자기펄스 성형법에 의한 TiO₂ 나노 분말의 치밀화

김효섭,이정구,이창규,구자명,홍순직,Kim, Hyo-Seob,Lee, Jeong-Goo,Rhee, Chang-Kyu,Koo, Jar-Myung,Hong, Soon-Jik 한국재료학회 2008 한국재료학회지 Vol.18 No.8

In this research, fine-structure TiO2 bulks were fabricated in a combined application of magnetic pulsed compaction (MPC) and subsequent sintering and their densification behavior was investigated. The obtained density of $TiO_2$ bulk prepared via the combined processes increased as the MPC pressure increased from 0.3 to 0.7 GPa. Relatively higher density (88%) in the MPCed specimen at 0.7 GPa was attributed to the decrease of the inter-particle distance of the pre-compacted component. High pressure and rapid compaction using magnetic pulsed compaction reduced the shrinkage rate (about 10% in this case) of the sintered bulks compared to general processing (about 20%). The mixing conditions of PVA, water, and $TiO_2$ nano powder for the compaction of $TiO_2$ nano powder did not affect the density and shrinkage of the sintered bulks due to the high pressure of the MPC.

Inhomogeneous Helmholtz equation for Water Waves on Variable Depth

김효섭,장창환,Kim, Hyo-Seob,Jang, Chang-Hwan The Korean Society for Marine Environment and Ener 2010 한국해양환경·에너지학회지 Vol.17 No.4

변동 수심에서의 파랑변형을 비균질 Helmholtz 방정식을 이용하여 계산하였다. 포텐셜 함수가 존재한다고 가정하였으며, 변수분리를 적용하였다. 본 논문에서는 조화파만을 고려하였다. 포텐셜 함수로 구성된 지배방정식을 정수면에 직접 적용하였고, 변동 수심에 대한 비균질 Helmholtz 방정식을 얻었다. 파랑의 진폭과 위상차로 얻어진 복합 포텐셜 함수의 지배방정식을 실수형 변수로 된 두 방정식으로 분리하였다. 분리된 방정식들은 각각 1차와 2차 상미분 방정식이며, 이 방정식들을 단순한 형태의 중앙차분 수치기법을 이용하여 차분식으로 변형하였다. 측면 경계조건에서의 파랑의 진폭, 진폭경사, 그리고 위상경사를 경계면에 적용하여 전방진행방법으로 전 영역에서 해를 구하였다 Booij의 경사면 있는 저면의 경우와 Bragg의 물결모양이 있는 저면의 경우에 적용하였다. 본 연구로 도출된 비균질 Helmholtz 방정식은 완전 선형방정식 계산 결과, Massel의 수정 완경사 방정식, 그리고 Berkhoff의 완경사 방정식의 적용 결과와 비교하였으며, 만족스러운 결과를 얻었다. The inhomogeneous Helmholtz equation is introduced for variable water depth and potential function and separation of variables are introduced for the derivation. Only harmonic wave motions are considered. The governing equation composed of the potential function for irrotational flow is directly applied to the still water level, and the inhomogeneous Helmholtz equation for variable water depth is obtained. By introducing the wave amplitude and wave phase gradient the governing equation with complex potential function is transformed into two equations of real variables. The transformed equations are the first and second-order ordinary differential equations, respectively, and can be solved in a forward marching manner when proper boundary values are supplied, i.e. the wave amplitude, the wave amplitude gradient, and the wave phase gradient at a side boundary. Simple spatially-centered finite difference numerical schemes are adopted to solve the present set of equations. The equation set is applied to two test cases, Booij’ inclined plane slope profile, and Bragg’ wavy bed profile. The present equations set is satisfactorily verified against other theories including the full linear equation, Massel's modified mild-slope equation, and Berkhoff's mild-slope equation etc.

텔레늄 소재의 현황 및 재자원화 기술동향

김효섭,홍순직,Kim, Hyo-Seob,Hong, Soon-Jik 한국분말야금학회 2012 한국분말재료학회지 (KPMI) Vol.19 No.3

밀링조건이 사용 후 PDP패널의 유가금속 용출효율에 미치는 영향

김효섭,김찬미,이철희,이성규,홍현선,구자명,홍순직,Kim, Hyo-Seob,Kim, Chan-Mi,Lee, Chul-Hee,Lee, Sung-Kyu,Hong, Hyun-Seon,Koo, Jar-Myung,Hong, Soon-Jik 한국분말야금학회 2013 한국분말재료학회지 (KPMI) Vol.20 No.2

In this study, the microstructure and valuable metals dissolution properties of PDP waste panel powders were investigated as a function of milling parameters such as ball diameter size, milling time, and rotational speed during high-energy milling process. The complete refinement of powder could achieved at the ball diameter size of 5 mm due to sufficient impact energy and the number of collisions. With increasing milling time, the average particle size was rapidly decreased until the first 30 seconds, then decreased gradually about $3{\mu}m$ at 3 minutes and finally, increased with presence of agglomerated particles of $35{\mu}m$ at 5 minutes. Although there was no significant difference on the size of the particle according to the rotational speed from 900 to 1,100 rpm, the total valuable metals dissolution amount was most excellent at 1,100 rpm. As a result, the best milling conditions for maximum dissolving amount of valuable metals (Mg: 375 ppm, Ag 135 ppm, In: 17 ppm) in this research were achieved with 5 mm of ball diameter size, 3min of milling time, and 1,100 rpm of rotational speed.

고에너지 밀링으로 제조된 폐디스플레이 패널 분말의 밀링시간에 따른 인듐 용출특성

김효섭,성준제,이철희,홍현선,홍순직,Kim, Hyo-Seob,Sung, Jun-Je,Lee, Cheol-Hee,Hong, Hyun-Seon,Hong, Soon-Jik 한국분말야금학회 2011 한국분말재료학회지 (KPMI) Vol.18 No.4

In this research, the indium dissolution properties of the waste LCD panel powders were investigated as a function of milling time fabricated by high-energy ball milling (HEBM) process. The particle morphology of waste LCD panel powders changed from sharp and irregular shape of initial cullet to spherical shape with an increase in milling time. The particle size quickly decreased to 15 ${\mu}m$ until the first minute, then decreased gradually about 6 ${\mu}m$ with presence of agglomerated particles after 5 minutes, which increased gradually reaching a uniform size of 13 ${\mu}m$ consist of agglomerated particles after 30 minutes. The glass recovery, after dissolution, was over 99% at initial cullet, which decreased to 90.1 and 78.6% with increasing milling time of 1 and 30 minute respectively, due to a loss in remaining powder of the surface ball and jar, as well as the filter paper. The dissolution amount of indium out of the initial cullet was 208 ppm before milling, turning into 223 ppm for the mechanically milled powder after 1 minute, and nearly 146~125 ppm with further increase in milling time because of the reaction surface decrease of powders due to agglomeration. With this process, maximum dissolving indium amount (223 ppm) could be achieved at a particle size of 15 ${\mu}m$ with 1 minute of milling.

가스분무공정을 이용한 (AgSbTe₂)₁₅(GeTe)₈₅ 열전분말의 제조 및 특성평가

김효섭,이진규,구자명,천병선,홍순직,Kim, Hyo-Seob,Lee, Jin-Kyu,Koo, Jar-Myung,Chun, Byong-Sun,Hong, Soon-Jik 한국분말야금학회 2011 한국분말재료학회지 (KPMI) Vol.18 No.5

In this study, p-type $(AgSbTe_2)_{15}(GeTe)_{85}$: TAGS-85 compound powders were prepared by gas atomization process, and then their microstructures and mechanical properties were investigated. The fabricated powders were of spherical shape, had clean surface, and illustrated fine microstructure and homogeneous $AgSbTe_2$ + GeTe solid solution. Powder X-ray diffraction results revealed that the crystal structure of the TAGS-85 sample was single rhombohedral GeTe phase, which with a space group $R_{3m}$. The grain size of the powder particles increased while the micro Vickers hardness decreased with increasing annealing temperature within the range of 573 K and 723 K due to grain growth and loss of Te. In addition, the crystal structure of the powder went through a phase transformation from rhombohedral ($R_{3m}$) at low-temperature to cubic ($F_{m-3m}$) at high-temperature with increasing annealing temperature. The micro Vickers hardness of the as-atomized powder was around 165 Hv, while it decreased gradually to 130 Hv after annealing at 673K, which is still higher than most other fabrication processes.

HOMER를 활용한 백령도와 외도의 신재생에너지발전 경제성 분석 및 최적 조합 제안

김효섭(Kim, Hyo-Seob),임진빈(Im, Jin-Bin),이경태(Lee, Kyung-Tae),김희정(Kim, Hee-Jeong),김주형(Kim, Ju-Hyung) 대한건축학회 2021 대한건축학회논문집 Vol.37 No.12

Most energy generating systems in island areas are diesel energy generation using fossil fuel. The transportation cost of fossil fuel to the island areas makes generation cost three to four times more expensive. To solve this economic loss, the establishment of energy independent island through introduction of renewable energy generation system in the island areas is being considered. Prior research are generally focus on major island areas such as Jejudo, Ulleungdo and Gapado etc. However, to verify about applying renewable energy generation systems on the island areas, considering the all types of characteristic of the island areas such as high economic loss from energy generation or small population of less than 100 people is essential. This study is conducted as case study on Baengnyeongdo which has high economic loss and Oedo which has small population of less than 100 people. To examine the feasibility of applying renewable energy generation system in Baengnyeongdo and Oedo, a combination of existing diesel energy generation system and renewable energy generation system was proposed and economic analysis using NPV(Net Present Value) and LCOE(Levelized Cost of Energy) was proceeded. The experiment was conducted using simulation, HOMER(Hybrid Optimization Model for Electric Renewable) was used as simulation program. Environment and weather data of Baengnyeongdo and Oedo and renewable energy genration system data obtained from KEPCO(Korea Electric Power Corporation), NREL(National Renewable Energy Laboratory) and HOMER were used as simulation dataset. The optimal combination of energy generation system for Baengnyeongdo and Oedo was proposed and it was confirmed that there would be economic benefits if the introduction of the renewable energy generation system continued for more than 9 years.

범용 파랑·흐름 공존시의 비점착성 퇴적물이동 예측식

김효섭(Kim, Hyo-Seob),장창환(Jang, Chang-Hwan) 한국해안해양공학회 2009 한국해안해양공학회 논문집 Vol.21 No.6

파랑과 흐름이 공존하는 해안에서의 비점착성 퇴적물이동에 대하여 육지-외해방향 총 퇴적물 이동률을 산정할 수 있는 경험식을 제안한다. 본 경험식은 파랑만 존재하는 경우와 흐름만 존재하는 경우에도 범용적으로 사용할 수 있다. 해수면 기준 비대칭인 파랑을 이용하여 퇴적물의 부상률과 이동거리의 곱으로 단위면적당 총 퇴적물 이동률을 계산할 수 있다. 대체로 파고가 큰 파랑이 입사하는 경우 퇴적물은 외해방향으로 이동하는 반면 파고가 작은 파랑의 경우 육지방향으로 퇴적물을 이동시키는 경향을 본 예측식이 잘 재현하고 있다. 또한 장주기 파랑의 경우 퇴적물을 육지방향으로 이동시키려는 경향을 본 예측식이 잘 보여준다. This study suggests a general formula of non-cohesive sediment transport rates for waves and currents which is also valid for wave only or current only condition. On-offshore sediment transport rates with the second order Stokes wave in the shallow water are calculated as the pickup rate times the distance. The formula depicts reasonably that high waves move material offshore, and low waves move material onshore. Also the formula, as is the case the waves with long period tend to move material onshore, shows good results.

KU-CFD-3D 실행 시, Karman Vortex의 인위적 촉발

김효섭(Kim, Hyo Seob),이승호(Lee, Seung Ho),김우연(Kim Woo Yeon) 대한토목학회 2016 대한토목학회 학술대회 Vol.2016 No.10

해상풍력발전기 기초주위 세굴의 예측과 대책에 관한 종설

김효섭(Hyo seob Kim),강성훈(Sung hun Kang) 한국연안방재학회 2017 한국연안방재학회지 Vol.4 No.2

Scour around subsea windfarm foundation is a threat to its stability and the cable’s functioning. Underwater scour is affected by waves, currents, bed material and water depth. Prediction of scour depth can be classified into empirical methods, numerical methods, and laboratory experiments. Recently time-evolution of scour depth has been described by a time-advancing computation with empirical formula. RANS-type modelling has been refined to simulate horse-shoe scour by including the jet effect. Recent scour protection methods include two-step protection: wait until scour hole develops and then put rock armour layer at the time.