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# Advance Mass Properties for NX Assembly based on WCS

Builder

Hi,

I am currently using the UF_WEIGHT_estab_part_props to get the Center of Mass and Moments of inertia for assemblies. This API is returning me the values based on absolute co-ordinate system.

The menu command in NX (Analysis->Advanced Mass Properties->Advanced Weight Management) gives the results based on the currently used WCS.

I also need to get the results based on the the WCS using a API.

Regards,
Santosh

Regards,
Santosh
5 REPLIES

# Re: Advance Mass Properties for NX Assembly based on WCS

Siemens Phenom
Well you could take the ACS answers and map them to the WCS. Volume, mass, and surface area are obviously independent of coordinate system. Centroid is just a point, so it's easy to map. Moments of inertia are more complicated, but the change-of-coordinates techniques are taught in physices and ME courses everywhere.See here for example: https://en.wikipedia.org/wiki/Moment_of_inertia#Calculating_moment_of_inertia_about_an_axis To do the basic mapping of point and vectors, you can use functions like NXOpen.UF.UFCsys.MapPoint or Snap.NX.CoordinateSystem.MapAcsToWcs.

# Re: Advance Mass Properties for NX Assembly based on WCS

Builder
I am actually using a formula to calculate the translation rotation of WCS and then calculating the Moments of Inertia Tensor, which will also give me products of inertia.

This is a big calculation and took me a while to complete only the partial (i.e., rotation) solution. I was wondering that if there is any API to do this for me.

I ll try the method you suggested.

It would be really helpful if there was a boolean flag which gives us the values in desired CSYS.

Regards,
Santosh

# Re: Advance Mass Properties for NX Assembly based on WCS

Siemens Phenom
Actually, now that I think about it, the function NXOpen.UF.UFModl.AskMassProps3d *does* return its answers relative to the WCS. Personally, I consider this to be a bug, since the rest of NX/Open uses the ACS almost exclusively. But, bug or not, it's documented, and it probably won't change, so it's safe to use it, if it helps.

# Re: Advance Mass Properties for NX Assembly based on WCS

Builder
But even there the inputs to that API is too much.
It does not take part/assembly tags, instead it takes solid bodies.
Also need to provide the type of the solid body which is not available directly.

Considering a large vehicular assembly doing such kind of operation is not possible as it might contain sheetmetal/surface/solid..etc bodies.
Regards,
Santosh

# Re: Advance Mass Properties for NX Assembly based on WCS

Innovator

>> It does not take part/assembly tags, instead it takes solid bodies.

If you would like to assert values (e.g. enter them manually), then the API does take part / component tags.

There is also an option to define a reference set containing the bodies for which to calculate the weight data with; see UF_WEIGHT_set_part_ref_set.

Marc Prosl
NX Software Developer