Biomedical Engineering Reference
In-Depth Information
the impact velocity of the base. This situation provides a simplified model
for a vehicle in a crash. The base can be identified with the vehicle and the
object is identified with an occupant to be protected from injuries.
Let the impact velocity,
V
, and the maximum acceleration allowed for
the object,
U
,bedefinedas
100 m/s
2
.
V
=
10 m/s
,
U
=
(3.173)
These data correspond approximately to the input data for the design of an
isolation system for a helicopter seat to prevent the pilot from severe spinal
injuries in the case of a hard or crash landing.
The absolute minimum of the peak magnitude of the relative displace-
ment of the object that can be achieved by the isolator without pre-action
is defined by Eq. (3.39) and is given by
V
2
2
U
=
J(u
0
)
=
50 cm
.
(3.174)
This quantity for the pre-acting isolator, in accordance with Eq. (3.149), is
V
2
16
U
=
J
1
(u
0
,t
∗
0
)
=
6
.
25 cm
.
(3.175)
From Eq. (3.95), the minimum value of the displacement's peak magnitude
that can be provided by a linear (
n
=
1) spring without pre-action is
V
2
U
=
J
1
(k
0
)
=
100 cm
,
(3.176)
and the corresponding value for the spring that has been cocked and
then released, thereby implementing the pre-action concept, according to
Eq. (3.172), is
V
2
4
U
=
J
1
(a
0
,k
0
,t
∗
0
)
=
25 cm
.
(3.177)
The minimum pre-action time of the isolator providing the limiting per-
formance characteristic is determined by Eq. (3.150) and for the input data
of Eq. (3.173) is
V
U
=
t
∗
0
=
0
.
1s
.
(3.178)
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