Ships and marine technology — Model test method for propeller cavitation noise evaluation in ship design — Part 2: Noise source localization

This document specifies a model test method for propeller cavitation noise evaluation in ship design, focusing mainly on the noise source localization. The procedure comprises the model test set-up, noise measurements, data processing and source localization. The target noise source being propeller cavitation, this document describes the test set-up and conditions to reproduce the cavitation patterns of the ship, which is the same as in ISO 20233‑1. The noise measurements are performed using a hydrophone array for the source localizations. Therefore, the instrumentation of the hydrophone array is also addressed, as well as a suitable array signal processing of the measured data. Finally, a method to visualize and to interpret the results is presented.

Navires et technologie maritime — Méthode d'essai sur modèle pour évaluer le bruit de cavitation des hélices dans la conception des navires — Partie 2: Localisation de la source de bruits

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Status
Published
Publication Date
06-Aug-2019
Current Stage
6060 - International Standard published
Start Date
07-Aug-2019
Completion Date
07-Aug-2019
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INTERNATIONAL ISO
STANDARD 20233-2
First edition
2019-08
Ships and marine technology — Model
test method for propeller cavitation
noise evaluation in ship design —
Part 2:
Noise source localization
Navires et technologie maritime — Méthode d'essai sur modèle
pour évaluer le bruit de cavitation des hélices dans la conception des
navires —
Partie 2: Localisation de la source de bruits
Reference number
ISO 20233-2:2019(E)
ISO 2019
---------------------- Page: 1 ----------------------
ISO 20233-2:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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Published in Switzerland
ii © ISO 2019 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 20233-2:2019(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Model test setup and conditions .......................................................................................................................................................... 2

5 Noise measurement instrumentation ............................................................................................................................................ 2

5.1 Hydrophone array ................................................................................................................................................................................ 2

5.1.1 General...................................................................................................................................................................................... 2

5.1.2 Hydrophone ......................................................................................................................................................................... 2

5.1.3 Array types ............................................................................................................................................................................ 3

5.1.4 Array setup ........................................................................................................................................................................... 3

5.1.5 Array calibration .............................................................................................................................................................. 3

5.2 Data acquisition ..................................................................................................................................................................................... 3

5.2.1 General...................................................................................................................................................................................... 3

5.2.2 Sampling frequency ....................................................................................................................................................... 4

5.2.3 Resolution .............................................................................................................................................................................. 4

5.2.4 Syncronization for multiple channel sampling ...................................................................................... 4

5.2.5 Filtering ................................................................................................................................................................................... 4

5.2.6 Acquisition time ............................................................................................................................................................... 4

6 Noise measurement procedure ............................................................................................................................................................. 4

6.1 Propeller cavitation noise measurement ......................................................................................................................... 4

6.2 Background noise measurement ............................................................................................................................................. 4

6.3 Reference field measurement .................................................................................................................................................... 4

7 Post processing ...................................................................................................................................................................................................... 5

7.1 Array signal processing ................................................................................................................................................................... 5

7.1.1 Bartlett processor ........................................................................................................................................................... 5

7.1.2 MV processor ...................................................................................................................................................................... 6

7.1.3 Other option for the processors ......................................................................................................................... 6

7.2 Graphical display of the output ................................................................................................................................................. 6

7.3 Spatial resolution .................................................................................................................................................................................. 6

Annex A (informative) Hydrophone array design method ............................................................................................................ 7

Annex B (informative) Signal model for array signal processing ........................................................................................... 8

Bibliography .............................................................................................................................................................................................................................10

© ISO 2019 – All rights reserved iii
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ISO 20233-2:2019(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso

.org/iso/foreword .html.

This document was prepared by Technical Committee ISO/TC 8, Ships and marine technology,

Subcommittee SC 8, Ship design.
A list of all parts in the ISO 20233 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2019 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 20233-2:2019(E)
Introduction

Propeller cavitation is the major noise source in commercial ships. The propeller cavitation noise can be

assessed by experimental and/or numerical methods in propeller design stage. The numerical methods,

such as computational fluid dynamics (CFD) or empirical formulae, might be a good alternative to

propeller cavitation noise evaluations. However, the model tests are still used widely for research on

propeller cavitation noise.

The objective of the model test is to reduce the propeller noise in ship design by evaluating propeller

cavitation noise characteristics at the design phase. Localizing the noise sources in the design stage,

as well as predicting its noise levels, might be very helpful. ISO 20233-1 addresses the prediction of

propeller noise levels. In order to specify the location of noise source, visual observation of cavitation is

the most practical way in view of spatial resolution and efficiency, as the main source of hydrodynamic

noise in merchant ship is cavitation. In addition to this observation, noise source localization technique

[1]

using hydrophone array is under development for verifying the observed noise source location . Thus

this document devotes to the source localization method as a new part of a model test method for

propeller cavitation noise evaluation in ship design.

The estimation methods of the propeller noise via model tests were widely studied for a long time and

can be used in the shipbuilding industry nowadays. However, the noise source localization is easily

accomplished by cavitation observation. This document also serves to provide an example of protocols

for acoustic localization which is a relatively new research area.
© ISO 2019 – All rights reserved v
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INTERNATIONAL STANDARD ISO 20233-2:2019(E)
Ships and marine technology — Model test method for
propeller cavitation noise evaluation in ship design —
Part 2:
Noise source localization
1 Scope

This document specifies a model test method for propeller cavitation noise evaluation in ship design,

focusing mainly on the noise source localization.

The procedure comprises the model test set-up, noise measurements, data processing and source

localization. The target noise source being propeller cavitation, this document describes the test set-up

and conditions to reproduce the cavitation patterns of the ship, which is the same as in ISO 20233-1. The

noise measurements are performed using a hydrophone array for the source localizations. Therefore,

the instrumentation of the hydrophone array is also addressed, as well as a suitable array signal

processing of the measured data. Finally, a method to visualize and to interpret the results is presented.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 20233-1:2018, Ships and marine technology — Model test method for propeller cavitation noise

evaluation in ship design — Part 1: Source level estimation
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
acoustic centre
position where all the noise sources are co-located as a single point source

Note 1 to entry: The acoustic centre is the centre of the expected cavitation extent.

3.2
background noise
noise from all sources other than the source under test
© ISO 2019 – All rights reserved 1
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ISO 20233-2:2019(E)
3.3
hydrophone
underwater electro-acoustic transducer
underwater microphone

device to measure acoustic pressure, including any signal conditioning electronics such as pre- or

charge amplifiers either within or exterior to it

Note 1 to entry: Piezoelectric hydrophones are usually used for the measurement of underwater sound pressure

in a test facility.
3.4
noise source
noise-generating mechanism or object

Note 1 to entry: For the purposes of this document, the main noise source is the propeller cavitation.

3.5
propeller plane

imaginary plane orthogonal to the shaft centre line and including the intersection (point) of the shaft

centre line and generator line
3.6
reference field

sound pressure field that is measured using a virtual source located at a given position, i.e. the

acoustic centre
Note 1 to entry: The reference field is used to calibrate the hydrophone array.
3.7
virtual source
artificial sound source of which the transmitting power is known a priori
4 Model test setup and conditions

In order to evaluate the propeller cavitation noise performance via model tests, it is important to

reproduce accurately the noise sources, i.e. the cavitation patterns, based on the similarity laws

between the model and the ship. Accuracy in reproducing the noise sources is required for the noise

source localization as well as for the source level estimation. The test setup and conditions described in

ISO 20233-1:2018, Clause 4, shall be applied t
...

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