- 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
- Type of paper
: Paper in journal
Title: On the applicability of the Coulter-counter to the
cavitation nuclei size distribution analysis
- Authors:
- DUBUR, 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
- 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
- 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
- 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
- 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
- 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