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Publications, papers published in August 1999/communications publiées en août 1999
- 1
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M. Jeanneau, D. Alazard, and Ph. Mouyon.
A semi-adaptative frequency control law for flexible structures : on
the way to adaptive Q-LQG control.
In AIAA Guidance Navigation and Control Conference, Portland
(USA), 9 - 11 August 1999. AIAA.
Piloting flexible structures has become a major concern for cntrol
law designers. Robustness to parameters variation of the flexible modes is
necessary to guarantee stability. The methode introduced in this paper makes
use of a semi-adaptive freque'ncy control law. Performance for the rigid
dynamics of the structure is obtained through a classical linear controller.
The adaptive part of the control deals only with updating a controller in
charge of following the flexible modes fluctuation. Dosing so our global
stategy satisfies both the robustness and the performance requirements, with
almost no compromise between these two. Then we present how this kind of
control can be changed into an equivalent Q-LQG adaptive controller and the
improvements it brings.
- 2
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V. Fromion, G. Scorletti, and G. Ferreres.
Nonlinear performance of a PI controlled missile : an explanation.
International Journal of Robust and Nonlinear Control,
9(8):485-518, August 1999.
The primary aim of this paper is to investigate the practical
interest of the incremental norm approach for analyzing (realistic) nonlinear
dynamical systems. In this framework indeed, incremental stability, a
stronger notion than L2-gain stability, ensures suitable qualitative and
quantitative properties. On the one hand, the qualitative properties
essentially correspond to (steady-state) input/output properties, which are
not necessarily obtained when ensuring only L2-gain stability. On the other
hand, it is possible to analyze quantitative robustness performance
properties using the notion of (nonlinear) incremental performance, the
latter being defined in the continuity of the (linear) Hinfinity performance
(i.e. through the use of a weighting function). As testing incremental
properties is a difficult problem, stronger, but computationally more
attractive, notions are introduced, namely quadratic incremental stability
and performance. Testing these properties reduces indeed to solving convex
optimization problems over Linear Matrix Inequalities (LMIs). As an
illustration, we consider a classical missile problem, which was already
treated using several (linear and nonlinear) approaches. We focus here on the
analysis of the nonlinear behavior of this PI controlled missile: using the
notions of quadratic incremental stability and performance, the closed loop
nonlinear missile is proved to meet desirable control specifications.
- 3
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D. Farcy, O. Renier, and D. Tristrant.
Wing blowing on fighter aircraft evaluation and gains in high angle
of attack maneuvers.
In Conférence AIAA "Atmospheric Flight Mechanics
Conference", Portland, OR (USA), 9 - 11 August 1999. AIAA.
The enhancement of maneuverability for fighter aircrafts is
increasingly important, in particular at high angles of attack. Flying in
this domain provides the ability to turn quickly and therefore the
opportunity to kill or avoid adverse aircraft. Fighter aircrafts have
generally highly swept wings. Aerodynamics on such wings is characterized by
the development of vortices at moderate to high angles of attack. The
structure of these vortices strongly depends on the angle of attack. In
particular vortex breakdown occurs at high angles of attack. This phenomenon
induces significant effects on aerodynamic efforts, and therefore on the
aircraft behaviour. The main consequences are : loss of lift and emergence of
rolling moment as a result of vortex breakdown asymetry on right and left
wing. This paper deals with experimental and analytical studies of the
control of the delta-wing vortices by axial blowing, i.e. into the vortex
core. The aim of the blowing is to re-energize the vortex and to increase the
axial velocity in the core, in order to control and delay the onset of vortex
breakdown. In a first part, experimental tools and results will be presented.
Then the effects of vortex blowing on the maneuverability and controlability
at high angles of attack will be discussed and illustrated through
comparisons of specific criteria.
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C. Pendaries, J.-L. Boiffier, and J. C. Barrau.
Sur la tenue des avions souples à la rafale.
In 14ème Congrès Francais de Mécanique, Toulouse (France), 30
August-3 September 1999.
- 5
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Ph. Mouyon and L. Didierjean.
Nonlinear observers applied to car suspension fault detection.
In ECC 99, Karlruhe (Allemagne), 31 August-3 September 1999.
To prevent for great damage it is important to early detect car shock
absorber performances degradation. This degradation is linked to a decreasing
of the fluid compressibility modulus. We study the design of a diagnostic
system based on vertical displacement and acceleration measurements of the
absorber. Our approach is based on the use of observers as parameter
estimators. A physical nonlinear model is developed. When the shock absorber
wears out, the damping characteristic curve presents an hysteresis phenomenon
while this characteristic is almost linear within the non faulty case. A
simplified model with linear parameter dependency is stated which is devoted
to diagnostic. Then several observation methods are compared from both design
methodology and performances point of view. A few design methodologies are
devoted to simultaneously state and parameter estimation. We present a
quasi-linear design based on bias/unbias linear observers, an adaptive
design, and a recent parametric estimator. When the methodologies apply,
simulations show that nominal performances are quite similar, in spite of
fairly different complexity. In each case the detection is achieved thanks to
a Page-Hinkley test applied to the estimated parameters. The use of state
estimators applied to an augmented model including the parameters as new
state variables is also studied. The classical extended Kalman filter
approach solves the diagnostic problem and is successfully applied. As
regards more recent methods based on quadratic stability such as robust
-methods, high gain observers, sliding observers, no solution exists,
since observability requirements are not fulfilled. This is clearly related
to the fact that unknown parameters are embedded into the state variables. It
is worth noting that as far as only fault detection is concerned, the
parameter estimation error need not to decrease up to zero. Indeed the
diagnostic procedure is based on the detection of changes in the estimated
values, no matter the absolute value is. Thus biased estimators make up the
basic tool. Weakening the observer convergence requirements might lead to
more general observation schemes that will be useful within the fault
detection framework.
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