Incompressible Equations Research Articles

Magnetic effects on the solvability of 2D incompressible magneto-micropolar boundary layer equations without resistivity in Sobolev spaces

In this paper, we consider the magnetic effect on the Sobolev solvability of the two-dimensional incompressible magneto-micropolar boundary layer system without resistivity. This gives a complement to the previous work of Lin et al. (2022), where the well-posedness and the convergence theory were established for the magneto-micropolar boundary layer system without monotonicity in Sobolev spaces. If the initial tangential magnetic field is not degenerate, a local-in-time well-posedness theory in Sobolev spaces is established without the monotonic condition on the velocity or the micro-rotational velocity. Moreover, when the tangential magnetic field of shear layer degenerates at the non-degenerate critical point of the initial velocity and the initial micro-rotational velocity, the linearized magneto-micropolar boundary layer system around a shear flow with general decay is ill-posed in Sobolev spaces.

Local and global existence of solutions of a Keller-Segel model coupled to the incompressible fluid equations

We consider a Keller-Segel model coupled to the incompressible fluid equations which describes the dynamics of swimming bacteria. We mainly take the incompressible Navier-Stokes equations for the fluid equation part. In this case, we first show the existence of unique local-in-time solutions for large data in scaling invariant Besov spaces. We then proceed to show that these solutions can be defined globally-in-time if some smallness conditions are imposed to initial data. We also show the existence of unique global-in-time self-similar solutions when initial data are sufficiently small in scaling invariant Besov spaces. But, these solutions do not exhibit (expected) temporal decay rates. So, we change the fluid part to the Stokes equations and we derive temporal decay rates of the bacteria density and the fluid velocity.

Exact Solutions to Navier–Stokes Equations Describing a Gradient Nonuniform Unidirectional Vertical Vortex Fluid Flow

The paper announces a family of exact solutions to Navier–Stokes equations describing gradient inhomogeneous unidirectional fluid motions (nonuniform Poiseuille flows). The structure of the fluid motion equations is such that the incompressibility equation enables us to establish the velocity defect law for nonuniform Poiseuille flow. In this case, the velocity field is dependent on two coordinates and time, and it is an arbitrary-degree polynomial relative to the horizontal (longitudinal) coordinate. The polynomial coefficients depend on the vertical (transverse) coordinate and time. The exact solution under consideration was built using the method of indefinite coefficients and the use of such algebraic operations was for addition and multiplication. As a result, to determine the polynomial coefficients, we derived a system of simplest homogeneous and inhomogeneous parabolic partial equations. The order of integration of the resulting system of equations was recurrent. For a special case of steady flows of a viscous fluid, these equations are ordinary differential equations. The article presents an algorithm for their integration. In this case, all components of the velocity field, vorticity vector, and shear stress field are polynomial functions. In addition, it has been noted that even without taking into account the thermohaline convection (creeping current) all these fields have a rather complex structure.

Unidirectional steady-state inhomogeneous Couette flow with a quadratic velocity profile along a horizontal coordinate

The paper presents an exact solution to the boundary value problem describing the steady-state unidirectional flow of a viscous incompressible fluid. The fluid moves in an infinite horizontal strip (infinite fluid layer). The fulfillment of the no-slip condition is postulated at the lower boundary of the viscous fluid layer. At the upper boundary, which is assumed to be rigid, non-uniform velocity distribution is specified. The deformation of the free boundary is neglected due to the use of the rigid-lid boundary condition. The exact solution to the equations of the hydrodynamics of incompressible fluids automatically satisfies the continuity equation (the incompressibility equation). The velocity function is harmonic in this case. The simplest exact solution satisfying the Laplace equation is constructed, which takes into account the features of the velocity field along the transverse (vertical) coordinate and one of the longitudinal (horizontal) coordinates. The paper analyzes the topological properties of the velocity field, the tangential stress field, the vorticity vector, specific kinetic energy, and specific helicity.

Incompressible limit of nonisentropic Hookean elastodynamics

We study the incompressible limit of the compressible nonisentropic Hookean elastodynamics with general initial data in the whole space Rd(d=2,3). First, we obtain the uniform estimates of the solutions in Hs(Rd) for s > d/2 + 1 being even and the existence of classic solutions on a time interval independent of the Mach number. Then, we prove that the solutions converge to the incompressible elastodynamic equations as the Mach number tends to zero.

A Well-Posed First Order System Least Squares Formulation of the Instationary Stokes Equations

In this paper, a well-posed simultaneous space-time First Order System Least Squares formulation is constructed of the instationary incompressible Stokes equations with slip boundary conditions. As a consequence of this well-posedness, the minimization over any conforming triple of finite element spaces for velocities, pressure and stress tensor gives a quasi-best approximation from that triple. The formulation is practical in the sense that all norms in the least squares functional can be efficiently evaluated. Being of least squares type, the formulation comes with an efficient and reliable a posteriori error estimator. In addition, a priori error estimates are derived, and numerical results are presented.

Uniform regularity and vanishing viscosity limit for the incompressible non-resistive magneto-micropolar equations

In this paper, we consider the vanishing viscosity limit for the incompressible non-resistive magneto-micropolar equations on the half-space with no-slip boundary condition (3). We prove that the vanishing viscosity limit is uniform over a time interval, which indicates that the incompressible non-resistive magneto-micropolar equations with the no-slip boundary condition have a strong solution and the solution is uniformly bounded in both the conormal Sobolev norm and norm. As a direct result, we obtain the vanishing viscosity limit for the incompressible non-resistive magneto-micropolar equations by a strong compactness argument.

Numerical Simulation of a Two-Dimensional Groundwater Pollute Transport Problem Using Incompressible Steady-State Navier-Stokes Equations and Diffusion-Convection Equations

Most of the real contaminant problems are defined domains that are geometrically complex and can have different boundary conditions in different areas. Therefore, it is usually difficult to find a solution analytically, so we use the approximate method to generate an approximate function. One answer to this problem is the finite element approach (FEM). This study presents a partial differential equation (PDE) simulation system that uses numerical techniques for the distribution of pollutant concentrations in groundwater in space and time. The movement of the liquid is described by the incompressible steady-state Navier-Strokes equation, while the transport of pollutants is described by the diffusion-convention equation. The variation formulation that forms the basis of FEM and MATLAB is discussed along with the selection of the abstract approximation space and the welfare of the weak formulation. The motivation for this study comes from a specific and considered water body with the discharge of factory effluents on the ground that ends up reducing the quality of groundwater. First, the fluid flow equation is solved to obtain velocity and pressure profiles. Steady-state concentration profiles were obtained for various values of diffusion coefficient (D), baseline, and input concentrations. The results showed that decreasing the diffusion coefficientDincreased the number of pollutants for convective transport and decreased the number of pollutants that diffused from the entrance. Although groundwater is not completely safe, it is concluded that experimental studies are necessary decision-making basis for water resource protection, especially in water pollution emergencies.

H-principle for the 2-dimensional incompressible porous media equation with viscosity jump

In this work we extend the results in [6,32] on the 2D IPM system with constant viscosity (Atwood number $A_{\mu}=0$) to the case of viscosity jump ($|A_{\mu}|<1$). We prove a h-principle whereby (infinitely many) weak solutions in $C_tL_{w^*}^{\infty}$ are recovered via convex integration whenever a subsolution is provided. As a first example, non-trivial weak solutions with compact support in time are obtained. Secondly, we construct mixing solutions to the unstable Muskat problem with initial flat interface. As a byproduct, we check that the connection, established by Sz\'ekelyhidi for $A_{\mu}=0$, between the subsolution and the Lagrangian relaxed solution of Otto, holds for $|A_{\mu}|<1$ too. For different viscosities, we show how a pinch singularity in the relaxation prevents the two fluids from mixing wherever there is neither Rayleigh-Taylor nor vorticity at the interface.

Localized Mixing Zone for Muskat Bubbles and Turned Interfaces

We construct mixing solutions to the incompressible porous media equation starting from Muskat type data in the partially unstable regime. In particular, we consider bubble and turned type interfaces with Sobolev regularity. As a by-product, we prove the continuation of the evolution of IPM after the Rayleigh–Taylor and smoothness breakdown exhibited in (Castro et al. in Arch Ration Mech Anal 208(3):805–909, 2013, Castro et al. in Ann Math. (2) 175(2):909–948, 2012). At each time slice the space is split into three evolving domains: two non-mixing zones and a mixing zone which is localized in a neighborhood of the unstable region. In this way, we show the compatibility between the classical Muskat problem and the convex integration method.

Well-posedness results for the 3D incompressible Hall-MHD equations

In this paper, we investigate the well-posedness results of the three-dimensional incompressible Hall-magnetohydrodynamic equations with fractional dissipation. More precisely, we provide a direct proof of the local well-posedness of smooth solutions for the Hall-magnetohydrodynamic equations with the diffusive term for the magnetic field consisting of the fractional Laplacian with its power bigger than or equal to one half. Furthermore, the small data global well-posedness results are also derived. In addition, we obtain the optimal decay rate when the fractional powers are further restricted to a certain range.

Phase ordering, topological defects, and turbulence in the three-dimensional incompressible Toner-Tu equation.

We investigate the phase-ordering dynamics of the incompressible Toner-Tu equationin three dimensions. We show that the phase ordering proceeds via defect merger events and the dynamics is controlled by the Reynolds number Re. At low Re, the dynamics is similar to that of the Ginzburg-Landau equation. At high Re, turbulence controls phase ordering. In particular, we observe a forward energy cascade from the coarsening length scale to the dissipation scale, clustering of defects, and multiscaling in velocity correlations.

A Galerkin/POD Reduced-Order Model from Eigenfunctions of Non-Converged Time Evolution Solutions in a Convection Problem

A Galerkin/POD reduced-order model from eigenfunctions of non-converged time evolution transitory states in a problem of Rayleigh–Bénard is presented. The problem is modeled in a rectangular box with the incompressible momentum equations coupled with an energy equation depending on the Rayleigh number R as a bifurcation parameter. From the numerical solution and stability analysis of the system for a single value of the bifurcation parameter, the whole bifurcation diagram in an interval of values of R is obtained. Three different bifurcation points and four types of solutions are obtained with small errors. The computing time is drastically reduced with this methodology.

Convergence of the pressure in the homogenization of the Stokes equations in randomly perforated domains

We consider the homogenization to the Brinkman equations for the incompressible Stokes equations in a bounded domain which is perforated by a random collection of small spherical holes. This problem has been studied by the same authors in Giunti and Höfer (2019) [7] where convergence of the fluid velocity field towards the solution of the Brinkman equations has been established. In the present we consider the pressure associated to the solution of the Stokes equations in the perforated domain. We prove that it is possible to extend this pressure inside the holes and slightly modify it in a region of asymptotically negligible harmonic capacity such that it weakly converges to the pressure associated with the solution of the Brinkman equations.

On the generalized Beltramian motion of the bidirectional vortex in a conical cyclone

This work presents an exact solution of Euler's incompressible equations in the context of a bidirectional vortex evolving inside a conically shaped cyclonic chamber. The corresponding helical flowfield is modeled under inviscid conditions assuming constant angular momentum. By leveraging the axisymmetric nature of the problem, a steady-state solution of the generalized Beltramian type is obtained directly from first principles, namely, from the Bragg–Hawthorne equation in spherical coordinates. The resulting stream function representation enables us to fully describe the ensuing swirl-dominated motion including its fundamental flow characteristics. After identifying an isolated singularity that appears at a cone divergence half-angle of 63.43°, two piecewise formulations are provided that correspond to either fluid injection or extraction at the top section of the conical cyclone. In this process, analytical expressions are readily retrieved for the three velocity components, vorticity, and pressure. Other essential flow indicators, such as the theoretically preferred mantle orientation, the empirically favored locus of zero vertical velocity, the maximum polar and axial velocities, the crossflow velocity, and other such terms, are systematically deduced. Results are validated using limiting process verifications and comparisons to both numerical and experimental measurements. The subtle differences between the present model and a strictly Beltramian flowfield are also highlighted and discussed. The conically cyclonic configuration considered here is relevant to propulsive devices, such as vortex-fired liquid rocket engines with tapered walls; meteorological phenomena, such as tornadoes, dust devils, and fire whirls; and industrial contraptions, such as cyclonic flow separators, collectors, centrifuges, boilers, vacuum cleaners, cement grinders, and so on.

Well-Posedness and Singularity Formation for Inviscid Keller–Segel–Fluid System of Consumption Type

We consider the Keller–Segel system of consumption type coupled with an incompressible fluid equation. The system describes the dynamics of oxygen and bacteria densities evolving within a fluid. We establish local well-posedness of the system in Sobolev spaces for partially inviscid and fully inviscid cases. In the latter, additional assumptions on the initial data are required when either the oxygen or bacteria density touches zero. Even though the oxygen density satisfies a maximum principle due to consumption, we prove finite time blow-up of its $$C^{2}$$ -norm with certain initial data.

Semi-discrete optimal transport methods for the semi-geostrophic equations

We give a new and constructive proof of the existence of global-in-time weak solutions of the 3-dimensional incompressible semi-geostrophic equations (SG) in geostrophic coordinates, for arbitrary initial measures with compact support. This new proof, based on semi-discrete optimal transport techniques, works by characterising discrete solutions of SG in geostrophic coordinates in terms of trajectories satisfying an ordinary differential equation. It is advantageous in its simplicity and its explicit relation to Eulerian coordinates through the use of Laguerre tessellations. Using our method, we obtain improved time-regularity for a large class of discrete initial measures, and we compute explicitly two discrete solutions. The method naturally gives rise to an efficient numerical method, which we illustrate by presenting simulations of a 2-dimensional semi-geostrophic flow in geostrophic coordinates generated using a numerical solver for the semi-discrete optimal transport problem coupled with an ordinary differential equation solver.

Robust multigrid methods for nearly incompressible elasticity using macro elements

Abstract We present a mesh-independent and parameter-robust multigrid solver for the Scott–Vogelius discretisation of the nearly incompressible linear elasticity equations on meshes with a macro element structure. The discretisation achieves exact representation of the limiting divergence constraint at moderate polynomial degree. Both the relaxation and multigrid transfer operators exploit the macro structure for robustness and efficiency. For the relaxation we use the existence of local Fortin operators on each macro cell to construct a local space decomposition with parameter-robust convergence. For the transfer we construct a robust prolongation operator by performing small local solves over each coarse macro cell. The necessity of both components of the algorithm is confirmed by numerical experiments.

The numerical modeling of lava dome evolution at volcán de Colima using VOF and SPH methods

Lava flows from extrusive volcanic eruptions can have catastrophic consequences both for human life and the environment. Modeling such situations is an important scientific problem. The main driving forces in the evolution of the mentioned lava flows are gravitational forces, viscous friction forces on the surface of the spill, and the processes of crystallization of molten rocks into lava plateau, tubes, and domes. In this paper, the mathematical model of an extrusive volcanic eruption includes the Navier–Stokes equation, the incompressibility equation, the viscous phase transfer equation, as well as the corresponding initial and boundary conditions. Mathematical models of volcanic lava flows are considered and compared within the Euler (Volume Of Fluid – VOF) and Lagrange (Smooth Particle Hydrodynamic – SPH) formulations. ANSYS Fluent, OpenFOAM, and SPlisHSPlasH packages were used for computer simulation. Computer simulation algorithms for the problem are implemented in C++ language. Numerical modeling of the evolution of a real lava dome formed at the Colima volcano (Mexico) in February–March 2013 was carried out. For this experiment, information about the dynamics of lava dome growth, collected during the eruption, was used. It is shown how the computer simulation approach makes it possible to establish the dependence of the lava dome morphology on the rheology of a highly viscous fluid and the intensity of lava outflow.

非定常熱・流体連成問題のトポロジー最適化

As regards thermal-fluid topology optimization problems, many beneficial results have been reported. However, only a few studies have considered the unsteady state thermal-fluid problem. In actual design problems, there are lots of cases in which temporal changes in temperature distribution are important rather than steady-state. In this study, the framework of a density-based topology optimization method for the unsteady thermal-fluid problem is proposed. The governing equations are unsteady-state incompressible Naiver-Stokes equation and thermal convection-diffusion equation, discretized with stabilized finite element method. The design sensitivity is computed accurately based on the adjoint variable method. The numerical analysis shows that the proposed framework captures the transient effect correctly and the results of optimization are physically reliable.