• Journal of the Korean Geotechnical Society
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• v.22 no.4
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• pp.5-10
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• 2006

A special finite difference method for nonlinear dynamic response analysis of semi-infinite foundation soil using mapping which transforms semi-infinite domain into finite domain is presented here. For the region of engineering interest, mapping is isometric, and fur far field, shrink mapping which transforms infinite interval into finite interval is adopted. At first, the responses of semi-infinite foundation soil with linear constituting model are computed, and compared with theoretical results and those of existing method. Good agreements are obtained among the results of the proposed method, Lamb's theory and FEM with extensive mesh model. Then the responses of infinite foundation soil are computed by the present method, using small and large mesh model. The results of small and large mesh models agree well with each other, demonstrating the effectiveness of the proposed method.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.3
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• pp.71-82
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• 1999

Irregular motions of nonlinear dynamic system are the result of an intrinsic characteristics that the system have, and sometimes occur unpredictable large motion. For a ship in a regular seaway, the capsizing occur because of this unexpectable motion. So, from the safety's point of view, nonlinear ship motions should be treated carefully. In this study, stable and unstable regions are investigated firstly under the variation of a control external force. Secondly, we consider the attractors to know how ship motions of the stable region that does not undergo capsizing change. Thirdly, bifurcation diagram is considered to study the range in detail where nonlinear chaotic motions are occurred.

• The Journal of the Korea Contents Association
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• v.2 no.4
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• pp.23-29
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• 2002

This paper suggest the image compression that is needed to process PACS in medical information system. The image decoding method is used Linear-predictor and Lloyd-Max quantizer(quantization) in the Wavelet transform domain. Wavelet Transform Method is processed the multi-resolution by dividing image into 10 sub-bands of 3 levels. Low frequency domain that is sensitive to human visual characteristic is encoded by DPCM which is lossless encoding methods, and Lloyed-Max quantizer, the optimal quantizer for reducing ringing and aliasing in the image of inter sub-band, is used in the remaining high frequency domain of sub-band. The examination verifies that decompressed images are superior by the result that PSNR is 28.53dB on the input image, 512$\times$152 abdominal CT image and Chest image.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.35T no.1
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• pp.14-21
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• 1998

In the conventional GaAs MESFET circuit simulation, the DC and transient simulation results are often failed due to the discontinuities of the first and second order derivatives arising from the use of separate models in linear, saturation, and transition regions. In this paper, we propose a unified drain current-voltage model by using a unified channel length modulation effect that is derived by extending the channel length modulation effect in the saturation region to the linear region. Calculated results from the proposed drain current-voltage model agree well with the results of Shur model. Also, we propose a unified capacitance model for linear, transition, and saturation regions by using a unified channel length modulation effect. Its results from the proposed capacitance model agree well with 2-D device simulation results. Thus, the proposed models are expected to be useful in circuit simulations.

• Journal of Energy Engineering
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• v.19 no.3
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• pp.143-150
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• 2010

Line source method of borehole system assumes the entire surrounding medium is uniform. However, thermal properties of grouting region are considerably different from those of surrounding soil. In this study we investigate the effect of grouting materials on the solution of line source method with the aid of numerical analysis. This numerical model generates the temperature of borehole fluid with which line source solution can be obtained. Then this solution can be compared with input condition of numerical model. The results of this comparison show that thermal conductivity and borehole thermal resistance of line source solution are approximately 86% and 91% of the input condition of numerical model. Chart method is developed in this study to find the numerical input conditions (thermal conductivity and borehole thermal resistance) from the line source solution. Thermal response test of test borehole is conducted, the results of which are approximately consistent with the Chart method. Thermal property changes of grouting materials on the line source solution are also examined.

• Economic and Environmental Geology
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• v.52 no.4
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• pp.291-297
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• 2019

Fluid flow through rock fractures has been quantified using equations such as Stokes equations, Reynolds equation (or local cubic law), cubic law, etc. derived from the Navier-Stokes equations under the assumption that linear flow prevails. Therefore, these simplified equations are limited to linear flow regime, and cause errors in nonlinear flow regime. In this study, causal mechanism of nonlinear flow and critical Reynolds number were presented by carrying out fluid flow modeling with both the Navier-Stokes equations and the Stokes equations for a three-dimensional rough-walled rock fracture. This study showed that flow regimes changed from linear to nonlinear at the Reynolds number greater than 10. This is because the inertial forces, proportional to the square of the fluid velocity, increased enough to overwhelm the viscous forces. This tendency was also shown for the unmated (slightly sheared) rock fracture. It was found that nonlinear flow was caused by the rapid increase in the inertial forces with increasing fluid velocity, not by the growing eddies that have been ascribed to nonlinear flow.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.3
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• pp.11-22
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• 2010

An analysis method is proposed for the transient linear or nonlinear analysis of dynamic interactions between a flexible dam body and reservoir impounding compressible water under earthquake loadings. The coupled dam-reservoir system consists of three substructures: (1) a dam body with linear or nonlinear behavior; (2) a semi-infinite fluid region with constant depth; and (3) an irregular fluid region between the dam body and far field. The dam body is modeled with linear and/or nonlinear finite elements. The far field is formulated as a displacement-based transmitting boundary in the frequency domain that can radiate energy into infinity. Then the transmitting boundary is transformed for the direct coupling in the time domain. The near field region is modeled as a compressible fluid contained between two substructures. The developed method is verified and applied to various earthquake response analyses of dam-reservoir systems. Also, the method is applied to a nonlinear analysis of a concrete gravity dam. The results show the location and severity of damage demonstrating the applicability to the seismic evaluation of existing and new dams.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7C
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• pp.627-634
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• 2007

When a higher-order modulation scheme (16QAM or 64QAM) is applied to the communications system using the nonlinear high power amplifier (HPA), the performance can be degraded by the nonlinear distortion of the HPA. The nonlinear distortion can be compensated by the adaptive nonlinear Volterra equalizer using the low-complexity LMS algorithm at the receiver. However, the LMS algorithm shows very slow convergence performance. So, in this paper, the parallel M-band discrete wavelet transformed LMS algorithm is proposed in order to improve the convergence speed. Throughout the computer simulations, it is shown that the convergence performance of the proposed method is superior to that of the conventional time-domain and transform-domain LMS algorithms.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2000.08a
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• pp.209-212
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• 2000

본 논문에서는 칼라 CCD 카메라로부터 입력된 얼굴 영상에서 칼라 정보와 눈, 코, 입 등의 얼굴 영역 특징자 및 턱선의 선형적 특징을 이용한 얼굴 인식 알고리즘을 제안하였다. 제안한 알고리즘에서는 인간의 시각 체계와 비교적 유사한 HSI좌표계 상에서 피부색에 대한 색상 정보와 명암값 정보를 함께 이용함으로써 얼굴영역 추출의 효율을 높였고, 적응적인 추출이 가능하도록 하였다. 또한 추출된 얼굴 영역에서 얼굴 인식율 개선을 위해 눈, 코, 입 등의 구조적 위치 정보와 턱선의 선형적인 특징값을 이용하여 얼굴 인식율을 개선하였다. 제안한 알고리즘에서는 기존의 명암 정보를 이용하는 방법과는 달리 색상 정보와 명암 정보를 함께 이용함으로써 정확한 얼굴 영역의 검출이 가능하였으며 인식 방법에 있어서 구조적 특징자 외에 턱선의 선형적인 관계값을 이용함으로써 인식 효율을 개선하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.04a
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• pp.29-29
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• 1998

고체 추진제 연소불안정에 관한 해석은 준-정상 1차원 해석인 QSHOD(Quasi-Steady Homogcneous One-Dimension)에 의하여 단순화된 지배방정식을 이용하여 응축영역을 해석하는 것이 일반적이다. 이때 외부교란에 대한 기체영역과 표면반응 영역의 응답은 화학반응이 발생하지 않는 고체영역의 응답에 비하여 매우 빠르므로 준-정상적인 거동을 한다. 본 연구에서는 복사열전달에 의한 열속(heat flux)이 고체 추진제의 표면에 존재하며 이 중의 일부가 고체영역에서 흡수될 때 표면에서의 선형교란을 고려한 ZN(Zeldovich-Novozhilov) 방법을 이용하여 연소불안정 현상을 이론적으로 해석하여 연소불안정 현상을 설명할 수 있는 연소 응답함수를 구하였다. 본 연구에서 얻어진 응답함수를 해석함으로써, Zebrowski등$^{(5)}$ 에 의하여 얻어진 복사열 교란에 대한 응답함수가 과소 평가된 응답특성을 나타내고 있음을 알았다. 또한 응답함수의 고유불안정성을 판별하는 민감계수 r과 k의 영역의 해석으로부터 SOn등$^{(6)}$ 에 의하여 밝혀진 안정 경계선의 안정한 영역보다 본 연구에서 구한 안정 경계영역이 줄어드는 경향을 보여주고 있다. 이것은 (6)에서 과소 평가된 복사열전달의 영향을 수정한 결과 때문이다.