divergent time step data, and let the fluent continue calculating with the previous convergent time step.

I really appreciate your helps.

LuckyTran · September 18, 2015, 10:58

No. You would have had to have saved the data beforehand. Fluent only keeps track of the most recent data, and there is no undo button. You need to save a .dat before you do the switch.

stevie-tran · September 18, 2015, 11:36

Quote:

Originally Posted by LuckyTran

You need to save a .dat before you do the switch.

Thank you for your help LuckyTran. I did save the data using "writing" setting. Therefore, May I ask how I can continue my simulation from the saved data?

Bruno Machado · September 18, 2015, 11:42

Quote:

Originally Posted by stevie-tran

Thank you for your help LuckyTran. I did save the data using "writing" setting. Therefore, May I ask how I can continue my simulation from the saved data?

when you read your case, you should read your data as well. Fluent will consider the data you read as the "initial condition".

stevie-tran · September 18, 2015, 11:51

Quote:

Originally Posted by Bruno Machado

when you read your case, you should read your data as well. Fluent will consider the data you read as the "initial condition".

Thank you Bruno. Basically, I have to run another simulation right? Then, it emerges another concern how I can combine results from 2 simulations in cfd-post?

Bruno Machado · September 18, 2015, 11:53

Quote:

Originally Posted by stevie-tran

Thank you Bruno. Basically, I have to run another simulation right? Then, it emerges another concern how I can combine results from 2 simulations in cfd-post?

What do you mean by combine? Do you mean to plot for different time steps?
If yes, for each time step you should save one .dat file and later add all of them on CFD-Post to compare, for example. If you mean something else, please, explain it a bit more so I can try help you.

stevie-tran · September 19, 2015, 02:32

Quote:

Originally Posted by Bruno Machado

What do you mean by combine? Do you mean to plot for different time steps?
If yes, for each time step you should save one .dat file and later add all of them on CFD-Post to compare, for example. If you mean something else, please, explain it a bit more so I can try help you.

Thank you Bruno! Actually I use cfd-post to see the change of flow variables. I afraid of cfd-post can not recognize the flow-time since there are two separated simulations. However, I will try your solution and ask you later if there is any trouble.

stevie-tran · September 19, 2015, 03:30

I come up with a solution for my problem. Firstly, in the export folder, I have 3 kinds of file for each writing interval: .cas, dat.gz and .cdat. I double click in selected .cas file to run a simulation, remember to change the export folder, then it works to continue my simulation.

But something not right. My simulation has udf for the inlet profile that relating to flow time. Then, it works but wrongly. it'd better to start the simulation again, although it took 2 days to finish the current work.

Thank you Bruno and LuckyTran.

September 17, 2015, 09:27	Transient simulation issue	#1
stevie-tran New Member Join Date: Mar 2015 Posts: 6 Rep Power: 11	I am doing a transient simulation with fluent. In the first 30s, I got a convergent solutions for each time steps. Then, I increased the time step size, I got a divergent error. I reverted to the time step size I used in the first 30s of the simulation, but I kept receiving the divergent error. May I ask if you have any idea I can delete the divergent time step data, and let the fluent continue calculating with the previous convergent time step. I really appreciate your helps.

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September 18, 2015, 10:58		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,672 Rep Power: 65	No. You would have had to have saved the data beforehand. Fluent only keeps track of the most recent data, and there is no undo button. You need to save a .dat before you do the switch.

September 19, 2015, 03:30		#8
stevie-tran New Member Join Date: Mar 2015 Posts: 6 Rep Power: 11	I come up with a solution for my problem. Firstly, in the export folder, I have 3 kinds of file for each writing interval: .cas, dat.gz and .cdat. I double click in selected .cas file to run a simulation, remember to change the export folder, then it works to continue my simulation. But something not right. My simulation has udf for the inlet profile that relating to flow time. Then, it works but wrongly. it'd better to start the simulation again, although it took 2 days to finish the current work. Thank you Bruno and LuckyTran.