Biomedical Engineering Reference
In-Depth Information
The occupant restraint system consists of a shoulder belt and a lap belt.
The upper end of the shoulder belt is anchored to the vertical stanchion
that is rigidly fixed to the platform and the lower end is attached to the
platform floor. Both ends of the lap belt are anchored to the platform floor.
Each seat belt is modeled by a chain of line spring segments. The seg-
ments are attached to one another by spherical joints that do not resist their
relative rotation. The springs resist tension but do not resist compression.
Accordingly, if the current length of a segment is less than the length of
the undeformed segment, the spring force is set equal to zero. It is assumed
that the contact between the seat belts and the occupant occurs only at the
joint points of the chain modeling the seat belts. The contact model takes
into account Coulomb's friction between the occupant's body and the seat
belts.
The model takes into account the elastic and damping properties of the
wheelchair wheels when in contact with the platform as well as the fric-
tion between the wheels and the platform floor. In addition, it takes into
account the stiffness of the wheelchair seat cushion and the backrest and
the Coulomb friction between the occupant and the wheelchair seat cushion
and between the occupant's feet and the footrest. The computer model was
validated (Balandin et al, 2008) based on results of crash tests performed
in three laboratories (Kang and Pilkey, 1998).
8.3.2
Goals of Simulation
The MADYMO software is used to simulate the behavior of the system
described in the previous section. The simulation involves the numerical
solution of the system of differential equations governing the behavior of
the dynamic model for a prescribed crash deceleration pulse applied to the
vehicle and appropriate initial conditions, the calculation of the response
criteria of the system, the formation of the output data characterizing the
transient behavior of the system, and the representation of these data in
the graphic or visual form convenient for the analysis and interpretation. The
system of governing equations is generated by MADYMO from the input
data characterizing the topology of the structure, as well as geometrical,
inertial, stiffness, and damping parameters of its components.
The purpose of the simulation is to compare the conventional tiedown
system in which the wheelchair is tied directly to the vehicle body with
the system in which the wheelchair is connected to a platform separated
from the vehicle by a shock isolator. In addition, the effect of pre-action
in the control of the platform on the response criteria of the system will
be discussed. When choosing the control for the platform, the objective is
to reduce the load on the wheelchair and the occupant, provided that the
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