SVIBOR - Papers - project code: 2-05-408

MINISTRY OF SCIENCE AND TECHNOLOGY

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SVIBOR

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Published papers on project 2-05-408


Quoted papers: 1
Other papers: 7
Total: 8


  1. Type of paper: Paper in journal

    Title: Signal decorrelation induced by transit-time and frequency fluctuations

    Authors:
    BAJIĆ, BRANKO (78490)
    Journal: Signal Processing
    ISSN: 0165-1684
    Volume: 36
    Year: 1994
    Pages: from 127 to 132
    Language: engleski
    Summary: Theoretical estimates of the change of signal autocorrelation function induced by transit-time and frequency fluctuations are derived. The signal and the fluctuations are assumed to be independent zero-mean stationary random processes, the signal being band-limited, the transit-time fluctuations Gaussian, and the frequency fluctuations slow varying compared to the signal.
    Keywords: correlation function, decorrelation, transit-time fluctuations, frequency fluctuations, spectral line broadening

  2. Type of paper: Paper in journal

    Title: On the applicability of the Coulter-counter to the cavitation nuclei size distribution analysis

    Authors:
    DŽUBUR, ADIL
    BAJIĆ, BRANKO (78490)
    JOVANOVIĆ, IVICA (179863)
    Journal: International Shipbuilding Progress
    ISSN: 0020-868x
    Volume: 40
    Year: 1993
    Pages: from 165 to 175
    Language: engleski
    Summary: The use of the Coulter-counter method in analysing the size distribution of cavitation nuclei and bubbles in a cavitation tunnel is discussed. Relevant physical details are modelled and tested, and an experimental system is carefully designed. Even when extensively modified, the Coulter-counter method poses serious difficulties not proving useful in experiments of this kind.
    Keywords: cavitation, cavitation bubbles, cavitation nuclei, cavitation tunnel

  3. Type of paper: Paper in journal

    Title: Signal decorrelation induced by linear distortion in a transfer system

    Authors:
    BAJIĆ, BRANKO (78490)
    Journal: Traitement du signal
    ISSN: 0765-0019
    Volume: 9
    Year: 1992
    Pages: from 367 to 370
    Language: engleski
    Summary: Theoretical estimates of the changes in signal correlation function caused by non-linear phase and non-constant amplitude characteristics of a transfer system are derived. Several simple approximations and bounds are presented. A review of the experimental verification is also given.
    Keywords: signal decorrelation, linear distortion

  4. Type of paper: Paper in proceedings

    Title: Flow-induced signal decorrelation

    Authors:
    BAJIĆ, BRANKO (78490)
    Proceedings title: 14th International Congress on Acoustics
    Language: engleski
    Place: Beijing, China
    Year: 1992
    Pages: from L4.4 to L4.4
    Meeting: 14th Inernational Congress on Acoustics
    Held: from 09/03/92 to 09/12/92
    Summary: Signal decorrelation induced by transit-time fluctuations is analysed. When described by the change of a signal autocorrelation function (acf), the decorrelation depends on the acf of fluctuations. In the case of small fluctuations, this change and the change of the squared relative bandwidth of a narrow-band signal spectrum line is proportional to the ratio of the variance and the square of the correlation time of the fluctuations, F. This description is used to model the decorrelation effects induced in an acoustic signal passing through a fluid with random inhomogeneities conveyed by a flow, the flow being turbulent. The field of inhomogeneities and the turbulence are assumed stationary, homogeneous and isotropic. Concerning the influence of the angle between the sound propagation direction and the flow, four terms are found in F: two nondirective and two dipole-like ones, with maxima at +-90 deg. To each of the two mechanisms a pair comprising one nondirective and one dipole-like term is related. The nondirective term related to the inhomogeneities does not depend on the flow velocity, while the dipole one is quadratic in it. The two terms related to the turbulence display the 3rd or 4th power dependence on the velocity.
    Keywords: signal decorrelation, turbulence, random inhomogeneities

  5. Type of paper: Paper in proceedings

    Title: Analysis of cavitation noise of an onboard propeller

    Authors:
    BAJIĆ, BRANKO (78490)
    TASIĆ, JADRANKA (94653)
    Editors
    Weitendorf, E.-A.
    Proceedings title: International Symposium on Propulsors and Cavitation
    Language: engleski
    Place: Hamburg, Germany
    Year: 1992
    Pages: from 215 to 223
    Meeting: International Symposium on Propulsors and Cavitation
    Held: from 05/22/92 to 05/25/92
    Summary: Broadband cavitation noise of an onboard propeller with a surface from heavily fouled to freshly polished was measured in a 4:1 range of the hydrostatic pressure, P, at a cavitation number to 37% of its critical value. By means of a carefully designed measuring set, free field conditions, low background noise, and stationarity of noise samples were ensured. Good scaling of propeller was obtained with the 10logP*EXP(2.2) correction. A modulation analysis method for acoustical diagnosis of weak or moderate propeller cavitation, which resolves contributions from blades and different wake segments, is presented. The method can be used to suppress scale effects in noise modelling.
    Keywords: cavitation noise, noise modelling, acoustical diagnosis, modulation analysis method, measuring set

  6. Type of paper: Paper in proceedings

    Title: Hybrid and polarity-coincidence correlation processing

    Authors:
    BAJIĆ, BRANKO (78490)
    Proceedings title: Oceans Engineering for Today's Technology and Tomorrow's Preservations
    Language: engleski
    Place: Piscataway, N.J., USA
    Year: 1994
    ISBN/ISSN: 0-7803-2056-5
    Pages: from II573 to II578
    Meeting: OCEANS 94
    Held: from 09/13/94 to 09/16/94
    Summary: Two simple definitions of correlation processors, based on hard limiting in one or both channels, yielding hybrid and polarity-coincidence correlation function, are analysed theoretically. Several practically, useful correlation schematics are proposed. In some if them, linearization by means of additional noise in the one-bit channel(s) is used. Errors due to random fluctuations and residual nonlinearity are estimated. If the linearization noise level is optimized, the total error is inversely proportional to the n-th power of the number of signal samples used in averaging, where n=1/2, 1/3, or 1/4, in the case that the linearization is performed in 0, 1, or 2 channels, respectively.
    Keywords: correlation processing, relay correlation, polarity-coincidence correlation

  7. Type of paper: Paper in proceedings

    Title: Spectrum normalization method in vibro-acoustical diagnostic measurements of hydroturbine cavitation

    Authors:
    BAJIĆ, BRANKO (78490)
    KELLER, ANDREAS
    Proceedings title: CAV'95, Proceedings
    Language: engleski
    Place: Deauville, France
    Year: 1995
    Pages: from 7 to 13
    Meeting: International Symposium on Cavitation CAV'95
    Held: from 05/02/95 to 05/05/95
    Summary: Full-scale vibro-acoustical diagnostic measurements of cavitation in four Francis 6 MW double runner turbines were performed. Two types of sensors were used - a hydrophone sensing waterborne noise at the pressure side of a runner, and an accelerometer mounted at various points at the outer turbine casing, facing the runner's pressure side. The correlation of noise and acceleration intensity with suction-side pressure fluctuations and runner position was checked. A simple but efficient method of spectrum normalization which reject the influence of the measurement set characteristics and vibro-acoustical characteristics of a turbine was developed. The resulting spectra reveal the dependence of cavitation source strength on the turbine power as a function of noise or acceleration frequency.
    Keywords: vibro-acoustical diagnostics, hydroturbine cavitation, cavitation erosion, cavitation noise


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