• Journal of the Korea Concrete Institute
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• v.15 no.3
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• pp.482-493
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• 2003

Flat plate structures subjected to lateral load have less deformability than conventional moment frames, due to the brittle failure of plate-column connection. In the present study, parametric study using nonlinear finite element analysis was performed to investigate the deformability of flat plates. The numerical results show that as number of continuous spans increases, the deformability of flat plates considerably decreases. Therefore, existing experiments using sub-assemblages with 1 or 2 spans may overestimate the deformability of flat plates, and current design provisions based on the experiments may not be accurate in estimating the deformability. A design method estimating the deformability was developed on the basis of numerical results, and verified by comparison with existing experiment. In the proposed method, the effects of primary design parameters such as direct shear force, punching shear capacity, aspect ratio of connection, number of spans, and initial stiffness of plate can be considered.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.241-244
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• 2008

In general, RC flat plate frames have been used as a gravity load resisting system(GLRS) in building. This system should be constructed with lateral force resisting system(LFRS) such as shear walls and brace frames. When lateral loads such as earthquakes occur, LFRS undergo displacement by which connected gravity systems experience lateral displacement. Thus, flat plate system designed as GLRS should be predict unbalanced moments and punching failure due to lateral deformation. This study developed an analytical mode for predicting nonlinear behavior of RC slab column connection for the seismic performance evaluation of RC flat plate frames. For verifying the analytical model, the test results of two flat plate specimens having two continous spans with the difference gravity shear ratio($V_g/{\phi}V_c$) were compared with the results of analysis. The developed model can predict the failure modes and punching failures.

• Proceedings of the KIEE Conference
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• 2006.10d
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• pp.101-103
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• 2006

외전형 유도전동기 모터는 내전형에 비해 소형화 및 경량화 시킬 수 있는 장점이 있다. 하지만 회전자와 고정자간의 공극사이에 이심률이 있을 때, 불균형 모멘트로 인한 토크 리플이 내 전형보다 더 크게 일어나는 단점이 있다. 이러한 토크리플은 모터의 정속적인 운전을 방해시킬 뿐만 아니라 불규칙한 출력토크로 인한 작동상의 오류를 초래한다. 본 논문에서는 의전형 모터에서 이심률에 따른 불균형력이 최소화 될 수 있는 슬롯 형태에 대해서 연구하기 위해, 전폐형, 반폐형, 개구형태의 3가지 슬롯 형태에 대한 특성을 비교 하였다. 개구형의 경우 슬롯 누설 리액턴스가 낮아져 토크 형성율이 매우 높아 높은 토크를 발생시킬 것을 예상 하였지만, 토크 리플에 따른 출력 감소로 오히려 출력토크가 감소할 뿐만 아니라 이심률 증가에 따른 불균형력 또한 매우 컸다. 이에 비해 전폐형태의 슬롯은 누설리엑턴스의 영향으로 토크 형성 자체는 10% 정도 저감 되었으나, 이심률 증가에 따른 분균형력이 가장 적어 의전형 모터에 가장 적함한 형태임을 알 수 있었다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.04a
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• pp.60-66
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• 1996

축어긋남이 존재하는 회전체-볼베어링계의 진동을 묘사할 수 있는 모델을 개발하였다. 축어긋남은 운동 방정식에서 축과 베어링에서의 변위벡터 변화로 묘사되고, 이로 인해 커플링과 베어링에 작용하는 힘과 모멘트는 축어긋남의 효과로서 고려되었다. 축의 유연성을 고려하기 위해 축방향의 동력학을 포함한 축과 원판에 대한 유한 요소 모델을 이용하였으며, 원판과 베어링에서의 불균형 응답으로부터 축어긋남과 관련된 진동특성을 조사하였다.

• Journal of the Korea Concrete Institute
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• v.15 no.3
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• pp.470-481
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• 2003

Exterior plate-column connection has an unsymmetrical critical section for eccentric shear of which perimeter is less than that of interior connection, and hence, around the connection, unbalanced moment and eccentric shear are developed by both gravity load and lateral loads. Therefore, exterior connection is susceptible to punching shear failure. Current design provision cannot accurately explain strength of existing experiments, partly due to the complexity in the behavior of exterior plate-column connection, or partly due to the theoretical deficiency of the strength analysis model adopted. In the present study, nonlinear finite element analyses were performed for exterior connections belonging to continuous flat plate. For each direction of lateral load, the behavior and strength of exterior plate-column connection were quite different. Based on the numerical result, strength prediction model for exterior connection was proposed for each direction of lateral load. Compared with existing experiments, the proposed method was verified.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.1-4
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• 2008

Flat plate slab has been widely used in high rise building for its remarkable advantages. However, Flat plate structures under lateral load are susceptible to punching shear of the slab-column connection. Exterior slab-column connections has an unsymmetrical critical section for eccentric shear of which perimeter is less than that of interior connection, and hence, around the connection, unbalanced moment and eccentric shear are developed by both gravity load and lateral loads. Therefore, exterior connections is susceptible to punching shear failure. For that reason, this study compare ACI 318-05 to CEB-FIP MC 90 that is based on experiment results and existing data of flat plate exterior connections. This study shows that compared to CEB-FIP MC 90 is more exact about eccentric shear stress, unbalanced moment and Both of all are not suitable in large column aspect ratio. Considering gravity shear ratio, These are suitable but design condition only consider gravity shear ratio. So these should be considered differences from change of design condition

• Journal of Aerospace System Engineering
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• v.12 no.1
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• pp.27-34
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• 2018

In this study, the generating of torque regarding the Control Moment Gyro (CMG) is proportional to the angular velocity of gimbal. This is the case because gimbal affects the attitude control of the satellite directly, and it is necessary to reduce the incidence of torque ripple of gimbal. In this paper, the cause of the torque ripple of gimbal is reviewed and mathematically modeled by assuming the friction imbalance of bearing, the magnetic field and the phase current imbalance of the motor. We are able to confidently estimate the modeling parameters of gimbal disturbance using a constant speed test, and then analyze the influence of applying feedforward control to our modeling. Additionally, the simulation results show that the torque ripple and angular velocity fluctuations are reduced when apply this modeling to the identified study parameters. Finally, we present the disturbance reduction technique using our disturbance modeling.

• Journal of Aerospace System Engineering
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• v.13 no.2
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• pp.26-33
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• 2019

Control moment gyro (CMG) employed as satellite actuators, generates a large torque through the steering of its gimbals. Although each gimbal holds a high-speed rotating wheel, the wheel imbalances induces disturbance and degrades the satellite control quality. Therefore, the disturbances ought to be detected and identified as a precaution against actuator faults. Among the method used in detecting disturbances is the state observers. In this paper, we apply a continuous second order sliding mode observer to detect single disturbances/faults in CMGs. Verification of the algorithm is also done on the hardware satellite simulator where four CMGs are installed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.7
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• pp.640-646
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• 2007

Actuator-induced disturbance is one of the crucial factors of spacecraft attitude pointing and stability in fine attitude control problems. The control moment gyros (CMGs) are known as very attractive actuators from the point of high power and low weight. In order to develop a CMG as an actuator for fine controls, CMG-induced disturbances should be analyzed. Therefore, this paper aims to develop an analytic model and predict the effect of disturbances of CMGs by assuming static and dynamic imbalances. The proposed model is induced by the Lagrangian method on the basis of the small signal assumption.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.599-609
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• 2009

This paper discusses generalized modeling schemes for both reinforced concrete (RC) and post-tensioned (PT) flat plate buildings. In this modeling approach, nonlinear behavior due to slab flexure, moment and shear transfer at slab-column connections, and punching shear was included along with linear secant stiffness of each member or connection that accounts for concrete cracking. This generalized model was capable of simulating all different scenarios of slab-column connection failures such as brittle punching, flexure-shear interactive failure, and flexural failure followed by drift-induced punching. Furthermore, automatic detection of drift-induced punching shear and subsequent backbone curve modifications were realistically modelled by incorporating the limit state model, in which gravity shear versus drift capacity relations were adopted. The validation of the model was conducted using one-third scale two-story by two-bay RC and PT flat plate frames. The comparisons revealed that the model was robust and effective.