• 한국표면공학회지
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• 제46권1호
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• pp.22-28
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• 2013

$WS_2$ particles were added to micro-diamond blades with Cu/Sn binding metal as lubricants to improve cutting efficiency. It was found in previous works that the added $WS_2$ lubricant could reduce remarkably the momentary energy consumption during dicing tests but increased wear rate slightly owing to weak bonding between lubricant particles and bond metals. In the present work, the surface of $WS_2$ lubricant particles were etched for activating the surface of $WS_2$ particles that provide even distribution of particles during powder mixing process and improvement of wetting at the interfaces between $WS_2$ particles and molten Cu/Sn bond metals during pressurized sintering so that could provide the improved strength of micro-blades and result in extended life. Chipping behavior of workpiece with the types of micro-blades including $WS_2$ were compared because it is important in semiconductor and micro-packaging industries to control average roughness and straightness of sliced surface which is closely related with quality.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집C
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• pp.380-385
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• 2001

The paper presents a new multidisciplinary design optimization architecture using optimal sensitivity and coordination of interdisciplinary design variables. Original design problem is decomposed into a number of sub-problems that represent individual engineering analysis. The coupled effects between sub-problems are computed by interdisciplinary design variables. System level coordination is determined by optimal parameter sensitivity calculated by finite difference method. The proposed. MDO strategy is applied to a simplified model of rotorcraft blade design associated with structures and aerodynamic disciplines.

• 한국정밀공학회지
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• 제24권7호
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• pp.60-68
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• 2007

This paper presents an efficient 5-axis roughing method for centrifugal impeller. The efficient roughing is minimization of cutting time through minimizing tool tilting and rotating motions. To minimized cutting time, machining area is divided into sub-cutting regions using control points on hub curves and shroud curves of blade used to design and analyze centrifugal impeller. For sub-cutting regions, diameters of cutting tools are determined as big as possible. Then, tool paths are generated with the tilting axis and rotating axis of 5-axis machine limited and fixed, which can give more efficient machining speed and machining stability than the conventional methods. Experimental results show that the proposed method is more efficient than the conventional methods to mill with the only one cutting tool without dividing area and the previous methods to mill with simultaneous 5-axis processing with dividing area.

• 국제학술발표논문집
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• The 8th International Conference on Construction Engineering and Project Management
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• pp.23-29
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• 2020

Multilayer sub-contracting is a significant practice among the world, including Hong Kong. When a principal contractor secured a project from a developer, the specific jobs will usually be breaking down and sub-contractors with the lowest bid [1]. The adoption of multilayer sub-contracting has been a controversy issue which is considered as a two-side blade. While certain studies have been carried out to examine both the contributions, damages and improvements for multi-layer subcontracting, the construction industry and researchers are still waiting for a solid measure to enhance the system. Hence, this research attempts to study the advantages, disadvantages, conducts a comparison between single and multilayer sub-contracting and measures of current Hong Kong construction industry based on literature review, questionnaire and in-depth interviews. To achieve the objectives, Analytic Hierarchy Process (AHP) and total weighted score methods are adopted to examine and rank the criterion. The findings of this study provide a good basis for understanding the major reasons and problems caused by the adoption of multilayer sub-contracting. Besides, the identified safety perspective explores a new perspective regarding to issues of multi-layer subcontracting, which will serve as a solid foundation for further research to enhance safety performance. Finally, the findings of measurements towards improvement of multilayer sub-contracting will also provide a solidsolution for construction industry.

• 한국정밀공학회지
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• 제18권5호
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• pp.171-176
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• 2001

Plasma Display Panel(PDP) is a type of flat panel display utilizing the light emission produced by gas discharge. Barrier Ribs of PDP separating each sub-pixel prevents optical and electrical crosstalks from adjacent sub-pixels. Mold for forming barrier ribs has been newly researched to overcome the disadvantages of conventional manufacturing process such as screen printing, sand-blasting and photosensitive glass methods. Mold for PDP barrier ribs have stripes of micro grooves transferring glass-material wall. In this paper, Stripes of grooves of which width 48${\mu}{\textrm}{m}$ and 270${\mu}{\textrm}{m}$, depth 124${\mu}{\textrm}{m}$, pitch 274${\mu}{\textrm}{m}$ was acquired by machining hard and brittle materials of WC, Silicon, Alumina with dicing saw blade. Maximum roughness of the bottom and sidewall of the grooves was respectively 120nm, 287nm in grooving WC. Maximum tilt angle caused by difference between upper-most width and lower-most width was 2$^{\circ}$. Maximum Radius of bottom curvatures was 7.75${\mu}{\textrm}{m}$. This results satisfies the specification for barrier ribs of 50 inch XGA PDP if the groove form of mold was fully transferred to the barrier ribs. Barrier ribs were formed with Silicone rubber mold, which is transferred from grooved hard materials. Silicone rubber mold has elasticity accommodating the waveness of lower glass plate of PDP.

• 고문화
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• 63호
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• pp.65-82
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• 2004

우리나라 후기구석기시대의 가장 전형적인 문화기는 돌날석기문화와 세형돌날문화와 연관이 있다. 최근 고례리유적과 진그늘유적의 발견으로 우리나라의 전형적인 돌날석기문화가 있음이 확인되었다. 세형돌날 문화는 동북아시아의 25,000년전에 시작된 아시아적인 소형화개넘(microlism)의 전형으로서 동북아시아의 석기문화가 통합되는 계기를 만들었으며 우리나라의 전역에 널리 퍼져있는 대표적인 문화기이다. 이러한 후기구석기시대의 일련의 유적들은 크게 돌날기법과 연관이 있으며, 우리나라 후기구석기시대의 몸돌 성형과 박리기법 등 기술적인 측면에서의 문화 맥락적인 연계성을 확인할 필요가 있다 자갈돌석기전통의 다층위유적 가운데 후기구석기시대 문화층으로 보고된 유적과 절대연대 상 40,000-25,000년 전의 후기구석기시대 유적들에서 확인되는 측면몸돌은 기술적 측면에서 전형적인 돌날석기문화와의 상관관계속에서 나타나는 다양한 문화적 변이를 설명해 주고 있다. 이 몸돌은 시베리아와 극동지역의 후기구석기시대에 자주 출토되는 대표적인 몸돌 중 하나이다. 측면몸돌은 몸돌의 좁은 측면에서 많은 돌날을 떼어내고 재생을 하기에도 용이한 기술적 특징을 갖고 있으며 석재의 제약을 비교적 털 받는 전략적인 몸돌이었다. 우리나리에서 출토되는 측면몸돌은 돌날기법과 연관이 있으며 후기구석기시대로 진입하는 단계에 동북아시아에 정착해 가던 돌날석기문화와의 기술적인 교류의 한 단면을 보여주는 것이라고 생각된다. 이러한 기술적 기반을 갖고 있던 한반도에 점거하며 살던 구석기시대 사람들은 돌날석기문화와 세형돌날문화가 등장하는 시기마다 적응 해 갈 수 있었을 것이며, 다양한 돌날몸돌을 다를 때 측면몸돌을 제작하던 기술로 인한 적응력도 높여 갈 수 있었을 것으로 보인다. 특히 우리나라의 후기구석기시대의 이른 단계로 편년되는 자갈돌석기전통의 유적들에서 이러한 몸돌들이 함께 나라나는 것은 후기구석기시대의 자갈돌석기전통의 연속성에 대한 또 하나의 증거이며 지역적인 적응의 결과의 하나로 볼 수 있다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 제26회 KOSCO SYMPOSIUM 논문집
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• pp.167-171
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• 2003

Acoustic characteristics of baffled combustion chamber to elucidate suppressing effect of baffle on combustion instability are numerically investigated by linear acoustic analysis. A hub-blade baffle of 5 blades is selected as a candidate one and five variants of baffles with various configuration are designed. Resonant-frequency shift and damping factor are analyzed quantitatively as damping parameters. When the hub is located radially at the pressure node, the decrease of resonant frequency and increase of damping factor in 1R mode are dominant. But sub-1T mode is formed within hub, therefore, there would be a possibility of initiating 1T mode in unbaffled region, which would occur another problem. For smaller hub size, four kinds of axial baffle length is selected. As the axial baffle length increases, resonant frequency shift and increase of damping factor of transverse acoustic modes is obtained. Especially, two close acoustic modes such as 1L and 1T could be overlapped for a certain axial length, resulting in extreme increase of damping factor. The present study based on linear acoustic analysis is expected to be a useful confirming tool to predict acoustic field and design a passive control devices such as baffle and acoustic cavity.

• 한국항공우주학회지
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• 제40권5호
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• pp.405-412
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• 2012

높은 효율의 풍력터빈 블레이드을 위해 와류 셀이 장착된 에어포일의 정지상태 및 동실 속 상태에서의 유동제어 특성을 수치적으로 연구하였다. 수치기법은 Roe의 flux-difference-splitting을 사용한 격자점 중심 유한체적법과 이중시간 전진 기법을 사용하는 내재적 시간적분법을 사용하였다. 계산결과 와류 셀을 장착한 경우 셀 내부의 부압으로 인해 양항비증가를 얻을 수 있음을 확인하였다. 동실속의 경우 셀 내부의 와류에 의해 hysterisis 현상을 상당히 감소시킬 수 있음을 확인하였다.

• 한국유체기계학회 논문집
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• 제5권2호
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• pp.29-35
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• 2002

The present study is concerned with the flow patterns induced by various impellers in a rectangular tank. Impellers are FBT (Flat blade turbine), PBT (Pitched blade turbine), Shroud turbine, Rushton turbine, and Helical ribbon turbine types. The solutions of flows in moving reference frames require the use of 'moving' cell zone. The moving zone approaches are based on MRF (Multiple reference frame), which is a steady-state approximation and sliding method, which is an unsteady-state approximation. Numerical results using two moving zone approaches we compared with experiments by Ranade & Joshi, which have done extensive LDA measurements of the flow generated by a standard six-bladed Rushton turbine in a cylindrical baffled vessel. In this paper, we simulated the flow patterns with above-mentioned moving zone approaches and impellers. Turbulence model used is RNG $k-{\epsilon}$ model. Sliding-mesh method is more effective than MRF for simulating the rectangular tank with inlet and outlet. RNG $k-{\epsilon}$ model strongly underestimates the velocity of experimental data and velocity by Chen & Kim's model, but it seems to be correctly predicted in overall distribution.

• 해양환경안전학회지
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• 제26권5호
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• pp.561-568
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• 2020

본 논문에서는 상용코드인 ANSYS CFX를 통한 해양레저 스포츠 및 야외 활동 시 사용 가능한 휴대용 수평축 수차의 유입유속(U) 및 주속비(TSR, Tip Speed Ratio) 변화에 따른 성능해석을 수행하였으며, 해석결과 및 유동장 분석을 통해 설계에 대한 검토 및 장치의 성능을 확인하였다. 또한, 추가적으로 블레이드의 피치각도(α_pitch) 변화에 따른 성능해석을 통해 수차의 성능개선에 필요한 데이터를 획득하고자 하였다. 본 논문의 연구 결과 수치해석 케이스 중 주속비 4인 경우, 모든 유입속도 및 블레이드 피치 각도에서 가장 높은 성능을 보였으며, 설계 유속 이하의 일부 조건에서도 설계 출력인 30 W 이상의 출력을 보였다. 그리고 수치해석 케이스 중 가장 높은 출력과 출력계수는 유입유속 1.5 m/s, 블레이드 피치 각도 3°, 주속비 4에서 보였으며, 출력 약 85 W, 출력계수 약 0.30이었다.