• 한국지진공학회논문집
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• 제10권2호
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• pp.21-29
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• 2006

자유도 수가 많은 고층 구조물의 해석하기 위해 모든 층에 sensors를 설치하는 것은 비 실용적이다. 따라서 이러한 문제를 해결하기 위해 "reduced-order control" 방법이 소개되었다. 본 논문은 동적압축법(dynamic condensation method)이 제안되었다. 이 압축법은 반복법으로 "Guyan condensation"의 initial approximation을 적용하였다. 본 논문에서 제시된 동적압축법(dynamic condensation)은 원하는 값을 얻을 때까지 지속적으로 updated가 되며, 결과는 기존의 "Guyan condensation"보다 정확한 결과를 나타내었다. 또한 "eigenvalue shifting technique"을 적용하여 iteration으로 계산되는 시간을 크게 단축하였다. "Reduced-order system"을 도입하기 위한 두가지 schemes이 토의되었다. 제시된 동적압축법 효과의 증명을 위해 능동 동조질량감쇠 고층빌딩의 수치 해석이 토의되었고, 단지 두 번의 반복(iterations)을 통한 결과는 매우 정확한 것으로 나타났다.

• 한국구조물진단유지관리공학회 논문집
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• 제2권2호
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• pp.177-184
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• 1998

The equation of motion on the vehicle-bridge system is established as the simultaneous equations which are combined the equation of vehicle and bridge by the interaction elements. A vehicle element is modeled as lumped masses supported by springs and dashpots, and a bridge element with pavement roughness is modeled as beam elements. An interaction element is defined to consist of a bridge element and the suspension units of the vehicle resting on the element. By the dynamic condensation method, the degrees of the freedom are eliminated, and compared with all the degrees of freedom on the bridge, the efforts of calculation is decreased. Thus, although a very small computational error is occured, the present technique appears to be computationally more efficient. It is particularly suitable for the simulation of bridges with a series of vehicles moving on the deck.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2008년도 정기 학술대회
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• pp.342-349
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• 2008

A selection method of primary degrees of freedom in dynamic condensation for nonproportional damping structures is proposed. Recently, many dynamic condensation schemes for complex eigenanalysis have been applied to reduce the number of degrees of freedom. Among them, iterative scheme is widely used because accurate eigenproperties can be obtained by updating the transformation matrix in every iteration. However, a number of iteration to enhance the accuracy of the eigensolutions may have a possibility to make the computation cost expensive. This burden can be alleviated by applying properly selected primary degrees of freedom. In this study, which method for selection of primary degrees of freedom is best fit for the iterative dynamic condensation scheme is presented through the results of a numerical experiment. The results of eigenanalysis of the proposed method is also compared to those of other selection schemes to discuss a computational effectiveness.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.1048-1055
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• 2006

Two ways can be used for dynamic condensation of viscously damped structural models. One is reducing the model in physical space at first and then transferring it to state space. The other is ,condensing the model in state space directly. Two iterative schemes for each way are given respectively. Hence four iterative schemes for dynamic condensation of nonclassically damped models are discussed in this paper. A high building with a tuned mass damper is applied to show the efficiency of these schemes.

• 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.

• 설비공학논문집
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• 제13권6호
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• pp.490-496
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• 2001

An experimental study on the behavior of the water hold-up by condensation of a fin-and-tube heat exchanger with regard to the surface characteristics, i.e., contact angle, was conducted. The static and dynamic contact angles were measured, and condensation experiments were conducted. Flow patterns on the fins with different surface characteristics were visualized. Results showed that the static contact angle is proportional to the dynamic contact angle within the range of this study. The water hold-up of the heat exchanger increases as the static or dynamic contact angle of its surfaces increases. Existence of transition of flow patterns was found as the static or dynamic angle increase. Due to the transition in the flow patterns, changes in the gradient of the water hold-up is occurred around the static angle of 8$0^{\circ}C$.

• 한국전산구조공학회논문집
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• 제19권2호
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• pp.213-219
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• 2006

위상 최적화 문제는 다양한 밀도 분포를 가지는 설계영역에서 목적함수와 요소단위의 설계 민감도의 반복적인 계산을 요구한다. 최근 제안된 2단계 축소기법은 축소 시스템을 구축하는데 매우 효과적이며 고유치 문제와 동적 문제의 해석에 정확도와 효율성을 동시에 제공한다. 본 논문에서는 구조 위상 최적화 문제에서 해석 부분과 민감도 계산 부분에 2단계 동적 축소기법을 사용한다. 축소시스템에 대한 위상 최적화 결과는 축소되지 않은 전체 시스템에 대한 최적화 결과와 비교하여도 공학적으로 요구되는 정확도 범위 내에서 2단계 축소기법이 높은 정확도와 계산 효율을 보장하는 것을 보여준다.

• Nuclear Engineering and Technology
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• 제54권3호
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• pp.1109-1114
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• 2022

The SMART (System-integrated Modular Advanced ReacTor) is an integral-type small modular reactor developed by KAERI (Korea Atomic Energy Research Institute). This paper discusses the feasibility and applicability of a 3D-based equivalent model using dynamic condensation method for seismic analysis of a SMART control rod drive mechanism. The equivalent model is utilized for complicated seismic analysis during the design of the SMART. While the 1D-based beam-mass equivalent model is widely used in the nuclear industry for its calculation efficiency, the 3D-based equivalent model is suggested for the seismic analysis of SMART to enhance the analysis accuracy of the 1D-based equivalent model while maintaining its analysis efficiency. To verify the suggested model, acceleration response spectra from seismic analysis based on the 3D-based equivalent model are compared to those from the 1D-based beam-mass equivalent model and experiments. The accuracy and efficiency of the dynamic condensation method are investigated by comparison to analysis results based on the conventional modeling methodology used for seismic analysis.

• 소음진동
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• 제2권1호
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• pp.61-66
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• 1992

In general, structures have various joints such as bonded joint, bolted joint, bearing joint and welded joint. Dynamic modelling of such joints has been the current topic of interest. In this study, the dynamic modelling of plate structures with bonded joint was investigated by using modal testing, sensitivity analysis and condensation-inverse condensation method of FEM. A proper modelling procedure was proposed and the validity was verified.

• Nuclear Engineering and Technology
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• 제29권1호
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• pp.45-57
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• 1997

The direct contact condensation phenomenon, which occurs when steam is injected into the subcooled water, has been experimentally investigated. Two plume shapes in the stable condensation regime are found to be conical and ellipsoidal shapes depending on the steam mass flux and the liquid subcooling. Divergent plumes, however, are found when the subcooling is relatively small. The measured expansion ratio of the maximum plume diameter to the injector inner diameter ranges from 1.0 to 2.3. By means of fitting a large amount of measured data, an empirical correlation is obtained to predict the steam plume length as a function of a dimensionless steam mass flux and a driving potential for the condensation process. The average heat transfer coefficient of direct contact condensation has been found to be in the range 1.0~3.5 ㎿/$m^2$.$^{\circ}C$. Present results show that the magnitude of the average condensation heat transfer coefficient depends mainly on the steam mass fin By using dynamic pressure measurements and visual observations, six regimes of direct contact condensation have been identified on a condensation regime map, which are chugging, transition region from chugging to condensation oscillation, condensation oscillation, bubbling condensation oscillation, stable condensation, and interfacial oscillation condensation. The regime boundaries are quite clearly distinguishable except the boundaries of bubbling condensation oscillation and interfacial oscillation condensation.