• 대한기계학회논문집B
• /
• 제26권4호
• /
• pp.524-530
• /
• 2002

Micro electric spark discharge device was fabricated on a FOTURAN glass wafer using MEMS processing technique and its performance of electron discharge and subsequent formation of ignition kernel were tested. Micro electric spark device is an essential subsystem of a power MEMS that has been under development in this laboratories. In a combustion chamber of sub millimeter scale depth, spark electrodes are formed by electroplating Ni on a base plate of FOTURAN glass wafer. Optimization of spark voltage and spark gap is crucial for stable ignition and endurance of the electrodes. Namely, wider spark gaps insures stable ignition but requires higher ignition voltage to overcome the spark barrier. Also, electron discharge across larger voltage tends to erode the electrodes limiting the endurance of the overall system. In the present study, the discharge characteristics of the proptotype ignition device was measured in terms of electric quantities such as voltage and currant with spark gap and end shape as parameters. Discharge voltage shows a little decrease in width of less than 50㎛ and increases with electrode gap size. Reliability test shows no severe damage over 10$\^$6/ times of discharge test resulting in satisfactory performance for application to proposed power MEMS devices.

• 대한기계학회논문집B
• /
• 제40권2호
• /
• pp.119-126
• /
• 2016

본 연구는 실험적인 방법과 열유동 해석 방법을 사용하여 대용량 압출형 히트싱크의 방열성능에 미치는 열원 대칭배열의 영향을 고찰하고, 이를 바탕으로 제조원가가 낮은 고효율의 히트싱크를 제안하고자 한다. 실험결과를 통해서 유사한 유효 유동단면적을 가지는 경우에 히트싱크의 전열면적이 방열성능에 큰 영향을 줌을 확인할 수 있었으며, 히트싱크의 양면 모두를 이용하는 방열이 훨씬 효과적인 방열이 가능함을 알 수 있었다. 또한, 대칭으로 열원을 배치한 경우가 비대칭 배치보다 효율적으로 방열됨을 알 수 있었다. 해석연구의 결과를 통해서는 실험결과와 정성적으로는 유사한 경향을 확인할 수 있었으며, 실험연구에서 확인하지 못한 질량유량별 및 투입열량별 추이, 단면과 양면 사용의 정량적 비교 등이 가능하였다.

• 비파괴검사학회지
• /
• 제16권2호
• /
• pp.86-94
• /
• 1996

파괴역학을 기초로 한 구조물의 수명 관리와 안전성 평가에 있어서, 결함의 크기는 매우 중요한 변수인자이다. 집중유도형 교류전위차법(ICFPD)은 구조물 부재의 표면, 이면 및 내면에 존재하는 결함을 검출하고, 그 크기를 측정하기 위하여 개발하였다. 본 비파괴법의 원리는 교류 전류가 흐르는 하나의 도선에 의하여 국부적인 영역에 전류를 집중적으로 유도하는 것을 이용하였다. 도선에 흐르는 전류는 일정 크기와 주파수를 갖는다. 금속표면에 유도된 전위는 탐촉자에 설치된 전위측정용 단자(potential pick-up pins)로 측정한다. 본 논문은 집중유도형 교류전위차법을 이용하여 평판 시험편에 도입한 표면결함과 이면결함을 평가하였다. 표면결함의 경우, 전위차 분포는 결함의 경사도에 따라 변화하고, 결함부와 결함단부의 전위차는 결함의 경사도 및 깊이에 따라 변화한다. 이면결함의 경우, 전위차 분포는 표면결함의 전위차 분포와 구분이 되며, 결함부에서의 전위차는 결함의 깊이에 따라 변화한다.

• 한국태양에너지학회:학술대회논문집
• /
• 한국태양에너지학회 2012년도 춘계학술발표대회 논문집
• /
• pp.96-101
• /
• 2012

An experimental study was conducted to investigate the performance of a concentrating photovoltaic cell (CPV) against temperature. It is know that a high efficiency of a CPV can be achieved only with proper cell temperature as well as high concentration ratio (CR). This study is concerned with appropriate cooling condition for a liquid-convection cooler for the best performance of a specific CPV. A series of experiments was conducted in a range of cell temperatures as a result of varying cooling conditions, while the concentration ratio was 390 and the solar irradiation flux was higher than 900 $W/m^2$ in outdoor environment. The CPV had a planar dimension of 10 by 10 mm. A Fresnel lens was used as a concentrator, of which the dimension was 221 mm(W) ${\times}$ 221 mm(L) ${\times}$ 3 mm(t) and the transmissivity was known to be 0.8. The cooler was attached to the bottom side of the CPV and had a contact area of 21 mm(W) ${\times}$ 26 mm(L), which was identical to the size of the base plate of the CPV. The coolant temperature was controlled by an isothermal bath and the flow rate was controlled and measured by a flowmeter. The experimental results showed that the average of power efficiency of the CPV decreased from 28.6 % to 24.7 % as the cell temperature increased from $36^{\circ}C$ to $97^{\circ}C$. An appropriate cooling method of a CPV might increase the power conversion efficiency by about 4% for the same concentration ratio. Discussion is included from the viewpoint of the combined efficiency in addition to the power efficiency.

• 한국철도학회논문집
• /
• 제14권3호
• /
• pp.240-247
• /
• 2011

본 연구에서는 콘크리트 궤도 침목 내에 설치되는 인서트에 예기치 못하게 침투된 수분의 결빙압이 앵커볼트의 인발강도에 미치는 영향을 유한요소해석을 통해 고찰하였다. 3차원 유한요소해석모델은 콘크리트 침목의 현장실험 결과, 도면 및 레일체결장치의 제원 실측치를 기반으로 수립되었으며, 비선형구성방정식과 파괴 모델은 측정된 압축강도로부터 CEB-FIP 1990 모델코드를 이용하여 추정하였다. 해석모델의 적정성은 철도기술연구원에서 수행한 현장 인발시험 결과 및 실내시험 결과와의 비교를 통해 확인하였다. 다양한 인자, 즉 결빙위치, 앵커볼트 초기 체결력의 크기 및 콘크리트 압축강도에 따른 해석을 수행하였으며, 그 결과를 제시하였다. 해석결과에 의하면, 매립전내 침투수의 결빙력은 균열손상의 가장 가능성 있는 직접적인 원인 중 하나로 간주될 수 있음을 확인하였다. 또한, 외측매립전의 결빙력이 내측 매립전 보다 작은 것으로 나타났으나 그 차이는 크지 않았다.

• 비파괴검사학회지
• /
• 제33권2호
• /
• pp.205-211
• /
• 2013

초음파 감쇠를 이용하여 티타늄 용접부에 대해 기계적 특성, 파단면 및 초음파특성을 연구하였다. 준비된 티타늄 시험편은 아르곤 가스를 이용하여 제작하였다. 티타늄 용접 시험편이 파단 되었을 때 변화하는 초음파 신호변화를 확인하기 위해서 인장시험을 실시하였다. 주사전자현미경을 이용하여 파단면을 관찰하고, 4 MHz 수직 탐촉자를 이용하여 초음파 시계열 신호를 획득하였다. 티타늄 판재에서 용접부는 모재부와 열영향부에 비하여 기계적 특성이 떨어지며 파단면분석을 통해 용접부의 입자크기가 모재부보다 큼을 확인할 수 있었다. RMS 신호 처리한 초음파 포락선의 면적과 인장강도의 상관관계를 나타내었다. 따라서 초음파를 이용하여 티타늄 용접부의 건전성 평가 방법이 유용함을 알 수 있었다.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2010년도 춘계학술발표대회 초록집
• /
• pp.57-57
• /
• 2010

For thin panel welded structure, the various welding distortions were found due to the low resistance against welding deformation. Especially, buckling distortion induced in the thin panel welded structure produce severe problems related to cost in production stage and safety in service life. So, many researches including mechanical and thermal tensioning method for preventing the occurrence of buckling distortion in the production stage have been performed. The purpose of this study is to identify the behavior of longitudinal residual stress at the SA butt weldment with thin plate of 6mm thickness under tension load by 3 dimensional FEA. For it, mesh design for 3D FEA was constructed with 20 nodes brick element for butt weldment and 8 nodes shell element for base metal. According to FEA results, the longitudinal compressive strain inducing tensile residual stress at the butt weldment decreased. It was because the compressive thermal strain in way of weldment was reduced by tension load. The control effect of residual stress increased with an increase in tension load. So, if the amount of tension load applied to the weldment exceeds 1.5 times of longitudinal shrinkage force, the amount of longitudinal residual stress decreased below the critical value inducing the buckling distortion at the SA butt weldment. Its validity was verified by experiment.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2010년도 춘계학술발표대회 초록집
• /
• pp.63-63
• /
• 2010

The pre-heat free consumables for GMAW, SAW and FCAW processes that matches the Cu-bearing PFS-700 steel which has yield strength over 700MPa were developed and evaluated to see the suitability in military such as submarine and battle ship. Explosion bulge test in underwater was developed and applied to see the reliability of welded structure. All welding was conducted without pre-heat before welding, the interpass temperature was below $150^{\circ}C$ for all welding conditions. Tensile strength for the weld metal in GMAW, SAW and FCAW process is 887MPa, 875MPa and 813MPa, respectively, these values are similar to the base metal of PFS-700 steel of 838MPa. EBT results in GMAW, SAW and FCAW show 14.0%, 14.02% and 15.9% reduction of thickness without generation of crack, respectively and stand-off distance was set up properly to have over 14.0% reduction of thickness. Through EBT results, the developed new consumables are applicable to the weapon systems such as submarine and battle ship.

• 한국해양공학회지
• /
• 제29권4호
• /
• pp.322-330
• /
• 2015

As a new technical approach, a hydraulic and magnetic clamp device was developed to realize a magnetic clamp crane system by simultaneously actuating eight individual hydraulic cylinders. In this approach, an Sr-type of ferritic permanent magnet (SrO· 6Fe₂O₃), rather than the previous electromagnet, was utilized for the purpose of lifting and transporting the large curved steel plates used for manufacturing ships. This study had the goal of developing and manufacturing a hydraulic, magnetic clamp prototype composed of three main parts, including the base frame, cylinder joint, and magnet joint, in order to safely transport curved steel plates. Furthermore, this research included a performance evaluation of the manufactured prototype and acquired the purposed quantity value in the performance test. The most significant item, the magnetic adhesive force (G), was evaluated in a performance test, which utilized a ferritic permanent magnet (Sr type) with 3700~4000 G of residual induction (Br) and 2640/2770 Oe of coercive force (Hc). In particular, relevant items such as the hoist tension (kN), transportation time (s), and applied load (Kgf) on the hydraulic cylinders were also evaluated in order to determine the optimum values.

• 한국기계가공학회지
• /
• 제19권7호
• /
• pp.52-59
• /
• 2020

Automatic tool changers (ATCs) can be divided into drum and chain types. Drum-type ATCs contain a magazine, where the tools are mounted, and a cam gearbox, which swaps the tools via roller gear and grooved plate cams. Drum-type ATCs are advantageous in that the operating time for the tool magazine is more rapid than that of chain-type ATCs and the length of the unit is shorter. Thus, drum-type ATCs can be fabricated into various shapes and forms depending on the number of tools and the magazine size in accordance with machining center requirements and consumer demand. In particular, the price competitiveness of a machining center with a drum-type ATC is higher, while drum-type ATCs are more rigid with fewer parts, possibly reducing the need for regular servicing. This study aims to verify the structural stability and design validity of the magazine base, which is the main structure of a drum-type ATC, using finite element analysis. This study kinematically verifies the specifications of the selected drive motor and reducer and assessed the design of the cam gearbox. It also conducts a structural analysis of the roller camp, which is the core component of the cam gearbox, based on the results of the kinetodynamic analysis, thus validating the structural design.