• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.91-93
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• 2003

A comprehensive numerical study is carried out to investigate for the understanding of the flow evolution and flame development in a supersonic combustor with normal injection of ncumally injecting hydrogen in airsupersonic flows. The formulation treats the complete conservation equations of mass, momentum, energy, and species concentration for a multi-component chemically reacting system. For the numerical simulation of supersonic combustion, multi-species Navier-Stokes equations and detailed chemistry of H2-Air is considered. It also accommodates a finite-rate chemical kinetics mechanism of hydrogen-air combustion GRI-Mech. 2.11[1], which consists of nine species and twenty-five reaction steps. Turbulence closure is achieved by means of a k-two-equation model (2). The governing equations are spatially discretized using a finite-volume approach, and temporally integrated by means of a second-order accurate implicit scheme (3-5).The supersonic combustor consists of a flat channel of 10 cm height and a fuel-injection slit of 0.1 cm width located at 10 cm downstream of the inlet. A cavity of 5 cm height and 20 cm width is installed at 15 cm downstream of the injection slit. A total of 936160 grids are used for the main-combustor flow passage, and 159161 grids for the cavity. The grids are clustered in the flow direction near the fuel injector and cavity, as well as in the vertical direction near the bottom wall. The no-slip and adiabatic conditions are assumed throughout the entire wall boundary. As a specific example, the inflow Mach number is assumed to be 3, and the temperature and pressure are 600 K and 0.1 MPa, respectively. Gaseous hydrogen at a temperature of 151.5 K is injected normal to the wall from a choked injector.A series of calculations were carried out by varying the fuel injection pressure from 0.5 to 1.5MPa. This amounts to changing the fuel mass flow rate or the overall equivalence ratio for different operating regimes. Figure 1 shows the instantaneous temperature fields in the supersonic combustor at four different conditions. The dark blue region represents the hot burned gases. At the fuel injection pressure of 0.5 MPa, the flame is stably anchored, but the flow field exhibits a high-amplitude oscillation. At the fuel injection pressure of 1.0 MPa, the Mach reflection occurs ahead of the injector. The interaction between the incoming air and the injection flow becomes much more complex, and the fuel/air mixing is strongly enhanced. The Mach reflection oscillates and results in a strong fluctuation in the combustor wall pressure. At the fuel injection pressure of 1.5MPa, the flow inside the combustor becomes nearly choked and the Mach reflection is displaced forward. The leading shock wave moves slowly toward the inlet, and eventually causes the combustor-upstart due to the thermal choking. The cavity appears to play a secondary role in driving the flow unsteadiness, in spite of its influence on the fuel/air mixing and flame evolution. Further investigation is necessary on this issue. The present study features detailed resolution of the flow and flame dynamics in the combustor, which was not typically available in most of the previous works. In particular, the oscillatory flow characteristics are captured at a scale sufficient to identify the underlying physical mechanisms. Much of the flow unsteadiness is not related to the cavity, but rather to the intrinsic unsteadiness in the flowfield, as also shown experimentally by Ben-Yakar et al. [6], The interactions between the unsteady flow and flame evolution may cause a large excursion of flow oscillation. The work appears to be the first of its kind in the numerical study of combustion oscillations in a supersonic combustor, although a similar phenomenon was previously reported experimentally. A more comprehensive discussion will be given in the final paper presented at the colloquium.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.2
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• pp.115-123
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• 2013

Stoker type incinerator is one of the most popular one used as municipal solid waste (MSW) incineration because, in general, it is quite suitable for large capacity and need no preprocessing facility. Nowadays, however, since the combustible portion of incoming MSW increases together with the decrease of the moisture content due to prohibition of directly burying food waste in landfill, the heating value of waste is remarkably increasing in comparison with the early stage of incinerator installation. Consequently, the increased heating value in incinerator operation causes a number of serious problems such as reduction of waste amount to be burned due to the boiler heat capacity together with the significant NO generation in high temperature environment. Therefore, in this study, a series of numerical simulation have been made as parameters of waste amount and the fraction of moisture in air stream in order to investigate optimal operating condition for the resolution of the problems associated with the high heating value of waste mentioned above. In specific, a detailed turbulent reaction flow field calculation with NO model was made for the full scale incinerator of D city. To this end, the injection method of moisturized air as oxidizer was intensively reviewed by the addition of moisture water amount from 10% and 20%. The calculation result, in general, showed that the reduction of maximum flame temperature appears consistently due to the combined effects of the increased specific heat of combustion air and vaporization heat by the addition of water moisture. As a consequence, the generation of NOx concentration was substantially reduced. Further, for the case of 20% moisture amount stream, the afterburner region is quite appropriate in temperature range for the operation of SNCR. This suggests the SNCR facility can be considered for reoperation. which is not in service at all due to the increased heating value of MSW.

• Journal of Korea Water Resources Association
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• v.54 no.12
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• pp.1243-1254
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• 2021

For water resources operation or agricultural water management, it is important to accurately predict evapotranspiration for a long-term future over a seasonal or monthly basis. In this study, reference evapotranspiration forecast (up to 12 months in advance) was performed using statistically predicted monthly temperatures and temperature-based Hamon method for the Han River basin. First, the daily maximum and minimum temperature data for 15 meterological stations in the basin were derived by spatial-temporal downscaling the monthly temperature forecasts. The results of goodness-of-fit test for the downscaled temperature data at each site showed that the percent bias (PBIAS) ranged from 1.3 to 6.9%, the ratio of the root mean square error to the standard deviation of the observations (RSR) ranged from 0.22 to 0.27, the Nash-Sutcliffe efficiency (NSE) ranged from 0.93 to 0.95, and the Pearson correlation coefficient (r) ranged from 0.97 to 0.98 for the monthly average daily maximum temperature. And for the monthly average daily minimum temperature, PBIAS was 7.8 to 44.7%, RSR was 0.21 to 0.25, NSE was 0.94 to 0.96, and r was 0.98 to 0.99. The difference by site was not large, and the downscaled results were similar to the observations. In the results of comparing the forecasted reference evapotranspiration calculated using the downscaled data with the observed values for the entire region, PBIAS was 2.2 to 5.4%, RSR was 0.21 to 0.28, NSE was 0.92 to 0.96, and r was 0.96 to 0.98, indicating a very high fit. Due to the characteristics of the statistical models and uncertainty in the downscaling process, the predicted reference evapotranspiration may slightly deviate from the observed value in some periods when temperatures completely different from the past are observed. However, considering that it is a forecast result for the future period, it will be sufficiently useful as information for the evaluation or operation of water resources in the future.

• Journal of Korea Water Resources Association
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• v.54 no.9
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• pp.731-745
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• 2021

In this study, the monthly temperature of the Han River basin was predicted by statistical multiple regression models that use global climate indices and weather data of the target region as predictors. The optimal predictors were selected through teleconnection analysis between the monthly temperature and the preceding patterns of each climate index, and forecast models capable of predicting up to 12 months in advance were constructed by combining the selected predictors and cross-validating the past period. Fore each target month, 1000 optimized models were derived and forecast ranges were presented. As a result of analyzing the predictability of monthly temperature from January 1992 to December 2020, PBIAS was -1.4 to -0.7%, RSR was 0.15 to 0.16, NSE was 0.98, and r was 0.99, indicating a high goodness-of-fit. The probability of each monthly observation being included in the forecast range was about 64.4% on average, and by month, the predictability was relatively high in September, December, February, and January, and low in April, August, and March. The predicted range and median were in good agreement with the observations, except for some periods when temperature was dramatically lower or higher than in normal years. The quantitative temperature forecast information derived from this study will be useful not only for forecasting changes in temperature in the future period (1 to 12 months in advance), but also in predicting changes in the hydro-ecological environment, including evapotranspiration highly correlated with temperature.

• Korean Journal of Environment and Ecology
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• v.37 no.6
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• pp.429-438
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• 2023

The forest in the lower Tumen River serves as an important ecosystem spanning the territories of North Korea, Russia, and China, and it provides habitat and movement corridors for diverse mammals, including the endangered Amur tiger (Panthera tigris) and Amur leopard (Panthera pardus). This study focuses on the Mijiang area, situated as a potential ecological corridor connecting North Korea and China in the lower Tumen River, playing a crucial role in conserving and restoring the biodiversity of the Korean Peninsula. This study aimed to identify mammal species and estimate their relative abundance, occupancy, and distribution based on the 48 camera traps installed in the Mijiang area from May 2019 to May 2021. The results confirmed the presence of 18 mammal species in the Mijiang area, including large carnivores like tigers and leopards. Among the dominant mammals, four species of ungulates showed high occupancy and detection rates, particularly the Roe deer (Capreolus pygargus) and Wild boar (Sus scrofa). The roe deer was distributed across all areas with a predicted high occupancy rate of 0.97, influenced by altitude, urban residential areas, and patch density. Wild boars showed a predicted occupancy rate of 0.73 and were distributed throughout the entire area, with factors such as wetland ratio, grazing intensity, and spatial heterogeneity in aspects of the landscape influencing their occupancy and detection rates. Sika deer (Cervus nippon) exhibited a predicted occupancy rate of 0.48, confined to specific areas, influenced by slope, habitat fragmentation diversity affecting detection rates, and the ratio of open forests impacting occupancy. Water deer (Hydropotes inermis) displayed a very low occupancy rate of 0.06 along the Tumen River Basin, with higher occupancy in lower altitude areas and increased detection in locations with high spatial heterogeneity in aspects. This study confirmed that the Mijiang area serves as a habitat supporting diverse mammals in the lower Tumen River while also playing a crucial role in facilitating animal movement and habitat connectivity. Additionally, the occupancy prediction model developed in this study is expected to contribute to predicting mammal distribution within the disrupted Tumen River basin due to human interference and identifying and protecting potential ecological corridors in this transboundary region.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.40 no.4
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• pp.1-14
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• 2022

The ancient North-East Asian royal garden is divided into three types, located in the north inside the palace, in the north outside the palace, and in the south inside or outside the palace, depending on the location relationship between the royal capital and the royal palace. The first is a typical royal garden that follows the ancient Chinese court system of the Chao-hu-chim(前朝後寢). The second is a royal garden located independently of the royal palace, which extends to Geumwon(禁苑). The third is located in the south of royal palace and is the royal garden specialized in Yurak(遊樂) or Hyangyeon(饗宴). The types of ancient North-East Asian royal gardens are classified according to the relationship between main palace(正宮) and secondary palace(別宮), detached palace(離宮), and Geumwon(禁苑), and each has unique characteristics. The first has been established as the garden of the main palace, including the royal garden at Wanggung-ri site in Iksan(益山 王宮里 遺蹟), Han Chang'an capital(漢 長安城), BeiWei Luoyang capital(北魏 洛陽城), Jiankang capital in Southern Dynasties(南朝 建康城), and Daminggong(大明宮) in Tang Dynasty. Here, the royal garden is divided into Naewon(內苑) inside the royal palace and Geumwon(禁苑), outside the royal palace. On the other hand, the second is the royal garden that the royal palace and Geumwon(禁苑) are united. The third is the royal garden that forms part of the royal palace or is independent of the royal palace, and has been specialized as a secondary palace(別宮) and detached palace(離宮). China created the model of ancient North-East Asian royal gardens, and based on this, Baekje, Silla, and Japan of Korea influenced each other and developed a unique palace by showing their originality. The royal garden at Wanggung-ri site in Iksan(益山 王宮里 遺蹟) was influenced by royal gardens of Wei-Jin and Northern & Southern Dynasties(魏晉南北朝). And royal gardens of the Sabi Capital(泗沘都城) were influenced by royal gardens of Jin(秦), Han(漢), Sui(隋), and Tang(唐), and royal gardens of Silla(新羅) were influenced by the royal gardens of Baekje(百濟) and Silla. However, each of these royal gardens also has its own unique characteristics. From this aspect, it can be seen that the ancient North-East Asian court had different lineages depending on the region. Anhakgung Palace in Pyongyang(平壤 安鶴宮) is more likely to be viewed as the Three Kingdoms period than the Goryeo Dynasty. However, it is difficult to raise it to the 5th and 6th centuries due to the overlapping relationship and relics of the lower part of Anhakgung Palace(安鶴宮), and it is generally presumed to be the middle of the 7th century. The royal garden at Anhakgung Palace is a secondary palace(別宮) or detached palace(離宮) that corresponds to the palace of Jang-an capital(長安城) in Pyongyang and is believed to have influenced Dongwon garden(東院庭園) of Heijokyu(平城宮) and Donggung(東宮) and Wolji(月池) in Gyeongju. From this point of view, Dongwon garden(東院庭園) of Heijokyu(平城宮) seems to be related to the palaces of Goguryeo, Baekje, and Silla. This study has many limitations as it focuses on its characteristics and transitions due to the location of the palace in the large framework of ancient North-East Asian royal capital. If these limitations are resolved little by little, it is expected that the understanding of ancient North-East Asian royal gardens will be much wider.