• Smart Structures and Systems
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• 제14권6호
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• pp.1269-1289
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• 2014

With the sub-stepping technique, the numerical analysis in real-time dynamic hybrid testing is split into the response analysis and signal generation tasks. Two target computers that operate in real-time may be assigned to implement these two tasks, respectively, for fully extending the simulation scale of the numerical substructure. In this case, the integration time-step of solving the dynamic response of the numerical substructure can be dozens of times bigger than the sampling time-step of the controller. The time delay between the real and desired feedback forces becomes more striking, which challenges the well-developed delay compensation methods in real-time dynamic hybrid testing. This paper focuses on displacement prediction and force correction for delay compensation in the real-time dynamic hybrid testing with a large integration time-step. A new displacement prediction scheme is proposed based on recently-developed explicit integration algorithms and compared with several commonly-used prediction procedures. The evaluation of its prediction accuracy is carried out theoretically, numerically and experimentally. Results indicate that the accuracy and effectiveness of the proposed prediction method are of significance.

• 소음진동
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• 제5권2호
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• pp.207-213
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• 1995

본 논문에서 구조동력학 문제를 풀기 위한 명시적(explicit) 예측 수정자 시간적분법을 개발하였으며, 이 알고리즘은 최근 개발된 암시적(implicit) 일반화된 $\alpha$ 방법으로부터 유도하였다. 암시적 방법과 같이 명시적 일반화된 .alpha. 방법도 하나의 변수를 갖는 알고리즘의 집합이며, 이 변수는 고주파 영역에서 수치 감쇠의 양을 정의한다. 제안된 알고리즘은 수치감쇠가 없는 시간적분법으로 파의 젼달 문제를 풀때 나타나는 가상의 진동을 감소시키는 수치감쇠를 가지고 있기 때문 에 선형 혹은 비선형의 구조동력학 문제에 효과적으로 이용될 수 있다.

• Earthquakes and Structures
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• 제7권2호
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• pp.119-139
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• 2014

A new method is proposed for random vibration anaylsis of hysteretic systems subjected to non-stationary random excitations. With the Bouc-Wen model, motion equations of hysteretic systems are first transformed into quasi-linear equations by applying the concept of equivalent excitations and decoupling of the real and hysteretic displacements, and the derived equation system can be solved by either the precise time integration or the Newmark-${\beta}$ integration method. Combining the numerical solution of the auxiliary differential equation for hysteretic displacements, an explicit iteration algorithm is then developed for the dynamic response analysis of hysteretic systems. Because the computational cost for a large number of deterministic analyses of hysteretic systems can be significantly reduced, Monte-Carlo simulation using the explicit iteration algorithm is now viable, and statistical characteristics of the non-stationary random responses of a hysteretic system can be obtained. Numerical examples are presented to show the accuracy and efficiency of the present approach.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1998년도 제2회 박판성형심포지엄 논문집 박판성형기술의 현재와 미래
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• pp.1-8
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• 1998

The explicit and implicit time integration methods are applied effectively to analyze sheet metal stamping processes, which include the forming stage and the springback stage consecutively. The explicit time integration method has better merits in the forming stage including highly complicated three-dimensional contact conditions. By contrary, the implicit time integration method is better for analyzing springback since the complicated contact conditions are removd and the computing time to get the final static state is short. In this work, brief descriptions of the formulation and the factor study for springback simulations are presented. Further, the simulated results for the S-rail and the roof pannel stamping processes are shown and discussed.

• Earthquakes and Structures
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• 제11권2호
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• pp.297-313
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• 2016

A virtual parameter is introduced into the formulation of the previously published integration method to improve its stability properties. It seems that the numerical properties of this integration method are almost unaffected by this parameter except for the stability property. As a result, it can have second order accuracy, explicit formulation and controllable numerical dissipation in addition to the enhanced stability property. In fact, it can have unconditional stability for the system with the instantaneous degree of nonlinearity less than or equal to the specified value of the virtual parameter for the modes of interest for each time step.

• 한국초등과학교육학회지:초등과학교육
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• 제38권4호
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• pp.484-495
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• 2019

This study divided pre-service elementary school teachers' knowledge conversion into four types, socialization, externalization, combination and internalization, based on their inquiry activities on the life cycle of cabbage butterfly. As research subjects, this study collected results from 24 pre-service elementary school teachers who carried out inquires on the life cycle of cabbage butterfly for about 2 months. The type of socialization indicates the conversion of tacit knowledge into tacit knowledge, and this study found out that pre-service elementary school teachers acquired and accumulated tacit knowledge from their fellow pre-service teachers, professors and even acquaintances inside and outside the lab. However, there appeared no process that they shared their tacit knowledge with other pre-service teachers or delivered it to them. The type of externalization indicates the conversion of tacit knowledge into explicit knowledge, and this study discovered some cases that pre-service elementary school teachers expressed their inner tacit knowledge into explicit knowledge. However, there was no case found that they converted the verbally-unexpressed tacit knowledge of their fellow teachers or experts into well-defined explicit knowledge. The type of combination indicates the conversion of explicit knowledge into explicit knowledge, and this study discovered some cases that they collected explicit knowledge and converted it into new explicit knowledge for the acquisition, integration and delivery or distribution of explicit knowledge. However, there were few cases that they creatively devised new explicit knowledge by acquiring new knowledge through direct observation and supplementing the existing explicit knowledge. The type of internalization indicates the conversion of explicit knowledge into tacit knowledge, and this study discovered both explicit knowledge embodied through personal experiences and explicit knowledge embodied through simulations and experiments that formed tacit knowledge in process of examining the existing explicit knowledge.

• 조명전기설비학회논문지
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• 제29권10호
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• pp.89-96
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• 2015

Explicit numerical integration methods for power system transient stability simulation require very small time steps to avoid numerical instability. The EXST1 exciter model is a primary source of fast dynamics in power system transients. In case of the EXST1, the required small integration time step for entire system simulation increases the computational demands in terms of running time and storage. This paper presents a practical exciter model reduction approach which allows the increase of the required step size and thus the method can decrease the computational demands. The fast dynamics in the original EXST1 are eliminated in the reduced exciter model. The use of a larger time step improves the computational efficiency. This paper describes the way to eliminate the fast dynamics from the original exciter model based on linear system theory. In order to validate the performance of the proposed method, case studies with the GSO-37 bus system are provided. Comparisons between the original and reduced models are made in simulation accuracy and critical clearing time.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제25권4호
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• pp.224-261
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• 2021

The interest in implicit-explicit (IMEX) integration methods has emerged as an alternative for dealing in a computationally cost-effective way with stiff ordinary differential equations arising from practical modeling problems. In this paper, we introduce implicit-explicit second derivative linear multi-step methods (IMEX SDLMM) with error control. The proposed IMEX SDLMM is based on second derivative backward differentiation formulas (SDBDF) and recursive SDBDF. The IMEX second derivative schemes are constructed with order p ranging from p = 1 to 8. The methods are numerically validated on well-known stiff equations.

• 대한기계학회논문집A
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• 제24권6호
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• pp.1499-1512
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• 2000

The dynamic explicit finite element method and the static implicit finite element method are applied effectively to analyze total auto-body panel stamping processes, which include the forming stage , the trimming stage and the spring-back stage.\The explicit time integration method has better merits in the forming stage including highly complicated three-dimensional contact conditions. On the contrary, the implicit time integration method is better for analyzing spring-back since the complicated contact conditions are removed and the computing time to get the final static state is short. In this work, brief descriptions of the formulation and the factor study are presented. Further, the simulated results for the total auto-body panel stamping processes are shown and discussed. The formability and the weld line movement in stamping with Tailor Welded Blanks were investigated through QTR-OTR-FRT.

• 한국해양공학회지
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• 제12권1호
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• pp.10-22
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• 1998

In the present work the elastic-plastic FE formulations using dynamic explicit time integration schemes are used for numerical analysis of a large auto-body panel stamping processes. For analyses of more complex cases with larger and more refined meshes, the explicit method is more time effective than implicit method, and has no convergency problem and has the robust nature of contact and friction algorithms while implicit method is widely used because of excellent accuracy and reliability. The elastic-plastic scheme is more reliable and rigorous while the rigid-plastic scheme require small computation time. In finite element simulation of auto-body panel stamping processes, the roobustness and stability of computation are important requirements since the computation time and convergency become major points of consideration besides the solution accuracy due to the complexity of geometry conditions. The performnce of the dynamic explicit algorithms are investigated by comparing the simulation results of formaing of complicate shaped autobody parts, such as a fuel tank and a rear hinge, with the experimental results. It has been shown that the proposed dynamic explicit elastic-plastic finite element method enables an effective computation for complicated auto-body panel stamping processes.