2025_programme: Simulation of Acoustic Scattering by Elastic Shells with Excitation of Bending Waves

• Day: June 16, Monday
    Location / Time: D. CHLOE at 12:00-12:20
• Last minutes changes: Cancelled.
• Session: 17. Target Echo Strength – Measurements and Modelling
  Organiser(s): David Nunn 
  Chairperson(s): David Nunn 
• Lecture: Simulation of Acoustic Scattering by Elastic Shells with Excitation of Bending Waves [Invited]
  Paper ID: 2180
  Author(s): Evgeny Chernokozhin, Amir Boag
  Presenter: Amir Boag
  Abstract: The target echo strength (TES) of an elastic shell immersed in water may be very different from that calculated on the basis of the models of hard, soft, or impedance body. This difference is caused by elastic waves exited in the shell (Lamb waves) and their resonances. Rigorous simulation of elastic waves leads to sophisticated and computation-intensive numerical models. In this work, we present a simplified model of acoustic scattering by thin elastic shells at frequencies at which bending waves are excited. The shell thickness h is considered a small parameter, and the shell is regarded as a neighborhood of its middle surface (midsurface). The 3D displacements and stresses are expanded around the midsurface in powers of h. Higher order derivatives are expressed via the lower order ones by means of the Navier equation. Bending waves can be described in the third-order approximation with respect to h. Satisfying the boundary conditions at the fluid–elastic material interfaces with approximate displacements and stresses leads to some effective boundary conditions relating the boundary pressures and normal displacements on both sides of the shell. These boundary conditions have the form of high-order surface differential equations that supplement the integral equations of fluid acoustics on both sides of the shell, which gives a well-defined problem. To make the resulting system solvable by the Boundary Element Method (BEM), it is converted into a system of surface integro-differential equations, which is solved using an efficient “fast” direct technique, based on the domain decomposition, multilevel interpolation, and singular-value decomposition of the discretized operators. The BEM calculated results are compared with the analytical solutions for hollow and flooded elastic spheres and semi-analytical solutions for elastic plates and finite cylinders. In particular, an enhancement of acoustic scattering due to bending waves has been observed.
• Corresponding author: Prof Amir Boag
  Affiliation: Tel Aviv University
  Country: Israel