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Active Member
randymusk
Posts: 9
Registered: ‎03-17-2013

SURFACE TEMPERATURE ON BEAMS AND PIPES WRONG RESULTS

126 Views, 6 Replies
08-28-2013 03:58 AM

Has anyone had a similar problem? I have tried both beams and pipes, applying 800F to the surface on a 360" long segment. I am holding the segment on one end like a cantilever beam expecting full expansion out the other end. However, the expansion growth is only half of the calculated value. Plus, if I divide this element in half, the new expansion value will be 1/2 that of a single element, which is 1/4 calculated. How can I trust this.

Has anyone else seen this?

 

Ranman3

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Valued Mentor
AstroJohnPE
Posts: 494
Registered: ‎08-30-2012

Re: SURFACE TEMPERATURE ON BEAMS AND PIPES WRONG RESULTS

08-28-2013 06:28 AM in reply to: randymusk

Hi Ranman3,

 

I have not seen such a problem, so hopefully it is a simple user error or misunderstanding.

 

Your subject line implies MES analysis which has various parameters for adjusting the approximation of the solution to the differential equation F=m*a. Perhaps one of those parameters is the cause for the inaccurate approximation. (The test I just did was right on, so the defaults should give you correct answers.)

 

Otherwise,

  1. Please tell us what analysis type you are using.
  2. Please provide your hand calculations.
  3. Please provide an archive of your model using the instructions in "Create, Post, or Provide an Archive of your model".

 

John Holtz, PE
Mechanical Engineer
Pittsburgh, PA

16 years experience with Simulation Mechanical
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Active Member
randymusk
Posts: 9
Registered: ‎03-17-2013

Re: SURFACE TEMPERATURE ON BEAMS AND PIPES WRONG RESULTS

08-28-2013 07:48 AM in reply to: AstroJohnPE
Attached is an archive of the file I am referring to. The temperature expansion is 1/2 what it should be.
(2) 45" segments for 90" total long, coef exp 9.8x10-6, ?temp 800 F

Randy J Musk, PE

"There are two kinds of people:?those who think they can, and those who think they can't.?They are both right."
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Valued Mentor
AstroJohnPE
Posts: 494
Registered: ‎08-30-2012

Re: SURFACE TEMPERATURE ON BEAMS AND PIPES WRONG RESULTS

08-28-2013 09:26 AM in reply to: randymusk

Hi Randy. Did you forget to attach the archive, or am I being blocked from seeing it? You may need to change the extension from .ACH to .ZIP in order to attach the file.

 

P.S. Your signature line reminded of the joke "There are 10 kinds of people in the world. Those who understand binary, and those who do not."

 

John Holtz, PE
Mechanical Engineer
Pittsburgh, PA

16 years experience with Simulation Mechanical
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Active Member
randymusk
Posts: 9
Registered: ‎03-17-2013

Re: SURFACE TEMPERATURE ON BEAMS AND PIPES WRONG RESULTS

08-28-2013 09:40 AM in reply to: AstroJohnPE

I attached the arch file after renaming it zip without zipping it. I may have forgot to attach it last time.

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Active Member
randymusk
Posts: 9
Registered: ‎03-17-2013

Re: SURFACE TEMPERATURE ON BEAMS AND PIPES WRONG RESULTS

08-30-2013 02:54 AM in reply to: AstroJohnPE
John,
Have you looked into this dilemma?
?

Randy J Musk, PE

"There are two kinds of people:?those who think they can, and those who think they can't.?They are both right."
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Valued Mentor
AstroJohnPE
Posts: 494
Registered: ‎08-30-2012

Re: SURFACE TEMPERATURE ON BEAMS AND PIPES WRONG RESULTS

08-30-2013 10:54 AM in reply to: randymusk

Hi Randy,

 

I was not able to look at your model because I do not have version 2014. I didn't think of creating a model with my 2013 and sending it to you (if curious).

 

The problem is that SURFACE temperatures do not work. You and I confirmed that they do not work on beams, you confirmed they do not work on pipe, and I would guess that they do not work on truss elements. (Actually, I do not remember if truss elements have thermal expansion in MES.) I could not determine what the problem really is, but I think it might be related to the temperature being applied to only some of the nodes but not all of the nodes. The beam that I divided into 10 segments CONTRACTED which could only occur if some of the elements were below my reference temperature of 70 F.

 

Use NODAL temperatures instead. Design scenario 2 in my attached model gives correct results of delta L = alpha*L*delta T = 9.8E-6 * 90" * (800-70 stress free reference) = 0.6439.

 

Sorry. I just remembered that my web filter blocks attachments to this discussion group, I cannot give you my model! Too bad, it was a great model. :-)

John Holtz, PE
Mechanical Engineer
Pittsburgh, PA

16 years experience with Simulation Mechanical
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