New finite element human models representing elderly, disabled and overweight people for aircraft seat comfort simulation
Résumé
In the growing but highly competitive market of the airline industry, airliners have to
differentiate themselves from their competitors while increasing or maintaining their
profitability. They request innovations in aircraft interior design to increase aircraft
capacity, reduce airplane turn time through fast boarding and unloading operations,
improve passenger comfort and living space, lighten aircrafts and meet safety
requirements. So many necessary yet conflicting expectations, which make aircraft
interior and seat design very challenging. In this context, it is easier to only manage
average standard passenger population in product development phase. But
morphology of passengers is evolving, as our population ages and increases in size
and weight. More and more elderly people travel, and the senior market cannot be
neglected by airliners. Regulations prevent also discrimination and airliners must now
cater to all types of passengers, whatever their age, weight or disability.
While standard passengers can board an airplane, walk in the cabin and sit without
difficulties, overweight, age and disability are usually associated with lower mobility,
which raises difficulties and lowers the air travel experience. If seat access is one
certain issue, seat comfort is somehow more important, especially for long range
flight. The more severe is the impairment or the higher is the weight, the least is the
satisfaction for the aircraft seat. That highlights the need for adapted design of
aircraft seat for overweighted, senior passengers as well as the ones with severe
mobility impairment, such as passengers that rely on permanent seating posture.
Such design investigation, fitting to these populations, is not easy, request lots of
difficult experimental tests with large group of volunteers. One alternative solution is
the use of digital human model, more specifically finite element models, representing
all these different populations, during the conception and development phases of
aircraft seat.
The present paper will describe the development methodology of new finite human
models, adapted to non-standard population of passengers, such as elderly,
overweighted and disabled people. These models have been developed starting from
an existing human model representing standard aircraft population as reference
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model, and based on literature review. These models have been then used in seating
simulations for the evaluation of aircraft seat comfort and comparison for different
postures.
For severe mobility impairment passengers, there is a need of accurate figures for
morphometric modification on the lower limb and lower trunk, as those segments may
not be fully functional and are the most stressed segments during sitting. In order to
identify morphometric modifications induced by permanent sitting posture,
methodologies and methods of the reviewed process are presented and focused on
permanent wheelchair users. Proposed modifications concern mainly bone, muscle,
fat, and skin tissues. The most of those changes are applied to the reference finite
element human model at pelvis region and lower extremities. That consists of the
adaptation of muscle and fat distribution as well as the modification of radius of
ischial apex curvature. Then, bony properties of these segments are updated.
For the senior and overweighted human models, an equivalent modification process
has been applied for the whole body, based on the available data and specificities of
the reference model. It concerns the adaptation of morphology as well as muscle and
fat distribution. For the senior model, bone properties are also modified.
Seating simulations have been then performed with these dedicated models to
evaluate their capabilities to highlight comfort problems encountered by these
passenger population with respect to the reference standard passenger population.
Three different postures, taxi, take-off and landing, inclined and relaxed ones, have
been evaluated and compared.