Linear instability implies nonlinear instability for various types of viscous boundary layers
Linear response of the gate system for protection of the Venice Lagoon. Note I: Transverse free modes
The free oscillations of the gate system proposed [1,2] to defend the Venice Lagoon from the phenomenon of high water are analyzed. Free transverse modes of oscillations exist which may be either subharmonic or synchronous with respect to typical waves in the Adriatic sea. This result points out the need to examine whether such modes may be excited as a result of a Mathieu type resonance occurring when the gate system is forced by incident waves. The latter investigation is performed in part 2 of...
Linear response of the gate system for protection of the Venice Lagoon. Note II: Excitation of transverse suhharmonic modes
We show that the transverse subharmonic modes characterizing the free oscillations of the gate system proposed to defend the Venice Lagoon from the phenomenon of high water (see Note I[1]) can be excited when the gate system is forced by plane monochromatic waves orthogonal to the gates with the typical characteristics of large amplitude waves in the Adriatic sea close to the lagoon inlets. A linear stability analysis of the coupled motion of the system sea-gates-lagoon reveals that for typical...
Linear stability results in a magnetothermoconvection problem.
Long-Wave Coupled Marangoni - Rayleigh Instability in a Binary Liquid Layer in the Presence of the Soret Effect
We have explored the combined long-wave Marangoni and Rayleigh instability of the quiescent state of a binary- liquid layer heated from below or from above in the presence of the Soret effect. We found that in the case of small Biot numbers there are two long- wave regions of interest k ~ Bi1/2 and k ~ Bi1/4. The dependence of both monotonic and oscillatory thresholds of instability in these regions on both the Soret and dynamic Bond numbers has been investigated. The complete linear stability...
Low Reynolds number stability of MHD plane Poiseuille flow of an Oldroyd fluid.
Marangoni Convection in a Photo-Chemically Reacting Liquid
Marangoni convection caused by a photochemical reaction of the type A B in a deep liquid layer is studied. Linear stability analysis is performed and the conditions for Marangoni convection to occur are obtained. It is shown that increasing the rate of the direct reaction, for example, by increasing the light intensity, destabilizes the steady state and causes convective motion of the fluid, whereas increasing the rate of the inverse reaction stabilizes the steady state. A weakly nonlinear analysis...
Marginally Stable inviscid flows with critical layers
Mathematical analysis of the stabilization of lamellar phases by a shear stress
We consider a 2D mathematical model describing the motion of a solution of surfactants submitted to a high shear stress in a CouetteTaylor system. We are interested in a stabilization process obtained thanks to the shear. We prove that, if the shear stress is large enough, there exists global in time solution for small initial data and that the solution of the linearized system (controlled by a nonconstant parameter) tends to 0 as goes to infinity. This explains rigorously some experiments.
Mathematical analysis of the stabilization of lamellar phases by a shear stress
We consider a 2D mathematical model describing the motion of a solution of surfactants submitted to a high shear stress in a Couette-Taylor system. We are interested in a stabilization process obtained thanks to the shear. We prove that, if the shear stress is large enough, there exists global in time solution for small initial data and that the solution of the linearized system (controlled by a nonconstant parameter) tends to 0 as t goes to infinity. This explains rigorously some experiments. ...
Mathematical models for laser-plasma interaction
We address here mathematical models related to the Laser-Plasma Interaction. After a simplified introduction to the physical background concerning the modelling of the laser propagation and its interaction with a plasma, we recall some classical results about the geometrical optics in plasmas. Then we deal with the well known paraxial approximation of the solution of the Maxwell equation; we state a coupling model between the plasma hydrodynamics and the laser propagation. Lastly, we consider the...
Mathematical models for laser-plasma interaction
We address here mathematical models related to the Laser-Plasma Interaction. After a simplified introduction to the physical background concerning the modelling of the laser propagation and its interaction with a plasma, we recall some classical results about the geometrical optics in plasmas. Then we deal with the well known paraxial approximation of the solution of the Maxwell equation; we state a coupling model between the plasma hydrodynamics and the laser propagation. Lastly, we consider the...
Modulational stability of Korteweg-de Vries and Boussinesq wavetrains.
Non dérivation des équations de Prandtl
Nonexistence of Coherent Structures in Two-dimensional Inviscid Channel Flow
Two-dimensional inviscid channel flow of an incompressible fluid is considered. It is shown that if the flow is steady and features no horizontal stagnation, then the flow must necessarily be a parallel shear flow.
Nonlinear compressible vortex sheets in two space dimensions
We consider supersonic compressible vortex sheets for the isentropic Euler equations of gas dynamics in two space dimensions. The problem is a free boundary nonlinear hyperbolic problem with two main difficulties: the free boundary is characteristic, and the so-called Lopatinskii condition holds only in a weak sense, which yields losses of derivatives. Nevertheless, we prove the local existence of such piecewise smooth solutions to the Euler equations. Since the a priori estimates for the linearized...
Nonlinear instability in an ideal fluid
Nonlinear interaction of waves in a hot inhomogeneous magnetized plasma.
Non-parallel plane Rayleigh Benard convection in cylindrical geometry
This paper considers the effect of a perturbed wall in regard to the classical Benard convection problem in which the lower rigid surface is of the form , s=ε r, in axisymmetric cylindrical polar coordinates (r,ϕ,z). The boundary conditions at s=0 for the linear amplitude equation are found and it is shown that these conditions are different from those which apply to the nonlinear problem investigated by Brown and Stewartson [1], representing the distribution of convection cells near the center....
Non-uniqueness and linear stability of the one-dimensional flow of multiple viscoelastic fluids