An experiment was conducted to measure the transmission loss of an acoustic signal in shallow water with a stable ice cover. Transmission loss was measured at acoustic receivers in the water and in air over 30 meters....
An experiment was conducted to measure the transmission loss of an acoustic signal in shallow water with a stable ice cover. Transmission loss was measured at acoustic receivers in the water and in air over 30 meters. Received levels at the microphones were greatly attenuated relative to the hydrophones with over 100 dB reduction across the spectrum. The experiment was modeled with the OASES model for estimating propagation in the time domain. Results indicated that despite the high transmission losses, enough acoustic energy can propagate through ice to air to make this a propagation pathway for ice dependent pinniped communication.
In addition to subject mastery and the focused effort required to complete a thesis project, graduate students also need to develop a broad understanding of their field and cultivate a familiarity with the larger comm...
In addition to subject mastery and the focused effort required to complete a thesis project, graduate students also need to develop a broad understanding of their field and cultivate a familiarity with the larger community of researchers and practitioners. The "summer school" format has been shown to enhance both subject-matter breadth and build community awareness in physical acoustics. Physical acoustics Summer School (PASS) has been held in late-May, in even-numbered years, since 1992. The format for each day is usually two three-hour lectures followed by evening discussion groups to answer questions and explore extensions of the day's lecture topics. One lecture session is typically dedicated to acoustics demonstrations. Attendance for the full week is required of all participants who also dine together three times each day. Venues are chosen to provide isolation that minimizes distraction and maximizes interactions among all participants. Typical enrollment has been ten distinguished lecturers (including many Silver Medal winners in Physical acoustics), ten discussion leaders, and thirty graduate students. This format has been successfully extended to one other ASA Technical Committee: the marine bioacoustics community has held their summer school twice (SeaBASS). PASS has now been functioning long enough that former students have become lecturers.
Bond integrity is of interest to researchers in non-destructive evaluation because it is used as an indicator when assessing the health of structures. In this study, a plate waveguide on a half space is examined to fi...
Bond integrity is of interest to researchers in non-destructive evaluation because it is used as an indicator when assessing the health of structures. In this study, a plate waveguide on a half space is examined to find features associated with bond integrity. Analytical and finite element models are developed to describe wave propagation. Mode and frequency selection optimization is discussed. Preliminary results suggest that changes in arrival time and amplitude can be used to detect the length of a very weak bond when using a special mode of strong in-plane displacement at the interface.
Cavitation detection and localization techniques generally require visual access to the fluid field, multiple high-speed cameras, and appropriate illumination to locate cavitation. This can be costly and is not always...
Cavitation detection and localization techniques generally require visual access to the fluid field, multiple high-speed cameras, and appropriate illumination to locate cavitation. This can be costly and is not always suitable for all test environments, particularly when the bubble diameter is small or duration is short. Acoustic detection and localization of cavitation can be more robust and more easily implemented, without requiring visual access to the site in question. This research utilizes the distinct acoustic signature of cavitation events to both detect and localize cavitation during experimental water tunnel testing. Using 22 hydrophones and the processing techniques plane-wave beamforming and Matched-Field Processing (MFP), cavitation is accurately and quickly localized during testing in a 12” diameter water tunnel. Cavitation is induced using a Nd:YAG laser for precise control of bubble location and repeatability. Accounting for and overcoming the effects of reflections on acoustic localization in acoustically small environments is paramount in water tunnels, and the techniques employed to minimize error will be discussed.
Several passive sonar signal processing methods have previously been developed for determining the location of a source radiating tonal acoustic energy while moving through a shallow water environment. These localizat...
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This paper describes an ongoing research study to design a simulation device that can accurately reproduce sonic booms over the outside surface of an entire house. Sonic booms and previous attempts to reproduce them w...
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ISBN:
(纸本)9781605607122
This paper describes an ongoing research study to design a simulation device that can accurately reproduce sonic booms over the outside surface of an entire house. Sonic booms and previous attempts to reproduce them will be reviewed. The authors will present some calculations which suggest that it will be very difficult to produce the required pressure amplitudes using conventional sound reinforcement electroacoustic technologies. However, an additional purpose is to make AES members aware of this research and to solicit feedback from attendees prior to a January 2009 down-selection activity for the design of an outdoor sonic boom simulation system.
A low-frequency noise study was performed to investigate human response to the low-frequency content of aviation noise. High levels of noise can impact communities surrounding airports. Current predictive noise models...
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ISBN:
(纸本)9781604238525
A low-frequency noise study was performed to investigate human response to the low-frequency content of aviation noise. High levels of noise can impact communities surrounding airports. Current predictive noise models and metrics may underestimate the impact of low-frequency noise (LFN) produced by aviation noise. Assessing the role of LFN in affecting human response will provide a better understanding of how this type of noise can impact communities. Indoor recordings of aircraft arrivals and departures at Washington Dulles International Airport (IAD) made in 2004 were used to assess subjective noise annoyance. These recordings variants having different levels of low-frequency noise were reproduced for subjects in the Gulfstream Supersonic Acoustic Signature Simulator II (SASS II);the subjects then rated the signatures for annoyance. Subjective judgments were statistically analyzed and compared between each signature and within each signature set against commonly used objective metrics. Results are shown that all other things being equal higher levels of low-frequency content in aircraft noise can result in increased annoyance in subjects and that the C-weighted sound exposure level correlated with this annoyance response with a coefficient of determination of 90%.
This effort focuses on measuring and predicting the discrete-frequency and broadband noise radiated by a diesel engine cooling fan. In such engine cooling systems, where space is very limited, it would be very difficu...
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ISBN:
(纸本)9781604238525
This effort focuses on measuring and predicting the discrete-frequency and broadband noise radiated by a diesel engine cooling fan. In such engine cooling systems, where space is very limited, it would be very difficult if not impossible to measure the fan inflow velocity field using the conventional, stationary hot-wire method. Instead, the fan inflow was measured with a twocomponent x-type hot-film probe attached very close to the leading edge of a rotating blade. The fan's radiated noise was measured without contamination from the engine noise by driving the fan with an electric motor. The spatially non-uniform mean velocity field was used in axial-flow fan noise theory to predict the discrete-frequency noise at the blade-pass frequency and harmonics. The influences due to an upstream finger guard were also investigated. The spacetime correlations of the inflow velocity fluctuations were utilized in stochastic lifting surface theory to calculate the unsteady blade lift and resulting broadband fan noise. The radiated sound power spectra that were measured for the fan are shown to be in excellent agreement with those predicted.
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