1,721,013 research outputs found
Uncertainties estimates of hull girder still water loads of bulk and dry cargo ships through Monte Carlo simulations
No full text
Noise 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
Control of airborne noise emissions from ships
No full textNoise pollution is an important part of the environmental impact of ships. The noise inside the vessel (affecting crew and passengers) has been regulated since a few decades, while the impact of emissions in water on the marine fauna has been under consideration at the International Maritime Organisation (IMO) only in the last few years. No specific effort seems to be in place towards a regulatory framework for external airborne noise emissions from sea going commercial ships. Only the particular cases of inland vessels and pleasure crafts are partially covered by rules. The airborne noise pollution from commercial ships, on the other hand, does affect people living near channels, in coastal areas with intense traffic or near ports, where ships enter and stay at wharf for loading/unloading processes. The actual dimension of the problem is remarked by several cases of complaints sent out by citizens living in the urban areas affected. Within the SILENV project (Ships oriented Innovative soLutions to rEduce Noise & Vibrations, funded by the E.U.) assessment criteria for the airborne noise emitted by sea-going ships have been proposed: the background information, the general criteria at the basis of the formulation, the aims as well as the verification procedure of the proposed limits are discussed in the paper
Onboard ship noise: Acoustic comfort in cabins
No full textThe acoustic comfort in passenger cabins on board six passenger ships is analyzed in this paper. The overall noise inside cabins is first evaluated, then the effect of HVAC (Heating, Ventilation and Air Conditioning) is investigated and several criteria, typical from the civil field (Noise Criterion, Room Criterion, etc.), are applied and compared. The effect of different operative conditions in terms of revolutions per minute of engines, propellers and generators, of propeller pitch and of engine power is investigated as well, highlighting the differences in terms of measured noise and of indicators performances. The results of the study suggest that the current normative framework and regulations about noise on board ships, based on dB(A) limits only, could effectively be revised to take into account spectral components, whose effect would otherwise be neglected
A method to assess safety and comfort for different ships types in a region of interest
No full textThe worldwide increase in ship traffic poses a series of challenges for the designer, the crew and the authorities involved in ship traffic management. Depending on the ship type, both onboard comfort and safety represent two key aspects to be taken into account during the ship life. In the present paper, the focus is on the assessment of the safety and comfort in service during navigation in real weather conditions by focusing on an entire route instead of on a single ship. A method for assessing the safety and comfort levels of specific routes is presented and discussed in the paper. In particular, a statistical approach to set up limit thresholds able to quantify the level of navigation safety and comfort for different ship types in a specific area is presented based on historical weather data. The method is based on the Automatic Identification System (AIS) data for the traffic characterization, a strip theory for the seakeeping calculations and historical meteorological data for the environment definition for a specific area in the Mediterranean Sea
Underwater noise emissions: Another challenge for ship design
No full textThe issue of the environmental impact of shipping activities is treated in this work from the specific viewpoint of underwater noise emissions from the vessels. There has been recently a rising concern about the negative effects that this kind of emissions can have on the marine wildlife in general and in particular on marine mammals. In these animals, acoustic communication and perception has acquired a privileged role compared with other senses and other zoological groups. The paper examines the role in this scenario of noise emissions from shipping and explores how their impact can be quantified, in order to establish a target for the control of such emissions. The standards recently issued for the characterisation of underwater noise signature by commercial vessels are also reviewed. The paper builds on the first results of the project SILENV, funded with the 7th Framework programme of the European Unio
Modelling the Outdoor Noise Propagation for Different Ship Types
No full textAirborne noise emissions from ships can be a significant source of annoyance. Therefore, it is important to
accurately predict ship noise in order to get an effective environmental noise control in planning new ports,
or in widening existing harbor, or in locating new mooring positions. To test the reliability of current
commercial simulators in predicting the noise field from complex sources such as ships, in the present
work the airborne noise propagation from two different vessels was modelled: a Multipurpose Ship and a
Fishing Research Vessel. The development of the model for both ships was performed in five steps:
acquisition of the input data; modelling of the ship in the sound propagation software; definition of the
noise sources; model validation; output data generation. Simulated data were then compared with on field
measurements. The obtained results rise some questions about the measurement techniques adopted to
characterize the source levels and the validation data, the simplifications made on the ship surface and the
typologies of sources utilized in the study. Future developments in numerical simulators are needed in
order to better describe outdoor noise propagation from ships, taking into account the specific nature and
complexity of such sources
Underwater Sound Characteristics of a Ship with Controllable Pitch Propeller
No full textThe time-dependent spectral characteristics of underwater sound radiated by an oceanic vessel have complex dependencies on ship machinery, propeller dynamics, and the hydrodynamics of the ship exhaust and motion, as well as onboard activities. Here, the underwater sound radiated by a ship equipped with a controllable pitch propeller (CPP) is analyzed and quantified via its (i) power spectral density for signal energetics, (ii) temporal coherence for machinery tonal sound, and (iii) spectral coherence for propeller amplitude-modulated cavitation noise. Frequency-modulated (FM) tonal signals are also characterized in terms of their frequency variations. These characteristics are compared for different propeller pitch ratios, ranging from 20% to 82% at a fixed number of propeller revolutions per minute (RPM). The efficacy and robustness of ship parameter estimation at different pitches are discussed. Finally, an analysis of one special measurement is provided: propeller pitch and RPM over the duration of the measurement when the ship changes speed. The 50% pitch was found to be a crucial point for this ship, around which the tonal characteristics of its underwater radiated sound attain their peak values while broadband sound and associated spectral coherences are at a minimum. The findings here elucidate the effects of pitch variation on underwater sound radiated by ships with controllable pitch propellers and has applications in ship design and underwater noise mitigation
- …
