Calculates
the mass properties of regions or 3D solids.
Access Methods
Menu: Toolbar: Inquiry
Summary
Refer to the Help system for a complete list
of definitions for each of the region or mass properties computed.
List of Prompts
The following prompts
are displayed.
Select objects: Use
an object selection method
If you select multiple regions, only those that
are coplanar with the first selected region are accepted.
MASSPROP displays the mass properties in the
text window, and then asks if you want to write the mass properties
to a text file (.mpr).
The
properties that MASSPROP displays depend on whether the selected objects
are
regions,
and whether the selected regions are coplanar with the XY plane
of the current user coordinate system (UCS), or
solids.
For a list of the parameters that control the MASSPROP units, see
Calculations Based on the Current UCS.
Regions
The following table shows the mass properties that
are displayed for all regions.
Mass properties for all
regions
|
Mass property
|
Description
|
Area
|
The surface area of solids or the enclosed area
of regions.
|
Perimeter
|
The total length of the inside and outside loops
of a region. The perimeter of a solid is not calculated.
|
Bounding box
|
The two coordinates that define the bounding
box. For regions that are coplanar with the XY plane of
the current user coordinate system, the bounding box is defined
by the diagonally opposite corners of a rectangle that encloses
the region. For regions that are not coplanar with the XY plane
of the current UCS, the bounding box is defined by the diagonally
opposite corners of a 3D box that encloses the region.
|
Centroid
|
A 2D or 3D coordinate that is the center of
area for regions. For regions that are coplanar with the XY plane
of the current UCS, this coordinate is a 2D point. For regions that
are not coplanar with the XY plane of the current UCS, this
coordinate is a 3D point.
|
If the regions are coplanar with the XY plane
of the current UCS, the additional properties shown in the following
table are displayed.
Additional mass properties
for coplanar regions
|
Mass property
|
Description
|
Moments of inertia
|
A value used when computing the distributed
loads, such as fluid pressure on a plate, or when calculating the
forces inside a bending or twisting beam. The formula for determining
area moments of inertia is
area_moments_of_inertia = area_of_interest *
radius2 The area moments of inertia has units of distance
to the fourth power.
|
Products of inertia
|
Property used to determine the forces causing
the motion of an object. It is always calculated with respect to
two orthogonal planes. The formula for product of inertia for the YZ plane
and XZ plane is
product_of_inertiaYZ,XZ =
mass * distcentroid_to_YZ * distcentroid_to_XZ This XY value is expressed in mass
units times the length squared.
|
Radii of gyration
|
Another
way of indicating the moments of inertia of a solid. The formula
for the radii of gyration is
gyration_radii = (moments_of_ inertia/body_mass)1/2 Radii of gyration are expressed in distance
units.
|
Principal moments and X,Y,Z directions about
centroid
|
Calculations that are derived from the products
of inertia and that have the same unit values. The moment of inertia
is highest through a certain axis at the centroid of an object.
The moment of inertia is lowest through the second axis that is
normal to the first axis and that also passes through the centroid.
A third value included in the results is somewhere between the high
and low values.
|
Solids
The following table shows the mass properties that
are displayed for solids.
Mass properties for solids
|
Mass property
|
Description
|
Mass
|
The measure of inertia of a body. Because a
density of one is used, mass and volume have the same value.
|
Volume
|
The amount of 3D space that a solid encloses.
|
Bounding box
|
The diagonally opposite corners of a 3D box
that encloses the solid.
|
Centroid
|
A 3D point that is the center of mass for solids.
A solid of uniform density is assumed.
|
Moments of inertia
|
The mass moments of inertia, which is used when
computing the force required to rotate an object about a given axis,
such as a wheel rotating about an axle. The formula for mass moments
of inertia is
mass_moments_of_inertia = object_mass * radiusaxis2 Mass moments of inertia unit is mass (grams
or slugs) times the distance squared.
|
Products of inertia
|
Property used to determine the forces causing
the motion of an object. It is always calculated with respect to
two orthogonal planes. The formula for product of inertia for the YZ plane
and XZ plane is
product_of_inertiaYZ,XZ =
mass * distcentroid_to_YZ * distcentroid_to_XZ This XY value is expressed in mass
units times the length squared.
|
Radii of gyration
|
Another way of indicating the moments of inertia
of a solid. The formula for the radii of gyration is
gyration_radii = (moments_of_inertia/body_mass)1/2 Radii of gyration are expressed in distance
units.
|
Principal moments and X,Y,Z directions about
centroid
|
Calculations that are derived from the products
of inertia and that have the same unit values. The moment of inertia
is highest through a certain axis at the centroid of an object.
The moment of inertia is lowest through the second axis that is
normal to the first axis and that also passes through the centroid.
A third value included in the results is somewhere between the high
and low values.
|
Calculations Based on the
Current UCS
The following table shows the parameters that control
the units in which mass properties are calculated.
Parameters that control
MASSPROP units
|
Parameter
|
Used to calculate
|
DENSITY
|
Mass of solids
|
LENGTH
|
Volume of solids
|
LENGTH*LENGTH
|
Area of regions and surface area of solids
|
LENGTH*LENGTH*LENGTH
|
Bounding box, radii of gyration, centroid, and perimeter
|
DENSITY*LENGTH*LENGTH
|
Moments of inertia, products of inertia, and principal
moments
|
