Seeking to quench airliners’ unending thirst for lightweight, reliable and more
comfortable seating solutions, designers are developing a new generation of
slim economy – class seats. Challenge in front of the designers is to carve out
additional “living space”, as well as to give a “lie – flat” experience to air
travellers with strict adherence to safety regulations. Present research tries to
address all these industry needs through an innovative and novel “Sleep Seat”.
A generous angle of recline (40 degree), movement of “Seat Pan” along the
gradient, fixed outer shell of backrest, and unique single “Forward Beam”
design distinguishes “Sleep Seat” form current generation seats. It is an ultralightweight
design weighing 8kg (typical seat weight is 11kg). It satisfies
“Generic Requirements (GR2)” which ensures “Comfort in Air”. It will be a “16g”
seat, means it can sustain the “Emergency landing” loads as specified by
“Certification Specifications (CS 25.561 and CS 25.562)”. For present research,
only CS 25.561 has been considered.
Since, the design of “Sleep Seat” is still in its conceptual phase, it is not
possible to build the prototypes and their physical testing, due to costs and time
involved. “Finite Element Analysis (FEA)” is a useful tool to predict the
response of the structure when subjected to real life loads. Hence, the aim of
research being undertaken is to develop a detailed FE model of the complete
seat structure, which will help designers to identify potential weak areas and to
compare different design concepts virtually, thereby reducing the development
cycle time.
In order to avoid handling of large number of design variables; major load
carrying members (called Primary Load Path) i.e. Forward beam and leg; are
designed for the most critical “Forward 9g” loads; using FEA results as a basis.
A robust framework to verify the FEA results is developed. “Sequential Model
Development Approach”; which builds the final, detailed FE model starting from
preliminary model (by continuously updating the FE model by addition of details
that are backed up by pilot studies); resulted in a FE model which could predict the stress induced in each of the components for applied CS 25.561 loads
along with “Seat Interface Loads”. The “Interface Load” is the force exerted by
the seat design on the floor and is one of the main contributing factors in seat
design.
“Optistruct” is used as a solver for linear static FEA, whereas “Abaqus /
Standard” is used for non-linear FEA. Stepwise methodologies for mesh
sensitivity study, modelling of bolt-preload, representing bolted joint in FEA,
preventing rigid body motion, and obtaining a converged solution for non-linear
FEA are developed during this research.
Free-Shape Optimisation is used to arrive at a final design of Seat-leg. All the
findings and steps taken during this are well documented in this report. Finally,
a detailed FE model (involving all the three non-linearities : Contact, material
and geometric) of the complete seat structure was analysed for the loads taken
from CS 25.561, and it was found that design of “Forward beam” and leg are
safe against CS 25.561.
Therefore, all the aims and objectives outlined for this research were
accomplished. For future work, first area to look for, would be validation of
present FEA results by experimental testing. FE model to simulate dynamic
loads CS 25.562 can be developed followed by design improvements and
optimisation.
| Identifer | oai:union.ndltd.org:CRANFIELD1/oai:dspace.lib.cranfield.ac.uk:1826/8352 |
| Date | 01 1900 |
| Creators | Gulavani, Omkar Vitthal |
| Contributors | Hughes, Kevin, Vignjevic, Rade |
| Publisher | Cranfield University |
| Source Sets | CRANFIELD1 |
| Language | English |
| Detected Language | English |
| Type | Thesis or dissertation, Masters, MSc by Research |
| Rights | © Cranfield University 2011. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright owner. |
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