• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.9
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• pp.938-943
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• 2014

The scattered field by a gap/crack on the PEC surface of a large object having low-observable RCS cannot be negligible, but may not be analyzed by the known high-frequency technique. If the electrical width of the crack is very small, the crack can be modeled by an impedance strip, whose scattering formulation can be analytically obtained based on a low-frequency approximation. The scattering solution is formulated for the 2D strip and TE(Transverse Electric) or TM(Transverse Magnetic) wave incidence, from which a 3D ILDC(Incremental Length Diffraction Coefficients) can be extracted. Using the ILDC formulation, the scattering by any arbitrary shaped crack can be estimated. In this paper, an improved ILDC equations are proposed, which combine the known TE and TM solutions. The improved accuracy of the proposed solution is numerically verified.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.862-865
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• 2012

유사량은 하천의 단면을 단위시간 동안 통과하는 토사의 양을 의미하며, 하천 구조물의 설계 및 유지관리를 위한 기본자료로 활용된다. 유사량은 하천 유역의 지형적인 특성과 기상요소에 영향을 받으며, 이를 규명하기 위한 많은 연구들이 수행되어 왔다. GIS기반의 유사량 예측모델로서 국내에서는 개정범용토양유실공식과 유사운송비(Sediment Delivery Ratio)를 이용하여 유역단위 유사량을 예측하는 연구가 이루어져왔다. Gavrilovi$\acute{c}$ 모델은 유역의 총 연유사량을 예측하고 토양침식의 정도를 정량화할 수 있는 경험적 모형으로 지질 및 토양, 지형조건, 기후인자(연평균 강우량, 연평균 온도), 토지이용의 6가지 입력변수로 구성되어 있다. 본 연구는 Gavrilovi$\acute{c}$ 모델의 국내 적용성을 검토하기 위한 것으로서, 왕숙천 유역을 대상으로 Gavrilovi$\acute{c}$ 모델을 적용하여 유사량을 산정해본 결과, 실측값을 약 20% 내외로 비교적 근사하게 추정할 수 있음을 알 수 있었다.

• Journal of Korea Water Resources Association
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• v.43 no.3
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• pp.265-273
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• 2010

This study proposed the method that can calculate discharge using hydraulic characteristics that can acquire easily-comparatively such as hydraulic radius, bed slope, depth to improve the stage-discharge curve equation considering only stage. Roughness coefficient n value and C value that hydraulic characteristics of rivers is reflected from Manning's equation and Chezy's equation using the measured data of the natural open channel in the report of Albert University estimated and calculated discharge on the basis of this. The method proposed in this study was calculated stunningly to measured discharge. And that compared with discharge by existent stage-discharge curve.

• Journal of Korea Water Resources Association
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• v.35 no.6
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• pp.693-701
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• 2002

In this study, one dimensional sediment movement numerical model(HEC-6) and semi-two dimensional sediment movement numerical model(GSTARS 2.1) were applied to solve the change of channel geometry in Bocheong stream. GSTARS 2.1 model was applied for the three selected sediment transport formulas(Ackers and White's, Engelund and Hanson, Yang formula) from 1993 to 2000 measured data on each section. The simulation results of Ackers and White formula for long -term bed changes are good when compared to the measured data. The HEC-6 model was applied for the simulation of one dimensional sediment movement for the same period. Comparison of the long-term simulations by GSTARS 2.1 and HEC-6 models with measured data shows that simulations by both models are in fair agreement with measured data in overall trend of the river bed changes. Comparisons of simulated cross sectional bed-elevations with measured data shows that GSTARS 2.1 model gives better agreement with than simulated results bed changes on the HEC-6 model.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.3
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• pp.202-208
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• 2001

Explicit approximation has been developed to estimate the run-up height on S-berm breakwater on the basis of Saville's hypothetical slope method. For the explicit expression of run-up height several relations are developed to represent the ratio of run-up height against breakwater slope with various conditions of water depth and wave steepness. For the verification of explicit approximation the results are compared with Saville's measurement data and simple expression of Delft Hydraulic Laboratory.

• The Korean Journal of Applied Statistics
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• v.3 no.1
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• pp.105-120
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• 1990

In this paper, a sequential test procedure is defined by using cumulative sum (CUSUM) of statistics. The properties as well as the efficiency of the CUSUM test are studied in comparison with the sequential probability ratio test (SPRT). It was shown that, the operating characteristic function and the average sample numbrer can be derived by Wald and Wiener process approximations. Also it was shown that the statistics used in the CUSUM test is determined to provide asymtotically equivalent efficiency compared to the SPRT. The efficiency of the CUSUM test and the SPRT are cpmpared by an example for some limited number of cases in the exponential distribution.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.697-700
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• 2011

본 논문에서는 X-FEM을 사용하여 혼합모드 하중 상태에서의 이차원 선형탄성체의 균열문제에 대한 형상 설계민감도 해석을 수행하였다. X-FEM이란 균열과 같은 특수한 해를 근사하는 방법으로써, 확장함수를 도입하여 FEM의 한계를 극복하는 방법론이다. X-FEM 하에서 해를 근사하는 데 쓰이는 확장함수들은 불연속성과 특이성을 포함하고 있어 물리적 영역에 의존한다. 이는 설계민감도 해석을 수행하는 과정에서 그러한 의존성을 고려해주는 것이 필요하다. 따라서 본 논문에서는 X-FEM 기반의 형상 설계민감도 해석해를 제안하고자 한다. 식의 유도는 전 미분 공식에 기초하고 있으며, 형상함수의 설계변분에 대한 의존성에 관한 항을 추가시켰다. 또한, 균열 주위의 국부적인 공간에서의 확장된 자유도에 설계속도를 가한다. 이에 대한 몇 가지 수치 예제를 통하여 개발된 방법론의 타당성을 확인하였다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.10a
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• pp.49-50
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• 2011

Receiving sensitivity of the power gain by using Soret typed FZPL antenna should be worse when obliquely incident wave is illuminated on the FZPL. To solve this problem, elliptic Fresnel Zone Plate Lens antenna system should be introduced. Some numerical results computed by PO method are compared with Kirchhoff's approximation and measurement result.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.11
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• pp.2170-2178
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• 1994

Our previously proposed method is further applied to find the queue length distribution of MMPP/D1 in an ATM multiplexer. We derive some useful relationship between the queue distribution seen by arriving cells and for a server befor each service. The relations were used to improve out approximation. For MMPP/D1 the calculated results show a good agreement with those obtained by a simulation of the system. Furthermore, our approximation provides fast numerical algorithms for general traffic models. These advantages demomstrate that our approximation method is useful for a fast and accurate traffic analysis in ATM networks.

• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.270-271
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• 2003

lens를 통과하는 두 광선(paraxial ray, marginal ray)이 lens의 축이나 focal plane과 만나는 지점이 서로 일치하지 않을 때, 두 개의 서로 다른 교차점 사이의 거리나 높이를 종, 횡 구면수차 (Lateral, Longitudinal Spherical aberration)이라 한다. 수차의 크기는 lens의 굽어짐 (bending)형태에 따라 달라지는데 3차 근사 lens 공식으로 유도한 식은 다음과 같으며, 그 결과의 그래프는 그림.1 과 같다. (중략)