Biomedical Engineering Reference
In-Depth Information
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FIgure 18.6
Acceleration of the human body in a Herbst maneuver.
The model introduced above was developed for analyzing pilot cervical spine injuries under mul-
tiaxial sustained loading during flight maneuvers. Figure 18.6 shows the flight simulation result of
pilot load under Herbst maneuver, the period of which is much longer (20 s) than the validation case
(0.3 s). Thus, calculating efficiency was an important factor for using this model under sustained
loading, and then a high-quality mesh with fewer elements was used. Moreover, the calculation
algorithm should be optimized for reducing the computation time in future work. This model can
also be used in other applications, such as in injury analysis of a pilot's head and neck during ejec-
tion and landing.
18.3
FInIte element model oF the thoraColumbar-PelvIS ComPlex
18.3.1 d
eVelopment
of
tHe
m
odel
To establish the finite element model, the geometry of the vertebrae and pelvis was obtained from
reconstruction of CT scans of a healthy male subject of height 174 cm and weight 75 kg. The ver-
tebrae were made up of post elements and the vertebral body consisted of a bony endplate, cortical
wall, and cancellous bone. The thickness of the endplate and cortex of the bone were assumed to be
0.35 mm (Silva et al., 1994). All these components were meshed in the finite element pre-processor
(Hypermesh 11.0; Altair Engineering Corp, Michigan, USA). The endplate and cortical bone could
be generated easily using element offset from a layer of shell elements. The post elements were
divided into blocks and a source surface was chosen to first mesh into shell elements, then the solid
map tool was used to drag the shell elements from block to block for building solid elements. All the
components of the vertebrae were meshed as eight-node brick elements. A detailed model of the
vertebrae (L2) is shown in Figure 18.7.
As in many previous investigations of the spine using finite element methods, the intervertebral
disc comprised the nucleus pulposus and fiber-reinforced annulus ground substance with a propor-
tion according to histological findings (44% nucleus, 56% annulus) (Schmidt et al., 2007). The
nucleus pulposus and ground substance used solid elements, as with the vertebrae, and the fibers
were modeled as three-dimensional cable elements that sustained only tension. Eight crisscross
fibrous layers were defined in the radial direction and were oriented at an average angle of ±30° to
the endplates. The disc structure is shown in Figure 18.7.
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