• The Transactions of The Korean Institute of Electrical Engineers
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• v.68 no.1
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• pp.27-35
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• 2019

There is a growing interest in various microgrid solutions that supply electricity 24 hours a day to off-grid areas where are not connected with the main grid, and Korea has many positive effects by constructing overseas microgrids as a country operating the emission trading scheme. Since it is not clear how to obtain load curves that is one of the inputs of the HOMER used to design a microgrid optimization plan, or it is necessary to examine whether electricity is supplied to the peak load level of the areas where have not received the electricity benefits from the viewpoint of the demand management, a methodology should be developed to know the load composition ratio and the shape of the daily load curve. In this paper, the relative coefficient and average load information for each load group obtained from the survey are used besides peak load and total average load. A mathematical model is proposed to derive the load composition ratio in the form of a Quadratic Programming and the load forecasting is performed using simple linear regression with future indicators. The effectiveness of the proposed method is confirmed for the Philippine island region supported by Korea Energy Agency and the Asian Development Bank.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.3
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• pp.891-910
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• 2021

Previous QoS-aware service composition methods mainly focus on how to generate composite service with the optimal QoS efficiently for a single request. However, in the real application scenarios, there are multiple service requests and multiple service providers. It is more important to compose services with suboptimal QoS and maintain the load balance between services. To solve this problem, in this paper, we propose a service composition method, named as dynamically change and balancing composition method (DCBC). It assumes that the QoS of service is not static, and the services can adjust the value of QoS to gain more opportunities to be selected for composition. The method mainly includes two steps, which are the preprocessing step and the service selection step. In the preprocessing step, a backward global best QoS calculation is performed which regarding the static and dynamic QoS respectively; then guided by the global QoS, the feasible services can be selected efficiently in the service selection step. The experiments show that the DCBC method can not only improve the overall quality of composite services but also guarantee the fulfill ratio of requests and the load balance of services.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.4
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• pp.289-296
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• 2001

The piezoelectric transformers of 2.0x10x48 ㎣ size were fabricated with PSN-PMN-PZT(T10 and PNW-PMN-PZT(T2) composition ceramics. Effects of micro structural and piezoelectric properties on the electrical characteristics of the piezoelectric transformers were investigated. Under the fixed output power of 6 W, temperature rise of T1 transformer at the optimum load was smaller than T2 one because of fine grain size effect. Voltage step-up ratio of T1 transformer showed higher value than T2 one T1 transformer showed an excellent properties with voltage step-up ratio of 12.41, efficiency of 95.23% and temperature rise of 7.2$^{\circ}C$ at 200㏀ load resistance. And also, T2 transformer showed an excellent properties with voltage step up ratio of 9.81, efficiency of 95.51% and temperature rise of 9$^{\circ}C$ at 150㏀ load resistance.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.10
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• pp.458-463
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• 2003

In order to develope piezoelectric transformer for the ballast of fluorescent lamp, a new shape and electrode pattern of piezoelectric transformer has been investigated in this work. The composition of piezoelectric ceramics was 0.95Pb(Zr$_{0.51}$Ti$_{0.49}$)O$_3$+0.03Pb(Mn$_{1}$3/Nb$_{2}$3/)O$_3$+0.02Pb(Sb$_{1}$2/Nb$_{1}$2/)O$_3$. The sample prepared by this composition system showed the characteristics which has about 1200 of relative dielecric constant, 1100 of the mechanical quality factor, 0.53 of the electromechanical coupling coefficient, 320 pC/N of the piezoelectric constant d$_{33}$, 0.3 % of the dissipation factor. Diameter and thickness of disk-type piezoelectric transformer was 45 mm and 4 mm, respectively. The driving and generating electrode with their gap of 1mm were fabricated on the top surface. But the common electrode was fabricated on the whole bottom surface. The electrode surface ratio of driving and generating part on the top surface ranges from 1.4:1 to 3:1. We investigated the electrical characteristics with the variation of the electrode surface ratio of driving and generating part in the range of load resistance of 100 $\Omega$～70 k$\Omega$. The set-up voltage ratio of this piezoelectric transformer increases with increasing both the electrode surface of driving part and the load resistance. The set-up voltage ratio at no load resistance was more than 60 times. On the other hand, the efficiency decreases with increasing the electrode surface of driving part. In the case of the electrode surface of both 1.4:1 and 2:1, maximum efficiency showed above 97 % at load resistance of 2 k$\Omega$. However, in the case of the electrode surface of 3:1, maximum efficiency showed about 94 % at load resistance of 3 k$\Omega$.>.>.>.

• Tribology and Lubricants
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• v.12 no.3
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• pp.55-62
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• 1996

Present study was undertaken to investigate the effects of composition ratio and temperature on the friction and wear of PTFE-polyimide composites under the atmosphere of nitrogen gas. The load range was 0.62-3.46 MPa, and the temperature range was room temperature and 200$^{\circ}$C. To mention some of the notable results, friction coefficient of PTFE 100% varied relatively little within the given load and temperature ranges. Polyimide 100% showed the lowest friction coefficient of 0.06 at 200$^{\circ}$C among all the experiments. PTFE 80%-polyimide 20% showed the lowest wear factors on the whole. Friction coefficient of PTFE 20%-polyimide 80% varied from the highest 0.35 to the lowest 0.09 among all the materials at room temperature, and showed almost the same lowest values with polyimide 100% at 200$^{\circ}$C. Suggestion of friction and wear mechanisms of the materials was tried to explain the observed phenomena including above mentioned results.

• Journal of Environmental Science International
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• v.21 no.10
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• pp.1235-1244
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• 2012

The objective of this study is to evaluate Flow-Pollutant load delivery ratio equations developed from rural watershed on main subwatersheds within Juam Lake. Two regression equations for BOD and three equations for T-P were evaluated on Bosung cheon, Dongbok cheon, Songgwang cheon, Naenam cheon, and Sinpyeon cheon. The results show that estimation of BOD delivery ratio using flow-delivery equation is reliable when relative composition of discharge load of pollutant sources of a watershed is similar to those of watershed where the equation developed. On the other hand, application of regression equation for T-P was feasible when the landuse pattern and relative composition of discharge load of pollutant sources of a watershed is similar to those of watershed where the equation developed.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.6
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• pp.128-139
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• 2000

Environmental concerns and shortage of petroleum have promoted considerable interest in the use of alternate fuels in stationary diesel engine. In this study, a heavy-duty, intercooler-turbocharged 6-cylinder stationary diesel engine was converted into stationary gas engine fueled with propane or natural gas for the cogeneration plants. One of the most important factors in the combustion features of a stationary gas engine is the fuel composition and operating parameters in terms of compression ratio, spark advance, and engine loads. Experiments with different fuel gas and load conditions were carried out with combustion pressure analysis and NOx measurement. Combustion analysis based on P-$\theta$ diagrams was also investigated by means of combustion duration and cycle variation. Compression ratio is 10.0 and ignition timing is set by using the gasoline setting as a base line and advanced toward BTDC. The results show that fuel composition and spark advance have dominant effects on combustion and NOx characteristics at operating conditions.

• Journal of Energy Engineering
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• v.22 no.2
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• pp.211-225
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• 2013

To run an optimal operation of Integrated energy supply facilities, we need to analyze heat consumption patterns of District heating users and derive optimum and maximum load ratio of heat production facilities unit. This study selects three District heat production facilities. It also classifies District heating users into residential apartment buildings and eight non-residential buildings and analyzes heat consumption results for an year. Finally it carries out the analysis of how the ratio change of each type affects maximum load ratio, facility utilization ratio, heat supply range. According to this study, three different District heat facilities of residential apartment building show similar daily and annual heat consumption patterns. Annual average load ratio, maximum load ratio and annual heat demand increase as outdoor temperatures decrease. Non-residential buildings in urban District focused on apartment buildings display similar by the daily and annual heat consumption patterns. Yet their daily and annual maximum load ratio differ according to outdoor temperature, District, building types and their composition ratio. In the case of urban District focused on apartment buildings reach optimum and maximum load ratio when apartment buildings reaches 60-70% of the total. At that point heat supply range becomes maximized and the most economic efficiency is obtained.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.6 s.237
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• pp.876-888
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• 2005

Tensile properties and fracture toughness of monolithic aluminum, fiber reinforced plastics and glass fiber/aluminum hybrid laminates under tensile loads have been investigated using plain coupon and single-edge-notched specimens. Elastic modulus and ultimate tensile strength of GFMLs showed different characteristic behaviors according to the Al kind, fiber orientation and composition ratio. Fracture, toughness of A-GFML-UD which was determined by the evaluation of $K_{IC}$ and $G_{IC}$ based on critical load was similar to that of GFRP-UD and was much higher than monolithic Al. Therefore, A-GFML-UD presented superior fracture toughness as well as prominent damage tolerance in comparison to its constituent Al. By separating Al sheet from GFMLs after the test, optical microscope observation of fracture zone of GFRP layer in the vicinity of crack tip revealed that crack advance of GFMLs depended on the orientation of fiber layer as well as Al/fiber composition ratio.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.2
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• pp.123-136
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• 1992

A preliminary thermodynamic design model of two-evaporator refrigerator/freezer system is constructed. This system is based on Lorentz-Meutzner cycle using refrigerant mixtures. This model screens alternative refrigerant (R32, R125, R143a, R22, R134a, R152a, R124, R142b, R123) mixtures to select the best performance-giving refrigerant mixtures and its composition for the system. Also, it estimates the effects of cooling temperatures of intercoolers, evaporator's area ratio, cooling load ratio on the performance of the system. The COP of the system ranges from 1.4 to 1.6, which is superior to that of the single evaporator system charged with R12 by 13% to 29%. Among 15 mixtures, R22/R123, R143a/R123, R32/R142b, and R32/R124 (in the order of high COP) are most recommendable. For the case of R22/R123, R22 mass fraction more than 0.5(Load Ratio=1.0) or 0.7(Load Ratio=0.33) is recomended in order to replace R12 without reduction in volumetric capacity when keeping the compressor as the same one. COP has the highest value with X(R22)=0.7 and 0.8, respectively. For the case of R143a/R123, in the similar manner, mass fraction of R143a is more than 0.5 or 0.6 while best performance occurs at X(R143a)=0.8. Higher temperature intercooler is more important for the performance of the system than lower temperature intercooler. The area ratio of evaporators is roughly proportional to load ratio of the evaporators.