part modify rigid_body mass_properties
Allows the modification of mass properties on an existing part.
The mass properties of a part include the mass, mass-inertia tensor, center-of-mass marker, and inertia marker. You may assign zero mass to a part whose six degrees of motion you constrain with respect to parts that do have mass. However, due to the number of changes that you may make to the data set in the course of defining a model, the probability of a later change requiring that the part have mass is high. Consequently, you are encouraged to assign finite (although insignificant) masses and inertias to parts you would otherwise give zero inertial properties. A part without mass cannot have moments of inertia. If you specify the mass and moments of inertia for a part, you must also specify the center-of-mass marker for the part.
Format:
interface menu create |
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part_name = | an existing part |
mass = | mass |
center_of_mass_marker = | an existing marker |
inertia_marker = | an existing marker |
ixx = | inertia |
iyy = | inertia |
izz = | inertia |
ixy = | inertia |
izx = | inertia |
iyz = | inertia |
density = | density |
material_type = | an existing material |
Example:
part modify rigid_body mass_properties & |
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part_name = | part_2 & |
mass = | 20 & |
center_of_mass_marker = | cm & |
inertia_marker = | cm & |
ixx = | 1.8e6 & |
iyy = | 1.8e6 & |
izz = | 1.8e6 & |
ixy = | 0 & |
izx = | 0 & |
iyz = | 0 |
Description:
Parameter | Value Type | Description |
|---|
part_name | A Existing Part | Specifies the name of a rigid body |
mass | Mass | Specifies the part mass |
center_of_mass_marker | An Existing Marker | Specifies the marker to define center of mass |
inertia_marker | An Existing Marker | Specifies the marker that defines the inertia properties of the rigid body |
ixx | Inertia | Specifies the xx component of the mass-inertia tensor |
iyy | Inertia | Specifies the yy component of the mass-inertia tensor |
izz | Inertia | Specifies the zz component of the mass-inertia tensor |
ixy | Inertia | Specifies the xy component of the mass-inertia tensor |
izx | Inertia | Specifies the zx component of the mass-inertia tensor |
iyz | Inertia | Specifies the yz component of the mass-inertia tensor |
density | Density | Specifies the part density |
material_type | An Existing Material | Specifies the material type |
Extended Definition:
1. The part name specifies the part to modify. You use this parameter to identify the existing part to affect with this command. You may identify a part by typing its name or by picking it from the screen. If the part is not visible on the screen, you must type the name. You may also find it convenient to type the name even if the part is displayed.If you created the part by reading an Adams data set or graphics file, the part name is the letters PAR followed by the Adams data set part ID number. The name of Adams PART/101 is PAR101, for example. If you created the part during preprocessing, you gave it a name at that time. If a part is available by default, you may identify it by entering its name only. If it is not, you must enter its full name. To identify a part under another model, for instance, you may need to enter the model name as well. For example, you may specify part 'arm' from model 'robot' by entering ".robot.arm". If you type a "?", Adams View will list the parts available by default. You must separate multiple part names by commas. If the part is visible in one of your views, you may identify it by picking on any of the graphics associated with it. You need not separate multiple part picks by commas.
2. Mass specifies the part mass. If the part has no mass, Adams uses the part LPRF to represent the position and orientation of the part internally. If the part has mass, Adams uses the position of the center-of-mass marker to represent the translational position of the part internally and uses the principal axes of the inertia tensor about the center-of-mass marker to represent the orientation of the part internally. This internal frame of reference is referred to as the part principal axes frame.
3. The center of mass marker specifies the marker that defines the part center of mass and, in the absence of the inertia marker, the axes for the inertia properties. If the part has mass, Adams uses the position of the center-of-mass (CM) marker to represent the translational position of the part internally and uses the principal axes of the inertia tensor about the CM marker to represent the orientation of the part internally. This internal frame of reference is referred to as the part principal axes frame.
4. The inertia marker specifies the marker that defines the axes for the inertia properties. If you do not supply an inertia marker, it defaults to the part center-of-mass marker.
5. The ixx, iyy, izz, ixy, iyz and ixz are the xx, yy, zz, xy, yz and xz components of the mass-inertia tensor, respectively.The mass-inertia tensor as computed about the origin of the inertia marker, and expressed in the coordinates of the inertia marker reference frame. The inertia matrix is defined as follows:
[ Ixx -Ixy -Ixz]
J = [-Ixy Iyy -Iyz]
[-Ixz -Iyz Izz]
It is a symmetrical, positive definite matrix. Compute the individual terms as follows:
Ixx = Integral (y**2 + z**2) dm
Iyy = Integral (x**2 + z**2) dm
Izz = Integral (x**2 + y**2) dm
Ixy = Integral xy dm
Ixz = Integral xz dm
Iyz = Integral yz dm
In the above formulae, x, y, and z are the components of the displacement of an infinitesimal mass particle of mass dm, measured from the origin of the inertia marker in the reference frame of the inertia marker. The integral is performed over the entire mass of the body. If you do not specify the inertia marker, then it defaults to the center-of-mass marker. In that case, you compute these quantities about the origin of the center-of-mass marker in the reference frame of the center-of-mass marker.
6. Density specifies the part density and that the mass properties of the part are to be automatically calculated. The calculated mass properties are based upon the solid geometry that belongs to the part.
7. The material type specifies the part material_type and that the mass properties of the part are to be automatically calculated. The calculated mass properties are based upon the solid geometry that belongs to the part.