SPINAL INJURY CONTROL - Injury Biomechanics and Control: Optimal Protection from Impact - page 170

to minimize the compression of the cushion, provided that the peak magni-
tude of the spinal compressive force and the seat pan stroke are constrained.
Analytical expressions are obtained for the optimal control force time histo-
ries and the minimum compression of the cushion. The analytical results are
refined by numerical optimization using MADYMO, a multibody modeling
tool, to simulate the response of the occupant to the shock load.

5.1 DESCRIPTION OF THE MODEL

Consider a seated person whose lower torso (including pelvis) is subjected
to a vertical shock load from the seat (Fig. 5.1). This load is transmitted
through the vertebral column to the upper torso, neck, and head, which
may lead to injuries caused by the spinal compression. This is the case,
for instance, for the pilot of a helicopter performing a hard landing with
high vertical velocity or for an aircraft pilot being ejected with his seat.
To reduce the risk of the spinal injury, there is a cushion between the
seat pan and the occupant's lower torso. This cushion plays the role of a
shock isolator. Normally, this isolator is passive, and the force transmitted
to the occupant's lower torso is determined by the elastic and dissipative

m 1

Upper torso

KC

m 2

X 1

Lower tor so

ˆ

F

Cushion

x 2

Seat pan

z

FIGURE 5.1 Spinal injury model for a seated person.