New formulation of the compressible Navier-Stokes equations and parabolicity of the density

In this paper we give a new formulation of the compressible Navier-Stokes by introducing an suitable effective velocity v=u+\n\va(\rho) provided that the viscosity coefficients verify the algebraic relation of \cite{BD}. We give in particular a very simple proof of the entropy discovered in \cite{BD}, in addition our argument show why the algebraic relation of \cite{BD} appears naturally. More precisely the system reads in a very surprising way as two parabolic equation on the density $\rho$ and the vorticity ${\rm curl}v$, and as a transport equation on the divergence ${\rm div}v$. We show the existence of strong solution with large initial data in finite time when (\rho_0-1)\in B^{\NN}_{p,1}. A remarkable feature of this solution is the regularizing effects on the density. We extend this result to the case of global strong solution with small initial data.Comment: 38 pages. arXiv admin note: text overlap with arXiv:1107.2332; and with arXiv:1302.2617 by other author

Weak-Strong uniqueness for compressible Navier-Stokes system with degenerate viscosity coefficient and vacuum in one dimension

We prove weak-strong uniqueness results for the compressible Navier-Stokes system with degenerate viscosity coefficient and with vacuum in one dimension. In other words, we give conditions on the weak solution constructed in \cite{Jiu} so that it is unique. The novelty consists in dealing with initial density $\rho_0$ which contains vacuum. To do this we use the notion of relative entropy developed recently by Germain, Feireisl et al and Mellet and Vasseur (see \cite{PG,Fei,15}) combined with a new formulation of the compressible system (\cite{cras,CPAM,CPAM1,para}) (more precisely we introduce a new effective velocity which makes the system parabolic on the density and hyperbolic on this velocity).Comment: arXiv admin note: text overlap with arXiv:1411.550

New entropy for Korteweg's system, existence of global weak solution and Prodi-Serrin theorem

This work is devoted to prove new entropy estimates for a general isothermal model of capillary fluids derived by J.E Dunn and J.Serrin (1985) (see \cite{fDS}), which can be used as a phase transition model. More precisely we will derive new estimates for the density and we will give a new structure for the Korteweg system which allow us to obtain the existence of global weak solution. The key of the proof comes from the introduction of a new effective velocity.The proof is widely inspired from the works of A. Mellet and A. Vasseur (see \cite{fMV}). In a second part, we shall give a Prody-Serrin blow-up criterion for this system which widely improves the results of \cite{Hprepa} and the known results on compressible systems

Existence of global strong solution for the compressible Navier-Stokes system and the Korteweg system in two-dimension

This paper is dedicated to the study of viscous compressible barotropic fluids in dimension N=2. We address the question of the global existence of strong solutions with large initial data for compressible Navier-Stokes system and Korteweg system. In the first case we are interested by slightly extending a famous result due to V. A. Vaigant and A. V. Kazhikhov in \cite{VG} concerning the existence of global strong solution in dimension two for a suitable choice of viscosity coefficient ($\mu(\rho)=\mu>0$ and $\lambda(\rho)=\lambda\rho^{\beta}$ with $\beta>3$) in the torus. We are going to weaken the condition on $\beta$ by assuming only $\beta>2$ essentially by taking profit of commutator estimates introduced by Coifman et al in \cite{4M} and using a notion of \textit{effective velocity} as in \cite{VG}. In the second case we study the existence of global strong solution with large initial data in the sense of the scaling of the equations for Korteweg system with degenerate viscosity coefficient and with friction term.Comment: arXiv admin note: text overlap with arXiv:1110.6100, arXiv:1201.5456, arXiv:1102.343

Blow-up criterion, ill-posedness and existence of strong solution for Korteweg system with infinite energy

This work is devoted to the study of the initial boundary value problem for a general isothermal model of capillary fluids derived by J.E Dunn and J.Serrin (1985), which can be used as a phase transition model. We will prove the existence of strong solutions in finite time with discontinuous initial density, more precisely $\ln\rho_{0}$ is in $B^{\N}_{2,\infty}(\R^{N})$. Our analysis improves the results of \cite{fDD} and \cite{fH1}, \cite{fH2} by working in space of infinite energy. In passing our result allow to consider initial data with discontinuous interfaces, whereas in all the literature the results of existence of strong solutions consider always initial density that are continuous. More precisely we investigate the existence of strong solution for Korteweg's system when we authorize jump in the pressure across some hypersurface. We obtain also a result of ill-posedness for Korteweg system and we derive a new blow-up criterion which is the main result of this paper. More precisely we show that if we control the vacuum (i.e \frac{1}{\rho}\in L^{\infty}_{T}(\dot{B}^{0}_{N+\e,1}(\R^{N})) with \e>0) then we can extend the strong solutions in finite time. It extends substantially previous results obtained for compressible equations

Well-posedness in critical spaces for barotropic viscous fluids

This paper is dedicated to the study of viscous compressible barotropic fluids in dimension $N\geq2$. We address the question of well-posedness for {\it large} data having critical Besov regularity. %Our sole additional assumption is that %the initial density be bounded away from zero. This improves the analysis of \cite{DL} where the smallness of $\rho_{0}$ for some positive constant $\bar{\rho}$ was needed. Our result improve the analysis of R. Danchin by the fact that we choose initial density more general in B^{\NN}_{p,1} with $1\leq p<+\infty$. Our result relies on a new a priori estimate for the velocity, where we introduce a new structure to kill the coupling between the density and the velocity. In particular our result is the first where we obtain uniqueness without imposing hypothesis on the gradient of the density