• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.7
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• pp.721-730
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• 2012

The present paper presents a numerical study on multiphase flows induced by wall adhesion. The continuum surface force (CSF) model with the wall adhesion boundary condition model is used for calculating the surface tension force; this model is implemented in an in-house solution code (PowerCFD). The present method (code) employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with a volume capturing method (CICSAM) in a volume of fluid (VOF) scheme for phase interface capturing. The effects of wall adhesion are then numerically simulated by using the present method for a shallow pool of water located at the bottom of a cylindrical tank with no external forces such as gravity. Two different cases are computed, one in which the water wets the wall and one in which the water does not wet the wall. It is found that the present method efficiently simulates the surface tension-dominant multiphase flows induced by wall adhesion.

• Journal of Aerospace System Engineering
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• v.12 no.3
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• pp.9-17
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• 2018

For Earth observation, a small satellite camera has relatively weak structural stability compared to medium-sized satellite, resulting in misalignment of optical components due to severe launching and space environments. These alignment errors can deteriorate the optical performance of satellite cameras. In this study, we proposed a 3-axis focus mechanism to compensate misalignment in a small satellite camera. This mechanism consists of three piezo-electric actuators to perform x-axis and y-axis tilt with de-space compensation. Design requirements for the focus mechanism were derived from the design of the Schmidt-Cassegrain target optical system. To compensate the misalignment of the secondary mirror (M2), the focus mechanism was installed just behind the M2 to control the 3-axis movement of M2. In this case, flexure design with Box-Behnken test plan was used to minimize optical degradation due to wave front error. The wave front error was analyzed using ANSYS. The fabricated focus mechanism demonstrated excellent servo performance in experiments with PID servo control.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• 2006.11a
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• pp.194-197
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• 2006

교량의 고성능화, 고효율화 및 센서기술의 발전에 따라서 최근의 장대교량의 경우 교량에 각종 센서를 부착하여 상태를 실시간으로 교량의 상태를 계측하는 시스템이 개발되어 사용되고 있다. 하지만, 기존의 센서와 데이터 로거를 이용한 계측시스템은 높은 설치비가 요구되며 센서 설치비의 50%이상이 통신케이블에 관련된 비용이다. 본 논문에서는 설치비용 절감과 저렴한 유지관리비용 및 센서의 추가 및 교체가 손쉬운 무선기반의 계측시스템 개발에 관하여 논하고자 한다. 교량의 부재에 부착되어있는 센서들 사이 근거리 무선통신은 ZigBee를 이용한 무선통신네트워크를 구성하였으며, 교량과 교량관리소 사이의 장거리 통신에는 국내 휴대전화에 사용되고 있는 CDMA 통신망을 이용하여 데이터를 전송하는 방식을 취하고 있다.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.6 no.2
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• pp.99-108
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• 2002

그리드 고정용 전자석은 절단금형에서 여러 조각으로 나누어진 매우 얇고 가벼운 그리드를 전자석에 흡착시켜 그리드를 부착한 장소까지 이송하는 역할을 하는 전자석이다. 설계목표는 (1)그리드 고정용 전자석이 착자, 탈자 및 이동시 전자석에 흡착된 그리드 조각의 정렬상태가 동요되지 않는 전자석의 설계, (2)금형(그리드 흡착면)에 잔류자기가 최소화되는 설계, (3)전자석이 탈자되었을 때, 잔류자기가 최소화되는 설계에 초점을 두었다. 자장분포는 유한요소법으로 계산하였고, 전자력 계산은 Maxwell stress tensor법을 사용하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.1
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• pp.47-54
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• 2012

We developed a novel method of fluidic self-assembly to replace the conventional pick-and-place method. This method is cheaper and more effective than the previous method. For this research, we compared mathematical models with experimental results using the parameters of the drag force, the capillary force, and the restoring force for effective chip assembly, and the results for the alignment to the substrate. We obtained a 96.5% attach rate and $5^{\circ}$-misalignment to the substrate in a 500 ${\mu}m$ solder ball.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.150.1-150.1
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• 2011

한국천문연구원은 미국 텍사스 대학 및 경희대와 함께 2개의 적외선 고분산 분광기 프로젝트를 진행하고 있다. 2013년 완성을 목표로 진행하고 있는 IGRINS ((the Immersion GRating INfrared Spectrograph) 는 최종 설계를 완료하여 지난 8월 25일 최종 설계 검토 회의를 진행하였으며, 내년 상반기까지 제작, 하반기 실험실 정렬을 거쳐 2013년맥도날드 2.7미터 부착 시험 관측을 예정하고 있다. 한국이 참여하고 있는 거대망원경 GMT (Giant Magellan Telescope)의 제 1세대 관측기 기로 제안한 고분산 적외선 분광기 GMTNIRS 는 IGRINS의 성능에 J, L, M band 분광기능을 더한 것이다. 총 6개의 개념 설계 기기중 하나로 선정되어 지난 1년간 개념설계를 진행해 왔으며, 10월 3일 최종 개념 설계 검토 회의를 진행할 예정이다. 이 두 기기의 성능, 현재까지의 진행상황 그리고 앞으로의 계획에 대해 설명한다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.6
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• pp.513-523
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• 2014

A fluid transport technique is a key issue for the development of microfluidic systems. In this study, the movement of a droplet on horizontal hydrophilic/hydrophobic surfaces, which is a new concept to transport droplets without external power sources that was recently proposed by the author, was simulated using an in-house solution code(PowerCFD). This code employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with interface capturing method(CICSAM) in a volume of fluid(VOF) scheme for phase interface capturing. The droplet transport mechanism is examined through numerical results that include velocity vectors, pressure contours, and total kinetic energy inside and around the droplet.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.881-885
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• 2004

We report a method for making a device on which semi-conducting single-walled carbon nanotubes are attached selectively between two metal electrodes. This method is divided two processes. First we can connect a rope of single-walled carbon nanotubes(SWNTs) between two electrodes using the electric field. But a SWNTs' rope obtained by the first process was composed of a few of metallic and semi-conducting SWNTs together. The second process is to burn the metallic and semi-conducting nanotubes through applying a voltage. As a result, we can obtain a semi-conducting SWNT device. To make the patterned electrodes, we deposited $SiO_2$(150nm) on a wafer. After then, we made a patterned samples with Ti(200 $\AA$)/Au(300$\AA$). We empirically obtained a electric condition 0.66 $V_{pp}$ /${\mu}{\textrm}{m}$@5MHz. From this result, we verified that most of current go through the metallic nanotubes in this device. When we apply DC voltage between two electrodes, the metallic carbon nanotubes are burnt. Finally, we can obtain a semi-conducting nanotube device which we desire to make. We got the I-V characteristic graph which has shown the semi-conducting property. We hope to apply to the various applications using this selective semi-conducting carbon nanotube deposition method.ethod.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.3 s.333
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• pp.17-24
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• 2005

We fabricated PIN-Photodiodes with a single mode fiber for analog communications and analyzed characteristics of the devices. The fabricated PIN-Photodiode shows a bandwidth of 1.5 GHz, a dark current of 20 p4 a capacitance of 0.48 pF, and the responsivity of 0.9 V/W, a second order distortion of -72 dBc. In this paper, we developed a new optical Packaging technology that is aligning in real-time monitoring of both responsivity and IM2 characteristics. As a result responsivity has been improved by 0.03 V/W, and also U has been improved by $3\~5\;dBc$. On the other hand, failure ratio has been reduced by $3.5\%$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.3
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• pp.263-270
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• 2014

A fluid transport technique is a key issue for the development of microfluidic systems. In this paper, a new concept for transporting a droplet without external power sources is proposed and verified numerically. The proposed device is a heterogeneous surface which has both hydrophilic and hydrophobic horizontal surfaces. The numerical simulation to demonstrate the new concept is conducted by an in-house solution code (PowerCFD) which employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with interface capturing method (CICSAM) in a volume of fluid (VOF) scheme for phase interface capturing. It is found that the proposed concept for droplet transport shows superior performance for droplet transport in microfluidic systems.