Learning Forum

[Julen]

Hello Everybody,

I set up my Simulation and I got the following error message:

"The problem Preprocessors    has not converged."

Yet I don't get any recommendation what to do next or any indication on where the problem might be in the Listing viewer. Does anybody know where I can find some input on where to look or is this common?

[Rob]

Maybe elaborate on which solver and what you were doing at the time? 

[Julen]

Hello,

I am using Ansys Polyflow and I am trying to model the way a polymer melt flows through a heat sink. I can't really tell you much more, the Listing Viewer doesn't give me much to work with. 

I will try to change some parameters and hope it works. Its trial and error from here I think.

 

[Rob]

I'm not sure with Polyflow. Check the model settings, mainly boundary conditions and material properties. 

[Julen]

Thank you, I will start there.

[Julen]

Hello Rob,

the Simulation I was asking about earlier started working, now I am on to the next iteration and I get the following error, do you know how I can fix it, or at leat tell me where to look. I am new to this, and I am trying as hard as possible to learn! Thanks in advance.

 

***************************
 ***   Starting Step 1   ***
 ***************************
   Parameters and Fields                        |   Progress bar(s)  |
 Evolution parameter S     =  7.5500000E-01     |>                   |
 Parameter fac             =  5.4328477E+04     |>                   |          
 Parameter expom           =  1.0000000E+00     |>                   |          

 Preprocessors   

 Convergence assumed : Rel. var. LT  1.00000E-03

 F.E.M. Task     

Divergence detected for field VELOCITIES: iterations cancelled by Expert System 

 

 Divergence of influent solver occurred !
           *** WARNING *** from [EVOLUT]
          First step does not converge
          It is not possible to start the evolution scheme

 

     *******************************
     *  Summary of the simulation  *
     *******************************

        The computation failed.

     *****************************
     *  Expert tool diagnostics  *
     *****************************

     The problem F.E.M. Task      has not converged.

 

This is the Error message I get in the Listing viewer. I don't really understand why it has a problem with the evolution parameters. I got a failure earlier and I set them to exactly what the Expert System recommended...

 

Julen

[Rob]

I don't, but the error is divergence related. I've reminded our internal team. 

[Julen]

Thanks. Do you know how much time they might need?

Also, I've changed some parameters and run it again. I get the exact same message except one additional thing:

 

     *****************************
     *  Expert tool diagnostics  *
     *****************************

     Out of convergence disk.

[Rob]

It's more when the US find their Polyflow specialist.  

[Prashanth]

Hello Julen

So, what kind of problem is this? On which parameter you are applying evolution? What is your evolution settings?

[Julen]

Hellor Parshanth,

I fixed the problem, thanks for asking though.

 

I have a different question:

I am trying to simulate the flow of a polymer melt inside an extruder and I need to impose a certain pressure on the outflow (roughly 60 bar). There doesn't seem to be an option to impose a pressure on the outlfow. How would you suggest I fix this problem. Will Polyflow automatically calculate the pressures in the extruder up to the inflow? I am using an imposed volumetric flow rate, so there shouldn't be any reversal of the flow. 

 

I don't expect you to give me the solution, but maybe enlighten me on how to approach this whole problem.

 

Thanks in advance

[Prashanth]

You cannot directly impose pressure values, you can impose suitable normal velocities at inlet and oulet at that pressure conditions.