Alexander Shnirelman
The author studies the flows of an ideal incompressible fluid in a 2-dimensional domain, and in particular questions of instability and controllability.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
继续探索
The goal of this article is to show a local exact controllability to smooth (C2) trajectories for the 2-d density dependent incompressible Navier-Stokes equations. Our controllability result requires some geometric condition on the ow of the target trajectory, which is remanent from the transport equation satisfied by the density. The proof of this result uses a fixed point argument in suitable spaces adapted to a Carleman weight function that follows the ow of the target trajectory. Our result requires the proof of new Carleman estimates for heat and Stokes equations.
In this paper, we consider the Stokes equations in a two-dimen- sional channel with periodic conditions in the direction of the channel. We establish null controllability of this system using a boundary control which acts on the normal component of the velocity only. We show null controllability of the system, subject to a constraint of zero average, by proving an observability inequality with the help of a Muntz-Szasz Theorem.
Small-time global approximate controllability for incompressible MHD with coupled Navier slip boundary conditions
本文研究二维或三维有界区域中不可压缩MHD流动的小时间全局近似可控性，通过分析耦合Navier摩擦滑移边界条件下边界层的渐近展开获得耗散性质，并证明在平面单连通区域中额外的类压力项不存在。
We study the local controllability properties of 2D and 3D bio-mimetic swimmers employing the change of their geometric shape to propel themselves in an incompressible fluid described by Navier-Stokes equations. It is assumed that swimmers' bodies consist of finitely many parts, identified with the fluid they occupy, that are subsequently linked by the rotational and elastic internal forces. These forces are explicitly described and serve as the means to affect the geometric configuration of swimmers' bodies. Similar models were previously investigated in [6]-[13].
Exact boundary controllability of the 3D incompressible ideal MHD system
本文证明了三维不可压缩理想MHD系统在部分边界上给定法向速度与磁场法向分量时的精确边界可控性，并首次给出了不使用Elsasser变量的局部适定性证明，同时简化了二维可控性证明。
Exact controllability of incompressible ideal magnetohydrodynamics in $2$D
本研究探讨了平面不可压缩理想磁流体力学的能控性，提出分而治之策略以克服MHD耦合与磁场拓扑障碍，并利用J.-M. Coron的返回方法求解非线性速度控制子问题，扩展了内部与边界能控性结果。
Regular and Singular Steady States of 2D incompressible Euler equations near the Bahouri-Chemin Patch
该研究针对二维环面上不可压缩Euler方程的稳态问题，围绕Bahouri-Chemin涡斑这一特殊奇异稳态，构造出收敛于该涡斑的光滑及奇异稳态解族，丰富了相关方程的稳态解类型。
We give an overview on the solution of the stationary Navier-Stokes equations for non newtonian incompressible fluids established by G. Dias and M.M. Santos (Steady flow for shear thickening fluids with arbitrary fluxes, J. Differential Equations 252 (2012), no. 6, 3873-3898)*, propose a definition for domains with unbounded curved channels which encompasses domains with an unbounded boundary, domains with nozzles, and domains with a boundary being a punctured surface, and argue on the existence of steady flow for incompressible fluids with arbitrary fluxes in such domains. *Cf. ArXiv: 1108.35…
We describe a method to construct smooth and compactly supported solutions of 3D incompressible Euler equations and related models. The method is based on localizable Grad-Shafranov equations and is inspired by the recent result \cite{gav}.
Global small-time approximate null and Lagrangian controllability of the viscous non-resistive MHD system in a $3D$ domain with Navier type boundary conditions
本文研究三维有界区域内无磁扩散粘性 MHD 系统，借助带快速时间尺度的控制与多尺度渐近展开，在光滑解中证明全局短时间近似零能控性和拉格朗日能控性。
Global exact controllability of ideal incompressible magnetohydrodynamic flows through a planar duct
本文研究矩形管道中理想不可压缩MHD的全局精确可控性，利用return method和类压力校正子处理速度与磁场的非线性耦合，并通过初始数据延拓和加权空间等专门构造克服控制困难。
Local null controllability of a class of non-Newtonian incompressible viscous fluids
本文研究 Ladyzhenskaya 型非牛顿不可压缩粘性流体的局部零能控性，利用 Pontryagin 最小值原理和自举论证证明线性化 Stokes 问题光滑控制的存在性并推广到非线性情形，同时提出收敛的拟牛顿算法并通过数值实验验证。
Weak solutions to the steady incompressible Euler equations with source terms
本文基于凸积分格式将带源项的定常不可压缩Euler方程转化为微分包含，通过构造高频扰动平面波解，结合迭代与Baire纲论证证明了其定常弱解的非唯一性，且存在大量满足给定能量剖面的弱解。
Comparative Analysis of Obstacle Approximation Strategies for the Steady Incompressible Navier-Stokes Equations
本文比较了定常不可压缩 Navier-Stokes 方程中的标准体积惩罚、高粘性逼近及其组合等障碍物逼近技术，提供了收敛率分析并通过数值实验验证了其性能。
Controllability for a non-local formulation of surface gravity waves
针对二维不可压缩无黏流体的非局部晃荡问题，论文通过建立唯一延拓结果，证明了内部局部源控制可实现系统的近似可控性。
Solutions to the two-dimensional steady incompressible Euler equations in an annulus
研究二维定常不可压缩Euler方程在环域中五类边值问题的适定性，结合Grad-Shafranov方法、变分技术与涡输运方法，证明不同正则性空间解的存在性与适定性。
In this paper, we investigate the decay properties of axially symmetric solutions to the steady incompressible magnetohydrodynamic equations in $\mathbb{R}^3$ with finite Dirichlet integral. We first derive the decay rates of general D-solutions to the axisymmetric MHD equations. In the special case where the magnetic field only has the swirl component ${\textbf {h}}(r,z)= h_θ(r,z) {\mathbf e_θ}$, we obtain better decay rates. The last result examines the decay rates along the axis $Oz$ also within the special class of D-solutions with only swirl magnetic field. The main tool in this paper is …
In this paper, we study nonlinear desingularization of steady vortex rings of three-dimensional incompressible Euler flows. We construct a family of steady vortex rings (with and without swirl) which constitutes a desingularization of the classical circular vortex filament in $\mathbb{R}^3$. The construction is based on a study of solutions to the similinear elliptic problem \begin{equation*} -\frac{1}{r}\frac{\partial}{\partial r}\Big(\frac{1}{r}\frac{\partialψ^\varepsilon}{\partial r}\Big)-\frac{1}{r^2}\frac{\partial^2ψ^\varepsilon}{\partial z^2}=\frac{1}{\varepsilon^2}\left(g(ψ^\varepsilon)…
It is well known that the incompressible Euler equations can be formulated in a very geometric language. The geometric structures provide very valuable insights into the properties of the solutions. Analogies with the finite-dimensional model of geodesics on a Lie group with left-invariant metric can be very instructive, but it is often difficult to prove analogues of finite-dimensional results in the infinite-dimensional setting of Euler's equations. In this paper we establish a result in this direction in the simple case of steady-state solutions in two dimensions, under some non-degeneracy …
Relaxation enhancement by controlling incompressible fluid flows
提出基于PDE可控性的方法增强被动标量场扩散混合，通过不可压缩Euler方程的状态轨迹构建时间依赖的弛豫增强向量场，并利用近似和精确可控性定理实现弛豫增强。
We investigate a steady planar flow of an ideal fluid in a bounded simple connected domain and focus on the vortex patch problem with prescribed vorticity strength. There are two methods to deal with the existence of solutions for this problem: the vorticity method and the stream function method. A long standing open problem is whether these two entirely different methods result in the same solution. In this paper, we will give a positive answer to this problem by studying the local uniqueness of the solutions. Another result obtained in this paper is that if the domain is convex, then the vor…
New Liouville type theorems for 3D steady incompressible MHD equations and Hall-MHD equations
本文通过能量方法和迭代论证，研究了三维稳态不可压缩磁流体动力学方程和霍尔磁流体动力学方程的李普希茨型定理，并通过引入对数因子改进了增长条件。
Stability of vertically charged steady magnetic field in 3D incompressible magneto-micropolar fluids without magnetic and angular viscosity in a strip domain
研究三维不可压缩磁微极方程在带状区域无磁和角粘性时的正则性与稳定性问题，给出稳态设置，证明小扰动有全局正则稳定解且解随时间趋于无穷以近指数速率收敛到稳态。
In [F. Jiang, S. Jiang, On instability and stability of three-dimensional gravity driven viscous flows in a bounded domain, Adv. Math., 264 (2014) 831--863], Jiang et.al. investigated the instability of Rayleigh--Taylor steady-state of a three-dimensional nonhomogeneous incompressible viscous flow driven by gravity in a bounded domain $Ω$ of class $C^2$. In particular, they proved the steady-state is nonlinearly unstable under a restrictive condition of that the derivative function of steady density possesses a positive lower bound. In this article, by exploiting a standard energy functional a…
We provide explicit time-varying feedback laws that locally stabilize the two dimensional internal controlled incompressible Navier-Stokes equations in arbitrarily small time. We also obtain quantitative rapid stabilization via stationary feedback laws, as well as quantitative null controllability with explicit controls having $e^{C/T}$ costs.
The aim of this work is to show the local null controllability of a fluid-solid interaction system by using a distributed control located in the fluid. The fluid is modeled by the incompressible Navier-Stokes system with Navier slip boundary conditions and the rigid body is governed by the Newton laws. Our main result yields that we can drive the velocities of the fluid and of the structure to 0 and we can control exactly the position of the rigid body. One important ingredient consists in a new Carleman estimate for a linear fluid-rigid body system with Navier boundary conditions. This work i…
In the Eulerian approach, the motion of an incompressible fluid is usually described by the velocity field which is given by the Navier--Stokes system. The velocity field generates a flow in the space of volume-preserving diffeomorphisms. The latter plays a central role in the Lagrangian description of a fluid, since it allows to identify the trajectories of individual particles. In this paper, we show that the velocity field of the fluid and the corresponding flow of diffeomorphisms can be simultaneously approximately controlled using a finite-dimensional external force. The proof is based on…
Steady Contiguous Vortex-Patch Dipole Solutions of the 2D Incompressible Euler Equation
本文通过新颖的不动点方法严格构造了二维不可压缩欧拉方程的首个连续涡斑偶极子稳态行波解，并证明了其边界光滑性等性质。
Approximate Controllability of the generalized Burgers-Huxley equation in one dimension
研究广义Burgers-Huxley方程通过内部控制的可控性，证明非全局近似可控，但可在适当时间内将系统从任一稳态驱动到另一稳态的任意小邻域，前提是两者在同一连通分量中。
Cost of controllability of the Burgers' equation linearized at a steady shock in the vanishing viscosity limit
研究Burgers方程在消粘极限下于稳态激波处的可控性成本，通过端点控制给出控制时间的上界和下界，并构造显式极限行为的可接受控制。
In this paper we study the solvability of different boundary value problems for the two dimensional steady incompressible Euler equation. Two main methods are currently available to study those problems, namely the Grad-Shafranov method and the vorticity transport method. We describe for which boundary value problems these methods can be applied. The obtained solutions have non-vanishing vorticity.
Uniqueness and stability of steady vortex rings for 3D incompressible Euler equation
本文通过变分原理和集中紧致性方法，证明了三维欧拉方程中特殊涡环的唯一性和非线性稳定性。
In this paper we investigate the uniqueness of solutions of the steady planar Navier-Stokes equations with different boundary conditions in the exterior domain. For a class of incompressible flow with constant vorticity, we prove the uniqueness of the solution under the enhanced Navier boundary conditions. At the same time, some counterexamples are given to show that the uniqueness of the solution fails under the Navier boundary conditions. For the general incompressible flow with Dirichlet boundary condition, we prove various sufficient conditions for the uniqueness of the solution.
Lagrangian controllability in perforated domains
本文研究小体积占比穿孔区域内黏性不可压 Navier-Stokes 流体的 Lagrangian 可控性，结合均匀化、弱-强稳定性与 Runge 型逼近，按孔洞和初始数据参数给出定量结果。
Given bounded vector field $b : \mathbb R^d \to \mathbb R^d$, scalar field $u : \mathbb R^d \to \mathbb R$ and a smooth function $β: \mathbb R \to \mathbb R$ we study the characterization of the distribution $\mathrm{div}(β(u)b)$ in terms of $\mathrm{div}\, b$ and $\mathrm{div}(u b)$. In the case of $BV$ vector fields $b$ (and under some further assumptions) such characterization was obtained by L. Ambrosio, C. De Lellis and J. Malý, up to an error term which is a measure concentrated on so-called \emph{tangential set} of $b$. We answer some questions posed in their paper concerning the proper…
We consider both the internal and boundary controllability problems for wave equations under non-negativity constraints on the controls. First, we prove the steady state controllability property with nonnegative controls for a general class of wave equations with time-independent coefficients. According to it, the system can be driven from a steady state generated by a strictly positive control to another, by means of nonnegative controls, when the time of control is long enough. Secondly, under the added assumption of conservation and coercivity of the energy, controllability is proved betwee…
We investigate the nonlinear instability of a smooth Rayleigh-Taylor steady-state solution (including the case of heavier density with increasing height) to the three-dimensional incompressible nonhomogeneous magnetohydrodynamic (MHD) equations of zero resistivity in the presence of a uniform gravitational field. We first analyze the linearized equations around the steady-state solution. Then we construct solutions of the linearized problem that grow in time in the Sobolev space $H^k$, thus leading to the linear instability. With the help of the constructed unstable solutions of the linearized…
We prove the existence of critical points of the $N$-vortex Hamiltonian $H_Ω(x_1,\ldots, x_N) =\sum\limits^N_{i=1}Γ^2_i h(x_i) + \sum\limits_{i,j=1\atop j\not= k}^N Γ_iΓ_jG(x_i,x_j)+2\sum\limits_{i=1}^NΓ_iψ_0(x_i)$ in a bounded domain $Ω\subset{\mathbb R}^2$ which may be simply or multiply connected. Here $G$ denotes the Green function for the Dirichlet Laplace operator in $Ω$, more generally a hydrodynamic Green function, and $h$ the Robin function. Moreover $ψ_0\in C^1(\overlineΩ)$ is a harmonic function on $Ω$. We obtain new critical points $x=(x_1,\dots,x_N)$ for $N=3$ or $N=4$ under condi…
A compactness framework is formulated for the incompressible limit of approximate solutions with weak uniform bounds with respect to the adiabatic exponent for the steady Euler equations for compressible fluids in any dimension. One of our main observations is that the compactness can be achieved by using only natural weak estimates for the mass conservation and the vorticity. Another observation is that the incompressibility of the limit for the homentropic Euler flow is directly from the continuity equation, while the incompresibility of the limit for the full Euler flow is from a combinatio…
We prove a null controllability result for the Vlasov-Navier-Stokes system, which describes the interaction of a large cloud of particles immersed in a fluid. We show that one can modify both the distribution of particles and the velocity field of the fluid from any initial state to the zero steady state, by means of an internal control. Indeed, we can modify the non-linear dynamics of the system in order to absorb the particles and let the fluid at rest. The proof is achieved thanks to the return method and a Leray-Schauder fixed-point argument.
Pressure estimates and classifications for steady $H^1_{\rm loc}$-solutions to two-dimensional incompressible Euler equations
本文研究二维稳态不可压缩欧拉流，证明有限总曲率流在无驻点时必为平行剪切流，压力在无穷远一致收敛，并给出总曲率下界，同时将刚性结果推广至更广条件并优化正则性假设。
In this paper, we study desingularization of vortices for the two-dimensional incompressible Euler equations in the full plane. We construct a family of steady vortex pairs for the Euler equations with a general vorticity function, which constitutes a desingularization of a pair of point vortices with equal magnitude and opposite signs. The results are obtained by using an improved vorticity method.
Regularity for the steady Stokes-type flow of incompressible Newtonian fluids in some generalized function settings
本文研究含p-Laplacian的稳态Stokes型系统弱解正则性，在广义Lorentz和ψ-广义Morrey空间中建立了速度梯度与压力的正则性估计。
In this paper, we consider the steady irrotational Euler flows in multidimensional nozzles. The first rigorous proof on the existence and uniqueness of the incompressible flow is provided. Then, we justify the corresponding low Mach number limit, which is the first result of the low Mach number limit on the steady Euler flows. We establish several uniform estimates, which does not depend on the Mach number, to validate the convergence of the compressible flow with extra force to the corresponding incompressible flow, which is free from the extra force effect, as the Mach number goes to zero. T…
We consider the motion of a rigid body immersed in a two-dimensional viscous incompressible fluid with Navierslip-with-friction conditions at the solid boundary. The fluid-solid system occupies the whole plane. We provethe small-time exact controllability of the position and velocity of the solid when the control takes the form of adistributed force supported in a compact subset (with nonvoid interior) of the fluid domain, away from the body.The strategy relies on the introduction of a small parameter: we consider fast and strong amplitude controls forwhich the ``Navier-Stokes+rigid body'' sys…
Asymptotic stability of Stationary solutions to 3D incompressible flow in porous media with diffusion
研究不可压缩流体在多孔介质中扩散的稳态解存在性、唯一性及渐近稳定性，并给出扰动衰减速率估计。
In this paper, we are concerned with the validity of Prandtl boundary layer expansion for the solutions to two dimensional (2D) steady viscous incompressible magnetohydrodynamics (MHD) equations in a domain $\{(X, Y)\in[0, L]\times\mathbb{R}_+\}$ with a moving flat boundary $\{Y=0\}$. As a direct consequence, even though there exist strong boundary layers, the inviscid type limit is still established for the solutions of 2D steady viscous incompressible MHD equations in Sobolev spaces provided that the following three assumptions hold: the hydrodynamics and magnetic Reynolds numbers take the s…
On the rigidity of the 2D incompressible Euler equations
该研究针对二维有界区域定常Euler流的刚性问题，证明了圆盘、环域中满足切向边界条件的对应驻点条件下流必为环流，还揭示无滑移边界下的绝对刚性，验证了相关猜想并解决公开问题。
We study the nonhomogeneous boundary value problem for the Navier--Stokes equations of steady motion of a viscous incompressible fluid in a three--dimensional exterior domain with multiply connected boundary. We prove that this problem has a solution for axially symmetric domains and data (without any smallness restrictions on the fluxes).
In this paper, we justify the low Mach number limit of the steady irrotational Euler flows for the airfoil problem, which is the first result for the low Mach number limit of the steady Euler flows in an exterior domain. The uniform estimates on the compressibility parameter $\varepsilon$, which is singular for the flows, are established via a variational approach based on the compressible-incompressible difference functions. The limit is on the Hölder space and is unique. Moreover, the convergence rate is of order $\varepsilon^2$. It is noticeable that, due to the feature of the airfoil probl…
This paper is concerned with the Rayleigh-Taylor instability for the nonhomogeneous incompressible Navier-Stokes equations with Navier-slip boundary conditions around a steady-state in an infinite slab, where the Navier-slip coefficients do not have defined sign and the slab is horizontally periodic. Motivated by [18], we extend the result from Dirichlet boundary condition to Navier-slip boundary conditions. Our results indicate the factor that "heavier density with increasing height" still plays a key role in the instability under Navier-slip boundary conditions.
Controllability of diffusive Lotka-Volterra strongly competitive systems under boundary constrained controls
该研究针对一维带Dirichlet边界约束的扩散型Lotka-Volterra强竞争系统，证明可引导至弱竞争物种灭绝稳态，而种间竞争失衡时无法实现强竞争物种消失的可控性，还构造屏障解解释障碍并通过数值模拟验证结果。
In this paper we consider steady vortex flows for the incompressible Euler equations in a planar bounded domain. By solving a variational problem for the vorticity, we construct steady double vortex patches with opposite signs concentrating at a strict local minimum point of the Kirchhoff-Routh function with $k=2$. Moreover, we show that such steady solutions are in fact local maximizers of the kinetic energy among isovortical patches, which correlates stability to uniqueness.
Consider steady-state weak solutions to the incompressible Navier-Stokes equations in six spatial dimensions. We prove that the 2D Hausdorff measure of the set of singular points is equal to zero. This problem was mentioned in 1988 by Struwe [24], during his study of the five dimensional case.
We are interested by the controllability of a fluid-structure interaction system where the fluid is viscous and incompressible and where the structure is elastic and located on a part of the boundary of the fluid's domain. In this article, we simplify this system by considering a linearization and by replacing the wave/plate equation for the structure by a heat equation. We show that the corresponding system coupling the Stokes equations with a heat equation at its boundary is null-controllable. The proof is based on Carleman estimates and interpolation inequalities. One of the Carleman estima…
Lie symmetry group method is applied to study the boundary-layer equations for two-dimensional steady flow of an incompressible, viscous fluid near a stagnation point at a heated stretching sheet placed in a porous medium equation. The symmetry group and its optimal system are given, and group invariant solutions associated to the symmetries are obtained. Finally the structure of the Lie algebra symmetries is determined.
Global controllability of Boussinesq flows by using only a temperature control
针对二维不可压缩 Boussinesq 系统，本文证明仅依靠小测度区域内的局部温度控制即可实现全局近似能控，并给出具有显式结构的控制。
In this paper we study the uniqueness property of solutions to the steady incompressible Euler equations with perturbations in $\Bbb R^N$. Our perturbations include as special cases the Euler equations with a `single signed' nonlinear term, the self-similar Euler equations, and the steady Navier-Stokes equations. For these equations show that suitable decay assumptions at infinity on the solution or its derivatives, imposed by the $L^q$ conditions imply that the only possible solution is zero.
In this paper, we investigate steady two-dimensional free-surface flows of an inviscid and incompressible fluid emerging from a nozzle, falling under gravity and impinging onto a horizontal wall. More precisely, for any given atmosphere pressure $p_{atm}$ and any appropriate incoming total flux $Q$, we establish the existence of two-dimensional incompressible impinging jet with gravity. The two free surfaces initiate smoothly at the endpoints of the nozzle and become to be horizontal in downstream. By transforming the free boundary problem into a minimum problem, we establish the properties of…
We introduce six families of three-dimensional space-periodic steady solenoidal flows, whose kinetic helicity density is zero at any point. Four families are analytically defined. Flows in four families have zero helicity spectrum. Sample flows from five families are used to demonstrate numerically that neither zero kinetic helicity density, nor zero helicity spectrum prohibit generation of large-scale magnetic field by the two most prominent dynamo mechanisms: the magnetic $α$-effect and negative eddy diffusivity. Our computations also attest that such flows often generate small-scale field f…
扫码添加微信好友，提出您的宝贵建议 👇
💡 备注请填写：网站反馈
发表机构由 AI 从论文文本抽取，如发现错误，欢迎反馈修正建议。