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Development of a numerical simulation tool for efficient and robust prediction of ship resistance
김건홍,박상훈 대한조선학회 2017 International Journal of Naval Architecture and Oc Vol.9 No.5
In this paper, a two-phase flow solver HiFoam® has been developed based on the OpenFOAM® to predict resistance of a ship in calm water. The VOF method of OpenFOAM® was reviewed and a simple flux limiter was introduced to enhance the robustness of the solver. The procedure for predicting ship motion was modified by introducing Quasi-Steady Fluid-Body Interaction (QS-FBI) with least square regression to improve the efficiency. Other minor factors were considered as well in terms of the efficiency and robustness. The HiFoam was applied to KCS and JBC simulations to validate its efficiency and accuracy by comparing the results to experimental data and STAR-CCM+. The HiFoam® was also applied to various ships and it showed good agreements to the experimental data.
구리 도금된 스테인리스 스틸 배관의 접합력 향상을 위한 배관 표면 처리 및 확산접합에 대한 연구
김건홍,오민철 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.11
스테인레스스틸(STS) 배관 표면에 Cu를 도금하여 Cu배관과 Cu가 도금된 STS배관을 브레이징 접합함으로써 Ag 함량이 높은 고가의 filler metal를 사용하지 않고, 기존의 동배관 브레이징 접합 시에 사용하는 인동합금(BCup-2) 용가재를 사용하여 제조 단가를 절감하고, 또한 브레이징 접합부 불량을 최소화 하는 것이 본 연구의 목적이다. 이를 달성하기 위해T SS배관과 Cu 도금층의 결합력이 중요하며, 박리현상을 최소화 하는 연구가 필요하다. 본 연구에서는 STS배관과 Cu 도금 층의 결합력을 높이기 위해 STS배관의 표면처리(STS배관과 Cu 도금 층의 계면의 면적을 높이기 위함)를 실시하였으며, 또한 원자 간의 상호 확산을 통해 결합력을 높일 수 있는 확산접합을 실시하였다. 확산접합은 고체 상태에서 물리적으로 접합된 계면에 열에너지를 공급하여 계면 사이의 금속 원자 간의 확산 메카니즘으로 접합시키는 방법이다. 확산접합 시간 및 온도에 따라 STS와 Cu의 계면을 분석하여 접합부의 확산 거리 및 Cu와 Fe의 확산 거동을 연구하였으며, 그 결과, STS 배관 표면에 매크로(macro)한 거칠기를 가지는 브러싱(면취솔) 표면처리 후 850℃에서 2시간 열처리 시 접합부의 약 5 μm 이상의 확산 거리를 확보하였으며, 900℃ 이상의 온도에서 열처리 시 Cu와 Fe의 확산 속도 차이로 인해 계면에서 기공(kirkendall void)이 발생하여 과도하게 높은 온도에서 확산접합 시 오히려 접합력을 감소시키는 것을 간접적으로 확인하였다.
김건홍,김영식 한국계량경제학회 2010 계량경제학보 Vol.21 No.2
For the purpose of explaining both business cycles and asset returns, we examine a real business cycle (RBC) model with habit-augmented preferences and endogenous costs of adjusting the capital stock. Following the agency-cost model of Carlstrom and Fuerst (1997), capital adjustment costs are affected by the level of entrepreneur’s net worth such that an increase in net worth (following a positive productivity shock) lowers agency costs associated with external financing, and hence makes it easier to expand the capital stock. Along with the restricted labor supply,the model resolves the asset pricing puzzles of the consumption-based model in the sense that the implied stochastic discount factor (or pricing kernel) reaches the Hansen-Jagannathan(1991) volatility bound. Further, this improvement in the asset pricing dimension is achieved without reducing its business cycle performance such as output and consumption volatility. This is in a sharp contrast to the standard RBC model with the reduced-form adjustment cost technology where sufficiently low supply elasticity of capital (or persistently high capital adjustment costs) is required to generate the equity premium at the expense of low output volatility. Here, the capital supply is highly elastic with respect to Tobin’s q under the plausible calibrations of the structural parameters affecting endogenous capital adjustment costs. The sluggish behavior of net worth, as a shifter of the capital supply curve, is the key mechanism by which capital adjustment is delayed, hampering consumption smoothing desired by households with habit persistence preferences. The agency-costs model reveals that a small curvature in the capital adjustment cost function, viewed as crucial for understanding the fluctuations in Tobin’s q, can be also consistent with both the historical equity premium and the key business cycle facts.
MoS<sub>2</sub> 첨가에 따른 Fe-Cr-Mn-C-V계 소결합금의 기계적 특성 평가
김건홍,양현석,공만식,Kim, Geon-Hong,Yang, Hyun Seok,Kong, Man-Sik 한국분말야금학회 2014 한국분말재료학회지 (KPMI) Vol.21 No.4
The connecting rod is one of the most important parts in automotive engines, transforming the reciprocal motion of a piston generated by internal combustion into the rotational motion of a crankshaft. Recent advances in high performance automobile engines demand corresponding technological breakthroughs in the materials for engine parts. In the present research, the powder metallurgy (P/M) process was used to replace conventional quenching and/or tempering processes for mass production and ultimately for more cost-efficient manufacturing of high strength connecting rods. The development of P/M alloy powder was undertaken not only to achieve the improvement in mechanical properties, but also to enhance the machinability of the P/M processed connecting rods. Specifically $MoS_2$ powders were added as lubricants to non-normalizing Fe-Cr-Mn-V-C alloy powder to improve the post-sintering machinability. The effects of $MoS_2$ addition on the microstructure, mechanical properties, and machining characteristics were investigated.
MoO<sub>3</sub> 침출공정 폐액으로부터 치환반응 시스템을 이용한 구리 분말 회수에 대한 연구
김건홍,홍현선,정항철,Kim, Geon-Hong,Hong, Hyun-Seon,Jung, Hang-Chul 한국분말야금학회 2012 한국분말재료학회지 (KPMI) Vol.19 No.6
Recovery of copper powder from copper chloride solution used in $MoO_3$ leaching process was carried out using a cementation method. Cementation is a simple and economical process, necessitating less energy compared with other recovery methods. Cementation utilizes significant difference in standard reduction potential between copper and iron under standard condition. In the present research, Cementation process variables of temperature, time, and added amount of iron scraps were optimized by using design of experiment method and individual effects on yield and efficiency of copper powder recovery were investigated using bench-scale cementation reaction system. Copper powders thus obtained from cementation process were further characterized using various analytical tools such as XRF, SEM-EDS and laser diffraction and scattering methods. Cementation process necessitated further purification of recovered copper powders and centrifugal separation method was employed, which successfully yielded copper powders of more than 99.65% purity and average $1{\mu}m$ in size.