1,721,022 research outputs found
On the possibility of estimating ship parameters using acoustical Lloyd's mirror effect
No full textThe Lloyd's mirror effect is an acoustic effect taking place when a source of noise moves parallel to a reflecting surface. In the case of ships, the underwater sources of noise, mainly the propeller, are at constant depth, i.e. a constant distance, from the free surface that can be considered a perfectly reflecting surface. In such a configuration, a destructive-constructive interference pattern is generated in the time-frequency domain by the combination of the direct and surface-reflected sound waves. As the shape of the acoustic patterns depends on the speed of the ship, the relative distance between the ship and the hydrophones and the sound celerity, it is in principle possible (it has been successively done for aircrafts) to derive the above mentioned characteristics simply analysing the corresponding Lloyd's mirror effect. This is particularly interesting when monitoring shipping noise traffic when data regarding ships cannot directly derived by the Automatic Identification System (AIS). In the paper a set of measurements carried out in the framework of two EU FP7 European Projects are analysed to discuss about the possibility of estimating ship parameters using acoustical Lloyd's mirror effect. During the measurements the main ship parameters have been monitored by GPS therefore representing a good reference test
New Requirements for Noise Radiated from Ships: Pre-normative Formulations and Background
No full textOne of the aims of the SILENV project, funded by the
E.U. within the 7FP, was the development of prenormative
requirements regarding the impact of shipradiated
noise into three different environments:
onboard the vessel and outside it, in air and in water.
The paper describes the background of the new formulations
which generally take into account the existing
requirements, the technical know-how in the field of
ship construction about the characterization of noise
source and transmission paths and the actual knowledge
of the way noise affects the various categories of receivers
involved. On these bases, objectives of the noise
control are defined in the various areas and the final
choices in terms of limits are reported, also highlighting
the motivations at the basis of the requirements. Possible
future trends in the redefinition of objectives for the
control of noise and in normative developments are also
discussed
Simulation based design of a fleet of ships under power and capacity variations
No full textAchieving the right balance between fixed and operating costs is a key but non-trivial task for optimizing the characteristics of a fleet of ships for a new trade at a very early stage of the design. A wide range of design choices as well as a significant number of uncertainties related to the operation of the fleet affects those two expense items. In the proposed analysis, operative uncertainties rising from rough sea conditions are taken into account in a Simulation Based Design (SBD) framework for fleet generation and evaluation. The costs-benefits analysis is aimed at understanding the effects of variations in the installed power and in the ship capacity on the overall fleet performances. These two major characteristics of the ship design (and, accordingly, of the fleet of ships realizing the trade) are introduced in the numerical model considering the sea margin and the nominal capacity as free design parameters instead of fixing them as commonly done in practice. From a design point of view, this corresponds to the introduction of two new variables, enlarging the dimensions of the design space to be explored, better than relaxing the boundaries of a simpler design space. The validity of this approach is demonstrated by a practical application to the design of a fleet of Compressed Natural Gas (CNG) carriers. In this context, the effects of variations in the fuel price and in the voyage length on the optimal fleet characteristics are analyzed and the results are discussed in comparison to those coming from the reference scenario
Un sistema flessibile per misure avanzate e analisi del rumore irradiato dalle navi
No full textUna sempre maggiore attenzione è volta all’effetto negativo he possono avere i veicoli marini come potenziale sorgente di rumore subacqueo. Sia per le navi militari, i pescherecci, le navi da ricerca, ma anche per le navi commerciali inclusi yacht e navi da crociera, la valutazione dei livelli di rumore subacqueo irradiato sta diventando un aspetto fondamentale. Pertanto la caratte rizzazione delle sorgenti di rumore e quindi le misure del rumore emesso sono il primo step nella valutazione degli effetti del rumore irradiato dalle navi. Mentre nel campo militare vengono utilizzati poligoni acustici in siti dedicati, in ambito civile sono necessari sistemi portatili e più flessibili. Un sistema di questo tipo è stato messo a punto e viene presentato inquesto paper. In particolare si ratta di una array di idrofoni ciascuno dotato di sensore di profondità. Un software di post-processing è stato sviluppato in Matlab® ed è in grado di coprire le necessità delle normative attuali, ma anche di fornire uno spettro più grande di informazioni
Editorial: Acoustical Impact of Ships and Harbors: Airborne and Underwater N&V Pollution
No full textNoise on board RO-Pax vessels: Measured levels on existing ships and new pre-normative requirements
No full textThe problem of noise annoyance on board ships has been addressed since a long time. The first document setting limits on onboard noise was the "Code on noise levels on board ships", issued by the International Maritime Organisation in 1981. More recently all the major Classification Societies introduced in their requirements the so called "Comfort Classes". They generally provide different ratings of the acoustic comfort of ships. The growing needs of passengers and workers for acoustical comfort on board pushed both Classification Societies and IMO to consider an update of limits and criteria for noise annoyance assessment. The normative framework in the field is therefore presently in an evolution phase. In the present work, a series of existing measurements of noise carried out on a set of Ro-Pax vessels is analysed and compared with the existing requirements and with the new proposals of the SILENV collaborative project (Ships oriented Innovative soLutions to rEduce Noise & Vibrations), funded within the 7th Framework Programme of the E.U. and running in the period 2009-2012. The comparison provides an indication of the possibility for shipbuilding to cope with the new requests in terms of noise performances, provided that such requests are inserted in the design process. Further efforts are needed similar to those already implemented to fulfill the present formulations of compulsory requirements and reflected in the measured values
Seafarers' work exposure to tonal noise components
No full textThe requirement of better workers' psychophysical health and the wish to guarantee a correct comfort also during work activities, induce to consider the presence of significant pure tones also for the working spaces. However, the current European legislation regarding professional exposure to the noise of the workers, and namely the EU Directive 2003/10/CE, does not take into consideration the possible presence of pure tones in working noise. The same lack can be noticed in the standard ISO 1999:2013. As regards seafarers, the reference codes are the International Maritime Organization (IMO) Resolution A.468(XII) for ships built before 1 July 2014, and Resolution MSC.337(91) for newer ships. While tonal components are mentioned in the first one, stating that, if these are "obvious", the ISO noise rating (NR) number should be also determined, in the latter and most recent IMO Resolution no reference to tonal components is present. Tonal components cause annoyance and, at the same time, they induce hearing damage and can alter the behavior of workers, with a potential risk for the safety of ships. In this study, noise measurements taken onboard different ships are analyzed in order to determine seafarers' work exposure to tonal components. The survey includes different work spaces. To assess the presence of tonal components in crew's work environments the methodology of environmental noise analysis, defined in the Annex B of Italian Decree D.M. 16/3/98, has been used, making reference to ISO 226:2003 for determining normal equal-loudness level contours. The method used in order to evaluate tonal components is well established for the environmental noise annoyance and therefore it can be operatively extended to the workplace noise exposure. Results show that the presence of tonal disturbing components is not sporadic and therefore worthy of further analysis and regulation
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