• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.25 no.4
• /
• pp.207-218
• /
• 2013

This study is based on a series of numerical modeling experiments to understand the circulation and its change in the Chunsu Bay (CSB), Yellow Sea of Korea. A skill analysis was performed for the tidal height and tidal current of the observation data using the amplitude and phase of the 4 major tidal constituents respectively for verification of modeling experimental results. As a result, most of the skill score was seen to be over 90%, so numerical model experiment results can be said to be in good agreement with the observed tidal height and tidal current. Tidal wave proceeded from the entrance of the CSB towards inside, and the tidal range gradually increased to the north. It took about 10 to 30 minutes for the tidal wave to reach to northern end. The tidal wave showed a characteristic to rotate counter-clockwise in the southern part. The tidal current flowed to the north-south direction along the bottom topography; the angle of the major axis appeared alongside the isobath. It showed the characteristics of reversing tidal current with the minor axis less than 10% of the major axis. The strength of the tidal residual current that is influenced by geographical factors including bathymetry and coastline showed the range of 1~30 cm/sec, greater in the south channel and smaller in northern Bay. Two pairs of cyclonic/anti-cyclonic eddies around Jukdo and 3~4 pairs of strong eddies at the southern part of CSB in hundreds of m to a few km size by relative vorticity derived from the tidal residual current.

• Polymer(Korea)
• /
• v.31 no.3
• /
• pp.206-214
• /
• 2007

The theoretical study is developed for predicting the thermal expansion changes of composites which include complex inclusion, which is used three-dimensional ellipsoid model ($a_1>a_2>a_3$), which has two aspect ratios (the primary aspect ratio, $\rho_{\alpha}=a_1/a_3$ and the secondary aspect ratio, $\rho_{\beta}=a_1/a_2$). We can predict the feature of general thermal expansion factors by theoretical approach of matrix with aligned ellipsoidal inclusion using the Eshelby's equivalent tensor. The coefficients of longitudinal linear thermal expansion ${\alpha}_{11}$ decrease to those of inclusions, ${\alpha}_f$, as both aspect ratios increase. The coefficients of transverse linear thermal expansion of composites ${\alpha}_{33}$ initially increase and show the parabolic corves with maximum values, as the concentrations of filler increase. The coefficient of thermal expansion, ${\alpha}_{22}$ in the transverse direction decreases, as $\rho_{\alpha}$ increases, however, ${\alpha}_{22}$ increases as $\rho_{\beta}$ increases. The coefficient of linear thermal expansion of composites, ${\alpha}_{33}$ in the normal direction increases, as $\rho_{\alpha}$ increases, while ${\alpha}_{33}$ decreases as $\rho_{\beta}$ increases.

• Journal of the Korean Vacuum Society
• /
• v.18 no.1
• /
• pp.60-65
• /
• 2009

We performed a study on optical properties of $BaSm_2Ti_4O_{12}$ thin films by vacuum ultra violet spectroscopic ellipsometry in the $0.92{\sim}8.6\;eV$ energy range. For the analysis of the measured ellipsometric spectra, a 5-layer model was applied where optical property of the $BaSm_2Ti_4O_{12}$ layer was well represented by a Tauc-Lorentz dispersion function. Our analysis clearly showed new structure in high energy region at about 7.5 eV Consistent changes of refractive index & extinction coefficient of the $BaSm_2Ti_4O_{12}$ thin film by the growth and annealing temperatures were also confirmed.

• Tunnel and Underground Space
• /
• v.11 no.1
• /
• pp.42-58
• /
• 2001

In order to protect the environment from waste disposal activities, the prediction of the flux and flow paths of the contaminants from underground facilities should be assessed as accurately as possible. Especially, the prediction of the pathways and travel times of the nuclides from high level radioactive wastes in a deep repository to biosphere is one of the primary tasks for assessing the ultimate safety and performance of the repository. Since the contaminants are mainly transported with groundwater along the discontinuities developed within rock mass, the characteristics of groundwater flow through discontinuities is important for the prediction of contaminant fates as well as safety assessment of a repository. In this study, the actual fracture network could be effectively generated based on in situ data by separating geometric parameter and hydraulic parameter. The calculated anisotropic hydraulic conductivity was applied to a 3D porous medium model to calculate the path flow and travel time of the large studied area with the consideration of the complex topology in the area. Using the model, the pathways and travel times for groundwater were analyzed. From this study, it was concluded that the suggested techniques and procedures for predicting the pathways and travel times of groundwater from underground facilities to biosphere is acceptable and those can be applied to the safety assessment of a repository for radioactive wastes.

• Journal of the Society of Naval Architects of Korea
• /
• v.37 no.2
• /
• pp.70-76
• /
• 2000

A numerical study on the viscous flow around a 2-dimensional circulation control foil is carried out for application on the field of naval architecture and ocean engineering. The governing equations are the RANS and the continuity equations. The equations are discretized by finite difference method and MAC method and the pressure poisson equation is calculate by a SOR method and an O-type non-staggered boundary fitted coordinate system which is overlapped near the slot is used to improve the numerical accuracy. Turbulence is approximated by a modified Baldwin-Lomax turbulence model. In the present paper, the Coanda effect on a 2-dimensional foil of a 20% thickness ellipse with modified rounded trailing edge has been numerically studied. The change in drag and lift of the foil with various jet momentums are calculated and compared to the experimental results to show good agreements.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.11C
• /
• pp.1071-1076
• /
• 2006

In this paper, we develop face and hand tracking for sign language recognition system. The system is divided into two stages; the initial and tracking stages. In initial stage, we use the skin feature to localize face and hands of signer. The ellipse model on CbCr space is constructed and used to detect skin color. After the skin regions have been segmented, face and hand blobs are defined by using size and facial feature with the assumption that the movement of face is less than that of hands in this signing scenario. In tracking stage, the motion estimation is applied only hand blobs, in which first and second derivative are used to compute the position of prediction of hands. We observed that there are errors in the value of tracking position between two consecutive frames in which velocity has changed abruptly. To improve the tracking performance, our proposed algorithm compensates the error of tracking position by using adaptive search area to re-compute the hand blobs. The experimental results indicate that our proposed method is able to decrease the prediction error up to 96.87% with negligible increase in computational complexity of up to 4%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.201-201
• /
• 2008

박형초음파모터의 구조는 그림 1(a) 와 같이 크로스형태의 앓은 스테이터에 윗면과 아랫면에 각각 8 개의 압전세라믹이 부착된 형태이다. 압전세라믹의 분극방향은 로터와 접촉하는 스테이터의 A, B, C, D 네 개의 타점에서 순차적인 타원변위가 생성되도록 결정된다. 유한요소해석프로그램인 ATILA 5.2.4를 사용하여 최적설계를 한 결과 폭 3[mm], 길이 18[mm], 두께 1.8[mm], Brass 재질, Mid surface clamp 조건에서 입력전압 18[Vrms] 일 때 0.3[${\mu}m$]의 변위를 보였다. 최적설계된 모델을 제작하였고, 정확한 실험결과를 얻기 위해서 푸쉬풀게이지, x-y스테이지, rpm 메타, 토크게이지를 이용하여 실험테이블을 구성하였다. 그림 1(b) 는 마이크로컨트롤러를 이용한 구동 드라이버를 보여준다. 한 주기에서 1/4분주의 순차적인 네 개의 구형파를 생성하고, 이를 push-pull회로를 동하여 90도의 위상차가 나는 정현파를 생성하여 초음파 모터의 구동전원으로 사용한다. 엔코더와 AD 컨버터를 이용하여 정속도 운전을 위한 피드백 제어가 된다. 제안된 구동드라이버를 이용하여 측정한 결과, 구동 주파수 88.6[kHz], 입력전압 [40Vrms], preload 0.2 [N]에서 130 [rmp] 의 속도와 25 [gfcm] 의 토크특성을 보였다. 압력전압을 증가시킬수록 속도는 선형적인 증가를 보였고, 토크는 이와 반대로 감소하는 특성을 보였다. 피드백 제어회로가 없는 경우에는 preload 변화에 따른 극심한 속도 변화를 보였고, 피드백 제어를 하였을 경우에는 0.2~0.4[N]의 범위에서 정속도 운전이 가능함을 확인하였다. 기존의 주파수발생기와 파워 엠프를 이용한 구동장비와의 특성비교에서도 큰 차이를 보이지 않았으며, 장시간의 운전에도 안정적인 구동이 가능함을 확인하였다.

• Journal of the Korean Geophysical Society
• /
• v.3 no.1
• /
• pp.13-24
• /
• 2000

In this study, GPS surveying at bench marks in Cheju Island and with these data, calculate GPS/Levelling geoid in Cheju area. And compare this geoid with PNU95 Geoid. The results are as follows : 1. The ellipsoidal height of each bench mark was measured ${\pm}3cm$ with accuracy in GPS surveying. 2. Calculated CPS/Levelling Geoid well represents the variations of Cheju terrain. The correlation formula between the geoid and elevation above sea level in Cheju area is as fellow : $$N\;=\;0.001082\;{\times}\;h\;+\;25.458\;{\pm}\;0.227\;s.d.$$ 3. Calculated GPS/Levelling Geoid and PNU95 Geoid are welt fitted and the RMS difference between the two Geoids is 0.14 m.

• Journal of the Korean Geotechnical Society
• /
• v.36 no.4
• /
• pp.5-15
• /
• 2020

This paper proposes a revised Modified Cam Clay type failure surface based on the critical state theory. In the plane of the mean effective and von Mises stresses, the original Modified Cam Clay model has an elliptic failure surface which leads the critical-state mean effective stress to be always half of the pre-consolidation mean effective stress without hardening and evolution rules. This feature does not agree with the real mechanical response of clay. In this study, the preconsolidation mean effective stress only reflects the consolidation history of the clay whereas the critical state mean effective stress only relies on the currenct void ratio of clay. Therefore, the proposed failure surface has a distorted elliptic shape without any fixed ratio between the preconsolidation and critical state mean effective stresses. Numerical simulations for various clays using failure surfaces as yield surface provide mechanical responses similar to the experimental data.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2009.04b
• /
• pp.51-51
• /
• 2009

Thin Cross 초음파모터의 구조는 그림 1(a)와 같이 크로스형태의 얇은 스테이터에 윗면과 아랫면에 각각 8개의 압전세라믹이 부착된 형태이다. 압전세라믹의 분극방향은 로터와 접촉하는 스테이터의 중심부인 네 개의 타 점에서 순차적인 타원변위가 생성되도록 결정된다. 유한요소해석프로그램인 ATILA 5.2.4를 사용하여 최적설계된 모델을 제작하였고, 푸쉬풀 게이지, x-y 스테이지, rpm 메타, 토크 게이지를 이용하여 구동시스템을 구성하였다. 그림 1(b)는 마이크로컨트롤러(ATmega)를 이용한 구동 드라이버를 보여준다. 한 주기에서 1/4분주의 순차적인 네 개 의 구형파를 생성하고, 이를 push-pull회로를 통하여 90도의 위상차가 나는 정현파를 생성하여 초음파 모터의 구동 전원으로 사용한다. 피드백 회로인 맨코더와 AD 컨버터는 정속도 운전을 위해서 사용되었다. 제안된 구동드라이버를 이용하여 측정한 결과, 기존의 제품화된 드라이버와 비교하여도 특성의 큰 차이를 보이지 않았으며 피드백 회로를 통하여 부하변화에 따른 속도의 극심한 변화를 비교적 안정화 시킬 수 있었다. 입력전압을 증가시킬수록 속도는 선형적인 증가를 보였고 토크는 이와 반대로 감소하는 특성을 보였다. 피드백 제어회로가 없는 경우에는 프리로드 변화에 따른 극심한 속도 변화를 보였고, 피드백 제어를 하였을 경우에는 0.2~0.4[N]의 범위에서 정속도 운전이 가능함을 확인하였으며, 장시간의 운전에도 온도 및 속도특성이 안정적인 특성을 보였다.