• Journal of the Korean Society for Railway
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• v.20 no.4
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• pp.466-473
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• 2017

Recently, domestic railway related institutes are developing pantographs for high speed trains; to lighten the upper arm, this device has a composite structure of CFRP (Carbon Fiber Reinforced Plastic) and aluminum instead of conventional steel. In the case of KTX-Sancheon, the pantograph must have a large current capacity because this system is of power-car type, supplying all necessary power for the train through a single pantograph. If the thickness of the pipe is arbitrarily increased in order to increase the current carrying capacity, without analyzing the thermal characteristics of the aluminum pipe, the increase in the weight of the upper arm may cause degradation of the current collecting performance. Therefore, in this paper, using the thermal analysis technique, we analyze the temperature change characteristics of the aluminum pipe of the upper arm over time, while receiving power at the stationary state of the KTX-Sancheon; we also examine the adequacy of the minimum thickness of the aluminum pipe in accordance with the proposed pantograph flow capacity.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.833-836
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• 2008

In this study, we would like to study on the apply properties to salt water environment of pre-hydrated bentonite for complement problem that water leakage to permit salt water that existing bentonite does not initial swelling. Accordingly, execute viscosity properties, swelling properties, permeability and confirmed apply properties to salt water environment. Did not permit initial permeable in test result salt water environment, and permeable did not happen until 72 hours by maximum $3kgf/cm^2$ water pressure. Fresh water environment enough progress of gelation confirm that viscosity and swelling properties confirmation result and as delamination phenomenon of platy formation looked in salt water environment but this as bentonite hydrates crystallization layer swelling that is done consider. Synthetic study results, if compaction condition such as press layer is formed to bentonite upper, applied to the salt water environment of the underground structures of expectations.

• Journal of the Korean Institute of Intelligent Systems
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• v.18 no.1
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• pp.78-85
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• 2008

In this paper, we propose the extension of cooperation protocol which realizes the autonomous control of QoS and show its effectiveness with implementation and experiments of our agent-based videoconference system. The autonomous QoS control in the agent-based videoconference system means the framework of adjusting its functions/abilities by itself to cope with the changes of user requirements and system resource situations. But, the original cooperation protocol used by the agent-based videoconference system is not enough to perform cooperation closely to use the limited resources effectively. In our proposal, the cooperation protocol is offended in the following points: (1) introducing a cooperation states, (2) extension of performatives, (3) introducing compromise levels. We embedded the proposed protocol to the agent-based videoconference system and experimented the behavior of the system. According to the experiments on this prototype system, we confirmed that the flexibility of the system is improved.

• Journal of Aerospace System Engineering
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• v.11 no.5
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• pp.42-49
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• 2017

The solid rocket motor(SRM) consists of a motor case, igniter, propellants, nozzle, insulation, controller, and driving device. The liquid rocket propulsion systems(LRPSs) cools the nozzle by the fuel and oxidizer but SRM does not cool the nozzle. The nozzle of SRM is high temperature condition and high velocity condition so occurs the erosion by combustion gas. This erosion occurs the change of nozzle throat and reduces thrust performance of rocket. The material of Rocket nozzle is minimization of erosion and insulation effect and endure the shear force, high temperature and high pressure. The purpose of this study is to investigate the erosion characteristics of solid rocket nozzles by each combustion time. Through the structure inspection of Graphite and C-C composite, identify the characteristics of the microstructure before and after erosion.

• Journal of IKEEE
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• v.17 no.2
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• pp.135-139
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• 2013

This paper presents the 8-channel active module operated in Ka-band. The module is designed for the mobile satellite communication antenna systems, and the module structure has the merit to minimize the size and weight of the antenna systems by 30% compared with the conventional systems using the active module composed of single channel. This module was designed to be optimally operated by prohibiting the electrical interference among the individual channels. From the test results of the fabricated 8-channel active module, it can be confirmed that the maximum channel gain error is ${\pm}1.3dB$, the minimum channel output power is 21.5dBm, and the maximum gain variation by phase control is ${\pm}1.0dB$.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.6
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• pp.401-408
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• 2019

The objective of this study is to develop a new type of buried sensor module that can directly assess pre-stressed concrete by measuring strain using a hetero-core optical fiber sensor. In this regard, experiments were conducted to evaluate the performance of the sensor using an exposure sensor module. Based on the experimental results, when the values of the displacement control velocity were 0.12 mm/min and 1.80 mm/min, the corresponding delays in the measurement were 52.1 s and 2.6 s respectively, which indicated that the maximum delay between the two measurements was a factor of 19. Due to the measurement delay phenomena, the sensor module used in the experiments cannot be employed to check the real-time state of the structure. Thus, additional experiments were needed to develop a new sensor module that can measure the real-time state of the structure. To investigate the cause of the measurement delay phenomena, three experiments were conducted. It was confirmed that measurement delay is mainly attributed to frictional resistance. The measurement delay phenomena were not observed in the experiments using the friction-removed device.

• Journal of the Korean Institute of Intelligent Systems
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• v.16 no.2
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• pp.131-137
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• 2006

In swarm robot systems, each robot must behaves by itself according to the its states and environments, and if necessary, must cooperates with other robots in order to carry out a given task. Therefore it is essential that each robot has both learning and evolution ability to adapt the dynamic environments. In this paper, the new learning and evolution method based on reinforcement learning having delayed reward ability and distributed genetic algorithms is proposed for behavior learning and evolution of collective autonomous mobile robots. Reinforcement learning having delayed reward is still useful even though when there is no immediate reward. And by distributed genetic algorithm exchanging the chromosome acquired under different environments by communication each robot can improve its behavior ability. Specially, in order to improve the performance of evolution, selective crossover using the characteristic of reinforcement learning is adopted in this paper. we verify the effectiveness of the proposed method by applying it to cooperative search problem.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.1
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• pp.187-192
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• 2015

Underwater acoustic communication channels have very complex channel characteristics caused by time-varying sea surface, submarine topography, sound speed, and geometry between transmitter and receiver. Especially, the channel has time-variance and doppler effect due to wind and sea current. We have to recognize the channel state and apply it to communication technique for increasing transmission efficiency in the underwater acoustic channel. In this paper, we present the frame recursive modulation and demodulation method using ambiguity function and autocorrelation function to estimate the doppler frequency. Furthermore, we conducted the simulation and sea experiment to evaluate the performance of the proposed method. When the channel coding technique was not used, the bit error rate performance of the proposed method was improved about 32 % compared with conventional method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.2
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• pp.244-253
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• 2016

The QRS complex of ECG signal represents the depolarization and repolarization activities in the cells of ventricle. Accurate informations of $QRS_{onset}$ and $QRS_{offset}$ are needed for automatic analysis of ECG waves. In this study, using the amount of change in the QRS complex voltage values and the distance from the $R_{peak}$, we determined the junction point from Q-wave to R-wave and the junction point from R-wave to S-wave. In the next step, using the integral calculation based on the connection point, we detected $QRS_{onset}$ and $QRS_{offset}$. We use the PhysioNet QT database to evaluate the performances of the algorithm, and calculate the mean and standard deviation of the differences between onsets or offsets manually marked by cardiologists and those detected by the proposed algorithm. The experiment results show that standard deviations are under the tolerances accepted by expert physicians, and outperform the results obtained by the other algorithms.

• Journal of Satellite, Information and Communications
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• v.7 no.2
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• pp.76-79
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• 2012

Satellite power system is critical for mission design and survival operation. Accordingly power conversion circuit has to stable design and verify for operation condition change (load, voltage, thermal condition). however, multi-stage make complicate for modeling and get all state solution. In this paper present all state solution for multi-stage converter by using Extended Describing Function(EDF) modelling. EDF modelling has merit to solve complex circuit but it has limit too. Because of fundamental approximation, EDF modeling is not match all topology. Consequently, we verify passible topology for EDF modeling and stable design multi-stage converter.