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Employee
INACTIVE_AstroJohn
Posts: 492
Registered: ‎03-25-2010

Re: !!!!Simulation Pro 2011 - Stagnation due to oscillations!!!!

08-20-2012 08:32 AM in reply to: jrm_1971

Hi jrm,

 

For 1, I want to make sure I understand the image.

  • First, the two images on the left side of the page are showing the complete model, correct? There is no part surrounding the coil in this analysis.  
  • It looks like you have some faces on the outside of the fluid selected.
  • Do you have a load applied to the outside of the fluid (on the selected faces), such as a convection or radiation load, that would cause heat to be transfer through the face?

I think the image at the bottom left is showing the heat flowing from the model (the gas) to the surrounding ambient (not modeled). I think you do not have a load on the outside of the fluid surface that simulates the environment pulling the heat out, so the heat flow rate should be 0. This is why the calculation is small (practically 0).

 

For item 2, the two images on the right side of the page show the fluid is split into two halves (the top and bottom) so that you can hide the top half in the Results to see what is happening inside the fluid.

 

What I see are prescribed velocities on the split plane between the top and bottom halves of the fluid along a portion of the length. Either you applied the zero velocities to the split plane by mistake, or the mesh between the top and bottom halves do not match up (so the processor thinks that it is a "free surface" since it doesn't match any other elements), or a bug. Without an archive of the model, I cannot be sure what is the cause.

 

Why this occurs in the model on the right-side of the page and not on the left side of the page is a mystery. Perhaps a different mesh size would eliminate the problem. Of course, you can mesh the model and so a "Analysis > Analysis > Check Model" to view where the zero-velocity conditions get applied befor you run the simulation.

 

 

Sincerely,
John Holtz, P.E.
Senior User Experience Designer, Simulation
Autodesk, Inc.

Current version of Mechanical & Multiphysics: 2013 SP1 (2013.01.00.0012 28-Jun-2012)
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Distinguished Contributor
jrm_1971
Posts: 112
Registered: ‎03-31-2011

Re: !!!!Simulation Pro 2011 - Stagnation due to oscillations!!!!

08-20-2012 10:33 PM in reply to: INACTIVE_AstroJohn

For 1, I want to make sure I understand the image.

  • First, the two images on the left side of the page are showing the complete model, correct? There is no part surrounding the coil in this analysis. That is correct, it's the two halves of just the fluid, no conduit surrounding it
  • It looks like you have some faces on the outside of the fluid selected. Yes, bottom left picture shows faces selected to obtain the heat rate at the face
  • Do you have a load applied to the outside of the fluid (on the selected faces), such as a convection or radiation load, that would cause heat to be transfer through the face? Uh, no just a temperature

I think the image at the bottom left is showing the heat flowing from the model (the gas) to the surrounding ambient (not modeled). I think you do not have a load on the outside of the fluid surface that simulates the environment pulling the heat out, so the heat flow rate should be 0. This is why the calculation is small (practically 0). Let me try that and get back with you. I eventually want to give you some Kudos for all this (not that you don't deserve them now).

 

For item 2, the two images on the right side of the page show the fluid is split into two halves (the top and bottom) so that you can hide the top half in the Results to see what is happening inside the fluid. Yes, same as on the left, but it has a conduit (turned off and not shown) in attempt to simulate real live heat transfer (if I can ever get past the fluid part).

 

What I see are prescribed velocities on the split plane between the top and bottom halves of the fluid along a portion of the length. Either you applied the zero velocities to the split plane by mistake, or the mesh between the top and bottom halves do not match up (so the processor thinks that it is a "free surface" since it doesn't match any other elements), or a bug. Without an archive of the model, I cannot be sure what is the cause. The velocity was applied to the end, on each half, just like the left side pictures. I have noticed with some meshing options, the applied velocity wants to "creep", or as mentioned, "free surface".

 

Why this occurs in the model on the right-side of the page and not on the left side of the page is a mystery. Perhaps a different mesh size would eliminate the problem. Of course, you can mesh the model and so a "Analysis > Analysis > Check Model" to view where the zero-velocity conditions get applied befor you run the simulation. Thanks let me check on this.

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Employee
INACTIVE_AstroJohn
Posts: 492
Registered: ‎03-25-2010

Re: !!!!Simulation Pro 2011 - Stagnation due to oscillations!!!!

08-21-2012 12:06 PM in reply to: jrm_1971

Hi,

 

I tried to reproduce the problem with the zero-velocity boundary conditions appearing on the split face, but I was not able to reproduce it. Perhaps the current software (2013) behaves differently than 2011 because of the new CAD kernel used in 2013.

 

The suspicion is that the mesh on the split face for each part is not identical (even though the nodes may line-up perfectly). If you think of a 4-sided element on the surface being split into two 3-sided elements, there are two ways to draw the diagonal line that splits them. If each part uses a different diagonal line for some of the elements, the software detects those elements as "not matching" another element; therefore, those elements must be on a wall and get a zero-velocity boundary condition! Try creating the mesh with the option "Use virtual imprinting" (located under "Mesh > mesh > 3D Mesh Settings > Options > Model") checked and unchecked.

 

If that doesn't work, the other option is to correct the problem manually by selecting the lines on one of the surfaces, deleting them, selecting the lines on the matching surface, duplicating them to the original part number. Finish up by doing a global snap.

Sincerely,
John Holtz, P.E.
Senior User Experience Designer, Simulation
Autodesk, Inc.

Current version of Mechanical & Multiphysics: 2013 SP1 (2013.01.00.0012 28-Jun-2012)
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Distinguished Contributor
jrm_1971
Posts: 112
Registered: ‎03-31-2011

Re: !!!!Simulation Pro 2011 - Stagnation due to oscillations!!!!

09-16-2012 03:12 PM in reply to: INACTIVE_AstroJohn

UUUUUGGGGGHHHHHH!!!! I have tried everything I know to get the heat transfer results out of this analysis. Please put a bullet in me. I have been working on this for a year now. I put it down, pick it up, put it down, pick it up out of frustration. It should not be this hard.

 

I have added convection and radiant loads. It still near zero heat transfer.

 

On the one with the tube model, the deleting, matching, snapping lines did not work, it just doesn't want to go through the fluid analysis. I get a bunch of dead node/elements warning with the analysis finishing (it does not go past the zeroeth step). I have tweaked the mesh to death on this.

 

I have tried putting a volume around the coil and temperature applied to the part (the volume), still near zero. The volume material is from the standard library.

 

Help!

 

 

 

 

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