How does CSE deal with low mass surfaces when using forward-difference

asked 2 years ago

cmui
143 ●5

updated 2 years ago

Aaron Boranian

14355 ●90 ●25 http://bigladdersoftware.com/

I've been reviewing the code for CSE and haven't been able to find an easy answer to the following question -

How does California Simulation Engine avoid numerical instability while using euler forward difference surface models with fixed time steps (usually 2 mins)? Thin exterior layers that see solar are particularly problematic.

Are there adaptive time steps, or are exterior layers treated as massless?

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answered 2 years ago

Chip Barnaby
21 ●1

My recollection is that fictious mass is added to lightweight layers to ensure numerical stability. Note that this approach can handle massless materials (ideal resistances) in addition to real light materials.

However, I could not find the details in the code with a bit of poking around.

If you make and send an example file with some cases that might cause trouble, I can trace through the code and find how the adjustment is made.

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Thanks for the reply Chip! The test case here has 9mm wood siding in CONSTRUCTION lw_wall. Could be a good way to see this code path.

https://github.com/cse-sim/cse/blob/main/test/1ZAttic.cse

cmui ( 2 years ago )

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answered 2 years ago

Neal Kruis

4755 ●10 ●17 http://bigladdersoftware.com/

CSE performs adaptive discretization of the material layers in order to ensure numeric stability. This discretization is performed once for each material layer in the simulation based on the timestep and the thermal properties of the material.

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Thanks! That's helpful. Do layers ever get merged in nodal representation if their time constant is too small. Ie. 9mm of wood siding on the outside of a wall construction, perhaps getting merged with the stud and fiberglass properties of the layer behind it.

cmui ( 2 years ago )

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