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Weak formulation of equations describing fluid flows
Dostalík, Mark ; Pokorný, Milan (advisor) ; Kaplický, Petr (referee)
The standard way of deriving the weak formulation of balance equations of continuum mechanics is derived from their localized form, and thus requires differentiability of functions involved in the corresponding balance law. However, the existence of classical solutions of these equations is often not known. It would be suitable to find a transition to the weak formulation of balance laws without the need of their differential form. The aim of this work is to show that the initial integral form of balance equations of continuum mechanics, provided relatively weak assumptions, directly implies their weak formulation, and thus that the weak solution is for these equations a more natural notion than the classical solution is.
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Mathematical Analysis of Fluids in Large Domains
Poul, Lukáš ; Feireisl, Eduard (advisor) ; Pokorný, Milan (referee) ; Vodák, Rostislav (referee)
This thesis contains a set of articles concerned with flow of a viscous, compressible and heat conducting fluid in large domains. In the first part of the thesis, the existence of the weak solutions in unbounded domains is studied. The results follow each other in the way they were obtained through the time, and range from a simple extension to bounded domains with Lipschitz boundary up to the most general existence theorem for fluid flow in general open sets. The existence results are supplemented with the study of existence of weak solutions in the unbounded domain case with prescribed nonvanishing boundary conditions for density and temperature at infinity. The last contribution then concerns with the low Mach number limit in the compressible fluid flow.
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Compressible fluid motion in time dependent domains
Sýkora, Petr ; Feireisl, Eduard (advisor) ; Pokorný, Milan (referee)
In this work we study the existence of weak solutions for compressible Navier-Stokes equations in unbounded time dependent domains. Using the methods introduced in Feireisl E. Dynamics of Viscous Compressible Fluids we extend the results of article Feireisl E. Neustupa J. Stebel J., Convergence of a Brinkman-type penalization for compressible fluid flows, which studies the flow with a "no-slip" boundary condition on bounded domains. Next, we extend results of article Feireisl E. Kreml O. Nečasová Š. Neustupa J. Stebel J., Weak solutions to the barotropic Navier- Stokes system with slip boundary conditions in time dependent domains, which studies flow with compete Navier boundary condition. Finally, we discuss solutions for rotating fluid system. In this case, there are new members in momentum equation, representing the Coriolis and centrifugal force, which cause problems.
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Generalized Stokes systems - theoretical analysis approach
Holeček, Martin ; Málek, Josef (advisor) ; Pokorný, Milan (referee)
We consider steady flows of homogenous incompressible fluid described by generalized Stokes system. We study two models, first with shear-rate dependent viskosity and second with pressure and shear-rate dependent viskosity. We investigate internal flows in bounded domains subject to Navier's boundary condition. First, to show the difference, we present proofs of existence and uniqueness of solutions for both systems. Then we investigate, what are the assumptions allowing to take the fluid mechanics limit, as Navier's boundary conditions approximate first no-slip and then (perfect) slip boundary conditions. Finally, we consider for simplicity specially periodic problem and show regularity result (integrability of the second derivatives of the velocity and the first derivatives of the pressure).
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Mathematical Analysis of Models for Viscoelastic Fluids
Kreml, Ondřej ; Pokorný, Milan (advisor) ; Skalák, Zdeněk (referee) ; Neustupa, Jiří (referee)
1 Title: Mathematical analysis of models for viscoelastic fluids Author: Ondřej Kreml Department: Mathematical Institute of Charles University Supervisor: Doc. Mgr. Milan Pokorný, Ph.D. Abstract: We consider several problems in the thesis. First we summarize key ideas of fluid mechanics theory and introduce several models describ- ing nonnewtonian behaviour of fluids. In the second chapter we prove local existence of solutions to the Oldroyd-type system achieved as a limit case with infinite relaxation and retardation times. We work with three types of boundary conditions, namely homogenous Dirichlet and periodic conditions and whole space, in 2D and 3D. We study also related system of PDE's which is equivalent to the Oldroyd-type system in 2D. In the third chapter we prove local existence of solutions to the system of PDE's describing the flow of a polymeric liquid. The polymer molecules are modeled as elastic dumbbells with spring force having the so-called FENE potential. Arising system con- sists of Navier-Stokes equations coupled with Fokker-Planck equation. In the fourth chapter we study asymptotic behaviour of solutions to equations desribing steady flow of a second grade fluid past an obstacle in three dimen- sions with prescribed nonzero velocity at infinity. Key point in the proof is using results of...
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On fluids with pressure-dependent viscosity flowing through a porous medium
Žabenský, Josef ; Pokorný, Milan (advisor)
Experimental data convincingly show that viscosity of a fluid may change significantly with pressure. This observation leads to various generalizations of well-known models, like Darcy's law, Stokes' law or the Navier-Stokes equations, among others. This thesis investigates three such models in a series of three published papers. Their unifying topic is development of existence theory and finding a weak solution to systems of partial differential equations stemming from the considered models.
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Compressible Navier-Stokes-Fourier system for the adiabatic coefficient close to one
Skříšovský, Emil ; Pokorný, Milan (advisor) ; Feireisl, Eduard (referee)
In the present thesis we study the compressible Navier-Stokes-Fourier sys- tem. This is a system of partial differential equations describing the evolutionary problem for an adiabatic flow of a heat conducting compressible viscous fluid in a bounded domain. Here we consider the problem in two dimensions with zero Dirichlet boundary conditions for velocity. The cold pressure term in the pressure law for the momentum equation is here considered in the form pC(ϱ) ∼ ϱ logα (1+ϱ) for some α > 0, for which we need to work on the scale of Orlicz spaces in order to obtain useful estimates and in those space we formulate the problem weakly and also establish the weak compactness of the solution. The main result of this thesis is Theorem 6.1 where we show the existence of a weak solution with no assumptions on the size of the data and on arbitrary large time intervals. 1
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On fluids with pressure-dependent viscosity flowing through a porous medium
Žabenský, Josef ; Pokorný, Milan (advisor) ; Pražák, Dalibor (referee) ; Breit, Dominic (referee)
Experimental data convincingly show that viscosity of a fluid may change significantly with pressure. This observation leads to various generalizations of well-known models, like Darcy's law, Stokes' law or the Navier-Stokes equations, among others. This thesis investigates three such models in a series of three published papers. Their unifying topic is development of existence theory and finding a weak solution to systems of partial differential equations stemming from the considered models.
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