7,470 research outputs found
A New Domain Decomposition Method for the Compressible Euler Equations
In this work we design a new domain decomposition method for the Euler
equations in 2 dimensions. The basis is the equivalence via the Smith
factorization with a third order scalar equation to whom we can apply an
algorithm inspired from the Robin-Robin preconditioner for the
convection-diffusion equation. Afterwards we translate it into an algorithm for
the initial system and prove that at the continuous level and for a
decomposition into 2 sub-domains, it converges in 2 iterations. This property
cannot be preserved strictly at discrete level and for arbitrary domain
decompositions but we still have numerical results which confirm a very good
stability with respect to the various parameters of the problem (mesh size,
Mach number, ....).Comment: Submitte
Multi-stage high order semi-Lagrangian schemes for incompressible flows in Cartesian geometries
Efficient transport algorithms are essential to the numerical resolution of
incompressible fluid flow problems. Semi-Lagrangian methods are widely used in
grid based methods to achieve this aim. The accuracy of the interpolation
strategy then determines the properties of the scheme. We introduce a simple
multi-stage procedure which can easily be used to increase the order of
accuracy of a code based on multi-linear interpolations. This approach is an
extension of a corrective algorithm introduced by Dupont \& Liu (2003, 2007).
This multi-stage procedure can be easily implemented in existing parallel codes
using a domain decomposition strategy, as the communications pattern is
identical to that of the multi-linear scheme. We show how a combination of a
forward and backward error correction can provide a third-order accurate
scheme, thus significantly reducing diffusive effects while retaining a
non-dispersive leading error term.Comment: 14 pages, 10 figure
Towards a new generation of multi-dimensional stellar evolution models: development of an implicit hydrodynamic code
This paper describes the first steps of development of a new multidimensional
time implicit code devoted to the study of hydrodynamical processes in stellar
interiors. The code solves the hydrodynamical equations in spherical geometry
and is based on the finite volume method. Radiation transport is taken into
account within the diffusion approximation. Realistic equation of state and
opacities are implemented, allowing the study of a wide range of problems
characteristic of stellar interiors. We describe in details the numerical
method and various standard tests performed to validate the method. We present
preliminary results devoted to the description of stellar convection. We first
perform a local simulation of convection in the surface layers of a A-type star
model. This simulation is used to test the ability of the code to address
stellar conditions and to validate our results, since they can be compared to
similar previous simulations based on explicit codes. We then present a global
simulation of turbulent convective motions in a cold giant envelope, covering
80% in radius of the stellar structure. Although our implicit scheme is
unconditionally stable, we show that in practice there is a limitation on the
time step which prevent the flow to move over several cells during a time step.
Nevertheless, in the cold giant model we reach a hydro CFL number of 100. We
also show that we are able to address flows with a wide range of Mach numbers
(10^-3 < Ms< 0.5), which is impossible with an anelastic approach. Our first
developments are meant to demonstrate that the use of an implicit scheme
applied to a stellar evolution context is perfectly thinkable and to provide
useful guidelines to optimise the development of an implicit multi-D
hydrodynamical code.Comment: 21 pages, 18 figures, accepted for publication in A&
- …