2025_programme: Sound scattering by nested cylindrically symmetric and linearly invariant anomalies

• Day: June 16, Monday
    Location / Time: C. THALIA at 11:00-11:20
• Last minutes changes: -
• Session: 09. Modeling techniques for underwater acoustic scattering and propagation (including 3D effects)
  Organiser(s): Boris Katsnelson, Pavel S. Petrov
  Chairperson(s): Boris Katsnelson, Sven Ivansson, Pavel Petrov
• Lecture: Sound scattering by nested cylindrically symmetric and linearly invariant anomalies [Invited]
  Paper ID: 2134
  Author(s): Sven Ivansson
  Presenter: Sven Ivansson
  Abstract: Several previous papers have applied the coupled-mode method to assess three-dimensional scattering by cylindrically symmetric anomalies (e.g., seamounts) or anomalies which are invariant in a horizontal direction (e.g., wedges and canyons). Based on a medium discretization with laterally homogeneous rings and strips, an extension to combinations of the two anomaly types has recently been made. For each anomaly, the computations involve recursively determined reflection matrices, which relate the expansion coefficients for incoming and outgoing normal modes. Concerning ring and strip anomalies, the horizontal variation of these expansion coefficients is conveniently described by cylindrical and plane wave functions, respectively. Iterative solution of a linear equation system for the amplitudes of the scattered cylindrical waves from the ring anomalies, involving formulas for transformation between plane and cylindrical waves, allows numerical computation of the field. Within this iterative solution procedure, adaptive numerical integration is used to compute discrete sets of expansion coefficients, resulting from strip-structure interaction, for cylindrical waves incident on the ring anomalies. \nThe present paper develops a further extension, where the ring anomalies need not be disjoint but can be nested within each other and within the strip structure of the medium. Additional translation formulas for cylindrical wave function come into play. Furthermore, the iterates for solution of a pertinent linear equation system for the amplitudes of the scattered cylindrical waves from the ring anomalies are now themselves determined iteratively. The field within a ring anomaly containing other ring anomalies follows by solving a multiple-source problem with the included ring anomalies as (additional) effective sources. Partial waves can be computed to study details of multiple scattering among individual ring and strip anomalies. It can thereby be convenient to use nested ring anomalies with common centre points.
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• Corresponding author: Dr Sven Ivansson
  Affiliation: -
  Country: Sweden