ISO/FDIS 21955

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 21955
ISO/TC 43/SC 1
Acoustics — Experimental method
Secretariat: DIN
for transposition of dynamic forces
Voting begins on:
2021­05­19 generated by an active component
from a test bench to a receiving
Voting terminates on:
2021­07­14
structure
Acoustique — Méthode expérimentale de transposition des forces
dynamiques générées par un composant actif d’un banc d’essai vers
une structure réceptrice
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 21955:2021(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. ISO 2021
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ISO/FDIS 21955:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

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

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

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

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

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

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

4 Principle of the method of transposition of the dynamic force ........................................................................... 5

4.1 General matters ...................................................................................................................................................................................... 5

4.2 General formulae ................................................................................................................................................................................... 6

4.3 Geometrical considerations ......................................................................................................................................................... 6

5 Operating mode ..................................................................................................................................................................................................... 7

5.1 General ........................................................................................................................................................................................................... 7

5.2 Synopsis of procedure ...................................................................................................................................................................... 7

5.3 Tasks and preliminary operations ......................................................................................................................................... 7

5.4 Transfer matrices determination ............................................................................................................................................ 9

5.4.1 General...................................................................................................................................................................................... 9

5.4.2 Final receiving structure transfer matrix determination Y .................................................. 9

5.4.3 Test bench transfer matrix determination, Y ................................................................................... 9

5.4.4 Connecting device spring-like matrix properties determination, S ................................ 9

5.4.5 Active Component transfer matrix determination, Y ................................................................ 9

5.5 Measured dynamic forces transmitted to the test bench ................................................................................10

5.6 Predicted dynamic forces transmitted to the final structure .......................................................................10

5.6.1 General...................................................................................................................................................................................10

5.6.2 Strong decoupling ........................................................................................................................................................10

5.6.3 Very similar bench and receiving structure ..........................................................................................11

5.6.4 Case of a rigid receiving structure .................................................................................................................11

5.6.5 Case of a non­rigid receiving structure .....................................................................................................12

6 Requirements for data in test report ...........................................................................................................................................14

6.1 Specification of the integrator to the supplier ..........................................................................................................14

6.2 Data sent by the supplier to the integrator .................................................................................................................14

Annex A (informative) Theoretical developments ..............................................................................................................................16

Annex B (informative) Frequency response functions measurement ............................................................................19

Annex C (informative) Dynamic forces measurement ....................................................................................................................22

Annex D (informative) Data processing .........................................................................................................................................................28

Annex E (informative) Study of a wiper system......................................................................................................................................31

Annex F (informative) Equivalent force torsor and block-sensor method ................................................................47

Bibliography .............................................................................................................................................................................................................................58

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

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

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This document was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.

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

The vibroacoustic behaviour of products has become a major challenge not only in terms of user health

protection through regulations, but also in terms of sound quality for safety, quality perception, and

At the same time, requirements on products development cycles are more and more stringent, reaching

the point where component suppliers and integrators should work independently, without physical

To master the transmission of dynamic forces (also called structure-borne noise), one needs to adapt

the components to the receiving structure, and hence exchange information prior to manufacturing

prototypes. This information will only be valuable for the integrator if it is clearly defined and intrinsic

This document, issued from a French experimental standard, addresses this issue. It is a user guidance

to characterize an active source on a test bench and predict the effects of its integration on a passive

structure. The component is characterized on its own, which makes the document complementary to

the ISO 20270 that describes the measurement of “in­situ” characteristics (blocked forces), where the

The intrinsic characterization of an active source requires measuring two quantities (expressed as

a function of the frequency): the first one characterizing the dynamic aspect, blocked forces, and the

The objective of this document is to help the user predict the component behaviour in a particular

assembly. The theoretical background is laid in Annex A. The user is then guided (see 5.2) all along the

— Static characterization of the component, the test bench and the receiving structure.

— Force measurement: the standard proposes here direct and indirect methods. Indirect methods are

generally easier to implement, but they need a particular focus on the measurement quality and

This whole procedure is based on a general formula expressing the dynamic forces in the assembly

as a function of blocked forces and static characteristics. Depending on these static characteristics,

Annex B and C guide the user to measure both transfer functions and dynamic forces. It should be noted

that, in general, these quantities are expressed in the 3 directions and 3 rotations, but the procedure

The Annex D informs about data processing. The Annex E contains a test example and the Annex F

— to drive the modification of the physical structure or the interface in order to improve the

This document specifies a method to predict the dynamic forces generated by an active component on a

It sets out the requirements applicable to test benches and setup measurement conditions of dynamic

forces: a criterion of validity of transfer functions measurements can be established for example.

The objective is to evaluate noise and vibrations generated by active components mounted on receiving

It can be applied to different systems connected to a building, such as a compressor or a power

generator, or to systems connected to a vehicle body, such as an engine powertrain or an electrical

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

mechanical interface with a specific “spring like” matrix structure which allows connecting the active

Note 2 to entry: Insulators at fixation points are typical “spring like” connecting devices.

Note 3 to entry: A “spring like” connecting device is a structure with no internal degrees of freedom and internal

Note 4 to entry: In the case of a connecting point, active component and receiving structure share the same

Note 5 to entry: In the case of seals at contact surfaces, direct connections or any other connection type, the

connecting device item 2 cannot be used, and a block diagram with items 1 and 3 and 4 shall be used (see

Note 6 to entry: In case of direct connection, the hypothetical surface between the active component and

Note 2 to entry: The receiving structure can be a test bench or the structure for which the dynamic forces will be

Note 3 to entry: The “test bench” can be a specific structure designed to test the active component (3.1), or any

Note 4 to entry: active device, connecting device and receiving structures are deformable structures.

NOTE An active component (left) connected via a connecting device (centre) transmits dynamic forces to a

n degrees of freedom through which structure­borne sound or vibration is transmitted from the active

complex force associated to a structure or an interface with n degrees of freedom, arranged into a n × 1

where f ()f is the complex Fourier transform of the i component of dynamic force at frequency f

Note 1 to entry: Forces f can be considered as generalised forces, that is, including moments.

Note 2 to entry: Generalised forces units are Newtons for dynamic forces and N·m for dynamic moments

Note 3 to entry: In case pseudo-random signals, statistical tools can help into describing the dynamic forces into

Note 4 to entry: In Table 1, the specific dynamic forces f applied at particular points used in this document are

Force generated by the active component at the interface of the connecting device

dynamic force (3.5) applied by an active component (3.1) transmitted to a rigid receiving structure (3.3)

Note 1 to entry: Blocked forces indirect measurement methods are detailed in Annex F and ISO 20270.

complex vibration velocity associated to a structure or an interface with n degrees of freedom, arranged

where v ()f is the complex Fourier transform of the i velocity component at frequency f

Note 2 to entry: Associated complex acceleration a ()f can be defined via derivation of the velocity.

Note 3 to entry: Associated complex displacement x ()f can be defined via integration of the velocity.

Note 4 to entry: In Table 2, the displacement, velocity and acceleration xa,,v generated at particular points

xa,v and dynamic displacement, velocity and acceleration generated by the active component.

xa,v and dynamic displacement, velocity and acceleration on the receiving structure.

frequency dependent ratio of the Fourier transform of the response to the Fourier transform of the

Note 2 to entry: The FRF denomination and associated unit depends on the two vibration quantities of the ratio

Note 3 to entry: In this document, any reference to mobility Y or impedance Z is related to:

— the free mobility, Y , which is defined as a ratio of a dynamic velocity response in degree of freedom i to

an excitation force in degree of freedom j, with all degrees of freedom free, except the one of the excitation

— the blocked impedance Z , which is defined as a ratio of the response force in degree of freedom j to

the dynamic velocity in degree of freedom i, with all degrees of freedom blocked, except the one of the

Table 3 — Denomination of frequency response functions FRF for various vibration quantities

Note 4 to entry: Thus, in terms of matrix writing, corresponding Y and Z matrices are related:

Note 1 to entry: In this document, the terms Y , Y and Y (see Table 4) can be related to free mobility,

dynamic compliance or accelerances, depending of the quantities that are commonly used by the reader, with the

connecting device (case of insulators at fixation points) transfer matrix (3.9) (see Table 5) can be

Table 5 — Different expressions of connecting device transfer matrix versus dynamic stiffness

with K homogeneous to a dynamic stiffness complex matrix of the connecting device.

set of conditions under which the source operates for the operational test, including speed, load and any

other settings or conditions particular to the source which might affect source operation

This subclause explains how to predict the forces generated by an active component (which comes with

its own sources) on a receiving structure from a series of measurements on a test bench and on specific

— there is no opportunity to measure directly any dynamic force of any sort (e.g. heavy and high cost

— there is only the possibility to work on a test bench, because the final receiving structure is still not

— the active source is provided by a component supplier to an integrator, and the integrator defines a

— internal forces matrix of a specific product is needed for noise comfort prediction, or for durability

The first Formula (1) which detail is given in Annex A can be written as follows:

The purpose of Formula (2) is to enable the prediction of a force transmitted to a receiving structure

To build this formula, there are intermediate steps that are detailed in Annex A.

Instead of a link from bench to receiving structure, in certain cases, the need is to go from receiving

Sizes and quantities handled in this document are defined in a specific coordinate system, usually the

During FRF functions measurements (see Annex B), it can be more practical to use a local coordinate

system for certain attachment points. In this case, it will be necessary to re-project in a global reference

In this subclause, an operating mode to apply this document is proposed, as an example.

This procedure is based on the general Formula (2) allowing to transpose the dynamic forces generated

by an active component from a test bench to a receiving structure. Depending on the assumptions on the

different transfer functions, this operating mode allows the use of simplified versions of Formula (2).

The frequency range(s) for which the formulated hypotheses and steps presented below are considered

The various special cases discussed below can be summarized in the form of a general diagram of the

A number of tasks and processes shall be performed previous to the application of this procedure:

a) During the development of the product, the component will determine the active component

transfer matrix at the connecting points. There are many cases for which the active component is

not only connected to its fixation points, but interacts with its environment through cables, rotation

axes, hoses, pipes, friction, which do not allow to measure the transfer matrix in free conditions for

all degrees of freedom. In this case, different alternatives are proposed in the document.

b) During the development of the product, the component chooses the properties of the connecting

device between the component and the receiving structure. It is remarked that this connecting

device matrix properties are of first order influence on the final transmitted forces: the product

shall ensure a perfect decoupling in order to minimize the vibration coupling between the

component and the receiving structure. Some advices are given hereunder in this operating mode.

c) To apply the methodology to predict the forces transmitted to the receiving structure in order to

check compliance with the specifications, a test bench is generally developed, transmitted forces to

the bench are measured. Usually, in the field of noise and vibration, an infinitely rigid bench, such

as a marble, is used, but this methodology is not mandatory. Therefore, the procedure covers the

The operating mode starts with the analysis of the general equation [Formula (2)] and attempts to

cover the different real cases that may be encountered in practice in the fields covered by the document.

The choices in the flow chart not only depend on the possibilities offered by the product, but also on

the relative order of scales of different transfer matrices in Formula (2). Three different examples are

Annex B is dedicated to frequency transfer functions measurement. These measurements are generally

performed with accelerometers and force sensors, leading to accelerance measurements.

In Formula (2), the transfer matrix at the connecting points is required to predict the forces on the final

structure; whenever there is a component integrator specification about the predicted forces, which

means that the component integrator shall provide to the component supplier the transfer matrix values

at the connecting points. These values are generally available at early stages of a project development

In many cases, it is impossible to decouple the active component from the receiving structure to pe