Kim, S., & Deng, S. (2023). Inference of Chemical Kinetics and Thermodynamic Properties from Constant-Volume Combustion of Energetic Materials. Submitted.
@article{kim2023inference,
title = {{Inference of Chemical Kinetics and Thermodynamic Properties from Constant-Volume Combustion of Energetic Materials}},
author = {Kim, Suyong and Deng, Sili},
year = {2023},
journal = {Submitted}
}
Kim, S., Johns, A. A., Wen, J. Z., & Deng, S. (2022). Burning structures and propagation mechanisms of nanothermites. Proceedings of the Combustion Institute.
@article{kim2022burning,
title = {{Burning structures and propagation mechanisms of nanothermites}},
author = {Kim, Suyong and Johns, Averitt A and Wen, John Z and Deng, Sili},
journal = {Proceedings of the Combustion Institute},
year = {2022},
doi = {10.1016/j.proci.2022.07.113},
publisher = {Elsevier}
}
Nanothermites demonstrate attractive combustion characteristics such as tunable reactivity and high energy density. There is however a lack of fundamental understanding on their burning structures and reaction mechanisms due to the multi-scale complexity associated with the material and reaction heterogeneities. This gap in turn hinders the optimization of nanothermite design with desirable microstructures and controllable burning properties. In this work, a high-speed microscopy imaging system was used to reveal the burning structure of Al/CuO nanothermites and to investigate the propagation mechanism of its flame front at micron and sub-millimeter scales which have not been studied. An Al/CuO nanothermite film was fabricated as a model structure. First, the previously proposed reactive sintering was confirmed as a micron-scale burning characteristic. Then, at the sub-millimeter scale, it was demonstrated that the non-uniform burning propagation of nanothermite films is featured with distinguishable roles of the active burning sites and the pre-ignition sites. The active burning sites are clusters of reactive sintering particles and the pre-ignition sites appear in the preheating regions where Al and CuO particles have not yet participated in the reaction due to insufficient ignition energy. These pre-ignition sites form randomly and are subsequently ignited by heat transferred from the adjacent active burning sites, resulting in an active burning propagation tangentially along the propagation front. At the same time, as the thermite reaction of nanoparticles in the unburnt region is initiated, the propagation front advances in the normal direction. This experimental work reveals that the burning propagation mechanism of nanothermite films is governed by active burning propagation in both tangential and normal directions of the propagation front. Although the rates of these two modes are on the same order of magnitude, the tangential propagation of active burning is slightly faster, implying that pre-ignition sites are readily ignited with lower ignition energy.
Kim, S., Ji, W., Deng, S., Ma, Y., & Rackauckas, C. (2021). Stiff neural ordinary differential equations. Chaos: An Interdisciplinary Journal of Nonlinear Science, 31(9), 093122.
@article{kim2021stiff,
title = {{Stiff neural ordinary differential equations}},
author = {Kim, Suyong and Ji, Weiqi and Deng, Sili and Ma, Yingbo and Rackauckas, Christopher},
journal = {Chaos: An Interdisciplinary Journal of Nonlinear Science},
volume = {31},
number = {9},
pages = {093122},
year = {2021},
doi = {10.1063/5.0060697},
publisher = {AIP Publishing LLC}
}
Neural Ordinary Differential Equations (ODEs) are a promising approach to learn dynamical models from time-series data in science and engineering applications. This work aims at learning neural ODEs for stiff systems, which are usually raised from chemical kinetic modeling in chemical and biological systems. We first show the challenges of learning neural ODEs in the classical stiff ODE systems of Robertson’s problem and propose techniques to mitigate the challenges associated with scale separations in stiff systems. We then present successful demonstrations in stiff systems of Robertson’s problem and an air pollution problem. The demonstrations show that the usage of deep networks with rectified activations, proper scaling of the network outputs as well as loss functions, and stabilized gradient calculations are the key techniques enabling the learning of stiff neural ODEs. The success of learning stiff neural ODEs opens up possibilities of using neural ODEs in applications with widely varying time-scales, such as chemical dynamics in energy conversion, environmental engineering, and life sciences.
Song, J., Kim, S., Park, T. C., Cha, B.-J., Lim, D. H., Hong, J. S., Lee, T. W., & Song, S. J. (2019). Non-Axisymmetric Flows and Rotordynamic Forces in an Eccentric Shrouded Centrifugal Compressor—Part 1: Measurement. Journal of Engineering for Gas Turbines and Power, 141(11), 111014.
@article{song2019non,
title = {Non-Axisymmetric Flows and Rotordynamic Forces in an Eccentric Shrouded Centrifugal Compressor—Part 1: Measurement},
author = {Song, Jieun and Kim, Suyong and Park, Tae Choon and Cha, Bong-Jun and Lim, Dong Hun and Hong, Joo Sung and Lee, Tae Wook and Song, Seung Jin},
journal = {Journal of Engineering for Gas Turbines and Power},
volume = {141},
number = {11},
pages = {111014},
year = {2019},
doi = {10.1115/1.4044874},
publisher = {American Society of Mechanical Engineers}
}
Centrifugal compressors can suffer from rotordynamic instability. While individual components (e.g., seals, shrouds) have been previously investigated, an integrated experimental or analytical study at the compressor system level is scarce. For the first time, non-axisymmetric pressure distributions in a statically eccentric shrouded centrifugal compressor with eye-labyrinth seals have been measured for various eccentricities. From the pressure measurements, direct and cross-coupled stiffness coefficients have been determined. Thus, the contributions of the pressure perturbations in the shroud cavity and labyrinth seals have been simultaneously investigated. The cross-coupled stiffness coefficients in the shroud and labyrinth seals are both positive and one order of magnitude larger than the direct stiffness coefficients. Furthermore, in the tested compressor, contrary to the common assumption, the cross-coupled stiffness in the shroud is 2.5 times larger than that in the labyrinth seals. Thus, not only eye-labyrinth seals but also shrouds need to be considered in rotordynamic analysis.
Kim, S. Y., Jin, D. H., Lee, K. B., & Kim, C. (2013). NUMERICAL ANALYSIS FOR SUPPRESSING UNSTEADY WAKE FLOW ON WIND TURBINE TOWER USING EDISON_CFD. Journal of Computational Fluids Engineering, 18(1), 36–42.
@article{kim2013numerical,
title = {NUMERICAL ANALYSIS FOR SUPPRESSING UNSTEADY WAKE FLOW ON WIND TURBINE TOWER USING EDISON\_CFD},
author = {Kim, SY and Jin, DH and Lee, KB and Kim, C},
journal = {Journal of computational fluids engineering},
volume = {18},
number = {1},
pages = {36--42},
year = {2013},
publisher = {Korean Society of Computational Fluids Engineering},
doi = {10.6112/kscfe.2013.18.1.036}
}
The performance of the wind turbine is determined by wind speed and unsteady flow characteristics. Unsteady wake flow causes not only the decline in performance but also structural problems of the wind turbine. In this paper, conceptual designs for the wind turbine tower are conducted to minimize unsteady wake flow. Numerical simulations are performed to inspect the shape effect of the tower. Through the installation of additional structures at the rear of the tower, the creation of Karman vortex is delayed properly and vortex interactions are reduced extremely, which enhance the stability of the wind turbine. From the comparative analysis of lift and drag coefficients for each structure, it is concluded that two streamwise tips with a splitter plate have the most improved aerodynamic characteristics in stabilizing wake flow.
Oh, S.-D., Lee, Y., Yoo, Y., Kim, J., Kim, S., Song, S. J., & Kwak, H.-Y. (2013). A support strategy for the promotion of photovoltaic uses for residential houses in Korea. Energy Policy, 53, 248–256.
@article{oh2013support,
title = {A support strategy for the promotion of photovoltaic uses for residential houses in Korea},
author = {Oh, Si-Doek and Lee, Yeji and Yoo, Yungpil and Kim, Jinoh and Kim, Suyong and Song, Seung Jin and Kwak, Ho-Young},
journal = {Energy Policy},
volume = {53},
pages = {248--256},
year = {2013},
publisher = {Elsevier},
doi = {10.1016/j.enpol.2012.10.057}
}
Various policies such as feed-in tariffs, quota obligations and capital subsides were enacted to expand the uses of renewable energy (RE) in many countries. This study examined whether capital subsidies are cost effective in relation to the installation of solar photovoltaic (PV) facility. To do this, the capacity factor, which is one of the crucial factors for determining the unit cost of electricity from a solar PV system, was estimated from the monthly average clearness index data collected at various cities in Korea. Thermoeconomic analysis was applied to calculate the unit cost of electricity based on the calculated capacity factor of the solar PV system. Instead of subsidizing the same percent of the capital cost of each PV system installation, it is reasonable for the government to adopt a measure to match the subsidy paid to the payback period of the initial investment for all 5 million potential solar PV users in Korea.
Refereed conference proceedings
Kim, S., Song, J., Park, T. C., Kim, K., & Song, S. J. (2019). Measurement of Shrouded Radial Compressor Stability under Eccentric Conditions. Proceedings of Global Power and Propulsion Society.
@inproceedings{kim2019measurement,
title = {{Measurement of Shrouded Radial Compressor Stability under Eccentric Conditions}},
author = {Kim, Suyong and Song, Jieun and Park, Tae Choon and Kim, Kilyoung and Song, Seung Jin},
year = {2019},
booktitle = {Proceedings of Global Power and Propulsion Society},
address = {Zürich, Switzerland},
doi = {10.33737/GPPS19-TC-068}
}
This paper reports on the measurement of the impact of impeller eccentricity on the stability of a radial compressor. The test radial compressor is a shrouded type with a vaneless diffuser. The relative eccentricity between the impeller and the casing has been achieved by offsetting the casing with precision shims. The eccentric impeller induces tangential flow redistribution, resulting in non-axisymmetric flow field, especially at the impeller exit. At the design condition, eccentricity has little influence on the compressor pressure rise. However, near the instability onset point, pressure rise decreases slightly as the eccentricity is increased. Under the baseline conditions, the compressor goes directly into classic surge at the flow coefficient of 0.0218. However, under eccentric conditions, the compressor goes into rotating stall first and then goes into surge. Before going into rotating stall, the compressor exhibits a modal-type stall behavior. With increasing eccentricity, rotating stall onset flow coefficient increases, but the subsequent surge appears at the same flow coefficient of 0.0218.