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2003 ACOUSTICS AREA SEMINARS ARCHIVE
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SPRING SEMINARS |
FALL SEMINARS
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2003 SPRING SEMINAR SCHEDULE
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Jan 24
Dr. Marcia Isakson,
Applied Research Laboratories,
The University of Texas at Austin
Comparison of Current Models for Water-Saturated Sand by Inversion of Reflection Loss Measurements
An accurate model of sediment acoustics is critical to understanding shallow water sound propagation and
the detection and classification of buried objects such as mines. Indeed, as SONAR becomes more important
in shallow water operations, an accurate high frequency acoustic model for ocean sediments becomes crucial
to its application. Several models exist for acoustic interaction with ocean sediments, including fluid, elastic
solid and poro -elastic model representations, with and without interface roughness and volume scattering
mechanisms. In this study, reflection data taken from a smooth water/sand interface are inverted using five
different models. The models considered are the visco -elastic model, the Biot -Stoll model, the composite
Biot -Stoll model, the effective density fluid model (EDFM) and the Buckingham model. Inversions were
performed using a simulated annealing algorithm with OASR as the forward model. Each model is
considered for its ability to produce realistic sediment parameters and its fit to the data. Inverted
parameter predictions will be compared with broadband dispersion and attenuation data and conclusions
will be drawn as to applicability of these models over a large frequency range.
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Jan 31
Nathan Crow,
Applied Research Laboratories,
The University of Texas at Austin
Diver-Held Sonar: The Integrated Navigation Sonar Sensor
Applied Research Laboratories has developed a diver-held sonar system for the U.S. Navy's Naval Special
Clearance Team One. This system, called the Integrated Navigation Sonar Sensor (INSS), was designed to
find mines in the very shallow water zone (water depths from 10 ft to 40 ft). In addition to functioning as
a sonar, the INSS is also part of a long baseline navigation system and thus allows divers to swim to a
series of predetermined waypoints, search the area for moored and bottom mines, and mark the positions
of mine-like objects. Once the diver has completed the mission, the data can then be transferred to a
computer where the maps and stored images can be combined with those from other divers and then
passed up the chain of command for analysis. The INSS system uses advanced motion-detecting sensors
to allow the diver to form a high-resolution image by manually panning a simple single-beam sonar. This
presentation will discuss the difficulties encountered detecting and classifying targets in the VSW
environment, the differences between older MCM sonars and the INSS, problems inherent in long baseline
navigation, and system enhancements sponsored by the Office of Naval Research.
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Feb 7
Jack Evans, P.E.,
JEAcoustics
Design and Remediation in Environmental Noise Control
JEAcoustics is an acoustical consulting firm specializing in architectural acoustics, mechanical, and
environmental noise and vibration. Two of our recent cases involving environmental noise control are
discussed in this seminar. The first involves an air-cooled chiller with rotary screw compressors installed
at a new hospital. The compressor generated a distinct and disturbing tone at 117 Hz not only in patient
rooms but in neighborhoods several blocks away. The required noise control, 5 to 8 dB of attenuation,
was determined by perceived annoyance according to Composite Noise Rating acceptability levels. Six
different mitigation proposals involving mechanical and acoustical modifications are discussed, including
installation of pulse diffusers, acoustic louvers, and discharge attenuators. The second case involves an
industrial research and development facility that incorporated engine test cells. The facility planned to
relocate from an urban environment with moderately high ambient noise levels to a semi-rural community
with quiet ambient conditions. To satisfy building code, the new noise contributions had to be limited to
5 dBA above the ambient environmental noise level. Design considerations focused on tonality, unbalanced
frequency spectra, intermittency, and other annoyance factors. This case study reviews muffler, silencer,
barrier, and directionality characteristics utilized in the noise mitigation solution to achieve acceptable
sound levels and smooth, balanced spectra at the receivers.
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Feb 14
Jeff G. Schmitt, P.E.,
VIAcoustics
Case Studies in Acoustical Consulting
Jeff G. Schmitt is the principal consultant of JGS Consulting, he is a 1983 UT graduate in acoustics and,
until 1995, he served as the President of Acoustic Systems, an Austin based manufacturer of acoustical
enclosures. He now practices as an independent acoustical consultant in a variety of areas. This
presentation will highlight several projects worked on over the past year, including ones at Caterpillar
Equipment Company, NASA Glenn Research Center, National Instruments, and XM Satellite Radio.
These projects will be used to illustrate a variety of acoustical consulting specialties, including isolation
of acoustic spaces, calibrated measurements, ISO quality systems, design of acoustic test software, and
organizing acoustics programs for industry.
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Feb 21
Professor Mark Hamilton,
Department of Mechanical Engineering,
The University of Texas at Austin
Acoustic Streaming Produced by Standing Waves
Acoustic streaming is the steady flow that is generated by momentum transfer associated with the
attenuation of sound. In a standing wave, shear stresses in the viscous boundary layer along the side
walls of an acoustic resonator produce a series of counter-rotating streaming vortices. The outer
vortices, first described by Rayleigh, are the dominant streaming patterns observed in wide channels.
In narrow channels, having widths that are comparable to the acoustic boundary layer, a second set of
streaming vortices dominates the steady flow, rotating in directions opposite those of the Rayleigh
vortices. Channels this narrow are required for efficient heat transfer in thermoacoustic engines, while
acoustic streaming acts to reduce this efficiency. The presentation will review some of the history
surrounding the study of acoustic streaming. New solutions will be presented for acoustic streaming in
channels of arbitrary width. Channels formed by either parallel plates or cylindrical tubes are considered,
with viscosity, thermal conductivity, and the dependence of viscosity on temperature are taken into account.
Measurements of acoustic streaming made recently at Penn State will also be discussed.
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Mar 3
Dr. Ron E. Kumon,
Department of Physics,
University of Windsor, Windsor, Ontario, Canada
Nonlinear Surface Acoustic Waves in Crystalline and Thin-Film Systems
The linear and nonlinear properties of surface acoustic waves (SAWs) in crystalline and laminated media are
significantly different from those of SAWs in an isotropic half-space. Selected numerical results are presented for
the propagation of initially monofrequency, finite-amplitude SAWs in a variety of surface cuts and directions in
several nonpiezoelectric, cubic crystals and thin-film systems. Measurements of pulsed waveforms in the (001), (110),
and (111) surface cuts of crystalline silicon obtained by collaborators at University of Heidelberg are shown to be
quantitatively reproduced by the calculated results. In thin-film systems, the combination of nonlinear harmonic
generation and frequency dispersion induced by the film can cause complicated harmonic evolution, including spatial
growth and decay cycles in some cases. Moreover, simulations indicate that the effects of large residual stresses in thin
films may significantly affect small- and finite-amplitude SAW propagation in these systems.
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Mar 7
Jeff G. Schmitt, P.E.,
VIAcoustics
Organizational Acoustics
Jeff G. Schmitt is a 1983 UT graduate in acoustics and, until 1995, he served as President of Acoustic Systems, an Austin
based manufacturer of acoustical enclosures. Since starting his own independent consulting firm he has worked with
a variety of large and small companies to build acoustical laboratories and integrate acoustical technology into their
products, services and business support structure. During his 20 years as a manager and consultant he has gained a
unique perspective into how organizations deal, or fail to deal, with acoustics as a business issue. This presentation
will focus on two areas. The first concerns tips on organizing an acoustics program for the acoustical engineer. It will be
shown how quality systems methods defined by ISO standard 17025 are used to create the foundation and
organizational structure for an acoustics program. The second focus is on integrating acoustics into the business for
the non-engineer. The roles of sales, marketing, finance and management, which are common struggles associated
with dealing with acoustics as a business issue, are discussed. The presentation will draw on materials used to teach
these concepts to engineers and support personnel in training seminars offered regularly by the speaker.
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Mar 21
Jack Evans, P.E.,
JEAcoustics
Case Studies in Architectural Acoustics and Noise Control
Two case studies will be presented involving architectural acoustics and noise control issues at the Denton A.
Cooley Texas Heart Institute Building in Houston . Very late in the construction phase the hospital management
decided to convert an unused atrium, designed originally as a purely aesthetic space, into an area for receptions
and meetings that may require the use of amplified sound. The meeting function of the atrium required an
acceptable acoustical environment yet one that would not produce unacceptable noise levels in adjacent patient
rooms. Design considerations focused on mechanical background noise, reverberation time, and wall transmission
losses. In the second case study, the architect designed a round auditorium with four conference rooms arrayed
across the back, separated from the auditorium by operable partitions which allow auditorium seating expansion
when opened. The acoustical challenges were to design diffusive and absorptive surface finishes to avoid focusing
from the round shape, provide good speech intelligibility, and to encourage beneficial reflections into the expansion
rooms when the operable partitions were open.
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Mar 31
Professor Preston Wilson,
Department of Mechanical Engineering,
The University of Texas at Austin
Sound Propagation and Scattering in Bubbly Liquids Across the Resonance Regime
For sonar-based naval operations to be successful in shallow water, significant knowledge of the acoustic behavior
of the ocean surface, the water column, and the ocean bottom is required. Natural and artificial processes produce
bubbles throughout this environment. Understanding the acoustics of bubbly media is therefore a necessity. For
air/water mixtures, asymptotic propagation theory and experiment at frequencies well below individual bubble
resonance (IBR) are in agreement. Due to high attenuation encountered near IBR, measurements in this regime are
difficult. Consequently, the full theory remains largely unverified. A novel impedance tube was constructed and
used to make measurements of phase velocity and attenuation in mixtures of air bubbles and water in the vicinity
of IBR. These experiments and comparison of results with existing theory are described. Acoustic scattering from
bubble clouds, which form beneath breaking waves, is also important. For frequencies well below IBR, an acoustically
compact bubble cloud can be modeled as a compressible sphere. The monopole scattering strength depends only on
spherical cloud volume and void fraction, not bubble size distribution or cloud shape. Measured bubble cloud target
strengths agree with this theory up to but not above the clouds monopole resonance frequency. To further understand
scattering from these objects, and to investigate the validity of the effective medium scattering theory for higher order
modes, laboratory scattering experiments were performed using geometrically well characterized bubbly-liquid targets.
Broadband measurements of scattering from bubbly-liquid-filled latex tubes are presented and compared with a
multi-mode effective medium theory.
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Apr 4
Dr. Diane Dalecki,
Department of Biomedical Engineering,
University of Rochester, Rochester, New York
Effects of Acoustic Fields on Tissues Containing Gas Bodies
Tissues known to contain gas bodies are particularly susceptible to damage from exposure to acoustic fields. Lung
and intestine contain gas bodies naturally and studies have demonstrated that ultrasound can produce damage to
these tissues. In response to low frequency acoustic fields, the lung acts as a resonant gas body. In addition to
tissues possessing gas bodies naturally, tissues containing gas-based ultrasound contrast agents are also susceptible
to damage from pulsed ultrasound and lithotripter fields. Studies with laboratory animals indicate that the presence
of contrast agents in the vasculature can increase the extent of ultrasound-induced hemolysis, vascular damage and
effects on cardiac rhythm. This lecture will discuss the bioeffects of acoustic fields in tissues that contain gas naturally
or after the addition of ultrasound contrast agents.
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Apr 11
Professor David Peterson,
Department of Mathematics,
University of Central Arkansas, Conway, Arkansas
Is There a Perfect Marimba Bar? The Art and Science of Bar Tuning
Vibrating bars have been extensively studied and the theory is well understood. But unlike a vibrating string, mode
frequencies are not integer multiples of the fundamental. By carving a bar in various ways it is possible to tune several
modes, most commonly to the ratio 1:4:10. Using a Timoshenko beam model it has been shown that tuning three modes
can be accomplished with parabolic arches, and so bars can be tuned to desired frequencies by manipulating two
parameters. My interest in bars began when I assigned a mathematics research student the task of tuning bars by
making two symmetrical cuts. So, is there a perfect marimba bar? In practice, each bar has a different shape (two
similar cuts won't do it ) . The selection of bar material (wood or fiberglass), tuning objectives, methodology (for
the most part mode frequencies can only be lowered and they are not independent), playability, and visual
appearance makes instrument building an art.
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Apr 17
Adam Dudley, Technical Coordinator/Audio Supervisor,
Bass Concert Hall,
The University of Texas at Austin
Tour of Bass Concert Hall
A technical tour of Bass Concert Hall will commence at the loading dock entrance on the back (west) side of the
building. The tour will describe how the technical team configures the auditorium and sound systems for a
particular performance, and it will include a walk-through of the auditorium, orchestra pit, and sound and amplifier rooms.
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2003 FALL SEMINAR SCHEDULE
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Aug 29
Professor Tom Muir,
Jamie Whitten National Center for Physical Acoustics,
University of Mississippi and the
U.S. Naval Postgraduate School, Monterrey, California
Seismic SONAR for Landmine Detection
Over 100 million landmines are buried in over 60 countries, worldwide, killing or maiming over 25,000 innocent
humans each year, mostly women and children. Present detection techniques that work (bayonets and metal
detectors) are primitive and slow. Ground penetrating radar is plagued by false targets and plastic mines. A
new method utilizing seismic interface waves that travel along the soil-air boundary has been developed by the
speaker and his colleagues. "Baby earthquakes," consisting of Rayleigh waves, are sent out by vibrational source
arrays on the ground. These waves propagate to the targets, reflect from them, and return to seismometer array
receivers. The range and bearing to suspected targets is determined. Confirmation of target type is made from
detection of the target's mechanical resonance modes in received echoes.
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Sep 12
Professor Preston Wilson,
Department of Mechanical Engineering,
The University of Texas at Austin
Acoustic Scattering from an Elastic Tube Filled with Bubbly Liquid
Sonar operation in shallow water is complicated by interaction with the sea surface. One difficulty is accounting
for scattering from near-surface bubble clouds, which are generated by breaking waves. This problem has been
addressed in the literature for low frequencies. An acoustically compact bubble cloud can be modeled as a
compressible sphere, where the scattering strength depends only on spherical cloud volume and mean void
fraction, not the bubble size distribution or cloud shape. This hypothesis was experimentally tested using freely
rising artificial bubble clouds [J. Acoust. Soc. Am. Vol. 92, 2993-2996 (1992)]. The low frequency monopole
target strength of the cloud agreed with this effective medium theory, but higher frequency results did not. To
resolve the issue, laboratory experiments were conducted using bubbly liquid targets with well-defined shape.
Measurements of scattering from a bubbly-liquid-filled latex tube are presented and compared to an effective
medium theory. Results indicate that the effective medium approximation remains valid well above the cloud's
monopole resonance frequency and up to 1/5th the individual bubble resonance frequency, once cloud shape is
considered. At higher frequencies, knowledge of the bubble size distribution becomes important, greatly
increasing the problem's difficulty.
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Sep 19
Professor Robert H. Flake,
Department of Electrical and Computer Engineering,
The University of Texas at Austin
Discovery of a New Signal Technology Providing Nondispersive Wave Propagation on Electrical Transmission Lines
as well as with Acoustic Waves in Lossy Media
A nondispersive propagating waveform has recently been discovered. This special signal, called Speedy Delivery
(SD), can theoretically be transmitted in many different categories of lossy, dispersive media without change in
shape or propagation speed. The extremely high SD signal shape fidelity and constant propagation speed have been
demonstrated experimentally in various cables, including coaxial and TWP electrical interconnects. The
nondispersive propagation property of the SD signal is predicted from the mathematical wave solutions of the lossy,
frequency dependent parameter telegrapher's equation, for acoustic plane waves in viscous media, and for the
propagation of sound in a chemically reactive fluid composed of two or more constituents (such as sea water). The
propagation of this signal, showing that its shape is preserved in a common coaxial cable, will be experimentally
demonstrated during the presentation and compared with the normal dispersive shape distortion experienced by
a rectangular pulse in the same cable. The experimental propagation of the acoustical variety of the SD waveform
has not yet been attempted.
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Oct 3
Xiang Yan,
Department of Mechanical Engineering,
The University of Texas at Austin
Statistical Model of Beam Distortion Due to Inhomogeneities in Tissue Harmonic Imaging
Tissue harmonic imaging (THI) is a new imaging technique in medical ultrasound. The images are created from the
nonlinearly generated second harmonics produced when ultrasound propagates inside the body. For many patients,
THI improves image resolution by reducing phase distortion due to the inhomogeneities in the body wall,
reverberation in this layer, and artifacts due to side lobes. This study was conducted to quantify the improvement
provided by tissue harmonic imaging in the presence of an inhomogeneous body wall layer. The layer is
approximated by a thin phase screen located directly in front of the source, and the random phase distribution across
the screen is characterized by its variance and correlation length. For a Gaussian source function, an integral solution
can be derived for the mean intensity of the second harmonic in the target plane. This statistical solution reveals
clearly the separate contributions due to the undistorted and scattered components in the beam. The solution is
verified by comparison with ensemble averages of direct numerical simulations of beam propagation through sample
phase screens. Overall good agreement is achieved. Experiments performed with circular piston sources, and etched
plastic plates to introduce phase distortion, support the theoretical model.
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Oct 10
Dr. Frank Boyle,
Applied Research Laboratories,
The University of Texas at Austin
Source Localization with Passive Line Arrays
An acoustic line array's finite aperture can be used to localize sources of detected acoustic signals in range as well
as azimuth. Two passive localization methods have been explored, including (1) a range focusing method wherein
images formed at different focal ranges are compared, and (2) a parallax ranging method wherein ranges are
computed by triangulation using images from spatially separated subarrays. The latter method is generally more
effective, particularly for long range sources. An important component of both methods is an image processing
technique, related to the Hough Transform, that enhances acoustic images for feature extraction. The presentation
will include a discussion of the influence of array geometry. An array's geometry will affect the structure of
ambiguities that can produce erroneous source location estimates. A two-dimensional beam pattern can be used to
model the ambiguities and assess the array's effectiveness. Possible techniques for assessing array geometry from
available sources of opportunity will be introduced.
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Oct 24
Dr. Brian R. La Cour and Mr. Michael Linford,
Applied Research Laboratories,
The University of Texas at Austin
Detection and Classification of Right Whales in the Bay of Fundy Using Independent Component Analysis
A novel method of detection and classification for marine mammals is presented which uses techniques from
independent component analysis to solve the blind source separation problem for right whales in the Bay of Fundy.
Using the fundamentally non-Gaussian nature of marine mammal vocalizations and data collected on multiple
hydrophones, we are able to separate right whale source spectra, up to an unknown scale, from ambient noise.
This technique assumes that the array data is a linear combination of the source signals but does not require specific
knowledge of the array geometry. A detector/classifier algorithm is demonstrated which compares the estimated
source spectra against known right whale vocalizations.
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Oct 31
Shihong Chi,
Department of Petroleum and Geosystems Engineering,
The University of Texas at Austin
Assessment of Mud Filtrate Invasion Effects on Full Waveform Acoustic Well Logging and Radial Profiling of
Formation Elastic Properties
Modern acoustic logging provides accurate descriptions of in-situ velocities of elastic waves propagating in rock
formations. These velocities are used to calibrate surface seismic data and to estimate the strength of rock formations
for wellbore stability analysis, hydro-fracturing, and sanding prevention. Integration of time-lapse acoustic logging
and rock physics can be used to monitor fluid movements and to find bypassed hydrocarbon zones after production.
Despite continued improvement in acoustic logging technology and interpretation methods of full waveform acoustic
data, acoustic logs processed with current industry standards are often affected by formation damage and
mud-filtrate invasion. Moreover, most of the amplitude information contained in borehole array acoustic waveforms
is not being used for interpretation. We develop efficient, accurate, and robust algorithms for modeling wave
propagation in fluid-filled boreholes in the presence of complex, near-wellbore, damaged zones. The new forward
modeling algorithm is based on the generalized reflection and transmission matrices method. An inversion algorithm
is also described to estimate radial profiles of elastic properties away from the borehole wall. The inversion
algorithm is a Gauss-Newton method that makes use of normalized array full waveform data in the frequency
domain. Assessment of mud-filtrate invasion effects on borehole acoustic measurements is performed through
simulation of time-lapse logging measurements. By comparing the velocities extracted from waveforms in
homogeneous and multilayered formations caused by mud-filtrate invasion, we evaluate the sensitivity of noisy
acoustic logs to the presence of radial variations of fluid saturation. Validation and testing of the algorithms is
performed against published results. Our studies indicate that the method of generalized reflection and transmission
coefficients is stable and efficient for the simulation of wave propagation in boreholes surrounded by complex
invasion zones. Mud-filtrate invasion effects are not observed on the P- and S- wave velocity logs for invasion
lengths around 2-3 borehole diameters. The inversion algorithm indicates that radial profiles of formation density,
and P- and S- wave velocities can be reconstructed from array waveforms data. Finally, a sensitivity study indicates
the estimation of rock formation properties is robust whenever the borehole fluid properties are known a priori.
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Nov 21
Dr. Jean-Claude Risset,
Composer and Director of Research at CNRS Laboratoire de Mcanique et d'Acoustique,
Marseille, France
The Perception of Musical Sound
Dr. Risset will give a talk on the perception of musical sound, with a number of sound examples on CD. He will
elaborate on the progress in perception of musical sound brought by the exploration of the resources of digital
sound synthesis (the process which permitted for the first time the manufacture of complex sounds with precisely
specified physical parameters): simulation of acoustic instruments; auditory and musical illusions as "errors of the
senses and truths of perception"; hearing as "auditory scene analysis" developed by evolution to yield information
as the outside world. He may also discuss his "Duet for One Pianist" - interactive music in the acoustic domain -
with some implications on the mechanics of the piano key.
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Dec 5
Bill McKenna,
Acoustic Systems
Tour of Acoustic Systems
This tour is a class field trip for Engineering Acoustics (ME 379N, EE 363N), but it is open to the public. Acoustic
Systems, located in Austin, Texas, has been designing, manufacturing, and installing acoustical products since 1971.
While Acoustic Systems does offer standard products, our focus is on custom designs, manufactured per customer
specifications. Acoustic Systems is staffed by highly qualified sales professionals who work in tandem with a team
of talented designers to provide responsive customer support throughout the design, manufacture and installation
phases of every project. The company operates a state-of-the-art manufacturing facility and a NVLAP (National
Voluntary Laboratory Accreditation Program) certified laboratory for the measurement of acoustic transmission loss,
absorption and noise reduction. The test facility is used for ongoing analysis and improvements to Acoustic Systems'
products as well as independent testing for companies throughout the United States.
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