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Multibody systems simulation software 85
3.2.3 Basic model components
When developing the data set for a model in a multibody systems analysis
program such as MSC.ADAMS the following can be considered to be basic
model components:
(i) Rigid bodies (parts)
(ii) Geometry (markers)
(iii) Constraints (joints, gears, couplers, …)
(iv) Forces (applied, spring forces, damping forces, …)
(v) User-defined algebraic and differential equations
3.2.4 Parts and markers
An example of a marker statement used to define the position and orientation
of a geometric point on a part is given below.
MARKER/0200,PART02,QP103.0,57.5,247.2,REU90D,90D,0D
In this example marker 0200 is defined to belong to part 02 and to be located
relative to the local part reference frame of part 02 by the co-ordinates
specified through the QP argument. The orientation of the axes of marker
0200 relative to the local part reference frame is specified by the Euler
angle rotations, in degrees, specified by the REU argument.
The part statement can be used to define any rigid body or lumped mass. For a
vehicle suspension system components such as the control arms and wheel
knuckle would typically be modelled as rigid bodies. The type of analysis
being performed will dictate the amount of data that must be defined for the
body. For a dynamic analysis a full definition will be required to include the
mass, centre of mass position, the mass moments of inertia, the orientation of
the axes about which the mass moments of inertia are measured and any initial
translational and angular velocities to be applied to the body. As mentioned
earlier it is also possible to define a local part reference frame to which any
markers belonging to the part can be referenced. Every input deck will also
include a ground part. The following are two examples of a part statement:
PART/01,GROUND
PART/02,MASS10.5,CM0200,IP3.8E3,0.02E3,3.8E3,
VX25000,WZ90.2
The first of these defines the ground part. Using the system of units used
throughout this text the second statement defines a part with a mass of
10.5 kg with a mass centre located at the position of marker 0200. The IP
argument specifies three sequential mass moments of inertia, these being the
mass moments of inertia in kg mm 2 about the x-axis, y-axis and z-axis. It is
possible to specify another marker belonging to the part about which these
are measured but in the absence of this the mass moments of inertia are
taken to be measured about the axes of marker 0200 defining the centre of
mass. Since the definition does not continue to include the cross product
moments of inertia it follows that the orientation of the centre of mass marker
0200 is aligned with the principal axes of the body. In this case the part has
also been given a translational velocity of 25 000 mm/s. This is measured
parallel to the axes of the ground reference frame. In this case the body is