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110 Mutibody Systems Approach to Vehicle Dynamics
FUNCTION STEP (x, x 1 , y 1 , x 2 , y 2 )
y
1
(x 2 , y 2 )
0
(x 1 , y 1 )
0 0.5
x
VARVAL (1)
Fig. 3.32
Step function for a bump stop force
J
I
X
Y
Z
Fig. 3.33
Modelling of suspension bushes
another FUNCTION. In this case VARIABLE/1,FUNCTION 50-DZ
(0206,0307,0206) is used to program the deformation of the bump stop.
The value of this, VARVAL(1) is used to define the variable on the x-axis
that is used to step from one state to another. In this the step function is
used to smooth the formulation of the contact force between 0 and 0.5 mm
of bump stop deformation.
Additional functions exist, such as an IMPACT function which might be
used to switch on a contact force or to extend the material model from the
initial linear one used here to a non-linear model. Another consideration
here is that the force formulation takes no account of the possibility that the
solution could find a point where the I marker actually moves through the
bump stop and past the J marker into the vehicle body. Although this makes
no sense physically there is nothing in the formulation to take account of
this and should it happen the force would actually reverse direction leading
to a probable failure of the solution. Clever programming can take this into
account. In addition to improving the material model this could include, for