• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.493-500
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• 2017

Based on the data accumulated through EMU fault management, this paper examines the reliability of old railway car parts and proposes measurements to improve safety. Subway Line 7 of the Seoul Metropolitan Rapid Transit Corporation, auxiliary power unit (Static Inverter) of the EMU second version is a core equipment to supply power to various room-service units in cars and make an effect directly on passenger satisfaction. To analyze the pattern of failure throughout the field data over a long period of time, this analysis of statistics and reliability considers the operating environment and stress factors. This statistical analysis presents the correlation between failure and the temperature stress factors related to frequent failure occurring intensively in summer. In addition, throughout the analysis of the life of the IGBT inverter, the effect of the temperature stress factor was observed before and after the repair. As a result of an analysis of the optimal operating conditions considering two variations of EMU, such as variable load and outside temperature, a difference in the cooling capacity between the optimal operating conditions and frequent failure conditions was observed. Based on this analysis, this paper suggests a way to minimize cooling capacity difference for the optimal operational conditions.

• Journal of Aerospace System Engineering
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• v.16 no.6
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• pp.35-44
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• 2022

This study aims to evaluate the stress and life of cylindrical roller bearings used in aircraft gearboxes, and to select a roller profile that minimises the contact stress between bearing rollers and raceways. The mounting clearance of four points contact ball bearing was determined, so that cylindrical roller bearings support all radial loads, and the bearing mounting position was determined to maximise the bearing lives. In addition, the static safety factor and dynamic life of bearing were predicted according to ISO 76 & ISO/TS 16281 using the load spectrum determined based on the operating load cases of aircraft gearboxes. Furthermore, the optimal roller profile was selected by analysing the contact stress according to the roller profile shape, and the safety of each roller was evaluated. The results stated that the required safety factor and lifetime were satisfied, and Johns Gohar roller profile was optimal.

• Journal of the Korean Institute of Gas
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• v.2 no.2
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• pp.26-33
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• 1998

The thickness of buried gas pipeline is determined mainly with internal pressure and location factor according to the requirements of ANSI B3l.8. But the stress of buried gas pipeline is determined by not only internal stress but also external loads. The change of burying and environmental conditions, therefore, may result in increasing stress of pipeline. In order to avoid the decrease of safety degree resulting from change of environmental condition, the evaluation of stress level shall be necessary. The reliable equations have been developed for calculating stress of buried pipeline from internal pressure, earth load, vehicle load, ground subsidence. But they are very difficult to understand and use for non-specialist. For easy calculation of non-specialist, the new computer program to calculate stress of buried natural gas pipeline have been developed. The program can calculate maximum stress resulted from earth load, vehicle load, thermal load, four type ground subsidence. The stress is calculated by the equations and extrapolation of the graph resulted from FEM. In this paper, as the series of paper I, the operating method and the functions of the program is explained.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.2
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• pp.132-140
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• 2001

A universal motor is a small dc series machine motor that is designed to operate from an ac machine. The characteristics of universal motors are high no-load and staring torque. Because of the high operating speed, the size of these motors for a given hp rating is typically smaller that other fractional hp ac machine, making it ideal for hand-held tools and appliances where weight, compactness, and speed are importance factors. A phase-angle control with AC drive system gains a high popularity due to their simple implementation, but contains the disadvantage of their poor input power factor, subharmonic current. Pulse width modulation control with DC drive systems increase the power factor as without delay phase angle. This paper analyzed the subharmonic characteristics of the phase angle control system that is controlled by zero voltage crossing similar to traditional method, and the dc chopper system that is used PWM.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.8
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• pp.962-968
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• 2013

Problem of greenhouse gases associated with global warming and the world rise in fuel oil prices due to the depletion of fossil fuel has attracted attention. For this reason, maritime transport business, has shown interest in green-ship technology to reduce the consumption of fuel and reduce greenhouse gas for environmental protection. Power system of the ship is one of the most important factors for safe operation. Therefore, at design of ship power system, most of existing vessel used comparative large capacity generator in order to respond peak load such as bow thruster, crane and etc. In the navigation of ship, marine generators most would be operated at low load operation. In the low load operation of the generation rate of 50% or less, the operation efficiency of the generator it deteriorated, to consume more fuel oil. It also, it means that adversely effect the life of the generator. In this paper, studied how to apply for a secondary battery in container ship that relatively frequent arrival and departure in port. As a result, in order to apply the secondary battery to increase the operating efficiency of the generator during the voyage, it was confirmed that it is possible to reduce fuel consumption.

• Tribology and Lubricants
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• v.34 no.4
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• pp.146-159
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• 2018

This paper presents a wear analysis procedure for calculating the wear of journal bearings of a four-strokes and four-cylinder engine operating at a constant angular crank shaft speed during firing conditions. To decide whether the lubrication state of a journal bearing is in the possible region of wear scar, we utilize the concept of the centerline average surface roughness to define the most oil film thickness scarring wear (MOFTSW) on two rough surfaces. The wear volume is calculated from the wear depth and wear angle, determined by the magnitude of each film thickness on a set of oil films with thicknesses lower than the MOFTSW at every crank angle. To calculate the wear volume at one contact, the wear range ratio during one cycle is used. The total wear volume is then determined by accumulating the wear volume at every contact. The fractional film defect coefficient, asperity load sharing factor, and modified specific wear rate for the application of the mixed-elasto-hydrodynamic lubrication regime are used. The results of this study show that wear occurs only at the connecting-rod big-end bearing. Thus, simulation results of only the big-end bearing are illustrated and analyzed. It is shown that the wear volume of each wear scar group occurs consecutively as the crank angle changes, resulting in the total accumulated wear volume.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.6
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• pp.55-64
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• 2007

This paper represents characteristics and design example of series loaded LCC type high frequency resonant DC-DC converter with variable parallel capacitor in the secondary side of inductive power transformer. In this converter, ZVS(zero voltage switching) technique is applied to reduce turn-off switching losses, and the applied converter used the PFM switching pattern to control output voltage. The operating characteristics of the proposed converter is analyzed using nomalized parameter such as switching frequency and load factor with varing the secondary parallel resonant capacitor. The results of analysis show the operating characteristics and design method of the proposed converter using characteristic values. And the proposed converter can be applied for the contactless power supply with linear transfer system such as dean room facilities of semiconductor and Flat Panel Display.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.34-42
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• 2017

Since existing nonintrusive appliance load monitoring (NIALM) studies assume that voltage fluctuations are negligible for load identification, and do not affect the identification results, the power factor or harmonic signals associated with voltage are generally not considered parameters for load identification, which limits the application of NIALM in the Smart Home sector. Experiments in this paper indicate that the parameters related to voltage and the characteristics of harmonics should be used to improve the accuracy and reliability of the load monitoring system. Therefore, in this paper, we propose an improved NIALM method that can efficiently analyze the types of household appliances and electrical energy usage in a home network environment. The proposed method is able to analyze the energy usage pattern by analyzing operation characteristics inherent to household appliances using harmonic characteristics of some household appliances as recognition parameters. Through the proposed method, we expect to be able to provide services to the smart grid electric power demand management market and increase the energy efficiency of home appliances actually operating in a home network.

• KIEE International Transactions on Power Engineering
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• v.11A no.4
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• pp.45-50
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• 2001

The impact evaluation of a DSM program is a very important issue since the results are used to determine the sustainability of a program. In general. to estimate the impacts of a DSM program it is required to measure the electricity usage changes before and after a program. Since the measurement-based approaches cost highly, most of the conventional evaluations are based on the average figures. However estimation of the average-based impacts can lead to both distorted results of over/under estimation of kW and kWh savings and non-optimal DSM planning. In this paper, we have developed a new multi-point measurement approach which can evaluate kW and kWh savings of a DSM program more exactly. To do this, the saving rate and operating rate are defined and set as the function of load factor of a customer, and these rates are incorporated with the conventional diffusion function of Bass to project the future impacts of a DSM program. The case study is performed on the inverter program of Korea by using the suggested approach.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.1
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• pp.81-86
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• 2006

High temperature superconducting (HTS) power cable requires forced sub-cooled LN2 flow cooling. Liquid nitrogen is circulated by a pump and cooled back by cooling system. Typical operating temperature range is expected to be between 65 K and 77 K. The HTS power cable needs sufficient cooling to overcome its low temperature heat load. For successful cooling, the hydraulic characteristics of the HTS power cable must be well investigated to design the cables. Especially, the pressure drop in the cable is an important design parameter, because the pressure drop decides the length of the cable, size of the coolant circulation pump and circulation pressure, etc. This paper describes measurement and investigation of the pressure drop of the cooling system. In order to reduce the total pressure drop of the cooling system, the flow rate of liquid nitrogen must be controlled by rotational speed of the circulation pump.