• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.3
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• pp.147-155
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• 2022

The accumulated ice and snow during the operation of aircraft and railway vehicles can degrade aerodynamic performance or damage the major components of vehicles. Therefore, it is crucial to predict the temporal growth of ice for operational safety. Numerical simulation of ice is widely used owing to the fact that it is economically cheaper and free from similarity problems compared to experimental methods. However, numerical simulation of ice generally divides the analysis into multi-step and assumes the quasi-steady assumption that considers every time step as steady state. Although this method enables efficient analysis, it has a disadvantage in that it cannot track continuous ice evolution. The purpose of this study is to construct a surrogate model that can predict the temporal evolution of ice shape using reduced-order modeling. Reduced-order modeling technique was validated for various ice shape generated under 100 different icing conditions, and the effect of the number of training data and the icing conditions on the prediction error of model was analyzed.

• (The)Study of the Eastern Classic
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• no.68
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• pp.283-317
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• 2017

Issues over morality and profit usually address relations between moral principles and material gains. In the history of traditional Oriental philosophy, discussions about them were called "Yi-Li zhi bian." The ideas of Confucius and Mencius also contain various discussions about Yi-Li. Both Confucius and Mencius defined Yi as a value concept to represent "natural," "appropriate" or "just" and regarded Yi as an external moral principle on the one hand and an internal moral emotion on the other hand. They had, at the same time, differences, as well. While Confucius placed importance on the external and acquired nature of Yi as a goal of morality, Mencius argued for the internal and innate nature of Yi as the nature of morality partially while recognizing its externality overall. Such Yi is a general term for subjective moral emotions and objective moral principles. Li was a concept of fact to represent "gain," "profit" or "profit-making." Both of them were against private interest and emphasized public interest. As for their differences, Confucius was positive about Li to some degree by saying "One should think of Yi when making profit," whereas Mencius was almost negative about Li and perceived it to be for Yi by saying "One should give up even his own life for Yi." He meant Li's dependence on Yi and also Yi's absoluteness for Ri. Both of them found a mix of opposite features in Yi such as internality and externality, subjectivity and objectivity, specificity and generality, and uniqueness and universality and also in Li such as individuality and specialty and public and private interest. Those features have both disadvantages including theoretical irrationality and logical contradiction and advantages including ideological diversity and conceptual polysemy. If efforts are made to avoid their disadvantages and highlight their advantages, they will provide some elements to consult in the creation of new global ethics required today when East and West are becoming one. In the modern society, the Yi-Li issues can be divided into the issues of morality and economy, personal and social profit, and moral ideal and material gain. If these modern Yi-Li issues are combined with the traditional Yi-Li issues, two paths will emerge over the order of Yi-Li. Of the many perceptions of Yi-Li issues of Confucius and Mencius, the idea of "Yi First, Li Later" can be very useful for creating a new ethics theory to represent "humanism" that we all need today when everyone considers their own pursuit of profit and satisfaction of needs as the best values. Sound Yi-Li relations will be possible only through Yi's orientation toward externality based on internality and Li's pursuit of private interest on the premise of public interest according to the spirit of "Yi First, Li Later."

• Journal of the Korean Institute of Gas
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• v.26 no.3
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• pp.45-53
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• 2022

In order to improve the emission of diesel engines, natural gas-diesel dual fuel combustion compression ignition engines are in the spotlight. In particular, a reactivity controlled compression ignition (RCCI) combustion strategy is investigated comprehensively due to its possibility to improve both efficiency and emissions. With advanced diesel direct injection timing earlier than TDC, it achieves spontaneous reaction with overall lean mixture from a homogeneous mixture in the entire cylinder area, reducing nitrogen oxides (NOx) and particulate matter (PM) and improving braking heat efficiency at the same time. However, there is a disadvantage in that the amount of incomplete combustion increases in a low load region with a relatively small amount of fuel-air. To solve this, sensitive control according to the diesel injection timing and fuel ratio is required. In this study, experiments were conducted to improve efficiency and exhaust emissions of the natural gas-diesel dual fuel engine at low load, and evaluate combustion stability according to the diesel injection timing at the operation point for power generation. A 6 L-class commercial diesel engine was used for the experiment which was conducted under a 50% load range (~50 kW) at 1,800 rpm. Two injectors with different spray patterns were applied to the experiment, and the fraction of natural gas and diesel injection timing were selected as main parameters. Based on the experimental results, it was confirmed that the brake thermal efficiency increased by up to 1.3%p in the modified injector with the narrow-angle injection added. In addition, the spray pattern of the modified injector was suitable for premixed combustion, increasing operable range in consideration of combustion instability, torque reduction, and emissions level under Tier-V level (0.4 g/kWh for NOx).