Dan Farrell | Acoustics.org

3pID3 – Hot topics in a warming ocean: How acoustical oceanography can help monitor climate change

Gabriel R. Venegas – gvenegas@arlut.utexas.edu

Applied Research Laboratories, The University of Texas at Austin
10000 Burnet Rd
Austin, TX 78758

Popular version of paper 3pID3
Presented Wednesday afternoon, December 4, 2019. 1:45pm-2:05pm
178th ASA Meeting, San Diego, CA

Sound is an effective way to study the ocean by non-invasively and quickly surveying large areas, and acoustical oceanography has lent an extra pair of ears to help scientists monitor climate change. This talk will showcase the work of some of the many acoustical oceanographers in the Acoustical Society of America (ASA) that have made valuable contributions to aid in climate change related monitoring, in the hope of inspiring other members to think of new potential acoustic monitoring applications.

Heat
The planet is warming and so are its oceans. This warming causes the seawater to expand and large volumes of ice to break off from glaciers and melt in the ocean, ultimately resulting in sea level rise. An acoustic technique called passive acoustic thermometry^1,2 takes the noise created by these calving events at the north and south poles to calculate the speed of sound averaged over path lengths as long as 132 km. Temperature can then be inferred from sound speed using a well-established formula relating the two quantities.

As the glaciers melt, they release tiny compressed air bubbles that make loud popping sounds underwater.³ If these popping sounds can be reasonably characterized at one or many glacial bays, at a safe distance, these sounds can be used to estimate the glacial melt rate.^4,5

An increase in ocean temperature also causes methane hydrate, a material in ocean sediments that can store large amounts of methane, to turn from solid to greenhouse gas, which bubbles up from the seafloor and is ultimately released into the atmosphere. The sound of these bubbles has also been exploited to estimate the volume of methane released from hydrates and seeps.^6–8

CO₂
Global CO₂ concentrations are higher than they have been over the last 800,000.⁹ A quarter of this gas is absorbed into the ocean and has caused the what is thought to be the fastest increase in ocean acidity in the last 60 million years.¹⁰ An increase in ocean temperature, actually decreases the ocean’s capacity to store CO₂, causing it to be released back into the atmosphere. The relationship between ocean acidity and the absorption of sound is well understood. A passive acoustic technique using the sound of wind over the water is being investigated to estimate the absorption and thus ocean acidity.¹¹

Ocean acidity also causes damage to many coastal ecosystems including valuable “blue carbon” stores such as mangroves, salt marshes, and seagrasses, which store 50% of the ocean’s organic carbon.¹² The destruction of these carbon stores can also release CO₂ back into the atmosphere. An ultrasonic sensor that will improve organic carbon estimates in these ecosystems is currently under development.¹³ These climate-altering feedback loops can cause rapid and catastrophic consequences for future generations, and should be the responsibility of all scientists, elected officials, and the general public, alike

References

¹K. F. Woolfe, S. Lani, K. G. Sabra, and W. A. Kuperman, “Monitoring deep-ocean temperatures using acoustic ambient noise,” Geophys. Res. Lett. 42, 2878-2884 (2015); https://doi.org/10.1002/2015GL063438

²K. G. Sabra, B. Cornuelle, W. A. Kuperman, “Sensing deep-ocean temperatures,” Physics Today 69, 32-38 (2016). https://doi.org/10.1063/PT.3.3080.

³R. J. Urick, “The noise of melting icebergs,” J. Acoust. Soc. Am. 50, 337-341, (1971); https://doi.org/10.1121/1.1912637

⁴E. C. Pettit, K. M. Lee, J. P. Brann, J. A. Nystuen, P. S. Wilson, S. O’Neel, “Unusually loud ambient noise in tidewater glacier fjords: A signal of ice melt,” Geophys. Res. Ltt. 42, 2309-2316 (2015); https://doi.org/10.1002/2014GL062950

⁵O. Glowacki, G. B. Deane, and M. Moskalik, “The intensity, directionality, and statistics of underwater noise from melting icebergs,” Geophys. Res. Ltt., 45, 4105–4113 (2018); https://doi.org/10.1029/2018GL077632

⁶C. A. Green, P. S. Wilson, “Laboratory investigation of a passive acoustic method for measurement of underwater gas seep ebullition,” J. Acoust. Soc. Am. 131, EL61 (2012); https://doi.org/10.1121/1.3670590

⁷T. G. Leighton and P. R. White, “Quantification of undersea gas leaks from carbon capture and storage facilities, from pipelines and from methane seeps, by their acoustic emissions,” Proc. R. Soc. A 468, 485-510 (2012); https://doi.org/10.1098/rspa.2011.0221

⁸T. C. Weber, L. Mayer, K. Jerram, J. Beaudoin, Y. Rzhanov, D. Lovalvo, “Acoustic estimates of methane gas flux from the seabed in a 6000 km2 region in the Northern Gulf of Mexico,” Geochem. Geophys. Geosys. 15, 1911-1925 (2014); https://doi.org/10.1002/2014GC005271j

⁹D. Lüthi, M. Le Floch, B. Bereiter, T. Blunier, J.-M. Barnola, U. Siegenthaler, D. Raynaud, J. Jouzel, H. Fischer, K. Kawamura, and T. F. Stocker, “High-resolution carbon dioxide concentration record 650,000–800,000 years before present,” Nature 453, 379-382 (2008); https://doi.org/10.1038/nature06949

¹⁰C. Turley and J.-P. Gattuso, “Future biological and ecosystem impacts of ocean acidification and their socioeconomic-policy implications,” Curr. Opin. Environ. Sustain. 4, 278-286 (2012); https://doi.org/10.1016/j.cosust.2012.05.007

¹¹D. R. Barclay and M. J. Buckingham, “A passive acoustic measurement of ocean acidity (A),” Conference & Exhibition Series on Underwater Acoustics, 5, 941 (2019).

¹²J. Howard, S. Hoyt, K. Isensee, E. Pidgeon, M. Telszewski (eds.). Coastal Blue Carbon: Methods for assessing carbon stocks and emissions factors in mangroves, tidal salt marshes, and seagrass meadows. Conservation International, Intergovernmental Oceanographic Commission of UNESCO, International Union for Conservation of Nature. Arlington, Virginia, USA. (2014).

¹³G. R. Venegas, A. F. Rahman, K. M. Lee, M. S. Ballard, P. S. Wilson, “Toward the Ultrasonic Sensing of Organic Carbon in Seagrass‐Bearing Sediments,” Geophys. Res. Ltt. 46, 5968-5977 (2019); https://doi.org/10.1029/2019GL082745

4pPPa6 – Benefits of a Smartphone as a Remote Microphone System

Dr. Linda Thibodeau, thib@utdallas.edu
Dr. Issa Panahi
The University of Texas at Dallas

Popular version of paper 4pPPa6
Presented Thursday afternoon, December 5, 2019
178^thASA Meeting, San Diego, CA

A common problem reported by persons with hearing loss is reduced ability to hear speech in noisy environments. Despite sophisticated microphone and noise reduction technology in personal amplification devices to address this challenge, speech perception remains compromised by factors such as distance from the talker and reverberation. Remote microphone (RM) systems have been shown to reduce the challenges hearing aid users face with communicating in noisy environments. The RMs worn by the speaker can stream their voice wirelessly to the users’ hearing aids which results in a significant improvement in the signal-to-noise ratio and make it easier to hear and understand speech.

Given that the additional cost of a RM may not be feasible for some individuals, the possible use of applications on a smartphone has been explored. In the past five years, it has become increasingly common for hearing aids to connect wireless to smartphones. In fact, one desirable feature of the connection to the Apple iPhone has been an application called ‘Live Listen’ (LL). This application allows the iPhone to be used as an RM with made for iPhone hearing aids.

The Statistical Signal Processing Research Laboratory at The University of Texas at Dallas has developed an application for the iPhone that is also designed to be used as an RM. The application, called SHARP, has been tested with persons with normal and impaired hearing and with several types of hearing aids in the Hearing Health Laboratory at the University of Texas at Dallas. A study was conducted to compare the benefit of LL and the SHARP application for participants with and without hearing loss on sentence recognition tasks in noise when listening through hearing aids connected to an iPhone. A video summary of the testing protocol is show in the following short video clip.

Both the LL feature and the SHARP app provide a range of benefits in speech recognition in noise from no benefit to 30% depending on the degree of hearing loss and type of aid. The results suggest that persons can improve speech recognition in noise and perhaps increase overall quality of life through the use of applications such as SHARP on the smartphone in conjunction with wirelessly connected hearing aids.

2pSA9 – Acoustic transients from the impact force excitation of beams and wind chimes

Peter Stepanishen, steppipr@uri.edu
University of Rhode Island
Department of Ocean Engineering
Narragansett, RI 02871

Popular version of paper 2pSA9
Presented on Tuesday December 3, 2019
178th ASA Meeting, San Diego, CA

The origin of wind chimes dates back to 1100 BC in Eastern and Southern Asia where the chimes were intended to ward off evil spirits and attract benevolent spirits. Modern wind chimes typically consist of 4 to 8 aluminum tubes with varying lengths and associated resonant frequencies corresponding to a specific musical scale. In addition the wind chimes also include a wind catcher and associated wind clapper to impact the chimes as illustrated in Figure 1 below:

The present paper addresses the underlying physics of wind chimes from the viewpoint of a structural acoustician. The impact excitation and vibration of the structure is addressed including the effects of the surrounding air on the vibration characteristics of the wind chime which is modeled as a sum of cylindrical pipes or beams. The directional characteristics of the transient acoustic field are then addressed.

The dominant sound producing features for each cylindrical pipe/beam are simply described as a sum of temporally decaying modal beam vibrations with different resonant frequencies which are inversely related to the square of the length of the pipe. A simple illustration of the predominant sound producing lowest frequency modal vibration is illustrated in the accompanying video:

The video simply illustrates the lowest modal vibration of a free free beam which is presented as a simple model of a cylindrical wind chime vis-à-vis a cylindrical shell model. The ends of the beam/pipe undergo the maximum transverse deflection and vibration whereas two nodal points with zero deflection are also apparent for the fundamental modal vibration. In contrast to stringed musical instruments, the higher order modal vibrations are associated with a nonharmonic series of resonant frequencies with an increasing number of nodal points as the modal number increases. Experimental results confirm the validity and usefulness of the cylindrical beam model of the wind chime pipes.

Acoustic transient radiation from a vibrating chime is addressed in the paper using a space-time superposition of ring sources along the axis of the chime. The ring sources are shown to result in a space-time varying force on the air in contact with the chime. Furthermore, the force is simply related to the previously noted sum of temporally decaying modal beam vibrations. The directional properties of the acoustic field are discussed and it is shown that the field exhibits nulls in the directions along and perpendicular to the axis of the chime.

2aSA9 – Acoustic black holes in airfoils

Kaushik Sampath – kaushik.sampath.ctr.in@nrl.navy.mil

NRC Postdoctoral Fellow, Acoustics Division, Code 7165,

U S Naval Research Laboratory

4555 Overlook Ave SW,

Washington, DC 20375

Caleb F. Sieck – caleb.sieck@nrl.navy.mil

Matthew D. Guild – matthew.guild@nrl.navy.mil

Charles A. Rohde – charles.rohde@nrl.navy.mil

Alec Ikei – alec.ikei@nrl.navy.mil

Acoustics Division, Code 7165,

U S Naval Research Laboratory

4555 Overlook Ave SW,

Washington, DC 20375

Popular version of paper 2aSA9 – “Incorporating acoustic black holes in hydrofoils”

Presented at 11.30 am on December 3, 2019

178th ASA Meeting, San Diego, California.

Read the abstract by clicking here.

Most of us who have flown in an airplane can recall how bumpy it gets when there is ‘turbulence’. It is scary to watch wings bend the way they do, even though they are designed to withstand such bumps. However, as one can imagine, these vibrations are not desirable and affect the aircraft’s longevity and performance. When we slice an aircraft wing somewhere in between (as highlighted in the sketch below), we find that it has a unique shape, called an ‘airfoil’. This is the shape that makes the plane fly, and also, as a result, bears the brunt of turbulent air and those vibrations.

In 1988, Mironov pointed out that vibrations that strike on one end of a beam may never make it through if the other end is tapered gradually enough all the way down to a ‘zero thickness’. In other words, those vibrations get trapped or absorbed inside forever – also known as the ‘acoustic black hole’ effect. In reality, since it isn’t possible to make an edge have zero thickness, scientists have figured out that sticking some damping material near the edge (similar to foam or rubber on furniture feet) works almost as well.

In this study, we explore a way this effect could help reduce those airfoil vibrations. For the airplane, only the shape on the outside of the airfoil matters, not the inside. We take advantage of this fact and show that it is possible to design an airfoil with these black holes inside, without changing either the outside shape or the total weight.

Shown below are three of the designs that we tested. We fix the mass of the structure and damping that we use, and redistribute them between the three cases. The first case has uniformly spread structure and damping, to represent a ‘standard’ design. We’re basically trying to improve on this. The second case has a single black hole inside along with appropriate damping, while the third case has three.

We use some of the latest in 3d printing technology to create these complex designs. For testing them, we vibrate all three airfoils on their front edge in the same way and measure how vibrations move through the airfoil length all the way to the back edge. Shown below are the vibration levels that we measured at the rear edge over three frequency ranges. Note, lower the vibration, the better.

When compared with the uniform case, the sample with one black hole does 10-15% in the low and mid frequency ranges, and ~30% better in the high frequency range. The three-black hole case does almost similar (~1% worse in fact) for the low frequency range, but performs 50-65% better for higher frequencies. These results are promising and motivate us to expand our research in this direction.

Work sponsored by the Office of Naval Research.

3pAA4 – Small town factory into modern multi-purpose music hall

David Manley – dmanley@dlrgroup.com
Rolando De La Cruz – rdelacruz@dlrgroup.com

DLR Group
6457 Frances Street
Omaha, NE 68106

Popular version of paper 3pAA4
Presented Wednesday afternoon, December 4, 2019
178^th ASA Meeting, San Diego, CA

A former oil boomtown, El Dorado, Arkansas has a rich history, unique historic architecture, and a well-established arts and entertainment community, which includes the South Arkansas Symphony Orchestra, the South Arkansas Arts Center, and numerous successful music festivals. Community leaders sought to develop these assets into a regional draw and community anchor. The intent is to improve the quality of life and re-brand the community as a cultural performance mecca, while also slowing the decline in population (currently at 18,500) and revitalizing the local economy.

DLR Group’s master plan and design leverages existing historic assets, including the National Register-listed Griffin Auto Building, five other legacy structures, and new construction, to create a multi-venue downtown arts and entertainment district that preserves and celebrates the unique identity of El Dorado while appealing to contemporary audiences and future generations.

Implemented in phases, the project encompasses a 125,868 SF site and comprises a 7,000-patron festival venue/amphitheater, a 2,000-seat indoor music venue, a 100-seat black box/multi-purpose room, an 850-seat multi-use theater, a restaurant/club with stage, a visual arts facility, a farmers’ market, a children’s activity center, a park, and considerable site improvements for festivals along with new structures to support that use.

Phase 1 transformed the historic Griffin Auto Building (two-level, historic filling station, automotive showroom/repair shop) into a restaurant and flat-floor, indoor music venue. The warehouse was converted to an 1,800 seat (2,400 max. standing capacity) music venue.

Controlling the reverberation time, the time it takes sound to decay 60 decibels in a space, was critical to the acoustical success of the music venue. At over 18,000 square feet of floor space and nearly 600,000 cubic feet of volume, and constructed of concrete, metal deck, and masonry walls, the existing warehouse reverberation time was over 10 seconds long.

With a desired program of top tier modern amplified shows including rock and roll, country, and comedic talent, plus the South Arkansas Symphony Orchestra, the design goal for the renovated warehouse was 1.5 seconds in reverberation time.

Achieving this goal required ample use of acoustically absorptive material. After renovations to ensure the structural integrity of the existing roof were completed, and fireproofing was applied, 75% of the 30-foot-high and 96-foot-wide barrel-vaulted ceiling was covered with four-inch-thick fabric wrapped fiberglass panels. On lower walls, perforated metal panels were used for impact protection with fiberglass insulation behind for acoustical absorption. A total of almost 20,000 square feet of acoustically absorptive material was added to the warehouse.

File missing (1-RTGraph.jpg)
Figure 1 – Reverberation time calculation comparison of the existing and proposed treated Warehouse

The open-air filling station was enclosed by a glass curtain wall and converted to a restaurant dining area with stage for performance of live music. Separating the two music venues, the showroom was partly converted to a commercial kitchen to serve the restaurant dining area, and partly converted to a VIP area for events.