A recent operational need for the development of a large (101,000 ft3) reverberant acoustic chamber at the Space Power Facility of NASA Glenn Research Center’s Plum Brook Station with the requirement of generating sound pressure levels (SPL) as high as 163 dB has resulted in the need to re-examine the generation of noise in reverberant rooms. Early in the design stage, it was realized that the acoustic power level capability (10-30 kW) of conventional electrodynamic air modulators, such as those supplied by the Wyle Corporation, would be required in unprecedented numbers to meet the test spectra requirements. The design team then turned to a lesser known modulator, the hydraulically driven air modulator supplied by the Team Corporation, which has 150-200 kW acoustic power capability. The advantage to the project was a significant reduction in the number of modulators required to meet the requirements. However, since only limited characterization of Team modulator’s performance has been reported, a test program was required in order to mitigate the risk of the design of the RATF. Aiolos Corporation, which is responsible for the acoustic design of the RATF, and the Institute of Aerospace Research (IAR) of the National Research Council of Canada (NRC), entered into a collaborative agreement with the objective of characterizing, optimizing and investigating the controllability of the Team modulators. The test program was performed at the NRC-IAR reverberant chamber, a 19,000 ft3 facility located in Ottawa, Ontario, Canada. The current paper provides details of the principle of operation of the Team modulators, including their servo control loops and provides of a summary of the characterization and controllability test program.

/pdf/high-intensity-noise-generation-for-extremely-large-2bpf9z54xi.pdf

High Intensity Noise Generation for Extremely Large Reverberant Room Test Applications

The European Space Agency (ESA) and their prime contractor Airbus Defense Space (ADS) are developing the European Service Module (ESM) for integration and utilization with other modules of NASAs Orion Multi-Purpose Crew Vehicle. As part of this development, ESA, ADS, NASA and the Lockheed Martin Company performed a series of reverberant acoustic tests in April-May 2016 on the ESM Structural Test Article (E-STA), the mechanical mock-up of the ESM designated for mechanical tests. Testing the E-STA under acoustic qualification loads verifies whether it can successfully withstand the medium and high frequency mechanical environment occurring during the vehicles lift-off and atmospheric phases of flight. The testing occurred at the Reverberant Acoustic Test Facility (RATF) at the NASA Glenn Research Centers Plum Brook Station site in Sandusky, OH, USA. This highly successful acoustic test campaign excited the E-STA to acoustic test levels as high as 149.4 dB Overall Sound Pressure Level. This acoustic testing met all the ESA and ADSs test objectives, including establishingverifying the random vibration qualification test levels for numerous hardware components of the ESM, and qualifying the ESMs Solar Array Wing electrical power system. This paper will address the test objectives, the test articles configuration, the test instrumentation and excitation levels, the RATF site and capabilities, the series of acoustic tests performed, and the technical issues faced and overcome to result in a successful acoustic test campaign for the ESM. A discussion of several test results is also included.

/pdf/overview-of-the-acoustic-testing-of-the-european-service-3mlr7zkp8b.pdf

Overview of the Acoustic Testing of the European Service Module Structural Test Article (E-STA)

The exposure of a customer's aerospace test-article to a simulated acoustic launch environment is typically performed in a reverberant acoustic test chamber. The acoustic pre-test runs that will ensure that the sound pressure levels of this environment can indeed be met by a test facility are normally performed without a test-article dynamic simulator of representative acoustic absorption and size. If an acoustic test facility's available acoustic power capability becomes maximized with the test-article installed during the actual test then the customer's environment requirement may become compromised. In order to understand the risk of not achieving the customer's in-tolerance spectrum requirement with the test-article installed, an acoustic power margin evaluation as a function of frequency may be performed by the test facility. The method for this evaluation of acoustic power will be discussed in this paper. This method was recently applied at the NASA Glenn Research Center Plum Brook Station's Reverberant Acoustic Test Facility for the SpaceX Falcon 9 Payload Fairing acoustic test program.

/pdf/an-evaluation-of-the-additional-acoustic-power-needed-to-26ki7qeiyi.pdf

An Evaluation of the Additional Acoustic Power Needed to Overcome the Effects of a Test-Article's Absorption During Reverberant Chamber Acoustic Testing of Spaceflight Hardware

Modern aircraft are exposed to intense pulsations of sound pressure arising both from engine noise, and from turbulent effects of the environment during flight. The pulsations cause vibrations of the structure leading to fatigue damage of the fuselage skin and primary elements of structure, as well as to the equipment failure. The operating experience shows the necessity of taking into account the acoustic fatigue starting with loads of 130 – 135 dB. At a load value above 160 dB, the acoustic fatigue becomes one of the main factors determining the strength of aircraft and space structures. Despite the development of computational methods for estimating durability under acoustic loads, the most reliable methods are still based on experimental studies. The frequency spectrum is the main characteristic of acoustic loading. Reproducing of acoustic loads in a controlled frequency range 150 – 600 Hz with the intensity of pulsations specified above appeared enough for testing most aircraft structures. However, space apparatus and equipment must be tested for the effect of acoustic noise within the frequency range from 150 to 1200 – 2000 Hz. Domestic low- and medium-frequency generators operating in a frequency range of 20 – 600 Hz are currently used in reverberation chambers in Russia. To generate higher frequencies of acoustic vibrations, we used an ERT-200 electropneumatic converter (LING (USA), the maximum frequency 1000 – 1250 Hz) and a most advanced SEPMOD modulator [SEREME (France), the maximum frequency is 1000 – 2000 Hz]. Information about the design of those sound modulators is not available to consumers. Further development of aerospace technology necessitates developing of domestic high-frequency sound generators for acoustic tests. We propose a method which ensures operation of the sound generator in a controlled frequency range of 150 – 1200 Hz. The essence of the method consists in designing a sound modulator (being part of the generator) which provide that an increase in the electromotive force, driving the movable element of the valve assembly into reciprocating motion, will not entail an increase in heat generation in the electromagnetic propulsion device. For this, we propose to perform the electric propulsion device in the form of synchronously operating two parts located at opposite ends of the movable element of the valve. Supplying each part with the maximum permissible current, we managed to increase the total excitation current by half. The calculations showed that the use of more energy-intensive permanent magnets of neodymium type NdFeB and considered principle of forming a propulsion unit provide a range of sound frequency control of 150 – 1200 Hz at a pulse acoustic load up to 160 dB.

Принцип построения высокочастотных модуляторов звука для акустических испытаний на прочность и ресурс летательных аппаратов

The filter wheel (FW) assembly (FWA), developed by the CBK Institute, is one of the critical subsystems of the wide field imager (WFI) instrument on board the Advanced Telescope for High Energy Astrophysics—mission of the ESA Cosmic Vision 2015-25 space science program (launch scheduled around 2035). The instrument has to collect soft x-rays with very high quantum efficiency, thus WFI requires extremely thin optical blocking filter (OBF). Due to its thickness (∼150 nm) and large area (∼170 mm × 170 mm) needed to achieve a 40 ′ × 40 ′ instrument field of view, the filter is extremely vulnerable to acoustic loads generated during Ariane 6 rocket launch. On the other side, FW mechanism has to provide high overall reliability, so it is more favourable to launch the instrument in atmospheric pressure (without vacuum enclosure for filter protection). Design efforts of the FW subsystem were focused on two issues: providing maximal possible sound pressure level suppression and smallest possible differential pressure across the OBF, which should prevent filters from damaging. We describe the design of a reconfigurable acoustic-demonstrator model (DM) of WFI FWA created for purposes of acoustic testing. Also, the acoustic test campaign is described: test methodology, test criteria, and results discussion and its implication on future FWA design. In general, tests conducted with the FWA DM showed that current design of WFI is feasible and the project can be continued without introducing a vacuum enclosure, which would significantly increase system complexity and mass. 

/pdf/design-and-acoustic-tests-of-the-athena-wfi-filter-wheel-1qrhv4ew.pdf

Design and acoustic tests of the ATHENA WFI filter wheel assembly development model towards TRL5

The National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) is leading the design and build of the new world-class vibroacoustic test capabilities at the NASA GRC's Plum Brook Station in Sandusky, Ohio, USA. Benham Companies, LLC is currently constructing modal, base-shake sine and reverberant acoustic test facilities to support the future testing needs of NASA s space exploration program. The large Reverberant Acoustic Test Facility (RATF) will be approximately 101,000 ft3 in volume and capable of achieving an empty chamber acoustic overall sound pressure level (OASPL) of 163 dB. This combination of size and acoustic power is unprecedented amongst the world s known active reverberant acoustic test facilities. The key to achieving the expected acoustic test spectra for a range of many NASA space flight environments in the RATF is the knowledge gained from a series of ground acoustic tests. Data was obtained from several NASA-sponsored test programs, including testing performed at the National Research Council of Canada s acoustic test facility in Ottawa, Ontario, Canada, and at the Redstone Technical Test Center acoustic test facility in Huntsville, Alabama, USA. The majority of these tests were performed to characterize the acoustic performance of the modulators (noise generators) and representative horns that would be required to meet the desired spectra, as well as to evaluate possible supplemental gas jet noise sources. The knowledge obtained in each of these test programs enabled the design of the RATF sound generation system to confidently advance to its final acoustic design and subsequent on-going construction.

/pdf/the-development-of-the-acoustic-design-of-nasa-glenn-mhjjwvb9rv.pdf

The Development of the Acoustic Design of NASA Glenn Research Center's New Reverberant Acoustic Test Facility

The National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) is leading the design and build of the new world-class vibroacoustic test capabilities at the NASA GRC’s Plum Brook Station in Sandusky, Ohio, USA. Benham Companies, LLC is currently constructing modal, base-shake sine and reverberant acoustic test facilities to support the future testing needs of NASA’s space exploration program.

/pdf/the-testing-behind-the-test-facility-the-acoustic-design-of-226qb2va8l.pdf

The Testing Behind the Test Facility: The Acoustic Design of the NASA Glenn Research Center's World-Class Reverberant Acoustic Test Facility

/pdf/reverberant-acoustic-test-facility-ratf-structural-design-3lsoluru4m.pdf

Reverberant Acoustic Test Facility (RATF) Structural Design for Vibroacoustic Loads

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