• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1998.09a
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• pp.88-93
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• 1998

수치 파수조기법은 해양구조물에 작용하는 비선형 파랑하중을 해석할 수 있는 가장 유망한 도구로 인식되고 있다. 이러한 수치 파수조기법은 새롭고 다양한 형태의 해양구조물에 대한 정확하고 엄밀한 설계는 물론이고, 실험 조파수조의 여러 가지 문제점을 극복하기 위해서도 매우 필요한 기법이라고 할 수 있다(Kim, 1995). 수치 과수조기법을 위한 경계치 문제 해석법으로는 고차경계요소법을 이용한 해석법이 가장 효율적인 것으로 알려져 있다. (중략)

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.8
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• pp.791-796
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• 2009

A hybrid iterative physical optics-method of moments(IPO-MoM) technique is presented for the analysis of jet engine structures which are both electrically large and complex. In this technique, the IPO method is used to analyze smooth inlet region and the MoM method is used to analyze electrically complex region inclusive of blades and hub. It is efficient and accurate by virtue of combining the respective merits of both methods. Numerical results are presented and validated through comparison with Mode-FDTD and measured results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.5
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• pp.640-647
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• 1998

Microstrip patch antennas are analyzed by a multiresolution wavelet method. The spectral Green's dyad of the structure is obtained and its joint spatial-spectral domain representations are presented. Based on the joint spatial-spectral domain representation, we show that the spectral-domain wavelets are useful in the analysis of this problem. We obtain the matrix equations of the integral equations of this Green's dyad by using the method of moment(MoM), and efficiently solve the problem using the spectral domain wavelet transform concepts in conjuction with the conjugate gradient method. The results for a single-layered square patch are compared with those of conventional MoM and CG-FFT.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.3
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• pp.77-82
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• 2023

In this paper, TM(tranverse magnetic) electromagnetic scattering problems for resitive strip grating between grounded double dielectric layers are analyzed by using the FGMM(fourier galerkin moment method) and PMM(point matching method) known as a numerical method of electromagnetic field. The boundary conditions are applied to obtain the unknown field coefficients, the resistive boundary condition is applied to analysis of resistive strip. Overall, when the unoform resistivity decreased, the magnitude of the current density induced in the resistive strip increased, and the reflected power also increased. Also, as the thickness and relative permittivity of the double dielectric layers increased, the overall reflected power increased. The numerical results obtained by using the numerical methods of FGMM and PMM to the structure proposed in this paper agree very well.

• Korean Journal of Remote Sensing
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• v.16 no.1
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• pp.65-72
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• 2000

Scattering coefficients of randomly rough lossy dielectric surfaces were computed by using the FDTD(Finite-Difference Time-Domain) method and the Monte Carlo method in this paper. The FDTD method was applied to compute electromagnetic wave scattering characteristics at any incident angles, any linear polarizations by dividing the computation region into the total-field region and the scattered-field region. The radar cross sections(RCS) of conducting cylinders have been computed and compared with theoretical results, measurement data and the results from the method of moment(MoM) to verify the FDTD algorithm. Then, to apply the algorithm to compute scattering coefficients of distributed targets, a two-dimensionally rough surface was generated numerically for given roughness characteristics. The far-zone scattered fields of 50 statistically independent dielectric rough surfaces were computed and the scattering coefficient of the surface was calculated from the scattered fields by using the Monte Carlo method. It was found that these scattering coefficients agree well with the SPM(Small Pertubation Method) model in its validity region.

• Journal of the Korean Society of Radiology
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• v.13 no.4
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• pp.589-596
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• 2019

X-rays used for diagnosis have a continuous energy distribution. However, photons with low energy not only reduce image contrast, but also contribute to the patient's radiation exposure. Therefore, clinics currently use filters made of aluminum. Such filters are advantageous because they can reduce the exposure of the patient to radiation. However, they may have negative effects on imaging quality, as they lead to increases in the scattered dose. In this study, we investigated the effects of the scattered dose generated by an aluminum filter on medical image quality. We used the relative standard deviation and the scatter degradation factor as evaluation indices, as they can be used to quantitatively express the decrease in the degree of contrast in imaging. We verified that the scattered dose generated by the increase in the thickness of the aluminum filter causes degradation of the quality of medical images.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.4
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• pp.354-361
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• 2004

This Paper describes a crack scattering model for SH wave based on the boundary integral equation(BIE) method, where the fundamental unknown is crack opening displacement(COD). When a time harmonic plane wave was incident on a 2-D isolated crack (slit) of width 2a, the COD distributions were numerically calculated as a function of ka. The calculated COD agreed well with results obtained with other methods. The far-field scattering amplitude, which completely characterizes the flaw response, was calculated in two ways. The Kirchhoff approximation and the BIE-COD exact formulation were compared in terms of incidence angle and frequency ka in a pulse-echo mode. Maximum response was obtained for both methods at the specular reflection direction. Away from the specular direction, the Kirchhoff approximation becomes less accurate. The time domain crack response was also calculated using a band-limited spectrum of center frequency 10 MHz. At oblique incidence to the crack both methods show the existence of an antisymmetric flash points occurring from the crack edge. The Kirchhoff approximation provides an exact time interval between flash points, although it unrealistically gives the same amplitude.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.3
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• pp.364-373
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• 1999

A combination of conjugate gradient and Levenberg-Marquardt method is used to estimate the spatially varying scattering coefficient, ${\sigma}(r)$, in the solid and hollow spheres by utilizing the measured transmitted beams from the solution of an inverse analysis. The direct radiation problem associated with the inverse problem is solved by using the $S_{12}-approximation$ of the discrete ordinates method. The accuracy of the computations increased when the results from the conjugate gradient method are used as an initial guess for the Levenberg-Marquardt method of minimization. Optical thickness up to ${\tau}_0=3$ is used for the computations. Three different values of standard deviation are considered to examine the accuracy of the solution from the inverse analysis.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.341-348
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• 1991

An efficient tool to deal with a multi-dimensional radiative heat transfer is in strong demand to analyze various thermal problems combined either with other modes of heat transfer or with combustion phenomena. The current study examined the discrete ordinates method (DOM) for a coupled radiative and conductive heat transfer in rectangular enclosures in which either nonscattering or scattering medium is present. The results were compared with the other benchmarked approximate solution. The efficiency and accuracy of the DOM were thus validated.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.204-209
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• 1998

핵연료 펠렛이 장입되어 있는 원전연료봉 피복관은 핵분열성 물질의 외부 유출에 대한 일차 방호벽 역할을 하므로 원전의 안전성을 위해서는 피복관의 구조건전성 확보가 매우 중요하다. 고온, 고압의 운전 조건 속에서 연료봉 피복관은 산화막이 생성 상장하여 연료봉을 취성 파괴시킬 가능성이 있으므로 이를 가동중에 비파괴적으로 측정할 수 있는 방법을 개발할 필요가 있다. 산화막이 존재하는 지르칼로이 피복관에 대한 음파의 공명산란을 이론적으로 모델링하고 수치해석을 수행하였다. 산화막이 피복된 원통형 쉘의 공명산란에서 공명 원주파의 전파 특성은 산화막의 존재 여부와 그 두께 증가에 따라 크게 변화한다. 수치 해석 결과 제 1차 반대칭 (A$_1$) 원주파의 특정 부분파의 경우에는 산화막의 존재에도 불구하고 위상속도가 일정한 특이성을 보였다. 이러한 위상속도 특성을 실험을 통하여 확인하였으며 이 현상을 이용하여 산화막의 두께를 측정할 수 있는 새로운 비파괴 평가 방법을 제안하였다.