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Box-to-ball radiation tutorial behaves strangely

4 REPLIES 4
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Message 1 of 5
bjorn_fallqvist
629 Views, 4 Replies

Box-to-ball radiation tutorial behaves strangely

Hello,

I was going to try to learn a bit more about radiation heat transfer in Algor, and found the tutorial titled "Ball in a box with body-to-body radiation". I have set the analysis up exactly as the tutorial tells me to, step by step. However, I do not get convergent behaviour. Instead, the log file looks like this:


Autodesk Algor Steady-State Heat Transfer
Version 2011.00.00.0111-W64/X64 12-MAR-2010
Copyright (c) 2010, Autodesk, Inc. All rights reserved.

**** Memory Dynamically Allocated = 16776192 KB
**** Steady-State Heat Transfer Analysis

----------------------------------------------------------------
DATE: APRIL 26, 2010
TIME: 09:43 AM
Input Model: C:\Documents and Settings\All Users\Documents\Projekt\Esrange\b2brad_input.ds_data\1\ds


PROGRAM VERSION: 201100000111
ALG.DLL VERSION: 201100000111
AlgConfig.DLL VERSION: 201100000111
Agsdb_AR.DLL VERSION: 201100000111
AMGSolve.DLL VERSION: 201100000111
AlgSolve.DLL VERSION: 201100000111
----------------------------------------------------------------

Options executed are:
NOMIN
SUPSTR


processing ...


**** Model Unit System Settings:
--------------------------------------------
Unit System : Metric mks (SI)
Force : N
Length : m
Time : s
Temperature (Absolute) : deg C (K)
Thermal Energy : J
Voltage : V
Current : A
Electrical Resistance : ohm
Mass : kg
--------------------------------------------

**** OPENING TEMPORARY FILES
NDYN = 10
**** BEGIN NODAL DATA INPUT
Node number= 382
Equation number= 872
**** END NODAL DATA INPUT
**** HARD DISK FILE SIZE INFORMATION FOR PROCESSOR:

Available hard disk space on C drive = 38173.020 megabytes

**** BEGIN NODAL HEAT FLOW INPUT
**** END NODAL HEAT FLOW INPUT

****
**** Invoking BCSLIB-EXT Sparse Solver ...
****


**** BEGIN NON-LINEAR ITERATIONS

Nonlin Iter. Incr. Norm(T) Incr. Norm(Q) Rel. Norm(T) Rel. Norm(Q)
----------- ------------- ------------- ------------ ------------
1 1.135E+02 1.025E+02 1.373E+00 1.000E+00
2 1.594E+02 2.854E+02 1.113E+00 7.383E-01
3 2.166E+02 1.230E+02 1.996E+00 4.343E-01
4 4.892E+03 1.271E+02 1.017E+00 3.336E-01
5 4.937E+03 1.273E+02 3.381E+01 4.298E-01
6 3.525E+15 1.337E+02 1.000E+00 3.541E-01
7 3.525E+15 6.754E+02 1.548E+13 9.456E-01
8 3.067E+18 1.261E+03 1.000E+00 1.403E+00
9 3.067E+18 1.263E+03 6.813E+15 1.459E+00
10 1.939E+19 1.521E+04 1.000E+00 1.034E+00
11 1.939E+19 2.968E+05 1.163E+14 1.011E+00
12 7.443E+26 4.764E+11 1.000E+00 1.000E+00
13 3.192E+27 1.279E+28 1.028E+00 1.000E+00
14 9.084E+91 2.320E+78 1.000E+00 1.000E+00
15 Infinity Infinity NaN NaN
16 NaN NaN NaN NaN
17 NaN NaN NaN NaN
18 NaN NaN NaN NaN
19 NaN NaN NaN NaN
20 NaN NaN NaN NaN
21 NaN NaN NaN NaN
22 NaN NaN NaN NaN
23 NaN NaN NaN NaN
24 NaN NaN NaN NaN
25 NaN NaN NaN NaN
26 NaN NaN NaN NaN
27 NaN NaN NaN NaN
28 NaN NaN NaN NaN
29 NaN NaN NaN NaN
30 NaN NaN NaN NaN
31 NaN NaN NaN NaN
32 NaN NaN NaN NaN

So the increment in temperature just grows and grows. What could this be due to? I have double-and triple checked the settings for the material properties, surface enclosures and analysis settings.
4 REPLIES 4
Message 2 of 5

Hi Bjorn,

I just went through the example, and my model converged. As you pointed out, the model is diverging. I suggest that you check the "Analysis > Parameters... > Advanced" tab and confirm that the last entry, the "Relaxation parameter" is set to 0.3. (Step 18 in the example.)

If that is set properly, then please create an archive of the model (File > Archive > Create > Model only) and post it. I have a utility that can compare the inputs between two models, so hopefully that will reveal a difference.

John Holtz
Product Design Engineer, Algor Simulation
Autodesk, Inc.


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 5

I am attaching my archive file for this example. Just tried running it, and got the same error as before.

/Björn
Message 4 of 5

Hi Bjorn,

The problem is on the "Advanced" tab of the "Analysis > Parameters..." window. Instead of setting the "Relaxation parameter" (last input on the tab) to 0.3, it was at the default value of 1. The "Relative tolerance" (second input from the bottom) had been set to 0.3.

P.S. lf you are viewing the interface in a language other than English, perhaps the labels are translated improperly or switched. This would explain why the 0.3 was entered in the wrong box. Let me know what langauge you are using if it is not English, and I will have the translation checked.

* * * The rest of this reply can be skipped if one is not interested in a little theory behind the process 🙂 * * *
Now might be a good time for me to describe what's going on and why a "relaxation parameter" is required. In any type of nonlinear solution, one solution method is to "guess" what the result is so that the nonlinear part of the solution can be calculated and removed, and then calculate the result. If the guess and calculated result matches, the solution has converged!

In this case of radiation in heat transfer, the heat flux due to radiation is nonlinear -- it is based on the fourth power of temperature. So the heat flux due to radiation is based on the assumed temperature result. This allows the matrices to be formed and solved for the temperature. If the assumed and calculated temperatures agree, the solution has converged! Of course, the assumed temperature is rarely accurate on the first iteration, so the calculated temperature is also "not very accurate". In some cases, the calculated temperature can be worse than the assumed temperature. Instead of using the calculated temperature for the next iteration, it is better to use something in between the assumed temperature and the calculated temperature. This is what the user-specified "relaxation parameter" does. If the value is 1, then the newly calculated temperature is used for the next iteration. If the value is 0, then the previously assumed temperature is used for the next iteration. (This is not a good choice since all iterations would be identical, and the analysis would never converge nor diverge!) A relaxation parameter between 0 and 1 will use a value in between the assumed and calculated temperature. The higher the nonlinear effect, the smaller the relaxation parameter should be.

I'm sure that the above description is not correct in all of the details; after all, I just a user like you guys. I didn't write the software ;-). But the concept is close enough to help with deciding on what relaxation parameter to use, and why the analysis may be diverging.


John Holtz
Product Design Engineer, Algor Simulation
Autodesk, Inc.


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 5

Hello, John.

First of all, thankyou for the explanation. 🙂

I would guess I mixed the relaxation parameter and relaxative tolerance up. Edited by: bjorn_fallqvist on Apr 28, 2010 6:38 AM

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