1、 ISO 2017 Space systems Acoustic testing Systmes spatiaux Essais acoustiques INTERNATIONAL STANDARD ISO 19924 First edition 2017-09 Reference number ISO 19924:2017(E) ISO 19924:2017(E)ii ISO 2017 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO 2017, Published in Switzerland All rights reserved.
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3、the address below or ISOs member body in the country of the requester. ISO copyright office Ch. de Blandonnet 8 CP 401 CH-1214 Vernier, Geneva, Switzerland Tel. +41 22 749 01 11 Fax +41 22 749 09 47 copyrightiso.org www.iso.org ISO 19924:2017(E)Foreword iv 1 Scope . 1 2 Normative references 1 3 T er
4、ms and definitions . 1 4 Abbreviated terms 3 5 Test purpose 4 6 General 4 7 Test system . 4 7.1 Test facility 4 7.2 Equipment requirement . 5 7.2.1 Chamber system . 5 7.2.2 Sound source system 6 7.2.3 Control system . 6 7.2.4 Measurement system . 6 8 Test technical requirements . 6 8.1 Laboratory en
5、vironment 6 8.2 Test condition and tolerance . 7 8.2.1 Test condition . 7 8.2.2 Fill effect 7 8.2.3 Test level tolerances 8 8.3 Specimen configuration requirements . 8 8.4 Specimen installation requirements 8 8.5 Control requirements 8 8.6 Measurement requirements .10 8.6.1 Structure response measur
6、ement .10 8.6.2 Sound measurement 10 8.7 Safety 10 9 Test procedure .10 9.1 Test flow .10 9.2 Test procedure 11 9.2.1 Before the test .11 9.2.2 Test implementation . .12 9.2.3 After the test .12 10 Test interruption and handling 12 10.1 Test interruption 12 10.2 Interruption handling 13 11 Test data
7、 and result evaluation 13 11.1 Test data .13 11.2 Result evaluation 13 12 Test documents .13 Annex A (informative) Methods for calculating the pa y load fill effect .14 Bibliography .17 ISO 2017 All rights reserved iii Contents Page ISO 19924:2017(E) Foreword ISO (the International Organization for
8、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 r
9、ight 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 procedu
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14、oreword.html. This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee SC 14, Space systems and operations.iv ISO 2017 All rights reserved INTERNATIONAL ST ANDARD ISO 19924:2017(E) Space systems Acoustic testing 1 Scope This document provides guidance fo
15、r test providers and interested parties to implement acoustic tests of aerospace systems, subsystems, modules and units for applicable spacecraft programs. This document specifies a framework to meet test and process requirements and acts as a supplement to ISO 15864. The acoustic test system, the t
16、echnical requirements and the procedures for acoustic tests in reverberant chambers are described. Furthermore, the criteria for the manual test interruption and evaluation are also described. The technical requirements in this document can be tailored to fulfil the objectives of tests. 2 Normative
17、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 amendme
18、nts) applies. ISO 15864:2004, Space systems General test methods for space craft, subsystems and units ISO 14620, Space systems Safety requirements 3 T erms a nd definiti ons For the purposes of this document, the following terms and definitions apply. ISO and IEC maintain terminological databases f
19、or use in standardization at the following addresses: IEC Electropedia: available at http:/ /www.electropedia.org/ ISO Online browsing platform: available at http:/ /www.iso.org/obp 3.1 acoustic reverberation chamber acoustic chamber built in hard and highly reflective surface walls such that the so
20、und field therein becomes diffused 3.2 d i f f u s e s o u n d f i e l d sound field that has uniform energy density in a given region so that all directions of energy flux at all parts of the region are equally probable 3.3 sound pressure p root mean square value of instantaneous sound pressure ove
21、r a given time interval, unless specified otherwise Note 1 to entry: Normally given in Pa. ISO 2017 All rights reserved 1 ISO 19924:2017(E) 3.4 sound pressure level SPL L p expressed by wherep is root mean square value of instantaneous sound pressure (3.3) over a given time interval (Pa);p 0 is refe
22、rence pressure at threshold (Pa), p o= 20 Pa. 3.5 overall sound pressure level OASPL value computed from one-third-octave (3.13) or octave band sound pressure levels, L i whereL g is the overall sound pressure level in dB;L i is the sound pressure level (3.5) in one-third-octave or octave band;m is
23、the number of one-third-octave or octave bands. 3.6 bandwidth difference between the nominal upper and lower cut-off frequencies 3.7 centre frequency geometric mean of the nominal cut-off frequencies of a pass-band Note 1 to entry: The definition of octave (3.12) and third-octave bands preferred cen
24、tre frequency values refers to ISO 266. 3.8 cut-off frequency of acoustic horn frequency below which an acoustic horn becomes increasingly ineffective 3.9 measurement point specific points spatially distributed in the sound field at which sound pressure levels (3.4) are measured during test 3.10 con
25、trol point measurement points (3.9), spatially distributed inside the reverberant chamber, whose signals are used for the sound pressure level test control 3.11 multipoint control control achieved by using the average of the signals at the control points (3.10)2 ISO 2017 All rights reserved ISO 1992
26、4:2017(E) 3.12 octave 1/1 Oct interval between two centre frequencies (3.7) which have a ratio equal to 2 3.13 one-third-octave 1/3 Oct interval between centre frequencies (3.7) which have a ratio equal to 2 1/3 3.14 test level tolerances allowance of superior limit and inferior limit of a test leve
27、l 3.15 closed-loop control feedback control system where the output acts upon the process in such a way as to reduce the difference between the measured value and the desired set-point value to zero SOURCE: ISO 16484-2:2004, 3.41 3.16 open-loop control control action not using any automatic means of
28、 deviations from the target value 3.17 statistical DOF number of independent variables in an estimate of some quantity 3.18 root mean square RMSobtained by squaring the amplitude at each instant, obtaining the average of the squared values over the interval of interest and then taking the square roo
29、t of this average 3.19 power spectral density PSD measure of the distribution of the energy (squared amplitude) of the signal as a function of frequency 3.20 b r o a d b a n d r e v e r b e r a n t f i e l d includes signals over a relative large frequency range of 22,5 Hz 10 000 Hz (1/3 oct) 4 Abbr
30、eviated terms All abbreviated terms in Table 1 are applied to this document. Table 1 Abbreviated terms Oct Octave DOF Degree of freedom PSD Power spectral density RMS Root mean square SPL Sound pressure level OASPL Overall sound pressure level ISO 2017 All rights reserved 3 ISO 19924:2017(E) 5 Test
31、purpose The purpose of acoustic test is to demonstrate the ability of the test specimen to endure acoustic levels imposed by the launch vehicle and to validate unit random vibration test levels. Depending on the product development stage, it can include qualification of the design with margin, detec
32、tion of workmanship defects, flaw of material and manufacturing failures. There are two types of acoustic tests. The first test addresses the specimen functional compatibility with acoustic environment. The second test addresses mechanical resistance of the structures. In this case, the use of accel
33、erometers shall be required to measure responses to low levels before and after high load testing. 6 General a) If there is no condition for a reverberant field acoustic test (RFAT), a direct field acoustic test (DFAT) may be applied. b) For compact specimen, random vibration may replace the acousti
34、c test if analysis and/or heritage data show that the payload responses are clearly dominated by random vibration compared to the acoustic field. It is important to make a decision knowing that vibration tests do not reach high frequency contents; whether the structure is sensitive to acoustic loads
35、 and the region that the equipment is embedded shall also be considered. The decision shall be made by customers. c) Generally, all structures and components requiring acoustic testing should be subjected to a broadband reverberant field. The corresponding acoustic random noise source shall have an
36、approximate normal amplitude distribution. 7 Test system 7.1 Test facility In general, an acoustic reverberation test facility is composed of a chamber system, gas supply system, sound source system, control system and measurement system. An example of acoustic reverberant test facility is shown in
37、Figure 1.4 ISO 2017 All rights reserved ISO 19924:2017(E) Figure 1 General composition of the acoustic reverberation test facility 7.2 Equipment requirement 7.2.1 Chamber system Chamber system general requirements are as follows. a) Generally, the shape of the chamber is a polyhedron. The surface of
38、 the reverberation chamber shall be smooth and rigid enough. b) The maximum OASPL of the chamber system shall be higher than the requirement of the tests to be performed. c) The chamber shall have enough channels that are connected to the control and measurement system outside the chamber to meet th
39、e requirement of the customers. d) The volume of the reverberation chamber should be 10 times bigger than the volume of the test specimen if it is possible. In all cases, the volume of the reverberation chamber shall be large enough to achieve the adequate test environment taking into account the vo
40、lume of the test specimen. The geometrical size of the reverberation chamber also defines the homogeneity of the SPL in the low frequency third-octave bands. Chamber size shall be considered when low-frequency noise loading is an essential test objective. ISO 2017 All rights reserved 5 ISO 19924:201
41、7(E) 7.2.2 Sound source system Generally, the sound source system is composed of modulators, power amplifiers and horns. a) The achievable sound spectrum shall meet the test requirements. b) Taking into account the reverberation time of the chamber and the additional damping of acoustic modes introd
42、uced by test articles and test installations, the sound power of the sound source system (i.e. number and type of the sound modulators and horns) shall meet the test requirements. c) The operational frequency range of the modulators and power amplifiers shall meet the test requirements. d) In order
43、to well represent the broadband frequency test requirements, different cut-off frequency horns can be used. 7.2.3 Control system Generally, the control system is composed of the controller, the control microphones and signal conditioners or signal pre-amplifiers. a) The control system shall have the
44、 function of multi-inputs average control. b) The control system shall be able to store controlled time history of SPL. c) The control system should allow calibration. d) The measurement range of the microphones shall meet the test requirements. e) 1/1 octave or 1/3 octave closed-loop control or ope
45、n-loop control method may be used. f) It should be possible to control power spectral density on an equal scale according to the test requirements. g) The control system should have the function to interrupt the test in adequate sequence when needed. 7.2.4 Measurement system Generally, the measureme
46、nt system is composed of sensors, signal conditioners, data acquisition system, data storage and processing system. a) The measurement system shall be able to acquire accelerometers, microphones and other required sensors, e.g. strain gauges and force sensors. The frequency range of the acceleromete
47、rs, strain gauges and force sensors should be at least 10 Hz 2 000 Hz. For microphones, the range should be at least 10 Hz 12 000 Hz. b) The data acquisition system shall have enough measurement channels to meet the requirement of the customers. c) Measurement uncertainties shall meet the requiremen
48、ts of the customers. All equipment shall be calibrated and used in the valid period. 8 Test technical requirements 8.1 Laboratory environment The laboratory environment shall follow the requirements of the related technical documents.6 ISO 2017 All rights reserved ISO 19924:2017(E) 8.2 Test conditio
49、n and tolerance 8.2.1 Test condition Test condition is specified in the respective launch vehicle user manual and design standard, generally including a) octave band or 1/3 octave band centre frequency, b) spectral SPL, c) OASPL, d) test level tolerance, reference to 8.2.3, and e) test duration, etc. As an example, the acoustic test level could be 138 dB OASPL with the 1/3 octave band sound pressure level as plotted in Figure 2. Figure 2 Exemplary acoustic level 8.2.2
