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Thermal Stress - Modelling of an interactive coupled Simulation

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Old   January 10, 2019, 06:14
Default Thermal Stress - Modelling of an interactive coupled Simulation
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Hello everybody,

Hope you all are fine.

Usually I do thermal simulations for electronics cooling (CHT simulations). This means, we can simulate the overall thermal behavior of the electronics. For that, we have a quite efficient and proper workflow.

An important detail is often the thermal resistance between two parts. E.g. how is the PCB (Printed Circuit Board) mounted on a heatsink. Due to the roughness of the surfaces and the not perfect planarity, there is always a small gap between two parts, usually in the range of 30 m air.
With the assumption of a homogenous thermal resistance of 30 m, we can achieve a very good agreement between simulation and measurements.

The next target now is to model and simulate the 30 m air gap more properly, as we know, the gap is not constant but can vary in a certain range.

For doing so, I think a common approach is a one way coupled thermal stress simulation:
- - Performing a thermal simulation as usual in order the get the thermal behavior of the parts
- - Map the result and perform a structural simulation considering the different coefficients of thermal expansion (CTE) and observe the deformation of the parts

Now, the gap is not constantly 30 m any more, but can vary in a range of let’s say 0 – 60 m due to the deformation (its now a function of the place).
Since the gap can have a big impact on the thermal results, I would like to perform another thermal simulation, with the new “air gap function” and not with the homogeneous 30 m. Thus I would expect slightly different thermal results. This new thermal result will end in a different deformation and air gap function respectively. If this works, I could do a slope thermal, stress, thermal, stress and so on until there is convergence.

Unfortunately the implementation of all that is not so easy. I did some investigations with different approaches, but the success is negligible so far

Do you have some ideas or hints of performing such "2 way coupled thermal stress simulations"?
I use Star-CCM+ and so far there are only two mechanical interfaces – bonded and Small Sliding Firctionless.

Attached you can find a sketch of the domain.
This example shows a simplified LED module mounted on a heatsink.
Thank you very much in advance.
Kind regards
Attached Images
File Type: jpg electronics1.jpg (41.5 KB, 5 views)
File Type: jpg electronicsdetail.jpg (71.5 KB, 6 views)

Last edited by macRC; January 10, 2019 at 08:12.
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