• Journal of the Korean Geophysical Society
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• v.3 no.4
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• pp.251-260
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• 2000

Applicabilities of two numerical methods, the 2-dimensional and the 3-dimensional method, are evaluated to inverse test results obtained from the underwater SASW(Spectral -Analysis-of-Surface-Waves) method. As a result of this study, it has been found that the 2-dimensional method can supposed to be applicable for the cases where stiffness of soil layer increases gradually with depth, and the stiffness is relatively low. For the other cases, however, it has been concluded that the 3-dimensional method needs to be applied to determine realistic theoretical dispersion curves. An example is also shown that in situ soil profile underwater is estimated from experimental dispersion curves using the 3-dimensional method. As a results, it can be concluded that the underwater SASW method can be effectively applied to explore the underwater soil condition.

• Journal of the Earthquake Engineering Society of Korea
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• v.4 no.1
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• pp.77-88
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• 2000

복소모드 중첩법은 점탄성 감쇠기가 설치된 비비례 감쇠시스템의 정확한 동적 거동을 예측할 수 있는 방법이지만 많은 자유도를 갖는 고층건물의 해석시 고유치 해석과 모드중첩과정에서 많은 시간과 노력이 필요하게 된다. 본 논문에서는 효율적인 모형화를 위하여 강막가정과 행렬응축기법을 적용하고 구조물의 진동에 영향을 주는 주요모드의 선택을 위한 복소모드 응답참여계수를 제안하므로써 복소모드 중첩법의 효율성은 높였다. 또한 비비례 감쇠시스템에서 감쇠를 고려하여 응답스펙트럼을 재구성한후 선택된 주요 모드를 중첩하여 최대층간변위가 발생하는 곳에 감쇠기를 설치하였다 이 방법은 감쇠기가 설치된 구조물에 대하여 만족되는 수준의 최대층간변위가 발생할 때 까지 고유치 해석만을 반복.수행하면서 감쇠기를 연속적으로 설치하는 방법이다. 제안된 방법의 정확성과 효율성을 검토하기 위하여 예제 구조물의 대상으로 해석한 결과 응답의 정확성을 유지하면서 해석에 필요한 시간을 대폭 절감할 수 있었다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.4
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• pp.671-679
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• 1999

건물의 진동에너지 소산능력을 향상하기 위하여 점탄성감쇠를 설치하게 되면 이른바 비비례 감쇠시스템이 되어 구조물은 복소수형태의 고유모드와 고유치를 가진다. 복소모드중첩법은 이러한 복소모드를 이용하여 중첩함으로써 비비례 감쇠시스템 구조물의 정확한 동적 거동을 얻을 수 있는 방법이다. 그러나 건물이 고층화되면 많은 자유도로 인하여 고유치해석 및 모드중첩과정에서 많은 시간과 노력이 필요하게 된다. 본 논문에서는 효율적인 구조물의 모형화를 위하여 강막가정과 행렬응축기법을 적용하였다. 또한 몇 개의 주요 모드만을 선택하여 중첩하는 방법에 대하여 연구하였으며 구조물의 진동에 영향을 주는 모드의 선택을 위한 복소모드 응답참여계수를 제안하였다. 제안된 해석방법의 정확성과 효율성을 검토하기 위하여 예제 구조물을 대상으로 해석한 결과, 응답의 정확성을 유지하면서 해석에 필요한 시간을 대폭 절감할 수 있었다.

• Magazine of the Korea Concrete Institute
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• v.6 no.3
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• pp.180-189
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• 1994

An approximate method of normal coordinate idealization for use in nonlinear R /C frames has been developed. Normal coordinate apporaches have been used for nonlinear problems in the past, but they are not recerved wide acceptance because of the need for eigenvector computation in each time step. The proposed method circumvents the eigenvector recalculation problem by evaluating a limited number of sets of mode shapes in performing the dynamic analysis. Then some of the predetermined sets of eigenvectors are used in the nonlinear dynamic repeatedly. The method is applied to frame structures with ductile R /C elements. The plastic hinge zones are modeled with hysteres~s loops which evince degrading stiffness and pinching effects. Effxiencies and accuracies of the method for this application are presented.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.3
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• pp.371-383
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• 1999

An efficient and numerically stable eigensolution method for structures with multiple natural frequencies is presented. The proposed method is developed by improving the well-known subspace iteration method with shift. A major difficulty of the subspace iteration method with shift is that because of singularity problem, a shift close to an eigenvalue can not be used, resulting in slower convergence. In this paper, the above singularity problem has been solved by introducing side conditions without sacrifice of convergence. The proposed method is always nonsingular even if a shift is on a distinct eigenvalue or multiple ones. This is one of the significant characteristics of the proposed method. The nonsingularity is proved analytically. The convergence of the proposed method is at least equal to that of the subspace iteration method with shift, and the operation counts of above two methods are almost the same when a large number of eigenpairs are required. To show the effectiveness of the proposed method, two numerical examples are considered.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.3
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• pp.139-150
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• 2005

Finite element method is applied to the determinations of the two eigenvalues(the elastic critical load and the natural frequence of lateral vibrations) of single story-3 equal bay rectangular frame. The analysis parameters are taper parameter ${\alpha}$ for column, and beam span to column height ratio, ${\beta}$ and second moment area ratio of beam to column, ${\Upsilon}$. Support condition at the column base and sway condition at the column top are also considered in the stability analysis of frame. The changes in the coefficient of eigenvalue are represented by algebraic function of analysis parameter. The coefficients estimated by the proposed algebraic function show good agreement with those determined by finite element method, which suggest the design aid role of the proposed function. By increasing the column axial forces step by step, the corresponding frequencies are also determined, which makes one examine or confirm the relationship suggested by other studies.

• 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.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.469-471
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• 2010

Supercavitating vehicles which cruise under water undergo high longitudinal force caused by thrust and drag. These combination may cause structural buckling. Static and dynamic buckling analysis method by using FEM can be used to predict this structural failure behavior. In this paper, some principles which include method for solution eigenvalue problem for buckling analysis are introduced. And before buckling analysis, we predicted some mode shape and natural frequency of cylindrical shell by using DIAMOND/IPSAP eigen-solver.

• Journal of Korean Association for Spatial Structures
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• v.9 no.1
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• pp.79-85
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• 2009

As a recent spatial structure have become long-spaned and light, stiffness of out-plane is reduced significantly. Due to this, it is necessary to calculate natural frequency correctly to check if structure is flexible or vortex-induced vibration is occurred. However, formula of frequency in domestic and foreign spatial structure has not been performed deeply. In this study, approximated formula obtained by eigenvalue analysis of seven domestic spatial structure is compared with two suggestions based on Japanese standard and formula by measurement of 28 spatial structure in Japan. Natural frequency of roof has a tendency to be reduced as the span of structure increases. Natural frequency of domestic structure is generally less than that of analysis and measurement of spatial structure in Japan. Therefore, it is confirm that roof of domestic spatial structure is relatively rather flexible than that of Japan.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.2
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• pp.169-179
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• 2005

An improved method for evaluating effective buckling lengths of beam-column members in plane frames is newly proposed based on system inelastic buckling analysis. To this end, the tangent stiffness matrix of be am-column elements is first calculated using stability functions and then the inelastic buckling analysis method is presented. The scheme for determining effective length of individual members is also addressed. Design examples and numerical results ?uc presented to show the validity of the proposed method.