Measure bodies

[vja]

Hello everyone
I am use analysis--measure bodies to get center of mass of a tapered body.
Its a multibody part.

In the information file,it gives me the values and error estimates.
The error estimates values are in thousands which made me approach this forum...

============================================================

Date : 4/13/2012 9:47:54 AM

============================================================
Measurement Mass Properties

Displayed Mass Property Values
Volume = 67858.10989569816 in^3
Area = 229256.34693012343 in^2
Mass = 19197.05928949301 lbm
Weight = 19197.05928949301 lbf
Radius of Gyration = 268.23425597988 in
Centroid = 0.00000006766, 409.14083502539, 5.08644062443 in

============================================================
Detailed Mass Properties
Analysis calculated using accuracy of 0.99000000000
Information Units lbm - in

Density = 0.28290000000
Volume = 67858.10989569816
Area = 229256.34693012343
Mass = 19197.05928949301

First Moments
Mx, My, Mz = 0.00129887103, 7854300.86773500030, 97644.70223961631

Center of Mass
Xcbar, Ycbar, Zcbar = 0.00000006766, 409.14083502539, 5.08644062443

Moments of Inertia (WCS)
Ix, Iy, Iz = 4594076121.81324480000, 4728866.71545003540, 4591660862.09269330000

Moments of Inertia (Centroidal)
Ixc, Iyc, Izc = 1380064242.26730700000, 4232202.73521834610, 1378145646.52698730000

Moments of Inertia (Spherical)
I = 1381221045.76475620000

Products of Inertia (WCS)
Iyz, Ixz, Ixy = 57074532.32435357600, 0.37765596938, 0.46118485916

Products of Inertia (Centroidal)
Iyzc, Ixzc, Ixyc = 17124097.31423184600, 0.37104933899, -0.07023632060

Radii of Gyration (WCS)
Rx, Ry, Rz = 489.19469685695, 15.69499507060, 489.06608693092

Radii of Gyration (Centroidal)
Rxc, Ryc, Rzc = 268.12190635878, 14.84792888050, 267.93546704505

Radii of Gyration (Spherical)
R = 268.23425597988

Principal Axes (Direction vectors relative to the WCS)
Xp(X), Xp(Y), Xp(Z) = 1.00000000000, 0.00000000277, -0.00000021808
Yp(X), Yp(Y), Yp(Z) = 0.00000021810, -0.01246083498, 0.99992236078
Zp(X), Zp(Y), Zp(Z) = 0.00000000005, -0.99992236078, -0.01246083498

Principal Moments
I1, I2, I3 = 1380064242.26730700000, 1378359043.64586830000, 4018805.61633741950

============================================================
Error Estimates

Volume = 37.47378610535
Area = 1.70501403591
Mass = 10.60133408920
Moments of Inertia (Spherical) = 0.45207876192
Center of Mass = 8683.37543481869, 13020.81411574129, 8737.29849048585
Moments of Inertia (WCS) = 29544060.32917690300, 20663990.09437890400, 29455451.10679721800
Products of Inertia (WCS) = 17010880.68397417700, 16944651.08697374900, 20519436.68664599600


Anyhow I will be using the cg values in my calculations.
Your help is appreciated.
thanks

 

[JohnRBaker]

What version of the software are you using and could you at least provide a 'picture' of what this model looks like?

Since these numbers appear quite large (almost 10 tons and 1600 square feet in area) I have to ask, how far away from absolute zero (XYZ) is the farthest point on the model?

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA

http://www.siemens.com/plm

UG/NX Museum:

http://www.plmworld.org/p/cm/ld/fid=209

To an Engineer, the glass is twice as big as it needs to be.

 

[vja]

sorry abt that...
nx7.5

 

[vja]

its about 80ft long....this model is a combination of sheetmetal and solid body....

 

[vja]

here is a sample tapered model.

I guess there is a problem finding CG in NX for Large models in sheetmetal.

 

[vja]

or even the short models with tapered section....

 

[JohnRBaker]

I've opened a PR. If and when I get some information about this I'll try and post what I've learned.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA

http://www.siemens.com/plm

UG/NX Museum:

http://www.plmworld.org/p/cm/ld/fid=209

To an Engineer, the glass is twice as big as it needs to be.

 

[vja]

thank you john

 

[JohnRBaker]

OK, we've figured out what the problem is.

Actually the values are correct, it's just that they're labeled incorrectly. Once you know what these numbers really represent, their magnitude is actually quite reasonable.

There's no problem with the labeling of the actual measurement results only with some of the 'Error Estimates'. Taking the example results from your original post and applying the correct label, would have now looked like this (corrected labels are in Italics):

============================================================
Error Estimates

Volume = 37.47378610535
Area = 1.70501403591
Mass = 10.60133408920
Radii of Gyration (Spherical) = 0.45207876192
Moments of Inertia (Centroidal) = 8683.37543481869, 13020.81411574129, 8737.29849048585
Moments of Inertia (WCS) = 29544060.32917690300, 20663990.09437890400, 29455451.10679721800
Principal Moments = 17010880.68397417700, 16944651.08697374900, 20519436.68664599600

The status fo the actual software fix will be the next full release of NX, which is planned for later in the year (and which beta testing started this past Monday).

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA

http://www.siemens.com/plm

UG/NX Museum:

http://www.plmworld.org/p/cm/ld/fid=209

To an Engineer, the glass is twice as big as it needs to be.

 

[vja]

got it

so i need to read error in th mass as error in the inertia...yes it males sense....its like .2% error...
thanks john

 

[cowski]

Seems like an important thing to get right, will the fix be included in MR's for current releases or only in the next full release?

http://www.nxjournaling.com

 

[JohnRBaker]

Unfortunately no. And while it looks easy to do, and it is, to a point, it runs into another issue which has nothing to do with Measure Body or even the modeling software in general, but rather with the user interface.

Some of you may not be aware of this but we provide the option to 'localize' (i.e. Translate) the content of the NX dialogs, menus AND listing windows so that we can offer NX in several different versions based on the language of the user. Currently we support 10 languages, in addition to English.

However, the scheme that we use to do this, which BTW is done 'on-the-fly' (even the English version of NX is 'translated' from ALL 'UPPERCASE' to the 'Mixed-Case' that you see when running NX), requires that we know upfront all of the unique words and phrases used in NX so that we can then have the experts create the necessary 'look-up' files where NX will find the properly 'translated' words and phrases in whatever language was chosen when the software was installed or NX was told to run in. The original 'source' files which are referenced are not allowed to be changed once a version of NX has been released. This is why some PR's have to wait until the next release because it required changing the text found in some Dialog, Menu or, as in this case, the Listing Window. Even planned enhancements which went into say NX 8.0.1.x or is going into NX 8.0.2.x, we had to know ahead of time all of the unique words and phrases which these enhancements will introduce into NX so that we can release a reference file with NX 8.0.0.x which will not need to be maintained, 11 times over. And the real kicker is that we allow customers to edit these files if they wish to tweak them or to accommodate them running say an NX Open program, with it's own unique menus and dialogs, written by a multinational company who then wants their employees in different countries to use the same software but running in their local languages. So you can see if we were to change these 'translation files' with ever MR or MP that we sent out, how this could put quite a burden on some of our largest customers, to say nothing of the many small companies in places like Mexico, Brazil, China, etc which is using NX in a local language.

Anyway, I hope that explains why we can only 'fix' this in the next full release of NX, which will be available later this year.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA

http://www.siemens.com/plm

UG/NX Museum:

http://www.plmworld.org/p/cm/ld/fid=209

To an Engineer, the glass is twice as big as it needs to be.