Biomedical Engineering Reference
In-Depth Information
where
F
z
and
M
y
are the axial force and the bending moment measured
by the upper neck load cell of a dummy, respectively;
F
zc
and
M
yc
are the
critical values for these quantities. The axial force can be tensile (
i
=
T
)or
compressive (
i
C
). The critical value
F
zc
is equal to 4170 N for tension
and 4000 N for compression. The bending moment can cause flexure (
j
=
=
F
) or extension (
j
=
E
). The critical value
M
yc
for this moment is equal
·
·
to 310 N
m for extension. The quantity
J
11
must
not exceed unity at any instant during the crash event.
Criteria
J
12
and
J
13
are the peak values of the tensile and compressive
forces, respectively, measured by the upper neck load cell of the dummy.
The value of
J
12
must not exceed 4170 N and the value of
J
13
must not
exceed 4000 N.
Criterion
J
14
is the maximum magnitude of the force developed in a
rear strap of the wheelchair tiedown system. There are two rear straps, but
the one in which the force is larger is used to calculate
J
14
. This measure
characterizes the load on the wheelchair in a crash.
m for flexure and 135 N
8.3.4
Simulation Technique
The simulation involves the solution of the differential equations governing
the motion of the system, the calculation of the response criteria
J
2
to
J
14
,
and the graphical representation of the motion of the wheelchair and the
occupant relative to the platform (Fig. 8.4). The absolute acceleration of
the platform is prescribed. For the system without a platform, the platform
is identified with the vehicle and, hence, the time history of its acceleration
coincides with that of the crash pulse. For the isolated platform, the accel-
eration is prescribed by the solution of the optimal control problems for a
single-degree-of-freedom system in Section 8.2. The equations of motion
are subject to zero initial conditions at the time when the motion of the
platform starts. This implies that until the acceleration has been applied to
the platform, the platform, the wheelchair, and the occupant do not move
relative to the vehicle, the vehicle moves at constant speed
v
0
,andthe
wheelchair and the occupant are in a state of equilibrium relative to the
platform.
8.3.5
Input Data
For the impact velocity
v
0
, the crash pulse duration
T
, the crash deceleration
amplitude
a
, and the maximum rattlespace
D
allowed for the platform
relative to the vehicle use the data of Eqs. (8.10) - (8.12).
In the MADYMO simulation of the behavior of the wheelchair and the
occupant, the platform plays the role of the base and the wheelchair-seated
occupant the role of the object to be protected. The system without a
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