Publications by Type: Conference Proceedings

2017
X. Xu, Pan, Z., Jia, B., Wang, Y., and Chen, R. T., “All-optical switch with 1 ps response time enabled by graphene oxide infiltrated subwavelength grating waveguide,” Silicon Photonics XII, vol. 10108. San Francisco, California, United States, pp. 1010805, 2017. Publisher's VersionAbstract
In this paper, we propose an all-optical switch using graphene oxide (GO) infiltrated subwavelength grating (SWG) waveguide. Benefiting from the extremely large Kerr coefficient of GO (four orders of magnitude larger than conventional materials) and large mode volume overlap factor of the SWG (4~10 times larger than conventional strip waveguides), the switch is capable of achieving THz speed with less than 1 fJ energy consumption per bit, which is more than three orders of magnitude smaller than THz switches reported so far.
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E. Bakolas, “Covariance Control for Discrete-Time Stochastic Linear Systems with
Incomplete State Information
,” American Control Conference. Seattle, WA, 2017.PDF icon eb_acc_2017.pdf
C. E. Tinney, Hill, B., Valdez, J., Sirohi, J., and Cameron, C., “Drone acoustics at static thrust conditions,” American Helicopgter Society 73rd Annual Forum. Fort Worth, Texas, USA, 2017.Abstract
Multirotor drones are becoming increasingly popular in both the civilian and military sectors of our society. These compact gadgets come in a variety of sizes with the smallest ones measuring less than two inches in diameter, while larger ones can be in excess of five feet. Surprisingly, very little is known about their acoustical footprint, which is becoming a topic of broad importance given that these vehicles most often operate in populated areas. Thus, the objective of this paper is to provide a first principles understanding of the acoustical characteristics of hovering drones. To accomplish this, a new test stand was constructed at the Applied Research Laboratories at The University of Texas at Austin for studying various multirotor drone configurations. The drone test stand is capable of powering up to eight DC electric motors with adjustable arms that allow different rotor diameters to be tested. Rotor diameters ranging from 8 in to 12 in are studied and with configurations comprised of an isolated rotor, a quadcopter configuration and a hexacopter configuration. A six degree-of-freedom load cell is used to assess the aerodynamic performance of each drone configuration. Meanwhile, an azimuthal array of 1/2-inch microphones is placed between 2 and 3 hub-center diameters from the drone center thereby allowing the acoustic near-field to be quantified. The analysis is performed using standard statistical metrics such as Sound Pressure Level and Overall Sound Pressure Level and is presented to demonstrate the relationship between the number of rotors, the drone rotor size and it’s aerodynamic performance (thrust) relative to the far-field noise.
C. E. Tinney, Scott, K., Routon, M., Sirohi, J., and Ruf, J., “Effect of aeroelasticity on vibroacoustic loads during startup of large area ratio nozzles,” 23rd AIAA/CEAS Aeroacoustics Conference. Denver, Colorado, USA, 2017.Abstract
The vibroacoustic loads that form during the startup of both rigid and compliant wallhigh area ratio nozzles is investigated. The rigid wall nozzle is fabricated from 6061 aluminum while the compliant wall nozzles are formed from urethane-based elastomers in orderto invoke aeroelastic coupling between the nozzle wall and the internal flow. Single pointmeasurements of the nozzle lip displacement are synchronized with a pressure field microphone located behind the nozzle where the base of a vehicle would reside. Particularattention is drawn to the sound field during transition from free-shock separated flow torestricted shock separated flow, as well as the end-effects regime loads. The findings revealthe sensitivity of the vibroacoustic loads to the aeroelasticity of the nozzle wall duringcritical stages in the startup process.
J. Selvakumar and Bakolas, E., “Evasion with Terminal Constraints from a Group of Pursuers using a
Matrix Game Formulation
,” American Control Conference. Seattle, WA, 2017.PDF icon jseb_acc17.pdf
J. Joseph, Tinney, C. E., and Murray, N., “Ideal gas effects in aeroacoustics,” 55th AIAA Aerospace Sciences Meeting, AIAA Paper 2017-0688. Grapevine, Texas, USA, 2017.Abstract
The use of helium-air mixtures to simulate the effects of elevated temperatures in aeroacoustics is plagued by the inability to match exactly the density and sound speed ratios between the jet flow and the ambient field, all the while maintaining the same gas dynamic Mach number and jet exit velocity. Real heated jet flows are typically achieved using either propane combustion in air or kerosene combustion in air, which results in the formation of carbon-dioxide and water vapor byproducts. In an effort to level the playing field between the heat simulated helium-air mixture system and the air breathing combustion system, a theoretical model is developed to isolate the effect of combustion byproducts on these aeroacoustic parameters to see if similar discrepancies arise. The motivation is to narrow the gap between laboratory and full-scale jet noise testing. Gas properties from the new combustion model are validated by laboratory measurements of a real propane combustion system as well as outputs from NASA’s Chemical Equilibrium with Applications code. The findings reveal how the additional combustion byproducts from propane combustion in air and kerosene combustion in air have a negligible effect on the parameters relevant to jet noise. Closer inspection of the helium-air mixture system demonstrates how variations in the Mach wave radiation angle at moderate pressure and temperature ratios of the nozzle is accurate to within a couple of degrees, relative to a pure heated air system. Similar accuracy is reported with the far-field intensity.
PDF icon c2017aiaa-grapevinejoseph-0688.pdf
D.Pylorof and Bakolas, E., “Robust Control of Input Constrained Nonlinear Systems Subject to
Unknown Bounded Disturbances Based on Convex Optimization
,” American Control Conference. Seattle, WA, 2017.
C. E. Tinney, “Wall pressure unsteadiness on the aft deck of a planar multi-stream supersonic nozzle,” 55th AIAA Aerospace Sciences Meeting, AIAA Paper 2017-0525. Grapevine, Texas, USA, 2017.Abstract
The unsteady wall pressure on the aft deck of a multi-stream, planar supersonic nozzle is studied over a range of nozzle operating conditions corresponding to independent changes to the core and bypass stream pressure ratios. The data are processed using time-frequency analysis and reveal various tones corresponding to transonic resonance as wellunsteady interactions of both separation and reflection shocks with the developing boundary layer. The position of the separation shock is shown to experience significant hysteresis effects, which subside at pressure ratios well above the design pressure ratio of the nozzle. Shadowgraphy images of the exhaust plume are also presented, which are then analyzed using the snapshot form of proper orthogonal decomposition. The findings from this low-dimensional analysis demonstrates how the first most energetic mode highlights the shock cell patterns whereas the second most energetic mode elucidates turbulence motions in the plume.
2016
V. Puzyrev and Torres-Verdín, C., “3D simulations of deep directional electromagnetic tools in high-angle and horizontal wells (Expanded Abstract).,” European Association of Geoscientists and Engineers (EAGE) 78th Ann. Conference and Exhibition. Vienna, Austria, May 30-June 2., 2016.
V. Puzyrev and Torres-Verdín, C., “3D simulations of deep directional electromagnetic tools in high-angle and horizontal wells (Expanded Abstract),” European Association of Geoscientists and Engineers (EAGE) 78th Ann. Conference and Exhibition. Vienna, Austria, May 30-June 2, 2016.
R. Xu*, Mehmani, A., Qajar, A., Prodanović, M., Daigle, H., and Nguyen, S., “Combination of Lattice Density Functional Theory and a Multi-Scale Network Model for Sorption Isotherms Study in Tight Formations,” Unconventional Resources Technology Conference, San Antonio, Texas, 1-3 August 2016. Society of Exploration Geophysicists, American Association of Petroleum Geologists, Society of Petroleum Engineers, pp. 2255-2266, 2016.
R. Singh, Kang, H., Cameron, C., and Sirohi, J., “Computational and Experimental Investigations of Coaxial Rotor Unsteady Loads,” 54th AIAA Aerospace Sciences Meeting. American Institute of Aeronautics and Astronautics, 2016. Publisher's Version
B. B. Hoxha, Sullivan, G., van Oort, E., Daigle, H., and Schindler, C., “Determining the zeta potential of intact shales via electrophoresis,” SPE Europec featured at 78th EAGE Conference and Exhibition. Society of Petroleum Engineers, 2016.
B. Zhang* and Daigle, H., “Direct Determination of Surface Relaxivity in Isolated Kerogen by Pulsed-Field Gradient NMR,” Unconventional Resources Technology Conference, San Antonio, Texas, 1-3 August 2016. Society of Exploration Geophysicists, American Association of Petroleum Geologists, Society of Petroleum Engineers, pp. 2149-2158, 2016.
R. Rojo, Tinney, C. E., and Ruf, J. H., “Effect of stagger on the vibroacoustic loads from clustered rockets,” 54th AIAA Aerospace Sciences Meeting, AIAA Paper 2016-1016. San Diego, California, USA, 2016.Abstract
The effect of stagger startup on the vibro-acoustic loads that form during the end-effects regime of clustered rockets is studied using both full-scale (hot-gas) and laboratory scale (cold gas) data with vehicle geometry. Both configurations comprise three nozzles with thrust optimized parabolic contours that undergo free shock separated flow and restricted shock separated flow as well as an end-effects regime prior to flowing full. Acoustic pressure waveforms recorded at the base of the nozzle cluster are analyzed using various statistical metrics as well as time-frequency analysis. The findings reveal a significant reduction in end-effects regime loads when engine ignition is staggered. However, regardless of stagger, both the skewness and kurtosis of the acoustic pressure time derivative elevate to the same levels during the end-effects regime thereby demonstrating the intermittence and impulsiveness of the acoustic waveforms that form during engine startup.
K. Yang, Yilmaz, A., and Torres-Verdín, C., “Efficient 3D parametric inversion of hydraulic fractures with low-frequency borehole tri-axial electromagnetic measurements (Expanded Abstract).,” Society of Exploration Geophysicists (SEG) 86th Ann. Internat. Mtg. Dallas, TX, October 16-21., 2016.
K. Yang, Yilmaz, A., and Torres-Verdín, C., “Efficient 3D parametric inversion of hydraulic fractures with low-frequency borehole tri-axial electromagnetic measurements (Expanded Abstract),” Society of Exploration Geophysicists (SEG) 86th Ann. Internat. Mtg. Dallas, TX, October 16-21, 2016.
J. D. Escobar, Torres-Verdín, C., Proett, M., and Ma, S. M., “Evaluating the impact of multiphase flow properties on formation-tester pressure transients (Expanded Abstract).,” Society of Petroleum Engineers (SPE) 2016 Annual Technical Conference and Exhibition. Dubai, UAE, September 26-28., 2016.
J. D. Escobar, Torres-Verdín, C., Proett, M., and Ma, S. M., “Evaluating the impact of multiphase flow properties on formation-tester pressure transients (Expanded Abstract),” Society of Petroleum Engineers (SPE) 2016 Annual Technical Conference and Exhibition. Dubai, UAE, September 26-28, 2016.
M. Lotfollahi, Kim, I., Beygi, M. R., Worthen, A. J., Huh, C., Johnston, K. P., Wheeler, M. F., and DiCarlo, D. A., “Experimental Studies and Modeling of Foam Hysteresis in Porous Media,” SPE Improved Oil Recovery Conference. Society of Petroleum Engineers, 2016. Publisher's VersionAbstract
The use of foam in gas enhanced oil recovery (EOR) processes has the potential to improve oil recovery by reducing gas mobility. Nanoparticles are a promising alternative to surfactants in creating foam in the harsh environments found in many oil fields. We conducted several CO2-in-brine foam generation experiments in Boise sandstones with surface-treated silica nanoparticle in high-salinity conditions. All the experiments were conducted at the fixed CO2 volume fraction (g = 0.75) and fixed flow rate which changed in steps. We started at low flow rates, increased to a medium flow rates followed by decreasing and then increasing into high flow rates. The steady-state foam apparent viscosity was measured as a function of injection velocity. The foam flowing through the cores showed higher foam generation and consequently higher apparent viscosity as the flow rate increased from low to medium and high velocities. At very high velocities, once foam bubbles were finely textured, the foam apparent viscosity was governed by foam shear-thinning rheology rather than foam creation. A noticeable "hysteresis" occurred when the flow velocity was initially increased and then decreased, implying multiple (coarse and strong) foam states at the same superficial velocity. A normalized generation function was combined with CMG-STARS foam model to cover the full spectrum of foam flow behavior observed during the experiments. The new foam model successfully captures foam generation and hysteresis trends observed in presented experiments in this study and other foam generation experiments at different operational conditions (e.g. fixed pressure drop at fixed foam quality, and fixed pressure drop at fixed water velocity) from the literature. The results indicate once foam is generated in porous media, it is possible to maintain strong foam at low injection rates. This makes foam more feasible in field applications where foam generation is limited by high injection rates (or high pressure gradient) that may only exist near the injection well. Therefore, understanding of foam generation, and foam hysteresis in porous media and accurate modeling of the process are necessary steps for efficient foam design in field.

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