PRC Shuttle Change & Defenses

PRC Shuttle Changes and Dissertation Defenses
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PRC Shuttle Changes

Last minute meeting announcement

We all should have gotten the announcement about the PRC shuttle changes coming up. In case you were unaware, the plan is to eventually get rid of the PRC shuttle and replace it with a new MetroRapid line.

I was the only grad student to attend their last public forum and I won't be making this one. I just wanted to make sure you are aware of it because PTS emails can easily slip under the radar. The details are repeated below.

Chair - Austin ASA

"Parking and Transportation Services and  Capital Metro will be hosting an upcoming public forum to discuss the proposed changes to the PRC Shuttle Route. The forum will be held at Burdine Hall (BUR), Room 112 on  Tuesday, April 22nd from 5:30 pm - 6:30 pm.

For more information on the proposed change to the PRC route please visit the following url:   

Students and Staff are encouraged to attend the PRC Shuttle Route Public Forum to obtain additional information."


Acoustics Defenses This Week

Come out and learn about some of the recent acoustics research and support your fellow grad-students. (Disclaimer: One of them is in fact my defense.)

Chair - Austin ASA

Extraction of Blade Vortex Interactions from Helicopter Acoustic Signals

Author: James H. Stephenson
When: Monday, April 21st, 3:00 pm

Where: WRW 410
      An extraction method to remove blade vortex interaction sound signatures from helicopter transient maneuvering flight acoustics is developed and implemented. The extraction method allows for the investigation of blade vortex interactions independent of other sound sources. The method is essentially a filter of the time-frequency representation of helicopter acoustic signatures, that identifies blade vortex interactions through their high amplitude, high frequency impulsive content. The filtered wavelet coefficients are then inverse transformed to create a pressure signature solely related to blade vortex interactions.
     This extraction technique, along with a prescribed wake model, is applied to experimental data extracted from three separate flight maneuvers performed by a Bell 430 helicopter. The maneuvers investigated include a steady level flight, fast- and medium-speed advancing side roll maneuvers. The extraction method is shown to perform admirably throughout each maneuver. One limitation with the technique is identified, and a proposal to mitigate its effects is made. Through the implementation of this technique it is identified that the blade vortex interaction sound pressure level is directly linked to the roll rate of the vehicle, which influences the miss distance of the rotor vortex during interactions.


Measuring the Acoustic Parameters of Fish Schools

Author: Craig N.  Dolder 
When: Friday, April 25, 2014, 4:00 p.m. 

Where: ETC 4.150

      While the literature contains extensive in situ measurements of scattering by fish schools, significant uncertainties exist with respect to characterizing the size, quantity, and distribution of fish within the schools that confound accurate measurement-model comparison. Measurements of the sound speed through collections of live fish (Danio rerio) were conducted in a laboratory setting. The sound speed was investigated using a resonator technique which yielded inferences of the phase speed within the fish school though measurements of the resonances of a one-dimensional waveguide. Fish densities were investigated ranging from 8.6 to 1.7 fish lengths per mean free path. Measurements agree well with a predictive model that is based on shell-free spherical bubbles, which indicates that the phase speed is not significantly affected by the fish flesh or swimbladder morphology for the species studied. The variation in phase speed due to individual fish motion within the model school was measured to be up to ±5.6%. This indicates that precise knowledge of the fish position is required to achieve greater model accuracy. To compliment the phase speed measurements, the attenuation through a cloud of encapsulated bubbles was evaluated through insertion loss measurements. Multiple arrangements of balloons of radius 4.68 cm were used to surround a projector. The insertion loss measurements indicated an amplification of around 10 dB at frequencies below the individual balloon resonance frequency and an insertion loss of around 40 dB above the individual balloon resonance frequency. Analytical modeling of the bubble collection predicted both the amplification and loss effect, but failed to accurately predict the level of amplification and insertion loss. Finally, effective medium models and full scattering models (requiring knowledge of bubble size and position) were evaluated for a model fish school. The two models agree for forward scattering for all frequencies except those immediately around the individual bubble resonance frequency. Back scattered results agree at low frequencies, however as soon as the wavelength becomes smaller than four mean free paths between fish the models diverge. Ramifications of these findings and potential future research directions are discussed.

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