How to update dynamic mesh in steady state simulations

Prikane · September 1, 2016, 05:01

Dear colleagues,

Earlier I worked with transient analysis and I know that in transient analysis, dynamic mesh is updated at the beginning of every time step.

I am now doing steady state analysis, and I want to update my dynamic mesh after every 25 iterations. Can someone tell me how to do it?

Thanks in advance,

Prikane

duri · September 1, 2016, 07:48

Could you able to run dynamic mesh with steady state? This has no meaning because of local time stepping. What problem are you solving?

Prikane · September 1, 2016, 08:11

Dear friend, thanks for answering.

I was wondering the same, is it possible, but I have found the following on the internet:

"You can use dynamic meshes for steady-state applications as well as for transient applications."

Source: https://www.sharcnet.ca/Software/Flu...ug/node447.htm

I was doing transient analysis of some analysis (in which force is acting on one surface and it needs to move), and I now want to do the same analysis but in the steady state conditions. I have also found, that when using dynamic mesh in steady state, you can use one option called "steady-pseudo-time-control", but I do not know how to properly use it.

Prikane

duri · September 1, 2016, 10:44

Pseudo transient is like unsteady. The iteration actually mean the time step. When solution is stopped all cells would be at same time level. This makes sense. But from the manual it appears mesh need to be updated after each steady state convergence manually. Also geometry trajectory need to be provided by user based on dtime=1s. This means you need to solve for steady state and compute the next position and update mesh. Again solve for steady state. There is noway mesh is updated like a transient solution.

Prikane · September 1, 2016, 13:19

Thank you for your help mate. So if I understood you correctly, the solution algorithm should be like this.

1. Set up steady state analysis (without UDF for dynamic mesh) and wait for convergence...

2. Hook dynamic mesh (in which I will specify conditions for mesh to move) and wait for convergence again...

3. Then change parameters in my UDF for dynamic mesh, hook it again and wait for convergence again...

And then repeat this procedure until I get results that I want...

Is there any possibility to automate this procedure? With using journal files or something like that....

I need to say that in my UDF for dynamic mesh, I need to set that 50 000 N of force is acting on one surface. But I need to slowly raise that force from 0 N to 50 000 N in order to avoid instabilities in the main equation, which calculates nodes coordinates after certain amount of force is applied on the surface. In the transient analysis, it was not hard thing to do, because UDF for dynamic mesh is applied on the beginning of every new step and the procedure of slowly rising force from 0 to 50 000 N can be automated.

But if I need to manually change force in UDF every time when convergence is reached, I will need to do that for a really long period of time...

duri · September 1, 2016, 13:38

Yes that is what I understood from manual. I am not sure whether to hook udf initially or at end of each convergence. This can be automated as batch process in command mode using journal file.

Prikane · September 1, 2016, 16:27

Thank you duri for all your replies. I am mechanical engineer, so I am not the most skilled with programming I need to ask you one more time.

You are absolutely sure that I can change my UDF for dynamic mesh after I get convergence with journal file? That includes the following steps:

1. Run steady state simulation
2. After convergence, hook UDF for dynamic mesh
3. Wait for convergence, then unload UDF for dynamic mesh, delete libudf folder from Fluent folder, change existing UDF for dynamic mesh that is in Fluent folder (that means to increase previous value of force), then again hook it with Ansys and activate dynamic mesh options
4. Then continue simulations and do it again after next convergence

If all these steps can be automated, I need to say that I have my answer and that I wasted a lot of my time so far....

duri · September 2, 2016, 05:39

Try and learn there is no waste of time in doing mistakes.

Prikane · September 2, 2016, 06:56

Thank you duri for your help. I will try to write journal file and we will see how it will go...

All the best.

Prikane

shaheen wahab · October 4, 2018, 06:36

Hello Prikane,
I am doing something similar as you have stated. Could you please tell me how you wrote your Journal file?
I have a steady state case with a UDF (that reads a csv file and adjusts the nodes) and then I need a Journal file to update the mesh and so on, on a repetitive basis.
Thank you
With regards
Shaheen

September 1, 2016, 05:01	How to update dynamic mesh in steady state simulations	#1
Prikane New Member Prikane Join Date: Mar 2016 Posts: 28 Rep Power: 10	Dear colleagues, Earlier I worked with transient analysis and I know that in transient analysis, dynamic mesh is updated at the beginning of every time step. I am now doing steady state analysis, and I want to update my dynamic mesh after every 25 iterations. Can someone tell me how to do it? Thanks in advance, Prikane

September 1, 2016, 13:19		#5
Prikane New Member Prikane Join Date: Mar 2016 Posts: 28 Rep Power: 10	Thank you for your help mate. So if I understood you correctly, the solution algorithm should be like this. 1. Set up steady state analysis (without UDF for dynamic mesh) and wait for convergence... 2. Hook dynamic mesh (in which I will specify conditions for mesh to move) and wait for convergence again... 3. Then change parameters in my UDF for dynamic mesh, hook it again and wait for convergence again... And then repeat this procedure until I get results that I want... Is there any possibility to automate this procedure? With using journal files or something like that.... I need to say that in my UDF for dynamic mesh, I need to set that 50 000 N of force is acting on one surface. But I need to slowly raise that force from 0 N to 50 000 N in order to avoid instabilities in the main equation, which calculates nodes coordinates after certain amount of force is applied on the surface. In the transient analysis, it was not hard thing to do, because UDF for dynamic mesh is applied on the beginning of every new step and the procedure of slowly rising force from 0 to 50 000 N can be automated. But if I need to manually change force in UDF every time when convergence is reached, I will need to do that for a really long period of time... shaheen wahab likes this.

September 1, 2016, 16:27		#7
Prikane New Member Prikane Join Date: Mar 2016 Posts: 28 Rep Power: 10	Thank you duri for all your replies. I am mechanical engineer, so I am not the most skilled with programming I need to ask you one more time. You are absolutely sure that I can change my UDF for dynamic mesh after I get convergence with journal file? That includes the following steps: 1. Run steady state simulation 2. After convergence, hook UDF for dynamic mesh 3. Wait for convergence, then unload UDF for dynamic mesh, delete libudf folder from Fluent folder, change existing UDF for dynamic mesh that is in Fluent folder (that means to increase previous value of force), then again hook it with Ansys and activate dynamic mesh options 4. Then continue simulations and do it again after next convergence If all these steps can be automated, I need to say that I have my answer and that I wasted a lot of my time so far.... shaheen wahab likes this.

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September 1, 2016, 07:48		#2
duri Senior Member duri Join Date: May 2010 Posts: 245 Rep Power: 17	Could you able to run dynamic mesh with steady state? This has no meaning because of local time stepping. What problem are you solving?

September 1, 2016, 08:11		#3
Prikane New Member Prikane Join Date: Mar 2016 Posts: 28 Rep Power: 10	Dear friend, thanks for answering. I was wondering the same, is it possible, but I have found the following on the internet: "You can use dynamic meshes for steady-state applications as well as for transient applications." Source: https://www.sharcnet.ca/Software/Flu...ug/node447.htm I was doing transient analysis of some analysis (in which force is acting on one surface and it needs to move), and I now want to do the same analysis but in the steady state conditions. I have also found, that when using dynamic mesh in steady state, you can use one option called "steady-pseudo-time-control", but I do not know how to properly use it. Prikane

September 1, 2016, 10:44		#4
duri Senior Member duri Join Date: May 2010 Posts: 245 Rep Power: 17	Pseudo transient is like unsteady. The iteration actually mean the time step. When solution is stopped all cells would be at same time level. This makes sense. But from the manual it appears mesh need to be updated after each steady state convergence manually. Also geometry trajectory need to be provided by user based on dtime=1s. This means you need to solve for steady state and compute the next position and update mesh. Again solve for steady state. There is noway mesh is updated like a transient solution.

September 1, 2016, 13:38		#6
duri Senior Member duri Join Date: May 2010 Posts: 245 Rep Power: 17	Yes that is what I understood from manual. I am not sure whether to hook udf initially or at end of each convergence. This can be automated as batch process in command mode using journal file.

September 2, 2016, 05:39		#8
duri Senior Member duri Join Date: May 2010 Posts: 245 Rep Power: 17	Try and learn there is no waste of time in doing mistakes.

September 2, 2016, 06:56		#9
Prikane New Member Prikane Join Date: Mar 2016 Posts: 28 Rep Power: 10	Thank you duri for your help. I will try to write journal file and we will see how it will go... All the best. Prikane

October 4, 2018, 06:36		#10
shaheen wahab New Member Shaheen Akhtar Wahab Join Date: Aug 2018 Location: Germany/Belgium Posts: 6 Rep Power: 8	Hello Prikane, I am doing something similar as you have stated. Could you please tell me how you wrote your Journal file? I have a steady state case with a UDF (that reads a csv file and adjusts the nodes) and then I need a Journal file to update the mesh and so on, on a repetitive basis. Thank you With regards Shaheen