arXiv subjects

Hermenegildo Borges de Oliveira

Publications and source records attributed to Hermenegildo Borges de Oliveira.

9 recordsLinked to original sources

arXiv2026

Optimal existence of weak solutions for the power-law Navier-Stokes-Voigt equations

We study the power-law Navier--Stokes--Voigt system in a bounded domain, subject to appropriate initial conditions and no-slip boundary conditions. The analysis is governed by the power-law exponent $p$, ranging from shear-thinning ($1 2$). We prove the global existence of weak solutions to the associated initial-boundary value problem. These results are optimal in the sense that they hold for the full admissible range of the exponent $p >1$ and for any space dimension $d\geq 2$. For $p>1$ when $2 \leq d \leq 3$, and for $p \geq \tfrac{d}{2}$ when $d>3$, existence follows from a classical approach combining compactness arguments with the theory of monotone operators. The remaining case, $1 3$, requires in addition a pressure decomposition technique and an $\mathrm{L}^\infty$--truncation argument. {Finally, we establish the uniqueness of weak solution for $p>1$ when $2\leq d\leq 4$, and for $p\geq \frac{d}{2}$ when $d>4$.}

math.AP↗

arXiv2024

Existence for turbulent flows through permeable media with unbounded turbulent-depending coefficients

A mathematical model that governs turbulent flows through permeable media is considered in this work. The model under consideration is based on a double-averaging concept which in turn is described by the time-averaging technique characteristic of the turbulence k-epsilon model and by the volume-averaging methodology that is used to model unstable flows through porous media. The functions of turbulence viscosity, turbulence diffusion and turbulence production are assumed to be unbounded with respect to the turbulent kinetic energy. For the associated initial-and boundary-value problem, we prove the existence of suitable weak solutions.

math.AP↗

arXiv2024

Existence and uniqueness of weak solutions for the generalized stochastic Navier-Stokes-Voigt equations

In this work, we consider the incompressible generalized Navier-Stokes-Voigt equations in a bounded domain $\mathcal{O}\subset\mathbb{R}^d$, $d\geq 2$, driven by a multiplicative Gaussian noise. The considered momentum equation is given by: \begin{align*} \mathrm{d}\left(\boldsymbol{u} - κΔ\boldsymbol{u}\right) = \left[\boldsymbol{f} +\operatorname{div} \left(-π\mathbf{I}+ν|\mathbf{D}(\boldsymbol{u})|^{p-2}\mathbf{D}(\boldsymbol{u})-\boldsymbol{u}\otimes \boldsymbol{u}\right)\right]\mathrm{d} t + Φ(\boldsymbol{u})\mathrm{d} \mathrm{W}(t). \end{align*} In the case of $d=2,3$, $\boldsymbol{u}$ accounts for the velocity field, $π$ is the pressure, $\boldsymbol{f}$ is a body force and the final term stay for the stochastic forces. Here, $κ$ and $ν$ are given positive constants that account for the kinematic viscosity and relaxation time, and the power-law index $p$ is another constant (assumed $p>1$) that characterizes the flow. We use the usual notation $\mathbf{I}$ for the unit tensor and $\mathbf{D}(\boldsymbol{u}):=\frac{1}{2}\left(\nabla \boldsymbol{u} + (\nabla \boldsymbol{u})^{\top}\right)$ for the symmetric part of velocity gradient. For $p\in\big(\frac{2d}{d+2},\infty\big)$, we first prove the existence of a martingale solution. Then we show the pathwise uniqueness of solutions. We employ the classical Yamada-Watanabe theorem to ensure the existence of a unique probabilistic strong solution.Then we show the pathwise uniqueness of solutions. We employ the classical Yamada-Watanabe theorem to ensure the existence of a unique probabilistic strong solution.

math.PR↗

arXiv2023

Strong solutions for the Navier-Stokes-Voigt equations with non-negative density

The aim of this work is to study the Navier-Stokes-Voigt equations that govern flows with non-negative density of incompressible fluids with elastic properties. For the associated non-linear initial-and boundary-value problem, we prove the global-in-time existence of strong solutions (velocity, density and pressure). We also establish some other regularity properties of these solutions and find the conditions that guarantee the uniqueness of velocity and density. The main novelty of this work is the hypothesis that, in some subdomain of space, there may be a vacuum at the initial moment, that is, the possibility of the initial density vanishing in some part of the space domain.

math.AP↗

arXiv2012

Existence for the steady problem of a mixture of two power-law fluids

The steady problem resulting from a mixture of two distinct fluids of power-law type is analyzed in this work. Mathematically, the problem results from the superposition of two power laws, one for a constant power-law index with other for a variable one. For the associated boundary-value problem, we prove the existence of very weak solutions, provided the variable power-law index is bounded from above by the constant one. This result requires the lowest possible assumptions on the variable power-law index and, as a particular case, extends the existence result by Ladyzhenskaya dated from 1969 to the case of a variable exponent and for all zones of the pseudoplastic region. In a distinct result, we extend a classical theorem on the existence of weak solutions to the case of our problem.

math.AP↗

arXiv2012

A note about existence for a class of viscous fluid problems

In this work the existence of weak solutions for a class of non-Newtonian viscous fluid problems is analyzed. The problem is modeled by the steady case of the generalized Navier-Stokes equations, where the exponent $q$ that characterizes the flow depends on the space variable: $q=q(\mathbf{x})$. For the associated boundary-value problem we show that, in some situations, the log-Hölder continuity condition on $q$ can be dropped and the result of the existence of weak solutions still remain valid for any variable exponent $q\geqα>\frac{2N}{N+2}$, where $α=\mathrm{ess}\inf q$.

math.AP↗

arXiv2011

On the existence of weak solutions for steady flows of generalized viscous fluids

In this work we investigate the existence of weak solutions for steady flows of generalized incompressible and homogeneous viscous fluids. The problem is modeled by the steady case of the generalized Navier-Stokes equations, where the exponent $q$ that characterizes the flow depends on the space variable: $q=q(\mathbf{x})$. For the associated boundary-value problem we prove the existence of weak solutions for any variable exponent $q\geqα>\frac{2N}{N+2}$, where $α=\mathrm{ess}\inf q$. This work improves all the known existence results in the sense that the lowest possible bound of $q$ is attained and no other assumption on the regularity of $q$ is required.

math.AP↗

arXiv2011

Existence of weak solutions for the generalized Navier-Stokes equations with damping

In this work we consider the generalized Navier-Stoke equations with the presence of a damping term in the momentum equation. % The problem studied here derives from the set of equations which govern the isothermal flow of incompressible, homogeneous and non-Newtonian fluids. % For the generalized Navier-Stokes problem with damping, we prove the existence of weak solutions by using regularization techniques, the theory of monotone operators and compactness arguments together with the local decomposition of the pressure and the Lipschitz-truncation method. The existence result proved here holds for any $q>\frac{2N}{N+2}$ and any $σ>1$, where $q$ is the exponent of the diffusion term and $σ$ is the exponent which characterizes the damping term.

math.AP↗

arXiv2009

The Navier-Stokes problem modified by an absorption term

In this work we consider the Navier-Stokes problem modified by the absorption term $|\textbf{u}|^{σ-2}\textbf{u}$, where $σ>1$, which is introduced in the momentum equation. % For this new problem, we prove the existence of weak solutions for any dimension $N\geq 2$ and its uniqueness for N=2. % Then we prove that, for zero body forces, the weak solutions extinct in a finite time if $1<σ<2$, exponentially decay in time if $σ=2$ and decay with a power-time rate if $σ>2$. % We prove also that for a general non-zero body forces, the weak solutions exponentially decay in time for any $σ>1$. In the special case of a suitable forces field which vanishes at some instant, we prove that the weak solutions extinct at the same instant provided $1<σ<2$.

math.AP↗