• Geotechnical Engineering
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• v.6 no.1
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• pp.25-34
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• 1990

The finite element and boundary element methods of underground analysis are both well established numerical techniques for determination of stress and displacement distributions at underground excavation. The finite element method presents antithetical advantages and limitations. Complex constitutive behaviour may be modelled, at the expense of numerical efficiency and, for infinite domain, inadequate representation of remote bounadry conditions. The inherent advantages of the boundary element method are the ease with which infinite domain problems may be analysed, and the efficiency of analysis typically associated with a boundary value solution procedure. Application of the method is limited by the requirements linear constitutive behaviour for the medium. A combined of the finite element and boundary element methods of underground analysis is shown to preserve the advantages of each procedure, and, eliminates their individual disadvantages. Procedures employed in this papers described combined FEBEM algorithm. Solutions of underground excavation verifying the performance of combined FEBEM code are compared with theoretical solution, boundary element solution and finite element solution.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 1999.12a
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• pp.411-419
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• 1999

EBPP는 소비자, 사업자간에 고지서 발송, 접수 및 지불을 네트워크를 통하여 전자적으로 처리하는데 필요한 환경을 의미하며, 인터넷을 기반으로 하여 전자우편 혹은 웹 페이지를 통하여 고지서를 처리한다 EBPP 시스템은 크게 소비자, 사업자 그리고 은행간의 거래로 이루어 지지만 컴퓨터 및 인터넷의 보급의 한계 등의 문제로 현재로서 모든 고지서를 전자적으로 처리하는 것은 무리가 따른다. 그럼에도 불구하고 EBPP 시스템은 1) 경쟁력 확보를 위해 기업/금융 기관들이 인터넷을 통한 고품질 서비스 개발에 주력하는 추세이고, 2) 고객과의 보다 긴밀한 관계 유지를 위한 수단 제공하며, 3) 인터넷 등 온라인 통신 인구가 급격한 증가(2701년에 전체 인구의 약 50%가 활용할 것으로 전망)하고 있으며,4) 소비자를게 보다 편리한 지불방법 제시해주며, 5) 또 다른 마케팅 매체로 활용 가능하므로 앞으로의 전망이 매우 밝다. EBPP시스템은 크게 금융기관, 기업, 소비자 부분으로 구성되며, 소비자와 접촉 방법으로는 대표적으로 Web과 전자우편을 생각할 수 있으며, EBPP 시스템을 구축하기 위해서는 기본적으로 상접 혹은 기업에서 청구에 필요한 정보를 등록시키는 통합 청구서버(Bill consolidation server), 소비자에게 청구 가능한 정보를 갖고있는 청구 제시서버 (Bill presentment server), 소비자의 지불요청에 따라 은행으로부터 지불을 요구하는 지불서버(Payment gateway) 등이 필요하며, 이들 각각의 서버들의 구성 요소들은 제공하는 서비스에 따라 달라질 수 있다. 통합 청구서버에서 청구 제시서버로 전송되는 청구 건은 통상적으로 실시간 처리되는 것이 아니라 통합 청구서버에 존재하는 Spool DB에 저장되어 그 양이 일정한도를 넘어서면 자동 전송되도록 하여, 망의 할용도를 높이는 역할을 수행한다. 청구 제시서버의 DB에 등록된 청구 건은 인터넷을 통해 소비자에게 청구되며, 소비자에게 전송 되는 청구서는 사용자DB를 참조하여 사용자가 미리 정의한 원하는 형태로 변환되어 전달되며, 필요시 암호화 과정을 거치는 것이 가능해야 한다. 전송된 청구서는 전자우편의 경우, 암호해독이 가능한 전용 브라우저를 통해 열람 되며, 이는 다시 전용 브라우저를 통해 지불인증이 승인되어 청구 제시서버에게 전송된다. EBPP 시스템의 제어 흐름은 크게 기업이 청구 정보를 소비자에게 제시하는 흐름과 소비자의 지불 승인으로 인해 기업이 은행에 지불을 요구하는 흐름으로 구분할 수 있다. 본 논문에서는 통합 청구서버 및 정구 제시서버의 역할 및 구성 요소들에 대해 서술하고, EBPP 시스템과 연동하여야 하는 메일 서버와의 상호 작용에 대해 서술할 것이다. 본 시스템을 아직 구현이 되지 않은 관계로 시스템의 성능 등의 수치적 결과를 제시할 수 없는 상태다.

• Tunnel and Underground Space
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• v.13 no.1
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• pp.20-32
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• 2003

To understand the behavior of migration of contaminants in a fractured porous medium is a key to assure the overall safety of a potential radwaste repository. The feasible retention mechanism of contaminant transport in a tinctured medium are sorption of contaminants on solid surface and matrix diffusion of contaminants from a fracture into an adjacent porous medium. The acceleration mechanisms are the migration of contaminants in the form of pseudo-colloids and the limit of a volume f3r matrix diffusion. In this paper, the effects of these two acceleration mechanisms are studied mathematically, then semi-analytically computed by the application of the Talbot theorem and verified. Results indicate that the acceleration processes cannot be neglected in the modeling of contaminant transport in a fractured porous medium.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.5
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• pp.333-339
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• 1999

It is well recognized that ultrasonic technique is one of the most common and reliable nondestructive evaluation techniques for quantitative estimation of defects in structures. For the quantitative and accurate estimation of internal defects. the characteristics of scattered ultrasonic wavefields must be understood. In this study. the scattered near-field and far-field due to a circular cavity embedded in infinite media subjected to incident SH-waves were calculated by the boundary element method. The frequency response of the scattered ultrasonic far-field was transformed into the time-domain signal by obtaining its inverse Fourier transform. It was found that the amplitude of time-domain signal decreases and its time delay increases as the distance between the detecting point of ultrasonic scattered field and the center of internal cavity increases.

• Geophysics and Geophysical Exploration
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• v.20 no.3
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• pp.129-136
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• 2017

3D seismic data processing methods such as full waveform inversion or reverse-time migration require 3D wave propagation modeling and heavy calculations. We compared efficiency and accuracy of a Xeon Phi coprocessor to those of a high-end server CPU using 3D frequency-domain wave propagation modeling. We adopted the OpenMP parallel programming to the time-domain finite difference algorithm by considering the characteristics of the Xeon Phi coprocessors. We applied the Fourier transform using a running-integration to obtain the frequency-domain wavefield. A numerical test on frequency-domain wavefield modeling was performed using the 3D SEG/EAGE salt velocity model. Consequently, we could obtain an accurate frequency-domain wavefield and attain a 1.44x speedup using the Xeon Phi coprocessor compared to the CPU.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.2
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• pp.16-30
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• 1990

The microwave imaging technique which is mostly analyzed in the spectral domain has been exploited the image reconstruction of object using the 2-dimensional inverse Fourier transform so far. In this paper, a new method of microwave imaging corresponding to a coherent tomographic scheme in the space domain is presented for the conducting objects. Also, it is shown that image reconstruction for lines targets and conducting circular cylinder is per-formed by computer simulation using the filtered-backprojection which is the reconstruction algorithm widely used in X-ray CT. The proposed method analyzed in the space domain can reconstruct the image without any problems such as interpolation and image artifact which results from the reconstruction in the spectral domain for the symmetric conducting objects located in the origin. The image reconstructed by the filtered-backprojection in the space domain has given the superior quality compared with that produced by 2-dimensional IFFT using the interpolation scheme in the spectral domain. Finally, the image of line targets using the moment-method in the space domain which does not require the wide-band signal as the spectral domain has shown a possibility of super-resolution in the microwave imaging.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.2
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• pp.191-198
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• 2011

In this paper, a method to approximate a multi-layer Green's function is proposed based on a FDTD scheme and a rational function approximation. For a given horizontal propagation wavenumber, time domain response is calculated and then Fourier transformed to the spectral domain Green's function. Using the rational function approximation, the pole and residue of the Green's function can be estimated, which are crucial for a calculation of a path loss. The proposed method can provide a wideband Green's function, while the conventional normal mode method can be applied to a single frequency problem. To validate the proposed method, We consider two problems, one of which has a analytical solution. The other is about multi-layer case, for which the proposed method is compared with the known normal mode solution, Kraken.

• The Journal of the Acoustical Society of Korea
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• v.36 no.1
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• pp.1-11
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• 2017

In this study, novel approximate form of the square-root operator of three dimensional acoustic Parabolic Equation (3D PE) is proposed using a rational approximant for two variables. This form has two advantages in comparison with existing approximation studies of the square-root operator. One is the wide-angle capability. The proposed form has wider angle accuracy to the inclination angle of ${\pm}62^{\circ}$ from the range axis of 3D PE at the bearing angle of $45^{\circ}$, which is approximately three times the angle limit of the existing 3D PE algorithm. Another is that the denominator of our approximate form can be expressed into the product of one-dimensional operators for depth and cross-range. Such a splitting form is very preferable in the numerical analysis in that the 3D PE can be easily transformed into the tridiagonal matrix equation. To confirm the capability of the proposed approximate form, comparative study of other approximation methods is conducted based on the phase error analysis, and the proposed method shows best performance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.3
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• pp.513-519
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• 2018

OFDM modulation has been used for a transmission scheme in 4G LTE (Long Term Evolution) and Wi-Fi systems to mitigate the effects of frequency selective fading channels. An OFDM modulation is a block transmission scheme because an OFDM symbol consists of multiple subcarriers with narrow bandwidth. Therefore, all OFDM symbols in a frame should be filled out with data and padding bits. Depending on the amount of data, more padding bits than information bits can occupy the last OFDM symbol. Such inefficiency causes the loss of throughput. To overcome this problem, an efficiency padding method is proposed by using the property of DFT (Discrete Fourier Transform). In the proposed method, symbol duration of the last symbol is changed depending on the number used data subcarriers in the last symbol. With numerical evaluation, it is examined that throughput enhancement achieved by the proposed method can be about 20% depending a transmission scheme and data length.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.182-182
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• 2018

한강의 제1지류인 홍제천 수계에 속하는 지방2급 하천인 불광천 유역을 연구대상지로 선정하여 기후변화에 따른 유출량 영향성 분석을 수행하였다. 연구대상지인 불광천은 서울특별시의 서북쪽에 위치하여 $21.72km^2$의 유역면적과 9.83km의 유로연장을 갖고 행정구역상 은평구, 마포구, 서대문구에 걸쳐있다. 본 연구에서는 불광천 유역을 503개의 소유역으로 분할하였으며, 유역의 하수관망은 976개의 노드와 989개의 링크를 사용하여 XP-SWMM 모형으로 구축하였다. 또한 국토지리정보원에서 제공하는 1:5000축척의 수치지도를 DTM으로 변환하여 하수관에서 월류된 이후의 2차원 흐름분석을 위한 지형자료로 활용하였다. 기후변화를 고려한 유출량을 분석하기 위해 S0(1961년~2016년)인 1개의 과거기간과 S1(2017년~2046년), S2(2047년~2076년), S3(2077년~2100년)인 3개의 미래기간을 설정하여 총 4개의 시나리오를 구성하였다. 과거기간인 S0는 강우관측소에서 계측된 자료를 사용하여 빈도별 확률강우량을 구하였으며, 미래기간인 S1, S2, S3는 기상청에서 제공하는 기후변화 시나리오인 RCP 4.5의 강우자료를 사용하여 확률강우량을 산출하였다. 빈도별 확률강우량은 S0기간의 강우자료와 가장 유사한 Gumbel 모형을 사용하였으며, 도출된 확률강우량은 치수에 가장 보수적인 Huff의 4분위로 강우를 분포시켜 유출모형에 적용하였다. 976개의 노드 중 불광천 유역의 주요 76개 지점을 선정하여 유역면적에 따른 기후변화의 영향성을 분석하였다. 그 결과 유역면적과 재현기간이 작을수록 최대 유출량은 큰 변동성을 보이는 것으로 나타났으며, 과거기간인 S0 대비 미래기간인 S1, S2, S3의 최대 유출량 비율은 유역면적 100ha를 기준으로 100ha 미만은 80%~200%의 변동성을 100ha이상에서는 120%에 수렴하는 양상을 보이는 것으로 확인되었다.