• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.2
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• pp.173-179
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• 2009

Reduction scheme is remarkably useful in the case requiring the repeated calculation procedure. Recently, the efficiency of the reduction scheme has been improved by combining scheme of sub-domain method. But, when the global domain is partitioned into a few sub-domains, sub-domains without constraints can be produced. it is needed to extract the ritz vector from each sub-domain to construct the reduced system of each sub-domain. it is easy to extract the ritz vector from sub-domain with constraint. on the other hand, pseudo inverse method should be employed to extract the ritz vector from sub-domain without constraint. generally, the pseudo inverse takes a large number of computing time to obtain a reduced system of a sub-domain without boundary condition. This trouble can be overcome by the reduced pseudo inverse scheme which proposed in this study. This scheme is based on the static condensation that is not related with selection of the primary degrees of freedom. Numerical examples demonstrate that present method saves computational cost effectively. In addition, it is shown that the reduced system based on the proposed scheme predicts the accurate eigenvalues of global system.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.4
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• pp.487-493
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• 2010

Most structural analyses are concerned with the deformations and stresses in a body subjected to external loads. However, in many fields, inverse problems have to be interpreted to determine surface tractions or internal stresses from displacements measured on a remote surface. In this study, the inverse processes are studied by using the finite element method for the evaluation of internal stresses. Small errors in the measured displacements often result in a substantial loss of stability of an inverse system. In order to improve the stability of the inverse system, the displacements on a section near the region of the unknown tractions are predicted by using orthogonal basis functions. We use the Gram-Schmidt orthogonal technique to determine two bases for the displacements on a section near the region of the unknown tractions. Advantages over previous methods are discussed by using numerical examples.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.4
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• pp.407-415
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• 2011

The stability condition and wideband characteristics of 3D ID-FDTD algorithm which has low dispersion error with isotropic dispersion are presented in this paper. 3D ID-FDTD method was proposed to improve the defect of the Yee FDTD such as the anisotropy and large dispersion error. The published paper calculated the stability condition of 3D ID-FDTD algorithm by using numerical method, however, it is thought that the examples were not sufficient to verify the stability condition. Thus, in this paper, various simulations are included in order to hold reliability under the conditions that the plane wave propagation is assumed with a single frequency and a wideband frequency. Also, the 3D ID-FDTD algorithm is compared to those that have the similar FDTD algorithm with ID-FDTD such as Forgy's method and non-standard FDTD method in a wideband. Finally, the radar cross section(RCS) for the large sphere with high dielectric constant is calculated.

• Information and Communications Magazine
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• v.19 no.10
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• pp.78-92
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• 2002

고용량 파장다중분할(WDM) 전송 시스템의 수요가 폭발적으로 증가함에 따라 기존의 erbium-doped fiber amplifiers(EDFA)가 제공하는 이득 대역을 넘어서는 대역폭의 광증폭기의 개발이 촉진되고 있다. 에르븀 이외의 새로운 회토류 첨가물을 사용한 증폭기와 광섬유 내에서의 비선형 현상인 라만 산란에 의한 라만 증폭기에 집중적인 연구가 그 예라 하겠다. 최근 몇 년간의 집중적인 연구를 통하여 현재의 광대역 광 증폭기는 기존의 EDFA(C 벤드 EDFA)가 제공하는 광이득대역의 4∼5배 정도를 쉽게 제공할 수 있다. 이러한 목적을 가지고 통신시장에서 사용될 수 있는 1500nm 근처 대역의 증폭에 대한 세가지의 증폭 기술이 연구되고 있다. 우선, S+밴드(1450-1480nm)와 S밴드(1480-1530nm)의 증폭을 위한 thulium-doped fluoride fiber amplifiers(TDFFA), C 밴드(1530-1560nm)와 L 밴드(1570-1610nm)를 위한 EDFA, 그리고 마지막으로 100nm 이상의 이득대역과 S+에서 L밴드까지 증폭파장대역의 선택이 자유로운 라만 증폭기가 있다. 또한 위의 세 기술을 직렬 또는 병렬로 조합하여 사용하는 증폭기가 있다. 이러한 증폭기 모두에 대해서 실험적인 보고는 많이 있었으나, 내부의 에너지 준위가 복잡하여 증폭 기제가 복잡하고, 실험 파라미터를 측정하기가 어려워서 광대역증폭기의 성능을 예측하기 어려운 점이 있었다. 게다가 이러한 상황에서 광대역증폭기에 대한 해석적이거나 수치해석적인 심도깊은 연구가 부족하여 앞으로 증폭기를 다양하게 응용하기 위한 성능의 예측이 어려울 것으로 보인다. 이는 광대역 증폭기 기반의 전송 시스템을 성공적으로 적용하는데 제한을 줄 것이다. 따라서 본 논문에서는 광대역 증폭기(C/L밴드 EDFA, 라만 증폭기, TDFA)에 대한 실험적인 분석뿐만 아니라 해석적, 수치해석적인 분석 방법까지 그 응용의 예와 함께 소개할 것이다.

• Journal of the Korean Geotechnical Society
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• v.22 no.8
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• pp.107-118
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• 2006

Among a variety of influencing components, time-variant seepage and long-term underground motion are important to understand the abnormal behavior of tunnels. Excessiveness of these two components could be the direct cause of severe damage on tunnels, however, it is not easy to quantify the effect of these on the behavior of tunnels. These parameters can be estimated by using inverse methods once the appropriate relationship between inputs and results is clarified. Various inverse methods or parameter estimation techniques such as artificial neural network and least square method can be used depending on the characteristics of given problems. Numerical analyses, experiments, or monitoring results are frequently used to prepare a set of inputs and results to establish the back analysis models. In this study, a back analysis method has been developed to estimate geotechnically hard-to-known parameters such as permeability of tunnel filter, underground water table, long-term rock mass load, size of damaged zone associated with seepage and long-term underground motion. The artificial neural network technique is adopted and the numerical models developed in the first part are used to prepare a set of data for learning process. Tunnel behavior, especially the displacements of the lining, has been exclusively investigated for the back analysis.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.9
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• pp.747-755
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• 2014

The heat transfer mechanism for radiation is directly related to the emission of photons and electromagnetic waves. Depending on the participation of the medium, the radiation can be classified into two forms: surface and gas radiation. In the present study, unknown radiation properties were estimated using an inverse boundary analysis of surface radiation in an axisymmetric cylindrical enclosure. For efficiency, a repulsive particle swarm optimization (RPSO) algorithm, which is a relatively recent heuristic search method, was used as inverse solver. By comparing the convergence rates and accuracies with the results of a genetic algorithm (GA), the performances of the proposed RPSO algorithm as an inverse solver was verified when applied to the inverse analysis of the surface radiation problem.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.139-145
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• 2009

Reduction scheme is remarkably useful in the case requiring the repeated calculation procedure. Recently, the efficiency of the reduction scheme has been improved by combining scheme of sub-domain method. But, when the global domain is partitioned into a few sub-domains, sub-domains without constraints can be produced. it is needed to extract the ritz vector from each sub-domain to construct the reduced system of each sub-domain. it is easy to extract the ritz vector from sub-domain with constraint. on the other hand, pseudo inverse method should be employed to extract the ritz vector from sub-domain without constraint. generally, the pseudo inverse takes a large number of computing time to obtain a reduced system of a sub-domain without boundary condition. This trouble can be overcome by the reduced pseudo inverse scheme which proposed in this study. This scheme is based on the static condensation that is not related with selection of the primary degrees of freedom. Numerical examples demonstrate that present method saves computational cost effectively and predicts the accurate eigenvalues.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.29 no.4
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• pp.329-341
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• 2011

The object of this paper is to compare the accuracy and the characteristic of various methods of solving the geodetic inverse problem for the geodesic lines which be in the standard case and special cases(antipodal, near antipodal, equatorial, and near equatorial situation) on the WGS84 reference ellipsoid. For this, the various algorithms (classical and recent solutions) to deal with the geodetic inverse problem are examined, and are programmed in order to evaluate the calculation ability of each method for the precise geodesic determination. The main factors of geodetic inverse problem, the distance and the forward azimuths between two points on the sphere(or ellipsoid) are determined by the 18 kinds of methods for the geodetic inverse solutions. After then, the results from the 17 kinds of methods in the both standard and special cases are compared with those from the Karney method as a reference. When judging these comparison, in case of the standard geodesics whose length do not exceed 100km, all of the methods show the almost same ability to Karney method. Whereas to the geodesics is longer than 4,000km, only two methods (Vincenty and Pittman) show the similar ability to the Karney method. In the cases of special geodesics, all methods except the Modified Vincenty method was not proper to solve the geodetic inverse problem through the comparison with Karney method. Therefore, it is needed to modify and compensate the algorithm of each methods by examining the various behaviors of geodesics on the special regions.

• Journal of the Society of Disaster Information
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• v.19 no.1
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• pp.31-43
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• 2023

Purpose: In this study, an analysis of the differences between the elastoplastic analysis and the numerical analysis and a study of the design ground constant recalculation method to derive similar trends in the analysis results were conducted. Method: The relational expression between the ground reaction force coefficient and the ground deformation coefficient at the time when the wall displacement becomes the same according to shallow excavation and deep excavation was derived. Result: Based on the measurement results, reverse analysis was performed to re-calculate the ground properties suitable for the site ground, and as a result of comparing and verifying the wall displacement using the derived formula and the literature formula, the proposed formula showed the most similar value. Conclusion: If the proposed formula is used, it will be helpful in practice because it is possible to infer the most similar ground properties to the actual at the time of design.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.1
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• pp.147-154
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• 2019

The finite element model updating can be defined as the problem of finding the parameters of the finite element model which gives the closest response to the actual response of the structure by measurement. In the previous researches, optimization based methods have been developed to minimize the error of the response of the actual structure and the analytical model. In this study, we propose an inverse eigenvalue problem that can directly obtain the parameters of the finite element model from the target mode information. Deep Neural Networks are constructed to solve the inverse eigenvalue problem quickly and accurately. As an application example of the developed method, the dynamic finite element model update of a suspension bridge is presented in which the deep neural network simulating the inverse eigenvalue function is utilized. The analysis results show that the proposed method can find the finite element model parameters corresponding to the target modes with very high accuracy.