An experimental Research on the Pressure Fluctuation due to Hydraulic Jump for the Design Reflection of Apron

HyungJu Yoo,DongHyun Kim,SoekIl Jeong,Seungoh Lee 한국콘텐츠학회 2018 한국콘텐츠학회 ICCC 논문집 Vol.2018 No.12

통계적 접근을 통한 하천 횡단구조물 하부의 압력 변동성 및 수면 변위 특성 분석

유형주(Yoo Hyungju),이승오(Lee Seoungoh),박문형(Park Moonhyung) 한국방재학회 2018 한국방재학회논문집 Vol.18 No.6

돌발성 강우 등 기후변화로 인하여 보 하류 구조물의 안정성에 많은 문제가 발생하고 있다. 보 안정성에 영향을 끼치는 다양한 요인 중 도수로 인한 압력변동성도 주요 원인이 될 수 있다. 이에 본 연구에서는 보 상ㆍ하류 수심 비를 이용하여 다양한 흐름조건에서 도수로 인한 압력변동성 및 수면변위를 수리실험을 통하여 분석하였다. 이상치 제거 등 측정 자료의 신뢰성을 높인 후, 선행 연구를 통하여 도수 특성을 검토하였다. 상ㆍ하류 수심 비 및 Froude 수가 증가함에 따라 최대, 최소 압력의 크기가 증가하는 것을 확인하였고, 최대ㆍ최소 압력의 발생 위치는 일정 Froude 수 이상에서 각각 도수길이의 30%, 20% 지점에서 발생하였다. 또한, 상관분석을 통하여 압력 변동성과 수면 변동성이 강한 양의 관계를 갖는 것을 확인하였다. 향후 다양한 도수 발생 조건에서 압력 변동성과 수면변동성의 정량적인 관계를 도출해 낸다면, 보 하류 구조물 설계인자 도출에 기여할 수 있을 것으로 판단된다. Abnormal climate change poses serious risks to the stability of river-crossing structures; these risks include piping, local bed scour and pressure fluctuation caused by hydraulic jumps. In this study, pressure fluctuation and free surface displacement were investigated by hydraulic experiments under various water depth ratios between the upstream and downstream sections of a weir. After removing outlier data by applying a statistical approach based on the confidence interval concept, the characteristics of a hydraulic jump were calculated from experimental results and compared to the results of previous studies. It was found that the maximum and minimum pressures increased with the water depth ratio and Froude number. In addition, above a certain Froude number, the maximum and minimum pressures occurred at 30% and 20% of the length of the hydraulic jump, respectively. The correlation analysis also indicated a strong positive relationship between the pressure fluctuation and the free surface fluctuation. Further quantification of this relationship under various hydraulic jump conditions would be useful for the design of the apron and bed protection.

Chemical Doping Effects in Multilayer MoS₂ and Its Application in Complementary Inverter

Yoo, Hocheon,Hong, Seongin,On, Sungmin,Ahn, Hyungju,Lee, Han-Koo,Hong, Young Ki,Kim, Sunkook,Kim, Jae-Joon American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.27

<P>Multilayer MoS<SUB>2</SUB> has been gaining interest as a new semiconducting material for flexible displays, memory devices, chemical/biosensors, and photodetectors. However, conventional multilayer MoS<SUB>2</SUB> devices have exhibited limited performances due to the Schottky barrier and defects. Here, we demonstrate poly(diketopyrrolopyrrole-terthiophene) (PDPP3T) doping effects in multilayer MoS<SUB>2</SUB>, which results in improved electrical characteristics (∼4.6× higher on-current compared to the baseline and a high current on/off ratio of 10<SUP>6</SUP>). Synchrotron-based study using X-ray photoelectron spectroscopy and grazing incidence wide-angle X-ray diffraction provides mechanisms that align the edge-on crystallites (97.5%) of the PDPP3T as well as a larger interaction with MoS<SUB>2</SUB> that leads to dipole and charge transfer effects (at annealing temperature of 300 °C), which support the observed enhancement of the electrical characteristics. Furthermore, we demonstrate a complementary metal-oxide-semiconductor inverter that uses a p-type MoSe<SUB>2</SUB> and a PDPP3T-doped MoS<SUB>2</SUB> as charging and discharging channels, respectively.</P> [FIG OMISSION]</BR>

Air-stable and balanced split-gate organic transistors

Yoo, Hocheon,Nakano, Masahiro,On, Sungmin,Ahn, Hyungju,Lee, Han-Koo,Takimiya, Kazuo,Kim, Jae-Joon Elsevier 2018 Organic electronics Vol.63 No.-

<P><B>Abstract</B></P> <P>Ambipolar organic electronics have been gaining interest as a simple alternative technology for implementing complementary-like circuits. Although practical applications require stable operation in the air, most previous studies on ambipolar organic electronics have reported results measured in high vacuum or N<SUB>2</SUB> atmosphere only. This is because ambipolar properties change to asymmetric p-type dominant or unipolar p-type characteristics when exposed to air. Little effort has been put into the fundamental investigation of the effects of the environmental atmosphere on ambipolar organic semiconductors. In this paper, we demonstrate ambipolar OTFTs with balanced p/n characteristics under ambient air using poly{[<I>N</I>,<I>N</I>′-bis(3-decylpentadecyl)-naphtho[2,3-<I>b</I>:6,7-<I>b</I>′]dithiophene-4,5,9,10-tetracarboxidiimide-2,7-diyl]-<I>alt</I>-5,5′-(2,2′-bithiophene)} (PNDTI-BT-DP). Based on the analysis using XPS, UPS, and electrical characterizations at various atmosphere, we concluded that the PNDTI-BT-DP has 0.45 eV higher than the target value for ambiplar charge injections with respect to Au contact electrode. The energy level of the PNDTI-BT-DP was up-shifted by 0.45 eV when the film was exposed to ambient air, which resulted in a change in the electrical properties. As a proof-of-concept application, we demonstrate the air-stable split-gate OTFTs that operate as either a unipolar p- or n-type device based on electrical control. Finally, we report results showing that the device characteristics for both p- or n-type operations were maintained after ∼120 h of atmospheric exposure.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Comprehensive analysis on air exposure effects by means of XPS, UPS, and electrical characterizations. </LI> <LI> Balanced p/n characteristics including mobility, turn-on voltage, and threshold voltage. </LI> <LI> Demonstration of air-stable split-gate organic transistors. </LI> <LI> Selective p- or n-type operation with on/off current ratio (~10<SUP>4</SUP>) for more than 120 h in ambient air. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>This study suggests a design methodology for air-stable ambipolar materials such that the HOMO/LUMO level of the ambipolar material is 0.3–0.5 eV higher than the target value to compensate for an eventual upward shift that occurs when the device is exposed to ambient air. Based on the methodology, we demonstrate air-stable split-gate OTFTs that show balanced p/n characteristics after ∼120 h of air exposure.</P> <P>[DISPLAY OMISSION]</P>

환경조절장치용 미세유로형 증발열교환기의 성능특성 연구

이형주(Hyungju Lee),유영준(Youngjune Yoo),민성기(Seongki Min),황기영(Kiyoung Hwang) 한국추진공학회 2011 한국추진공학회 학술대회논문집 Vol.2011 No.11

본 논문에서는 항공기 탑재용 환경조절장치에 사용하기 위한 미세유로형 증발열교환기의 성능 특성에 관한 연구결과를 제시하였다. 미세유로형 증발열교환기는 가능한한 적은 양의 냉매로 고온부의 열량을 흡수할 수 있도록 저온부 냉매의 증발잠열을 이용하고 단위 체적당 열전달 면적의 극대화를 위해 미세유로를 이용하는 개념이다. 설계된 공기 및 냉각수 유로를 에칭을 통해 가공하고, 이들을 적층하여 브레이징으로 접합한 후 입출구 포트를 용접함으로써 열교환기를 제작하였다. 제작된 열교환기는 기본 성능시험을 통해 요구조건대로 설계/제작되었음을 확인하였고, 다양한 운용조건에 대한 성능 맵 시험을 수행하여 입구 공기온도, 공기 유량 및 냉각수 유량 변화에 따른 열교환 성능특성을 정량적으로 파악하였다. An experimental study on performance characteristics of an evaporative heat exchanger based on tests for various operating conditions was presented. The heat exchanger maximizes the heat transfer rate per unit volume by applying mini-channels for both the air and coolant flow paths, and minimizes the amount of the coolant by using its latent heat of evaporation. The heat exchanger was manufactured by etching the flow paths, brazing the heat exchange plates, and welding the in/out ports of the media. The basic performance test has confirmed that the heat exchanger met its design requirements, and the results of the map test were analyzed to produce the performance characteristics quantitatively depending on the air inlet temperature, the air flow rate, and the coolant flow rate.

Nanoporous Block Copolymer Membranes for Ultrafiltration: A Simple Approach to Size Tunability

Ahn, Hyungju,Park, Sungmin,Kim, Sang-Woo,Yoo, Pil J.,Ryu, Du Yeol,Russell, Thomas P. American Chemical Society 2014 ACS NANO Vol.8 No.11

<P>Nanoporous structures were obtained by the self-assembly of polystyrene-<I>b</I>-poly(methyl methacrylate) (PS-<I>b</I>-PMMA) block copolymers (BCP) where, in thick films, cylindrical microdomains were oriented normal to the substrate and air interfaces, and in the interior of the films, the microdomains were randomly oriented. Continuous nanopores that penetrated through the film were readily produced by a simple preferential swelling of the PMMA microdomains. The confined swelling and rapid contraction of PMMA microdomains generated well-defined uniform pores with diameters to 17.5 nm. The size selectivity and rejection of Au nanoparticles (NPs) for these ultrafiltration (UF) membranes were demonstrated, suggesting an efficient route to tunable, noncomponent-degradative UF membranes.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-11/nn505234v/production/images/medium/nn-2014-05234v_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn505234v'>ACS Electronic Supporting Info</A></P>

물의 증발잠열을 이용하는 미니채널 열교환기의 실험적 연구

이형주(Hyungju Lee),유영준(Youngjune Yoo),민성기(Seongki Min) 한국추진공학회 2010 한국추진공학회 학술대회논문집 Vol.2010 No.11

본 연구에서는 물의 증발잠열을 이용한 새로운 형태의 미니채널 열교환기의 제작 및 시험결과를 제시하였다. 서로 다른 세가지 형태의 물 유로를 가지는 열교환기를 제작하여 주어진 설계조건에서 실험을 통해 서로간의 냉각성능 및 압력손실 효과를 확인하였다. 고려된 세 가지 형태의 물 유로 형상에 대한 실험 결과 완전식각된 Type 2 열교환기의 공기 냉각성능이 가장 우수한 것으로 확인되었으며, 따라서 향후 제작성 및 열교환 성능을 고려하면 Type 2를 채택하는 것이 타당할 것으로 생각된다. 그러나 고온조건에서의 실험 결과 Type 1의 성능도 우수한 것으로 확인되어 고온조건의 운용을 고려할 경우에는 Type 1에 대한 추가의 성능 및 특성 확인시험을 통한 보다 면밀한 분석이 필요하다. 본 연구로 개발된 열교환기는 항공기용 환경조절장치 적용을 목표로 하였으며, 특히 공간과 중량의 제한이 있는 이동시스템 내에서 유한한 시간동안 외부로부터 냉매의 추가 공급 없이 많은 열을 흡수해야 하는 경우에 효과적으로 이용될 수 있을 것으로 기대된다. The present study shows some results of developing evaporative heat exchangers with mini-channels. Heat exchangers with three different water paths were manufactured and tested to compare performances of cooling and pressure drop. Among the three types of heat exchangers, Type 2 with full-etching was proved to be the best in the cooling performances for considered operating conditions, and thus it is recommended to adopt Type 2 for its simplicity of production and outstanding performance. However, Type 1 was shown to be better when it is operated at a high air inlet temperature condition. The developed evaporative heat exchanger will be installed in Environmental Control Systems(ECSs) for aerial vehicles, and it can be used effectively in case an ECS is not only limited in its weight and volume but also required to absorb heats without supplying water (or a coolant) for a certain period of time.

Prediction of Clogging sediment in offline Detention Storage System with Numerical Particle Tracking Method

DongHyun Kim,Hyungju Yoo,Seung-Jin Maeng,Seungoh Lee 한국콘텐츠학회 2018 한국콘텐츠학회 ICCC 논문집 Vol.2018 No.12

Low-Temperature Solution-Processed Soluble Polyimide Gate Dielectrics: From Molecular-Level Design to Electrically Stable and Flexible Organic Transistors

Park, Hyunjin,Yoo, Sungmi,Ahn, Hyungju,Bang, Joohee,Jeong, Yuri,Yi, Mihye,Won, Jong Chan,Jung, Sungjune,Kim, Yun Ho American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.49

<P>Aromatic soluble polyimides (PIs) have been widely used in organic field-effect transistors (OFETs) as gate dielectric layers due to their promising features such as outstanding chemical resistance, thermal stability, low-temperature processability, and mechanical flexibility. However, the molecular structures of soluble PIs on the electrical characteristics of OFETs are not yet fully understood. In this work, the material, dielectric, and electrical properties are evaluated to systematically investigate the chemical structure effect of aromatic dianhydride and diamine monomers on the device performance. Four soluble PIs based on 4,4'-(Hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 5-(2,5-Dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, in which the monomeric precursors contain different backbones, side groups, and linkages, were employed to compare the chemical structure impact. The dielectric properties, which significantly affect the charge transport and crystallinity of OSC thin films, clearly depended on the soluble PI types as well as the surface energy and the thermal stability. Furthermore, the electrical characteristic measurement and parameter extraction of OFETs based on TIPS-pentacene revealed that the 6FDA-based soluble PIs, which lead to high field-effect mobility, near-zero threshold electric field, and outstanding electrical stability under bias stress, are the most promising gate dielectric candidates. Finally, low-temperature solution-processed OFETs are successfully integrated with ultrathin flexible substrates, and they exhibit no significant electrical performance loss after mechanical flexibility tests. This work presents a step forward in the development of soluble PI gate dielectrics for flexible electronic devices with high device performance.</P> [FIG OMISSION]</BR>

시행 착오법을 활용한 재난 위험도 예측모델 개발 : 폭풍해일

김동현,유형주,정석일,이승오,Kim, Dong Hyun,Yoo, HyungJu,Jeong, SeokIl,Lee, Seung Oh 한국방재안전학회 2018 한국방재안전학회 논문집 Vol.11 No.2

태풍에 의해 발생하는 폭풍해일은 태풍의 경로, 강도, 발생위치 등을 예측하기가 어려운 실정이기 때문에 발생 시나리오를 기반으로 연구가 수행되어왔다. 국내는 다양한 시나리오에 대해 수치모의를 수행하였고 그 결과를 침수 예측지도로 제작하였다. 하지만, 이 같은 방법은 수행한 시나리오 외에 발생가능한 모든 경우에 대해 예측하기 어렵고, 실제로 수치모의 수행시간이 길기 때문에 실시간으로 대응하기 어렵다는 단점이 있다. 따라서 본 연구에서는 기존의 데이터베이스를 활용하여 폭풍해일의 위험도를 예측하는 방법을 개발하였다. 동해안 지역을 대상으로 폭풍해일에 의한 위험도 예측을 수행하였고 예측을 위한 방정식을 산정하기 위해 COMSOL AB사에서 개발한 COMSOL을 이용하였다. 몇 가지 가정사항과 제한조건으로 기본방정식을 유도하였으며 방정식의 계수와 상수는 시행착오법으로 도출하였다. 그 결과, 해일에 의한 침수 예측지도와 공간적 분포는 지도의 상부를 제외하면 매우 유사하게 나타났다. 오차가 큰 지도 상부의 경우 기초 데이터로 사용한 지도의 해상도로 인해 저항상수 k의 값이 제대로 반영되지 못한 것으로 판단된다. SIND 모형은 실시간 예측이 가능한 모형으로 향후 모형의 정확성을 향상시킨다면 이상기후로 인해 재난이 발생하였을 경우 빠르게 대처가 가능할 것으로 기대된다. The storm surge is caused by an typhoons and it is not easy to predict the location, strength, route of the storm. Therefore, research using a scenario for storms occurrence has been conducted. In Korea, hazard maps for various scenarios were produced using the storm surge numerical simulation. Such a method has a disadvantage in that it is difficult to predict when other scenario occurs, and it is difficult to cope with in real time because the simulation time is long. In order to compensate for this, we developed a method to predict the storm surge damage by using research database. The risk grade prediction for the storm surge was performed predominantly in the study area of the East coast. In order to estimate the equation, COMSOL developed by COMSOL AB Corporation was utilized. Using some assumptions and limitations, the form of the basic equation was derived. the constants and coefficients in the equation were estimated by the trial and error method. Compared with the results, the spatial distribution of risk grade was similar except for the upper part of the map. In the case of the upper part of the map, it was shown that the resistance coefficient, k was calculated due to absence of elevation data. The SIND model is a method for real-time disaster prediction model and it is expected that it will be able to respond quickly to disasters caused by abnormal weather.