In a multibody system, a rigid body is an ideal representation of solid body/part of
fixed size and shape in which deformation is insignificant or neglected, or in other words,
the distance between any two points of a rigid body remains unchanged (irrespective of the
external forces acting on it). A rigid body will have six degrees of freedom (DOF) and
therefore every additional rigid body in a multibody system adds an additional six DOF to
the system.
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If the Bodies panel is not currently displayed, select the desired body by
clicking on it in the Project Browser or in the modeling window.
The Bodies panel is automatically displayed.
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Select the Properties tab and specify the mass and
inertia properties of the body by entering in the values in the appropriate
fields.
Note: If the selected body is a pair entity, first distinguish between the
Left and Right tabs in the
panel, and then edit the properties.
Tip:
- Check Flex Body (CMS) to convert a rigid body
definition to a flexible/deformable body.
- Check Symmetric properties to make the body
properties symmetric. Once this option is activated, MotionView will ask you which side of the
values of the pair entity (Left or Right) is to be used. Selecting
any one side will make values of that side as “leader” and the
values of the other side will gray out and follow the values on the
leader side.
- Check Get Properties from associated Graphics
to get the mass and inertia properties from the graphic associated
with the body. Activating this option will deactivate the Mass and
Inertia properties fields, and the CM Coordinates and Inertia
Coordsys tabs.
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Click the CM Coordinates tab.
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Click the Use center of mass coordinate system check box
to select a point as the origin of center of mass for the body.
Note: If a center of mass coordinate system is not specified, HyperWorks assumes that it coincides with the global frame of
the model.
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Click the Point collector and select the appropriate
center of mass point from the modeling window, or
double-click Point to display the Model Tree (from which the desired point can be
selected).
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Use the orientation options to orient the
coordinate system.
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Following the same steps as the center of mass, specify
the inertia coordinate system and the body coordinate system by using the
Inertia Coordsys and Body
Coordsys tabs respectively.
Note: The inertia coordinate system is the reference frame with respect to which
the inertia properties of the body are specified. If a unique inertia
coordinate system is not specified, then the specified moment of inertia
values are assumed to be defined about the center of mass marker. If a
unique body coordinate system is not specified, then it is assumed to be at
the global reference frame. This is valid for both single and pair body
types.
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Define initial conditions.
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Click the Initial Conditions tab on the
panel.
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Activate the desired check boxes and enter values for translational and
rotational velocity.
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Select a marker for VM and WM.
The translational initial conditions for a body are assumed to be with
respect to the global reference frame in absence of a unique VM (linear
velocity reference marker), and the rotational initial conditionals are
applied about the center of mass marker in absence of a unique WM
(angular velocity reference marker).
Note:
- The inertia values are specified with regard to the inertia coordinate
system.
- MotionView does not check for the physical
correctness of the properties entered in the field (for example: I1 +I2 >=
I3 where I1, I2, and I3 are the principal moment of inertia of the
body).
- Specifying symmetric properties makes both pairs have the same values.
Verify the correctness of data by considering the orientation of the Inertia
coordinate system.
- When the Get Properties from associated Graphic(s) option is activated:
- The property values (mass, inertia, and CM origin) are obtained from
the following type of graphics: cylinder (both ends capped), box,
sphere and CADGraphic. File Graphics (H3D) is currently not
supported.
- The CM marker orientation is aligned with Global Frame. The Inertia
coordinate system is deactivated, which means that the inertia
properties displayed are with respect to the CM marker.