2019_programme: INFERENCE OF SOUND SPEED WITHIN A GRANULAR SEDIMENT IN A LABORATORY LAYERED WAVEGUIDE: IMPLICATIONS FOR THE FLUID MODEL

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  • Session: 12. Marine sediment acoustics
    Organiser(s): Ballard Megan , Lee Kevin
  • Lecture: INFERENCE OF SOUND SPEED WITHIN A GRANULAR SEDIMENT IN A LABORATORY LAYERED WAVEGUIDE: IMPLICATIONS FOR THE FLUID MODEL [invited]
    Paper ID: 836
    Author(s): Venegas Gabriel R, Wilson Preston S
    Presenter: Venegas Gabriel
    Presentation type: oral
    Abstract: Water-saturated granular sediments are commonly modeled as dispersionless fluids with constant density and sound speed. Some rationales for this approach are that shear moduli of granular sediments are typically orders of magnitude lower than their bulk moduli, and many poroelastic model parameters are either unknown or difficult to measure. However, the Effective Density Fluid Model (EDFM) is a fluid model that preserves poroelastic physics, where the dynamics of the grain/pore water system is represented as a frequency-dependent effective density. The aim of this work is to experimentally demonstrate the implications of neglecting poroelastic effects on sound speed estimation in a controlled laboratory waveguide inference paradigm. The waveguide consisted of a 20-mm-outer-diameter sediment cylinder comprised of water-saturated 1-mm-diameter glass beads, suspended in a 26-mm-inner-diameter water-filled glass tube. Phase speed in the waveguide was measured from 1 kHz to 7 kHz, and a finite element simulation of the experiment was performed, in which the sediment was either modeled as a fluid or using the EDFM. In the inference process, sediment model parameters were varied in the simulation in order to match the phase speed observed in the experiment. An independent set of direct sound speed measurements were also performed and compared with the inferred values for the two sediment models. Within the frequency range of the experiment, applying the fluid model to the granular sediment using a constant bulk density resulted in the sediment sound speed inference exceeding the directly measured sound speed by 30 m/s to 150 m/s, whereas the sound speed inference assuming the EDFM agreed with direct measurements. [Work supported by ONR.]
  • Corresponding author: Dr Venegas Gabriel
    Affiliation: Applied Research Laboratories
    Country: United States
    e-mail:

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