• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.35 no.3
• /
• pp.175-182
• /
• 2022

In many engineering problems, the dynamic substructuring can be useful to analyze complex structures which made with many substructures, such as aircrafts and automotive vehicles. It was originally intended as a method to simplify the engineering problem. The powerful advantage to this is that computational efficiency dramatically increases with eliminating unnecessary degrees-of-freedom of the system and the system targets are concurrently satisfied. Craig-Bampton method has been widely used for the linear system reduction. Recently, multi-level optimization (such as target cascading), which propagates the system-level targets to the subsystem-level targets, has been widely utilized. To this concept, the genetic algorithm which one of the global optimization technique has been utilized to the substructure optimization. The number of internal modes for each substructure can be obtained by the genetic algorithm. Simultaneously, the reduced system meets the top-level targets. In this paper, various numerical examples are tested to verify this concept.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2008.04a
• /
• pp.356-361
• /
• 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.

• Smart Structures and Systems
• /
• v.14 no.6
• /
• pp.1005-1030
• /
• 2014

The need for assessing dynamic response of typical industrial piping systems subjected to seismic loading motivated the authors to apply model reduction techniques to experimental dynamic substructuring. Initially, a better insight into the dynamic response of the emulated system was provided by means of the principal component analysis. The clear understanding of reduction basis requirements paved the way for the implementation of a number of model reduction techniques aimed at extending the applicability range of the hybrid testing technique beyond its traditional scope. Therefore, several hybrid simulations were performed on a typical full-scale industrial piping system endowed with a number of critical components, like elbows, Tee joints and bolted flange joints, ranging from operational to collapse limit states. Then, the favourable performance of the L-Stable Real-Time compatible time integrator and an effective delay compensation method were also checked throughout the testing campaign. Finally, several aspects of the piping performance were commented and conclusions drawn.

• Journal of Mechanical Science and Technology
• /
• v.18 no.9
• /
• pp.1529-1536
• /
• 2004

A structure is broken down into a number of substructures by means of the finite element method and the substructures are synthesized for the complete structure. The divided substructures take two types: fixed-free and free-free elements. The flexibility and stiffness matrices of the free-free elements are the Moore-Penrose inverse of each other. Thus, it is not easy to determine the equilibrium equations of the complete structure composed of two mixed types of substructures. This study provides the general form of equilibrium equation of the entire structure through the process of assembling the equilibrium equations of substructures with end conditions of mixed types. Applications demonstrate that the proposed method is effective in the structural analysis of geometrically complicated structures.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.14 no.2
• /
• pp.193-202
• /
• 2001

현재 국내에서는 아파트 건물을 짓는데 벽과 바닥판으로만 이루어진 벽식 구조형식을 많이 사용하고 있다. 이러한 고층 아파트건물을 해석하기 위해서 ETABS나 MIDAS/BDS 같은 상용프로그램이 주로 사용되고 있다. ETABS는 해석상의 편의를 위하여 바다판을 강막으로 가정하여 모형화 하고 바닥판의 휨강성은 고려하지 않고 있다. 이러한 가정은 프레임 구조물을 해석할 때에는 합리적이라고 할 수 있다. 그러나 벽식 구조물은 바닥판의 휨강성이 전체 구조물의 횡방향 강성에 큰 영향을 미치므로 바닥판의 휨강성을 고려하지 않으면 전체 구조물의 강성을 과소평가하게 된다. 따라서 바닥판을 판요소로 세분하여 모형화 하는 것이 필요하다. 그러나 이때 많은 양의 해석 시간과 컴퓨터 메모리가 필요하게 된다. 따라서 본 연구에서는 부분구조법과 행렬응축기법을 사용하여 해석 시간과 컴퓨터 메모리의 사용을 줄이면서도 바닥판의 휨강성을 효율적으로 해석할 수 있는 해석 기법을 제안하였고 예제를 통하여 검증하였다.

• International Journal of Aeronautical and Space Sciences
• /
• v.15 no.2
• /
• pp.113-122
• /
• 2014

The objective of the paper is to clarify a methodology based on the use of the existing component mode synthesis methods for the case of two damped substructures which are coupled through a linking viscoelastic flexible substructure and for which the structural modes with free geometrical interface are used for each main substructure. The proposed methodology corresponds to a convenient alternative to the direct use either of the Craig-Bampton method applied to the three substructures (using the fixed geometric interface modes) or of the flexibility residual approaches initiated by MacNeal (using the free geometric interface modes). In opposite to a geometrical interface which is a topological interface on which there is a direct linkage between the degrees of freedom of substructures, we consider a physical flexible interface which exists in certain present technologies and for which the general framework linear viscoelasticity is used and yields a frequency-dependent damping and stiffness matrices of the physical flexible interface.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.5 s.176
• /
• pp.1133-1145
• /
• 2000

It is necessary to develop an efficient analysis method to identify the dynamic characteristics of a large mechanical structure and update its finite element model. That is because these processes need the huge computation of a large structure and iterative estimation due to the use of the first- order sensitivity. To efficiently carry out these processes, a new method, called the generalized free-interface mode sensitivity method, has been proposed in the authors' preceeding paper. This method is based on substructuring approach such as a free-interface method and a generalized synthesis algorithm. In this paper, the proposed method is applied to the model updating of a car body structure to verify its accuracy and reliability for a large mechanical structure.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.10 no.1
• /
• pp.16-22
• /
• 2001

In this study for reduction degree of freedom of dynamic model, a mixed method to combined finite element method and transfer matrix method is presented. This offers the advantages of an automatic reduction in the size of the eigenvalues problem and of a straightforward means of dynamic substructuring. The analytical procedure in this method for dynamic analysis of 3-dimensional cantilevered box beam are described. the result of numerical example is shown to demonstate the efficiency and accuracy of this method. The result form this example agree well those obtained by ANSYS, By using this technique, the number of nodes required in the regular finite element method is reduced and therefore a smaller com-puter can be used.

• Journal of KSNVE
• /
• v.8 no.1
• /
• pp.139-145
• /
• 1998

A great deal of effort has been invested in upgrading the performance and the efficiency of dynamic analysis of mechanical structures. Using experimental modal analysis(EMA) or finite element analysis(FEA) data of mechanical structures, the performance and efficiency can be effectively evaluated. In order to analyze complex structures such as automobiles and aircrafts, for the sake of computing efficiency, the dynamic substructuring techniques that allow to predict the dynamic behavior of a structure are widely used. Through linking a modal model obtained from EMA and an analytical model obtained from FEA, the best conditioned strucutres can be proposed. In this study, a new algorithm of substructre synthesis method, Multi-FRF synthesis method, is proposed to analyze a structure composed of many substructures.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.11a
• /
• pp.173-178
• /
• 2001

부분구조 합성법(substructuring or substructure synthesis)은 부분구조(substructure)의 주파수 응답함수(FRFs, frequency response functions)를 이용하여 합성된 전체 구조물의 동특성(dynamic behavior)을 파악하는 기술로서 이에 관한 이론은 명확하며 간단하다. 즉, 역행렬 계산과 같은 기본적인 행렬연산으로 부분구조 합성을 수행한다. 그러나, 여러 가지 요인으로 인하여 계산된 합성 결과는 실제로 결합된 전체 구조물의 동특성과는 차이를 보인다. 현실적인 이유로 고려하지 못하는 회전자유도와 실험에서 수반되는 여러 가지 측정오차는 주요한 요인이며 이에 대한 연구 또한 많이 진행되었다. 본 연구에서는 이러한 요인 중, 상대적으로 덜 중요하게 평가된 모드자름 오차(modal truncation error)의 영향을 고려한다. 단순한 구조물에 대하여 모의실험을 수행함으로써, 모드자름 오차로 인하여 완전히 잘못된 합성 결과가 나을 수 있다는 것을 보인다. 측정된 FRE를 이용하여 이러한 오차를 보정(compensation)하는 소개하고 이를 대상 구조물에 적용하여 모드자름 오차의 영향을 상당히 줄일 수 있다는 것을 보인다. 복잡한(complicated) 구조물에 대하여 모드자름 오차의 영향을 줄이기 위해서 모든 FRFs를 보정하는 것은 어려우므로 현실적인 대안을 모색한다.