• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.5
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• pp.63-68
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• 1998

The absolute pressure sensor using SDB wafer has been fabricated. the structure of the sensor consists of two wheatstone bridges and a diaphragm. One of the two wheatstone bridges is located on the edge of diaphragm, and the other is located on the center of diaphragm. The diaphragm cavity is sealted in vacuum (~10$^{5}$ Torr) to reduce the effect of temperature due to the vapor in the cavity on the sensitivity of pressure sensor. This is the minor method of temperature compensation method. In this experiment the main compensation method is to use the difference of the two bridge offset voltages. The drift of offset voltage with temperature is reduced by using this method so that temperature charcteristics is improved. In this method the temperature effect in the range of 22~100.deg. C was compensated over 80%.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1751-1753
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• 2000

다결정 실리콘 박막 트랜지스터 (poly-Si TFT)의 누설전류를 억제하기 위해 게이트 절연막(gate oxide)의 가장자리에 캐비티(cavity)를 가지는 새로운 구조의 다결정 박막 트랜지스터를 제안하였다. 캐비티는 드레인(drain) 공핍영역(depletion region) 위에 형성되어 드레인 주변에 유도되는 수직전계를 감소시켜 누설전류를 억제하고 소자의 안정성을 향상시킬 수 있다. 본 연구에서 제작된 poly-Si TFT는 기존의 TFT에 비해 온-오프 전류비가 향상되었고 전기적 스트레스 후의 문턱전압 변화가 작음을 확인하였다.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.387-392
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• 2013

본 연구에서는 천음속 전투기 무장창 내부의 압력 진동을 제어하기 위해 F-111의 무장창을 2차원 공동(Cavity)으로 모델링하고, EDISON_전산열유체 시스템을 활용하여 공동의 형상 변화에 따라 발생하는 유동 특성을 분석하였다. 최근의 전투기들은 항력 감소와 스텔스 기능을 위해 무기를 기체 안에 내장하는데, 덮개를 열 때 발생하는 공동 형상에 의해 강한 압력 진동이 유발된다. 이러한 진동은 무장창과 주변 기계 장치에 구조적 진동을 일으키고 고장 또는 파괴를 유발하므로, 근본적인 해결책이 필요한 중요한 문제이다. 본 연구에서는 진동의 원인이 되는 전단층(Shear layer) 불안정성을 해결하기 위해 기존에 연구된 형상(Leading edge extension 및 Ramp)과 본 연구에서 새로 제안한 Ramp extension을 적용해 보았다. 그 결과 압력 진동의 원인이 되는 유동 특성이 줄어들고 압력 진동 역시 감소했음을 관찰할 수 있었다.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.3
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• pp.41-50
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• 1989

A basic formulation of the panel method, which is based on the potential field formulation, is reviewed for the case of two-dimensional hydrofoil problems. Numerical procedures to improve the computational efficiency of the panel method are suggested. By investigating local behavior of the flow around the trailing edge, a wedge type Kutta condition is formulated. By subdividing the trailing edge panels, where dipole strengths of the subdivided panels follow the local behavior of the potential values of the flow outside a wedge, the circulation around a hydrofoil is calculated accurately with a relatively small number of panels. The subdividing technique to improve the accuracy of the numerical Kutta condition is proved to be efficient. A local behavior of the flow around the leading edge is also investigated. By matching the flow around the leading edge with that around a parabola, a very accurate velocity distribution is obtained with relatively small number of panels. An accurate prediction of the stagnation point and the pressure distribution near the leading edge may contribute to improve the accuracy of cavity predictions and boundary layer calculations around hydrofoils.

• International Journal of Fluid Machinery and Systems
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• v.2 no.3
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• pp.206-214
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• 2009

Alternate blade cavitation, rotating cavitation and cavitation surge in rocket turbopump inducers were simulated by a three dimensional commercial CFD code. In order to clarify the cause of cavitation instabilities, the velocity disturbance caused by cavitation was obtained by subtracting the velocity vector under non-cavitating condition from that under cavitating condition. It was found that there exists a disturbance flow towards the trailing edge of the tip cavity. This flow has an axial flow component towards downstream which reduces the incidence angle to the next blade. It was found that all of the cavitation instabilities start to occur when this flow starts to interact with the leading edge of the next blade. The existence of the disturbance flow was validated by experiments.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1753-1755
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• 1996

This paper presents an analysis of the 3D microwave oven considering its forming. The results were compared with experimental data. Finite Element Method(FEM) using edge clement is employed for the analysis. For solving the large sparse system matrix equation was solved using the parallelized QMR method. Analysis of the 3d cavity has troublesome difficulties such as spurious solutions, too many memory and long computation time. We overcome this difficulties by using edge clement for spurious solutions and the parallelized QMR method by the aid of Paralle Virtual Machine(PVM) for the memory and computation time.

• Progress in Superconductivity
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• v.2 no.2
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• pp.86-91
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• 2001

Temperature dependences of the unloaded Ｑ(Ｑ$_{0}$) and the resonant frequency ( $f_{0}$) of YB $a_2$C $u_3$ $O_{7-{\delta}}$ (YBCO) microstrip ring resonators and rutile-loaded cylindrical cavity resonators were measured at low temperatures. Dc magnetron-sputtered YBCO films grown on Ce $O_2$-buffered r-cut sapphire (CbS) substrates were used fur this purpose. The surface resistances ( $R_{s}$) of YBCO films measured by both a microstrip ring resonator and a TE $01\delta$/ mode rutile-loaded cylindrical cavity resonator are compared with each other. It turned out that the values of $R_{s}$ measured by the microstrip resonator technique are comparable to those by the rutile-loaded resonator technique at temperatures lower than ~50 K. However, above 50 K, the $R_{s}$ measured by the microstrip resonator technique appeared higher according to the temperature. Our results show that the current crowding effects near the edge of a microstrip resonator become more significant at temperatures near the critical temperature.emperature.e.e.e.e.e.e.

• Journal of Chest Surgery
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• v.7 no.2
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• pp.163-168
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• 1974

Five cases of traumatic diaphragmatic hernia were repaired in the Department of Thoracic Surgery, Seoul National University Hospital, during the period from 1967 to 1974. The first case, a 14-year aid girl, was diagnosed as diaphragmatic hernia during laparotomy because of jejunal perforation 3 days after traffic accident. Herniated stomach, transverse colon, spleen and left lobe of the liver were repositioned and the diaphragmatic rupture on left posterolateral portion was repaired with two layers of nonabsorbable sutures by transthoracic approach. The second case, a 26-year old man,was diagnosed immediately after traffic accident at a local clinic and transferred to this hospital 24 hours later. Herniated stomach, transverse colon and jejunum were repositioned amd diaphragmatic rupture,about 9 cm in length,from the posterolat.edge to the base of pericardium was sutured in two layers. The third case, a 26-year old man who had stab wound on the left lower lateral chest two years ago,was admitted with sudden abdominal pain and vomiting. Upper gastrointestinal series with barium meal revealed diaphragmatic hernia. The herniated stomach and transverse colon through the defect,about 3.5cm in diameter, at anterolateral portion on the left side,were repositioned and repaired with two layers of nonabsorbable sutures. The forth case, a 26-year old man, sustained blunt trauma to the chest by a roller and was transferred to the emergency room complaining of dyspnea 40 minutes after the accident. The diaphragmatic rupture extended from left midaxillary line to contralateral anterior axillary line,about 20cm long, at anterior portion of diaphragm, which was repaired with two layers, of nonabsorbable sutures. The fifth case, a 4-year old girl, had two separate diaphragmatic ruptures on both sides, which were caused by traffic accident. Immediate upper gastrointestinal series after injury showed herniated stomach, colon and spleen into left Chest cavity. Another small rupture with anterior edge of right lobe of the liver in chest cavity was noted. These were repaired with non-absorbable sutures via thoracotomy.

• Wind and Structures
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• v.28 no.5
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• pp.285-298
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• 2019

For super long-span bridges, the aerodynamic forces induced by the flow passing the box girder should be considered carefully. And the Reynolds number sensitively of aerodynamic characteristics is one of considerable issue. In the study, a numerical study on the Reynolds number sensitivity of aerodynamic characteristic (flow pattern, pressure distribution and aerodynamic forces) of a twin-box girder were carried out using large eddy simulation (LES) with the dynamic Smagorinsky-Lilly subgrid model. The results show that the aerodynamic characteristics have strong correlation with the Reynolds number. At the leading edge, the flow experiences attachment, departure, and reattachment stages accompanying by the laminar transition into turbulence, causing pressure plateaus to form on the surface, and the pressure plateaus gradually shrinks. Around the gap, attributing that the flow experiences stages of laminar cavity flow, the wake with alternate shedding vortices, and turbulent cavity flow in sequence with an increase in the Reynolds number, the pressures around the gap vary greatly with the Reynold number. At the trailing edge, the pressure gradually recovers as the flow transits to turbulence (the flow undergoes wake instability, shear layer transition-reattachment station), In addition, at relative high Reynolds numbers, the drag force almost does not change, however, the lift force coefficient gradually decreases with an increase in Reynolds number.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.2
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• pp.159-173
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• 1991

This paper describes a potential-based panel method formulated for the analysis of a super-cavitating two-dimensional hydrofoil. The method employs normal dipoles and sources distributed on the foil and cavity surfaces to represent the potential flow around the cavitating hydrofoil. The kinematic boundary condition on the wetted portion of the foil surface is satisfied by requiring that the total potential vanish in the fictitious inner flow region of the foil, and the dynamic boundary condition on the cavity surface is satisfied by requiring thats the potential vary linearly, i.e., the tangential velocity be constant. Green's theorem then results in a potential-based integral equation rather than the usual velocity-based formulation of Hess & Smith type. With the singularities distributed on the exact hydrofoil surface, the pressure distributions are predicted with improved accuracy compared to those of the linearized lilting surface theory, especially near the leading edge. The theory then predicts the cavity shape and cavitation number for an assumed cavity length. To improve the accuracy, the sources and dipoles on the cavity surface are moved to the newly computed cavity surface, where the boundary conditions are satisfied again. This iteration process is repeated until the results are converged. Characteristics of iteration and discretization of the present numerical method are much faster and more stable than the existing nonlinear theories. The theory shows good correlations with the existing theories and experimental results for the super-cavitating flow. In the region of small angles of attack, the present prediction shows and excellent comparison with the Geurst's linear theory. For the long cavity, the method recovers the trends of the Wu's nonlinear theory. In the intermediate regions of the short super-cavitation, the method compares very well with the experimental results of Parkin and also those of Silberman.