• Journal of Magnetics
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• v.18 no.1
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• pp.50-56
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• 2013

In this paper, the 6-switch inverter for the Flux-Reversal Motor (FRM) has been presented and compared to the 4-switch inverter for the FRM, which is more popular in cost effective applications. To analyze the FRM, we adopted the two-dimensional time-stepped voltage source finite element method (FEM) that uses the actual pulse width modulation (PWM) voltage waveforms as the input data. As the FRM characteristic analysis of actual pwm voltage input, the torque ripples and iron losses (eddy current and hysteresis loss) of the FRM can be precisely calculated. With the simulated and experimental results, the performance and limitations of the 4-switch FRM which is the cost effective drive compared to the 6-switch FRM drive are provided in more detail.

• Computers and Concrete
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• v.32 no.5
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• pp.513-525
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• 2023

Recently, research on predicting the behavior of reinforced concrete (RC) columns using machine learning methods has been actively conducted. However, most studies have focused on predicting the ultimate strength of RC columns using a regression algorithm. Therefore, this study develops a successive machine learning process for predicting multiple nonlinear behaviors of rectangular RC columns. This process consists of three stages: single machine learning, bagging ensemble, and stacking ensemble. In the case of strength prediction, sufficient prediction accuracy is confirmed even in the first stage. In the case of displacement, although sufficient accuracy is not achieved in the first and second stages, the stacking ensemble model in the third stage performs better than the machine learning models in the first and second stages. In addition, the performance of the final prediction models is verified by comparing the backbone curves and hysteresis loops obtained from predicted outputs with actual experimental data.

• Structural Engineering and Mechanics
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• v.39 no.6
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• pp.795-812
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• 2011

Estimation of damage probability of buildings under a future earthquake is an essential issue to ensure the seismic reliability. Fragility curves are useful tools for showing the probability of structural damage due to earthquakes as a function of ground motion indices. The purpose of this study is to compare the damage probability of R/C buildings with low and high level of strength and ductility through fragility analysis. Two different types of sample buildings have been considered which represent the building types mentioned above. The first one was designed according to TEC-2007 and the latter was designed according to TEC-1975. The pushover curves of sample buildings were obtained via pushover analyses. Using 60 ground motion records, nonlinear time-history analyses of equivalent single degree of freedom systems were performed using bilinear hysteretic model and peak-oriented hysteretic model with stiffness - strength deterioration for each scaled elastic spectral displacement. The damage measure is maximum inter-story drift ratio and each performance level considered in this study has an assumed limit value of damage measure. Discrete damage probabilities were calculated using statistical methods for each considered performance level and elastic spectral displacement. Consequently, continuous fragility curves have been constructed based on the lognormal distribution assumption. Furthermore, the effect of hysteresis model parameters on the damage probability is investigated.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.282.1-282.1
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• 2016

The remarkable physical properties of two-dimensional (2D) semiconducting materials such as molybdenum disulfide ($MoS_2$) and tungsten disulfide ($WS_2$) etc. have attracted considerable attentions for future high-performance electronic and optoelectronic devices. The ongoing studies of $MoS_2$ based nonvolatile memories have been demonstrated by worldwide researchers. The opening hysteresis in transfer characteristics have been revealed by different charge confining layer, for instance, few-layer graphene, $MoS_2$, metallic nanocrystal, hafnium oxide, and guanine. However, limited works built their nonvolatile memories using entirely of assembled 2D crystals. This is important in aspect view of large-scale manufacture and vertical integration for future memory device engineering. We report $WS_2$ based nonvolatile memories utilizing functional van der Waals heterostructure in which multi-layered graphene is encapsulated between $SiO_2$ and hexagonal boron nitride (hBN). We experimentally observed that, large memory window (20 V) allows to reveal high on-/off-state ratio (>$10^3$). Moreover, the devices manifest perfect retention of 13% charge loss after 10 years due to large graphene/hBN barrier height. Interestingly, the performance of our memories is drastically better than ever published work related to $MoS_2$ and black phosphorus flash memory technology.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.457-461
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• 2001

Advantages of switched reluctance motor(SRM) drives make it an attractive candidate for replacing adjustable speed ac and dc drives in both industrial and consumer applications. Furthermore, a simple, low cost and robust SRM drive can be efficiently operated in the hostile environment of an automobile. Generally, the speed control of SRM has a large step change or large torque reference, the output of its PI controller is often saturated. When this happens, the integral state is not consistent with the SRM input, while may give rise to the windup phenomenon. This paper proposes anti-windup control method for SRM speed control system by hysteresis current controlled asymmetry bridge converter. The experimental results show that the speed response has much improved performance, such as a small overshoot and fast settling time at the acceleration and particulary deceleration period with braking mode.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.355-359
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• 2001

This paper presents an implementation of digital control system of speed sensorless for Reluctance Synchronous Motor (RSM) drives with DTC. The control system consists of stator flux observer, rotor position/speed/torque estimator, two hysteresis band controllers, an optimal switching look-up table, IGBT voltage source inverter, and TMS320C31 DSP controller by using fully integrated control software. The stator flux observer is based on the combined voltage and current model with stator flux feedback adaptive control that inputs are current and voltage sensing of motor terminal with estimated rotor angle for wide speed range. The rotor position is estimated by observed stator flux-linkage space vector. The estimated rotor speed is determined by differentiation of the rotor position used only in the current model part of the flux observer for a low speed operating area. It does not require the knowledge of any motor parameters, nor particular care for motor starting, In order to prove the suggested control algorithm, we have a simulation and testing at actual experimental system. The developed sensorless control system is shown a good speed control response characteristic results and high performance features in 50/1000 rpm with 1.0Kw RSM having 2.57 ratio of d/q reluctance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.11
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• pp.2597-2615
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• 2013

This paper proposes a dynamic downlink load control scheme that jointly employs dynamic load threshold management and virtual coverage management schemes to reduce the degree of performance degradation due to traffic overload in two-tier femtocell networks. With the proposed scheme, the downlink load in a serving macrocell is controlled with a load threshold which is adjusted dynamically depending on the varying downlink load conditions of neighboring macrocells. In addition, traffic overloading is alleviated by virtually adjusting the coverage of the overloaded serving macrocell, based on the adjusted load threshold of the serving macrocell. Simulation results show that the proposed scheme improves the performance of two-tier femtocell networks in terms of the outage probability and sum throughput. This improvement is significantly increased with appropriate values of load thresholds and with an intermediate-level adjustment of the virtual coverage area (i.e., handover hysteresis margin: HOM). Furthermore, the proposed scheme outperforms both a previously proposed load control scheme with a static load threshold and the LTE system without a HOM adjustment.

• Polymer(Korea)
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• v.31 no.1
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• pp.47-52
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• 2007

Polyurethane flexible foams have been widely used for automotive seat cushions because of their excellent performance. It has been required so far to reduce the density of seat cushion foam. However, recently, improving the riding comfort of seat cushions becomes more important. With regard to riding comfort, we investigated the improvement of static properties such as the ball rebound property and the hysteresis loss. We also studied the vibration characteristics, which are well known as an important factor to affect the comfort performance during driving.

• Proceedings of the KIPE Conference
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• 2001.12a
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• pp.23-26
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• 2001

This paper presents a digital motion control system for Reluctance Synchronous Motor (RSM) drives with direct torque control (DTC). The system consists of stator flux observer, torque estimator: two hysteresis band controllers, an optimal switching look-up table, IGBT voltage source inverter(VSI), and TMS320C31 DSP controller by using fully integrated control software. The stator flux observer is based on the combined voltage and current model with stator flux feedback adaptive control of which inputs are current, voltage and actual rotor angle for wide speed range. In order to prove the suggested motion control algorithm, There are some simulation and testing at actual experimental system. The developed digitally high-performance motion control system are shown a good motion control response characteristic results and high performance features using 1.0Kw RSM.

• Earthquakes and Structures
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• v.3 no.1
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• pp.59-81
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• 2012

A ductility inverse-mapping method for SDOF systems including passive dampers is proposed which enables one to find the maximum acceleration of ground motion for the prescribed maximum response deformation. In the conventional capacity spectrum method, the maximum response deformation is computed through iterative procedures for the prescribed maximum acceleration of ground motion. This is because the equivalent linear model for response evaluation is described in terms of unknown maximum deformation. While successive calculations are needed, no numerically unstable iterative procedure is required in the proposed method. This ductility inverse-mapping method is applied to an SDOF model of bilinear hysteresis. The SDOF models without and with passive dampers (viscous, viscoelastic and hysteretic dampers) are taken into account to investigate the effectiveness of passive dampers for seismic retrofitting of building structures. Since the maximum response deformation is the principal parameter and specified sequentially, the proposed ductility inverse-mapping method is suitable for the implementation of the performance-based design.