<p>We consider the incompressible viscous MHD system without magnetic diffusion in a 3<i>D</i> bounded domain with Navier type boundary condition. We establish the global small-time approximate null controllability and the Lagrangian controllability of the system, in the class of smooth solutions, by following the approach initiated in [<CitationRef CitationID="CR7">7</CitationRef>] to establish the global small-time null controllability of the incompressible Navier-Stokes equations in the class of weak solutions and extended in [<CitationRef CitationID="CR34">34</CitationRef>] to establish the global small-time null and Lagrangian controllability of the incompressible Navier-Stokes equations in the class of strong solutions. This approach makes use of controls with an extra fast scale in time and some corresponding multi-scale asymptotic expansions of the controlled solution. This expansion is constructed by an iterative process which requires some regularity. The extra-difficulty here is that the MHD system at stake is mixed hyperbolic-parabolic, without any regularizing effect on the magnetic field. Although our strategy makes use of a quite precise asymptotic expansion, we succeed to cover the case where the initial velocity belongs the Sobolev space <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(H^{24}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>H</mi> <mn>24</mn> </msup> </math></EquationSource> </InlineEquation> and the initial magnetic field belongs to the Sobolev space <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(H^8\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>H</mi> <mn>8</mn> </msup> </math></EquationSource> </InlineEquation>.</p>

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Global Small-Time Approximate Null and Lagrangian Controllability of the Viscous Non-Resistive MHD System in a 3 D Domain with Navier Type Boundary Conditions

  • Jiajiang Liao,
  • Franck Sueur,
  • Ping Zhang

摘要

We consider the incompressible viscous MHD system without magnetic diffusion in a 3D bounded domain with Navier type boundary condition. We establish the global small-time approximate null controllability and the Lagrangian controllability of the system, in the class of smooth solutions, by following the approach initiated in [7] to establish the global small-time null controllability of the incompressible Navier-Stokes equations in the class of weak solutions and extended in [34] to establish the global small-time null and Lagrangian controllability of the incompressible Navier-Stokes equations in the class of strong solutions. This approach makes use of controls with an extra fast scale in time and some corresponding multi-scale asymptotic expansions of the controlled solution. This expansion is constructed by an iterative process which requires some regularity. The extra-difficulty here is that the MHD system at stake is mixed hyperbolic-parabolic, without any regularizing effect on the magnetic field. Although our strategy makes use of a quite precise asymptotic expansion, we succeed to cover the case where the initial velocity belongs the Sobolev space \(H^{24}\) H 24 and the initial magnetic field belongs to the Sobolev space \(H^8\) H 8 .