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- 저자 : 조맹효(Meanghyo Cho) (검색결과 4 건)
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System Identification by Sub-domain approach
백승민(Sungmin Baek),조맹효(Meanghyo Cho),김기욱(Ki-Ook Kim),김혁(Hyuk Kim),최형길(Hyunggil Choi),최재락(Jearak Choi) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
A number of approximate techniques have been developed to determine primary degrees of freedom of the reduced eigenvalue problem. In general, sequential elimination can be used with reliability. But it takes excessively large amount of time to construct a reduced system. To reduce computational time and resources, two-level selection scheme combined with improved sub-structuring method are used. In the present study, nonlinear inverse perturbation method is used to solve inverse problem. It is the form of optimal design problem with the objective function which is the residual error of dynamic equilibrium equations. Design variables are limited not to all the perturbed quantities of the elements in the global domain but only to the perturbed quantities in the particular sub-domain which is expected to possess damages. The present method requires only small number of design variables and convergence in nonlinear problem is much faster than that of a single global system.
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반복적인 동적 축소법과 대형 구조물 해석을 위한 부구조화 기법의 적용
최동수(Dongsoo Choi),조맹효(Meanghyo Cho) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
This work presents an iterative dynamic condensation procedure combined with sub-structuring scheme for large structures. Iterative dynamic condensation techniques 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 very expensive computational cost and even makes analyses impossible because of the limited computer storage. Therefore, the application of subtructuring scheme is necessary to calculate eigenproperties for large structures. Because the large structures are subdivided into several (or more) sub-domains, the construction of dynamic condensation matrix does not need much computation cost in every iteration. This makes the present method much more efficient to compute the eigenpairs both in lower and higher modes. Numerical examples are applied to demonstrate the features of this method.
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효율적 동적 시스템 축소를 위한 주자유도 선정에 관한 연구
백승민(Sungmin Baek),조맹효(Meanghyo Cho) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Dynamic system condensation scheme provides efficient eigenvalue solutions that approximate the lower eigenmodes which represent the global behavior of the structures in large-scale problem. For the reliable reduction, the selection of primary degrees of freedom (PDOFs) has to be appropriate. In the previous study, we proposed an enhancement of the two-level condensation scheme (TLCS) with iterated improved reduced system (IIRS). After the selection of candidate region by element-wise energy estimation through Ritz vector calculation, the PDOFs are selected by the sequential elimination method. Additionally, the IIRS is applied to increase accuracy of the higher modes in the intermediate range. In this study, we propose the DOFs-wise energy estimator which select PDOFs through Rayleigh quotient type energy estimation. Finally, numerical examples demonstrate the performance of the proposed method, and efficiency and accuracy of various selection techniques of the PDOFs are compared.
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백승민(Sungmin Baek),김현기(Hyungi Kim),김기욱(Ki-Ook Kim),조맹효(Meanghyo Cho) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
In the inverse perturbation method, enormous computational resource was required to obtain reliable results, because all unspecified DOFs were considered as unknown variables. Thus, in the present study, a reduced system method is used to condense the unspecified DOFs by using the specified DOFs. In general, it is hard to obtain reliable solution of inverse perturbation problems by the conventional reduction methods due to the error in the transformation matrix between the unspecified DOFs and the specified DOFs. This numerical trouble is resolved in the present study by adopting iterative improved reduced system. In this reduction method, system accuracy is related to the selection of the primary DOFs and iteration time. And both are dependent to each other. So, the two-level condensation method is selected as Selection method of primary DOFs. Finally, numerical verification results of the present iterative inverse perturbation method (IIPM) are presented.
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