• 신재생에너지
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• 제9권4호
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• pp.3-12
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• 2013

This paper proposes the hybrid fuel cell system that can solve disadvantages of existing fuel cell system and ensure high reliability and high stability. The system consists of PEM fuel cell, Ni-MH battery and power management system. In this system, when the power provided from the fuel cell is higher than the load power, the extra energy may be used to charge the Ni-MH battery. When the fuel cell can not provide enough energy to the load, the shortage of energy will be supplied by the Ni-MH battery. Experimental results show that the output voltage is regulated well during load variations. Also, high system efficiency is achieved.

• 대한기계학회논문집
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• 제18권5호
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• pp.1087-1095
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• 1994

Chain drive power transmission system was developed for a low head hydro-turbine which generates power by energy transformation on the turbine blades attached to chains. Also, experimental and theoretical analysis for the sprocket wheel tooth load distribution were performed. The tooth load was measured by the specially designed load sensor. It was found that the tooth load distribution for the steady state operation was in good accordance with the quasi-static state results showing the peak load at the final meshing tooth. The trend of the experimental results agreed with the theoretical results based on the spring model analysis and difference in the magnitude of the maximum tooth load was considered to be the effect of the variable spring constant due to the moving contact point between the roller and sprocket wheel tooth.

• 소성∙가공
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• 제13권8호
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• pp.689-695
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• 2004

This paper is concerned with the analysis of the forming load characteristics of a forward-backward can extrusion process. The analysis in this paper is extended to the selection of press frame capacity for producing efficiently final product at low cost. The possible extrusion processes to shape a forward-backward can part with different outer diameters are categorized to investigate quantitatively the forming load, forming energy and maximum pressure exerted on the die-material interface. The categorized processes are composed of combined and/or some basic extrusion processes. After the analysis of the forming load characteristics, the frame capacity of press suitable for a selected process could be determined along with securing the load capacity and with considering productivity. In addition, it is also suggested that different load capacities be selected for different dimensions of a part such as the wall thickness in forward direction. The work in this paper could be a good reference for analysis of complex extrusion and selection of proper frame capacity of press to achieve low production cost and thus high productivity.

• 한국유체기계학회 논문집
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• 제18권1호
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• pp.29-36
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• 2015

Recently, Stirling engines are emerging as a key device for power conversion of renewable energy or waste energy. This study develops a LTDSE(Low Temperature Differential Stirling Engine) using a water spray for higher heat transfer and performs load performance tests for various flow rates and temperatures of hot water spray for variable engine loads emulated by a mechanical friction device. Internal temperature and pressure, working frequency and inlet and outlet temperature of the supply water are measured. As a result, the increases in flow rate and temperature of hot water respectively enhance the power output, efficiency and the working frequency, while the increasing engine load leads to decreases in working frequency but increases in the pressure amplitude. Eventually, it is revealed there exists a maximum shaft power of the test engine.

• 대한기계학회논문집A
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• 제31권8호
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• pp.880-888
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• 2007

This article describes the load capability of bending piezoelectric actuators with a thin sandwiched PZT plate in association with the stored elastic energy induced by an increased dome height after a curing process. The stored elastic energy within the actuators is obtained via a flexural mechanical bending test. The load capability is evaluated indirectly in terms of an actuating displacement with a load of mass at simply supported and fixed-free boundary conditions. Additionally, a free displacement under no load of mass is measured for a comparison with an actuating displacement. The results reveal that an actuator with a top layer having a high elastic modulus and a low coefficient of thermal expansion exhibits a better performance than the rest of actuators in terms of free displacement as well as actuating displacement due to the formation of the large stored elastic energy within the actuator system. When actuators are excited at AC voltage, the actuating displacement is rather higher than the free displacement for the same actuating conditions. In addition, the effect of PZT ceramic softening results in a slight reduction in the resonance frequency of each actuator as the applied electric field increases. It is thus suggested that the static and dynamic actuating characteristics of bending piezoelectric composite actuators with a thin sandwiched PZT plate should be simultaneously considered in controlling the performance.

• 한국통신학회논문지
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• 제31권12B호
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• pp.1028-1036
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• 2006

Energy conservation is an important issue in wireless networks, especially for self-organized, low power, low data-rate impulse-radio ultra-wideband (IR-UWB) networks, where every node is a battery-driven device. To conserve energy, it is necessary to turn node into sleep state when no data exist. This paper addresses the energy consumption analysis of Direct-Sequence (DS) versus Time-Hopping (TH) multiple accesses and two kinds of sleeping protocols (slotted and unslotted) in PHY-MAC for Un networks. We introduce an analytical model for energy consumption or a node in both TH and DS multiple accesses and evaluate the energy consumption comparison between them and also the performance of the proposed sleeping protocols. Simulation results show that the energy consumption per packet of DS case is less than TH case and for slotted sleeping is less than that of unslotted one for bursty load case, but with respect to the load access delay unslotted one consumes less energy, that maximize node lifetime.

• 조명전기설비학회논문지
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• 제28권9호
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• pp.67-72
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• 2014

Inflow or outflow from the water treatment plant and the sewage water has potential energy. If this potential energy can be converted into electrical energy by water turbine generator, it can help to save energy because of the high capacity utilization. So recently, micro hydro power plant is reviewed in the water treatment facility. If generation capacity is low, induction generator is primarily used. If output capacity is low, generated power is supplied to the inside load. Induction generator can cause voltage drop by the inrush current at a start-up and requires reactive power for magnetization. In this study, we analyzed the flow of power and voltage variation against inrush current that occurs when the induction generator starts under the terms that loads of linear and non-linear of the water purification plant are used. Analysis results are that the voltage drop is within an allowable range and the power factor is slightly reduced by the need of reactive power.

• Computers and Concrete
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• 제30권1호
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• pp.19-32
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• 2022

This paper presents an investigation into the failure of RC columns under impact loadings. A numerical simulation of 19 identical RC columns subjected to single and repeated impact loadings was performed. A free-falling hammer was dropped at midspan with the same total kinetic energy input but varying mass and momentum. The specimens under the repeated impact test were struck two times at the same location. The colliding index, defined as the impact energy-momentum ratio, was proposed to explain the different impact responses under equal-energy impacts. The increase of colliding index from low to high indicates the transition of the impact response from static to dynamic and failure mode from flexure to shear. This phenomenon was more evident when the column had a greater axial load and was impacted with a high colliding index. The existence of the axial load had an inhibitory effect on the crack development and increased the shear resistance. The second impact changes the failure mode from flexural to brittle shear as found in the specimen with 20% axial load subjected to high a colliding index. Moreover, a deflection prediction equation based on the impact energy and force was limited to the low colliding index impact.

• 한국태양에너지학회 논문집
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• 제31권6호
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• pp.95-102
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• 2011

The purpose of study is to estimate heating, cooling load performance and economic efficiency in office building with applied the functional paint. this paint can reduced SHGC(Solar Heat Gain Coefficient) on the glazing surface by coating. In this study, estimated to compared with double glazing, low-e glazing, IP(Insulation Paint) and IPu(Insulation UV-Cut Paint) coating glazing. As a result of this study, 1)heating & cooling load Analysis, SHGC value and U-factor of double glazing is about 0.70 and 3.29($W/m^2K$). low-E glazing is about 0.65 and 2.70($W/m^2K$). Two-side it is about 0.27 and 3.25($W/m^2K$). When compared to double glazing, annual heating & cooling load of low-E glazing, Two-side IPu and IP paint coating glazing is 3,012MWh($124kWh/m^2$), 2,910MWh($120kWh/m^2$), 2,867MWh($118.4kWh/m^2$) and 2,867MWh($118.4kWh/m^2$). It i sreduced to 2.0%, 5.2%, 6.7%, and 6.7% respectively. 2)the estimation of economic efficiency, low-e glazing installed in office building can not recover the investment within a lifetime 40years. but IPu and IP paint, two-side coating in glazing, have a payback period of 13 years respectively.

• 한국태양에너지학회 논문집
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• 제26권4호
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• pp.39-45
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• 2006

The decrease in the summer peak electric load in our country is very important. The government has arranged and implemented a lot of support policies and statutes to decrease the peak electric load. And the ice thermal energy storage system is known as one of the alternatives. The purpose of this paper is to evaluate the efficiency and thermal characteristics of the closed ice thermal energy storage system using screw capsules. The measured thermal energy storage density is about 18.4 USRT-h/m3 (=232.9 MJ/m3), which is higher than 13.0 USRT-h/m3 (=164.6 MJ/m3), a low criterion of normal performance. And The efficiency of the discharging process and the total energy utilization is 96.2% and 2028.4 kcal/kWh respectively.