Silent Ships - a New Challenge for the Shipbuilding Industry (original) (raw)

The application of sound intensity technique in research on noise abatement in ships

Applied Acoustics, 1995

One of the main advantages of the sound intensity (SI) technique is the possibility of identtfying the energy transmitted through dflerent parts of composite panels and walls. This paper presents the application of the SI technique to the measurement of the acoustic radiation of ship cabin partitions. On the basis of the near field acoustic intensity measurement with the$xedpoint method, the distribution of spatial intensity vectors in a plane close to the ship partition is presented. As a result of the investigation, a three-dimensionalflow map of active intensitv vectors B graphically illustrated for the heterogeneous partitions with 'acoustic leaks' (door and windows). The measurement technique described, as well as the method of graphical presentation of results, can enrich the knowledge of the mechanism of acoustic energy flux through real partitions.

The Use of Acoustic Vectors Decomposition of Sound Fields to Vibroacoustic Protection on Ships

Archives of Acoustics, 2017

In this paper, numerous examples will be illustrated as principles of applying the sound intensity measurements to practical problems at the noise abatement on ships and offshore constructions. The paper presents the results of transmission loss measurements together with flanking transmission for ship bulkheads and partitions with doors and windows. Investigations carried out with sound intensity measurement techniques will be compared against those made by classical methods. Finally for a few examples, the graphic presentation of spatial distribution of sound intensity vectors risen close to vibrating ship cabin partitions and inside the cabin will be shown in 2D and 3D graphical form. As a result, a two-dimensional acoustic wave flow map of time-averaged active intensity vectors propagated along curved streamlines and a vector perpendicular to measured plane are graphically illustrated. The technique of acoustic vectors decomposition of sound fields described, can enrich the know...

Analysis of literature data on shipboard noise

2020

The objective of this work is to perform a statistical characterization of noise onboard ships from available data in the literature, classifying the spectral noise measurements by different spaces and ship typologies. Data analysis of experimental measurements in octave bands was developed, classifying the noise into 3 categories based on International Maritime Organization (IMO) recommendations: accommodation spaces, navigation spaces, and work spaces. Additionally, the following ship typologies were considered: military or commercial. Relevant aspects were searched, such as high noise levels and low frequency (LF) noise components associated with induced vibrations. The results of the analysis show an average dB(A) noise level of 69 dB(A) but with different frequency distribution depending on space typology, in which workplaces had a higher mean value and dispersion in comparison with accommodation and navigation spaces. Mitigation of noise in ships is a very important issue and efforts must be made to reduce LF noises and sound pressure levels in general in all onboard spaces. To achieve more comfort and safety, the normative framework should be updated and modernized to include more sophisticated noise indicators that consider quality aspects of the spectrum such as vibrations and tonal components.

Acoustic impact of ships: noise-related needs, quantification and justification

The evaluation of the acoustic impact of ships is a complex problem, involving not only different sources but also different kinds of receivers and transmission paths. The problem of health and comfort for crew and passengers on board has been considered since a few decades, leading to quite a structured and detailed framework of Norms and Requirements. On the other hand, only in recent years a growing attention has been devoted to air-borne noise emissions outside the ship, for which requirements are not present. Underwater noise emissions have, even more recently, gained attention for their potential interference with mammals' communications and with the sophisticated use such animals make of acoustic signals for interacting with their living environment. An aim of the present work is to review the state of the art in the three areas above identified outlining the differences in the specific fields as regards: the present knowledge of the phenomena involved; the accuracy of the models available for the description of noise propagation; the accuracy of the models available for the quantification of noise effects.

Analysis of noise on board a ship during navigation and manoeuvres

In the present study, full-scale noise levels measurements on board a Ro-Pax ferry have been carried out in various compartments of the ship, both in stationary conditions (navigation) and during manoeuvres. Noise levels have been surveyed in various categories of spaces located in all decks accessible to both passengers and crew, with the purpose of giving a complete and effective picture of the acoustic climate on board. The measured noise levels have been compared with current and proposed limits for working and living spaces, obtaining a clear identification of the most critical spaces on board the ship both in respect to acoustic comfort and noise exposure of crew during working hours. In cabins, different operating conditions for air conditioning have been tested, to analyse the specific contribution to annoyance of the ventilation noise, which turned out to be in many cases determinant. Transient conditions during manoeuvres entering and leaving harbours have been analysed by spectral time histories in cabins and public spaces close to the main propulsion plant and to bow thrusters. These situations correspond to considerably high levels, which may limit significantly operation during night time.

Acoustical Impact Of The Ship Source

The ship as whole represents quite a complex noise source. The generated noise affects definitely people on board the vessel (crew and passengers, directly exposed to sound pressure levels) but third parties as well, which may be reached by airborne or underwater noise transmission from the ship: inhabitants of areas near the coastline and near ports, the marine fauna living in zones with intense maritime traffic). The threefold aspect of the acoustical impact of ships (internal to the vessel, external in air and in water) is covered in the paper, which identifies in each context the main sources of noise, the potential receivers and the transmission paths linking sources and receivers. The state of the art and new trends in the characterization of the sources are evaluated, as well as the means available to model the transmission of acoustical power along the various effective paths. The available means for charactering the perception by the receivers in the various contexts are considered, in order to assess the impact of the noise radiation. The more or less recent introduction of norms and requirements in the different fields are discussed and analyzed, in order to highlight the evolution of the societal concern about the ship noise impact on second and third parties of the maritime transportation process. Such concern justifies the undergoing process of further implementations in the normative framework. The trends of this evolution are finally discussed, with description and motivation of pre-normative proposals covering the three aspects above mentioned. The work builds on the results of project SILENV, recently funded by the EU.

Predicting shipboard noise using 3-D acoustic modeling

Noise Control Engineering Journal, 2007

Predicting and controlling shipboard noise is a daunting task, particularly when the commonly accepted, one-dimensional prediction approaches are used. Numerous powerful acoustic sources are often located in close proximity to sensitive receiver spaces and the ship's structures and systems themselves are not amenable to straightforward abatement techniques. In addition, treatments usually impose adverse space, weight and cost impacts yet the crew and passengers need to be protected. This paper presents an alternative to the common spreadsheet and hand calculation methods of shipboard noise analysis. The paper discusses an SEA based noise prediction method. The primary purpose of this engineering prediction method is to facilitate rapid predictions that preserve the accuracy required for the design of effective treatment of shipboard noise. Two case studies are presented indicating the features and application of the tool.

A Simple Model for the Underwater Noise Source Level of Ships

2014

Underwater noise becomes a field of growing concern because of the possible interaction with sound vocalization of marine mammals. Modeling the effect of shipping noise being a predominant contribution worldwide requires more than statistics of measured ships in the field. This article is an attempt to characterize the underwater radiated noise level of a ship by relating spectral components of noise to naval architectural features of the ship.

The examination of position of ship's noises sources based on hydroacoustics method

2008

The paper presents the experimental research associated with the transmission of acoustic energy generated by moving ship into the water. The paper present the methodology of evaluations acoustics energy from the mechanisms of ship into the water environment. For that purpose the research of noise distribution over ship's hull were conducted along with the hydroacoustic field. The hull is source of waves of complex surface shape inducing waves of different amplitudes and phases depending on the position of ship's machinery. As a result of the hull vibrations generated wave distribution depending on the primary sources, as the main propulsion units, generators or other mechanisms. This research allowed to determine position of the main noises' sources of acoustics energy of machinery and propulsion system depending on class of ships.

Active control of marine noise using the sound intensity technique

WIT Transactions on the Built Environment, 1995

The article presents the application of the sound intensity technique to the graphical presentation of the spatial distribution of the intensity field radiated by the part of cabins wall with windows. For the region of a window box there is illustrated a two-dimensional flow map of the time-averaged active intensity space vector as a projection onto the measured ,,xy" plane and a vector ,,z" perpendicular to the measured plane. Additionally, the distribution of the acoustic energy streamlines is presented. The analysis of an acoustic field shape produced near the windows of a ship's cabin before and after installing the shipboard wall makes it possible to estimate local radiation sources and regions of vibro-acoustic bridges through which the energy is passed over to the shipboard wall of the cabin. The tests also enable to estimate how the lack of vibro-acoustic bridges and window isolation sheltering affect a level of the noise being radiated into the cabin.