4569846498

Multibody systems simulation software 81
01
Z n
GROUND
LPRF
Z G
O n
Y n
{QG} 1
GRF
X n
Part n
X
O 1
G Y G
{QP} n
Y m
Marker m
MRF
O m
Z m
X m
Fig. 3.4
Relative position definition of the LPRF and MRF
01
GROUND
ZG
{QP} 1
Y m
Marker m
X m
MRF
O m
Z m
XG
GRF
O 1
YG
Part n
Fig. 3.5
Relative position definition of the MRF in the absence of the LPRF
co-ordinates of a point, such as the end of a spring, where a local definition
of the orientation is not important. In other instances the orientation of the
marker does require definition. An example of this would be the definition of
revolute joints for which the axis of rotation must be specified. A marker
has therefore an associated reference frame, the Marker Reference Frame
(MRF), and is defined relative to the local part reference frame.
The relationship between the three reference frames, in terms of position,
is illustrated in Figure 3.4. The position of the local part reference frame O n
for any body, in this case part n, is defined using, in MSC.ADAMS terminology,
a position vector {QG} 1 . The position of any markers belonging to
part n, for example marker m with marker reference frame O m , is defined
relative to O n , using a relative position vector {QP} n . Note that the x, y and
z components of {QP} n are resolved parallel to O n .
As mentioned earlier the definition of the local part reference frame is
optional and if omitted the local part reference frame is taken to be coincident
with and parallel to the ground reference frame when setting up the
model. The position of the marker reference frame O m is then defined relative
to the ground reference frame by the position vector {QP} 1 as illustrated
in Figure 3.5. Note that the x, y and z components of {QP} 1 are now
resolved parallel to the ground reference frame O 1 .
There are a number of different methods by which the orientation of one
reference frame to another may be established when defining a model.