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112 Mutibody Systems Approach to Vehicle Dynamics
Bush without voids
X
XP
Bush with voids
Y
ZP
Y
ZP
Fig. 3.34
Orientation of bush axis system
the axis of the bush. For the bush with voids the radial stiffness will require
definition in both the x and y directions as shown.
An example of the command used to define a massless bush with linear
stiffness and damping properties is:
BUSH/03,I0203,J0503,
,K7825,7825,944,KT2.5E6,2.5E6,944
,C35,35,480,CT61E3,61E3,40
It is also possible to extend the definition of bushes from linear to non-linear.
Examples of this will be given in the next chapter. The most advanced
examples of the modelling of force elements extend to the incorporation of
finite element type representations of beams and flexible bodies into the
multibody systems model. In modelling a vehicle the most likely use of a
beam type element is going to be in modelling the roll bars or possibly if considered
relevant an appropriate suspension member such as a tie rod.
The beam element in MSC.ADAMS requires the definition of an I marker
on one body and a J marker on another body to represent the ends of the
beam with length L as shown in Figure 3.35. The beam element transmits
forces and moments between the two markers, has a constant cross-section
and obeys Timoshenko beam theory.
The beam centroidal axis is defined by the x-axis of the J marker and when
the beam is in an undeflected state, the I marker lies on the x-axis of the J
marker and has the same orientation. The forces and moments shown in
Figure 3.35 are:
Axial forces F Ix and F Jx
Shear forces F Iy , F Iz , F Jy and F Jz
Twisting moments M Ix and M Jx
Bending moments M Iy , M Iz , M Iy and M Jz