Organizational Unit:
Engineering Acoustics Academic Committee (EAAC)

Description

The academic character of the programs in Engineering Acoustics is interdisciplinary, with courses and laboratory work drawn principally from the fields of physics and electrical engineering. Although broadly based, the emphasis of the programs is on those aspects of acoustics and signal processing applied to undersea warfare. Subjects covered include the generation, propagation and reception of sound in the ocean; military applications of underwater sound; and acoustic signal processing. These programs are designed specifically for students in the Applied Physics of Combat Systems, Undersea Warfare, and Underwater Acoustic Systems curricula, government employees in acoustics-related laboratories and systems commands, and international students.

Type

Program

Website of the organization

https://nps.smartcatalogiq.com/current/academic-catalog/groups-and-committees/engineering-acoustics-academic-committee/

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Publication Search Results

Now showing 1 - 10 of 37

Improving the visual perception of sonar signals with stochastic resonance
(Monterey, CA; Naval Postgraduate School, 2007-06) Went, Allison P.; Kalpolka, Daphne; Engineering Acoustics Academic Committee (EAAC)
The goal of this research project is to improve the detection of low-level tonals in LOFARgrams by reducing the negative effects of background noise using stochastic resonance. Stochastic resonance (SR), in general, is a phenomenon whereby the effect of low level signals is enhanced through the addition of noise. It has been invoked as an explanation for a wide range of observations from the periodicity of ice ages to the behavior of crayfish neurons. Recent work has focused on the possibility of applying it to image processing. Both static and moving image improvements have been reported. The basic technique behind the use of stochastic resonance in image processing is to first add a random amount of noise to each pixel in the image. Second, a threshold is applied to the image, so that pixels above the threshold are rounded up to the maximum pixel value, and pixels below the threshold are rounded down to the minimum. The images produced can either be averaged into a single image, or shown in series as a movie. In this thesis, a simulated signal was created and tested to find the amount of noise to add and the threshold to apply in order to maximize the signal-to-noise ratio of an averaged image. It was found that the best result was produced when a threshold was applied without adding any additional noise. This finding shows that the process does not demonstrate stochastic resonance for static images. A theoretical analysis of this result is provided. Although no improvement in the moving images was obvious, an SR effect in the optical nerves cannot be ruled out at this time. A future experiment is recommended that would use human test subjects to determine whether or not SR movies can be used to improve the detectability of low-level signals.
Extending the calibration in the Underwater Sound Reference Division (USRD) reciprocity coupler to incorporate phase
(Monterey, CA; Naval Postgraduate School, 2016-09) Slater, William H.; Baker, Steven R.; Crocker, Steven E.; Engineering Acoustics Academic Committee (EAAC)
In this report, a phase measurement is added to the Underwater Sound Reference Division (USRD) reciprocity coupler primary calibration procedure for an H48 reference hydrophone. Data acquisition equipment is added to record time-series data from the hydrophone under test and from the reciprocal transducers. The complex-valued hydrophone sensitivity is calculated. The sensitivity magnitude is compared to measurements from the standard coupler calibration procedure, and the complex sensitivity data are also fitted to a simple high-pass circuit model. The model is used to estimate the low-frequency cutoff of H48 hydrophone SN4. The low-frequency cutoff measured in this report is about 0.2 Hz higher than that originally measured and specified when the H48 hydrophones were first built. The new results show significant roll-off in phase below 10-20 Hz, a range where the phase is typically assumed flat during the standard calibration. By 1 Hz the phase roll-off is about 20°. The error analysis of the original coupler is summarized and error and uncertainty due to new data acquisition equipment and phase measurement added. Some errors due to simplifications in the acoustics of the coupler are left to future work.
REAL-TIME DETECTION OF SMALL UNMANNED AERIAL VEHICLES USING A BIO-INSPIRED MEMS SENSOR
(Monterey, CA; Naval Postgraduate School, 2023-06) Cruz, Rafael A.; Fargues, Monique P.; Durante Pereira Alves, Fabio; Engineering Acoustics Academic Committee (EAAC); Electrical and Computer Engineering (ECE)
Ormia Ochracea-inspired microelectromechanical systems (MEMS) sensors can be arranged in a configuration that detects the direction of arrival (DoA) of incident sound. Previous research results indicate that unambiguous DoA can be determined over 360 degrees in azimuth. To this date, analog readouts have been conducted using laboratory instrumentation. The objective of this study was to develop, build and test a circuit configuration that includes housing and power for the MEMS sensor, and the design of a graphical user interface (GUI) to read the DoA from an array of sensors and triangulate the position of a multi-rotor small UAV using GPS position data. Test fields were performed using a configuration of two nodes to detect a small rotor UAV. The operation scenario was displayed on a map. This new configuration can detect sound from any detectable source and provide the coordinates of the source of the sound.
On the use of sympathetic resonators to improve low frequency transducer performance
(Monterey, CA; Naval Postgraduate School, 1990-09) Ellsworth, John Merle; Baker, Steven R.; Engineering Acoustics Academic Committee (EAAC); Antisubmarine Warfare Academic Group (ASWAG); Wilson, Oscar B.
The achievable gain in the radiation resistance and directivity of a low frequency underwater transducer due to the presence of an array of sympathetic resonators was analyzed. The resonators were all taken to be air bubbles, and both the resonators and transducer were taken to be compact (ka1) . The resonators were taken to be equally spaced around a circle of radius R, with the transducer located on the axis. The gain was calculated for various numbers of resonators as a function of ka (resonators), ka transducer and kR, for the transducer in the plane of the resonators and out of the plane a distance of one quarter wavelength. For the transducer in the plane, a gain in radiation resistance of approximately two possible with six or more resonators. For the transducer out of the plane, it is shown that a significant gain in directivity can be achieved at the expense of a slight decrease in the gain in the radiation resistance.
DEVELOPMENT OF PHYSICS LECTURE DEMONSTRATIONS FOR UNDERSEA WARFARE
(Monterey, CA; Naval Postgraduate School, 2015-09) Khan, Faisal A.; Denardo, Bruce; Engineering Acoustics Academic Committee (EAAC); Kapolka, Daphne
The importance of educational research is evidenced by many STEM programs (science, technology, engineering, and mathematics), including those by the U.S. Navy. This thesis focuses on the development of new physics lecture demonstrations that are especially relevant for the Undersea Warfare curriculum at the Naval Postgraduate School. Three different phenomena are investigated: (i) reciprocity in linear passive electrical networks, (ii) a Cartesian diver including neutral buoyancy, and (iii) neckless Helmholtz resonators. In (i), we investigate reciprocity in a large two-dimensional resistor grid and a randomly generated network of resistors, capacitors, and inductors. Reciprocity is important in underwater acoustics transduction. In (ii), we investigate the sinking of a floating body and the instability of a neutrally buoyant body, which are important in the motion of submarines. In (iii), we investigate a resonator consisting of a thin plastic sphere with a hole, and describe an experiment with a precision cylindrical resonator. Helmholtz resonators can be used for the generation of underwater sound, and can unintentionally occur on submarine surfaces. The pursuit of physics demonstrations can contribute to forefront research. In our case, this occurred for the parametric stabilization of a neutrally-buoyant body and for the resonance frequency and quality factor of neckless Helmholtz resonators.
EXPERIMENTS IN PASSIVE SUPPRESSION OF LOW-FREQUENCY BROADBAND UNDERWATER SOUND
(Monterey, CA; Naval Postgraduate School, 2021-12) Wyman, Richard L., III; Denardo, Bruce C.; Godin, Oleg A.; Engineering Acoustics Academic Committee (EAAC)
A theoretical article by O. A. Godin and A. B. Baynes in 2018 predicts that an air-filled bladder near an underwater sound source can substantially suppress the sound emission. Practical applications include reducing the acoustic signature of naval vessels by placing a bladder near the propellers. We performed experiments in a Spanagel Hall tank and in Monterey Bay, comparing data to the theory. To improve previous thesis data gathered in the tank, we procured a more suitable sound source and a better bladder, and we increased the mass of the anchor that tethers the bladder, so that a larger bladder could be submerged. In addition, the method of gathering data was improved so that essentially continuous values occurred over our frequency range of 0.5 to 5.0 kHz. Data were gathered with and without the air bladder, and the ratio of the amplitudes were compared to predicted values, yielding positive trends. In Monterey Bay, an imploding lightbulb was used as a source while large balloons were used as a bladder. The bulb was burst at depth 10 meters with and without the balloons, and the sound was measured by a distant receiver. The data were compared to advanced theoretical models, accounting for some aspects of the environment. This initial attempt yielded encouraging results, indicating that the theory should be further tested by more controlled experiments in the ocean environment.
LOW-FREQUENCY ACOUSTIC VECTOR FIELD STABILITY IN THE PRESENCE OF ENVIRONMENTAL VARIABILITY
(Monterey, CA; Naval Postgraduate School, 2018-09) Laksana, Fahmi Chandra; Smith, Kevin B.; Engineering Acoustics Academic Committee (EAAC); Joseph, John E.
The Department of Physics at the Naval Postgraduate School recently collected data from a low-frequency vector sensor system off the coast of Big Sur, California, in May 2018. During the test, signals from numerous surface craft were recorded. In this study, a numerical model was employed to estimate the vector field transmission loss at low frequency in order to estimate performance of the system during the test. In order to provide realistic ranges of values, the impact of environmental variability was examined and the primary factors affecting transmission loss were identified. The range-dependent environmental features included varying bathymetry as well as a rough pressure release surface that can predict the effects of rough surface scattering. During the field test, sound speed profile measurements were made, and surface wave buoy data was collected that provided realistic estimates of these features in the vicinity of the sensor system. Various geoacoustic bottom parameters were modeled in order to estimate the potential variability in transmission loss levels due to uncertainty in bottom type. Finally, models of merchant ship source levels were combined with the range of transmission loss predictions to develop estimates for received levels on the vector sensor system during the test. These estimates will then provide a guide during the post-processing of the data collected and may lead to improvements in source level modeling.
MODELING ACOUSTIC PROPAGATION FROM CONICAL SHAPED AND STANDARD BLOCK EXPLOSIVE SOURCES IN COMPLEX OCEAN ENVIRONMENTS
(Monterey, CA; Naval Postgraduate School, 2020-03) Chiu, Wei-Ming; Hooper, Joseph P.; Olson, Derek; Engineering Acoustics Academic Committee (EAAC); Oceanography (OC)
Detection of underwater explosions by acoustic means, which has been widely researched, is simple, given the large peak pressures produced by these types of sources. By contrast, estimation of the explosive yield and type of explosive by such means has received less attention. This research compares the propagation of acoustic waves in a shallow water waveguide generated by underwater detonations producing broadband impulse signals. Typically, broadband waves are dispersive due to the waveguide in shallow water regions. Data was drawn from experiments conducted near Oahu, Hawai’i, using two explosive sources for different configurations: a conical shaped charge and a standard block. Both sources consisted of Composition C-4 explosive material and were detonated at comparable depths. This thesis focuses on differentiating the propagation of acoustic waves in multiple environments from these two kinds of sources. Simulations were used to explore different seabed properties, which varied by location, and how they impacted peak pressure variability across the Indo-Pacific region. By enhancing the understanding of acoustic propagation of explosive sources in complex environments, this research is helpful in cross domain operations. The developed models can also be applied defensively to determine the optimal placement and number of sensors required to monitor critical infrastructure on the seabed.
Detection of binary phase-shift keying signal in multipath propagation
(Monterey, CA; Naval Postgraduate School, 2002-06) Jung, Du San; Therrien, Charles W.; Engineering Acoustics Academic Committee (EAAC); Tummala, Murali
Time-varying dispersion and multipath propagation in a shallow underwater environment causes intersymbol interference in underwater communication. This thesis investigates a mitigation procedure for communication using a Binary Phase-Shift Keying (BPSK) signal. The method employed uses the time-reversed ocean impulse response to mitigate the degradation of the bit error rate performance. All results were achieved by the use of computer simulation of typical shallow water environments.
A study of the vertical component of ocean floor vibrations in two geographical chokepoints
(Monterey, CA; Naval Postgraduate School, 2017-03) Hankins, Jeremy R.; Kapolka, Daphne; Engineering Acoustics Academic Committee (EAAC); Libby, Steve
The purpose of this thesis is to characterize typical levels of vibrational noise on the ocean floor to ascertain the vibration's effect on possible future bottom mounted sensors. The data used for this thesis was obtained from publicly available recorded information from four ocean bottom seismometers (OBS). The OBSs were located in two geographical choke points: the Luzon Strait and west of the Strait of Juan de Fuca. These highly trafficked choke points were considered to be a good representation of where these experimental bottom mounted sensors might be located should they be built. Unix-based seismic processing software available from the Incorporated Research Institutions for Seismology (IRIS) proved essential to obtaining calibrated data, and the methodology used to get the calibrated data is discussed in detail. The results showed that one OBS out of the four was highly variable, with decibel levels varying widely from day to day. The other OBSs remained fairly consistent. In addition, there were no common discrete frequencies between sensors that were in the same geographic area. Recommended future research involves the study of environmental effects on the OBSs, additional research to correlate the results observed in the Luzon Strait, and a look into the electronic noise floors of the OBSs used.