크기 효과와 열 경계 저항을 고려한 다결정 초격자 황화아연 나노와이어의 열전도율 예측

문정환(Junghwan Moon),Min Zhou,조맹효(Maenghyo Cho) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11

The thermal conductivity of single-crystalline ZnS nanowires with the wurtzite (WZ), zinc-blende (ZB) and polytypic superlattice structures at 300K is analyzed using the reverse non-equilibrium molecular dynamics (NEMD) approach. The focus is on the effect of phonon scattering on the thermal transport in superlattice nanowires (SLNWs) with periodic lengths of 1.85-29.62 nm and specimen lengths of 14.81-59.25 nm. Results show that the conductivity of ZnS SLNWs (2-6 W/mK) is up to 55% lower than that of the corresponding single-crystalline nanowires. As the periodic length of the wires and the overall wires decrease, the conductivity further decreases by up to 30%. A relation between the thermal conductivity of the wires and the effective mean free path is established using the kinetic theory of heat conduction and the acoustic mismatch model. The predictions by the models and NEMD results are in a good agreement.

발전플랜트 지중 냉각수 취수시스템의 서지 해석에 관한 연구

문정환(Junghwan Moon),김진호(Jin-Ho Kim),이승철(Seung-Chul Lee) 대한설비공학회 2021 설비공학 논문집 Vol.33 No.11

In this study, surge analysis was performed to investigate the risk for overflow in a pump station of power plant with different design cases. In case of a reference model with intake bay length of 36 m, the water level of pump station increased to a maximum of 4.1 m if all intake pumps stopped. This result means that there is no overflow at the pump station, the launching shaft, or the end shaft. In case of alternative model with inlet bay length shorter than the reference model by 9 m, there was no possibility of overflow occurrence since the water level of pump station increased up to 4.4 m. If four pumps were tripped, the water level of pump station increased under the height of structure in both reference and alternative models. It was found that the stability of sea water intake system could be secured in spite of a reduction of inlet bay length for construction cost reduction.

수공양용 수직이착륙 무인항공기(VTOL)을 활용한 해양 교통 및 안전 발전전략에 관한 연구

문정환(JungHwan Moon) 한국해양교통학회 2022 Journal of Korean Association of Maritime Transpor Vol.1 No.1

본 연구에서는 해양교통 및 안전에 있어서 무인항공기의 활용 및 효과를 높이기 위해서 수공양용이라는 공간적 범위와 VTOL이라는 운용상의 제약을 해결할 수 있는 무인항공기에 대하여 PEST-7S-SWOT 분석을 연계하여 외부 및 내부 환경분석을 실시하고 이를 Matirx분석을 통해 수공양용 VTOL 발전방향을 수립하고 추진전략을 도출했다. 우선, 해양환경이라는 특수성을 고려해야 한다. 해양교통 및 안전을 위한 목적에 따라 무인항공기가 운영되기 위해서는 공간적인 제약을 극복한 수공양용이 가능해야 하고, 악천후 등의 환경적 제약과근해, 원거리 등의 지리적 제약을 극복할 수 있는 기술개발이 필요하다. 둘째, 기술개발뿐만 아니라 산업으로의 성장을 위한 생태계를 조성하기 위해 수공양용 VTOL 법제도적 지원과 범죄악용 예방과 처벌 기준을 마련해야 한다. 셋째, 융복합 기술을 활용하여 해양교통 및 안전 서비스를 제공하기 위하여 AI 및 자율항법을 탑재하고, 증강현실(AR), 가상현실(VR) 등의 메타버스 서비스공간을 마련해야 한다. In this paper, in order to increase the utilization and effectiveness of unmanned aircraft system in maritime traffic and safety, for unmanned aircraft system that can solve the spatial scope of air-sea double use and operational constraints of VTOL, external and internal environment analysis is performed by linking PEST-7S-SWOT analysis, and the development direction is established and devised a strategy. First of all, the special characteristics of the marine environment must be considered. In order for the unmanned aerial vehicle to be operated according to the purpose of maritime traffic and safety, it must be capable of being able to air-sea double use it, which overcomes spatial limitations. It is necessary to develop technology that can overcome environmental constraints such as bad weather and geographical constraints such as near sea and long distances. Second, in order to create an ecosystem for technological development as well as industrial growth, legal and institutional support and criminal abuse prevention and punishment standards should be prepared for air-sea double use VTOL. Third, in order to provide marine traffic and safety services using convergence technology, AI and autonomous navigation should be installed, and service spaces of metaverse such as augmented augmented reality(AR) and virtual reality(VR) should be provided.

엑서지를 이용한 지역난방 열요금 제도 제안

문정환(Junghwan Moon),유호선(Hoseon Yoo),이재헌(Jae-Heon Lee),문승재(Seungjae Moon) 대한설비공학회 2017 설비공학 논문집 Vol.29 No.4

In this study, the exergy that can be reflected in the energetic and economic values was used to assess the heat tariff of a district heating (DH) system instead of the enthalpy. It is difficult to directly apply the exergy to the current heat-charge system because of the complicated calculation; therefore, the difference between the supply and return temperatures was converted to the exergy-temperature difference for the ease of the heat-amount calculation. As a result of the exergy analysis for a DH substation, the exergy-temperature difference did not affect the surrounding temperature and pressure loss. The supply temperature and the maximum difference between the supply temperature and the return temperature exerted the main effect on the exergy-temperature difference. The new heat charge of a DH user was slightly reduced in winter compared with the previous charge, but the heat charges in the other seasons are almost the same. It is concluded from the assessment of the heat tariff for which the exergy is used that this tariff is more feasible for both DH suppliers and consumers compared with enthalpy.

신체장애인의 동력수상레저기구 면허취득을 위한 실기시험 개선방안

문정환(JungHwan Moon) 한국해양교통학회 2023 Journal of Korean Association of Maritime Transpor Vol.2 No.1

본 논문은 장애인이 누려야 할 수상레저활동에 관한 권리를 충족하며, 수상안전을 확보할 수 있는 면허취득을 위하여 현재 수행되고 있는 동력수상레저기구 실기시험 체계를 검토하여 신체장애인이동력수상레저기구 면허취득을 위한 실기시험의 개선방안을 제시했다. 우선, 동력수상레저기구 면허취득을 위한 신체적 장애로 인한 결격사유를 명확하게 명문화해야 한다. 둘째, 동력수상레저기구 조종하기 위한 운동능력 측정하기 위해 장애인이 착용할 수 있는 보조장비와 보조기기에 대한 기준을 마련하고 해당 장비의 개발이 반드시 필요하다. 셋째, 수상레저활동을 하더라도 안전사고를 방지하고 예방할 수 있는 범위 내에서 동력수상레저기구 실기시험에 대한 체계를 개선해야 한다. This paper satisfies the rights of people with disabilities regarding water leisure activities and reviews the currently implemented practical test system for water leisure equipments to obtain a license to ensure water safety, allowing physically disabled people to obtain a license and improve the practical test for acquisition was presented. First of all, the reasons for disqualification due to physical disability for obtaining a license for motorized water leisure equipment must be clearly stipulated. Second, in order to measure piloting skills to operate motorized water leisure equipment, it is necessary to establish standards for auxiliary equipment and auxiliary devices that can be worn by disabled people and to develop such equipment. Third, even when engaging in water leisure activities, the system for practical testing of water leisure equipments must be improved to the extent that safety accidents can be prevented.

단일 결정과 다결정 초격자 황화아연 나노와이어의 열기계적 거동의 구조적 의존성

문정환(Junghwan Moon),Min Zhou,조맹효(Maenghyo Cho) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12

Molecular dynamics simulations are carried out to compare thermal and mechanical properties of single-crystalline wurtzite(WZ), zinc-blende(ZB) and polytypic superlattice ZnS nanowire under tensile loading. Green-Kubo method is used to calculate thermal conductivity at each strain state. And non-equilibrium molecular dynamics (NEMD) approach is used to observe thermal transport at the interface between two different structures. As a result, Mechanical and thermal properties of ZB nanowire are lower than those of WZ nanowire. The difference in the configuration of surface atoms dominantly affects these lower properties of ZB nanowire. And the thermal conductivity of polytypic superlattice nanowire is lower than that of single-crystalline nanowire due to the phonon scattering on the interface between two different structures.

축소 분자동역학 전산 모사를 활용한 액정 고분자 광변형의 메조 스케일 해석

문정환(Junghwan Moon),김병조(Byungjo Kim),최준명(Joonmyung Choi),조맹효(Maenghyo Cho) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11

Photo-induced isomerization of Azo-functional group and corresponding mechanical deformation of crosslinked liquid crystal polymer can be applied to manufacture the artificial muscle, micromotor, micropump, and so on. Recently, many researchers are trying to impose the complex programmable deformation and mechanical rigidity on the photo-responsive polymer (PRP) via utilizing combination of various liquid crystalline phases (such as nematic, smectic, chiral nematic) and polydomatin nematic structure. However, full-atomistic description of molecular dynamics simulation has limitation on describing these structures due to high computational costs. Therefore, we have developed the meso-scale potential parameters to describe various liquid crystalline phases and photo-isomerization of azobenzene moieties via the coarse-grained molecular dynamics (CG-MD) simulation. We observed the smectic layered structure of crosslinked liquid crystal polymer, which cannot be realized using conventional full-atom description. The proposed methodology and results can be utilized to analyze the meso-scale phenomena of light-induced deformation and bridge the atomistic and continuum scale simulation techniques.

Gate-Bias Control Technique for Envelope Tracking Doherty Power Amplifier

Junghwan Moon(문정환),Jangheon Kim(김장헌),Ildu Kim(김일두),Jungjoon Kim(김정준),Bumman Kim(김범만) 한국전자파학회 2008 한국전자파학회논문지 Vol.19 No.8

본 논문에서는 선형성 증가를 위해 도허티 증폭기의 게이트 바이어스를 조정하는 방식을 제시하였다. 도허티 증폭기의 선형성 향상은 출력 결합 지점에서의 고조파 상쇄를 통해 이루어진다. 하지만 고조파의 상쇄는 그 크기와 위상이 출력 지점에서 같은 크기와 서로 다른 위상을 가지고 있어야 이루어질 수 있는데, 넓은 출력 전력범위에서 위와 같은 조건을 만족시키는 것은 쉽지 않다. 선형성 증가를 위해 도허티 증폭기의 캐리어 증폭기와 피킹 증폭기의 선형성 특성을 입력 전력과 각 증폭기의 게이트 바이어스를 조정함으로써 살펴보았다. 살펴본 특성을 기본으로 하여 고조파 상쇄 전력 범위를 증가시키기 위해, 각 전력 레벨에 맞는 게이트 바이어스를 증폭기에 인가하였다. 게이트 바이어스 제어를 통한 선형성 향상을 알아보기 위해, 2.345 ㎓에서 Eudyna사의 10-W PEP GaN HEMT EGN010MK 소자를 이용하여 도허티 전력 증폭기를 설계하였고, P1㏈로부터 10 ㏈ back-off 지점인 33 ㏈m에서 고효율과 고선형성을 위해 최적화 되었다. WCDMA 1-FA 신호에 대해 제안된 게이트 바이어스 컨트롤 된 도허티 증폭기는 2.8 ㏈의 선형성 개선을 확인할 수 있었으며, 26 %의 PAE를 확인할 수 있었다. 또한, 802.16-2004 신호에 대해 RCE가 2 ㏈ 증가됨을 확인할 수 있었다. The gate-biases of the Doherty power amplifier are controlled to improve the linearity performance. The linearity improvement mechanism of the Doherty amplifier is the harmonic cancellation of the carrier and peaking amplifier at the output power combining point. However, it is difficult to cancel the harmonic power for the broader power range because the condition for cancelling is varied by power. For the linearity improvement, we have explored the linearity characteristic of the Doherty amplifier according to the input power and gate biases of the carrier and peaking amplifier. To extend the region of harmonic power cancellation, we have injected the proper gate bias to the carrier and peaking amplifier according to the input power levels. To validate the linearity improvement, the Doherty amplifier is designed using Eudyna 10-W PEP GaN HEMT EGN010MKs at 2.345 ㎓ and optimized to achieve a high linearity and efficiency at an average output power of 33 ㏈m, backed off about 10 ㏈ from the P1㏈. In the experiments, the envelope tracking Doherty amplifier delivers a significantly improved adjacent channel leakage ratio performance of -37.4 ㏈c, which is an enhancement of about 2.8 ㏈, maintaining the high PAE of about 26 % for the WCDMA 1-FA signal at an average output power of 33 ㏈m. For the 802.16-2004 signal, the amplifier is also improved by about 2 ㏈, -35 ㏈.

상대적 방향성에 따른 아조벤젠-탄소나노튜브 복합재의 광 · 기계적 거동 변화

문정환(Junghwan Moon),최준명(Joonmyung Choi),조맹효(Maenghyo Cho) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

Photo-responsive liquid crystal polymer networks (LCPNs) are novel materials that can change their macroscopic shapes by an irradiation of the light with specific wavelength ranges. Recently, in order to improve the mechanical properties and thermal response of these photo-responsive polymers (PRPs), carbon nanotubes (CNTs) are inserted into the cross-linked polymer networks. In this study, a molecular dynamics (MD) simulation was utilized to model the azobenzene-CNT nanocomposites and estimate their photoinduced deformations. Especially, we investigated the effect of relative orientation between namatic polymer matrix and CNT on their interfacial interaction and hence, the load transfer characteristics and photo-mechanical properties. We expect the results will help to design the photo-deformable nanocomposites.

병원건물의 에너지 저감을 위한 에너지성능 평가에 관한 사례연구

조진균(Jinkyun Cho),문정환(Junghwan Moon),강호석(Hosuk Kang) 대한설비공학회 2017 설비공학 논문집 Vol.29 No.1

Hospitals contribute to energy consumption and have a negative environmental impact. This study aims to find how meaningful energy performance, reflecting good energy management and design, can be planned for hospital buildings, a category encompassing complex buildings with different setups and large differences between them. Energy-consumption characteristics were surveyed throughout Korea to establish statistical energy models. Findings confirm that different hospital departments have hugely different energy-demand profiles. Energy efficiency and energy-saving potentials on HVAC systems are presented. The energy performance analysis can be applied to a wide range of problems in energy-system design and planning, including simulations and optimizations of community energy systems.