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Author Topic: ANSYS: Varying temperatures between load sets  (Read 32 times)

JanPio

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ANSYS: Varying temperatures between load sets
« on: April 16, 2018, 08:41:31 AM »
Hello,
we currently use HyperSizer 7.3.50 with ANSYS 18.2 to evaluate various designs of a Reusable Space Launch Vehicle with metallic materials.

First, our understanding of the thermal behavior when connecting HS to ANSYS: The help page on “Thermal Loads” says that “ANSYS thermal loads are not supported.” However, as HyperSizer only imports the resultant element forces from the ANSYS results file and BF-commands are also included in the newly created "*_i.cdb", thermal strains/stresses  seem to be considered. Therefore, the only relation HyperSizer cannot build up is which material property to use at which region of the structure, because the current temperature is not known. Is this right?

Now to our problem: Different parts of the structure, such as the tank or the wings, have different temperatures assigned in a wide range. Additionally, these temperatures should change for different load sets, such as liftoff or reentry. Thermal strains/stresses seem to be included in the results, but we cannot change the loads between load sets.

Workaround: For considering temp-dependent material properties in the parts of the structure we created separate materials for different temperatures, such as "Alu 20K" and "Alu 293K". But this obviously neglects temperature changes between load sets, because there is no possibility to change these materials between load sets.

Questions: Is our understanding of the use of temperatures in HS/ANSYS correct? Is there another workaround to include variable thermal setups in load sets?

Thank you in advance,
Jan

Brent

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Re: ANSYS: Varying temperatures between load sets
« Reply #1 on: April 16, 2018, 10:38:10 AM »
Hi Jan,

You are correct in your assumption. Since HyperSizer cannot import temperatures from ANSYS, it does not know where to apply the temperature dependent material properties.

The work around we suggest is the following:

1. Import your thermal load sets as mechanical. (Skip this step if the thermal loads are already combined to mechanical loads in your FEM)
2. Assign a unique reference temperature to each "Thermal" load set.
3. Assign a different material to each part of the structure that would have a constant applied temperature.
4. Assign reference temperatures to each material system that is consistent with the "applied temperatures" of the "thermal" load set. 

EXAMPLE:
1. When sizing a single component for one load case, HyperSizer will use the temperature dependent properties associated with the reference temperature assigned to the load set.

2. For one "thermal" load case with multiple components that have different applied temperatures, the different material systems for these components will have different temperature dependent properties for the same reference temperature.

Careful attention must be used when managing the various temperature dependent properties and reference temperatures for each material system on each structural location. Supporting ANSYS temperature loads will be evaluated for future software releases. 

Question: Will you need to update the FEM with the temperature dependent properties unique to each thermal case? Or, will the room temperature properties for used in the FEA runs?

Hope this helps!

Brent