Abating low-frequency noise using encapsulated gas bubbles

Air bubbles may be used to reduce radiated underwater noise. Two modalities of sound attenuation by air bubbles were shown to provide a reduction in radiated sound: bubble acoustic resonance damping and acoustic impedance mismatching. The bubbles used for acoustic resonance damping were manifested using gas-filled containers coupled to a support, and the acoustic impedance mismatching bubbles were created using a cloud of freely-rising bubbles, which were both used to surround an underwater sound source.Board of Regents, University of Texas Syste

Ontogenetic change in predicted acoustic pressure sensitivity in larval red drum (Sciaenops ocellatus)

Author Posting. © Company of Biologists, 2019. This article is posted here by permission of Company of Biologists for personal use, not for redistribution. The definitive version was published in Journal of Experimental Biology 222(16), (2019): jeb.201962, doi:10.1242/jeb.201962.Detecting acoustic pressure can improve a fish's survival and fitness through increased sensitivity to environmental sounds. Pressure detection results from interactions between the swim bladder and otoliths. In larval fishes, those interactions change rapidly as growth and development alter bladder dimensions and otolith–bladder distance. We used computed tomography imagery of lab-reared larval red drum (Sciaenops ocellatus) in a finite-element model to assess ontogenetic changes in acoustic pressure sensitivity in response to a plane wave at frequencies within the frequency range of hearing by fishes. We compared the acceleration at points on the sagitta, asteriscus and lapillus when the bladder was air filled with results from models using a water-filled bladder. For larvae of 8.5–18 mm in standard length, the air-filled bladder amplified simulated otolith motion by a factor of 54–3485 times that of a water-filled bladder at 100 Hz. Otolith–bladder distance increased with standard length, which decreased modeled amplification. The concomitant rapid increase in bladder volume partially compensated for the effect of increasing otolith–bladder distance. Calculated resonant frequency of the bladders was between 8750 and 4250 Hz, and resonant frequency decreased with increasing bladder volume. There was a relatively flat frequency dependence of these effects in the audible frequency range, but we found a small increase in amplification with increasing excitation frequency. Using idealized geometry, we found that the larval vertebrae and ribs have negligible influence on bladder motion. Our results help clarify the auditory consequences of ontogenetic changes in bladder morphology and otolith–bladder relationships during larval stages.This work was supported by the American Museum of Natural History Lerner Gray Fund for Marine Research (to A.K.S.), the Perry R. Bass Endowment at the University of Texas Marine Science Institute (to L.A.F.), and the Office of Naval Research Ocean Acoustics Program (grant number N00014-15-1-2032 to P.S.W.).2020-08-0

An Audible Demonstration Of The Speed Of Sound In Bubbly Liquids

The speed of sound in a bubbly liquid is strongly dependent upon the volume fraction of the gas phase, the bubble size distribution, and the frequency of the acoustic excitation. At sufficiently low frequencies, the speed of sound depends primarily on the gas volume fraction. This effect can be audibly demonstrated using a one-dimensional acoustic waveguide, in which the flow rate of air bubbles injected into a water-filled tube is varied by the user. The normal modes of the waveguide are excited by the sound of the bubbles being injected into the tube. As the flow rate is varied, the speed of sound varies as well, and hence, the resonance frequencies shift. This can be clearly heard through the use of an amplified hydrophone and the user can create aesthetically pleasing and even musical sounds. In addition, the apparatus can be used to verify a simple mathematical model known as Wood's equation that relates the speed of sound of a bubbly liquid to its void fraction. (c) 2008 American Association of Physics Teachers.Mechanical Engineerin

Effects of frequency-dependent spatial variation in soundscape settlement cues for reef fish larvae

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Salas, A. K., Ballard, M. S., Mooney, T. A., & Wilson, P. S. Effects of frequency-dependent spatial variation in soundscape settlement cues for reef fish larvae. Marine Ecology Progress Series, 687, (2022): 1-21, https://doi.org/10.3354/meps14012.The mechanisms that link reef soundscapes to larval fish settlement behaviors are poorly understood, yet the management of threatened reef communities requires we maintain the recruitment processes that recover and sustain populations. Using a field-calibrated sound propagation model, we predicted the transmission loss in the relevant frequency band as a function of range, depth, and azimuth to estimate the spatial heterogeneity in the acoustic cuescape. The model highlighted the frequency- and depth-dependence of the sound fields fishes may encounter, and we predict these complex spatial patterns influence how sounds function as settlement cues. Both modeling and field measurements supported a non-monotonic decline in amplitude with distance from the reef. We modeled acoustic fields created by sounds at frequencies from 2 common soniferous reef-based animals (snapping shrimps and toadfish) and estimated detection spaces of these sounds for larvae of 2 reef fish species. Results demonstrated that larval depth will influence cue availability and amplitude, and these spatial patterns of detection depend on cue frequency and the larval receiver’s auditory sensitivity. Estimated spatial scales of detection coupled with field measurements suggest cue amplitudes might allow some larvae to detect reef-based sounds at a range exposing them to the predicted spatial variation in the acoustic cuescape. In an individual-based model, cues available to even the shortest modeled distances improved settlement success. Our results emphasize the need to consider the frequency- and depth-dependence of the acoustic cues larval fishes encounter to increase understanding of the role of soundscapes in larval settlement.We thank the following funding sources for partial support: The University of Texas at Austin Integrative Biology Department’s Zoology Scholarship Endowment for Excellence award (A.K.S.), Smithsonian Tropical Research Institute (STRI) Short-term Fellowship (A.K.S.), Office of Naval Research (P.S.W. and M.S.B), and National Science Foundation (OCE-15-36782; T.A.M). We thank P. Gondola for support through the STRI Bocas del Toro Research Station and Dr. Andrew Altieri for assistance in site selection and knowledge of local ecosystem

Underwater noise abatement panel and resonator structure

A system for reducing noise emissions in underwater environments is presented. The system can be extended to applications in any two-fluid environments where one fluid (gas) is contained in an enclosed resonator volume connected to the outside environment at an open end of the resonator body. The resonators act as gas-containing (e.g., air) Helmholtz resonators constructed into solid panels that are submerged in the fluid medium (e.g., sea water) in the vicinity of a noise generating source. The oscillations of the trapped air volume in the resonators causes reduction of certain noise energy and a general reduction in the transmitted noise in the environment of the system.Board of Regents, University of Texas Syste

Toward the Ultrasonic Sensing of Organic Carbon in Seagrass-Bearing Sediments

Ten percent of all organic carbon (Corg) absorbed by the ocean each year is stored in seagrass-bearing sediments. The preservation of these carbon stores is considered a vital method to mitigate climate change. Seagrass-bearing sediments have been correlated with sediment geophysical properties yet have not been related to sediment acoustic properties. For this purpose, sediment cores were collected from a Thalassia testudinum seagrass meadow in South Texas, USA, where geophysical, acoustical, and Corg properties were measured. It is hypothesized that when deposits of Corg adsorb onto mineral surfaces and are stored in pore spaces, compliant layers between grain contacts and the formation of an organic-rich suspension reduce sediment stiffness. Results from this seagrass meadow demonstrated a strong correlation between sediment P wave modulus and Corg and show promise toward the development of an in situ ultrasonic sediment probe to more rapidly quantify and monitor seagrass carbon stores

Mechanical Impact Performance of Additively Manufactured Negative Stiffness Honeycombs

Negative stiffness honeycombs materials are comprised of negative stiffness beams arranged in ordered arrays. They are capable of providing isolation from impacts and returning to their initial shape. Previous research by the authors focused on the behavior of negative stiffness honeycombs to quasi-static loading conditions. This paper investigates the behavior of similar negative stiffness honeycombs under impact. The construction of an impact testing rig for the experimental evaluation of negative stiffness honeycombs is discussed. Experimental results from impact tests performed on honeycomb prototypes manufactured using selective laser sintering (SLS) in nylon 11 material are presented and compared with analytical and finite element predictions as well as quasi-static test results.Mechanical Engineerin

Common mortality modeling and coherent forecasts. An empirical analysis of worldwide mortality data

A new common mortality modeling structure is presented for analyzing mortality dynamics for a pool of countries, under the framework of generalized linear models (GLM). The countries are first classified by fuzzy c-means cluster analysis in order to construct the common sparse age-period model structure for the mortality experience. Next, we propose a method to create the common sex difference age-period model structure and then use this to produce the residual age-periodmodel structure for each country and sex. The time related principal components are extrapolated using dynamic linear regression (DLR) models and coherent mortality forecasts are investigated. We make use of mortality data from the “Human Mortality Database”

Application of acoustical remote sensing techniques for ecosystem monitoring of a seagrass meadow

Seagrasses provide a multitude of ecosystem services and serve as important organic carbon stores. However, seagrass habitats are declining worldwide, threatened by global climate change and regional shifts in water quality. Acoustical methods have been applied to assess changes in oxygen production of seagrass meadows since sound propagation is sensitive to the presence of bubbles, which exist both within the plant tissue and freely floating the water as byproducts of photosynthesis. This work applies acoustic remote sensing techniques to characterize two different regions of a seagrass meadow: a densely vegetated meadow of Thalassia testudinum and a sandy region sparsely populated by isolated stands of T. testudinum. A Bayesian approach is applied to estimate the posterior probability distributions of the unknown model parameters. The sensitivity of sound to the void fraction of gas present in the seagrass meadow was established by the narrow marginal probability distributions that provided distinct estimates of the void fraction between the two sites. The absolute values of the estimated void fractions are biased by limitations in the forward model, which does not capture the full complexity of the seagrass environment. Nevertheless, the results demonstrate the potential use of acoustical methods to remotely sense seagrass health and density