887 research outputs found
Asymptotic description of solutions of the exterior Navier Stokes problem in a half space
We consider the problem of a body moving within an incompressible fluid at
constant speed parallel to a wall, in an otherwise unbounded domain. This
situation is modeled by the incompressible Navier-Stokes equations in an
exterior domain in a half space, with appropriate boundary conditions on the
wall, the body, and at infinity. We focus on the case where the size of the
body is small. We prove in a very general setup that the solution of this
problem is unique and we compute a sharp decay rate of the solution far from
the moving body and the wall
CNES â Chalmers â IAP â ONERA - XLIM activities in the domain of high RF power breakdown phenomena
Existence of global strong solutions to a beam-fluid interaction system
We study an unsteady non linear fluid-structure interaction problem which is
a simplified model to describe blood flow through viscoleastic arteries. We
consider a Newtonian incompressible two-dimensional flow described by the
Navier-Stokes equations set in an unknown domain depending on the displacement
of a structure, which itself satisfies a linear viscoelastic beam equation. The
fluid and the structure are fully coupled via interface conditions prescribing
the continuity of the velocities at the fluid-structure interface and the
action-reaction principle. We prove that strong solutions to this problem are
global-in-time. We obtain in particular that contact between the viscoleastic
wall and the bottom of the fluid cavity does not occur in finite time. To our
knowledge, this is the first occurrence of a no-contact result, but also of
existence of strong solutions globally in time, in the frame of interactions
between a viscous fluid and a deformable structure
Self consistent radio-frequency wave propagation and peripheral direct current plasma biasing: Simplified three dimensional non-linear treatment in the 'wide sheath' asymptotic regime
Weak solutions to a thin film model with capillary effects and insoluble surfactant
The paper focuses on a model describing the spreading of an insoluble
surfactant on a thin viscous film with capillary effects taken into account.
The governing equation for the film height is degenerate parabolic of fourth
order and coupled to a second order parabolic equation for the surfactant
concentration. It is shown that nonnegative weak solutions exist under natural
assumptions on the surface tension coefficient
ANSYS HFSS as a new numerical tool to study wave propagation inside anisotropic magnetized plasmas in the Ion Cylotron Range of Frequencies
The paper demonstrates the possibility to use ANSYS HFSS as a versatile
simulating tool for antennas facing inhomogeneous anisotropic magnetized
plasmas in the Ion Cyclotron Range of Frequencies (ICRF). The methodology used
throughout the paper is first illustrated with a uniform plasma case. We then
extend this method to 1D plasma density profiles where we perform a first
benchmark against the ANTITER II code. The possibility to include more complex
phenomena relevant to the ICRF field in future works like the lower hybrid
resonance, the edge propagation of slow waves, sheaths and ponderomotive forces
is also discussed. We finally present a 3D case for WEST and compare the
radiation resistance calculated by the code to the experimental data. The main
result of this paper - the implementation of a cold plasma medium in HFSS - is
general and we hope it will also benefit to research fields besides controlled
fusion.Comment: 15 pages, 14 figure
On discretization in time in simulations of particulate flows
We propose a time discretization scheme for a class of ordinary differential
equations arising in simulations of fluid/particle flows. The scheme is
intended to work robustly in the lubrication regime when the distance between
two particles immersed in the fluid or between a particle and the wall tends to
zero. The idea consists in introducing a small threshold for the particle-wall
distance below which the real trajectory of the particle is replaced by an
approximated one where the distance is kept equal to the threshold value. The
error of this approximation is estimated both theoretically and by numerical
experiments. Our time marching scheme can be easily incorporated into a full
simulation method where the velocity of the fluid is obtained by a numerical
solution to Stokes or Navier-Stokes equations. We also provide a derivation of
the asymptotic expansion for the lubrication force (used in our numerical
experiments) acting on a disk immersed in a Newtonian fluid and approaching the
wall. The method of this derivation is new and can be easily adapted to other
cases
bounds for numerical solutions of noncoercive convection-diffusion equations
International audienceIn this work, we apply an iterative energy method Ă la de Giorgi in order to establish bounds for numerical solutions of noncoercive convection-diffusion equations with mixed Dirichlet-Neumann boundary conditions
- âŠ