Change 3D solid density or volume without changing the shape

[Anonymous]

Hi All,

I need the different data of 'PrincipalMoments' for a 3D entity with different volume or density.
So I try to change the density or volume, but cannot make it.

Anyone can tell me how can I edit the density of the 3D entity to get current 'PrincipalMoments'?

Thanks,


Regards,
woon

[Anonymous]

wtl07 wrote:

I
need the different data of 'PrincipalMoments' for a 3D entity with
different volume or density.

So I try to change the density or volume, but cannot make it.



Anyone can tell me how can I edit the density of the 3D entity to get
current 'PrincipalMoments'

The moments of inertia (I, Ix, Iy),
section modulus (S), and radii of gyration (r, rx,
ry), of a given shape depend only upon its geometry,
and are independent of its density.



-Bill

[Anonymous]

That depends on which moment of inertia you are using.  I believe autocad calculates the Mass Moment of Inertia, not the Area moment of inertia.  I really don't know, actually trying to figure this out is what led me to here.  It is true that all those numbers are independent of mass for an area moment, but not for a mass moment.

[dgorsman]

Its been a while since Statics and Dynamics... since each object would be of uniform density, wouldn't a density change factor out in the calculations resulting in the same values?

If you are attempting to deal with multiple parts with different densities, or a single part with variable density, or (ugh) multiple parts with variable densities, thats probably best handled with a dedicated mechanical analysis software like Inventor.