• 대한기계학회논문집A
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• 제31권2호
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• pp.211-220
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• 2007

This work presents an iterated improved reduced system (IIRS) procedure combined with sub-structuring scheme for large structures. Iterated IRS methods are usually more efficient than others because the dynamic condensation matrix is updated repeatedly until the desired convergent values are obtained. However, using these methods simply for large structures causes expensive computational cost and even makes analyses intractable because of the limited computer storage. Therefore, the application of sub-structuring scheme is necessary. Because the large structures are subdivided into several (or more) sub-domains, the construction of dynamic condensation matrix does not require much computation cost in every iteration. This makes the present method much more efficient to compute the eigenpairs both in lower and intermediate modes. In Part I, iterated IRS method combined with sub-structuring scheme for undamped structures is presented. The validation of the proposed method and the evaluation of computational efficiency are demonstrated through the numerical examples.

• Nuclear Engineering and Technology
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• 제56권6호
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• pp.2120-2130
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• 2024

This study significantly reduced the seismic analysis time of PCSG assembly by introducing a reduced model using homogenization and sub-structuring methods. The homogenization method was applied to the primary and secondary micro-channel sheets, and the sub-structuring method was applied to the PCSG module sets. Modal analysis and frequency response analysis were then performed to validate the accuracy of the reduced model. The analysis results were compared with the full model and it was confirmed that the reduced model provided almost the same analysis results as the full model. To verify the computational efficiency of the reduced model, the computational time was then compared with the full model, and it was confirmed that the modal analysis time was reduced by 3.42 times and the frequency response analysis time was reduced by 4.59 times.

• 대한기계학회논문집A
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• 제31권2호
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• pp.221-230
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• 2007

An iterated improved reduced system (IIRS) procedure combined with sub-structuring scheme for nonclassically damped structural systems is presented. For dynamic analysis of such systems, complex eigenproperties are required to incorporate properly the nonclassical damping effect. In complex structural systems, the equations of motion are written in the state space from. Thus, the number of degrees of freedom of the new equations of motion and the size of the associated eigenvalue problem required to obtain the complex eigenvalues and eigenvectors are doubled. Iterated IRS method is an efficient reduction technique because the eigenproperties obtained in each iteration step improve the condensation matrix in the next iteration step. However, although this reduction technique reduces the size of problem drastically, it is not efficient to apply this technique to a single domain finite element model with degrees of freedom over several thousands. Therefore, for a practical application of the reduction method, accompanying sub-structuring scheme is necessary. In the present study, iterated IRS method combined with sub-structuring scheme for nonclssically damped structures is developed. Numerical examples demonstrate the convergence and the efficiency of a newly developed scheme.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 추계학술대회 논문집
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• pp.635-635
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• 2014

최근 지하철 인접 부지에 고층 주거 시설이 입지함에 따라 지하철 통행시의 소음 및 진동관련 민원이 증가하고 있는 추세이다. 따라서, 지하철 인접에 위치하는 구조물의 경우 계획단계에서부터 지하철로 인한 소음 및 진동 문제를 예측하고 평가하는 과정이 필수적이다. 건물이 시공되기 전 지하철 통행으로 인하여 건물에 유입되는 진동을 예측 및 평가하기 위해서는 해석적 방법으로 접근해야 하며, 본 연구에서는 sub-structuring method를 활용한 지하철 진동 해석 방법과 실제 구조물에 적용한 사례를 제시한다.

• 한국지반신소재학회논문집
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• 제20권2호
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• pp.35-43
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• 2021

본 논문에서는 고속철도 교량-열차 상호작용 해석을 위한 단순 3 차원 상호작용 해석모델을 기반으로 하여 정식화한 부구조화 기법 적용 상호작용 해석모델을 제시한다. 부구조화 기법에서는 철도 교량의 상부 구조와 지지 구조를 각각 부구조로 모델링하고, 열차-교량 상호작용 해석을 효율적으로 수행할 수 있다. 열차 해석 모델로는 2차원 열차 모델을 사용하고, Lagrange 운동방정식을 적용하여 2차원 열차의 운동방정식을 유도한다. 부구조화 기법에서는 응축 방법을 사용하여 자유도(Degree of freedom)의 수를 줄일 수 있으므로 고유 값 및 고유 벡터 계산을 위한 소요 시간 및 비용과 후속 계산의 소요시간 및 비용이 줄어든다. 본 논문에서는 부구조화 기법으로 Guyan 감소 방법을 사용한다. 단순 3 차원 교량-열차 상호작용 해석과 Guyan 감소 방법을 결합하여 효율적이고 정확한 교량-열차 상호작용 해석을 수행할 수 있다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2008년도 정기 학술대회
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• pp.356-361
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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.

• 한국레이저가공학회지
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• 제18권3호
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• pp.14-19
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• 2015

A helical fabricating method using $CO_2$ laser was utilized for producing cone-shaped structure on a silica substrate. Output power and the number of scanning radiation were modified in order to control the structure. The experiment shows that the depth and width of cone-shape were increased with higher output power of the laser and the number of scanning. We demonstrate fabrication of multidirectional side-firing optical fiber with diameter of 440 um using the $CO_2$ laser fabrication technique.

• 한국전산구조공학회논문집
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• 제21권3호
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• pp.281-285
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• 2008

축소시스템 기법은 전체 구조의 거동을 나타내는 저차 고유모드를 근사화한다. 지난 연구에서 축소시스템을 구축하기 위한 2단계 축소기법을 제안하였다. 또, 기존의 2단계 축소기법을 반복적 IRS기법을 통해 중간 주파수 대역의 고유모드에 대한 해의 정확도를 높이는 방안에 대해 연구가 제안되었다. 본 연구에서는 기존의 향상된 2단계 축소기법에 다단계 부구조화 기법을 적용하는 기법을 제안한다. 첫 단계에서는 전체 시스템을 그래프 분할을 통해 계층적으로 부구조로 분할되고, 두 번째 단계에서는 각각의 부구조를 개선된 2단계 축소기법을 이용하여 축소한다. 각각의 축소된 분절화된 고유치문제의 조합을 총해 최종적 축소시스템을 구축하고 이렇게 구한 축소된 고유치 문제를 란초스 기법(ARPACK)을 통해 해석한다. 최종적으로 제안된 기법의 성능을 수치 예제를 통해 검증한다.

• Structural Engineering and Mechanics
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• 제38권4호
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• pp.429-441
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• 2011

In large-scale problem, a huge size of computational resources is needed for a reliable solution which represents the detailed description of dynamic behavior. Recently, eigenvalue reduction schemes have been considered as important technique to resolve computational resource problems. In addition, the efforts to advance an efficiency of reduction scheme leads to the development of the multi-level system condensation (MLSC) which is initially based on the two-level condensation scheme (TLCS). This scheme was proposed for approximating the lower eigenmodes which represent the global behavior of the structures through the element-level energy estimation. The MLSC combines the multi-level sub-structuring scheme with the previous TLCS for enhancement of efficiency which is related to computer memory and computing time. The present study focuses on the implementation of the MLSC on the direct time response analysis and the frequency response analysis of structural dynamic problems. For the transient time response analysis, the MLSC is combined with the Newmark's time integration scheme. Numerical examples demonstrate the efficiency of the proposed method.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 추계학술대회 논문집
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• pp.411-412
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• 2012