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Numerical study on ship-generated unsteady waves based on a Cartesian-grid method

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Journal of Hydrodynamics 2020年第5期32卷 953-968页

作者： kyung-Kyu yang Masashi Kashiwagi Yonghwan kim Department of Naval Architecture and Ocean Engineering Seoul National UniversitySeoulKorea Department of Naval Architecture and Ocean Engineering Osaka UniversityOsakaJapan

The added resistance of a ship in waves can be related to ship-generated unsteady *** the present study,the unsteady wave-pattern analysis is applied to calculate the added resistance in waves for two modified Wigley models using a Cartesian-grid *** the present numerical method,a first-order fractional-step method is applied to the velocity-pressure coupling in the fluid domain,and one of volume-of-fluid(VOF)methods is adopted to capture the fluid interface.A ship is embedded in a Cartesian grid,and the volume fraction of the ship inside the grid is calculated by identifying whether each grid is occupied by liquid,gas,and solid *** sensitivity to the location of measuring position of unsteady waves as well as the number of solution grids is *** added resistance computed by direct pressure integration and wave pattern analysis is compared with experimental *** addition,nonlinear characteristics of the added resistance in waves are investigated by detailed analyses of unsteady flow field and resulting wave pattern.

关键词： Unsteady wave pattern added resistance in waves Cartesian-grid method grid convergence index

Stability of neodymium:YAG laser posterior capsulotomy in eyes with capsular tension rings

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International Journal of Ophthalmology(English edition) 2023年第6期16卷 891-896页

作者： yang kyung Cho Min Sun kim Department of Ophthalmology St.Vincent’s HospitalCollege of MedicineThe Catholic University of KoreaSeoul 06591Republic of Korea

·AIM: To evaluate the stability of neodymium(Nd):YAG laser posterior capsulotomy in eyes with capsular tension rings(CTRs).·METHODS: A total of 60 eyes that underwent cataract surgery and laser posterior capsulotomy postoperatively were included in this retrospective cohort study. To evaluate the safety and stability of capsulotomy, changes in the size of posterior capsulotomy and anterior chamber depth(ACD) in three groups: the group without CTR, the group with 12 mm CTRs, and the group with 13 mm CTRs, at 1wk, 3, 12, and 15mo after capsulotomy, were compared. ·RESULTS: In the group without CTR and the group with 12 mm CTR, there was no significant change in ACD at every post-laser follow-up. In the group with 13 mm CTR, the ACD change was significant until 3mo after capsulotomy. In all groups, there was a significant increase in the area of capsulotomy between 1wk and 3mo post-laser. Between 3 and 12mo post-laser, only the group with 13 mm CTR showed a significant increase in the area of capsulotomy(P<0.01). ·CONCLUSION: Laser posterior capsulotomy is safe in all three groups. The capsulotomy and ACD become stabilized and have not shown significant changes since 1y postlaser, even with larger CTRs. The maintenance of centrifugal capsular tension can last longer with larger CTRs, and the stability of the capsulotomy site can be reached about 12mo after capsulotomy in pseudophakic eyes with larger CTRs.

关键词： Nd:YAG laser capsulotomy capsular tension ring

Aging Behavior of Mg-Y-Zr and Mg-Nd-Zr Cast Alloys

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Journal of Materials Science & Technology 2008年第1期24卷 80-84页

作者： yang-Do kim Nam-Hyun Kang Il-Guk Jo kyung-Hyun kim In-Bae kim School of Materials Science and Engineering Pusan National University 30 Jangjun-dongGeumjeong-guBusan 609-735Korea Deptartment of Materials Engineering Korea Institute of Machinery & Materials 66 Sangnam-dongChangwonGyeongsangnam-do 641-010Korea

Aging behavior of Mg-3.6Y-0.5Zr and ***-0.5Zr alloys was investigated by microhardness measurement and transmission electron *** the case of Mg-Y-Zr alloy,the presence ofβ″phase,a major strength- ener,having base centered orthorhombic structure with its lattice constants of a-（β″）=0.64 nm,b-（β″）=2.22 nm, and c-（β″）=0.52 nm was *** the case of Mg-Nd-Zr alloy aged at 250℃,the presence ofβ″andβ′phases was *** crystal structure ofβ″phase was found to be DO-（19） and its orientation relationships with Mg matrix were [0001]-（β″）//[0001]-（Mg） and [01（？）0]-（β″）//[01（？）0]-（Mg）.Theβ′phase had face centered cubic structure and its orientation relationships with Mg matrix were [011]-（β′）//[0001]-（Mg） and [（？）1（？）]β′//[（？）110]）-（Mg）. The ***-0.5Zr alloy showed higher hardness compared with Mg-3.6Y-0.5Zr alloy.

关键词： Mg-Y-Zr alloy Mg-Nd-Zr alloy Precipitation sequence

MICROMECHANICS OF ROUGH SURFACE ADHESION:A HOMOGENIZED PROJECTION METHOD

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Acta Mechanica Solida Sinica 2009年第5期22卷 377-390页

作者： kyung-Suk kim Division of Engineering Brown UniversityProvidenceRI 02912USA

A quasistatic homogenized projection is made to characterize the effective cohesive zone behavior for rough-surface adhesion. In the context of the homogenized projection, the traction versus separation relation for the homogenized cohesive zone （HCZ） of a rough interface can be highly oscillatory due to instabilities during microscopic adhesion and decohesion processes. The instabilities are found to occur not only individually but also collectively among the adhesive micro-asperity contacts, leading to extensive energy dissipation. Based on the behaviors of the HCZ relations, a framework for describing instability-induced energy dissipation in rough-surface adhesion is proposed to elucidate the effect of roughness on apparent interface adhesion. Two non- dimensional parameters, α related to roughness morphology and n related to flaw distribution, are identified to be most crucial for controlling the energy dissipation. For an interface with a shallow roughness and a strong intrinsic adhesive strength, the interface adhesion can be stronger if we make it rougher （reducing α） or lower its flaw density （increasing n）. The HCZ projection method can be potentially extended and employed to bridge the apparent adhesion from intrinsic adhesion properties for engineering surfaces with multi-scale shallow roughness.

关键词： homogenized cohesive zone interface adhesion roughness effect instability energy dissipation

In situ synthesis of chemically bonded NaTi2（PO4）3/rGO 2D nanocomposite for high-rate sodium-ion batteries

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Nano Research 2016年第6期9卷 1844-1855页

作者： Ha-kyung Roh Hyun-kyung kim Myeong-Seong kim Dong-Hyun kim kyung Yoon Chung Kwang Chul Roh Kwang-Bum kim Department of Material Science & Engineering Yonsei University 50 Yonsei-ro Seodaemun-gu Seou103722 Republic of Korea Department of Materials Science and Metallurgy University of Cambridge 27 Charles Babbage Road Cambridge CB30FS UK Center for Energy Convergence Korea Institute of Science and Technology 5 Hwarang-ro 14-gil Seongbuk-gu Seou102792 Republic of Korea Energy & Environmental Division Korea Institute of Ceramic Engineering & Technology 101 Soho-ro Jinju-si Gyeongsangnam-do 52851 Republic of Korea

A phase-pure NaTi2（PO4）3/reduced graphene oxide （rGO） nanocomposite was prepared using a microwave-assisted one-pot method and subsequent heat treatment. The well-crystallized NaTi2（PO4）3 nanoparticles （30-40 nm） were uniformly precipitated on rGO templates through Ti-O-C bonds. The chemical interactions between the NaTi2（PO4）3 nanoparticles and rGO could immobilize the NaTi2（PO4）3 nanoparticles on the rGO sheets, which might be responsible for the excellent electrochemical performance of the nanocomposite. The NaTi2（PO4）B/rGO nanocomposite exhibited a specific capacity of 128.6 mA-h.g-1 approaching the theoretical value at a 0.1 C-rate with an excellent rate capability （72.9% capacity retention at 50 C-rate） and cycling performance （only 4.5% capacity loss after 1,000 cycles at a high rate of 10 C）. These properties were maintained even when the electrodes were prepared without the use of an additional conducting agent. The excellent sodium storage properties of the NaTi2（PO4）B/rGO nanocomposite could be attributed to the nano-sized NaTi2（PO4）3 particles, which significantly reduced the transport lengths for Na＋ ions, and an intimate contact between the NaTi2（PO4）3 particles and rGO due to chemical bonding.

关键词： NaTi2(PO4)dreducedgraphene oxide (rGO)nanocomposite chemical bonding energy-efficiency in situ synthesis high-rate sodium-ion batteries

Utilizing 3,4-ethylenedioxythiophene(EDOT)-bridged non-fullerene acceptors for efficient organic solar cells

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Journal of Energy Chemistry 2022年第2期31卷 194-204页

作者： Sung Jae Jeon Young Hoon kim Ie Na kim Nam Gyu yang Ji Hee Yun Doo kyung Moon Nano and Information Materials(NIMs)Laboratory Department of Chemical EngineeringKonkuk University120 Neungdong-ro Gwangjin-guSeoul 05029South Korea Department of Academy of Applied Science and Technology Konkuk University120 Neungdong-ro Gwangjin-guSeoul 05029South Korea

A rational design of efficient low-band-gap non-fullerene acceptors(NFAs)for high-performance organic solar cells(OSCs)remains challenging;the main constraint being the decrease in the energy level of the lowest unoccupied molecular orbitals(LUMOs)as the bandgap of A-D-A-type NFAs ***,the short current density(J_(sc))and open-circuit voltage(V_(oc))result in a trade-off relationship,making it difficult to obtain efficient ***,three NFAs(IFL-ED-4 F,IDT-ED-4 F,and IDTT-ED-2 F)were synthesized to address the above-mentioned issue by introducing 3,4-ethylenedioxythiophene(EDOT)as aπ-*** NFAs exhibit relatively low bandgaps(1.67,1.42,and 1.49 eV,respectively)and upshifted LUMO levels(-3.88,-3.84,and-3.81 eV,respectively)compared with most reported low-band-gap ***,the photovoltaic devices based on IDT-ED-4 F blended with a PBDB-T donor polymer showed the best power conversion efficiency(PCE)of 10.4%with a high J_(sc) of 22.1 mA cm^(-2) and Voc of 0.884 V among the examined *** contrast,IDTT-ED-4 F,which was designed with an asymmetric structure of the D-p-A type,showed the lowest efficiency of 1.5%owing to the poor morphology and charge transport properties of the binary ***,when this was introduced as the third component of the PM6:BTP-BO-4 Cl,complementary absorption and cascade energy-level alignment between the two substances could be ***,the IDTT-ED-4 F-based ternary blend device not only improved the Jscand Voc,but also achieved a PCE of 15.2%,which is approximately 5.3%higher than that of the reference device with a minimized energy loss of 0.488 *** addition,the universality of IDTT-ED-2 F as a third component was effectively demonstrated in other photoactive systems,specifically,PM6:BTPe C9 and PTB7-Th:IEICO-4 *** work facilitates a better understanding of the structure–property relationship for utilizing efficient EDOT-bridged NFAs in high-performance OSC applications.

关键词： Non-fullerene acceptor 3,4-ethylenedioxythiophene Organic solar cell π-bridge π-spacer

Tribology of multilayer coatings for wear reduction: A review

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Friction 2017年第3期5卷 248-262页

作者： Mahdi KHADEM Oleksiy V.PENKOV Hee-kyung yang Dae-Eun kim Department of Mechanical Engineering Yonsei University Seoul 03722 Republic of KoreaCenter for Nano-Wear Yonsei University Seoul 03722 Republic of Korea Center for Nano-Wear Yonsei University Seoul 03722 Republic of Korea Department of Mechanical Engineering Yonsei University Seoul 03722 Republic of Korea

Friction and wear phenomena encountered in mechanical systems with moving components are directly related to efficiency,reliability and life of the ***,minimizing and controlling these phenomena to achieve the desired system performance is *** the numerous strategies developed for reducing friction and wear,coatings have been successfully utilized in various engineering applications to mitigate tribological *** of the benefits of coatings is that they may be fabricated using a variety of materials in several different forms and structures to satisfy the requirements of the operating *** many types,coatings that are comprised of a combination of materials in the form of a multilayer have been gaining much interest due to the added degree of freedom in tailoring the coating *** this paper,the properties and development status of multilayer coating systems for tribological applications were reviewed with the aim to gain a better understanding regarding their advantages and ***,focus was given to Ti-based and Cr-based coatings since Ti and Cr were identified as important elements in multilayer coating *** was given to materials,design concepts,mechanical properties,deposition method,and friction and wear characteristics of these types of coatings.

关键词： multilayer coating friction wear tribology

Enhanced electrical and optical properties of single- layered MoS2 by incorporation of aluminum

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Nano Research 2018年第2期11卷 731-740页

作者： Hyung-Jun kim Suk yang Hojoong kim Jin Young Moon kyung Park Yun-Jin Park Jang-Yeon Kwon School of Integrated Technology Yonsei University Incheon Republic of Korea Yonsei Institute of Convergence Technology Incheon Republic of Korea

Electrical and optical enhancements of single-layer semiconducting materials such as transition metal dichalcogenides have recently been studied to achieve sensitive properties via external treatments, such as the formation of organic/ inorganic protecting layers on field-effect transistors （FETs）, thermal annealing, and nano-dot doping of sensors and detectors. Here, we propose a new analytical approach to electrical and optical enhancement through a passivation process using atomic layer deposition （ALD）, and demonstrate a synthesized MoS2 monolayer incorporated with A1 atoms in an A1203 passivation layer. The incorporated A1 atoms in the MoS2 monolayer are dearly observed by spherical aberration-corrected scanning transmission electron microscopy （Cs-STEM） and TEM-energy-dispersive X-ray spectroscopy results. We demonstrate that the chemically incorporated FETs exhibit highly enhanced mobilities of approximately 3.7 crn2-V-los-1, forty times greater than that of as-synthesized MoS2, with a three- fold improvement in the Dhotoluminescence properties.

关键词： MoS2 aluminum incorporation chemical vapor deposition atomic layer deposition

Maximizing biomass utilization: An integrated strategy for coproducing multiple chemicals

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Journal of Energy Chemistry 2025年第1期100卷 180-191页

作者： Byeongchan Ahn Sua Jo Jonggeol Na J.Jay Liu Young-Ju kim Wangyun Won Department of Chemical and Biological Engineering Korea University Department of Chemical Engineering (Integrated process) Kyung Hee University Department of Chemical Engineering and Materials Science Ewha Womans University Department of Chemical Engineering Pukyong National University Resources Engineering Plant Research Department Korea Institute of Geoscience and Mineral Resources

Lignocellulosic biomass is one of the viable solutions to alleviate the global warming. However, the limited utilization of biomass majorly focused on cellulose and hemicellulose restricts the economic and environmental feasibilities. To cope with this issue, we proposed an integrated process of co-producing 1,6-hexanediol（1,6-HDO） with tetrahydrofuran and adipic acid from biomass, referred to as Strategy A. To compare the impacts of lignin upgrading and feedstock, Strategy B, which co-produces tetrahydrofuran alone, and Strategy C, which is the traditional route to produce 1,6-HDO from fossil fuels, were used. Heat networks are also designed to reduce operating costs and indirect carbon emissions due to energy consumption, saving 87% and 83% of the heat and cooling requirements, respectively, in Strategy A. The market competitiveness of Strategy A was evaluated by determining the minimum selling price through techno-economic analysis, and sustainability was thoroughly investigated by quantifying the environmental impacts through both midpoint and endpoint life-cycle assessments（LCAs）.Strategy A was found to be the most favorable both economically（USRDSCHARDOLLAR3,402/ton） and environmentally（-26.9 kg CO2eq.）. This indicates that lignin valorization is not only economically but also environmentally preferred. Finally, changes in economic and environmental feasibilities depending on economic, process, and environmental parameters were investigated using sensitivity and uncertainty analyses. The results of these analyses provide valuable insight into bio-based chemical production.

关键词： Biorefinery Carbon mitigation Climate change Global warming Lignin utilization Bioeconomy