• 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 Korean Society for Railway
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• v.20 no.3
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• pp.356-364
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• 2017

The process of inspecting electric railway vehicles is complicated and these vehicles accompany a risk of safety accidents. This developed system will be a great help in simplifying the shunting process and be very useful in terms of ensuring safety and providing user convenience. In this paper, the results of performance evaluation tests are studied on a movable catenary system for railway vehicles that secured mechanical durability, convenience, and operator safety by applying a specific rigid bar catenary of an existing mobile train line. We presented an analysis of the basic characteristics for site installation including sorting. In conclusion, this developed system was obtained in good results through durability test, durable mechanical load test and safety test in require specifications.

• Journal of the Korea Society of Computer and Information
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• v.7 no.3
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• pp.80-91
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• 2002

A general goal of the AT%(Asynchronous Transfer Mode) network is to support connect across various network. On ATM networks, ABR services are provided using the remained ban after allocation CBR and VBR traffic. Realtime services such as transmitting audio or video data may be provided using CBR ado VBR which have a constrained transmission delay, but in these cases, the communications bandwidth may be wasted. In this paper a simulation has been performed to compare and evaluate the performance between the ERICA(Explicit Rate Indicate Avoidance) and EPRCA(Enhanced Proportional Rate Control Algorithm) switches which use Explicit Rate switch algorithm for ABR switch. The variation of the ACR at the source end system, the queue length, the utilization rate of the link bandwidth and the share fairness at the transient and steady states are used as the evaluation criteria for the simulation. As a result of simulation, ERICA algorithm switch was ten times long compared to ERPCA switch to achieve assigned fair share. so EPRCA switch is superior to ERICA about load response. For Fair share and stability, ERICA switch is excellent to EPRCA switch.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.6_3
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• pp.1297-1303
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• 2023

Research on enhancing the mechanical strength, lightweight properties, electrical conductivity, and thermal conductivity of composite materials by incorporating nano-materials is actively underway. Thermoplastic resins can change their form under heat, making them highly processable and recyclable. In this study, Polyamide-Nylon 6 (PA6), a thermoplastic resin, was utilized, and as reinforcing agents, fused carbon nano-materials (FCN) formed by structurally combining Carbon Nanotube(CNT) and Graphene were employed. Nano-materials often face challenges related to cohesion and dispersion. To address this issue, Silane functional groups were introduced to enhance the dispersion of FCN in PA6. The manufacturing conditions for the composite materials involved determining the use of a dispersant and varying FCN content at 0.05 wt%, 0.1 wt%, and 0.2 wt%. Tensile strength measurements were conducted, and FE-SEM analysis was performed on fracture surfaces. As a result of the tensile strength test, it was confirmed that compared to pure PA6, the strength of the polymer composite with a content of 0.05 wt% was improved by about 60%, for 0.1 wt%, about 65%, and for 0.2 wt%, the strength was improved by 50%. Also, when compared according to the content of FCN, the best strength value was shown when 0.1 wt% was added. The elastic modulus also showed an improvement of about 15% in the case of surface treatment compared to the case without surface treatment, and an improvement of about 70% compared to pure PA6. Through FE-SEM, it was confirmed that the matrix material and silane-modified nanomaterial improved the dispersibility and bonding strength of the interface, helping to support the load evenly and enabling effective stress transfer.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.67-75
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• 2019

The diaphragm used for CFT columns has a small amount of steel to be used, but has a disadvantage that welding is difficult and openings are required because the steel tube and four sides must be welded. The improved diaphragm to be examined in this study was cut into four corners by cutting the center hole for concrete filling. In the improved diaphragm, the width of the center hole is the same as that of the previous diaphragm, but the width of the diaphragm contacting the steel tube is reduced, thereby reducing the welding length by about 70% compared to the previous diaphragm. The in-plane strain of each specimen was analyzed when the same load was applied to the interior diaphragm through a simple tensile test. Using the general FEM program(ANSYS 19.2), the analysis was performed under the same conditions as the actual simple tensile test, and the load transfer between the improved diaphragm and the previous diaphragm was compared. When the width of the diaphragm is equal to or smaller than the flange width, stress is concentrated from the end of the diaphragm, and when the flange width is larger, stress is concentrated at the center.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.12
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• pp.715-732
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• 2009

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2008. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) Research trends in thermal and fluid engineering have been surveyed in the categories of general fluid flow, fluid machinery and piping, new and renewable energy, and fire. Well-developed CFD technologies were widely applied in developing facilities and their systems. New research topics include fire, fuel cell, and solar energy. Research was mainly focused on flow distribution and optimization in the fields of fluid machinery and piping. Topics related to the development of fans and compressors had been popular, but were no longer investigated widely. Research papers on micro heat exchangers using nanofluids and micro pumps were also not presented during this period. There were some studies on thermal reliability and performance in the fields of new and renewable energy. Numerical simulations of smoke ventilation and the spread of fire were the main topics in the field of fire. (2) Research works on heat transfer presented in 2008 have been reviewed in the categories of heat transfer characteristics, industrial heat exchangers, and ground heat exchangers. Research on heat transfer characteristics included thermal transport in cryogenic vessels, dish solar collectors, radiative thermal reflectors, variable conductance heat pipes, and flow condensation and evaporation of refrigerants. In the area of industrial heat exchangers, examined are research on micro-channel plate heat exchangers, liquid cooled cold plates, fin-tube heat exchangers, and frost behavior of heat exchanger fins. Measurements on ground thermal conductivity and on the thermal diffusion characteristics of ground heat exchangers were reported. (3) In the field of refrigeration, many studies were presented on simultaneous heating and cooling heat pump systems. Switching between various operation modes and optimizing the refrigerant charge were considered in this research. Studies of heat pump systems using unutilized energy sources such as sewage water and river water were reported. Evaporative cooling was studied both theoretically and experimentally as a potential alternative to the conventional methods. (4) Research papers on building facilities have been reviewed and divided into studies on heat and cold sources, air conditioning and air cleaning, ventilation, automatic control of heat sources with piping systems, and sound reduction in hydraulic turbine dynamo rooms. In particular, considered were efficient and effective uses of energy resulting in reduced environmental pollution and operating costs. (5) In the field of building environments, many studies focused on health and comfort. Ventilation. system performance was considered to be important in improving indoor air conditions. Due to high oil prices, various tests were planned to examine building energy consumption and to cut life cycle costs.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.634-640
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• 2020

Failure analysis and heat-resistant were performed for an electric fuel pump that is installed in the fuel tank to transfer fuel to the engine of combat vehicles. The fuel pump with a DC motor was disassembled and inspected to determine the cause of failure. The failure phenomenon was classified into three categories based on observations of the inside of the housing: burnt winding, quick brush abrasion, and fuel leak into the pump. Based on the inspection results, it was estimated that overheating was the main cause of failure. The thermal test was conducted under the no-load condition in 24 hours, and the thermal sensor was installed on the stator surface and the brush holder to check the possibility of damage to the winding due to overheating. When the ambient temperature of the fuel pump was set to 68 ℃, the stator temperature increased to 135.9 ℃, and the winding of the motor was almost damaged. The test results confirmed the lack of heat resistance of fuel pump windings, and suggested that the type F of insulation class (below 155 ℃) of the windings and varnish should be replaced with type C or higher that can be used above 180 ℃.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.5
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• pp.583-592
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• 2016

IMO (International Maritime Organization) in the UN (United Nations) set up that aim at reducing $CO_2$ emission from ship by up to 30 percent until 2030. The final purpose of this study is the development of marine thermoelectric generation system using waste heat from vessel of internal combustion engines. Before the development of marine thermoelectric generation system, this paper carried out the fundamental heat analysis of marine thermoelectric generation system. It was able to obtain the valuable results about the efficiency improvement of the thermoelectric generation system. The results is as follows : 1) It was confirmed that the efficiency of thermoelectric generation system improves to 8.917 % with increasing the temperature difference of peltier module by reducing the temperature difference between peltier module and heat source at the hot side. 2) System efficiency according to change in the external load resistance was confirmed that the change width of about 6 % which does not significantly occur. 3) System efficiency in the case stainless steel at the same condition is 8.707 %. System efficiency could be confirmed that the stainless steel is higher than duralumin (8.605 %), copper (8.607 %).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.10
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• pp.54-62
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• 2017

This paper describes the behavior and failure probability of the basic structural members in a fire for the fire safety assessment of offshore structures. A fire safety assessment can be accomplished by comparing the fire resistance of the members with the fire severity of the heat load due to fire. The fire severity is represented as the maximum temperature of the members using the Eurocode 1 standard fire curve and heat transfer equation. On the other hand, the fire resistance is the limiting temperature calculated by a simplified formula in the case of simple structural members. Considering the complexity of FPSOs and offshore structures, a general-purpose structural analysis program should be used and the limiting temperature obtained by analyzing the structural strength of the members through an elasto-plastic analysis with a large deflection, and compared with the maximum temperature. Also, the equality of these two methods of evaluating the fire resistance was confirmed by comparing them. Following three criteria, the strength, serviceability and stability, three failure modes, namely the first failure of a hinge, large deflection and buckling, were chosen. The failure temperature was verified for each failure mode. using the AFOSM method in the equation of the fire severity and fire resistance, thereby giving the failure probability of the member. By applying these processes to the example of a beam and plate, the behavior of the structure and failure (temperature?) of each failure mode can be determined.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.112-120
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• 2012

A numerical model considering the internal vaporization and the creep effect, in the form of a analytical program, for tracing the behavior of high strength concrete(HSC) members exposed to fire is presented. The two stages, i.e., spalling procedure and fire resistance time, associated with the thermal, moisture flow, creep and structural analysis, for the prediction of fire resistance behavior are explained. The use of the analytical program for tracing the response of HSC member from the initial pre-loading stage to collapse, due to fire, is demonstrated. Moisture evaporates, when concrete is exposed to fire, not only at concrete surface but also at inside the concrete to adjust the equilibrium and transfer properties of moisture. Finite element method is employed to facilitate the moisture diffusion analysis for any position of member, so that the prediction method of the moisture distribution inside the concrete members at fire is developed. The validity of the numerical model used in this program is established by comparing the predictions from this program with results from others fire resistance tests. The analytical program can be used to predict the fire resistance of HSC members for any value of the significant parameters, such as load, sectional dimensions, member length, and concrete strength.