Since my PhD with
J.-M. Ghidaglia,
I've been working on dispersive equations and their application in
optics, plasma physics and water-waves.
The general question is the following one: how can we describe complex,
nonlinear, high frequence propagation phenomena can be described using
asymptotic analysis? For optics, plasma physics and water-waves the
answer is: WKB-theory. The solutions are decomposed using a phase and
an amplitude
assuming that the amplitude vary slowly compared tp the phase. All the
game consists :
i) to find a small parameter that has a physical signification in the
orginal system,
ii) to be able to perform a multiscale asymptotic expansion in
the suitable time and space scale,
iii) to keep the main feature of the physical situation.
The basic theory is now well understood and one obtains transport
equations, nonlinear Schrödinger equations, Zakharov systems,
Davey-Stewartson systems,
KdV equations.... but the justification of the convergence and of the
stability of the expansions is for from beeing complete (the problems
are still open for
Zakharov systems, Davey-Stewartson and Nonlinear Schrödinger in
some cases!)
The physical situations are often more complicated and the reallity
exhibits more complex situation and one has to keep coupling phenomena.
It is especially usefull
for water-waves (counter-propagating waves), laser-plasma interaction
(Raman amplification) and nolinear optics (ultra-short pulse).
One has to build intermediate
model that are less complexe that the original systems like Maxwell or
Euler but that are less caricatural that the simple enveloppe model. A
challenge is to be able
to describe complexe physical situation, with a reasonable numerical
cost. On of the main challenge is to produce 3D numerical simulations
in real physical configurations.
My collaborators in this direction are
G. Métivier,
D. Lannes,
J. Bona, C. Galusinski, G.
Gallice,
B. Nkonga,
M. Colin.
Interaction of two solitons with
KdV:
Raman amplification (Colin-Colin):
