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Your search keyword '"Choi, K. K."' showing total 142 results
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142 results on '"Choi, K. K."'

16. Compact thermal imager: a flight demonstration of infrared technology for Earth observations

Author

Jennings, D. E., primary, Jhabvala, M. D., additional, Tucker, C. J., additional, Lunsford, A. W., additional, La, A. T., additional, Flatley, T. P., additional, Choi, K. K., additional, Wu, D. L., additional, Morton, D. C., additional, Holmes, T. R., additional, Fitts, Y., additional, Cappelaere, P. G., additional, Cillis, A. N., additional, Turck, K. A., additional, and Hewagama, T., additional

Published
2022
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18. Effects of parametric uncertainty on multi-scale model predictions of shock response of a pressed energetic material.

Author

Lee, Sangyup, Sen, Oishik, Rai, Nirmal Kumar, Gaul, Nicholas J., Choi, K. K., and Udaykumar, H. S.

Subjects
MULTISCALE modeling, THERMAL conductivity, MECHANICAL shock measurement, MONTE Carlo method, THERMOMECHANICAL properties of metals, PROBABILITY density function, SPECIFIC heat
Abstract

Predictive simulations of shock-to-detonation transitions (SDTs) of energetic materials must contend with uncertainties in the material properties, reactive models, and the microstructures of the material. In this work, we analyze the effects of uncertainties in the run-to-detonation distance h of a pressed energetic (HMX) material due to variabilities in the thermomechanical properties of HMX. The run distances are computed using a recently developed machine-learning based multiscale modeling framework, viz., the Meso-informed Ignition and Growth (MES-IG) model. The input uncertainties are first used in the MES-IG model to quantify the variabilities in the hotspot dynamics at the mesoscale. A Kriging-based Monte Carlo method is used to construct probability density functions (pdfs) for the mesoscale reaction-product formation rates; these are used to propagate the mesoscale uncertainties to the macroscale reaction-progress variables to construct pdfs for the run-to-detonation distance h. We evaluate uncertainties in h due to variabilities in six material properties, viz., specific heat, Grüneisen parameter, bulk modulus, yield strength, thermal expansion coefficient, and the thermal conductivity of the material. Among these six properties, h is found to be most sensitive to the variabilities in the specific heat of the material; the uncertainties in the specific heat amplify exponentially across scales and result in logarithmic pdfs for h. Thus, the paper not only quantifies and propagates uncertainties in material properties across scales in a multiscale model of SDT, but also ranks the properties with respect to the sensitivity of the SDT response of heterogeneous energetic materials on each property. [ABSTRACT FROM AUTHOR]

Published
2019
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21. AVT-248 Next-Generation NATO Reference Mobility Model (NG-NRMM) Development

Author

Balling, Ole, Bradbury, Michael, Bruce, Jonathan, Cammarere, Mark, Choi, K. K., Dasch, Jean, Foster, Craig, Funk, Matthew, Gaul, Nicholas, Hodges, Henry, Jain, Abhinandan, Jayakumar, Paramsothy, McCullough, Michael, Niemann, Jeffrey, Ramyar, Elham, Scalia, Joseph, Wasfy, Tamer, and Wojtysiak, Brian

Published
2019

27. Gold plasmonic material for enhanced Hg1–xCdxTe infrared absorption.

Author

Das, Naresh C. and Choi, K. K.

Subjects
*PLASMONICS, *INFRARED absorption, *GOLD, *SIGNAL-to-noise ratio
Abstract

There are potential applications for high operating temperature (HOT) Hg1-xCdxTe (MCT) infrared (IR) devices for both defense and commercial applications. MCT absorption can be raised either by increasing the absorber thickness or by lowering the operating temperature. However, if we can increase MCT absorption by using plasmonic materials, it will help in both HOT operation and increasing signal to noise ratio. We studied three Gold (Au) plasmonic structures for the absorption enhancement of MCT materials in the wavelength band of 3-7 μm. By using RF module in COMSOL multiphysics software, we found a large increase (1.85X) of MCT absorption when the optimized Au plasmonic structure is used. The increase in absorption at 4.5-6 μm is higher than that at 3-4 μm. The increased absorption due to plasmonic structure allows absorber thickness to decrease which leads to decrease in dark current and HOT devices. We report here record 90% increase in absorption of MCT material at room temperature at peak wavelength around 3.4 μm by using optimized plasmonic structure. [ABSTRACT FROM AUTHOR]

Published
2019
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