Current Search: Underwater acoustics  Mathematical models (x)
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 Title
 Numerical models to simulate underwater turbine noise levels.
 Creator
 Lippert, Renee'., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

This work incorporates previous work done by Guerra and the application of fluid dynamics. The structure attached to the turbine will cause unsteady fluctuations in the flow, and ultimately affect the acoustic pressure. The work of Guerra is based on a lot of assumptions and simplifications to the geometry of the turbine and structure. This work takes the geometry of the actual turbine, and uses computational fluid dynamic software to numerically model the flow around the turbine structure....
Show moreThis work incorporates previous work done by Guerra and the application of fluid dynamics. The structure attached to the turbine will cause unsteady fluctuations in the flow, and ultimately affect the acoustic pressure. The work of Guerra is based on a lot of assumptions and simplifications to the geometry of the turbine and structure. This work takes the geometry of the actual turbine, and uses computational fluid dynamic software to numerically model the flow around the turbine structure. Varying the angle of the attack altered the results, and as the angle increased the noise levels along with the sound pulse, and unsteady loading increased. Increasing the number of blades and reducing the chord length both reduced the unsteady loading.
Show less  Date Issued
 2012
 PURL
 http://purl.flvc.org/FAU/3355622
 Subject Headings
 Underwater acoustics, Mathematical models, Turbines, Vibration, Mathematical models, Fluid dynamics
 Format
 Document (PDF)
 Title
 Estimation of the scattering function of fading channels for acoustic communications in shallow waters.
 Creator
 Allemand, Vincent., Florida Atlantic University, Beaujean, PierrePhilippe
 Abstract/Description

The measurement of the Scattering function of timevariant fading channels is of strong interest in the field of underwater acoustic communications, as it indicates the limitations of the channel capacity. It also helps reducing the development time of acoustic communication systems and the need for onsite tests using socalled "fading simulators". The Scattering function is interpreted as the expected power received at a given timedelay and frequency shift for a given signal transmitted...
Show moreThe measurement of the Scattering function of timevariant fading channels is of strong interest in the field of underwater acoustic communications, as it indicates the limitations of the channel capacity. It also helps reducing the development time of acoustic communication systems and the need for onsite tests using socalled "fading simulators". The Scattering function is interpreted as the expected power received at a given timedelay and frequency shift for a given signal transmitted through the acoustic channel. It has been estimated using a fourthmoment method developed by Kailath from 18 to 30 kHz, 8ms broadband chirps and 2028 kHz, 28ms pseudo noise sequences. These signals were transmitted periodically in the shallow coastal waters of South Florida from a static source, and recorded from a 64channel receiver array located at a distance of 1000 meters. Spatial beamforming has been applied to study the spatial sensitivity of the scattering function.
Show less  Date Issued
 2005
 PURL
 http://purl.flvc.org/fcla/dt/13230
 Subject Headings
 Underwater acoustic telemetry, Signal processingDigital techniques, Underwater acousticsMathematical models, Adaptive signal processing
 Format
 Document (PDF)
 Title
 Development and implementation of integrated acoustic and oceanographic numerical modeling in coastal regions.
 Creator
 Walker, Natasha Maria., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

An integrated coastal ocean and acoustic propagation model has been implemented to determine the effects of the ocean variations on the acoustic propagation field applied specifically to SFOMC. The ocean dynamics were modeled using the sigma coordinate, orthogonal curvilinear grid, Princeton Ocean Model. By using forcing conditions of tide, river runoff, wind and realistic bottom topography, the resulting time variant regional sound velocity outputs from the model were used as inputs to the...
Show moreAn integrated coastal ocean and acoustic propagation model has been implemented to determine the effects of the ocean variations on the acoustic propagation field applied specifically to SFOMC. The ocean dynamics were modeled using the sigma coordinate, orthogonal curvilinear grid, Princeton Ocean Model. By using forcing conditions of tide, river runoff, wind and realistic bottom topography, the resulting time variant regional sound velocity outputs from the model were used as inputs to the range dependent, parabolic equation, acoustic propagation model, RAM. The results show that the fluctuations in the ocean result in scintillation in the acoustic propagation field, and for higher frequencies this variability is uniformly distributed and at times as much as +/3 dB. High resolution in the POM grid and the range and depth sizes for RAM were important for obtaining reliable simulation results.
Show less  Date Issued
 2002
 PURL
 http://purl.flvc.org/fcla/dt/12901
 Subject Headings
 OceanographyMathematical models, Underwater acousticsMathematical models, Coastal engineering
 Format
 Document (PDF)
 Title
 Timedependent multipath modeling for underwater acoustic wave propagation in shallow water.
 Creator
 Boulanger, Florent Jacques., Florida Atlantic University, Beaujean, PierrePhilippe
 Abstract/Description

A novel acoustic wave propagation model has been developed to determine the effects of the ocean variations on the acoustic propagation field, and to determine the signal measured by a receiver at any distance from an omnidirectional source. The model accounts for environmental conditions. First, a stationary estimate of the complex sound attenuation is computed as a function of frequency and location, using the parabolic equation numerical technique. For a given range, the vertical profile...
Show moreA novel acoustic wave propagation model has been developed to determine the effects of the ocean variations on the acoustic propagation field, and to determine the signal measured by a receiver at any distance from an omnidirectional source. The model accounts for environmental conditions. First, a stationary estimate of the complex sound attenuation is computed as a function of frequency and location, using the parabolic equation numerical technique. For a given range, the vertical profile of the attenuation frequency spectrum is decomposed in the wave number domain. A specific Doppler shift is associated with each wave number. The spacefrequency attenuation filter obtained is applied to the transmitted signal to create timefrequency selective fading. This model has been used to simulate the performance of the General Purpose Acoustic Modem, which transmits MFSK modulated sequences between 15.6 kHz to 32.1 kHz. The range of operation varies from 1 to 5 km, in 15 meters of water. Experimental data have been collected under seastate 2 conditions. The model has been successfully validated when compared to experimental data and to the Crepeau model.
Show less  Date Issued
 2003
 PURL
 http://purl.flvc.org/fcla/dt/12978
 Subject Headings
 Underwater acousticsMathematical models, SoundTransmission, Ocean wavesMathematical models
 Format
 Document (PDF)
 Title
 Source speed estimation using a pilot tone in a highfrequency acoustic modem.
 Creator
 Kathiroli, Poorani., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

This thesis proposes to estimate the speed of a moving acoustic source by either linear or non linear processing of the resulting Doppler shift present in a highfrequency pilot tone. The source is an acoustic modem (Hermes) which currently uses moving average to estimate and compensate for Doppler shift. A new auto regressive approach to Doppler estimation (labeled IIR method in the text) promises to give a better estimate. The results for a simulated peak velocity of 2 m/s in the presence...
Show moreThis thesis proposes to estimate the speed of a moving acoustic source by either linear or non linear processing of the resulting Doppler shift present in a highfrequency pilot tone. The source is an acoustic modem (Hermes) which currently uses moving average to estimate and compensate for Doppler shift. A new auto regressive approach to Doppler estimation (labeled IIR method in the text) promises to give a better estimate. The results for a simulated peak velocity of 2 m/s in the presence of additive noise showed an RMSE of 0.23 m/s using moving average vs. 0.00018 m/s for the auto regressive approach. The SNR was 75 dB. The next objective was to compare the estimated Doppler velocity obtained using the two algorithms with the experimental values recorded in real time. The setup consisted of a receiver hydrophone attached to a towing carriage that moved with a known velocity with respect to a stationary acoustic source. The source transmitted 375 kHz pilot tone. The received pilot tone data were preprocessed using the two algorithms to estimate both Doppler shift and Doppler velocity. The accuracy of the algorithms was compared against the true velocity values of the carriage. The RMSE for a message from experiments conducted indoor for constant velocity of 0.4 m/s was 0.6055 m/s using moving average, 0.0780 m/s using auto regressive approach. The SNIR was 6.3 dB.
Show less  Date Issued
 2011
 PURL
 http://purl.flvc.org/FAU/3171396
 Subject Headings
 Underwater acoustics, Measurement, SIgnal processing, Digital techniques, Digital filters (Mathematics), Radio frequency, Mathematical models
 Format
 Document (PDF)
 Title
 Characterizing magnetic noise of AUV for use in towed magnetometer study of internal waves.
 Creator
 Tilley, Dylan., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

As part of a project to study internal waves, FAU plans to utilize an AUV to tow a magnetometer to study electromagnetic signatures from internal waves. This research is focused on the electromagnetic noise issues related to using an AUV to tow the magnetic sensor package. There are active sources of electromagnetic noise caused by an AUV that are present in addition to those induced by the Earth's magnetic field and permanent magnets. To characterize the magnetic noise associated with the...
Show moreAs part of a project to study internal waves, FAU plans to utilize an AUV to tow a magnetometer to study electromagnetic signatures from internal waves. This research is focused on the electromagnetic noise issues related to using an AUV to tow the magnetic sensor package. There are active sources of electromagnetic noise caused by an AUV that are present in addition to those induced by the Earth's magnetic field and permanent magnets. To characterize the magnetic noise associated with the AUV magnetometer tow system, the various active source elements were identified, the orientation sensitivity of the sensors being used was determined, and the magnetic anomaly of a similar AUV which may be eventually be used in a magnetic sensing arrangement was measured. The results are used to show the proposed sensing arrangement will likely not achieve the necessary sensitivity to measure subtle internal wave signals.
Show less  Date Issued
 2012
 PURL
 http://purl.flvc.org/FAU/3352881
 Subject Headings
 Automatic control, Mathematical models, Electromagnetic measurements, Fluctuations (Physics), Oceanographic submersibles, Underwater acoustics
 Format
 Document (PDF)
 Title
 A Study of the Underwater Acoustic Propagation in a Turning Basin Modeled as a ThreeDimensional Duct Closed at One End Using the Method of Images.
 Creator
 Staska, Matthew D., Beaujean, PierrePhilippe, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

A computerefficient model of the underwater acoustic propagation m a shallow, threedimensional duct closed at one end has been developed using the method of images. Presented in this research is the development of this threedimensional method of images analysis for a rectangular duct. Using this analysis, a model of the impulse response of the acoustic channel is constructed. Also presented in this work is the actual impulse response collected during field experimentation in the south...
Show moreA computerefficient model of the underwater acoustic propagation m a shallow, threedimensional duct closed at one end has been developed using the method of images. Presented in this research is the development of this threedimensional method of images analysis for a rectangular duct. Using this analysis, a model of the impulse response of the acoustic channel is constructed. Also presented in this work is the actual impulse response collected during field experimentation in the south turning basin of Port Everglades in Fort Lauderdale, Florida. The results demonstrate that the impulse response is modeled with a relative echo magnitude error of 1.62 dB at worst, and a relative echo location error varying between 0% and 4% when averaged across multiple measurements and sensor locations.
Show less  Date Issued
 2007
 PURL
 http://purl.flvc.org/fau/fd/FA00012557
 Subject Headings
 Underwater acousticsMeasurement, Wave motion, Theory of, Wave equationNumerical solutions, SoundwavesTransmissionMathematical models
 Format
 Document (PDF)