Polar Moment of Inertia?

[davehaigh]

Is there a way to get the Polar Moment of Inertia from the Mass Properties output?

MASS PROPERTIES OF THE PART PRT0001

VOLUME = 3.0630528e+01 INCH^3
SURFACE AREA = 1.0210176e+02 INCH^2
DENSITY = 1.0000000e+00 POUND / INCH^3
MASS = 3.0630528e+01 POUND

CENTER OF GRAVITY with respect to _PRT0001 coordinate frame:
X Y Z 0.0000000e+00 5.0000000e-01 0.0000000e+00 INCH

INERTIA with respect to _PRT0001 coordinate frame: (POUND * INCH^2)

INERTIA TENSOR:
Ixx Ixy Ixz 1.8059245e+02 0.0000000e+00 1.1941113e-04
Iyx Iyy Iyz 0.0000000e+00 3.4076463e+02 0.0000000e+00
Izx Izy Izz 1.1941113e-04 0.0000000e+00 1.8059253e+02

INERTIA at CENTER OF GRAVITY with respect to _PRT0001 coordinate frame:
(POUND * INCH^2)
INERTIA TENSOR:
Ixx Ixy Ixz 1.7293482e+02 0.0000000e+00 1.1941113e-04
Iyx Iyy Iyz 0.0000000e+00 3.4076463e+02 0.0000000e+00
Izx Izy Izz 1.1941113e-04 0.0000000e+00 1.7293490e+02

PRINCIPAL MOMENTS OF INERTIA: (POUND * INCH^2)
I1 I2 I3 1.7293473e+02 1.7293498e+02 3.4076463e+02

ROTATION MATRIX from _PRT0001 orientation to PRINCIPAL AXES:
0.00000 1.00000 0.00000
0.00000 0.00000 1.00000
1.00000 0.00000 0.00000

ROTATION ANGLES from _PRT0001 orientation to PRINCIPAL AXES (degrees):
angles about x y z -90.000 0.000 -90.000

RADII OF GYRATION with respect to PRINCIPAL AXES:
R1 R2 R3 2.3760954e+00 2.3760971e+00 3.3354160e+00 INCH

David Haigh
Phone: 925-424-3931
Fax: 925-423-7496
Lawrence Livermore National Lab
7000 East Ave, L-362
Livermore, CA 94550

[RodGiles]

David,

Polar moment of inertia is just the inertia of the object about its constrained axis. Looking at your values I would guess that the part is a thick disc. If the part is rotating about the Y axis, then the polar moment of inertia is 340.76463 lb-in^2. If the axis of rotation isn't about one of the _PRT0001 csys axes, then make a new csys and measure relative to that csys.

Sometimes the polar moment of inertia refers to the maximum moment of inertia. If this is what you want, just take the I3 value, which happens to be the same as the inertia about the y-axis for this case. The rotation matrix will give the directions of the principal axes of inertia, row 1 = Max. Prin. Inertia, row2= Mid Prin. Inertia & row3= Min. Prin. Inertia.

Regards,

Rod

Rod Giles
Senior Design Engineer

[cid:235285807@17082010-0DDF]

[jnanesh.sajjan]

Hi,



If you are looking for polar moment of inertia at a section, you can do
by Model Analysis --> X-Section Mass props







And, then selecting required plane of section:







Cheers,

Jnanesha KS

[AndreasRingler]

Ip=(Ixx+Iyy+Izz)/2

for the origin of the coordinate system.