• Journal of Energy Engineering
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• v.9 no.4
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• pp.309-318
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• 2000

핀-관 열교환기의 효율을 증대시키기 위하여는 열저항을 결정하는 데 있어서 중요한 역할을 하는 공기측 열전달 특성의 향상이 필요하다. 본 연구에서는 핀-관 열교환기의 공리측 성능을 해석하기 위해서 3차원 비압축성 Navier-Stokes 코드를 개발하였으며 이 코드는 시간항에 스칼라 내재적 근사분해법(scalar implicit approximate factorization)절차, 공간항에 유한체적법과 2차의 풍상차분법(upwind differencing)을 사용한다. 서로 다른 3개의 핀형상(평판핀, 슬릿핀, 파형핀)을 고려하였고 이들의 유동 및 열전달 특성을 연구하였다.

• Journal of Korean Society of Steel Construction
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• v.9 no.2 s.31
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• pp.229-235
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• 1997

In order to check the influence of the randomness in yield strengths on the energy dissipation capacity of steel structures, behaviour factors applied for the "Response Spectrum Method" and their distributions are determined in this study with 7 steel framed models. Also 4 artificial accelerograms simulated with a given spectrum are applied to check the influence of the randomness in seismic action on the behviour factor. To execute numerous time-step calculations for the investigation a time-step analysis method is developed and applied after the reliability estimation to determine the action effects.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.2
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• pp.127-136
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• 2007

In this paper, the equations of the scaled boundary finite element method are derived for non-homogeneous half plane and analyzed numerically In the scaled boundary finite element method, partial differential equations are weaken in the circumferential direction by approximation scheme such as the finite element method, and the radial direction of equations remain in analytical form. The scaled boundary equations of non-homogeneous half plane, its elastic modulus varies as power function, are newly derived by the virtual work theory. It is shown that the governing equation of this problem is the Euler-Cauchy equation, therefore, the logarithm mode used in the half plane problem is not valid in this problem. Two numerical examples are analysed for the verification and the feasibility.

• Journal for History of Mathematics
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• v.18 no.4
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• pp.49-66
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• 2005

Finite element Methods(FEM) have been the primary computational methodologies in science and engineering computations for more than half centuries. One of the main limitations of the finite element approximations is that they need mesh which is an artificial constraint, and they need remeshing to solve in some special problems. The advantages in meshfree Methods is to develop meshfree interpolant schemes that only depends on particles, so they relieve the burden of remeshing and successive mesh generation. In this paper we describe the development of meshfree particle Methods and introduce the numerical schemes for Smoothed Particle hydrodynamics, meshfree Galerkin Methods and meshfree point collocation mehtods. We discusse the advantages and the shortcomings of these Methods, also we verify the applicability and efficiency of Meshfree Particle Methods.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.843-850
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• 2002

Linear transformation theory has been effectively used in the design and analysis of prestressed concrete structures. The underlying assumptions of the theory, which were often overlooked, are investigated in the respect of equivalent load method. As a result, it is found that the same equivalent loading system is produced for all the cases of the linear transformation by the assumptions of the conventional equivalent load method. On the other hand, equivalent loading systems in a strict and accurate sense do not satisfy the classical theories of the linear transformation. Also, it is shown that a little different equivalent loading system from the conventional one is obtained for each linear transformation according to the proposed equivalent load method that is derived from the self-equilibrium property of the tendon-induced forces. Therefore, it can be concluded that the linear transformation theory is valid only when referring to the conventional approximate equivalent load method. The discussions are further extended to the eccentrically located circumferential tendon in the wall of containment structures, where the problem of eccentricity is analyzed also from the view point of the linear transformation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.5
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• pp.1383-1393
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• 2014

Recently, with rapid improvement in computer hardware and theoretical development in the field of computational fluid dynamics, high-order accurate schemes also have been applied in the realm of computational hydraulics. In this study, numerical solutions of 1D shallow water equations are presented with TVD Runge-Kutta discontinuous Galerkin (RKDG) finite element method. The transcritical flows such as dam-break flows due to instant dam failure and transcritical flow with bottom elevation change were studied. As a formulation of approximate Riemann solver, the local Lax-Friedrichs (LLF), Roe, HLL flux schemes were employed and MUSCL slope limiter was used to eliminate unnecessary numerical oscillations. The developed model was applied to 1D dam break and transcritical flow. The results were compared to the exact solutions and experimental data.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.12
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• pp.36-43
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• 2001

We evaluate the optical characteristics of planar distributed feedback (DFB) waveguides with quarter-wavelength phase-shifter. To analyze explicitly its band-pass and resonance properties, we present and newly develop a modal transmission-line theory (MTLT) based on Floquet's theorem and Babinet's principle. The numerical results reveal that this approach offers a simple and analytic algorithm to analyze either the filtering or the oscillating characteristic of DFB gratings with quarter-wavelength phase-shifter, and has a novel physical insight that may not be achieved in other approximating approaches

• The Journal of the Acoustical Society of Korea
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• v.16 no.5
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• pp.105-111
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• 1997

Before application of the angular spectrum method to calculate acoustic fields in stratified water, its efficiencies and errors were analyzed by using a virtual boundary in homogeneous water. As the results, it was confirmed that the angular spectrum method was able to calculate an acoustic field rapidly though some errors due to the limitation of reference field size and number of data in FFT ware included. A modified method combined the angular spectrum with Lommel's approximation, which was newly proposed in this paper, was useful to reduce the errors.

• Computational Structural Engineering
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• v.4 no.2
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• pp.119-129
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• 1991

This study is directed for the development of an efficient Importance Sampling Technique for system reliability analysis of bridge structures. Many methods have been proposed for structural reliability assessment such as the First-order Second-Moment Method, the Advanced Second-Moment Method, Monte Carlo Simulation, etc. The Importance Sampling Technique can be employed to obtain accurate estimates for the system reliability with reasonable computation effort. Based on the results of example analysis, it may be concluded that Importance Sampling Technique is a very effective tool for the system reliability analysis.

• Journal of Energy Engineering
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• v.10 no.2
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• pp.166-175
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• 2001

핀-관 열교환기의 효율을 증대시키기 위하여는 열저항을 결정하는데 있어서 중요한 역할을 하는 공기측 열전달 특성의 향상이 필요하다. 본 연구에서는 슬릿핀과 같은 핀 형상의 개선으로 인한 높은 압력손실을 감소시키기 위하여 타원관형 열교환기를 고려하였으며 이를 자체 개발한 3차원 비압축성 Navier-Stokes 코드를 이용하여 공기측 성능을 해석하였다. 이 코드는 시간항에 스칼라 내재적 근사분해법(scalar implicit approximate factorization)절차, 공간항에 유한체적법과 2차의 풍상차분법을 사용한다. 핀 형상이 평판핀인 타원관에 대하여 세장비가 0.3, 0.5, 0.75인 경우와 핀 형상이 슬릿핀이고 세장비가 0.5인 타원관에 대하여 공기측 유동을 해석하였으며 이를 원관의 성능과 비교하였다. 평판핀의 경우, 압력강하량은 원관과 비교하여 세장비가 작아질수록 감소하는 것을 볼 수 있었으며, 열전달 계수는 고려한 유입속도 범위에서 원관을 기준으로 약 5%이하의 변화로 거의 동일하게 유지되는 것을 볼 수 있었다. 슬릿핀의 경우 역시 문제되는 높은 압력강하량은 타원관을 도입함으로써 효과적으로 낮출 수 있음을 볼 수 있었다.