• 대한전자공학회논문지TC
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• 제39권7호
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• pp.38-45
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• 2002

본 논문은 손실 매질 내에 매설된 선 전류 안테나에 의한 크기가 큰 완전도체 표적의 산란파를 해석하기 위한 전장적분식을 도출하였다. Sommerfeld 형태의 적분은 어떤 해석영역에 대하여 계산의 어려움과 제약들을 가지고 있으며, 많은 계산시간이 필요하다. 반면 최대 경사적분은 빠른 결과의 산출을 제공하였으며, 또한 그 계산 결과는 모든 해석 영역에 적용 가능하다. 임의의 완전도체 표적의 산란파는 최대경사적분법과 MOM 방법이 사용되었으며, 계산 결과는 가우시안 구적법과 GPOF 방법에 의해 비교되었다.

• 전자공학회논문지A
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• 제31A권1호
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• pp.33-38
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• 1994

In this paper, waveguide banpass filters using H-plane step discontinuities are designed based on the field theory analysis and optimization of the resonator lengths as well as dimensions of discontinuities, instead of the conventional synthesis method based on the equivalent circuit. The waveguide inductive obstacles introduced by H-plane step discontinuities analyzed using mode-matching method and the generalized scattering parameters are derived. Using the derived scattering parameters of the discontinuities as well as those of resonators, waveguide bandpass filters are designed through optimization method, modified Razor search method proposed by J.H.Bandler. Using this design procedures, waveguide bandpass filters are designed and tested at X-band(center frequency 10GHz) as well as Ka-band(center frequency 35GHz).

• Nuclear Engineering and Technology
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• 제49권6호
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• pp.1114-1124
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• 2017

Acceleration/preconditioning strategies available in the SCEPTRE radiation transport code are described. A flexible transport synthetic acceleration (TSA) algorithm that uses a low-order discrete-ordinates ($S_N$) or spherical-harmonics ($P_N$) solve to accelerate convergence of a high-order $S_N$ source-iteration (SI) solve is described. Convergence of the low-order solves can be further accelerated by applying off-the-shelf incomplete-factorization or algebraic-multigrid methods. Also available is an algorithm that uses a generalized minimum residual (GMRES) iterative method rather than SI for convergence, using a parallel sweep-based solver to build up a Krylov subspace. TSA has been applied as a preconditioner to accelerate the convergence of the GMRES iterations. The methods are applied to several problems involving electron transport and problems with artificial cross sections with large scattering ratios. These methods were compared and evaluated by considering material discontinuities and scattering anisotropy. Observed accelerations obtained are highly problem dependent, but speedup factors around 10 have been observed in typical applications.

• Bulletin of the Korean Chemical Society
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• 제21권11호
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• pp.1095-1100
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• 2000

we have proposed a three-dimensional GLE approach to gas-surface reactive scattering, model H + H $${\rightarrow}$H_2/Si(100)-(2$ ${\times}$1) system, and the implementation of 3D GLE method on the hydrogen on silicon surface has been presented. The formalism and algori thm of the 3D GLE are worked properly in the reactive scattering system. The calculated normal mode frequencies of surface vibrations were almost identical to previous harmonic slab calculations. The reaction probabilities were calculated for two energies. The calculations show that a very large amount of energy is transferred in surface in low energy scattering. Three different types of reaction mechanisms has been observed, which can not be shown in flat and rigid surface models. Further work on the reaction mechanisms and calculations of the vibrational and rotation distributions of products is in progress. The results will be reported elsewhere soon.

• Journal of Mechanical Science and Technology
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• 제15권12호
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• pp.1801-1807
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• 2001

In multiphase flne the bubble size and velocity. To achieve this, one of approaches is to utilize laser phase-Doppler anemometry. However, it was found that the second order refraction has great impact on PDA sizing method when the relative refractive index of media is less than one. In this paper, the problem of second order refraction is investigated and a model of phase-size correlation to eliminate the measurement errors is introduced for bubble sizing. As a result, the model relates the assumption of single scattering mechanism in conventional phase-Doppler anemometry. The results of simulations based on this new model by using Generalized Lorenz Mie Theory (GLMT) are compared with those based on the conventional method. An optimization method for accurately sizing air-bubble in water has been suggested.

• Nuclear Engineering and Technology
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• 제49권6호
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• pp.1143-1156
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• 2017

This paper describes recent development activities of the GENESIS code, which is a transport code for heterogeneous three-dimensional geometry, focusing on applications to reactor core analysis. For the treatment of anisotropic scattering, the concept of the simplified Pn method is introduced in order to reduce storage of flux moments. The accuracy of the present method is verified through a benchmark problem. Next, the iteration stability of the GENESIS code for the highly voided condition, which would appear in a severe accident (e.g., design extension) conditions, is discussed. The efficiencies of the coarse mesh finite difference and generalized coarse mesh rebalance acceleration methods are verified with various stabilization techniques. Use of the effective diffusion coefficient and the artificial grid diffusion coefficients are found to be effective to stabilize the acceleration calculation in highly voided conditions.

• 대한수학회논문집
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• 제11권4호
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• pp.1147-1157
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• 1996

Nonlinear ill-posed problems arise in many application including parameter estimation and inverse scattering. We introduce a least squares regularization method to solve nonlinear ill-posed problems with constraints robustly and efficiently. The regularization method uses Trust-Region approach to handle the constraints on variables. The Generalized Cross Validation is used to choose the regularization parameter in computational tests. Numerical results are given to exhibit faster convergence of the method over other methods.

• 한국통신학회논문지
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• 제28권4A호
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• pp.256-266
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• 2003

본 논문에서는 내부의 타원형 금속봉에 의한 구형 도파관의 산란 특성과 금속봉의 등가 임피던스를 모드매칭법과 일반 산란계수법을 사용한 수치적 방법으로 해석하였다. 타원형 금속봉에 의한 구형 도파관의 산란특성은 봉의 이심률과 높이에 따라 미세하게 변화되고 있으며, 봉의 높이가 낮은 경우(w.54mm, 4mm) 구형 도파관의 산란 특성 변화는 전체 주파수 대역에서 나타나는 반면, 봉의 높이가 높아질수록(7.62mm, 9mm) 이러한 특성의 변화는 높은 주파수 대역에서 뚜렷해짐을 알 수 있었다. 계산결과는 HFSS와 비교하여 잘 일치하였다. 본 논문에서 제시한 구조와 해석법은 튜닝 소자로 타원의 원통형 금속봉을 사용하는 도파관 관련 부품의 설계와 제작에 쉽게 이용될 수 있다.

• 한국전자파학회논문지
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• 제16권10호
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• pp.982-988
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• 2005

본 논문에서는 모드 변환기나 필터, 매칭 구조가 모두 연결되어 있는 개구면 안테나의 특성을 예측을 위해 급전 부분에 전이 구조가 붙어 있는 원형 개구면 안테나의 해석적인 산란 해를 제시한다. 개구면의 모양이 원형이기 때문에 길이가 짧고 반지름이 다른 원형 도파관이 연결되어 있는 구조로 모델링하여 안테나를 해석했다. 안테나의 해석에서 급전 도파관과 개구면 사이의 영역은 일반화된 산란 행렬을 이용하여 전기장과 자기장을 나타냈고, 개구면에서 복사되는 전기장과 자기장은 적분 변환을 이용하여 나타내어 전체 구조를 해석했다. 여기서 필요한 산란 행렬과 적분 변환은 모두 해석적으로 계산 가능하고, 엄밀한 해이므로 안테나의 반사 특성, 복사 특성 등을 정확하게 예측 가능하다.

• 한국해양공학회지
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• 제36권2호
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• pp.132-142
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• 2022

We investigate the performance of multi-body wave energy converters (WECs). This investigation considers multiple scattering of water waves by the buoys of a WEC under the generalized mode approach. Predominantly, the effect of a WEC's configuration on its energy extraction is studied in this research. First, single-row terminator and single-column attenuator arrays of vertical cylinders have been studied. The performance of these attenuator arrays shows that the wall effect induced by the periodic buoys influences the wave propagation and energy extraction in these WECs. Further studies show that a single-row terminator array of vertical cylinders performs better than the corresponding single-column attenuator array. Subsequently, multi-row terminator arrays of vertical cylinders are investigated by conducting a parametric study. This parametric study shows that the hydrodynamic property of three resonance phenomena makes energy extraction efficiency drop down, and the magnitude of energy extracted oscillates between the resonance points in these WECs. Finally, a 4×8 terminator array of vertical cylinders is studied to determine the effect of various d_x (x-directional distance between adjacent rows) within this WEC on its performance. In particular, this study enforces at least two equal d_x values within the 4×8 terminator array of vertical cylinders. It shows that a small value of this d_x leads to better energy extraction efficiency in some of these various d_x arrays than that of a corresponding regular array with the same d_x.