## Section: Research Program

### Design and analysis of structure-preserving schemes

#### Numerical analysis of nonlinear numerical methods

Up to now, the numerical methods dedicated to degenerate parabolic problems that the mathematicians are able to analyze almost all rely on the use of mathematical transformations (like e.g. the Kirchhoff's transform). It forbids the extension of the analysis to complex realistic models. The methods used in the industrial codes for solving such complex problems rely on the use of what we call NNM, i.e., on methods that preserve all the nonlinearities of the problem without reducing them thanks to artificial mathematical transforms. Our aim is to take advantage of the recent breakthrough proposed by C. Cancès & C. Guichard [83], [4] to develop efficient new numerical methods with a full numerical analysis (stability, convergence, error estimates, robustness w.r.t. physical parameters,...).

#### Design and analysis of asymptotic-preserving schemes

There has been an extensive effort in the recent years to develop numerical methods for diffusion equations that are robust with respect to heterogeneities, anisotropy, and the mesh (see for instance [98] for an extensive discussion on such methods). On the other hand, the understanding of the role of nonlinear stability properties in the asymptotic behaviors of dissipative systems increased significantly in the last decades (see for instance [85], [110]).

Recently, C. Chainais-Hillairet and co-authors [79], [86] and [87] developed
a strategy based on the control of the numerical counterpart
of the physical entropy to develop and analyze AP numerical methods.
In particular, these
methods show great promises for capturing accurately the behavior of the solutions to dissipative problems
when some physical parameter is small with respect to the discretization characteristic parameters, or in the long-time asymptotic.
Since it requires the use of nonlinear test functions in the analysis,
strong restrictions on the physics (isotropic problems) and on the mesh (Cartesian grids, Voronoï boxes...)
are required in [79], [86] and [87]. The schemes proposed in [83] and [4] allow
to handle nonlinear test functions in the analysis without restrictions on the mesh and on the anisotropy of the problem.
Combining the nonlinear schemes *à la* [83]
with the methodology of [79], [86], [87] would provide schemes that are robust both
with respect to the meshes and to the parameters. Therefore, they would be also robust under adaptive mesh refinement.

#### Design and stability analysis of numerical methods for low-Mach models

We aim at extending the range of the `NS2DDV-M` software by introducing new physical models, like for instance the low-Mach model, which gives intermediate solutions between the compressible Navier–Stokes model and the incompressible Navier–Stokes one.
This model was introduced in [109] as a limiting system which describes combustion processes at low Mach number in a confined region.
Within this scope, we will propose a theoretical study for proving the existence of weak solutions for a particular class of models for which the dynamic viscosity of the fluid is a specific function of the density. We will propose also the extension of a combined Finite Volume-Finite Element method, initially developed for the simulation of incompressible and variable density flows, to this class of models.