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Thermal Set

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James:
The initial temperature should represent the "stress free" temperature. The duration of the temperature shouldn't matter. The mechanical loads for your cruise condition are occurring at the same time as your 750K applied temperature so I think your delta T = 750-300 to determine the thermal stresses.

Your assessment of the mass increase due to increasing the material reference temperature makes sense to me.

So when you set Temp(init)=300, deltaT=350K and there is a huge mass increase. This sounds like a problem with the CTE properties (alpha) in the FEM. Can you double check the magnitude and that the units work out?
 

ULBsha:
Thanks James.

No, the CTE seems to be fine (a variation between 8.5e-6 m/mK and 10e-6 m/mK). However, the Gii values are quite strange according to me: a huge increase when the delta T goes from: DeltaT=(600-300)  to  DeltaT=(800-300) !!!

Please find attached the 3 *.PM files for which a uniform temperature of 295K, 600K and 800K are applied as thermal load, with initial temperature of 295K for the three studies. For instance, on the component "200003 FuselageSkin_2", you will see this huge increase...  (you can also notice the huge increase of masse/unit area given in the PSHELL card).

Do you have any idea about this problem ?

Just one thing to be sure: I read the MSC Quick User Guide and it's mentioned that for the initial temperature, we have to use TEMP(INIT) and in this way we don't have to put any Tref in the MAT card.
However, in my initial material properties (my input bdf file for HyperSizer), I used the TEMP(INIT) command, but I also used this Tref as 295, which is the same than my TEMP(INIT) value... Could this cause any issue ? 

Thanks again

James:
If both temp(init) and Tref are specified, then the Temp(init) will be used instead of Tref on the property cards. I have used the Temp(init) card before and I can confirm this behavior.

The increased Gij and NSM on the Mat cards is likely because the panels are sizing up in HyperSizer. HyperSizer will then export the ABD stiffness terms for the stiffened panel to the MAT2 cards that are referenced in the PSHELL card. See: http://hypersizer.com/help_7.0/#FE-Update/update-stiffened_panel_export.php%3FTocPath%3DFEM%2520Interface%7CUpdating%2520the%2520Model%7C_____3

Can you confirm the Gij values in the .pm1 file are the same ABD values represented in the sizing form > properties tab?

Can you look at the input loads from your cases where deltaT = 800-300. I think the thermal loads are probably really high which is causing the panels to size up in HyperSizer.

ULBsha:
Dear James,

Thanks for your help.

Actually, the Gij values in the .pm1 file are the same ABD values represented in the sizing form. However, I noticed that some of my components show Invalid Geometry for the MOS (I have one single component in a group, to fully optimise the structure). I know what this means, but I don't understand why it happens when my deltaT goes from '600-300' to '800-300'...

Indeed, I am using the Object Model ability, so I have some scripts written in Matlab that update the variable bounds automatically after each set of X iterations between HyperSizer and Nastran (HyperFEA). So, the process is the same, but apparently it doesn't work correctly with high applied temperatures...
I also get this issue when I try to size the AP1 (given as tutorial) with a applied uniform thermal load of 1000K ! Please note that I get a vehicle mass of less than 5 tonnes if we apply a 750K load, with positive MOSs, but it increases to 32tonnes if it's 1000K, with some Invalid Geometries...

Regarding the input load, I don't really understand what you mean. If you mean the forces in different elements shown in my *_i.f06 file, it's quite difficult to compare the different cases... but when I compare element by element for both cases, it seems that the forces for the deltaT=800-300 are higher than those for deltaT=600-300... (some times 1 or 2 orders of magnitude higher)...

Do you have any solution... ?

Thanks again.

James:
It sounds like your components are oversizing. Oversizing occurs when HyperSizer can't find a solution that fits within your sizing bounds so it returns the heaviest solution. The geometric checks are a pass/fail check. The "INVLD GEOM" is treated as a negative margin. What happens when you turn off the geometry checks and resize the  case with deltaT=800-300?

The element forces for the thermal case can be viewed in the HyperSizer graphics window. What is the magnitude of the element forces for the thermal case?

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