topic Re: thermal-stress simulation for component in vacuum. in Fusion Design, Validate & Document Forum

thermal-stress simulation for component in vacuum.

pblase — Mon, 13 Jul 2020 03:32:33 GMT

I'm trying to do a thermal-stress simulation of a small spacecraft system. I have a heat source, the electronics, and a heat dump, a radiator. The problem is the "ambient temperature" setting on the radiation thermal load. The whole system ends up at that "ambient" setting regardless of where I set the initial temperature (20 C) in the "settings" box. In this case there really is no "ambient" temperature, just a radiation sink (I'm not trying to model the outside world, yet).

I'm using the thermal-stress simulation because there's one component that flexes depending on the absolute temperature, and I'm trying to calculate how the thermal flux from the source to the radiator affects that piece.

Re: thermal-stress simulation for component in vacuum.

John_Holtz — Tue, 14 Jul 2020 12:33:35 GMT

Hi @pblase

A thermal stress analysis is a steady state analysis. So the results at time infinity should be independent of the initial temperature (20 C) at time 0. Also, the temperature that is entered in the Settings > General is not the initial temperature. The Settings input is the stress free reference temperature. That is unrelated to the thermal analysis and is only used for the stress analysis. (The Thermal Stress analysis performs two analyses: a steady state heat transfer analysis, followed by a separate linear static stress analysis that uses the temperature results.)

You wrote "I'm not trying to model the outside world, yet", but that is exactly what you are doing with the radiation load in Fusion. Radiation (and all other thermal loads) are between the outside world (the environment) and the model. It sounds like you were expecting the radiation load to be between the components of the model. Fusion does not have that capability. If that is what you are trying to model, you need to use different software such as Autodesk CFD.

Re: thermal-stress simulation for component in vacuum.

pblase — Thu, 16 Jul 2020 01:48:12 GMT

"It sounds like you were expecting the radiation load to be between the components of the model."

No, I'm trying to figure out what the "ambient temperature" value has to do with anything for the radiative load. What does that temperature represent in this case?

Re: thermal-stress simulation for component in vacuum.

John_Holtz — Thu, 16 Jul 2020 03:10:42 GMT

Hi. I may have misunderstood which dialog you are referring to. For example, when you wrote "the initial temperature (20 C) in the "settings" box", I do not understand what dialog you are referring to or which input box.

Hopefully this will clear up our understanding, but if you are referring to something different, please provide a screenshot to clarify your question.

The "Ambient Temperature > Temperature Value" for the Radiation Thermal Load is the temperature of the environment. The selected faces on the model and the environment exchange heat directly by radiation. It is a direct path; no part of the model blocks the radiation.

In other words, radiation is not from one face of the model to another. This type of radiation (also known as body-to-body or surface-to-surface radiation) is not available in Fusion. Fusion only handles radiation from an unblocked face of the model (such as the outside surface) to the environment ("the world") which is at a constant temperature that you specify.

The "Default Stress-free Temperature" for the Settings > Thermal Stress is used to calculate the thermal expansion (which in turn creates stress). Thermal expansion = length*thermal expansion coefficient*(calculated temperature - default stress-free temperature).

I hope this helps.