클리핑방법을 이용한 non-conformal interface 경계를 갖는 열전도 해석

이주희(Juhee Lee),장진우(Jinwoo Jang),이용준(Yongjun Lee),이상환(Sanghwan Lee),이현균(Hyeonkyun Lee) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12

In CFD(Computational Fluid Dynamics) or heat transfer problem using an unstructured grid, it is possible to divide a complex domain into several simple domains. However, the grid points on the interface between two domains are not matched completely so called non-conformal mesh. Thus, mesh handling technique is needed to deal with this problem. Especially, a similar problem occurs in multi-phase or multi-material system. Since fluxes are calculated two neighbor cells sharing a surface in a finite volume method, it is difficult to calculate the proper flux. In order to overcome the problem, we employed the clipping method that calculates the connectivity and geometrical informations between non-conformal cells on the interface. The clipping method is generally used for comptuer graphics and searches the shape information of the overlapped polygons. In this study, we implemented the clipping algorithm that calculates the area and center of overlapped polygons. To validate the clipping method, the 3-dimensional heat conduction with a non-conformal interface was performed and then, it represented the reasonable solutions.

Prediction of Solidification Paths in Al-Si-Fe Ternary System and Experimental Verification: Part II. Fe-Containing Eutectic Al-Si Alloys

Lee, Sanghwan,Kim, Bonghwan,Lee, Sangmok The Japan Institute of Metals 2011 Materials transactions Vol.52 No.6

<P>The effects of Fe content and cooling rate on the solidification path and formation behavior of the Al<SUB>5</SUB>FeSi (β) phase in Fe-containing eutectic Al-Si alloys were studied based on thermodynamic analysis and pertinent experiments. To predict solidification path in Fe-containing eutectic Al-Si alloys, the thermodynamic calculations in the Al-Si-Fe ternary system, including the high Fe region, were systematically performed using the Thermo-Calc program and updated database. To experimentally verify the predicted results, designed two eutectic Al-Si alloys with different Fe levels were solidified under slowly- and rapidly-cooled conditions, respectively. The cooling curves of the solidified alloys were recorded by thermal analysis. Microstructures of the casting samples were studied by the combined analyses of optical microscopy (OM) and scanning electron microscopy (SEM). For the slowly-cooled condition with the high Fe level, the primary β phase was mainly formed by the quasi-peritectic reaction of L+γ→α+β (656°C). For the rapidly-cooled condition with high Fe level, the primary β phase was mainly formed by the reaction of L→β (583∼649°C).</P>

Ambient Fine and Ultrafine Particle Measurements and Their Correlations with Particulate PAHs at an Elementary School Near a Highway

Sanghwan Song,백도명,Young-Mee Lee,Chulwoo Lee,Chunghee Park,Seung-Do Yu 한국대기환경학회 2012 Asian Journal of Atmospheric Environment (AJAE) Vol.6 No.2

Ambient particulate matter (PM) and particle-bound polycyclic aromatic hydrocarbon (PAH) concentrations were measured continuously for 70 days at a Korean elementary school located near a highway. The PM10,PM2.5, and PM1 values were measured with a lightscattering,multi-channel, aerosol spectrometer (Grimm, Model 1.107). The number concentrations of the particles were measured using a scanning mobility particle sizer and counter (SMPS+C) which counted particles from 11.1 to 1083.3 nm classified in 44 channels. Particle-bound PAHs were measured with a direct reading, photoelectric aerosol sensor. The daily NO2, SO2, and CO concentrations were obtained from a national air-monitoring station located near the school. The average concentrations of PM10,PM2.5, and PM1 were 75.3, 59.3, and 52.1 μg/m3, respectively. The average number concentration of the ultrafine particles (UFPs) was 46,307/cm3, and the averaged particle-bound PAHs concentration was 17.9ng/m3 during the study period. The ambient UFP variation was strongly associated with traffic intensity, particularly peak concentrations during the traffic rush hours. Particles ⁄100 nm corresponded to trafficrelated pollutants, including PAHs. Additional longterm monitoring of ambient UFPs and high-resolution traffic measurements should be carried out in future studies. In addition, transient variations in the ambient particle concentration should be taken into consideration in epidemiology studies in order to examine the short-term health effects of urban UFPs.

Risk factors for SARS-CoV-2 transmission during a movie theater outbreak in Incheon in the Republic of Korea, November 2021: a retrospective study

Lee Hye Young,Park Young-Joon,Lee Sang-Eun,Yoo Han-Na,Kim Il-Hwan,No Jin Sun,Kim Eun-Jin,Yu Jungyeon,Bae Sanghwan,Yu Mi 질병관리청 2024 Osong Public Health and Research Persptectives Vol.15 No.1

Objectives: We examined factors contributing to the transmission of an acute respiratory virus within multi-use facilities, focusing on an outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in a movie theater in the Republic of Korea.Methods: This retrospective cohort study involved a descriptive analysis of 48 confirmed cases. Logistic regression was applied to a cohort of 80 theater attendees to identify risk factors for infection. The infection source and transmission route were determined through gene sequencing data analysis.Results: Of the 48 confirmed cases, 35 were theater attendees (72.9%), 10 were family members of attendees (20.8%), 2 were friends (4.2%), and 1 was an employee (2.1%). Among the 80 individuals who attended the 3rd to 5th screenings of the day, 35 became infected, representing a 45.0% attack rate. Specifically, 28 of the 33 third-screening attendees developed confirmed SARS-CoV-2, constituting an 84.8% attack rate. Furthermore, 11 of the 12 cases epidemiologically linked to the theater outbreak were clustered monophyletically within the AY.69 lineage. At the time of the screening, 35 individuals (72.9%) had received 2 vaccine doses. However, vaccination status did not significantly influence infection risk. Multivariate analysis revealed that close contacts had a 15.9-fold higher risk of infection (95% confidence interval, 4.37–78.39) than casual contacts.Conclusion: SARS-CoV-2 transmission occurred within the theater, and extended into the community, via a moviegoer who attended the 3rd screening during the viral incubation period after contracting the virus from a family member. This study emphasizes the importance of adequate ventilation in theaters.

Prediction of Solidification Paths in Al-Si-Fe Ternary System and Experimental Verification: Part I. Fe-Containing Hypoeutectic Al-Si Alloys

Lee, Sanghwan,Kim, Bonghwan,Lee, Sangmok The Japan Institute of Metals 2011 Materials transactions Vol.52 No.5

<P>The effects of Fe content and cooling rate on the solidification path and formation behavior of the Al<SUB>5</SUB>FeSi (β) phase in Fe-containing hypoeutectic Al-Si alloys were studied based on thermodynamic analysis and pertinent experiments. The thermodynamic calculations were performed using the Thermo-Calc program. For analyses in the high alloy region of the Al-Si-Fe ternary system, a thermodynamic database for Thermo-Calc was correctly updated and revised by the collected up-to-date references. For thermodynamics-based predictions of the solidification path in Fe-containing hypoeutectic Al-Si alloys, liquidus projection (including various invariant, monovariant, and bivariant reactions and isotherms) and equilibrium phase fraction were calculated as functions of composition and temperature in the Al-Si-Fe ternary system. The calculated results were compared to experimental results using various casting runs. In order to analyze the solidification path as a function of Fe content, two representative hypoeutectic Al-Si alloys with different Fe levels were designed. To better understand the influence of cooling rate on the formation behavior of the β phase, the two alloys were solidified under slowly- and rapidly-cooled conditions, respectively. The cooling curves of the solidified alloys were recorded by thermal analysis and various important solidification events were detected using the first derivative of the cooling curves. Microstructures of the casting samples were studied by combined analyses of optical microscopy (OM) and scanning electron microscopy (SEM). For the slowly-cooled condition with the high Fe level, the primary β phase enveloping the Al<SUB>8</SUB>Fe<SUB>2</SUB>Si (α) phase was mainly formed by the quasi-peritectic reaction of L + α → (Al) + β (612°C). For the rapidly-cooled condition with the high Fe level, the primary β phase with morphology of a curved needle was mainly formed by the reaction of L → (Al) + β (579∼612°C).</P>

Benzoyl Peroxide의 반복투여 독성과 생식 및 발생독성

송상환(Sanghwan Song),김수현(Su-Hyon Kim),배희경(Heekyung Bae),김미경(Mikyung Kim),구현주(Hyun Ju Koo),박광식(Kwangsik Park),이상균(Sangkyun Lee),박중훈(Joonghoon Park),최은실(Eun-Sil Choi),이문순(Moon-Soon Lee) 한국독성학회 2003 Toxicological Research Vol.19 No.2

This study was carried out to assess the combined repeated dose, reproduction and developmental toxicities of benzoyl peroxide for OECD SIDS (Screening Information Data Set) program. Male and female Sprague-Dawley rats were exposed to benzoyl peroxide at dose levels of 0, 250, 500 and 1,000 mg/kg/day for 29 days for males and for 41~51 days for females. No deaths were found in all animals including control group during exposure period. No hematological effects attributable to benzoyl peroxide were observed in all treated groups. Significant decrease in the weight of testes and epididymis were observed in males at 1,000 mg/kg/day. In females at 1,000 mg/kg/day, slight histopathological effects in uterus such as epithelial vacuolation or hyperplasia were observed. No treatment-related changes in precoital time and rate of copulation, fertility and gestation period were noted in all treated groups. There was no evidence of teratogenic effect of benzoyl peroxide, but body weight of pups at 1,000 mg/kg/day was significantly decreased. NOAEL for combined repeated dose and reproduction/developmental toxicity was 500 mg/kg/day.

초고속 자기부상열차 추진시스템용 선형 동기 전동기의 추력 리플 저감을 위한 근사최적 설계

함상환(SangHwan Ham),김경범(Kyoungbum Kim),이형우(Hyungwoo Lee),이주(Ju Lee) 한국자동차공학회 2010 한국자동차공학회 학술대회 및 전시회 Vol.2010 No.11

In this paper, the basic design of linear synchronous motor(LSM) for high speed propulsion system is performed. By characteristics analysis of designed LSM, peak to peak magnitude of thrust force ripple is almost 88% of total thrust force. Because of this reason, designed LSM required an application of module phase set shift(MPSS) in order to reduce the thrust force ripple. Using design of experiments, Taguchi method, and approximate design, sub optimal design is established.

chandelier garden

이상환(Sanghwan Lee) 한국디자인학회 2016 한국디자인학회 국제초대전도록 Vol.2016 No.12

3차원 입자와법을 이용한 급출발한 원형 제트의 유동해석

이상환(Sanghwan Lee),이호근(Hokeun Lee),안철오(Cheol-O An) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.8

실내 무선 메쉬 네트워크에서의 간섭 최소화를 위한 메쉬 라우터 배치 기법

이상환(Sanghwan Lee) 한국정보과학회 2010 정보과학회 컴퓨팅의 실제 논문지 Vol.16 No.4

무선 메쉬 네트워크는 쉬운 설치와 향상된 커버리지로 인해 많은 관심과 연구가 진행되고 있다. 예를 들면 메쉬 네트워크에서 throughput을 향상시키는 라우팅 프로토콜에 관한 연구나, 메쉬 링크의 품질을 측정하는 방법 등 다양하다. 하지만 이러한 연구들 중 대부분은 메쉬 라우터의 위치가 고정되어있다고 가정한다. 하지만 실내 메쉬 네트워크의 경우 관리자가 메쉬 네트워크를 독점적으로 관리하기 때문에 설치 시에 메쉬 라우터를 설치할 위치를 마음대로 결정할 수 있다. 따라서 처음부터 메쉬 네트워크의 성능을 고려하여 메쉬 라우터를 설치하는 것은 성능향상에 필수적이다. 이 논문에서는 유전자 기반 최적화 알고리즘을 바탕으로 메쉬 네트워크의 특성 (간섭, 패킷 전달 토폴로지 등)을 고려한 메쉬 라우터 위치 선정 기법을 제시한다. 기존에 메쉬 네트워크는 아니지만 다양한 무선 내트워크에서 기지국이나 AP등을 설치하는 문제가 연구되었고, 메쉬 네트워크의 고정된 메쉬 라우터 집합에서 게이트웨이를 선택하는 문제등이 연구되었지만, 메쉬 라우터의 위치를 선택하는데 있어서, 메쉬 라우터들의 위치나 메쉬 라우터 상에서의 패킷 전송 토폴로지에 의한 간섭을 고려한 연구는 없었다. 다양한 시뮬레이션을 통해 이 논문에서 제시된 기법이 랜덤 선택 기법에 비해 30-40%의 향상을 달성하였음을 보였다. Due to the ease of deployment and the extended coverage, wireless mesh networks (WMNs) are gaining popularity and research focus. For example, the routing protocols that enhance the throughput on the WMNs and the link quality measurement schemes are among the popular research topics. However, most of these works assume that the locations of the mesh routers are predetermined. Since the operators in an Indoor mesh network can determine the locations of the mesh routers by themselves, it is essential to the WMN performance for the mesh routers to be initially placed by considering the performance issues. In this paper, we propose a mesh router placement scheme based on genetic algorithms by considering the characteristics of WMNs such as interference and topology. There have been many related works that solve similar problems such as base station placement in cellular networks and gateway node selection in WMNs. However, none of them actually considers the interference to the mesh clients from non-associated mesh routers in determining the locations of the mesh routers. By simulations, we show that the proposed scheme improves the performance by 30-40% compared to the random selection scheme.