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Click Measure Inertia
 .
In DMU, you can also select Analyze > Measure Inertia from the
menu bar. The Measure Inertia dialog box appears.
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Click Measure 2D Inertia
 .
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Dialog box options
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A Keep Measure option in the dialog box lets you
keep current and subsequent measures as features. Some measures
kept as features are
associative
and can be
used as parameters.
Note: This option is not available in the
Drafting workbench.
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An
Export
option lets you write results to a text file.
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A Customize... option
lets you define what will be computed and displayed in the dialog
box.
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Click to select a plane 2D surface in the geometry area
or the specification tree. The Dialog
Box expands to display the results for the selected item.
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The dialog box identifies the selected item, in our
case a DMU section, and indicates whether the calculation is exact or
approximate:
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In Design mode, measures access exact data and
wherever possible true values are given. Note that it is possible
to obtain an exact measure for most items in design mode.
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In Visualization mode, measures are made on
tessellated items and approximate values are given.
In addition to the center of gravity G, the principal
moments of inertia M and the
matrix of
inertia, the dialog box also gives the area of the selected item.
The center of gravity G is computed with respect to
the document axis system. The matrix of inertia is expressed in an
axis system whose origin is the center of gravity and whose vectors
are the axes of inertia. |
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Notes:
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The matrix of inertia and the principal moments do
not take density into account.
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You can also compute and display the
principal axes
A. To do so, you must first activate the appropriate option in
the Measure Inertia Customization
dialog box.
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The number of decimal places, the display of trailing
zeros and limits for exponential notation is controlled by the Units
tab in the Options dialog box (Tools > Options,
General > Parameters and Measure).
To find out more about
notations
used |
In the Geometry Area
The axes of inertia are highlighted and a bounding
box parallel to the axes and bounding the selected item also appears.
To obtain the same type of inertia matrix for
similar shapes independent from the space orientation
of the surface being measured (i.e. invariant); the x-axis is set along the
Principal Moment axis with the smallest value (M1), i.e. along the
longest side (red) and the y-axis is set along the second Principal
Moment axis (M2) (green).
Principal Axis matrix (A) expresses the axes orientations in the
Global Axis System.
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Color coding of axes:
The principal axes are invariant within the
object i.e., they are independent from the object's space
orientation.
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When you move the cursor over the geometry or
specification tree, its appearance changes to reflect the measure
command you are in.  |
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Click OK in the Measure Inertia dialog box. If
you checked the Keep Measure option in the Measure Inertia dialog box,
your measures are kept as features.
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You can, at any time, define what will be computed and
displayed in the tabs of the Measure Inertia dialog box.
When measuring 2D plane surfaces, in addition to the
properties computed by default, you can compute and display the
principal axes. |
