Biomedical Engineering Reference
In-Depth Information
120
100
80
60
40
100G/s
150G/s
300G/s
20
0
0.00
0.05
0.10
Time (s)
0.15
0.20
FIgure 18.17
Effect of various onset rates of impact loading on the maximum stress on the thoracolumbar
spine.
The effect of the angle (θ) between the direction of ejection and the back of the seat on the
dynamic response of the thoracolumbar spine can also be investigated. When the ejection line is
parallel to the seat back, θ is 0°. If the direction of ejection causes the spine to flex, θ will be positive,
whereas θ will be negative if the direction of ejection leads the spine to a state of extension. From
the simulation results, it was found that a negative value of θ resulted in a greater degree of lumbar
lordosis and generated high pressure in the nucleus pulpous in each segment of the spine.
Two popular approaches to investigate the effect of a dynamic environment on pilots are mul-
tibody techniques and finite element techniques. Both approaches offer specific advantages and
disadvantages. Multibody techniques are attractive for simulating dummy segment motions and
complex joint behavior with low computational expense. Finite element techniques allow the calcu-
lation of local deformations in dummy segments and more detailed and more accurate mechanical
information can be obtained. However, detailed finite element models require excessive computing
power. Moreover, in constructing these models, the choice of materials, mesh of the medium, and
technique for the numerical calculations tends to be rather complex. Hence, constructing models
and running analyses using finite element techniques is a time-consuming process.
With the advent of super agile aircraft having significant maneuverability, the overall G environ-
ment experienced by the pilot during flight and ejection is becoming ever more severe. A compre-
hensive study on the dynamic response of pilots in this complicated environment may be essential
and beneficial for understanding how to protect the body from injury. With rapid advances in recent
years, numerical simulation has become widely used for analyzing the dynamic response of the
human body in impact situations. Information about displacement, velocity, and acceleration of
the body can be obtained, and the joint reaction force and restraint tension can be predicted using
multibody dynamics. Multibody techniques are more suitable for simulating dynamic situations
in which loading is applied over a prolonged period (such as several seconds) since this approach
requires less computing power. However, by using multibody dynamics methods, it is difficult to
know where and when the injury will take place under the impact conditions because detailed
internal mechanical information on the body cannot be obtained. Furthermore, finite element mod-
els can be used to investigate injury to soft tissue, which is usually accompanied by bone fracture
during impact.
Since both multibody dynamics and finite element methods have different advantages and disad-
vantages when dealing with dynamic problems, a combination of these two methods will be helpful
for studying the spine in aviation applications. As used in this study, the integration of the influence
of the belt on the pilot evaluated by a multibody dynamics model to a finite element model can per-
mit more accurate analyses of the dynamic response of the spine following impact loading.
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