ISO 20233-2:2019

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 2019
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

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
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

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.
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
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
...