On weak (measure-valued)-strong uniqueness for compressible MHD system with non-monotone pressure law

<p style='text-indent:20px;'>In this paper, we define a renormalized dissipative measure-valued (rDMV) solution of the compressible magnetohydrodynamics (MHD) equations with non-monotone pressure law. We prove the existence of the rDMV solutions and establish a suitable relative energy inequality. And we obtain the weak (measure-valued)-strong uniqueness property of this rDMV solution with the help of the relative energy inequality.</p>

Modes of magnetic field generation in the low-mode αΩ-dynamo model with dynamic regulation of the α-effect by the field energy

В работе используется маломодовая модель αΩ-динамо для моделирования режимов генерации магнитного поля при незначительных изменениях поля скорости вязкой жидкости. В рамках этой модели интенсивность α-эффекта регулируется процессом с памятью, который вводится в магнитогидродинамическую систему (МГД-система) как аддитивная поправка в виде функционала Z(t) от энергии поля. В качестве ядра J(t) функционала Z(t) выбрана функция, определяющая затухающие колебания с варьируемым коэффициентом затухания и постоянной частотой затухания, принятой равной единице. Исследование поведения магнитного поля проводится на больших временных масштабах, поэтому для численных расчётов используется перемасштабированная и обезразмеренная МГД-система, где в качестве единицы времени принято время диссипации магнитного поля (104 лет). Управляющими параметрами системы выступают число Рейнольдса и амплитуда α-эффекта, в которых заложена информация о крупномасштабном и турбулентном генераторах. Результаты численного моделирования режимов генерации магнитного поля при различных значениях коэффициента затухания и постоянной частоте затухания отражены на фазовой плоскости управляющих параметров. В работе исследуется вопрос о динамике изменения картины на фазовой плоскости в зависимости от значения коэффициента затухания. Проводится сравнение с результатами, полученными ранее при постоянной интенсивности α-эффекта и при изменении интенсивности α — эффекта, которое определялось функционалом Z(t) с показательным ядром и аналогичными значениями коэффициента затухания. In this paper, we use a low-mode αΩ-dynamo model to simulate the modes of magnetic field generation with insignificant changes in the velocity field of a viscous fluid. Within the framework of this model, an additive correction is introduced into the magnetohydrodynamic system to control the intensity of the α-effect in the form of a function Z(t) from the field energy. As the kernel J(t) of the function Z(t) is chosen the function that determines damped oscillations with the different values of the damping coefficient and a constant damping frequency taken equal to one. The study of the magnetic field behavior is carried out on a large time scales, therefore, for numerical calculations, a rescaled and dimensionless MHD-system is used, where the time of the magnetic field dissipation (104 years) is accepted as the unit of time. The main parameters of the system are the Reynolds number and the amplitude of the α-effect, which contains information about the large-scale and turbulent generators, respectively. According to the results of numerical simulation, an increase in the values of the damping coefficient is characterized an increase in the inhibition effect of the process Z(t) on the α-effect and decrease of the magnetic field divergence region on the plane of the main parameters.

The global solvability of the Hall-magnetohydrodynamics system in critical Sobolev spaces

We are concerned with the 3D incompressible Hall-magnetohydrodynamic system (Hall-MHD). Our first aim is to provide the reader with an elementary proof of a global well-posedness result for small data with critical Sobolev regularity, in the spirit of Fujita–Kato’s theorem [On the Navier–Stokes initial value problem I, Arch. Ration. Mech. Anal. 16 (1964) 269–315] for the Navier–Stokes equations. Next, we investigate the long-time asymptotics of global solutions of the Hall-MHD system that are in the Fujita–Kato regularity class. A weak-strong uniqueness statement is also proven. Finally, we consider the so-called 2[Formula: see text]D flows for the Hall-MHD system (that is, 3D flows independent of the vertical variable), and establish the global existence of strong solutions, assuming only that the initial magnetic field is small. Our proofs strongly rely on the use of an extended formulation involving the so-called velocity of electron [Formula: see text] and as regards [Formula: see text]D flows, of the auxiliary vector-field [Formula: see text] that comes into play in the total magneto-helicity balance for the Hall-MHD system.

Global well-posedness for the three-dimensional incompressible viscous non-resistive MHD equations in an infinite slab

In this paper, we investigate the global well-posedness of the system of incompressible viscous non-resistive MHD fluids in a three-dimensional horizontally infinite slab with finite height. We reformulate our analysis to Lagrangian coordinates, and then develop a new mathematical approach to establish global well-posedness of the MHD system, which requires no nonlinear compatibility conditions on the initial data.

Global strong solution to the 2D inhomogeneous incompressible magnetohydrodynamic fluids with density-dependent viscosity and vacuum

In this paper, we investigate an initial boundary value problem for two-dimensional inhomogeneous incompressible MHD system with density-dependent viscosity. First, we establish a blow-up criterion for strong solutions with vacuum. Precisely, the strong solution exists globally if $\|\nabla \mu (\rho )\|_{L^{\infty }(0, T; L^{p})}$ ∥ ∇ μ ( ρ ) ∥ L ∞ ( 0 , T ; L p ) is bounded. Second, we prove the strong solution exists globally (in time) only if $\|\nabla \mu (\rho _{0})\|_{L^{p}}$ ∥ ∇ μ ( ρ 0 ) ∥ L p is suitably small, even the presence of vacuum is permitted.

Stability for the 2D MHD equations with horizontal dissipation

In this paper we consider the following 2D MHD system with horizontal dissipation in a strip domain T × R. ∂ t u + u · ∇ u + ∂ 11 u + ∇ p = b · ∇ b , ∂ t b + u · ∇ b + ∂ 11 b = b · ∇ u , ∇ · u = ∇ · b = 0 , u ( 0 ) = u 0 ( x ) , b ( 0 ) = b 0 ( x ) . A bootstrapping argument together with a more accurate energy functional is employed in order to get the stability for the above system. Moreover, using a suitable transform, we also investigate the 2D MHD system with vertical dissipation in a strip domain R × T.