• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.4
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• pp.329-334
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• 2017

The structures, which are made up with the huge number of degrees-of-freedom and the assembly of substructures, have a great complexity. In order to increase the computational efficiency, the analysis models have to be simplified. Many substructuring techniques have been developed to simplify large-scale engineering problems. The techniques are very powerful for solving nonlinear problems which require many iterative calculations. In this paper, a modal derivatives-based model order reduction method, which is able to capture the stretching-bending coupling behavior in geometrically nonlinear systems, is adopted and investigated for its performance evaluation. The quadratic terms in nonlinear beam theory, such as Green-Lagrange strains, can be explained by the modal derivatives. They can be obtained by taking the modal directional derivatives of eigenmodes and form the second order terms of modal reduction basis. The method proposed is then applied to a co-rotational finite element formulation that is well-suited for geometrically nonlinear problems. Numerical results reveal that the end-shortening effect is very important, in which a conventional modal reduction method does not work unless the full model is used. It is demonstrated that the modal derivative approach yields the best compromised result and is very promising for substructuring large-scale geometrically nonlinear problems.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.3
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• pp.281-285
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• 2008

Eigenvalue reduction schemes approximate the lower eigenmodes that represent the global behavior of the structures. In the previous study, we proposed a two-level condensation scheme (TLCS) for the construction of a reduced system. And we have improved previous TLCS with combination of the iterated improved reduced system method (IIRS) to increase accuracy of the higher modes intermediate range. In this study, we apply previous improved TLCS to multi-level sub-structuring scheme. In the first step, the global system is recursively partitioned into a hierarchy of sub-domain. In second step, each uncoupled sub-domain is condensed by the improved TLCS. After assembly process of each reduced sub-eigenvalue problem, eigen-solution is calculated by Lanczos method (ARPACK). Finally, Numerical examples demonstrate performance of proposed method.

• Journal of Korean Society of Steel Construction
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• v.22 no.4
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• pp.335-344
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• 2010

This paper presents both of an investigation on the ultimate responses and a verification study on the structural methodology using beam-truss element of steel transmission towers using experimental study. The partially scaled tower which verified with analytical model was fabricated and the horizontal load was applied up to failure in the laboratory. The structural methodology for finite element analyses was verified against experimental results and both the ultimate load capacity and collapse mechanism were shown in the test to give sufficiently accurate results with those of analytical study. It was shown as well that the ultimate failure is primarily attributed to instability of the main posts in the leg parts.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.14 no.1
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• pp.28-35
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• 2006

Substructure coupling or component mode synthesis may be employed in the solution of dynamic problems for large, flexible structures. The model is partitioned into several subdomains, and a generalized Craig-Bampton representation is derived. In this paper the mode sets (normal modes, constraint modes) is employed for model reduction. A generalized model reduction procedure is described. Vaious reduction methods that use constraint modes is described in detail. As examples, a flexible structure and a 10 DOF damped system are analyzed. Comparison with a conventional reduction method based on a complete model is made via eigenpair and dynamic responses.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1370-1375
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• 2001

Substructure coupling or component mode synthesis may be employed in the solution of dynamic problems for structure. The model is partitioned into several subdomains. and a generalized Craig-Bampton representation is derived. In this paper the mode sets(normal modes. constraint modes) have been employed for model reduction. A generalized model reduction procedure has been described. Those reduction methods which adapt constraint modes have been described in detail. As examples. a flexible structure and a 10 DOF damped system are analyzed. Comparison with a conventional reduction method based on a complete model has been made via eigenpairs and dynamic responses.

• Korean Journal of Computational Design and Engineering
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• v.8 no.2
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• pp.109-114
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• 2003

In order to develop the reduced tire modal model for analyzing a full tire model, the Craig-Bampton method is utilized in this paper. When the tire contacts the road, the Abaqus solver extracts the condensed stiffness, coupled mass and mode shape matrix about the node, which contacts the road. The Abaqus full tire model is reduced using the substructure method utilizing Craig-Bampton algorithm. Then, the extracted matrices are interfaced with the superelement, which is fed to the Nastran reduction algorithm. Eventually, the reduced tire model is verified from experiment and various reduction parameters (i.e. modal number, reduction point, etc.) are studied for the effectiveness of the proposed paper.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.04a
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• pp.34-39
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• 1995

최근 승용차의 급격한 수요증가와 더불어 차량의 승차감 개선에 많은 관심이 집중되면서, 저진동 저소음 차량에 대한 연구가 활발히 이루어지고 있다. 이러한 연구의 일부로서, 수치해석법 및 진동실험에 의하여 복잡한 전체 구조물을 해석할 경우, 계산기의 기억용량, 계산시간, 비용이 많이 들게 되고, 한번 해석을 행한 구조물을 부분적으로 변경할지라도 전체의 계산을 다시 수행해야만 한다. 그래서, 복잡한 전체 구조물을 몇 개의 부분구조물로 나누어, 분계의 특성에 맞게 각기 수치해석법이나 모달실험을 적용한 후, 다시 합성하는 방법이 제시되었는데, 이것이 부분구조합성법이다. 이 방법을 사용하면, 유한요소 모델링이 쉬운 분계와 실험이 쉬운 분계를 서로 구분하여 각기 해석한 후 합성함으로써, 각 분계의 특성에 맞는 효율적인 해석을 수행할 수가 있다. 지금까지의 연구를 살펴보면, 유한요소해석에 의한 모드합성법에서는 Hurty가 구속모드법을 제안한 이래, 불구속모드법, 주종계법 등 많은 연구가 있었으나, 실험모달해석을 병행할 경우에는 결합부에서의 회전자유도의 처리문제, 특성 행렬의 동정문제, 많은 절점으로부터 데이타를 얻어야 하는 등의 어려움이 있었다. 이러한 문제를 개선시켜서 Hermanski등은 회전자유도가 보간된 모드합성법(interpolated mode synthesis, IMS)을 연구하여, 적은 실험데이타만을 사용하면서 단순지지 보에 적용함으로써 타당성을 입증하였다. 한편, 차체는 복잡한 부분구조물들로 이루어져 있으므로, 본 연구에서는 유한요소모델링의 용이함, 실험의 간편성, 계산의 효율성등을 추구하며, 실험과 유한요소해석을 병행한 부분구조합성법을 차량의 BIW(body in white)에 적용하는 방법을 연구하게 되었다. 그 기본연구로서 실험과 유한요소해석을 병행하여 회전자유도를 보간하는 방법을 먼저 단순한 판구조물에 적용을 하고, 나아가 실제 BIW를 축소하여 자체 제작한 모형차에 적용시켜 보았다.물은 분계 A(16개의 사각요소)와 분계 B(8개의 사각요소)로 이루어져 있으며 두개의 스프링으로 결합되어 있다. 설계변수는 강성에 국한하였으며 결합부의 결합형태는 탄성결합과 강결합으로 하였다. 감도해석과 축소임피던스 합성법에 의해 구해진 고유진동수와 FRF를 상용 유한 요소 해석 패키지인 MSC/NASTRAN을 통하여 검증하여 이 연구의 타당성을 검토하였다.인풋기어에서의 회전수 변동을 측정하고, 이 실험 데이타를 기초로 하여 엔진 토크 및 변속기에서의 드래그 토크를 계산하여 엔진-변속기 인풋기어의 반한정계 2자유도 진동모델과 비틀림 특성을 가진 클러치 디스크의 프리댐퍼 영역에 대해 시뮬레이션을 수행하여 클러치 비틀림 기구의 설계인자인 비틀림 강성, 히스테리시스 토크에 따른 비틀림 진동 저감 효과를 연구하고자 한다.성을 확인하였다. 여기서는 실험실 수준의 평 판모델을 제작하고 실제 현장에서 이루어질 수 있는 진동제어 구조물에 대 한 동적실험 및 FRS를 수행하는 과정과 동일하게 따름으로써 실제 발생할 수 있는 오차나 error를 실험실내의 차원에서 파악하여 진동원을 있는 구조 물에 대한 진동제어기술을 보유하고자 한다. 이용한 해마의 부피측정은 해마경화증 환자의 진단에 있어 육안적인 MR 진단이 어려운 제한된 경우에만 실제적 도움을 줄 수 있는 보조적인 방법으로 생각된다.ofile whereas relaxivity at high field is not affected by τS. On the other hand, the change in τV does not affect low field profile but strongly in fluences on both inflection fie이 and the maximum relaxivity value. The results shows a fluences on both inflection field and the maximum relaxivity value. Th

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.393-398
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• 2015

A very important part in vibration analysis is to calculate the frequency response function (FRF). In general, a large sized or/and complicated structure has many thousands to millions of degrees. Therefore, the FRF cannot be calculated by the traditional analysis method using an inverse matrix. This paper presents a new FRF calculation method of a superstructure by synthesizing sub-structure modes, of which the DOF can be deduced by partitioning into some sub-structures. To confirm its analysis results, the method was applied to an assembled plate ($B300{\times}L900{\times}t5mm$) with three diagonal sub-plates($B300{\times}L300{\times}t5mm$) in series and compared with the measured data. The test results have were comparable those of the calculated ones with an error less than 5%.

• Magazine of the Korea Concrete Institute
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• v.8 no.2
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• pp.139-150
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• 1996

The objective of this study is to provide the information on the manufacturing and exper- , ructures. imental techniques of small scale modeling of precast concrete(P.C.) large panel :-t The ad~~pted scale was one-fifth. 4 types of experiments were performed : nlaterial tests for model concrete and model reinforcement, compressive test of horizontal joint, shear test of vertical joint and cyclic static test of 2-story subassemblage structure. Based on the experimental results, the following conclusions are drawn : i 1) Model concrete had in general larger compressive strength than expected. (2) Model reinforcement showed less ductility if the annealing processes were performed without using vaccuum tube. 131 Failure niotles of horizontal and vertical joints were almost same for both prototype and model. But the strength of model appears to be higher than required by similitude law. (41 Hysteretic behavior of 1 /T, scale subassemblage model can be made quite similar to that of prototype if the ductility of model reinforcement and compressive strength of model concrete could be representative of those of prototype.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.56-64
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• 2005

It is prerequisite that we have to fomulate the nonlinear mathematical modeling to design the guidance and control system of rotorcraft-based unmanned aerial vehicle using a small-scaled commercial helicopter. The small-scaled helicopters are very different from the full-scale helicopters in dynamic behavior such as high rotation speed and high frequency dynamic characteristics. In this paper, the formulation of the mathematical model of the small-scaled helicopter to minimize the complexity is presented by component and source build-up approach. It is linearized at the trim condition of hovering and forward flight and analyzed the flight modes. The results of this approach have general trends but a little difference. To verify this approach, it is necessary to compare this theoretical model with experimental results by system identification using flight test as a next research topic.