Active control of passive acoustic fields: Passive synthetic aperture/Doppler beamforming with data from an autonomous vehicle

2006 ◽  
Vol 120 (6) ◽  
pp. 3635-3654 ◽  
Author(s):  
Gerald L. D’Spain ◽  
Eric Terrill ◽  
C. David Chadwell ◽  
Jerome A. Smith ◽  
Stephen D. Lynch
Keyword(s):  
Active Control ◽  
Autonomous Vehicle ◽  
Synthetic Aperture ◽  
Acoustic Fields ◽  
Passive Acoustic

scholarly journals Search and recovery of aircraft parts in ice-sheet crevasse fields using airborne and in situ geophysical sensors

2020 ◽  
Vol 66 (257) ◽  
pp. 496-508
Author(s):  
Kenneth D. Mankoff ◽  
Dirk van As ◽  
Austin Lines ◽  
Thue Bording ◽  
Joshua Elliott ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
Autonomous Vehicle ◽  
Synthetic Aperture ◽  
Search Area ◽  
Surrounding Structure ◽  
Drifting Snow ◽  
Field Campaigns ◽  
Fall Arrest ◽  
Ground Penetrating

On 30 September 2017, an Air France Airbus A380-800 suffered a failure of its fourth engine while over Greenland. This failure resulted in the loss of the engine fan hub, fan blades and surrounding structure. An initial search recovered 30 pieces of light debris, but the primary part of interest, a ~220 kg titanium fan hub, was not recovered because it had a different fall trajectory than the light debris, impacted into the ice-sheet's snow surface, and was quickly covered by drifting snow. Here we describe the methods used for the detection of the fan hub and details of the field campaigns. The search area included two crevasse fields of at least 50 snow-covered crevasses 1 to ~30 m wide with similar snow bridge thicknesses. After 21 months and six campaigns, using airborne synthetic aperture radar, ground-penetrating radar, transient electromagnetics and an autonomous vehicle to survey the crevasse fields, the fan hub was found within ~1 m of a crevasse at a depth of ~3.3 to 4 m and was excavated with shovels, chain saws, an electric winch, sleds and a gasoline heater, by workers using fall-arrest systems.

Low-Frequency Thermoacoustic Instability Mitigation Using Adaptive-Passive Acoustic Radiators

2011 ◽  
Author(s):  
Reza Kashani ◽  
Jeff Monfort
Keyword(s):  
Active Control ◽  
Control Strategies ◽  
Low Frequency ◽  
Acoustic Energy ◽  
Acoustic Damping ◽  
Thermoacoustic Instability ◽  
Acoustic Radiator ◽  
Passive Acoustic ◽  
Instability Frequency ◽  
Combustion Environment

A commonly used technique for mitigating thermoacoustic instability in an enclosed combustion environment is removing more acoustic energy from the combustor, at the frequency corresponding to the acoustic mode(s) of the combustor which are sympathetic to such instability. This approach is based on adding tuned acoustic damping to the combustion environment. By incorporating in-situ adjustability into acoustic damping devices, they can change their mechanical attributes, e.g., mass and/or stiffness, and adapt themselves in a semi-active manner to the varying instability frequency. Adaptive-passive thermoacoustic mitigation solutions have less weight penalty than the alternative active solutions mainly because the adaptation is done in a semi-active way, at slow pace, with a small and less power-hungry actuation mechanisms. Moreover, the flexibility they offer make them highly desirable for land and marine instability mitigation applications. In this work, semi-active adjustment of a novel tuned acoustic damper, namely an acoustic radiator, is explored. The paper describes the inner working of a semi-active (adaptive-passive) acoustic radiator and the relevant control schemes to adapt them to the instability frequency on hand. The damping effectiveness of the proposed damper, is demonstrated experimentally. It should be mentioned that the semi-active control strategies developed for acoustic radiators can also be used, with minor modifications, for semi-active control of other acoustic damping mechanisms such as Helmholtz resonators and quarter-wave tubes.

scholarly journals On the gain available from passive acoustic synthetic aperture processing.

1992 ◽  
Vol 91 (4) ◽  
pp. 2446-2446
Author(s):  
Edmund J. Sullivan ◽  
William M. Carey
Keyword(s):  
Synthetic Aperture ◽  
Passive Acoustic
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