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steady state flow

16 REPLIES 16
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Message 1 of 17
Dan_Margulius
1767 Views, 16 Replies

steady state flow

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

16 REPLIES 16
Message 2 of 17

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.
Message 3 of 17

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

Message 4 of 17

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

 

Thanks

Message 5 of 17
Joey.X
in reply to: Dan_Margulius

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
Message 6 of 17

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

Message 7 of 17
Dan_Margulius
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  

Message 8 of 17
Joey.X
in reply to: Dan_Margulius

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
Message 9 of 17
Dan_Margulius
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

Message 10 of 17
modi20077
in reply to: Dan_Margulius

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

Message 11 of 17
AstroJohnPE
in reply to: modi20077

Hi Mohammed,

 

It is very difficult to determine the problem from the limited information given in the summary file that you provided. It would be better to attach an archive of your model. Do a search for the words "create" and "archive" to find the post that describes how to do it.

 

  1. What load do you have applied that would cause a flow?
  2. What is the magnitude of that load?
  3. What load curve is that load assigned to? 
  4. Does that load curve have a magnitude that is not zero?
  5. Where is the load applied? (X number of surfaces, N number of nodes)
  6. Do you have an inlet and an outlet location for the flow?
  7. Is the load that you applied somehow overwritten with another load or constraint that effectively makes your load zero?

The last item can be determined by looking at the model in the Results environment, and specifically whether there are zero magnitude velocities appearing at the locations of your load.

Message 12 of 17
Sualp.Ozel
in reply to: Dan_Margulius

Hello Mohammed Fayed

 

Looking at the PDF file, I see that you are using a 2012 - Student version of the software. The latest version is 2014 and I always recommend being on the latest version.

 

Please create an ARCHIVE file and attach it to this case so we can investigate further.

 

Sualp Ozel

Product Manager

Digital Simulation
Autodesk, Inc.

 

Direct: 412.447.0316

Mobile: 412.334.2555   

e-mail: sualp.ozel@autodesk.com

 

Message 13 of 17
hxq0707
in reply to: AstroJohnPE

Sualp:

If I understand correctly, there is no Simulation Multiphysics 2014 anymore, there is only Simulation Mechanical 2014 without Fluid Flow analysis capacity. So, Mohammed Fayed will not be able to do steady state flow analysis if he installs version 2014 as you suggested.

 

Is there any plan to put fluid flow module back? Thanks.

 

hxq

 

Message 14 of 17
Sualp.Ozel
in reply to: AstroJohnPE

If a user is trying to simulate a CFD analysis using the 2014 software, they cannot do that within Simulation Mechanical. They will have to use Simulation CFD 2014.

 

-Sualp

Message 15 of 17
hxq0707
in reply to: AstroJohnPE

Sualp:

 

How about my previous fluid flow (CFD) analysis data performed by Autodesk Simulation Multiphysics until version 2013?  I cannot open those analyses/files  any more??  ---- As I know, you guys have taken away not only Fluid Flow analysis module but also Coupled multiphysics analysis module.   A mechanical FEA package should include fluid flow analysis capability, just like “ANSYS Mechanical” includes CFD, CFX CFD and Fluent CFD modules (Only Fluent CFD module needs extra money).

 

Autodesk Simulation CFD software (formerly CFdesign) is a different package and it’s expensive.

 

hxq

 

 

Message 16 of 17
AstroJohnPE
in reply to: hxq0707

Please read this discussion to understand how to perform fluid flow analyses, coupled analyses, (and probably a lot more) using Simulation Mechanical 2014:

 

http://forums.autodesk.com/t5/Autodesk-Simulation-Mechanical/Simulation-Multiphysics-2014/td-p/38760...

 

Note that there is no cost for this much improved product provided your service is current.

 

Message 17 of 17
Sualp.Ozel
in reply to: AstroJohnPE

All of our commercial customers with an active subscription to Autodesk Simulation Multiphysics 2013 were automatically migrated to a combination of Simulation Mechanical 2014 and Simulation CFD Advanced 2014 (+ CFD’s UI = design study environment)

If you have old Fluid flow results you analyzed in Autodesk Simulation Multiphysics 2013, you can still look at those results in the 2013 software, since you can have both the 2013 and 2014 version of Autodesk Simulation installed on the same computer side by side.

The decision to “end of life” Multiphysics was in an effort to provide our customers with our best in class CFD offering from Autodesk, which in this case is Autodesk Simulation CFD 2014. This tool can help you simulate MANY Multiphysics scenarios including thermal-fluid transient cases including compressible flow and cavitation effects none of which Simulation Multiphysics could simulate.

Also thanks to the interoperability between Simulation Mechanical 2014 and Simulation CFD 2014 you can transfer the thermal results from CFD to Mechanical (example: Linear static stress or MES analyzes) to perform thermal stress calculations. Here is a link to the video: http://vp.telvue.com/preview?id=T01885&video=147697

Using an add-on-app to CFD (free) which we released on the Autodesk Simulation App store, you can also map pressure results from Simulation CFD to Simulation Mechanical.

Here is the link: http://apps.exchange.autodesk.com/SCFD/en/Detail/Index?id=appstore.exchange.autodesk.com%3asimcfdtos...

You can also watch the following episode of SIMTV to learn more about this new technology to map pressures from CFD to Mechanical: http://vp.telvue.com/preview?id=T01885&video=149819

 

Best regards

Sualp Ozel

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