Simulation Mechanical and Multiphysics

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*Expert Elite*
Dan.M
Posts: 588
Registered: ‎01-19-2009
Accepted Solution

steady state flow

1172 Views, 16 Replies
08-30-2010 11:29 PM

Hello ,

 

Sometimes when I run flow analyses I get the following warning :

Warning: Quit for zero loading !

Please check model parameters and try again.

 

What does it mean? then the analysis is stopping.

I check the parametrs again to see if i forgor something abd run it again and I see the same warning bur the analysis is starting.

Is there an explanation?

 

Thanks,

Dan

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Employee
Jacob.Xu|Autodesk
Posts: 22
Registered: ‎06-13-2007

Re: steady state flow

09-01-2010 05:39 AM in reply to: Dan.M

Hi Dan,

 

It seems that the model does not consist of a valid load (e.g. prescribed velocity, fan surface, etc.). Do you mind uploading the model so that I can help take a look?

------------
Jacob Xu
QA Engineer, Algor Simulation
Autodesk, Inc.
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*Expert Elite*
Dan.M
Posts: 588
Registered: ‎01-19-2009

Re: steady state flow

09-02-2010 07:34 AM in reply to: Dan.M

Hello ,

The files from algor are big. I am attaching the report.

Now i have an new warning:

Warning: Converge with stagnation due to oscillation.

 

Thanks,

Dan

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*Expert Elite*
Dan.M
Posts: 588
Registered: ‎01-19-2009

Re: steady state flow

09-02-2010 07:36 AM in reply to: Dan.M

Everytime i get another warning and i have no idea why it does that.

 

Thanks

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Employee
Joey.X
Posts: 259
Registered: ‎06-14-2010

Re: steady state flow

09-03-2010 01:57 PM in reply to: Dan.M

Warning might be okay depending what kind of physical model and what knind of model setup user specified.
 
One typical example is vortex shedding problem (flow through a cylinder), where shedding vortex always happen in the suction side of the cylinder, and there is no steady solution, if user really want to make the model as steady state analysis, then the oscillation with stagnation warning message will be there, the solution is a quaso-average of the true unsteady solution.
 
Another typical example is that using large time step to simulate fast changing phenomena, the similar warning will be there as well.

 

Thanks,

 

Jianhui

Jianhui Xie, Ph.D
Principal Engineer
MFG-Digital Simulation
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*Expert Elite*
Dan.M
Posts: 588
Registered: ‎01-19-2009

Re: steady state flow

09-04-2010 07:05 AM in reply to: Jacob.Xu|Autodesk

Hello Jacob,

 

I have defined inlet velocity and 3 inlet/outlets. Again i get the warning zero loading and the analysis is stopping.

I have attached an ach file for you to see.

What am i doing wrong?

 

Thanks

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*Expert Elite*
Dan.M
Posts: 588
Registered: ‎01-19-2009

Re: steady state flow

09-04-2010 07:10 AM in reply to: Joey.X

 

Hello  Jianhui,

 

Thank you for your explanation. I have attached a file where another warning zero loading is recieved although i have defined everything.

Hope you guys can take a look and help me understand how to prevent this. .

 

Thanks,

Dan  

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Employee
Joey.X
Posts: 259
Registered: ‎06-14-2010

Re: steady state flow

09-04-2010 03:36 PM in reply to: Dan.M

Hi, Dan

    Thanks for attach the archived model, the reason is that the  mesh is too coarse so that the there are no internal free nodes inside the pipes (not on the wall), for fluid flow, your specified surface velocity will be decoded in the free nodes on the inlet surface, however, this model has zero free nodes on the inlet surface, that's why you get zero loading no
matter how much inlet velocity and what kind of load curves you specified there.  Also the three outlets have zero free fluid nodes which also causes convergence issues.
   Usually the free nodes (velocity or pressure to be solved) in any cut section of a pipe should at least 8 to 10 nodes, notes CFD is different from structure analysis, it 's more computational expensive, and more dependent and sensentive on mesh.
  
Thanks,

Jianhui

 

Jianhui Xie , Ph.D

Sr. Software Engineer

Autodesk, Inc.
150 Beta Drive
Pittsburgh, PA 15238 

 

 

Jianhui Xie, Ph.D
Principal Engineer
MFG-Digital Simulation
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*Expert Elite*
Dan.M
Posts: 588
Registered: ‎01-19-2009

Re: steady state flow

09-04-2010 11:16 PM in reply to: Joey.X

Hello Jianhui ,

 

I redefined the mesh and now the analysis has started,thank you. I also wanted to ask 2 things :

1. How many time steps should I define ( 10,50,100)...are these time steps like  iterations wich I see in CfDesign?

2. At the begining this model was full with solid. How can I make fluid generation on full part? In CfDesign the programs recognize a closed model and generates the internal fluid alone.

 

Thanks,

Dan

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New Member
modi20077
Posts: 2
Registered: ‎05-03-2013

A queston

05-10-2013 11:55 PM in reply to: Dan.M

HI

i have a problem during the analysis an error

Quit for zero loading !

               Please check model parameters and try again.

i checked the prameters  and tryed again so many times and the same error repeated

so i attached the report 

i hope some one to help me

 

thanks

mohammedfayed

senior piping enginer

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