Jun Fan

Modeling of Low-frequency Source Levels from Fishing Vessels Using an Acoustic Observatory in the East China Sea

For the past few decades, there has been a focus on the ocean ambient noise in research, one of which is the effect of human-generated noise on marine mammals. The shipping noise has been considered as the main contributor, especially in coastal areas. Less concern has been paid to the research on the underwater radiated noise (URN) from fishing vessels at frequencies below 100 Hz. In the present work, the URN from six fishing vessels measured with an opportunistic bottommounted acoustic observatory in the East China Sea was chosen for the analysis. Inspired by the methodology of RANDI-3, a modified URN model to predict the spectral source levels (SSLs) of fishing vessels at third-octave frequencies below 100 Hz was proposed, in which the corresponding SSL could be expressed as a function of frequency and ship length. Finally, we applied this modified model to estimate the SSL of a reference fishing vessel. The results show that this modified URN model has certain credibility for six fishing vessels as well as other fishing vessels within certain limits.

Vibroacoustic behavior of an infinitely long cylindrical shell with periodic internal lengthwise ribs

The vibroacoustic behavior of an infinitely long cylindrical shell with periodic lengthwise ribs is studied. The shell motion is described by the Donnell equations, and the lengthwise rib is modeled as an elastic beam whose motion is decomposed into longitudinal and flexural vibrations. Analytical expressions are obtained for the shell motion via a circumferential mode expansion based on the periodicity in the circumferential direction and the Fourier transform in the longitudinal direction. Furthermore, the far-field radiated pressure is obtained via the stationary-phase approach. The shell vibration and sound radiation are analyzed using discrete circumferential wavenumbers. Multi-order flexural Bloch waves exist in the circumferential direction when the cylindrical shell is equipped with periodic lengthwise ribs. The supersonic components of the flexural Bloch waves radiate efficiently and lead to acoustic radiation resonances in the far field.

Analysis and Modelling on Radiated Noise of a Typical Fishing Boat Measured in Shallow Water Inspired by AQUO Project’s Model

The shipping noise near channels and ports is an important contribution to the ambient noise level, and the depth of these sites is often less than 100 m. However less attention has been paid to the measurement in shallow water environments (Brooker, Humphrey, 2016). This paper presents extensive measurements made on the URN (underwater radiated noise) of a small fishing boat in the South China Sea with 87 m depth. The URN data showed that the noise below 30 Hz was dominated by the background noise. The transmission loss (TL) was modelled with FEM (finite element method) and ray tracing according to the realistic environmental parameters in situ. The discrepancy between the modelled results and the results using simple law demonstrates both sea surface and bottom have significant effect on TL for the shallow water, especially at low frequencies. Inspired by the modelling methodology in AQUO (Achieve QUieter Oceans) project (Audoly, Enrico, 2015), a predicted model applied to a typical fishing boat was built, which showed that the URN at frequencies below and above 100 Hz was dominated by non-cavitation propeller noise and mechanical noise, respectively. The agreement between predicted results and measured results also demonstrates that this modelling methodology is effective to some extent.

Experimental analysis of backscattering by cylindrical shell with internal plate at oblique incidence

Through an experimental approach, this paper studies the flexural wave coupling on a cylindrical shell with internal structural. Impulse response backscattering measurements are presented and interpreted for the scattering of obliquely incident plane waves by a fluid-loaded stiffened cylindrical shell and a corresponding empty cylindrical shell respectively. The stiffened cylindrical shell is reinforced by a thin internal plate which is diametrically attached to the shell along its axial direction. The time series data are fast Fourier transformed and the modulus normalized according to the direct wave spectrum. Result are plotted as frequency-angle spectra. Compared with that from the corresponding empty cylindrical shell, the subsonic flexural waves on the cylindrical shell will interact between the attachments and some of their energy can be converted into radiating waves.

Modeling on low-frequency underwater noise radiated from a typical fishing boat based on measurement in shallow water

As evidenced in documents during the past decades, the impact of man-made underwater noise on the marine environment has always attracted more and more interest of the global researchers. About ten kinds of models have been proposed to predict underwater radiated noise (URN) by ships, and most of which are applicable above 100 Hz. This paper is aimed to modeling the low-frequency URN. Extensive measurements were made of the URN of a small fishing boat (length 43 m, displacement 500 tons) at South China Sea. The URN data show the high-level noise below 100 Hz is mainly contributed by the mechanical noise (e.g., main engine and service diesel generator) and propeller cavitation, and performs complex varying characteristics with the speed. The effect on the Transmission Loss (TL) from the sound-speed profile and bottom has been analyzed, compared with the empirical function, which show the estimated TL has an important influence on the spectral source levels (SSLs). Inspired by the method in AQUO (Achieve QUieter Oceans) project, a predicted model applied to typical fishing boat was built.As evidenced in documents during the past decades, the impact of man-made underwater noise on the marine environment has always attracted more and more interest of the global researchers. About ten kinds of models have been proposed to predict underwater radiated noise (URN) by ships, and most of which are applicable above 100 Hz. This paper is aimed to modeling the low-frequency URN. Extensive measurements were made of the URN of a small fishing boat (length 43 m, displacement 500 tons) at South China Sea. The URN data show the high-level noise below 100 Hz is mainly contributed by the mechanical noise (e.g., main engine and service diesel generator) and propeller cavitation, and performs complex varying characteristics with the speed. The effect on the Transmission Loss (TL) from the sound-speed profile and bottom has been analyzed, compared with the empirical function, which show the estimated TL has an important influence on the spectral source levels (SSLs). Inspired by the method in AQUO (Achieve QU...

Modeling method on acoustic scattering from penetrable objects using a hybrid Kirchhoff/ray approach

A method is put forward to investigate the acoustic scattering from double-sided water loaded targets which is penetrable even in high frequency. The present approach is an extension of the TriKirch method which was elaborated for non-penetrable targets [J. Acoust. Soc. Am. 140(3), 1878-1886 (2016)] and complex targets are dispersed into many triangular planar facets. Reflection coefficient of plane facet is introduced to calculate the scattering amplitude of each non-rigid triangular facets combined with TirKirch method, and the total scattering amplitude of target is obtained by superposing the amplitude of all facets’ contributions coherently. Double bounce (DB) contributions to the scattering is calculating by ray-tracing method. Computations are made for a double-sided water loaded finite cylindrical shell with perforated ring ribs, and are compared with the experimental results，and both results show good agreement.