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Brian G Ferguson - One of the best experts on this subject based on the ideXlab platform.

  • Flight Parameter Estimation Using Instantaneous Frequency Measurements From a Wide Aperture Hydrophone Array
    IEEE Journal of Oceanic Engineering, 2014
    Co-Authors: Brian G Ferguson
    Abstract:

    In this paper, a narrowband method based on the acoustical Doppler effect is proposed for estimating the full set of five flight parameters, along with the propeller Blade Rate, of a turboprop aircraft as it transits over a wide aperture hydrophone array in a straight line at constant speed and constant altitude. The five flight parameters describe fully the linear trajectory of the aircraft's transit. The basic principle of the proposed method is to measure the temporal variation of the instantaneous frequency (IF) of the acoustic signal received by each sensor of the array and then to minimize the sum of the squared deviations of the IF estimates from their predicted values over a sufficiently long period of time for all sensors. The minimization is performed numerically subject to a set of constraints on the source parameters to be estimated. The IF model for the received signal at each sensor of the array and the initial parameter estimates required for the numerical minimization are derived. The effectiveness of the proposed method is demonstRated using both simulated and real data.

  • Sensing the underwater sound field produced by a moving airborne signal source
    OCEANS 2009-EUROPE, 2009
    Co-Authors: Brian G Ferguson, Kam W. Lo, Gary C. Speechley
    Abstract:

    Sound emitted by a turboprop aircraft in level flight is received by each of the uniformly spaced hydrophones of a horizontal line array located below the sea surface. The primary signal emitted by the source is an acoustic tone corresponding to the propeller Blade Rate of the aircraft. As the airborne source is in relative motion with respect to the array, the received signal at each hydrophone is Doppler-shifted in frequency. For each transit of the aircraft, the variation with time of the observed Doppler-shifted Blade Rate is found to match the theoretical curve predicted by a basic ray path propagation model. This model assumes that the sound propagates from the airborne acoustic source to a subsurface sensor through two sepaRate isospeed media (air and water) that are sepaRated by a planar boundary (the air-sea interface). More importantly, as a result of beamforming the hydrophone array data, it is shown that the variations with angle of arrival of the observed Doppler-shifted Blade Rate are in close agreement with the variations predicted for both the direct refraction and bottom bounce propagation paths. In addition, the observed temporal variation of the differential time-of-arrival of the signal at two spatially sepaRated sensors is shown to agree with the predicted variation. This paper also reviews other contributions made by the authors to the underwater sensing of transiting aircraft using different passive acoustic signal processing methods.

  • Acoustic Detection and Localization of a Turboprop Aircraft by an Array of Hydrophones Towed Below the Sea Surface
    IEEE Journal of Oceanic Engineering, 2009
    Co-Authors: Brian G Ferguson, G.c. Speechley
    Abstract:

    The acoustic spectrum of a propeller-driven aircraft is dominated by a series of spectral lines that are harmonically related to the Blade Rate (which is equal to the product of the propeller rotation Rate and the number of Blades on the propeller). We show that an array of acoustic sensors towed below the sea surface can be used for the passive detection and localization of such an aircraft. The acoustic energy from an aircraft is found to reach the subsurface sensors via two propagation paths: a bottom reflection path that enables the aircraft to be detected at long ranges, and a direct path that is present only when the aircraft passes overhead. For each of these paths, the observed variation with horizontal range of the Doppler shift in the Blade Rate closely matches the variation predicted by the simple model presented in this paper. Good agreement between theory and experiment is also obtained for the variation with horizontal range of the aircraft's apparent bearing. Thus, by using the observed Doppler shift and apparent bearing information, we were able to estimate the aircraft's horizontal range, speed, direction, and altitude.

  • Transiting aircraft parameter estimation using underwater acoustic sensor data
    IEEE Journal of Oceanic Engineering, 1999
    Co-Authors: Brian G Ferguson
    Abstract:

    Sound from an airborne source travels to a receiver beneath the sea surface via a geometric path that is most simply described using ray theory, where the atmosphere and the sea are assumed to be isospeed sound propagation media sepaRated by a planar surface (the air-sea interface). This theoretical approach leads to the development of a time-frequency model for the signal received by a single underwater acoustic sensor and a time-delay model for the signals received by a pair of spatially sepaRated underwater acoustic sensors. The validity of these models is verified using spatially averaged experimental data recorded from a linear array of hydrophones during various transits of a turboprop aircraft. The same approach is used to solve the inverse time-frequency problem, that is, estimation of the aircraft's speed, altitude, and propeller Blade Rate given the observed variation with time of the instantaneous frequency of the received signal. Similarly, the inverse time-delay problem is considered whereby the speed and altitude of the aircraft are estimated using the differential time-of-arrival information from each of two adjacent pairs of widely spaced hydrophones (with one hydrophone being common to each pair). It is found that the solutions to each of the inverse problems provide reliable estimates of the speed and altitude of the aircraft, with the inverse time-frequency method also providing an estimate that closely matches the actual propeller Blade Rate.

  • Time-frequency signal analysis of hydrophone data
    IEEE Journal of Oceanic Engineering, 1996
    Co-Authors: Brian G Ferguson
    Abstract:

    The acoustic spectrum of a transiting aircraft, when received by a hydrophone located beneath the sea surface, changes with time due to the acoustical Doppler effect. The traditional method for analysing signals whose frequency content changes with time is the short-time Fourier transform that selects only a short segment of the signal (or window of data) for spectral analysis at any one time. The short-time Fourier transform requires the frequency content of the signal to be stationary during the analysis window, otherwise the frequency information will be smeared by the transformation. Recently, joint time-frequency distributions, which highlight the temporal localisation of a signal's spectral components, have been used to analyse nonstationary signals whose spectra are time dependent. In this paper, the short-time Fourier transform and the Wigner-Ville time-frequency distribution are applied to time-series data from a hydrophone so that the instantaneous frequency of the propeller Blade Rate of a turbo-prop aircraft can be estimated at short time intervals during the aircraft's transit over the hydrophone. The variation with time of the estimates of the Doppler-shifted Blade Rate is then compared with the corresponding temporal variation predicted using a model that assumes the sound propagates from the airborne acoustic source to the subsurface receiver through two distinct isospeed media (air and water) sepaRated by a plane boundary (the air-sea interface). The results for five transits are presented in which the altitude of the aircraft ranged from 350 to 6050 ft with the speed of the aircraft varying from 232 to 245 kn.

Jui-hsiang Kao - One of the best experts on this subject based on the ideXlab platform.

  • An innovative propeller with experimental and sea trial verifications
    Journal of Marine Science and Technology, 2019
    Co-Authors: Young Zehr Kehr, Huan-jia Xu, Jui-hsiang Kao
    Abstract:

    An end plate propeller (ENDP) shaped by a diffused endplate bent to the pressure side is proposed in the paper. The ENDP differs from a contracted and loaded tip (CLT) propeller, and possess remarkable performance in terms of cavitation, efficiency, vibration, and noise comparing with that of CLT and conventional propeller, particularly operating at inclined shaft condition. According to experiments conducted in the cavitation tunnel of National Taiwan Ocean University, it is observed that the diffused endplate can effectively restrain tip vortex cavitation, and eliminate tip-plate cavitation typically found on the outer surface of the tip-plate of a CLT propeller. The optimal diameter of the ENDP is smaller than that of a conventional propeller; thus, the ENDP is more suitable for ships with small stern space. Besides, the thrust of the ENDP is contributed much more from its pressure side, therefore, the cavitation on the back is reduced, and the efficiency is increased. Sea trials using a yacht with the ENDP were carried out and the results show that vibrations due to the sheet cavitation at Blade-Rate frequencies by the ENDP are significantly decreased in comparison with those of conventional propeller, and overall broad-band amplitude caused by the tip vortex cavitation by the ENDP at high frequencies are nearly disappeared.

  • Underwater acoustic field and pressure fluctuation on ship hull due to unsteady propeller sheet cavitation
    Journal of Marine Science and Technology, 2011
    Co-Authors: Young Zehr Kehr, Jui-hsiang Kao
    Abstract:

    The main objective of this paper is to develop an efficient numerical method which can predict the underwater acoustic field and pressure fluctuation on a ship hull due to unsteady propeller sheet cavitation by linear acoustic theory. In addition, the noise scattered from the ship hull and reflected from the free surface are included. Concerning the computation of the acoustic field induced by unsteady sheet cavitation and forces of a marine propeller, a method is derived without making any approximation about the distance function between the noise source and field point. Thus, this method can be used to predict acoustic pressure at both far and near fields, and this is very important for the scattering problem because the ship hull is located very close to the propeller. For the computation of the scattering problem, a more efficient and robust method is derived in time domain, which can treat multi-frequency waves scattered from underwater obstacles. The acoustic fields of a container ship radiated by the propeller and scattered from the ship hull with free surface is investigated in this paper. The pressure fluctuations of low Blade Rate on the ship hull induced by the propeller are also computed by the present method and are found to be similar to the results obtained by a panel method satisfying the Laplace equation for the points near the propeller due to the small retarding time. However, for the points on the ship hull away from the propeller, the differences of the results between two methods will increase.

  • Numerical prediction of the Blade Rate noise induced by marine propellers
    Journal of Ship Research, 2004
    Co-Authors: Young Zehr Kehr, Jui-hsiang Kao
    Abstract:

    The main objective of this paper is to derive discrete Blade Rate noise induced by an unsteady sheet cavitation (monopole) and unsteady forces (dipole) of a propeller operating in a nonuniform ship wake. These unsteady forces include two components: axial thrust and tangential torque force. In the present method, an exact analytic solution of the linear wave equation can be derived directly in time domain and then used for calculating acoustic pressure at both far field and near field. From the computational results, it is found that the acoustic pressure at far field, due to the variation in distance between the noise source and the observer, is negligibly small compared with that due to the variation of the noise source strength in time. For computing far-field acoustic pressure, induced by the unsteady sheet cavitation and thrust, noise sources on a Blade can be replaced by an effective point noise source. However, in doing so, errors will appear for the computation of the acoustic pressure induced by the unsteady torque force. For the near-field computation, the noise source distribution on the entire propeller Blade should be considered, especially for unsteady thrust and torque.

Young Zehr Kehr - One of the best experts on this subject based on the ideXlab platform.

  • An innovative propeller with experimental and sea trial verifications
    Journal of Marine Science and Technology, 2019
    Co-Authors: Young Zehr Kehr, Huan-jia Xu, Jui-hsiang Kao
    Abstract:

    An end plate propeller (ENDP) shaped by a diffused endplate bent to the pressure side is proposed in the paper. The ENDP differs from a contracted and loaded tip (CLT) propeller, and possess remarkable performance in terms of cavitation, efficiency, vibration, and noise comparing with that of CLT and conventional propeller, particularly operating at inclined shaft condition. According to experiments conducted in the cavitation tunnel of National Taiwan Ocean University, it is observed that the diffused endplate can effectively restrain tip vortex cavitation, and eliminate tip-plate cavitation typically found on the outer surface of the tip-plate of a CLT propeller. The optimal diameter of the ENDP is smaller than that of a conventional propeller; thus, the ENDP is more suitable for ships with small stern space. Besides, the thrust of the ENDP is contributed much more from its pressure side, therefore, the cavitation on the back is reduced, and the efficiency is increased. Sea trials using a yacht with the ENDP were carried out and the results show that vibrations due to the sheet cavitation at Blade-Rate frequencies by the ENDP are significantly decreased in comparison with those of conventional propeller, and overall broad-band amplitude caused by the tip vortex cavitation by the ENDP at high frequencies are nearly disappeared.

  • Underwater acoustic field and pressure fluctuation on ship hull due to unsteady propeller sheet cavitation
    Journal of Marine Science and Technology, 2011
    Co-Authors: Young Zehr Kehr, Jui-hsiang Kao
    Abstract:

    The main objective of this paper is to develop an efficient numerical method which can predict the underwater acoustic field and pressure fluctuation on a ship hull due to unsteady propeller sheet cavitation by linear acoustic theory. In addition, the noise scattered from the ship hull and reflected from the free surface are included. Concerning the computation of the acoustic field induced by unsteady sheet cavitation and forces of a marine propeller, a method is derived without making any approximation about the distance function between the noise source and field point. Thus, this method can be used to predict acoustic pressure at both far and near fields, and this is very important for the scattering problem because the ship hull is located very close to the propeller. For the computation of the scattering problem, a more efficient and robust method is derived in time domain, which can treat multi-frequency waves scattered from underwater obstacles. The acoustic fields of a container ship radiated by the propeller and scattered from the ship hull with free surface is investigated in this paper. The pressure fluctuations of low Blade Rate on the ship hull induced by the propeller are also computed by the present method and are found to be similar to the results obtained by a panel method satisfying the Laplace equation for the points near the propeller due to the small retarding time. However, for the points on the ship hull away from the propeller, the differences of the results between two methods will increase.

  • Numerical prediction of the Blade Rate noise induced by marine propellers
    Journal of Ship Research, 2004
    Co-Authors: Young Zehr Kehr, Jui-hsiang Kao
    Abstract:

    The main objective of this paper is to derive discrete Blade Rate noise induced by an unsteady sheet cavitation (monopole) and unsteady forces (dipole) of a propeller operating in a nonuniform ship wake. These unsteady forces include two components: axial thrust and tangential torque force. In the present method, an exact analytic solution of the linear wave equation can be derived directly in time domain and then used for calculating acoustic pressure at both far field and near field. From the computational results, it is found that the acoustic pressure at far field, due to the variation in distance between the noise source and the observer, is negligibly small compared with that due to the variation of the noise source strength in time. For computing far-field acoustic pressure, induced by the unsteady sheet cavitation and thrust, noise sources on a Blade can be replaced by an effective point noise source. However, in doing so, errors will appear for the computation of the acoustic pressure induced by the unsteady torque force. For the near-field computation, the noise source distribution on the entire propeller Blade should be considered, especially for unsteady thrust and torque.

B G Quinn - One of the best experts on this subject based on the ideXlab platform.

  • application of the short time fourier transform and the wigner ville distribution to the acoustic localization of aircraft
    Journal of the Acoustical Society of America, 1994
    Co-Authors: Brian G Ferguson, B G Quinn
    Abstract:

    The dominant feature in the acoustic spectrum of a propeller‐driven aircraft is the spectral line corresponding to the propeller Blade Rate that is equal to the product of the propeller shaft rotation Rate and the number of Blades on the propeller. The frequency of this line, when measured by a stationary observer on the ground, changes with time due to the acoustical Doppler effect. In this paper, the short‐time Fourier transform and the Wigner–Ville distribution are used to estimate the propeller Blade Rate at short time intervals for a turbo‐prop aircraft flying at a constant altitude and speed over an acoustic sensor located just above ground level. The temporal variation in the observed Blade Rate is then used to estimate the speed and altitude of the aircraft, together with the source (or rest) frequency of the Blade Rate. Finally, the estimated values for these parameters are compared with the actual values recorded onboard the aircraft during each of the eighteen transits formed by pairing each element of a set of speeds: 150, 200, and 250 kn, with each element of a set of aircraft altitudes: 250, 500, 750, 1000, 1250, and 1500 ft.

  • Application of the short‐time Fourier transform and the Wigner–Ville distribution to the acoustic localization of aircraft
    The Journal of the Acoustical Society of America, 1994
    Co-Authors: Brian G Ferguson, B G Quinn
    Abstract:

    The dominant feature in the acoustic spectrum of a propeller‐driven aircraft is the spectral line corresponding to the propeller Blade Rate that is equal to the product of the propeller shaft rotation Rate and the number of Blades on the propeller. The frequency of this line, when measured by a stationary observer on the ground, changes with time due to the acoustical Doppler effect. In this paper, the short‐time Fourier transform and the Wigner–Ville distribution are used to estimate the propeller Blade Rate at short time intervals for a turbo‐prop aircraft flying at a constant altitude and speed over an acoustic sensor located just above ground level. The temporal variation in the observed Blade Rate is then used to estimate the speed and altitude of the aircraft, together with the source (or rest) frequency of the Blade Rate. Finally, the estimated values for these parameters are compared with the actual values recorded onboard the aircraft during each of the eighteen transits formed by pairing each element of a set of speeds: 150, 200, and 250 kn, with each element of a set of aircraft altitudes: 250, 500, 750, 1000, 1250, and 1500 ft.

R. Martinez - One of the best experts on this subject based on the ideXlab platform.

  • BROADBAND SOURCES OF STRUCTURE-BORNE NOISE FOR PROPULSORS IN HAYSTACKED TURBULENCE
    Computers & Structures, 1997
    Co-Authors: R. Martinez
    Abstract:

    Abstract This article reviews some of the statistical and probabilistic concepts underlying a number of classical and modern studies whose objective has been to predict broadband propulsor forces due to turbulence ingestion. Part of the material is new, extending a recent “closed-form” solution for thrust to apply now to any interpretation of isotropic turbulence. The more general theory dispenses altogether with the integral scale as a modeling parameter in the problem of rotor/turbulence interaction. The new formula for the net random thrust still requires only that the three-dimensional rotor analyzed have a realistically large number of Blades (> 5 or 6). Also reported are asymptotic results for the broadband frequency spectrum of a propulsor's net random side force due to turbulence ingestion, as well as the torque and diametric moment. The theory provides analytical and physical explanations for the details of the “haystacks” of the force frequency spectrum of a formally three-dimensional propulsor, i.e. for the size and shape of the broad humps that are both observed and rigorously computed over the Blade-Rate frequency and harmonics.