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1

Dependence of acoustic noise emission on the dissipated energy of plunging waves

Klusek Zygmunt, Paprota Maciej, Sulisz Wojciech, Zdolska Aneta, Sorek Sebastian

Oceanologia

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2020

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No. 62 (1)

70--82

EN

The results of experiments performed in a wave flume designed to explore associations between the dissipation of surface wave energy during breaking and acoustic noise emission are presented. The experiments were carried out using tap water in the wave laboratory of the Institute of Hydro-Engineering of the Polish Academy of Sciences, Gdańsk, Poland. In particular, being shown are the parameters of empirical dependency between the dissipated wave energy during plunging and the energy of pre-breaking wave trains. Relationships between wave energy losses in the case of breakers with an amplitude of about 10 cm and the noise acoustic energy in the frequency band from 80 to 12,500 Hz were estimated. Taking into consideration the phenomena of reverberations and propagation in an acoustical waveguide, a numerical model was used for the correction of the observed noise's acoustic spectra. A detailed analysis of the factors affecting the noise level in the semi-enclosed volume allowed us to specify the rate of conversion of the wave energy dissipated during breaking into acoustic energy, which was found to be in the order of 10−8.

2

Impact of Spatial Noise Correlation on Bearing Accuracy in DIFAR Systems

Rudnicki Mariusz, Marszal Jacek, Salamon Roman

Archives of Acoustics

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2020

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Vol. 45, No. 4

709--720

EN

DIFAR type underwater passive systems are one of the more commonly used tools for detecting submarines. At the design stage, which usually uses computer simulations, it is necessary to generate acoustic noise of the sea. It has been shown that correlating noise significantly reduces these errors compared to the assumption that noise is uncorrelated. In addition, bearing errors have been shown to be the same in systems with a commonly used antenna containing five hydrophones, as in a system without a central hydrophone, which may be useful in some DIFAR system design solutions.

3

Underwater noise emitted during small-scale air entrainment events

Szuszkiewicz J., Klusek Z.

Oceanological and Hydrobiological Studies

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2018

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Vol. 47, No. 1

87--97

EN

The breaking wave phenomenon significantly takes part in the mechanisms of mass, heat and gas exchange at the air-water boundary and depends on the wind velocity. Some of the energy dissipated during this process is converted into underwater sound emitted by oscillating gas bubbles and bubble plumes. However, the underwater noise accompanying the lowest wind speed conditions has received only little attention. This report describes a study aimed at advancing the knowledge of underwater noise emission from air bubbles injected during small-scale breaking events occurring on the water surface. Results of model experiments performed in a small tank are presented. The object of the research is the relationship between the generated noise and the dissipated potential energy of water poured into a tank filled with water of varying physical water properties. Additionally, the impact of various water properties such as salinity, surface tension or microscale gas bubbles was examined. The experiment revealed that noise spectra are affected by different water properties and most likely reffect the varying efficiency of bubble formation and bubble size spectra.

4

Impact of salinity on the underwater noise generated by small scale air entrainment events

Szuszkiewicz J., Klusek Z., Gorska N.

Hydroacoustics

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2017

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Vol. 20

167--172

EN

Some part of the energy released in the wave breaking process is transformed into the energy of the noise. This sound depends on the water properties, however, there is a lack of reliable data concerning the underwater noise generated by less energetic events. The aim of this study was to understand the impact of salinity on the underwater noise produced during small scale air entrainment events, typical for low wind speed conditions. The tipping trough experiment was performed in a small tank to generate the small scale air injections. Four, linearly placed hydrophones HTI-96-MIN were used to record the acoustic noise accompanying this phenomenon. The bubble plume development, and underwater noise spectra, were compared for salty and fresh water. The potential energy of the modeled events resulted in different spectra, and salinity played an essential role in the emitted underwater noise.

5

Prediction of Tonal Underwater Noise Pattern from Cavitating Propellers with Special Attention to Ice Cover Effects

Streckwall H., Bretschneider H.

Polish Maritime Research

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2014

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nr 4

35--40

EN

To predict underwater noise spectra associated to regular occurrence of propeller cavitation we have extended an existing method [1] (used for the prediction of fluctuating hull pressures) to become applicable for effects that are linked to a finite speed of sound. In [2] an intermediate approach was realized where (besides the hull) far field boundaries were introduced but the incompressible flow assumption was kept. However compressibility effects become noticeable in the far field, which may be judged to start at some 2-3 propeller-diameters distance from the centre of the cavitation events, if we confine to emissions at 1st- 4th blade frequency. It was a logical continuation of our former efforts to realize a compressible flow model and integrate the propeller as a noise source. Having increased the functionality of our approach by referencing the speed of sound, the precision of the method was also somehow reduced. In our former approach, like in comparable approaches (see for instance [3] and [4]), the singularity system generating the near field propeller induced pressures involved various sources and vortices distributed on the propeller blades. With our current compressible approach this complexity was dropped, as a single point source substitutes the cavitating propeller. Such a simplification correlates with the assumption, that the monopole character of a noise source is decisive for the far field noise levels. In this contribution we outline the steps characterizing the procedure for predicting tonal underwater noise from cavitating propellers. In the first step a Vortex Lattice Method (VLM) is used to access the cavitation pattern on the propeller with special focus on the cavity volume attached to one blade. The second step accumulates the distributed cavities to establish a fluctuating point source of equivalent far field noise characteristic. As relevant limits the hull, the free surface, the sea bottom and an ice cover are introduced. Using finally a Boundary Element Method (BEM) approach the relevant noise characteristics are derived, accounting for external boundaries and for the finite speed of sound. The results provided here are focused on a comparative treatment of different scenarios, mainly addressing ice cover effects at finite the water depth.

6

Estimation on Audibility of Large Cetaceans for Improvement of the Under Water Speaker

Yamada H., Kagami L., Yonehara Y., Matsunaga H., Kato H., Terada M., Takahashi R., Okanoya K., Kawamoto T.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2012

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Vol. 6, no. 4

589--593

EN

In order to avoid collisions between the hydrofoil (HF) and cetaceans, the Under Water Speaker (UWS) has been installed on the HF. Because of its potential in utility, we tried to improve the UWS to minimize the risk of the collisions. Under our project, we examined three subprojects; 1) Analyzing the characteristics of the HF underwater noise; 2) Assessing audibility of major large cetaceans by measuring their vocalizations and 3) An anatomical prediction of the audible range by examining the cochlear basal membrane. Through the analyses, it was identified that the noise produced by the HF was a broad-band noise with approximately 150dB re 1μPa-m.That noise level was lower than those of larger boats suggesting difficulties for cetaceans in sensing approach of the vessels. In addition, analysis of their vocalizations and anatomical obervation indicated that dominant frequency of their audible range was lower than signals produced by the existing UWS.

7

Ship's underwater noise measurements using sound intensity method

Gloza I.

Hydroacoustics

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2009

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Vol. 12

53-60

EN

Ship noise is a most important part of the field of underwater acoustics. Its reduction and monitoring is an important aspect in the performance of underwater acoustic systems and in the habitability of the vessel for the crew and passengers. In naval operations the noise radiated by a ship is also dominant source of information for underwater sonar systems. Sound intensity is the vector quantity which informs us about the sound power flux, the position and the direction of the sound source. The probe tracks the position of source and at the same time, measures the component of sound-intensity vector. Generally only one component of vector sound intensity was measured, perpendicular to a given measurement surface. The sound intensity of a moving source includes effects such as flow noise that are not present when the source is stationary. The accuracy of measuring acoustic intensity using two closely spaced hydrophones by correcting the phase mismatch error by measuring the transfer function between the two detector systems was examined. The two measuring hydrophone instrumentation systems were earlier calibrated. Our results have been obtained using digital methods, where was used PULSE measuring system.

8

Detekcja źródeł szumów podwodnych z wykorzystaniem falki Malvara

Jerzman B.

Pomiary Automatyka Kontrola

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2007

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R. 53, nr 9

48-51

PL

W referacie zamieszczono wyniki badań modelu detekcji źródeł szumów podwodnych, bazującego na estymacji funkcji gęstości prawdopodobieństwa rozkładu energii w pasmach dekompozycji falkowej sygnałów pomiarowych. Celem badań było ilościowe porównanie wyników detekcji zaburzeń powodowanych przez płetwonurka w środowisku podwodnym, z wykorzystaniem w procesie przetwarzania sygnałów pomiarowych falek Daubechies oraz Malvara. Wyniki badań wskazują, że wykorzystanie lokalnych transformacji Malvara pozwala na bardziej efektywne wykorzystanie zastosowanej metody detekcji.

EN

The paper presents the results of the research on the model of detection of the underwater noise sources. This model is based on the multivariate kernel density estimate of the energy of multidimensional wavelet coefficients. The conventional method of signal decomposition using Daubechies wavelet is compared with the algorithm which implements Malvar wavelet. This type of decomposition was adapted to the method of detection of underwater disturbances coming from unnatural sources. The outcome of theoretical considerations was supported by the figures presenting the results of simulation experiments on the real noise signals. The aim of the research was the numerical comparison and the evaluation of the effectiveness of the detection of signals generated by the diver using the Malvar wavelet or the standard Daubechies wavelet. The specific and distinct character of Malvar wavelet implementation strongly affects the method of detection thus the analysis of the results of the modification seems to be interesting. The research proved that the exploitation of local Malvar transforms reduces the number of computations, minimizes the detection result. Moreover, it enables greater flexibility as far as the parameter selection is concerned.