• Journal of the Society of Naval Architects of Korea
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• v.32 no.1
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• pp.83-93
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• 1995

A numerical and experimental investigation on the flow characteristics in the rectangular duct of an MHD propulsion system has been carried out. In numerical analysis, three-dimensional, steady-state, viscous, incompressible electrically conducting fluid flow under the influence of uniformly applied magnetic and electric fields was treated using a finite-difference technique. It was found from the numerical study that when the Lorentz force is weak, the typical parabolic velocity profile under a laminar flow condition changes to an M shaped profile near the electrode region and that the pressure increases linearly from the inlet toward the outlet of the MHD duct under constant electro-magnetic field. In experiment, thrust of the MHD propulsion system can be controlled easily by varying electrode current. The measured pressure gradient along the MHD duct is proportional to the Lorentz force, which is in agreement with the numerical results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.9
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• pp.3583-3589
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• 2010

The semi-implicit scheme proposed by Backhaus is introduced to solve two-dimensional shallow water equation. This mothod is applied for the numerical model solving surface elevation and velocity field of Geum River estuary. For the verification of the method, numerical solutions by this model are compared with ones by Heap's well known explicit model. Solutions of two models resemble each other. The time-step chosen for the semi-implicit scheme turned out to be 3 to 6 times longer than explicit model depending on the stringent CFL criterion. The computation time could be reduced at least 50%. It was proved that this scheme is easy to handle dry banks which can be seen in Geum River estuary and numerical stability is obtained for long time computation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.6
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• pp.825-835
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• 2019

When the tunnel is designed, the ground is classified into several grades and the corresponding support system is applied according to the support pattern table. However, a simple pattern application based on rock grade does not take into account the longitudinal stress transitions occurring at rock grade boundaries. In this study, three-dimensional numerical analysis was performed to estimate the stress change in the longitudinal rock grade change of NATM tunnel, and the influence zone of load transfer was investigated using the influence line and trend line. As a result, the downward change of rock grade in the direction of tunnel excavation occurs in the range of 0.35~0.7D from low-strength rock to high-strength rock around the grade change boundary. It is necessary to apply a downward pattern of about 1.0D to the safety direction in consideration of the influence range of 0.35D to 0.7D.

• The Journal of the Korea Contents Association
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• v.9 no.8
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• pp.57-63
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• 2009

Object recognition technologies using PCA(principal component analysis) recognize objects by deciding representative features of objects in the model image, extracting feature vectors from objects in a image and measuring the distance between them and object representation. Given frequent recognition problems associated with the use of point-to-point distance approach, this study adopted the k-nearest neighbor technique(class-to-class) in which a group of object models of the same class is used as recognition unit for the images in-putted on a continual input image. However, the robustness of recognition strategies using PCA depends on several factors, including illumination. When scene constancy is not secured due to varying illumination conditions, the learning performance the feature detector can be compromised, undermining the recognition quality. This paper proposes a new PCA recognition in which database of objects can be detected under different illuminations between input images and the model images.

• Journal of Korea Water Resources Association
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• v.49 no.4
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• pp.347-359
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• 2016

Flow input from the basin will not remain the same as before due to climate changes. Since the predictions on river discharge due to climate change is given by scenarios, various discharge scenarios were prepared in this study. For a long term and reach prediction, semi-two dimensional sediment transport model, GSTARS, was used. The flood water surface elevations predicted by GSTARS model were analysed statistically and it was concluded that the model is applicable for the South Han River. Three stream tubes is the most suitable to simulate two dimensional river geometric change River geometric changes. For sediment load computation, Ackers and White equation and Yang equation were resonable. River will become narrower regardless of discharge variation, more discharge results in deeper channel.

• Geophysics and Geophysical Exploration
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• v.5 no.3
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• pp.169-177
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• 2002

We develop the weighted-averaging finite-element method which uses four kinds of element sets. By constructing global stiffness and mass matrices for four kinds of element sets and then averaging them with weighting coefficients, we obtain a new global stiffness and mass matrix. With the optimal weighting coefficients minimizing grid dispersion and grid anisotropy, we can reduce the number of grid points required per wavelength to 4 for a $1\%$ upper limit of error. We confirm the accuracy of our weighted-averaging finite-element method through accuracy analyses for a homogeneous and a horizontal-layer model. By synthetic data example, we reconfirm that our method is more efficient for simulating a geological model than previous finite-element methods.

• The KIPS Transactions:PartD
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• v.10D no.1
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• pp.133-142
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• 2003

The major challenge for post-genomic study is to identify structural similarity and relationships of proteins. SCOP (Structural Classification of Proteins) is a typical database for this purpose, providing a derailed description of the structural and functional relationships of the proteins whose three-dimensional structures have been determined. Unfortunately, since the SCOP data is only available as a plain text format, it is cumbersome and error-prone to develop tools and resources to utilize the data more effectively. To meet these researchers to utilize the data more effectively. To meet these requirements, we have developed an XML representation for the SCOP site, users of the tool, named, SCOPBrowser, for effective search of SCOP database. In addition to the information available from the SCOP site, users of the tool can obtain various information such as viewing the tree hierarchy of structure classification of proteins, searching into whole protein domains, showing XML contents of a specific domain, and some useful statistics about protein structures.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.325-325
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• 2012

1차원구속 반도체인 nanowires (NWs)는 전기적, 광학적으로 일반 bulk구조와 다른 특성을 가지고 있어서 현재 많은 연구가 되고 있다. 일반적으로 NWs는 Au 등의 금속 촉매를 이용하여 성장을 하게 되는데 이때 촉매가 오염물로 작용을 해서 결함을 만들어서 bandgap내에 defect level을 형성하게 된다. 본 연구는 Si (111) 기판 위에 GaAs NWs 와 InAs NWs를 촉매를 이용하지 않고 성장 하였다. vapour-liquid-solid (VLS)방법으로 성장하는 GaAs NWs는 Ga의 droplet을 이용하게 되는데 Ga이 Si 기판위에 자연 산화막에 존재하는 핀홀(pinhole)로 이동하여 1차적으로 Ga droplet 형성하고 이후 공급되는 Ga과 As은 SiO2 보다 GaAs와 sticking coefficient 가 좋기 때문에 Ga drolept을 중심으로 빠른 선택적 성장을 하게 되면서 NWs로 성장을 하게 된다. 반면에 InAs NWs를 성장 할 시에 droplet 방법으로 성장을 하게 되면 NWs가 아닌 박막 형태로 성장을 하게 되는데 이것으로 InAs과 GaAs의 $SiO_2$와의 sticking coefficient 의 차이를 추측을 할 수 있다. InAs NWs는 GaAs NWs는 달리 native oxide를 이용하지 않고 InAs 과 Si 사이의 11.5%의 큰 lattice mismatch를 이용한다. 이종의 epitaxy 방법에는 크게 3종류 (Frank-van der Merwe mode, Stranski-Krastanov mode, Volmer-Weber mode)가 있는데 각기 다른 adatom 과 surface의 adhesive force로 나누어지게 된다. 이 중 Volmer-Weber mode epitaxy는 adatom 의 cohesive force가 surface와의 adhesive force보다 큰 경우 성장 되는 방식으로 InAs NWs 는 이 방식을 이용한다. 즉 droplet을 이용하지 않는 vapour-solid (VS) 방법으로 성장을 하였다. 이 때 In 의 migration을 억제하기 위해서 VLS mode 의 GaAs NWs 보다 As의 공급을 10배 이상 하였다. FE-SEM 분석 결과 GaAs NWs는 Ga droplet을 확인 할 수 있었고 InAs NWs는 droplet이 존재하지 않았다. GaAs와 InAs NW는 density와 length가 V/III가 높을수록 증가 하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.11-21
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• 2005

A three-dimensional parallel Euler flow solver has been developed for the simulation of unsteady rotor-fuselage interaction aerodynamics on unstructured meshes. In order to handle the relative motion between the rotor and the fuselage, the flow field was divided into two zones, a moving zone rotating with the blades and a stationary zone containing the fuselage. A sliding mesh algorithm was developed for the convection of the flow variables across the cutting boundary between the two zones. A quasi-unsteady mesh adaptation technique was adopted to enhance the spatial accuracy of the solution and to better resolve the wake. A low Mach number pre-conditioning method was implemented to relieve the numerical difficulty associated with the low-speed forward flight. Validations were made by simulating the flows around the Georgia Tech configuration and the ROBIN fuselage. It was shown that the present method is efficient and robust for the prediction of complicated unsteady rotor-fuselage aerodynamic interaction phenomena.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.1
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• pp.25-33
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• 2015

Following the previous works on the natural frequency of heaving circular cylinder, i.e. Lee and Lee (2013) and Kim and Lee (2013), an investigation of the same spirit on the 2-dimensional cylinder of Lewis form has been conducted. As before, the natural frequency is defined as that corresponding to the local maximum of the MCFR (Modulus of Complex Frequency Response), which is given by the equation of motion in the frequency domain analysis. Hydrodynamic coefficients were found by using the Ursell-Tasai method, and numerical results for them were obtained up to much higher frequencies than before, for which the method was known as numerically unstable in the past. For a wide range of H, the beam-draft ratio, and ${\sigma}$, the sectional area coefficient, including their practical ranges for a ship, results for the natural frequency were computed and presented in this work. Two approximate values for the natural frequency, one proposed by Lee (2008) and another one by the damped harmonic oscillator, were also compared with the current results, and for most cases it was observed that the current result is between the two values. Our numerical results showed that the values of the local maximum of MCFR as well as the natural frequencye increase as ${\sigma}$ increases while H decreases. At present, extension of the present finding to the 3-dimensional ship via the approximate theory like the strip method looks promising.