• Structural Engineering and Mechanics
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• 제23권6호
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• pp.691-711
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• 2006

This paper uses the finite element method to simultaneously consider the coupled cable-deck vibrations and the parametric vibrations of stay cables in dynamic analysis of a cable-stayed bridge. The stay cables are represented by some cable finite elements, which can consider the parametric vibration of the cables. In addition to modeling stay cables using multiple link cable elements, a procedure for removing the self-weight term of cable element is proposed. A eigenvalue analysis process using dynamic condensation method for sorting out the natural modes of the girder-tower vibrations and the Rayleigh damping considering element damping for damping matrix are also proposed for dynamic analyses of cable-stayed bridges. The possibilities of using cable elements and of using global and local vibrations to evaluate the parametric vibrations of stay cables in a cable-stayed bridge are confirmed, respectively.

• 한국지진공학회논문집
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• 제2권3호
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• pp.27-35
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• 1998

Steel structures with added viscoelastic dampers are analysed to investigat their behavior under earthquake excitation. The direct integration method, which produces exact solution for the non-proportional or non-classical damping system, is used throughout the analysis. The results from modal strain energy method are also provided for comparison. Then a new analytical a, pp.oach, based on the rigid floor diaphragm assumption and matrix condensation technique, is introduced, and the results are compared with those obtained from direct integration method and modal strain energy method. The well known phenomenon, that the effectiveness of the viscoelastic dampers depends greatly on the location of the dampers, is once again confirmed in the analysis. It is also found that the modal strain energy method generaly underestimates the responses obtained from the direct integration method, especially when the dampers are placed in only a part of the building. The proposed method turns out to be very efficient with considerable saving in computation this and reasonably accurate considering the reduced degrees of freedom.

• 대한기계학회논문집A
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• 제30권9호
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• pp.1070-1077
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• 2006

In the present study, sizing and shape optimizations are performed based on the reduced system of large-scaled problem. In the analysis part to achieve efficiency and reliability of computation, two-level condensation scheme is applied. In the construction of reduced system of large scaled problems, it is much more efficient to use sub-domain method. Thus, in the present paper, two-level reduction method combined with sub-domain method is employed. Once the reduced system is constructed, it is straightforward to obtain design sensitivities from the analysis results of the reduced system We use semi-analytic method to obtain design sensitivities. Performance of the efficiency and reliability of the present reduction method in the structural optimization problem is demonstrated through the numerical examples. The present framework of reduction method should serve as a fast and reliable design tool in analysis and design of large-scaled dynamic problems.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.615-619
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• 1995

The unbalance response analysis is one of the essential area in the forced vibration analysis of rotor-bearing systems. Local bearing parameters in ortor-bearing systems are the major sources which give rise to a difficulty in unbalance response computation due to the complicated dynamic properties such as rotational speed dependency and anisotropy. In the present paper, an exact condensation procedure is introduced to easily take into account bearing parameters in computation of unbalance responses for rotor bearing systems. The present method is illustrated through a numerical example and compared with the conventional method.

• Architectural research
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• 제10권2호
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• pp.21-26
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• 2008

The number of measured degrees of freedom for detecting the damage of any structures is usually less than the number of model degrees of freedom. It is necessary to expand the measured data to full set of model degrees of freedom for updating modal data. This study presents the expansion methods to estimate all static displacements and dynamic modal data of finite element model from the measured data. The static and dynamic methods are derived by minimizing the variation of the potential energy and the Gauss's function, respectively. The applications illustrate the validity of the proposed methods. It is observed that the numerical results obtained by the static approach correspond with the Guyan condensation method and the derived static and dynamic approaches provide the fundamental idea for damage detection.

• 한국전산구조공학회논문집
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• 제20권3호
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• pp.347-352
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• 2007

축소시스템 기법은 전체 구조의 거동을 나타내는 저차 고유모드를 근사화한다. 지난 연구에서 축소 시스템을 구축하기 위한 2단계 축소기법을 제안하였다. 첫 단계에서 리츠벡터를 이용한 각 요소의 레일리 지수를 통해 요소 에너지를 예측 하고 이를 토대로 후보영역을 선정한다. 다음 단계에서 후보영역에 포함된 자유도로 축소된 1단계 축소 시스템에 순차적 소거법을 적용하여 최종적인 주자유도를 선정한다. 이번 연구에서는 2단계 축소 기법에 축소시스템 개선을 위한 반복적 기법을 적용하여 중간영역에서의 고차모드의 정확도를 추가적인 시스템의 확장없이 구하는 방법을 제안한다. 이 방법은 축소시스템에서 고유치와 고유모드의 정확도를 조절하는 것까지도 가능하다. 최종적으로 제안된 기법의 성능을 수치 예제를 통해 검증한다.

• Structural Engineering and Mechanics
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• 제39권5호
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• pp.669-682
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• 2011

A Chebyshev spectral method (CSM) for the dynamic analysis of non-uniform Timoshenko beams under various boundary conditions and concentrated masses at their ends is proposed. The matrix-based Chebyshev spectral approach was used to construct the spectral differentiation matrix of the governing differential operator and its boundary conditions. A matrix condensation approach is crucially presented to impose boundary conditions involving the homogeneous Cauchy conditions and boundary conditions containing eigenvalues. By taking advantage of the standard powerful algorithms for solving matrix eigenvalue and generalized eigenvalue problems that are embodied in the MATLAB commands, chebfun and eigs, the modal parameters of non-uniform Timoshenko beams under various boundary conditions can be obtained from the eigensolutions of the corresponding linear differential operators. Some numerical examples are presented to compare the results herein with those obtained elsewhere, and to illustrate the accuracy and effectiveness of this method.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.873-880
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• 2006

Since the mega frame structure has significant numbers of elements and nodes, it takes tremendous times and computer memories to analyze and design the structures. Therefore, the exclusive structural analysis program for mega frame system is developed to reduce the efforts and time required for the analysis and design of mega frame structure. To this end, an efficient modelling technique using the characteristics of mega frame structures and an efficient analytical model, which uses a few DOFs selected by the user using the matrix condensation method. are developed in tins study. Static and dynamic analyses are conducted using an example structure.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1996년도 가을 학술발표회 논문집
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• pp.239-246
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• 1996

Very stiff floor system in a residential-commercial building causes some problems in the numerical analysis procedure due to significant difference in stiffness with adjacent structural elements. Static analysis of structure with a stiff transfer-floor can be peformed approximately in two steps for upper and lower pons for the structure. However, it is impossible to perform dynamic analysis in two steps with separate models. An efficient method for dynamic analysis of a structure with a rigid floor system is proposed in this study. The matrix condensation technique is employed to reduce the degree of freedom for upper and lower parts of the structure and a beam elements with rigid bodies of both ends are introduce to model the rigid floor system. Efficiency end accuracy of the proposed method ore verified through analysis of several example structures.

• 한국지진공학회논문집
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• 제8권6호통권40호
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• pp.55-66
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• 2004

현재 국내에서는 벽과 바닥판만으로 이루어진 벽식 구조형식의 아파트 건물이 많이 건설되고 있다. 아파트와 같은 주거구조물에서는 다양한 진동원에 의하여 진동이 발생하고 이러한 진동은 벽과 바닥판을 통하여 이웃한 세대 및 위, 아래층 세대로 전달되게 된다. 벽식구조물의 진동해석을 정확하게 수행하기 위해서는 벽과 바닥판을 많은 수의 유한요소로 세분한 모델을 사용하는 것이 필요하다. 그러나 아파트와 같은 벽식구조물 전체를 수많은 유한요소로 세분하여 모형화하면 막대한 해석시간과 컴퓨터 메모리가 필요하게 된다. 따라서 본 연구에서는 상당히 줄어든 해석시간과 컴퓨터 메모리를 사용하여 정확한 해석결과를 얻기 위하여 행렬응축기법으로 벽과 바닥판에 수직인 자유도만 가지는 효율적인 진동해석 모델을 제안한다. 벽식구조물에서 벽과 바닥에 수직인 자유도만을 남기고 나머지 자유도를 행렬응축기법을 통하여 한꺼번에 소거를 한다면 행렬응축과정에서 상당히 많은 양의 시간이 소요된다. 따라서 본 연구에서는 벽이나 바닥판에 수직인 자유도만을 가진 수퍼요소를 생성한 후 이를 조합하여 한 층을 나타내는 부분구조를 만들고 최종적으로 부분구조를 조합하여 전체 구조물을 구성하는 모형화 기법을 제안하였다. 제안된 해석기법의 정확성과 효율성을 검증하기 위하여 3층 및 5층의 벽식구조물을 예제구조물로 사용하여 동적해석을 수행하였다. 예제해석 결과 제안된 해석방법의 결과는 절점당 6개의 자유도를 모두 사용한 해석모델의 결과와 비슷한 정확성을 보이면서도 소요되는 해석시간과 컴퓨터 메모리를 대폭 줄일 수 있었다.