Feb 16, 2016 - Sanders, James. ... Yasaman Farsiani, Shahrouz Mohagheghian, Mcclain Robinson, Brad McNealy, Alex Johnson, and Kah Hooi Quah.
Development of a reference infrasonic sensing system for integration with UAS Arnesha Threatt, Brian R. Elbing, & Madison Likins Mechanical & Aerospace Engineering Oklahoma State University, Stillwater, OK
02/16/2016
Photo courtesy of TornadoHunter.com
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Outline • • • • •
Motivation UAV Integration Infrasonic Source Creation Instrumentation Results – Subwoofer – Propane Torch
• Future Work • Conclusions 02/16/2016
High Speed video of subwoofer 2
Motivation • Numerous natural occurrences emit infrasonic frequencies: – – – –
Supersonic Aircrafts Volcanos Earthquakes Tornadoes
• Infrasonic signals, which attenuate over very large distances, are emitted hours before tornados forms • This infrasonic noise could potentially be used for early, more accurate detection of tornadoes. 02/16/2016
http://neuroresearchproject.com/2013/02/19/1289/
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Motivation •
Correlation of infrasound with the flow field of the storm
•
Physics of tornados are dictated by a region close to the ground
•
This region lacks measurements due to the limitations of instrumentation − Radar measures above this area − Weather towers measure below this area
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Photo courtesy of Kelly DeLay
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UAV Integration •
UAVs will deploy instrumentation to measure various characteristics of the atmosphere
•
Creation of Infrasonic system to integrate with UAVs to measure infrasound from inside the storm
•
Photo Courtesy of Alyssa Avery
Infrasonic signals may change with distance, compare measurements from UAV with measurements from on-ground array.
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Infrasonic Source Creation • Two infrasonic sources – Subwoofer – Propane torch wand • C Smith & T Gabrielson (2015) propane torch wand experiments Penn State Experiment
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Experimental Setup Subwoofer Experiment: • Function Generator inputs signal to subwoofer • Microphone records signal at various distances Microphone hose end
Subwoofer
Function Generator
Propane Torch Experiment: • Torch is pulsed at various time intervals • Microphone records signals utilizing windscreens Propane Torch
Windscreens
Mic.
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Microphone • Infiltec-Infra 20 microphone • Microphone Specs:
Filter
Microcontroller
– Roughly 50 samples per second – 0.02 mV/Pa Sensitivity – Must be connected to a computer in order to record – Records to Amaseis program
Filter
Pressure Transducer 02/16/2016
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Windscreen • Windscreens reduce the effect of wind noise on an infrasonic signal • Three Windscreen options – Conventional design, long hoses connected to microphone – Current Windscreen Modeled after Alcoverra & Pichon 2004 – Eventual Windscreen choice: Shams & Zuckerwar spherical waterproof windscreen
Qamar A. Shams, Allan J. Zuckerwar*, Howard K. Knight NASA Langley Research Center, Hampton VA USA *Analytical Services & Materials Inc., Hampton VA USA
http://www.nasa.gov/larc/nasa-langley-researchersnab-invention-of-the-year-for-infrasound-detectionsystem/
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Subwoofer Analytical Solution The position of the first local maximum axial pressure (r1) is given by:
The pressure amplitude on the axis of the piston
• • •
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𝑟1
P/2ρ0cU0
• • •
1 𝑃 𝑟 = 𝜌0 𝑐𝑈0 𝑘𝑎(𝑎 𝑟) 2 ρ0 : Density of air c : speed of sound U0 : speed of the face of the piston r : distance of measurement a : radius of piston k : 2πf/c
r/a Kinsler et al. Fundamentals of Acoustics
𝑎 λ 𝑎 = λ − 4𝑎
• r > r1 : far field axial pressure approaches 1/r • For our tests r1 ranged from -562.5 to -15.45 • Experiments are in the far field.
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Subwoofer- Initial Results • •
Distance from source vs Spectral Peak graph Spectral Peaks should collapse onto far-field estimate (1/r) Normalized
Spectral Peak
1.2 1
0.8 0.6 0.4 0.2 0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
r (ft) Freq. 0.5 Hz
0.007181
1 Hz
0.0156
3 Hz
0.02917
18.2 Hz 02/16/2016
Max Peak
3 Hz
18.2 Hz
.5 Hz
1 Hz
1/r (far field)
0.185 11
Subwoofer- Initial Results – Comparing analytical results found in “Fundamental of Acoustics” to results experimentally
10-2
|Suu (f)|
• Indoor Subwoofer experiments
10-3 100
Frequency (Hz)
101
– Input Signal: Square Wave Amplitude: 5V
|Suu (f)|
10-2
100
Frequency (Hz)
101
Top: Frequency 0.5 Hz, 0 inches from source Bottom: Frequency 1 Hz, 0 inches from source 02/16/2016
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Localization • Using an array of microphones the location of a sound source, in our case a tornado, can be triangulated. • The setup of localization experiment performed is shown in the diagram on the bottom right Mic 2
30 ft
Mic 3 Dowling & Sabra (2015)
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30 ft
Mic 1 30 ft
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Propane Results • No clear frequency output from propane torch experiment • Microphones with increased sensitivity and/or louder sound source needed to produce desired results
|Suu (f)|
10-3
Shadow of flame from propane torch during testing
10-4
100 02/16/2016
Frequency (Hz)
101 14
Microphone • Purchasing of higher quality microphone – B&K – Chaparral – NASA system
• New microphones will have higher sensitivity and less electronic noise
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Future Work • Use higher quality subwoofer for lower frequency recordings at larger distances • Perform experiments with mechanically oscillating propane torch • Improving current microphones and purchasing of infrasonic microphones with higher sensitivity http://www.esrl.noaa.gov/psd/programs/infrasound/isnet/
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Conclusions • UAVs are critical for weather monitoring with infrasound – A trusted infrasonic sound source is needed in order to verify measurements from infrasonic array
• For field testing a louder sound source and better infrasonic microphones are needed
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Questions?
Photo courtesy of TornadoHunter.com
Acknowledgements: • Yasaman Farsiani, Shahrouz Mohagheghian, Mcclain Robinson, Brad McNealy, Alex Johnson, and Kah Hooi Quah
References:
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C Smith & T Gabrielson (2015) Acoust Soc Am Spring Meeting, 4pPA2, Pittsburg, PA.
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Kinsler, Lawrence. Frey, Austin. Coppens, Alan. Sanders, James. Fundamentals of Acoustics. Wiley (1999) Section 7.4 (Pages: 179-184) Alcoverro, Beniot & Le Pichon, Alexis “Design and optimization of a noise reduction system for infrasonic measurements using elements with low acoustic impedance” (2005) Acoustical Society of America Vol. 117, No. 4, Pt. 1 David R. Dowling and Karim G. Sabra “Acoustic Remote Sensing” (2015) The Annual Review of Fluid Mechanics.47:221243
• •
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