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Margin of error in mass properties calculations?

Valued Contributor
Valued Contributor

Hey Everyone,

                 I am currently working on a Journal that performs hundreds or sometimes even thousands of mass properties calculations. I am seeing an interesting trend in my results. It seems that the more calulations I do during the run time of the Journal the less accurate the overall mass properties is. If I do less calculations the results are more accurate. Either way I am having an issue getting accurate volumes, and as a result other mass properties as well. These calculations include using the trim bodies command to trim a model a long the Z axis in small increments (typically in mm) and get mass properties for each slice.

 

Is there a perhaps a margin of error for each mass properties calculation that is compounded over the run time?

5 REPLIES

Re: Margin of error in mass properties calculations?

Esteemed Contributor
Esteemed Contributor

Note there is a customer default (Analysis -> Weight management) that controls calculation accuracy

There is also a preference (File -> Preferences -> Measurement -> ...)

 

You might want to investigate these.

 

But you could also have found a bug - I would report this to GTAC.

 

 

Ken Akerboom Sr CAx Systems Engr, Moog, Inc.
Production: NX10.0.3.5 MP5 + patch/TC11.2
I'd rather be e-steemed than e-diseaseled


Re: Margin of error in mass properties calculations?

Siemens Phenom Siemens Phenom
Siemens Phenom

I agree with Ken. This sounds like it might be a bug. There are parameters that control the accuracy of mass properties calculations, but accuracy should not be degrading all by itself.

山田
yamada

Re: Margin of error in mass properties calculations?

Phenom
Phenom

Just out of (intellectual) interest...

 

Are you saying that

running  your code with with slice = 10 produces a different answer to running your code with slice = 1000

or

running your code a number of time (on the same volume with same number of slices!) produces a "degradation" of the calculated volume?

 

thanks

Regards

Production: NX9.0.3.4, NX10.0.2.6
Development: VB.NET (amateur level !)
Highlighted

Re: Margin of error in mass properties calculations?

Valued Contributor
Valued Contributor

The first one, the more mass properties calculations you do in one run time the less accurate your accumulative results are. Now this degradation usually results in decimal places out to the 3rd or 4th place (and so on) for properties like volume and mass. However, for moments of inertia and centroidal moments of inertia, this loss in accuracy has a bigger effect on the total results.

Re: Margin of error in mass properties calculations?

Phenom
Phenom
Most likely beyond my programming skills but.. One would need some details on the code to understand how the data/variables are handled/defined but some thoughts What is the definition of variable type (Double, etc)? Do you add the calculated data (say mass) to one variable as you loop though the "slices" or add the result to an array then deal with the array? Thanks Regards
Production: NX9.0.3.4, NX10.0.2.6
Development: VB.NET (amateur level !)