충돌분무의 액적 거동에 미치는 비등방성 난류특성의 영향에 대한 수치해석 연구

고권현(G. H. Ko),유홍선(H. S. Ryou) 한국전산유체공학회 2003 한국전산유체공학회지 Vol.8 No.4

It is an aim of this study to perform extensive numerical study for analyzing the anisotropic turbulence effects on spatial and temporal behaviors of droplet for impinging sprays. The turbulence model of Durbin is used for comparisons with the k-E model. The turbulence-induced dispersions of droplets are consider to describe the anisotropy of turbulence effectively and spray/wall interactions are simulated using the model of Lee and Ryou. Present study investigates the overall and the internal structures of impinging diesel sprays such as spray shapes, radius and height of wall sprays, Sauter mean diameter (SMD), local droplet velocity, and local gas velocity and compared the results with experimental data by two adopted turbulence models. When the anisotropy effect of turbulence is included, better predictions for both gas and droplet tangential velocities are obtained, compared to the k-ε model. It is concluded that anisotropic effect of turbulence should be considered for simulating impinging diesel sprays.

Host People's Kindness and Migrant Workers' Cultural Adaptation: Evidence from South Korea

Jihyun Ryou(Jihyun Ryou),Sang-Yeon Kim(Sang-Yeon Kim) 한국학술연구원 2022 Korea Observer Vol.53 No.4

This study purports to determine the predictors of migrant workers' cultural adaptation in South Korea. In the main, we examined the extent to which the level of inter-/intracultural socializing, exposure to local/native media, and host culture receptivity affect the level of cultural adaptation in cognitive, affective, behavioral domains. Potential impacts of demographic factors (e.g., age, sex, ethnicity, marital status, living alone vs. with family, education level, residency in years, perceived cultural similarity) were also explored. To find answers to the research questions, a total of 634 migrant workers from 37 different nations were reached using a snowball sampling. Surveys were collected in 12 districts of Seoul, the capital of South Korea, and 21 adjacent metropolitan areas. Results indicate that intercultural interaction with host people and media exposure to local contents tend to help improve their knowledge about South Korea (e.g., language, culture). With all else equal, migrant workers treated kindly by Koreans at the workplace and in service sectors, and those living with family, compared to those who live alone, tended to enjoy a greater satisfaction with work and life in South Korea and were more willing to stay. Practical implications for Korean policymakers include encouraging competent migrant workers to move together with the family, making administrative efforts to further simplify the documentation process, and initiating public campaigns to raise host culture receptivity among Korean citizens.

Development and Application of a New Spray Impingement Model Considering Film Formation in a Diesel Engine

Ryou, Hong-Sun,Lee, Seong-Hyuk,Ko, Gwon-Hyun,Hong, Ki-Bae The Korean Society of Mechanical Engineers 2001 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.15 No.7

The present article presents an extension to the computational model for spray/wall interaction and liquid film processes that has been dealt with in the earlier studies (Lee and Ryou, 2000a). The extensions incorporate film spread due to impingement forces and dynamic motion induced by film inertia to predict the dynamic characteristics of wall films effectively. The film model includes the impingement pressure of droplets, tangential momentum transfer due to the impinging droplets on the film surface and the gas shear force at the film surface. Validation of the spray/wall interaction model and the film model was carried out for non-evaporative diesel sprays against several sources of experimental data. The computational model for spray/wall interactions was in good agreement with experimental data for both spray radius and height. The film model in the present work was better than the previous static film model, indicating that the dynamic effects of film motion should be considered for wall films. On the overall the present film model was acceptable for predication of the film radius and thickness.

An Experimental and Numerical Study on Thermal Performance of a Regenerator System with Ceramic Honeycomb

Ryou, Hong-Sun,Noh, Dong-Soon,Hong, Sung-Kook,Lee, Seong-Hyuk The Korean Society of Mechanical Engineers 2001 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.15 No.3

The aim of this paper is to perform the experiment and the numerical simulation for investigating the heat transfer in a regenerator system with ceramic honeycomb and to suggest a useful correlation for optimization of the regenerator system. For achieving this, the effects of some parameters were investigated, e. g., switching time, cell size and length of honeycomb on the mean temperature efficiency. The measured temperatures by R-type thermocouples were compared with the predictions by means of the commercial package, STAR-CD. A useful correlation for thermal efficiency was newly proposed as a function of the normalized switching time, defined in terms of switching time, cell size and length of honeycomb. The results showed that the thermal efficiency is above 90% and the normalized heat exchange rate is higher than 80% when the normalized switching time is less than 1000.

A Study on Consumers` Characteristics according to their Fashion Leadership : Focused on Body Cathexis, Self-Efficacy and Shopping Orientation

Ryou, Eun-Jeong 한국의류산업학회 2001 한국의류산업학회지 Vol.3 No.5

The purposes of this study were to determine consumers' characteristics that were shown according to their fashion leadership through examining the differences found with consumers' self-conception like the body cathexis and self-efficacy and clothing shopping orientation. The data were collected from 263 female college students using questionnaire. The results could be summarized as follows: First, the household income, subjective social class and clothing expenditure of the fashion leader group was larger than those of the fashion follower and laggard groups. Second, the fashion leader group showed higher body cathexis than the fashion follower and laggard groups in the lower body, the abdominal region, the bust shape, and the whole body shape. Thirdly, the higher was the fashion leadership, the higher was the self-efficacy. Forth, it was proved that the higher was the fashion leadership, the higher were the clothing shopping orientation such as home-shopping preference, hedonic shopping, impulsive purchasing, and brand loyalty.

The Effects of Water Mist on the Compartment Fire

Ryou, Hong-Sun,Kim, Sung-Chan The Society of Air-Conditioning and Refrigerating 2004 International Journal Of Air-Conditioning and Refr Vol.12 No.1

The present study investigates the fire suppression characteristics using a water mist fire suppression system. Numerical simulations of fire suppression with water mist are performed with considering the interaction of fire plume and water spray. The predicted temperature fields of smoke layer are compared with those of measured data. Numerical results agree with the experimental results within $10^{\circ}C$ in the case without water mist. In the case of fire suppression with water mist, numerical results do not predict well for temperature field in the gradual cooling region after water mist injection. But the predicted results of initial fire suppression are in good agreement with those of measured data. The reason for the discrepancy between predicted and measured data is due to the poor combustion modeling during the injection of water mist. More elaborate models for numerical simulation are required for better predictions of the fire suppression characteristics using water mist.

Investigations of Vacancy Structures Related to Their Growth in <i>h</i> -BN Sheet

Ryou, Junga,Park, Jinwoo,Hong, Suklyun SPRINGER SCIENCE + BUSINESS MEDIA 2017 NANOSCALE RESEARCH LETTERS Vol.12 No.1

<P>The atomic, electronic, and magnetic properties of vacancy structures with triangular shape related to their growth in single hexagonal boron nitride (<I>h</I>-BN) sheet are investigated using density functional theory calculations. We find that the optimized structures of triangular vacancies depend on the vacancy sizes with N-terminated zigzag edge. Then, vacancy structures obtained during the vacancy evolution in <I>h</I>-BN sheet are considered by removing a boron-nitrogen pair (BN pair) from edges of triangular vacancies. The magnetic properties of those vacancy structures are investigated by local density of states and spin densities. It is found that the stability of the optimized structures with a BN missing pair depends on the BN-pair missing position: the most stable structure is a BN-pair missing structure at the edge face region with the smallest magnetic moment.</P>

Low temperature NO adsorption over hydrothermally aged Pd/CeO₂ for cold start application

Ryou, YoungSeok,Lee, Jaeha,Lee, Hyokyoung,Kim, Chang Hwan,Kim, Do Heui Elsevier 2018 CATALYSIS TODAY - Vol.307 No.-

<P><B>Abstract</B></P> <P>Pd/CeO<SUB>2</SUB> catalyst hydrothermally aged at 750°C for 25h was employed for NO adsorption at low temperature (80–160°C). For comparison, Pt or Pt-Pd supported on CeO<SUB>2</SUB> or Al<SUB>2</SUB>O<SUB>3</SUB> catalysts were also applied. Analysis of the hydrothermally aged catalysts clearly indicates that PGM (Pt and/or Pd) on CeO<SUB>2</SUB> is more resistant to sintering than that on Al<SUB>2</SUB>O<SUB>3</SUB> support. Reducibility test of Pd/CeO<SUB>2</SUB> by H<SUB>2</SUB>-TPR exhibits H<SUB>2</SUB> spillover from Pd to CeO<SUB>2</SUB> support, attributed to the strong interaction between Pd and CeO<SUB>2</SUB>. NO adsorption/desorption results demonstrate that CeO<SUB>2</SUB>-based catalysts exhibit superior NO adsorption ability than Al<SUB>2</SUB>O<SUB>3</SUB>-based catalysts. In addition, PGM/CeO<SUB>2</SUB> catalysts shows the desirable desorption temperature for cold start application. The influence of reactant in stream, NO adsorption time, and temperature on low temperature NO adsorption over Pd/CeO<SUB>2</SUB> is also examined to advance the understanding of NO adsorption/desorption behavior. DRIFT results of adsorbed NO<SUB>x</SUB> species on Pd/CeO<SUB>2</SUB> during NO adsorption/desorption prove that NO<SUB>x</SUB> desorption peaks at 250, 300, and 450°C originate from weakly bound nitrite, nitro-nitrito species, and nitrate species, respectively. In Pd/CeO<SUB>2</SUB> catalyst, Pd plays a role in providing additional NO adsorption site arising from the intimate interaction between Pd and CeO<SUB>2</SUB> and promoting the oxidation from adsorbed nitrite to nitrate. It can be summarized that Pd/CeO<SUB>2</SUB> can be a good candidate as low temperature NO adsorption catalyst for cold start application.</P> <P><B>Highlights</B></P> <P> <UL> <LI> PGM on CeO<SUB>2</SUB> is more stable than that on Al<SUB>2</SUB>O<SUB>3</SUB> after hydrothermal treatment. </LI> <LI> CeO<SUB>2</SUB>-based catalyst has better NO adsorption ability than Al<SUB>2</SUB>O<SUB>3</SUB>-based catalysts. </LI> <LI> Pd improves NO adsorption ability of CeO<SUB>2</SUB> by promoting oxidation of NO<SUB>x</SUB> on CeO<SUB>2</SUB>. </LI> <LI> Pd on CeO<SUB>2</SUB> activates new NO adsorption sites which desorb NO at around 300°C. </LI> <LI> Pd/CeO<SUB>2</SUB> has highest NO adsorption capacity and desirable desorption temperature. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

A note on Fuzzy Vietories Topology

Ryou, J.H. Korean Institute of Intelligent Systems 2000 한국지능시스템학회논문지 Vol.10 No.2

We introduce the concept of a fuzzy Vietories topology and we obtain some properties.

OVERBORROWING AND OVERINVESTMENT IN EAST ASIA : THE CASE OF THE KOREAN FIRMS

RYOU, JAI-WON,KIM, TAE-JOON 한국경제학회 2003 The Korean Economic Review Vol.19 No.2

This paper examines whether there has been overinvestment by Korean firms in the 1990s, particularly during the few years leading up to the crisis in Korea. Overinvestment is defined as the statistically significant discrepancy between the forecasted value from an econometric model of investment and the actual investment. Our analysis shows that overinvestment was found most frequently for chaebol firms. Moreover, it was most evident in a few industries showing viable exports in the 1990s, such as electronic and communication equipments, basic metals and transport equipments other than motor vehicles. However, capital account liberalization was not found critical in inducing overinvestment. Overinvestment by chaebols during 1994-1996 period indicates that loosening strict restrictions on lending in the financial sector to chaebols backfired. In this sense, the Korean crisis was caused by structural weaknesses in corporate and financial sectors.