Carrying out the mass balance
Carrying out the mass balance of a thermal model is a standard activity which makes it possible to verify the assumptions that were made at the time of thermal model construction. The objective being of course to preserve, for the thermal model, the same mass as the mechanical model (CAD model) given that the thermal capacitances of the nodes depend on the mass and that the thermal couplings depend on the volumes of the nodes on which the mass depends on.
The thermal model is built based on the mechanical model CAD.
The thermal model is built based on the mechanical model (CAD model). When building the thermal model from the CAD model, you make assumptions about the geometry. For example, you remove all the small features which will have no impact on the final temperature results because their geometries are very small compared to the geometry of the whole thermal model.Learn how The 7 steps to build the geometry from CAD models for thermal analysis
After making these assumptions on the geometry, the mass of the thermal model is likely to be less than the mass of the mechanical model. If the mass of the thermal model is slightly less than that of the mechanical model, it is not necessary to adjust the mass. In fact, having the thermal model slightly lighter than the mechanical model is a good practice; a conservative approach is likely to cause the highest temperature gradients on the spacecraft or satellite subsystem.
However, if the mass of the thermal model is significantly lighter or heavier, you need to change the mass to bring it closer to the mass of the mechanical model.
How it works
You compare the mass of the mechanical model with that of the thermal model, part by part. If the design of the mechanical model changes, you update the thermal model mass accordingly. Today, this operation is done in most cases manually.
Results
Benefits: Known approach.
Limitations: Requires many iterations.
Why it matters.
Standardising and automating this process will allow these iterations to be carried out independently of the user's action, which will free up a lot of engineers' time.
We’re thinking:
We will standardise and fully automate this process using a Model-Based System Engineering (MBSE) approach so every time the mechanical engineer makes a modification on the mechanical design of the space system, this change is automatically carried out on the thermal model and therefore the comparison of the mass between the thermal and mechanical model is also updated at the same time.
We will make it accessible to the entire space thermal engineers’ community via our website our Digital Engineer® Try it now
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