• ETRI Journal
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• v.36 no.3
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• pp.396-406
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• 2014

We have designed and investigated a new congestion control scheme, called optimal and fully explicit (OFEX) controller. Different from existing relatively explicit controllers, this new scheme can provide not only optimal bandwidth allocation but also a fully explicit congestion signal to sources. It uses the congestion signal from the most congested link instead of the cumulative signal from the flow path. In this way, it overcomes the drawback of relatively explicit controllers exhibiting bias toward multi-bottlenecked users and significantly improves their convergence speed and source throughput performance. Furthermore, our OFEX-controller design considers a dynamic model by proposing a remedial measure against the unpredictable bandwidth changes in contention-based multi-access networks. Compared with former works/controllers, this remedy also effectively reduces the instantaneous queue size in a router and thus significantly improves queuing delay and packet loss performance. We have evaluated the effectiveness of the OFEX controller in OPNET. The experimental comparison with the existing relatively explicit controllers verifies the superiority of our new scheme.

• Journal of Mechanical Science and Technology
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• v.17 no.4
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• pp.521-527
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• 2003

Modern automatic transmissions equip torque converters with lock-up clutches to reduce the energy loss of hydraulic systems. Instead of simply engaging the clutch disks, the new technology of clutch slip has been developed to improve the overall efficiency of power transmission. There are two major problems with the clutch slip system. The first is how to keep the slip between the two disks within a small range and the second is when to start or stop the slip. In this paper, the second problem is discussed in view of the vehicle economy. With a simple vehicle dynamic model, the fuel economy is calculated to determine the lock-up strategy. Then the lock-up strategy is developed for a slip schedule.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.1129-1132
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• 1992

This paper proposes a high frequency resonant inverter consisting of equivalent half bridge model using MOSFET. In this paper time-sharing control method is applied. as a result the output frequency is two times as high as switching frequency of device, and average current of device is incresed because of decreasing switching loss.

• Journal of Mechanical Science and Technology
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• v.17 no.11
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• pp.1650-1658
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• 2003

This paper deals with a novel shunt circuit, which is capable of suppressing multimode vibration amplitudes by using a pair of piezoceramic patches. In order to describe the characteristic behaviors of a piezoelectric damper connected with a series and a parallel resistor-negative capacitor branch circuit, the stiffness ratio and loss factor with respect to the non-dimensional frequency are considered. The mechanism of the shunt damper is also described by considering a shunt voltage constrained by shunt impedance. To obtain a guideline model of the piezo/beam system with a negative capacitive shunting, the governing equations of motion are derived through the Hamilton's principle and a piezo sensor equation as well as a shunt-damping matrix is developed. The theoretical analysis shows that the piezo/beam system combined with a series and a parallel resistor-negative capacitor branch circuit developed in this study can significantly reduce the multiple-mode vibration amplitudes over the whole structural frequency range.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.202-207
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• 2002

This paper deals with a novel shunted actuator, which has a capability to suppress multi-mode vibration amplitudes by using a pair of piezoceramic patches. In order to describe the characteristic behaviors of shunted dampers connected with a series and a parallel resistor-negative capacitive branch circuit, the stiffness ratio and loss factor with respect to the non-dimensional frequency are considered. To obtain a guideline model of a piezo/beam system connected with a series and a parallel resistor-negative capacitor branch circuit, the governing equations of motion is derived through Hamiltons principle and a piezo sensor equation as well as a shunt damping matrix is developed. The theoretical analysis shows that the shunted actuator developed in this study can significantly reduce multiple-mode vibration amplitudes simultaneously over the whole structural frequency range.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.18 no.34
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• pp.173-183
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• 1995

Life cycle cost has been one of the key criteria in design or purchasing of systems, particularly in the flying weapon system. Unexpected cost increase or system breakdown during the system life can be reduced by controlling maintenance cost A system should be designed for maintainability in early stage of product life cycle. The design should be insensitive to its environmental, organizational, and human factors in the stage of customer's utilization. This paper presents LCC as a controllable variable and also suggests a new control model for LCC analysis. The estimation of maintenance cost based upon maintenance scenario, design of maintainability followed by minimizing maintainability loss function in the beginning stage of design, and increase of useful life of systems are among the factors to control LCC.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.88-91
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• 2000

In this paper we approach the problem of congestion control for TCP traffic over ATM-UBR networks by focusing on the fact that to get best performance. We study how to efficiently support TCP traffic in the subnet ATM model, when ATM is only a single link in the whole path. We show that when UBR connection. We analyze the ATM-UBR network service using the BSD 4.3 Reno, Tahoe TCP. However we found the fact that the characteristic of fast recovery algorithm makes a serious degradation of performance in multiple cell loss drop situation. We propose new fast recovery algorithm to solve the problem.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.546-551
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• 2001

In this paper, an algorithm to improve the optimal engine operation is suggested by increasing the CVT shift speed. By rearranging the CVT shift dynamic equation, it is found that the CVT shift speed depends on the line pressure as well as the primary pressure. Based on the shift dynamics, an algorithm to accomplish a faster shift speed is presented by increasing the line pressure. In order to apply the algorithm, dynamic models of the line pressure control valve and the ratio control valve are obtained by considering the CVT shift dynamics and model based controllers are designed. It is found from the simulation results that fuel economy can be improved by 2% in spite of the increased hydraulic loss due to the increased line pressure.

• Proceedings of the KIEE Conference
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• 2002.06a
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• pp.166-171
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• 2002

We are in transitional period of welding technique, which has changed from the stage of quantity and quality to the stage of future technique, imported and introduced from many advanced countries. Therefore, many researches and studies for development on high speeding and making welding machines with high effectiveness has been doing vigorously. In this dissertation, I have studied on a pulsed MAG welding machine, with which welding of thin plates may perform high speeding and effecting. First, I produced a phase shifted full bridge DC-DC convert, which is the type of reduced conduction loss and the power supply for welding machine. And then, I found out an output waveform control algorithm about one pulsed one droplet and short waveform control for thin plates with high speed by deriving the circuit model utilizing the circuit averaged method for full bridge converter.

• Journal of the Korea Society of Computer and Information
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• v.5 no.3
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• pp.112-118
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• 2000

In this paper, a hybrid UPC algorithm is proposed, which combines the representative Leaky Bucket UPC algorithm with the EWMA window algorithm in the ATM network and then its performance Is evaluated. The hybrid UPC algorithm is made up of Leaky Bucket and EWMA, which control the Peak bit rate and the mean bit rate, respectively. According to the result of the simulation using BONeS with the On/off traffic source model. it is revealed that the proposed UPC algorithm has superior performance to the existing Leaky Bucket UPC algorithm with regard to both the cell loss rate and the buffer size.