Marges robustes de flottement et opérateurs d'incertitude

Contact:

Mevel Laurent
+33 2 99 84 73 25
Equipe Sisthem



Context:

The SISTHEM team is working on identification and damage detection in civil structures as well as monitoring aero-elastic phenomena in aeronautical structures under natural or controlled excitation. This work has been conducted under both national and European Eureka projects (Sinopsys, FliTE, FliTE2).

Subject:

The SISTHEM team is currently investigating how to detect and prevent flutter to happen in mechanical structures. Applications include aircrafts and bridges. Typically, such structures are modelled using a linear discretization of the (M,C,K) continuous equation. In such modelling it has been shown at SISTHEM that evolution of modes can be tracked to prevent flutter scenario to happen (for example, crossing of frequencies or fluctuation of dampings).
Within NASA Flight Research Center (Lind et al.), extended non linear models have been proposed to include aeroelasticity models into the linear system driving the dynamics of the structure. From a practical point of view, for aircraft manufacturers, defining flutter relates to determine the flight envelope devoid of unstabilities for any new aircraft or new configurations of current aircrafts. Critical flutter conditions are defined by the region closest to the flight envelope where unstability starts. The end problem is to define the maximum deviation allowed with respect to a nominal condition (usually defined on ground).

 An approach for computing worst case flutter margin has been formulated in a robust stability framework within NASA Flight Research Center. Uncertainty operators are used to describe errors and flutter variations. It consists in small perturbation of the system operator. Then, the mu-margins are robust margins that indicate worst case stability estimates with respect to the defined uncertainty. This theory relates to the small gain theorem to define upper bounds on the norm of the operator and the methods end up with finding the smallest maximum eigen value over all set of perturbations Delta statisfying: det (I - P Delta) = 0.

The objective of this work is to pave the road for a flutter monitoring method combining the flutter margin approach of NASA with our local approach to the design of detection algorithms.

INRIA strategic priority:

This subject takes place within the INRIA scientific and technological challenge no 4: Coupling models and data to simulate and control complex systems.

Desired profile of the candidate:

This postdoc position involves understanding the relation between adding aeroelasticity terms in the linear system, the mu-method and the classical realization theory.