What about wtmass in get_mass_breakdown_detailed

[clarkbr...@gmail.com]

Steve, we have struggled with this for several years. In 2021, we concluded one thing, then reversed it, now it seems to need to be back.

We calculate the weight of structure via the subject func. I go through the returned pids_to_mass and add up the m's.

We use wtmass = 1/32.2 so user inputs can be in lbf.

What units does pids_to_mass return mass in? Does it apply wtmass so I get mass in lbs?

I really guess, this is about what (MSC) Nastran is doing internally. The intent of wtmass is to let Nastran do all its internal calculations in slug-ft^3 per fortnight or whatever. 

I suppose it gives you the masses in those internal units. Do you manually do anything to re-apply wtmass?

Should I be summing the returned m's * wtmass so we get lbs?

There was a conversation in pyNastran Discuss back in 2015 where the then-current mass getter let the user provide wtmass. It isn't that way anymore I guess.

Thanks,

Clark

[Steven Doyle]

Clark,

I"m having a bit of trouble following everything, but the function has barely been modified since 2018. An additional was added in 11/2021 for testing, but it's been pretty static since then. The function does not apply WTMASS.

I'm not sure which post you were referring to, but if it's this: https://groups.google.com/g/pynastran-discuss/c/VZ7HbmITJ64/m/9RRfM3oPCgAJ, that refers to mass_properties, which does have a scale parameter, which is still there.

Internally, MSC/NX/Optistruct Nastran is building a mass matrix and reducing that at the origin prior to transforming it to the cg or a specified node for the Output Grid Point Weight table. The math is documented in the dynamics guide. The functions get_mass_breakdown and mass_properties calculate mass in the same way, but only mass_properties calculates inertia and that does it using the m*r^2 method prior to transforming it (and is the same way FEMAP does it).

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[clarkbr...@gmail.com]

Thanks, Steve.

"The function does not apply WTMASS."

This is what I was looking for.
Clark