An explicit granular-mechanics approach to marine sediment acoustics

TL;DR

This paper develops a granular mechanics-based theoretical and computational framework to understand the frequency-dependent acoustic properties of marine sediments, highlighting the importance of granular packing structure.

Contribution

It introduces a novel granular physics approach to sediment acoustics, revealing anomalous scaling laws and emphasizing the role of granular packing structure.

Findings

Disordered granular packings cause anomalous scaling in phase speed and attenuation.

Granular structure significantly influences sediment acoustic properties.

The approach offers a foundation for more comprehensive future models.

Abstract

Here we theoretically and computationally study the frequency dependence of phase speed and attenuation for marine sediments from the perspective of granular mechanics. We leverage recent theoretical insights from the granular physics community as well as discrete-element method simulations, where the granular material is treated as a packing of discrete objects that interact via pairwise forces. These pairwise forces include both repulsive contact forces as well as dissipative terms which may include losses from the fluid as well as losses from inelasticity at grain-grain contacts. We show that the structure of disordered granular packings leads to anomalous scaling laws for frequency-dependent phase speed and attenuation that do not follow from a continuum treatment. Our results demonstrate that granular packing structure, which is not explicitly considered in existing models, may play a crucial role in a complete theory of sediment acoustics. While this simple approach does not explicitly treat sound propagation or inertial effects in the interstitial fluid, it provides a starting point for future models that include these and other more complex features.