Analysis of the outdoor noise propagation from a multipurpose ship berthed near an urban residential area

8/12/2019 Analysis of the outdoor noise propagation from a multipurpose ship berthed near an urban residential area

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Analysis of the outdoor noise propagation from a multipurpose ship

berthed near an urban residential area

Aglaia Badinoa) Departement of of Mecanical Engineering, University of Genoa Via all’Opera Pia 15/A, Genoa 16145, Italy

Corrado Schenoneb)

Departement of of Mecanical Engineering, University of Genoa Via all’Opera Pia 15/A, Genoa 16145, Italy

In noise mapping of urban areas, road traffic, rail traffic, airports and industrial plants are

the main examined sources of annoyance and sleep disturbance. Another category of noise

sources should be considered when noise maps of port cities are worked out: the ships. The

population can be markedly annoyed by the exposition of noise due to the ships, when the

wharfs are placed near urban areas. In order to analyze the outdoor noise propagation

from this kind of sources, the airborne noise emitted by a multipurpose ship has been

modelled. Since commercial simulators do not usually include modules for ship noise and

no specific tool is disposable in software libraries, ship geometry was recreated by the tools

provided for other categories of sources, while ship were characterized as a noise sources

by means of specific measurements. The model validation was then developed by the

comparison between calculated and measured SPL, making different tests because of the

complexity of the ship as a noise source. Then the sound field produced by the ship in an

urban context was simulated, considering a residential area of a port city. Calculated noise

levels indicate a remarkable exposure of the resident population to the port noise.

1 INTRODUCTION

In the last years several European projects, like EcoPorts, NoMEPorts, SIMPYC and

HADA, have tried to define guidelines in order to characterize the noise due to ports on the basis

of the European Directive 2002/49/EC1. The partners involved in those projects have dealt, in

particular, with the problem how to characterize ships as noise sources.

The ship is a complex source to be described and therefore to be analyzed. First of all the

ship can have the characteristics of a stationary source or of a mobile source on the basis of

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b) email: [email protected]



operating conditions. When the ship is berthed at wharf, it can be considered as a stationary

source, whereas, when the ship is under way, it is to all effects a mobile source.Other two aspects make complicate the characterization of the ship as a noise source. One

aspect concerns the dimensions: there are ships of several size, which differ a lot each other. Thisimplies that the engines are less or more powerful and the noise sources are placed at very

different heights in respect of the ground surface. The second aspect regards the several sources

that are within a ship: there are noise sources common to all ship categories and noise sources

specific for each type of vessel. The specific sources change on the basis of intended vessel use2.

These elements differentiate deeply ships from other sources of environmental noise.

At present, the most of the studies aimed to characterize ship noise only consider the

operating condition of berthed ship at wharf. In NoMEPorts project each berthed ship was

considered as point source3, placed in correspondence of the funnel, in accordance with Imagine

project4 recommendations. In another European project, the BESST project5, the noise

propagation from a specific type of vessel, i.e. a cruise ship, has been modelled. In this case

several point sources were placed around the funnel, which correspond to openings for both theengine rooms and auxiliary rooms ventilation systems and for the combustion air supply of the

main engines and auxiliaries. The air conditioning openings, usually located along the ship’ssides, were considered as single point sources6.

Currently, SILENV project is ongoing, to the aim to assess methodologies and criteria in

analyzing outdoor noise from ships. One of the tasks of this EU project is to model the outdoor

noise propagation in air for various kinds of ship, by using different commercial software. Theassessment of the noise generated by different categories of ships, will contribute to define

guidelines for noise control in harbors.

During this project a multipurpose ship (128 m long, 16 m large and 25 m height) has been

modelled We calculated the airborne sound field outside the ship by means of a ray-tracing

simulator: the commercial software SoundPlan Version 6.5. The modelling work out was dividedin four steps: acquisition and processing of the input data, drawing of the ship geometry,

characterization and modelling of the noise sources and model validation.

The noise propagation model was implemented taking into account the operating conditionof berthed ship at wharf. Therefore the noise sources present on the ship were considered as

stationary sources. The ISO 9613-2:19967 for industrial sources was used as standard for the

propagation model because the noise of the ship is generated by openings of intakes and exhausts

of the engine or the air-conditioning and cooling systems.After all, the multipurpose ship model was applied to a large urban area close to a port in

order to simulate the effects of the ship noise on the residential area, taking into account the

morphology of the ground and the screening effect of the buildings.

2 ACQUISITION AND PROCESSING OF THE INPUT DATA

Concerning the ship characterization as a noise source, two different kinds of measurements

have been made: local and on sound field: Local measurements are defined as the measurements

to be carried out near specific sources (vents, cranes, heat exchangers, etc..) to the aim of their

characterization. On sound field measurements have been performed both close to the vessel and

at a certain distance from that. The target is to characterize the ship as a total source, in

consideration of its global emissions. Measurements near the main sources were taken at 1 m

from the openings, as ISO 2922:20008 standard suggests. During on field measurements,

microphones were placed in correspondence of the nodal points of three different grids: one

horizontal grid along the entire length of the ship at a constant height of 1.2 m and 3 different



distances from the hull (Figure 1); two vertical mesh grids perpendicular to the vessel near to the

main sources at 3 different heights and 3 different distances (Figure 2).In the nodes of all grids, the background noise was measured: only values of environmental

noise higher of 10 dB, if compared to the background noise, were taken into account. If thebackground level was higher, between 6 dB and 10 dB, a correction factor equal to -1dB was

added to the value.Weather conditions acquired during the measurements were used for the noise propagation

modelling.

Measurements aimed to characterize the multipurpose ship, have been provided by the

Technical University of Varna, that is partner of DIME-UNIGE in SILENV project, as well as

drawings of the multipurpose ship and climatic data.

3. DRAWING OF THE SHIP GEOMETRY

In general commercial software contains modules for different typologies of noise source asroads, railways, aircrafts, industries and, in general, for point, line and area sources. However,

currently there is no specific module for ships both for the shape and for the sources. The same

occurs for the software we used to analyze present issue. So the different ship parts must bedrawn using general purpose tools, usually utilized to draw buildings, walls or floating screens.

These general tools do not allow to recreate complex shapes. Therefore, it was necessary the

simplify the ship shape by considering only the hull, the decks, the funnel and some other main

parts which form reflective surfaces or diffracting edges along noise paths. Consequently thedrawing procedure was separated in two phases.

The first phase consisted in the basic drawing: the shape was greatly simplified, deleting

elements not significant to the sound propagation. In the second phase the ship, simplified in the

first step, was imported in the simulation software and the different elements were modelled inform of buildings, walls or floating screens, so creating a configuration by which the simulator

was able to model noise propagation. Such a configuration is shown in Figure 3, by means of a3D view.

Concerning the drawings, it was very important to introduce a specific layer for each ship

part. Thanks to this share-out, the several parts of the multipurpose ship could be easilyidentified. So, knowing the ship structure, the modelling of the ship shape for the sound

propagation model was made, reducing the error due to an incorrect simplification.

4 CHARACTERIZATION OF THE SOURCES

During the measurements, 7 main sources were identified in the superstructure and in theamidship: the funnel, 2 ventilation fans of the engine room, 4 ventilation fans of the cargo holds.

Thanks to the measurements taken at 1 m from the sources, in front of the openings and behindthem, it was possible to assess the sound power levels of the sources starting from the knowledgeof the sound pressure levels. The values of the sound pressure levels were provided in 1/3 octave

bands in the range 31.5 Hz - 8 kHz.

The evaluation of the sound power levels was implemented according with ISO

2922:200010

and ISO 3744:200911

standards. Three different attempts were made to describe the

characteristics of each source. Simulations were then carried out, with the aim to assess which

type of representation (point, line, area) was more suitable in describing the real behavior of ship

noise sources.



In the first attempt all sources were considered like point sources. In order to improve the

accuracy of the model, in the second attempt each fan was simulated as an area source, using thetool “industrial building” of the software and placing the area source on the surface (front side)

where openings were set. With this tool (industrial building) the air terminals corresponding tothe different fans can be defined as noise sources, choosing which type (point, line and area) is

more suitable. In order to better characterize their actual behavior, in the third attempt every

ventilation fan, i.e. its external terminal, was finally described by means of a couple of sources,

which is a dipole. Each source was then modeled by a front pole and a rear pole, both operating

like area sources of specific characteristics. In all models the funnel was considered like a point

source3 and it was placed on top the funnel structure. The sound propagation was considered

spherical but an ID equal to 1 dB was applied to take into account obstructions not drawn in the

model.

In order to assess which approach to the sources modelling was more effective, for eachattempt noise levels measured on field close to the sources were compared with those ones

calculated by the simulator in the same positions. In the first case deviations were quite small,whereas for the second method differences resulted to be greater. In the third modality the

smallest deviations were obtained. Therefore noise sources were modelled in accordance with

the third method. In Table 1 global sound power level (linear and A weighted) are reported foreach dipole source (front/rear); in the model 1/3 octave band sound power levels were

introduced, here not shown for the sake of brevity.

The complete validation of the model is reported in the following section.

5 MODEL VALIDATION

The validation of the ship model was made by comparing the measured noise levels with

the calculated noise levels. For this purpose 10 measurements near the sources, 37 measurementsalong the ship hull and 18 measures at different heights were utilized.

On the basis of the measurements on field, two different comparisons were done to validate

the model of the multipurpose ship: the comparison of the noise propagation taking into account

the grid along the ship length (Figure 1); the comparison of the noise propagation at differentheights and distances, taking into account the two mesh grids placed near the ventilation fans of

the engine room and of the cargo holds (Figure 2)

Concerning the first comparison, the differences between calculated and measured valuesresulted to be greater than 1.5 dB in the majority of cases and only for 6 positions the deviationwas equal or less than 1.5 dB. Differences between calculated and measured values were in the

range 1.5 - 3 dB for 15 positions; in the range 3 - 6 dB for 16 positions. No difference presented

value greater than 6 dB.The panels in front of the fans openings, the metal floor of the boat deck and the

wheelhouse, placed above the fans, create a high number of reflections. The presence of theseelements close to the sources might explain the irregular sound pressure levels distribution in the

far field: focalizations and rarefactions can be observed in different areas of the sound field, with

a not plane correspondence of far levels with sources positions. As there are more reflective

surfaces in the superstructure, the noise propagation paths are fragmented.

About the second comparison, the sound pressure levels calculated by the simulator werecompared with the sound pressure levels measured on field in the nodal points of the two mesh

grids. The differences between the two levels are shown in Table 2 and Table 3, respectively for

the mesh grid near the fans of the engine room and for the mesh grid near the fans of the cargo

holds. In the cross grid near the engine room the highest difference was observed in



correspondence of the receiver I.1 and it had minus sign. In the first row all deviations had minus

sign, even if the differences referring to receivers I.2 and I.3 were very limited and lesser thanthe difference for receiver I.1. The mean deviation between measured and calculated levels

regarding the 9 nodal points of this grid is equal to 0.5 dB, whereas the standard deviation isequal to 2.8 dB.

The major deviations in the cross grid near cargo holds were observed in the third row, and

particularly in positions III.2 and III.3. Except for these positions, differences are generally quite

small. The mean deviation relative to the 9 differences between measured and calculated levels

for this grid is equal to 1.1 dB, whereas the standard deviation is equal to 2.7 dB.

From the point of view of the model validation, this comparison is considered to give the

most meaningful contribution, since it allows verifying the sound propagation at different

heights, taking into account that the main noise sources are located in the superstructure.In general, the model seems to give a precise description of outdoor noise propagation: the

calibration of noise sources permitted to properly describe their emissions; deviations of

simulated levels from of measured ones are acceptably low and indicate that implemented modelaccurately describes acoustical impact of the multipurpose ship.

6 SHIP NOISE PROPAGATION TOWARD A CLOSE URBAN AREA

After the model validation, noise propagation toward an urban area was simulated in order

to demonstrate the efficiency of the modelling and assess the effects of this kind of source on theresident population. An urban area located in the territory of the Municipality of Genoa (Italy)

was chosen for this purpose, since several complaints were coming from residents in respect of

noise produced by the ships berthed in the close port area. Resident people greatly complain

about ships noise, especially during nighttime, when the ship noise is not masked by the other

noise sources, as railway and road traffic. The noise field is markedly influenced by the groundmorphology: annoyed people live in the hilly area of the neighborhood, which is in view of the

harbor and directly exposed to the emissions. Nevertheless the long distance between port wharfs

and hilly residential buildings (as far as 1 km), the elevated position of the sources and theabsence of obstructions along sound paths cause high noise levels on buildings facades and a

consequent nuisance.

6.1 Description of the Urban Area

The wharf modelled in our simulations is a large platform, 1700 m long and 550 m large,

placed parallel to the coast. The wharf is utilized as storage area for containers. Different cranes

are placed along the quay for the load/unload from the container ships. In front of the wharf anarea of the port is intended to recreational crafts, fishing vessels and sheds of fishermen.

Immediately beside the port area, the residential area begins, which is separated from the harborby a main road. First, starting from the sea, we have a plane area; then, at a distance varying

from 0.2 to 0.6 km, the ground rises to a hilly residential area. Behind the road the urban plane

area starts and, beside it, the hill area (Figure 4). The east side of the urban area is more leaning

than the west one and it is occupied by residential buildings, whereas the west side presents a

miscellany of land uses: residential buildings are mixed with auxiliary buildings (public

buildings, commercial stores, churches, industrial sheds). In Figure 5 a 3D view of the area

considered in this study is reported, in the same way it has been modelled in the simulator. Theresidential buildings are colored in beige with red roof, whereas the auxiliary buildings are in

gray.



6.2 Analysis of the Results

The nighttime was chosen for the simulations, because it is considered the critical period ofthe day in respect of the annoyance due to ship noise. According to the Italian Legislation and in

particular to the Legislative Decree n. 194/200512, the nighttime lies between 10 p.m. and 6 a.m.

The above mentioned Decree was issued when Italy adopted the European Directive

2002/49/EC, concerning the assessment and management of environmental noise. Noise sources

were considered always working during this period.

During simulations following settings were input: the angle increment was set equal to 1°,

the number of simulated reflections was set equal to 3 and the max search radius was set equal to

1000 m.In order to represent noise field from the ship to the urban area, two horizontal maps are

reported in Figure 6. The map in Figure 6.a refers to a height of 4 m from the ground level,

whereas Figure 6.b describes level curves 9 m above the ground. A square grid with meshdimension 5 m was adopted for both horizontal maps. Chromatic scale varies with range steps of

5 dB(A). The comparison between maps indicates higher noise levels at 9 m from the ground,sincemain sources are placed in the superstructure of the ship. Moreover, in the lower area the

buildings closest to the harbor screen the buildings placed behind, whereas facades in the hills

are directly in view of ship noise sources (funnel, air terminals, fans, etc.). These elements can

explain why the hill zone is more affected by the ship noise than the plane zone, even if thedistance from the ship is greater. In particular, the absence of obstructions along sound paths

permits noise to reach far receivers and the lower plane area reflects sound, thus increasing

sound pressure levels in correspondence of buildings on the hill.In both horizontal maps level curves are fragmented, especially in the starboard side of the

ship (south direction). This fragmentation can be explained by the presence of several reflectivesurfaces, which are more numerous on starboard side because of the asymmetrical geometry of

ship superstructures. These surfaces produce a high number of reflective waves and justify the

above mentioned irregularities.In order to better analyze noise propagation, vertical maps were drawn (Figure 7). This

vertical map cuts the ship next to the ventilation fans of the cargo holds and crosses the east side

of the hill zone. Figure 7 clearly indicates noise propagation toward hill zone is not obstructed by

any screens. Sound rays directly hit the facades of the buildings facing the port, thus determiningannoyance, perceived by the resident population.

Other horizontal and vertical maps similar to those shown in the present paper have been

drawn, which confirm the results above discussed and have not been reported for the sake of

brevity. Numerical simulations allow obtaining also for ship noise a meaningful modelling ofnoise propagation, as well as in the well known cases of roads, railways and airports. Currentcommercial software seems adequate to the aim to model port noise, just requesting a carefuldescription of sources.

7 CONCLUSIONS

The use of current commercial software devoted to environmental noise modelling to

analyze ship noise propagation has been tested, referring to the case of a multipurpose ship.

Firstly, the multipurpose was modelled as a complex noise source, i.e a combination of differentpunctual/linear/area sources. Noise propagation was then simulated and numerical results were

validated by the comparison with measured sound pressure levels in several positions around the



ship. Finally, numerical model was applied to a real environmental scenario: a neighborhood

close to the port of Genoa, in Italy, was studied in terms of exposure to ship noise, being carefulto taking into account morphology of the ground and housing screen.

Some relevant issues result from the research:- Model validation suggests ship noise modelling can be implemented by using current

commercial software, in spite of the need to realize a deep simplification of the ship

geometry. Nevertheless a better accuracy could be achieved if specific tools were added, as

for other kind of sources (road vehicles, trains, aircrafts), allowing to deal with the

complexity of the ship shape and of onboard noise sources.

- Regarding the ship as a noise source, great attention must be paid to a proper definition ofinput data, both in terms of drawing of ship shape and of characterization of sources. The

poor quality and/or the lack of the input data can definitely compromise the final output. In

particular, following input data seem to be crucial to get an accurate modelling: SPL valuesin accordance with ISO 3744:2009, directivity characteristics of the sources, SPL values

along the noise propagation paths at different heights and distances from the hull,background noise levels, geometrical characteristics of the ship and of the surrounding area

and weather information as temperature, humidity, speed and directivity of the wind. Some

aspects are obviously common with other fields, some other are specific for ships, as theneed to make SPL measurements at a certain distance from the ground or the complexity of

the source geometry. All these input elements must be carefully considered.- The ship is a kind of source characterized by a very complex geometry, also for rather

small vessels. Many reflecting surfaces of different dimensions are onboard, whichgenerate a lot of reflective waves. In the same time, a simplification of the ship shape is

necessary in order to create a quite simple ship model in the simulator. The way we took is

to select surfaces, introducing in the model only those ones closest to the sources and with

biggest dimensions. We operated by an heuristic approach; a standardized procedure canhelp a correct modelling of real geometry and avoid too drastic simplification. This subject

should be took into account in implementing specific tools for ship noise modelling.

- When operating inside a harbor, the sea conditions do not affect noise propagation, so that

no relevant difference were observed in respect of other kinds of outdoor noisepropagation, except for the elevated position of the sources. This position reduces ground

effect and building screen and increases ship noise exposure of population living in tall

buildings or in hills close to the port.In short, current simulation software seems to be able to analyze ship noise propagation,

even if great attention must be paid in respect of several aspects: sources characterization,

sources modelling, ship geometry simplification, measurements aimed to model validation. This

tends to limit ship noise modelling to expert and particularly skilled technicians. Implementationof specific tools could make easier to face this issue and help generic technicians involved in

noise control in approaching to a such complex matter.

6 ACKNOWLEDGMENT

This work was developed in the frame of the collaborative project SILENV—Ships oriented

Innovative soLutions to rEduce Noise & Vibrations, funded by the E.U. within the Call FP7-

SST-2008-RTD-1 Grant Agreement SCP8-GA-2009-234182



7 REFERENCES

1. EU 2002, Directive 2002/49/EC of The European Parliament and of The Council relating to

assessment and management of environmental noise, 25 June 2002

2. A. Badino, D. Borelli, T. Gaggero, E. Rizzuto and C. Schenone, “Analysis of airborne noise

emitted from ships”, Sustainable Maritime Transportation and Exploitation of Sea

Resources, Leiden: CRC Press/Balkema, (2011)

3. NoMEPorts European Project. Good Practice Guide on Port Area Noise Mapping and

Management, Technical Annex, (2008)

4. Imagine European Project. Guidelines for producing strategic noise maps on industrial

sources, Deliverable [14] of the IMAGINE project , (2007)

5. http://www.besst.it/index.php/project.html

6. L. Moro, Setting of on board noise sources in numerical simulation of airborne outdoor ship

noise. Proceeding of 9th

Youth Symposium on Experimental Solid Mechanics, Trieste, Italy,

July 7-10, 2010

7. ISO 9613-2:2006, Acoustics -- Attenuation of sound during propagation outdoors -- Part 2:

General method of calculation

8. ISO 2922:2000, Measurement of airborne sound emitted by vessels on inland waterways and

harbor

9. SILENV European project, Subtask 4.1.2 : Modelling of ship noise radiation and

propagation into air and water, Deliverable D2, (2012)

10. ISO 3744:2009, Acoustics – Determination of sound power levels of noise sources using

sound pressure – Engineering method in an essentially free field over a reflecting plan

11. M. Biot, L. Moro, Methods and criteria to manage airborne outdoor ship noise, Advances in

Marine Structures, Leiden: CRC Press/Balkema, (2011)

12. D.lgs n. 194, Attuazione della direttiva 2002/49/CE relativa alla determinazione e allagestione del rumore ambientale, 19 August 2005



Table 1 – Sound power levels of the ship sources

Kind of source PositionLw

[dB] [dB(A)]

Funnel - 92.4 72.6

Engine room ventilation fan (SB) front 108.7 99.5

Engine room ventilation fan (SB) rear 97.9 88.7

Engine room ventilation fan (PS) front 108.7 99.5

Engine room ventilation fan (SB) rear 97.9 88.7

Cargo Hold Ventilation Fan 1 front 102.5 99.6

Cargo Hold Ventilation Fan 1 rear 97.3 92.7


Cargo Hold Ventilation Fan 2 rear 96.3 91.7Cargo Hold Ventilation Fan 3 front 103.3 100.6




Table 2 – Model validation –cross grid near the fans of the engine room

Position I.1 I.2 I.3 II.1 II.2 II.3 III.1 III.2 III.3

Height (m) 1.2 1.2 1.2 3 3 3 6 6 6

Distance from the hull [m] 1.0 11.0 19.0 1.0 11.0 19.0 1.0 11.0 19.0

Calculated noise level [dB(A)] 63 70.2 64.5 69.7 70.7 64.8 74.9 71.4 65.4

Measured noise level [dB(A)] 68.9 67.2 62.8 69.8 67.9 65.2 75.6 68.3 64.6

Difference [dB(A)] -5.9 3 1.7 -0.1 2.8 -0.4 -0.7 3.1 0.8

Table 3 – Model validation –cross grid near the fans of the cargo holds

Position I.1 I.2 I.3 II.1 II.2 II.3 III.1 III.2 III.3

Height (m) 1.2 1.2 1.2 3.0 3.0 3.0 6.0 6.0 6.0Distance from the hull [m] 1.0 11.0 19.0 1.0 11.0 19.0 1.0 11.0 19.0

Calculated noise level [dB(A)] 62.4 64.2 63.9 64.9 66.3 65.7 72.5 71.2 69.3

Measured noise level [dB(A)] 62.2 65.6 65.9 65.1 66.2 64.5 71.8 65.5 64.0

Difference [dB(A)] 0.2 -1.4 -2.0 -0.2 0.1 1.2 0.7 5.7 5.3



Fig. 1 – Measurement grid placed along the ship9

Fig. 2 – Measurement grids placed near the main sources9

Fig. 3 – 3D view of the multipurpose ship as modeled by SoundPlan 6.5 Software



Fig. 4 – Satellite view of the urban area examined in present study

Fig. 5 – 3D view in SoundPlan 6.5 of the urban area examined in present study



Fig. 6 – Horizontal maps of the ship noise propagation at two different heights: a) 4 m from theground; b) 9 m from the ground

Fig. 7 – Vertical map of the noise field.

a) b)

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Analysis of the outdoor noise propagation from a multipurpose ship berthed near an urban residential area