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      The effect of AC magnetic fields on liquid-metal free surfaces in industrialMHD.

      Spragg, Kirk John
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      Spragg, K. J. (2009). The effect of AC magnetic fields on liquid-metal free surfaces in industrialMHD. (Thesis, Doctor of Philosophy (PhD)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/3517
      Permanent Research Commons link: https://hdl.handle.net/10289/3517
      Abstract
      In this thesis we investigate free-surface instabilities which occur in various

      industrial processes involving liquid metal. Specifically, we examine a number

      of simple problems with a view to developing a plausible theoretical description

      based on MHD. Of particular interest is the behaviour of the free surface of a

      pool of liquid metal when it is submitted to an alternating magnetic field.

      The first problem we examine considers the effect of a low-frequency mag-

      netic field on a pool of liquid metal. An initially circular pool is deformed into

      radially oscillating starfish modes at certain critical magnetic field strengths.

      We study these azimuthal modes theoretically by investigating the behaviour

      of an isolated mode. We also consider the influence of geometry in our studies

      of a related problem invloving a rectangular strip of liquid metal. At certain

      critical magnetic field strengths, an elongated pool is deformed into transverse

      modes. Aside from complicated mode coupling, the behaviour of these trans-

      verse modes is similar to the starfish . Both the starfish and transverse

      modes are caused by a Mathieu-type subharmonic instability.

      We next consider the effect of a medium-frequency magnetic field on an

      initially circular pool of liquid metal. Experimentally we study the effect of

      a vertical alternating medium-frequency magnetic field on an initially circular

      pool. We observe two types of behaviour: slow radial oscillation of the pool

      perimeter and rotation of the pool about its centre. The physics of this problem

      are significantly more complicated than the starfish and strip problems.

      Accordingly a description in terms of the previous theory is not possible.

      The final problem we consider is the effect of a high-frequency magnetic

      field the surface of a conductor. Using a phase-field approach we consider two

      simple problems: the first is to calculate the rest shape of an infinite strip

      of liquid resting on a substrate in a vertical gravitational field; the second is

      to calculate the equilibrium shape of the cross-section of a column of a liquid

      conductor submitted to a high-frequency magnetic field whose field lines are

      parallel far from the conductor. Our numeric solutions compare well with

      previously known analytic solutions.
      Date
      2009
      Type
      Thesis
      Degree Name
      Doctor of Philosophy (PhD)
      Publisher
      The University of Waikato
      Rights
      All items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.
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