Optimization Potential of the Method - Preventive Biomechanics - page 330

Fig. 7.54 a Initial non-optimized seat geometry in the transversal plane and b deformed state at

static equilibrium during mechanical interaction with male model E-BCSS-3 exhibiting

maximum compressive stress underneath the ischial tuberosity

Furthermore, optimized support shapes, derived in the previous sections, are
based on the particular conditions of the employed lower leg model, i.e. pre-
dominantly defined body weight, anatomy of the buttocks and tissue material
parameters. It is most likely that different cushion shapes result from the optimi-
zation process when varying any of these parameters. An approach towards a
general cushion shape, if existent, may require considering all of this information.

7.3 Shape Optimization of a Car Seat

Car seat 'B' was employed for the mechanical interaction simulations between
'E-BCSS-3' (male model) or 'E-BCSS-4'' (female model) and the seat, Sect.
6.3.4.1 . Topology optimization simulation followed the guidelines provided in
Sect. 7.2.3 . The optimization criteria aimed to minimize the direct tissue stress
component S 22 (i.e. the vertical stress component in the direction of gravitational
loading) at the bone surface of the ischial tuberosity, where interaction simulation
indicated maximum values. The optimization was performed using plane-strain
models of the initial seat cushion design shape in two planes. The transversal and
sagittal plane intersected at the point and line, respectively, situated at the location
of maximum stress S 22 . The upper (seat contact) surface was iteratively altered for
both models by the optimization routine, until the tissue stress S 22 in the desired
region was minimized.
Note: The plain strain abstraction (of the continuum lower body model) in
A BAQUS requires modeling in the 1-2-plane. Due to this requirement, the 1 and 3-
direction of the respective coordinate systems in Figs. 7.54 and 7.55 and Figs. 7.57
and 7.58 permute in transversal and sagittal modeling. The stress values derived
from both configurations refer to the permuted coordinate system axes and should
not be confused. The indices of the respective stress components must be changed