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Standing Heat Waves

7 REPLIES 7
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Message 1 of 8
Emily.I
765 Views, 7 Replies

Standing Heat Waves

Hi,

 

I created a flat plate and put an applied temperature heat load on a node at one end, and a radiation load on the surface. I have set up the body-to-body radiation and played around with the parameters, however it keeps creating standing heat waves. I set the ambient temperature at 0 and the nodal temperature at 30 and end up with a minimum temperature -98.

 

I have the non-linear solutions running, and it still converges, but is clearly wrong...

 

Any thoughts?

 

Thank you,

Emily

7 REPLIES 7
Message 2 of 8
John_Holtz
in reply to: Emily.I

Hi Emily,

 

Are you performing a steady state or transient heat transfer analysis?

 

Can you clarify what you mean by a "standing heat waves"?

 

Where does the erroneous temperature occur? My guess is that it is related to using a single node to supply the heat source. It would be better if you use a surface load to distribute the source.

 

Perhaps some images attached to the reply would be helpful.

 



John Holtz, P.E.

Global Product Support
Autodesk, Inc.


If not provided already, be sure to indicate the version of Inventor Nastran you are using!

"The knowledge you seek is at knowledge.autodesk.com" - Confucius 😉
Message 3 of 8
Emily.I
in reply to: John_Holtz

Its steady state heat transfer. I had stripes of hot and cold all the way across it, ending with a hot line at the end, the cold was always the negative of whatever I had set the plate at.

 

I have managed to get what I am meant to get for just a normal conductor by adjusting the relaxation parameter, however for smaller thermal conductivity I still get a small cold patch (cooler than the ambient temperature) near where the heat source is.

 

A similar thing happens using nodes as well.

 

Thank you,

Emily

Message 4 of 8
John_Holtz
in reply to: Emily.I

I see what you mean by a standing wave. Very cool!

 

I suggest that you create an archive ("File > Archive > Create") and attach it (.ach file) to this thread. The archive can be of the "Model Only" since it looks like that analysis will take a few minutes.

 

By the way, it looks like your version of the software is at least 3 versions out-of-date.  Smiley Wink What version are you using? (Help > About)

 

 



John Holtz, P.E.

Global Product Support
Autodesk, Inc.


If not provided already, be sure to indicate the version of Inventor Nastran you are using!

"The knowledge you seek is at knowledge.autodesk.com" - Confucius 😉
Message 5 of 8
Emily.I
in reply to: John_Holtz

Its V22, its just the one the university loaded on the laptop for me...

 

It won't let me upload it, it says the extension isn't valid?

Message 6 of 8
Emily.I
in reply to: Emily.I

Any help?

 

Thanks,

Emily

Message 7 of 8
Emily.I
in reply to: John_Holtz

Downloaded the new version of Autodesk Simulation, but I still have the same problem, clearly something is wrong with the parameters as I have an unphysical cold patch. Do you know what it could be?

 

Thanks,

Emily

Message 8 of 8
John_Holtz
in reply to: Emily.I

Hi Emily,

 

The model that you sent is not converging in design scenario 8; hence, the results are meaningless.

 

I suggest that you lower the "Relaxation parameter" from 1 to 0.2, and lower the stiffness of the applied temperatures from (too many zeros for me to count Smiley Wink) to 100. The first change will minimize the oscillations in the calculations, and the second change may help with making the solution matrix more stable.

 

BUT THEN, I think what you are trying to analyze does not make physical sense. Or you need a much, much finer mesh at the hot end. Your arrangement can be solved "by hand" by using standard heat transfer equations for fin cooling. Performing the "integration" using Excel and "element" size of 1 mm, I calculate that the model cools to 12 degrees in the first 100 mm. 100 mm is the size of the mesh in your plate model, so the mesh is just not accurate enough to capture the steep temperature gradient at the hot wall.

 

Because I had a little problem with the hand calculations Smiley Sad, I also created a fine mesh using rod elements. (Your model is really a 1D analysis at this time, so rod elements work fine.) I got good agreement between the software and the hand calculations. (See attached)

 



John Holtz, P.E.

Global Product Support
Autodesk, Inc.


If not provided already, be sure to indicate the version of Inventor Nastran you are using!

"The knowledge you seek is at knowledge.autodesk.com" - Confucius 😉

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