• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.2
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• pp.183-190
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• 2016

Engine torque is transferred to the transmission where drag torque is minimized improving fuel efficiency. This is particularly true in a wet clutch pack. This study measures slip friction when the wet clutch pack in a DCT (Dual-Clutch Transmission) is disengaged, and the friction pads are slipping. Shudder engagement velocity, and applied forces can be measured under various working conditions through these torque transfer experiments. Test results demonstrate that the design parameters, and engagement conditions of wet clutch packs can be optimized to reduce shudder and frictional vibration during engagement in a dual clutch transmission.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.5B no.2
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• pp.181-188
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• 2005

In this paper, a DC smoothing filterless soft switching pulse modulated high frequency AC power conversion circuit connected to utility. frequency AC power source is proposed for consumer induction heating hot water producer, steamer and super heated steamer. The operating principle of DC link filterless utility frequency AC-high frequency AC (HF AC) power conversion circuit defined as high frequency cycloinverter is described, which can operate under a principle of ZVS/AVT and power regulation based on alternate asymmetrical PWM in synchronization with the utility frequency single phase AC positive or negative half wave voltage. The dual mode modulation control scheme based on high frequency PWM and commercial frequency AC voltage PDM for the proposed high frequency cycloinverter are discussed to enlarge its soft switching commutation operating range for wide HF AC power regulation. This high frequency cycloinverter is developed for high frequency IH Dual Packs Heater (DPH) type boiler used in consumer and industrial fluid pipeline systems. Based on the experiment and simulation results, this high frequency cycloinverter is proved to be suitable for the consumer use IH-DPH boiler and hot water producers. The cycloinverter power regulation and power conversion efficiency characteristics are evaluated and discussed.

• Transactions of the Korean hydrogen and new energy society
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• v.15 no.1
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• pp.1-11
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• 2004

Hybrid power systems with fuel cells and batteries have the potential to improve the operation efficiency and dynamic response. A proper load management strategy is important to better system efficiency and endurance in hybrid systems. In this paper, a fuzzy logic algorithm has been used to determine the fuel cell output power depending on the external required power and the battery state of charge(SoC). If the required power of the hybrid system is small and the SoC is small, then the greater part of the fuel cell power is used to charge the battery pack. If the required power is relatively big and the SoC is big, then fuel cell and battery are concurrently used to supply the required power. These IF-THEN operation rules are implemented by fuzzy logic for the energy management system of hybrid system. The strategy is evaluated by simulation. The results show that fuzzy logic can be effectively used to optimize the operational efficiency of hybrid system and to maintain the battery SoC properly.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.4
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• pp.89-101
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• 2006

This paper addresses Electrical Power Subsystem(EPS) design and verification of HAUSAT-2 small satellite through energy balance analysis(EBA) depending on individual operation modes. GaAs solar cells are used for satellite power generation and digital peak power tracking is implemented for EPS architecture. One battery pack is consisted of 4 Li-Ion cells. Battery charge is accomplished by peak power tracker and battery charge regulator. Power conditioning assembly uses three DC-DC converters, and power distribution assembly which consists of commercial IC and MOSFET switch distributes power to subsystems and payloads. The altitude of 650km and sun-synchronous LEO with various local time ascending node(LTAN) are considered in EBA.

• Journal of Communications and Networks
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• v.7 no.2
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• pp.126-134
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• 2005

Reducing energy consumption in mobile hosts (MHs) is one of the most critical issues in wireles/mobile networks. IP paging protocol at network layer and power saving mechanism (PSM) at link layer are two core technologies to reduce the energy consumption of MHs. First, we investigate the energy efficiency of the current IEEE 802.11 power saving mechanism (PSM) when IP paging protocol is deployed over IEEE 802.11 networks. The result reveal that the current IEEE 802.11 PSM with a fixed wakeup interval (i.e., the static PSM) exhibits a degraded performance when it is integrated with IP paging protocol. Therefore, we propose an adaptive power saving mechanism in IEEE 802.11-based wireless IP networks. Unlike the static PSM, the adaptive PSM adjusts the wake-up interval adaptively depending on the session activity at IP layer. Specifically, the MH estimates the idle periods for incoming sessions based on the exponentially weighted moving average (EWMA) scheme and sets its wake-up interval dynamically by considering the estimated idle period and paging delay bound. For performance evaluation, we have conducted comprehensive simulations and compared the total cost and energy consumption, which are incurred in IP paging protocol in conjunction with various power saving mechanisms: The static PSM, the adaptive PSM, and the optimum PSM. Simulation results show that the adaptive PSM provides a closer performance to the optimum PSM than the static PSM.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.8
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• pp.1565-1576
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• 2002

By way of driving a 2-way on/off solenoid hydraulic valve with a pulse width modulation (PWM) signal, control of the pressure in a certain volume is frequently used in various applications. However, the pressure built-up according to the duty ratio and carrier frequency of the PWM signal is not so well understood. In order to clarify the characteristics of 2-way valve hydraulic pressure control systems, in this paper two formula fur the mean and ripple of the load pressure were derived through theoretical analysis. And the accuracy of the derived formula were verified by comparison with the experimental test result. Generally 2-way valve systems are constructed as a bleed-off circuit, while 3-way valves are used as a control element in a meter-in circuit pressure control system. In a bleed-off circuit, the system supply pressure from a hydraulic power pack does not remain constant, but changes according to their external load. In turn, the relief valve in the hydraulic power pack reacts accordingly showing complicated dynamic behavior, which makes an analytical study difficult. In order to resolve the problem, simple but accurate empirical dynamic models fer a bleed-off system were used in the course of formula derivation. As the result, selection criteria for two major control parameters of the driving signal is established and the basic strategy to suppress the unnecessary pressure fluctuation can be provided for a hydraulic pressure control system using a 2-way on/off solenoid valve.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.12
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• pp.819-828
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• 2022

Sensitivity of aircraft sizing depending on battery performance was studied for a generic quad tilt rotor type electric vertical takeoff and landing vehicle. The mission requirements proposed by Uber Elevate and NASA were used for initial sizing, and the calculated gross weight is ranged between 5,000lb and 11,000lb for battery specific energy range of 200-400Wh/kg in pack level and continuous discharge rate range of 4-5C. For the assumed gross weight of 7,000lb, the required battery performance was calculated with two different criteria: available power and energy, and the effects of battery specific energy and discharge rate are analyzed. The maximum discharge rate is also recommended considering failure cases such as one battery pack inoperative and one prop rotor inoperative.

• Special Issue of the Society of Naval Architects of Korea
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• 2009.09a
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• pp.71-79
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• 2009

The world-wide ship construction market is forecast that the considerable portion of shipbuilding and oceanic plant industry will be transferred consequently in China after 5 or 10 years. This point of view where the Korean ship construction industry seizes the initiative from the world-wide ship construction/oceanic field, we must cultivate technical power of base technology, and focus our interests on the development of core parts. In this study, our proprietary remotely operated valve actuator system with power line technology was developed to enhance the installation and commissioning process by our own technology. This paper describes the new design and functions of the remotely operated valve system for shipbuilding and offshore market especially for FPSO.

• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.1166-1168
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• 2003

In most power electronic applications, the AC power input provided by the electronic utility needs to first converted to a DC voltage. Such conversion is accomplished by a diode rectifier due to its circuit simplicity and low cost. However, since diode rectifiers have some intrinsic problems such as low power factor and high harmonic distortion, a wide use of such rectifiers may cause noises, malfunction and heat damage in both electrical power systems and electrical machinery systems. This paper proposes soft switched three-phase single switch boost-type converter. The proposed circuit can perform Zero Voltage Switched(ZVS) without using any current and voltage sensors. For this circuit, both simulation and experiments have been performed. The results not only confirmed the ZVS but also indicated that, compared to the conventional hard switched converter, the prosed circuit can improve the efficiency as much as 1.7 to 4.7[%] while keeping the same high power factor and small harmonic distortion in their AC input.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1296-1298
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• 1995

This paper presents the power cable with the concentric neutral wires of S-Z stranding. This type Cables, 22.9KV CN/CV Cables used in the distribution systems have been developed in order to improve bend, bend after torsion and tension charateristics. We have designed and made S-Z stranding machine, testing equipment etc., and have established the manufacturing technology of the equipment and the testing technology.