Etude du comportement dynamique linéaire et non-linéaire d'un ...

ABSTRACT
The development of computing power and optimisation methods used by the
engineers leads to a better design of structures. It has for first consequence the appearance of
non linear phenomena affecting the dynamic behaviour which can modify in a large part the
linear response.
The first part of this work deals also with the insertion of non linearities in the
modelling of helicopter rotor dynamics. We will show that non linearities can't be always
neglected and leads sometimes to chaotic behaviour and even instability. A particular
analysis of these phenomena is made using well-known methods - Volterra's series, normal
form theory - in order to identify the main non linear parameters. The original aspect of this
work lies in the application of non linear analysis to a multi-dimensional system which is
close to reality.
We will study afterwards the coupling between two linear structures. In the
case of helicopter, the particularity is that the rotor is strongly gyroscopic. We will use a
modal approach of the fuselage to simplify the analysis. Two directions will be explored. A
simplified model permits us to identify the coupled degrees of freedom. A second modelling,
taking into account numerous aerodynamic effects, will be used as a tool for conception and
design of helicopters. At last, we will study an unstable coupling between rotor and fuselage
through particular mechanical organs.
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