143 research outputs found

    Broadband Passive Sonar Signal Simulation in Shallow Ocean

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    The broadband plane wave model is valid only in the far-field of a point source under free-field propagating conditions. However the acoustics in ocean is characterized by multi-modal acoustic propagation due to its top-bottom limited boundary conditions. The effect of multi-modal field is to alter the source spectrum while the effect of dispersion is to modify the pulse shape. Moreover the use of a plane wave beamformer in a multi-modal field leads to a bias in the bearing estimates. These effects are highly dependant on the environment parameters and have important ramifications for target localization and classification in an ocean waveguide. We propose a more realistic simulator which essentially models these effects and therefore serves to provide test signals for first hand verification of signal processing algorithms to be developed for such scenarios. This model is to be understood as a better model than the naรฏve plane wave model which is entirely oblivious of even the gross features such as wave propagation in an oceanic waveguide. The channel parameter so estimated from the present simulation can be convolved with the radiated noise spectra of the source to generate the passive sonar signal.Defence Science Journal, 2011,ย 61(4), pp.370-376,ย DOI:http://dx.doi.org/10.14429/dsj.61.8

    Localization of Multiple Moving Targets Based on Matched Field Processing

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    ๊ณ ์†Œ์Œ์˜ ๊ฐ„์„ญํ‘œ์ ๊ณผ ์ €์†Œ์Œ์˜ ํ‘œ์ ์ด ์กด์žฌํ•˜๋Š” ์ฒœํ•ดํ™˜๊ฒฝ์—์„œ ๋‹ค์ค‘ํ‘œ์ ์˜ ๋ถ„๋ฆฌํƒ์ง€ ์„ฑ๋Šฅ์„ ํ–ฅ์ƒ์‹œํ‚ค๊ธฐ ์œ„ํ•˜์—ฌ ๋‘ ๊ฐ€์ง€์˜ ์ •ํ•ฉ์žฅ์ฒ˜๋ฆฌ ๊ธฐ๋ฒ•์„ ์ œ์•ˆํ•˜๊ณ  ์„ค๋ช…ํ•˜์˜€๋‹ค. ์ฒซ ๋ฒˆ์งธ๋กœ, ์—ฌ๋Ÿฌ ๊ฐœ์˜ ๊ตฌ์†์กฐ๊ฑด์„ ๋™์‹œ์— ์ค„ ์ˆ˜ ์žˆ๋Š” MCM ๊ธฐ๋ฒ•์˜ ์„ฑ์งˆ์„ ์ด์šฉํ•˜์—ฌ ์ธ์ ‘ํ•œ ๊ฐ„์„ญํ‘œ์ ์˜ ์˜ํ–ฅ์„ ์ค„์ด๋Š” ์‹œ๋„๋ฅผ ํ•˜์˜€๋‹ค. MCM ๊ธฐ๋ฒ•์„ ์ด์šฉํ•˜๋ฉด ์กฐํ–ฅ์œ„์น˜ ์ด์™ธ์˜ ๊ตฌ์†์กฐ๊ฑด์„ ์ถ”๊ฐ€๋กœ ์ง€์ •ํ•˜์—ฌ ๊ฐ„์„ญํ‘œ์ ์˜ ๋ถ€์—ฝ์„ ํšจ๊ณผ์ ์œผ๋กœ ํ•„ํ„ฐ๋งํ•  ์ˆ˜ ์žˆ๋‹ค. ์ด๋ฅผ ์œ„ํ•˜์—ฌ ๋‹ค์ค‘ ๊ตฌ์†์กฐ๊ฑด์— ์กฐํ–ฅ์œ„์น˜์˜ ์œ„์น˜ ๋ฒกํ„ฐ์™€ ๊ฐ„์„ญํ‘œ์ ์˜ ์œ„์น˜๋ฒกํ„ฐ๋ฅผ ํฌํ•จ์‹œํ‚จ NDC๋ฅผ ์ด์šฉํ•œ๋‹ค. NDC ๊ตฌ์†ํ–‰๋ ฌ์€ ๊ฐ๊ฐ์˜ ์‹ ํ˜ธ๋‹จํŽธ์— ํฌํ•จ๋œ ๊ฐ„์„ญ ๋ถ€๊ณต๊ฐ„์„ ์ถ”์ •ํ•˜์—ฌ ์ œ๊ฑฐํ•˜๋Š” ํ•„ํ„ฐ ์—ญํ• ์„ ํ•  ์ˆ˜ ์žˆ๋‹ค. NDC๋Š” ๊ณ ์†Œ์Œ์˜ ๋น ๋ฅธ ํ‘œ์ ์— ์˜ํ•ด ์ž ์‹๋œ DOF๋ฅผ ๋ณต์›์‹œํ‚ด์œผ๋กœ์„œ ๊ฒฐ๊ณผ์ ์œผ๋กœ DOF๊ฐ€ ์ฆ๊ฐ€๋˜์–ด ์ธ์ ‘ํ•œ ์ €์†Œ์Œ ํ‘œ์ ์˜ ๋ถ„๋ฆฌํƒ์ง€๊ฐ€ ๊ฐ€๋Šฅํ•˜๊ฒŒ ๋œ๋‹ค. ๊ฐ„์„ญ ๋ถ€๊ณต๊ฐ„์— ๋Œ€ํ•œ NDC๋ฅผ ์ถ”์ •ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ์ž์œ ๋กœ์šด ์œ„์น˜ ์„ ํƒ์˜ ์žฅ์ ์ด ์žˆ๋Š” ๋ณต์ œ์Œ์žฅ์„ ์ด์šฉํ•˜์˜€๋‹ค. MCM ๊ธฐ๋ฒ•์˜ ์ˆ˜์น˜์‹คํ—˜์œผ๋กœ๋ถ€ํ„ฐ ํ‘œ์ ์˜ ์‹ ํ˜ธ๋“ค์ด ์„œ๋กœ ์ƒ๊ด€๋˜์–ด ์žˆ๋Š” ๊ฒฝ์šฐ์—๋„ ๊ฐ„์„ญํ‘œ์ ์ด ์ž˜ ์ œ๊ฑฐ๋˜๊ณ  ํ‘œ์ ์˜ ๋ถ„๋ฆฌ๊ฐ€ ๊ฐ€๋Šฅํ•จ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ๋‹ค. SWellEx-96 ํ•ด์ƒ์‹คํ—˜ ์ž๋ฃŒ๋ฅผ ์ฒ˜๋ฆฌํ•œ ๊ฒฐ๊ณผ ๊ฐ„์„ญํ‘œ์ ์˜ ์ถœ๋ ฅ๊ณผ ์ฃผ๋ณ€์˜ ๋ถ€์—ฝ๋“ค์ด ํ•จ๊ป˜ ๋‚ฎ์•„์ง์œผ๋กœ์จ ์ €์†Œ์Œ ํ‘œ์ ์˜ ๊ฒฝ๋กœ๊ฐ€ ๋ถ„๋ฆฌ๋จ์„ ํ™•์ธํ•˜์˜€๋‹ค. ๋‘ ๋ฒˆ์งธ๋กœ ๋„ํŒŒ๊ด€ ๋ถˆ๋ณ€์„ฑ ํ˜„์ƒ์„ ์ด์šฉํ•˜์—ฌ ๋น ๋ฅด๊ฒŒ ์›€์ง์ด๋Š” ๊ฐ„์„ญํ‘œ์ ์˜ ์†๋„๋ฅผ ๋ณด์ •ํ•˜๋Š” ์•Œ๊ณ ๋ฆฌ์ฆ˜์„ ์„ค๋ช…ํ•˜์˜€๋‹ค. ํ‘œ์ ์˜ ์ด๋™์„ ์ •ํ™•ํ•˜๊ฒŒ ์ถ”์ •ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ์กฐํ–ฅ๋น”์ฒ˜๋ฆฌ ๊ธฐ๋ฒ•์„ ์ œ์•ˆํ•˜์˜€๋‹ค. ๋˜ํ•œ ๋„ํŒŒ๊ด€ ๋ถˆ๋ณ€์„ฑ์ด ๋ฏธ์•ฝํ•ด์„œ ์ผ๊ด€์„ฑ์ด ๋‚ฎ์€ ๊ฐ„์„ญํ˜•ํƒœ๋ฅผ ๊ฐ–๋Š” ๋„ํŒŒ๊ด€์— ์ ํ•ฉํ•œ ์ด๋™๋ณด์ƒ ์•Œ๊ณ ๋ฆฌ์ฆ˜์œผ๋กœ์จ ๊ธด ๊ด€์ธก์‹œ๊ฐ„ ๋™์•ˆ์˜ ์‹ ํ˜ธ๋‹จํŽธ๋“ค๋กœ ๊ตฌ์„ฑํ•œ ํ•˜๋‚˜์˜ CSDM ๋Œ€์‹ ์— ์—ฌ๋Ÿฌ ๊ฐœ์˜ CSDM์œผ๋กœ ๋‚˜๋ˆ„์–ด ์งง์€ ์‹œ๊ฐ„์— ๋Œ€ํ•œ ์ด๋™๋ณด์ƒ ํ›„์— ๋น„์ƒ๊ด€์ฒ˜๋ฆฌ ํ•˜๋Š” ์‹œ๊ฐ„๋ถ„ํ•  ์ด๋™๋ณด์ƒ ์•Œ๊ณ ๋ฆฌ์ฆ˜์„ ์ ์šฉํ•˜์˜€๋‹ค. ์ด๋™๋ณด์ƒ ์•Œ๊ณ ๋ฆฌ์ฆ˜์˜ ์„ฑ๋Šฅ์„ ๊ฒ€์ฆํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ์ˆ˜์น˜์‹คํ—˜์„ ์ˆ˜ํ–‰ํ•˜๊ณ , SWellEx-96 ํ•ด์ƒ์‹คํ—˜ ์ž๋ฃŒ๋ฅผ ๋ถ„์„ํ•˜์˜€๋‹ค. ํ‘œ์ ์˜ ์ด๋™์„ ๋ณด์ƒํ•œ ๊ฒฐ๊ณผ SBNR์ด ๊ฐœ์„ ๋˜๊ณ , ๋ถ€์—ฝ์ด ์ „๋ฐ˜์ ์œผ๋กœ ๋‚ฎ์•„์ง์œผ๋กœ์จ ํƒ์ง€์„ฑ๋Šฅ์ด ํ–ฅ์ƒ๋จ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค.The propeller for propelling a ship is installed at the stern side end of propeller shaft protruding from its stern. Therefore the propeller shaft is deflected by the propeller weight or any external force and the stern side of stern tube bearing will be loaded larger load than its bow side end. This one-side load tends to cause local contact between the shaft and bearing and causes bearing such as wear, burning, etc. of bearing metal. In this study, to clarify the performance of the stern tube bearing, Reynolds equation under deflected condition is solved by using computer. Oil-film pressure distribution and variation of the bearing are also calculated. And the shaft declination within the stern bearing is expressed by declination curve obtained from the deflection calculations for the entire shafting system, calculated simultaneously with the stern tube bearing by ANSYS software. Oil film characteristics are obtained, based on the finite width hydrodynamic theory and solved through the convergence calculations.Abstract = โ…ก ์ œ 1 ์žฅ ์„œ ๋ก  = 1 1.1 ์—ฐ๊ตฌ ๋ชฉ์  = 1 1.2 ์—ฐ๊ตฌ ๋ฐฐ๊ฒฝ = 2 1.3 ๋…ผ๋ฌธ ๊ตฌ์„ฑ = 6 ์ œ 2 ์žฅ ์ •ํ•ฉ์žฅ์ฒ˜๋ฆฌ = 8 2.1 ์‹ ํ˜ธ ๋ชจ๋ธ = 8 2.2 ์ •ํ•ฉ์žฅ ์Œ์›์œ„์น˜ ์ถ”์ • ์•Œ๊ณ ๋ฆฌ์ฆ˜ = 11 ์ œ 3 ์žฅ ๋„ํŒŒ๊ด€ ๊ณต๊ฐ„์˜ ๊ฐ„์„ญํ‘œ์  ํ•„ํ„ฐ๋ง = 26 3.1 ์˜ ๋ฐฉํ–ฅ ๊ตฌ์†์กฐ๊ฑด์„ ๊ฐ–๋Š” MCM ์•Œ๊ณ ๋ฆฌ์ฆ˜ = 26 3.2 ๋ชจ์˜ ์ˆ˜์น˜์‹คํ—˜ = 30 3.3 ํ•ด์ƒ์‹คํ—˜ ์ ์šฉ ๊ฒฐ๊ณผ = 39 ์ œ 4 ์žฅ ๋„ํŒŒ๊ด€ ๋ถˆ๋ณ€์„ฑ ๊ธฐ๋ฐ˜์˜ ์ด๋™๋ณด์ƒ = 51 4.1 ๋„ํŒŒ๊ด€ ๋ถˆ๋ณ€์„ฑ ์ด๋ก  = 53 4.2 ์ด๋™๋ณด์ƒ ์•Œ๊ณ ๋ฆฌ์ฆ˜ = 58 4.3 ๋ชจ์˜ ์ˆ˜์น˜์‹คํ—˜ = 62 4.4 ํ•ด์ƒ์‹คํ—˜ ์ ์šฉ ๊ฒฐ๊ณผ = 78 ์ œ 5 ์žฅ ๊ฒฐ ๋ก  = 96 ์ฐธ๊ณ ๋ฌธํ—Œ = 9

    Digital Signal Processing Research Program

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    Contains table of contents for Section 2, an introduction, reports on sixteen research projects and a list of publications.Bose CorporationMIT-Woods Hole Oceanographic Institution Joint Graduate Program in Oceanographic EngineeringAdvanced Research Projects Agency/U.S. Navy - Office of Naval Research Grant N00014-93-1-0686Lockheed Sanders, Inc./U.S. Navy - Office of Naval Research Contract N00014-91-C-0125U.S. Air Force - Office of Scientific Research Grant AFOSR-91-0034AT&T Laboratories Doctoral Support ProgramAdvanced Research Projects Agency/U.S. Navy - Office of Naval Research Grant N00014-89-J-1489U.S. Navy - Office of Naval Research Grant N00014-93-1-0686National Science Foundation FellowshipMaryland Procurement Office Contract MDA904-93-C-4180U.S. Navy - Office of Naval Research Grant N00014-91-J-162

    Blind deconvolution in multipath environments and extensions to remote source localization

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    In the ocean, the acoustic signal from a remote source recorded by an underwater hydrophone array is commonly distorted by multipath propagation. Blind deconvolution is the task of determining the source signal and the impulse response from array-recorded sounds when the source signal and the environmentโ€™s impulse response are both unknown. Synthetic time reversal (STR) is a passive blind deconvolution technique that accomplishes two remote sensing tasks. 1) It can be used to estimate the original source signal and the source-to-array impulse responses, and 2) it can be used to localize the remote source when some information is available about the acoustic environment. The performance of STR for both tasks is considered in this thesis. For the first task, simulations and underwater experiments (CAPEx09) have shown STR to be successful for 1.5-4 kHz broadcast signal. Here STR is successful when the signal-to-noise ratio is high enough, and the receiving array has sufficient aperture and element density so that conventional delay-and-sum beamforming can be used to distinguish ray-path-arrival directions. Also, an unconventional beamforming technique (frequency-difference beamforming) that manufactures frequency differences from the recorded signals has been developed. It allows STR to be successful with sparse array measurements where conventional beamforming fails. Broadband simulations and experimental data from the focused acoustic field experiment (FAF06) have been used to determine the performance of STR when combined with frequency-difference beamforming. For the source localization task, the STR-estimated impulse responses may be combined with ray-based back-propagation simulations and the environmental characteristics at the array into a computationally efficient scheme that localizes the remote sound source. These localization results from STR are less ambiguous than those obtained from conventional matched field processing in the same bandwidth. However, when the frequency of the recorded signals is sufficiently low and close to modal cutoff frequencies, STR-based source localization may fail because of dispersion in the environment. For such cases, an extension of mode-based STR has been developed for sound source ranging with a vertical array in a dispersive underwater sound channel using bowhead whale calls recorded with a 12-element vertical array (Arctic 2010).PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102443/1/shimah_1.pd

    Theory and Application of Autoproducts

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    Acoustics is a branch of physics largely governed by linear field equations. Linearity carries with it the implication that only the frequencies broadcast by acoustic sources can be measured in the surrounding acoustic medium. However, nonlinearities introduced not in the physical world, but in the mathematical and signal processing realm, have the potential to change frequency content. In this dissertation, nonlinear mathematical constructions termed โ€˜autoproductsโ€™ are created which have the potential to shift frequencies from the measured, in-band frequencies to other higher or lower frequencies which may no longer be in-band. These out-of-band autoproduct fields did not physically propagate in the environment, and yet, this research has found that autoproducts can nonetheless mimic genuine out-of-band fields in a number of different acoustic environments. Approximately half of this dissertation addresses the theory of autoproducts. More specifically, mathematical analyses and simple acoustic models are used to uncover the reasons for how this frequency-shifting behavior works, and what its limitations are. It is found that there are no inherent limitations on the frequencies considered, and that in single-path environments, like plane or spherical waves, autoproducts mimic out-of-band fields in all or nearly all circumstances, respectively. However, in multipath environments, the mimicry of out-of-band fields by autoproducts is no longer so complete. Though, with bandwidth averaging techniques, it is found that the difference in time-of-arrivals of multiple paths is an important parameter: if it is larger than the inverse of the bandwidth available for averaging, then autoproducts can succeed in mimicking out-of-band fields. Other theoretical considerations include the effects of diffraction behind barriers and the effects of strong refraction. Strengths and limitations of autoproducts are assessed with a variety of simple acoustic models, and conclusions are drawn as to the predicted capabilities of autoproduct-based techniques. The other half of this dissertation covers applications of autoproducts. More specifically, it focuses on the use of autoproducts to perform physics-based source localization, especially for applications in the shallow ocean. Existing techniques are well-known to be very sensitive to uncertainties in the acoustic environment (e.g. the sound speed), especially at high frequencies (nominally greater than 1 kHz in the shallow ocean). Through the use of autoproducts, measured fields at high frequency can be shifted to much lower frequencies, where they can be processed with much more robustness to environmental uncertainties. In one of the main results of this dissertation, it is shown that a remote acoustic source broadcasting sound between 11 and 33 kHz in a 106-meter-deep, downward refracting sound channel could be localized using measurements from a sparse array located 3 km away. The data from the method suggest that autoproduct-based source localization can make physics-based array signal processing robust at arbitrarily high frequencies โ€“ a novel and important contribution to existing literature. Overall, by developing the theory for, and exploring applications of, these nonlinear mathematical constructions, the extent to which autoproducts are fundamentally limited is assessed, and new signal processing techniques are developed which have the potential to significantly improve the robustness of source localization algorithms for uncertain multipath environments. Through this study, significant portions of the necessary theoretical foundation have been laid, which will aid in the further development of robust, autoproduct-based signal processing techniques.PHDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/145865/1/bworthma_1.pd

    Array design considerations for exploitation of stable weakly dispersive modal pulses in the deep ocean

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    ยฉ The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Journal of Sound and Vibration 400 (2017): 402-416, doi:10.1016/j.jsv.2017.03.035.Modal pulses are broadband contributions to an acoustic wave field with fixed mode number. Stable weakly dispersive modal pulses (SWDMPs) are special modal pulses that are characterized by weak dispersion and weak scattering-induced broadening and are thus suitable for communications applications. This paper investigates, using numerical simulations, receiver array requirements for recovering information carried by SWDMPs under various signal-to-noise ratio conditions without performing channel equalization. Two groups of weakly dispersive modal pulses are common in typical mid-latitude deep ocean environments: the lowest order modes (typically modes 1โ€“3 at 75 Hz), and intermediate order modes whose waveguide invariant is near-zero (often around mode 20 at 75 Hz). Information loss is quantified by the bit error rate (BER) of a recovered binary phase-coded signal. With fixed receiver depths, low BERs (less than 1%) are achieved at ranges up to 400 km with three hydrophones for mode 1 with 90% probability and with 34 hydrophones for mode 20 with 80% probability. With optimal receiver depths, depending on propagation range, only a few, sometimes only two, hydrophones are often sufficient for low BERs, even with intermediate mode numbers. Full modal resolution is unnecessary to achieve low BERs. Thus, a flexible receiver array of autonomous vehicles can outperform a cabled array
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