Numerical design of Alberich anechoic coatings with superellipsoidal cavities of mixed sizes

Abstract

Thin rubber coatings with cavities in a doubly periodic lattice are able to reduce reflections of underwater sound by redistributing normally incident energy such that absorption in the surrounding rubber is enhanced. For spherical scatterers, the anechoic effect can be studied numerically by the layer-multiple-scattering (LMS) method. In comparison to more flexible but also more computer intensive methods, such as finite-element method modeling, there are two important advantages. An improved physical understanding of the anechoic effect can be achieved by simplified semianalytical analysis, and the high computational speed allows modern global optimization techniques to be applied for coating design. In this paper, the flexibility of the LMS method is improved by combination with an efficient algorithm for numerical computation of transition matrices for superellipsoidal scatterers. (A superellipsoid is a generalization of an ellipsoid, allowing more box-filling shapes, for example.) Extensions to mixtures of nonspherical scatterers of different types are also considered, in order to enhance the broadband performance. Symmetry properties are used to reduce the size of the pertinent equation systems. Examples of numerical coating design for underwater acoustic applications are presented, using differential evolution algorithms for the optimization.

Underwater sound transmission through arrays of disk cavities in a soft elastic medium

“…The numerical model was checked by computing the total scattering cross section of an oblate spheroidal cavity of AR 2 in a non-viscous medium as reported in Ref. 11.…”

“…13 In previous work, the disk cavity is referred to as a penny-shaped crack or a pancake shape. 12,[14][15][16] Although a single layer of what is considered resembles the arrays studied in the context of Alberich underwater anechoic coatings, 11,17,18 this study is distinct in examining large AR disk cavities in both single-and multilayered geometries with both sides exposed to water. At the ultrasonic frequencies considered (>50 kHz), the shear loss factor of PDMS is large, which affects the quality of the resonance of an individual cavity.…”

Magnetic–acoustic biphysical invisible coats for underwater objects

“…Like the EM counterpart, however, these advanced acoustic devices are still far from practice when considering their structure complexity, thickness, and bandwidth. However, in practice, a thin absorber is equally important and highly desired for stealth technology based on the measurement of returning loss 30 . This consideration is valid for a far-field, single-station wave characterization system, but not suitable for a near-field system, including the magnetic field probe.…”

The Three-Dimensional Phononic Crystals

“…It applies to any material type combination (fluid or solid) and with the same efficiency, it can treat, also, coated spheres and generally spherical particles consisting of an arbitrary number of concentric spherical shells by a powerful recursive algorithm [46]. Recently, the method has been extended to scatterers of arbitrary shape with the addition of the extended-boundary-condition (EBC) technique [9,15]. Thus, in addition to the physical clarity and computational efficiency, the generalized LMS method would offer an efficient and versatile alternative to treat a variety of complex phononic structures.…”