• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.38-39
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• 2017

This paper proposes a new control method for an AC-DC Buck converter which is utilized as a front-end converter of a 2-stage high power density adapter. In the conventional adapter applications, 2-stage configuration shows higher power transfer efficiency and higher power density than those of the single stage flyback converter. In the 2-stage AC-DC converter, the boost converter is widely used as a front-end converter. However, an efficiency variation between high AC line and low AC line is large. On the other hand, the proposed conduction band control method for a buck front-end converter has an advantage of small efficiency variation. In the proposed control method, switching operation is determined by a band control voltage which represents output load condition, and an AC line voltage. If the output load increasesin low AC line, the switching operation range is expanded in half of line cycle. On the contrary, in light load and high line condition, the switching operation is narrowed. Thus, the proposed control method reduces switching loss under high AC line and light load condition. A 60W prototype which is configured the buck and LLC converter with the proposed control method is experimented on to verify the validity of the proposed system. The prototype shows 92.16% of AC-DC overall efficiency and 20.19 W/in 3 of power density.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.859-864
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• 2001

An effective live load model for analyzing probable maximum live load effects such as moment and shear in transverse direction was developed. The main procedure of this live load model is composed of four parts, i.e., firstly, determination of the appropriate influence lines in longitudinal direction, secondly, application of the characteristics of vehicles and traffic patterns in longitudinal direction, thirdly, determination of the appropriate influence lines in transverse direction, and fourthly, application of the characteristics of vehicles and traffic patterns in transverse direction. Through this procedure, the probabilistic distributions of maximum probable load effects are deduced in the form of probability density function (PDF) and/or cumulative density function(CDF). This live load model is able to consider local or global deterioration of bridges in the structural analysis.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.305-310
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• 2001

Within some degree of journal misalignment, maximum pressure, maximum temperature, bearing load, friction and side leakage in high-speed journal bearing operation are examined under the condition of variable density and specific heat. The results are compared with the calculation results under the conditions of constant density and specific heat, and variable density and constant specific heat. It is found that the effects of variable density and specific heat on shaft misalignment are significant in determining the load capacity of a journal bearing operating at high speed.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.287-292
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• 2001

Under the condition of variable density and specific heat, maximum pressure, maximum temperature, bearing load, friction and side leakage in high-speed journal bearing operation are examined. The results are compared with the calculation results under the conditions of constant density and specific heat, and variable density and constant specific heat. It is found that the condition of variable density and specific heat play important roles in determining friction and load of journal bearing at high speed operation.

• Journal of the Korea Furniture Society
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• v.20 no.4
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• pp.281-289
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• 2009

This research examined the technical feasibility of composite that had two layers of fiberglass reinforcement to enhance the load carrying capacity of lumber. Specimens were prepared from standard lumber made of thinning crop trees such as Larix kaempferi, Pinus koraiensis, and P. rigida. Results indicated that bending properties, hardness, and wood screw withdrawal load of low density lumber from the P. koraiensis increased as the number of layers of fiberglass reinforcement increased. Composite produced by VARTM method showed the MOE increased in all specimens, while the MOR differed on the location, whether the 2-layers of FRP is put on tensile zone or compressive zone. The MOR of high density lumber from Larix kaempferi and P. rigida decreased when they placed into tensile zone, but low density lumber from P. koraiensis increased in same location. The bending toughness only increased high density lumber of Larix kaempferi as the number of layers of fiberglass reinforcement increased. The technique developed by this study may increase an opportunity to use small diameter log with low density for commercial purposes.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.12
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• pp.1204-1209
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• 2005

In-situ measurement was made to evaluate chiller performance and thermal storage density of an ice thermal storage system. The system belonged to a big hotel and the measurement was conducted during late October. Owing to very small cooling load, the data logging was possible for a single thermal storage cycle. However, operation history of the chiller showed a relatively good spectrum of data for performance evaluation. COP and thermal storage density were calculated. The COP at full load was about 4.07, which was lower than $4.8\~6.4$ of new chillers. The measured storage density was about $10.9RT-h/m^3\;(=152MJ/m^3)$, which also was lower than a criterion of normal performance $(above\;13.0RT-h/m^3\;or\;181MJ/m^3)$. The study result provides technical basis for quantitative ESCO business scenario.

• Geomechanics and Engineering
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• v.31 no.1
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• pp.53-69
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• 2022

In densely built areas, the development of underground transportation systems often involves twin excavations, which are sometimes unavoidably constructed adjacent to existing piled foundations. Because soil stiffness degrades with induced stress release and shear strain during excavation, it is vital to investigate the piled raft responses to subsequent excavation after the first tunnel in a twin-excavation system. The effects of deep excavations on existing piled foundations have been extensively investigated, but the influence of twin excavations on a piled raft is seldom reported in the literature. In this study, three-dimensional numerical analyses were carried out to investigate the influence of sand density on an existing piled raft (with a working load on top of the raft) due to twin excavations. A wide range of relative density (D_r) from loosest (30%), loose to medium (50% and 70%), and densest (90%) were selected to investigate the effects on settlement and load transfer mechanism of the piled raft during twin excavations. An advanced hypoplastic sand model (which can capture small-strain stiffness and stress-state dependent dilatancy of sand) was adopted. The model parameters are calibrated against centrifuge test results in sand reported in the literature. From the computed results, it is found that twin excavations in loose sand (D_r=30%) caused the most significant settlement. This is because of the higher stiffness of denser sand (D_r=90%) than that of loose sand. In contrast, a much larger tilting (maximum magnitude=0.18%) was computed in dense sand than in loose sand after the completion of the first excavation. As far as the load transfer mechanism along the piles is concerned, an upward load transfer to mobilize shaft resistance is observed in loose sand. On the contrary, a downward load transfer is observed in dense sand.

• Korean Journal of Soil Science and Fertilizer
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• v.50 no.5
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• pp.345-356
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• 2017

We investigated 52 livestock farming complexes in Gyeong-Gi and Incheon provinces based on low, medium, and high livestock density and groundwater quality. The objective of this study was to evaluate a relationship between nitrate N concentration in groundwater and animal factors, such as livestock density and animal species. 2,200 groundwater samples for 3 years from 2012 to 2014 at Gyeong-Gi and Incheon provinces were collected and analyzed for pH, EC, DO, ORP, temperature, major anions and cations, such as $NO_3-N$, ${HCO_3}^-$, ${PO_4}^-$, ${SO_4}^{2-}$, $Cl^-$, $NH_4-N$, $K^+$, $Na^+$, $Ca^{2+}$, $Mg^{2+}$, T-N, and TOC. Average concentration of total N for generated load density was $23,973g\;day^{-1}\;km^{-2}$ for cattle, $51,551g\;day^{-1}\;km^{-2}$ for pig, and $52,100g\;day^{-1}\;km^{-2}$ for poultry. For animal feeding species, average ratio for generated load over discharge load was 16.1% for cattle, 7.8% for pig, and 7.1% for poultry. Therefore, cattle feeding region is highly vulnerable for water pollution compared to pig and poultry feeding areas. The concentrations of chloride, nitrate, and total N in the groundwater samples were higher at high animal farming regions than other regions. The average concentration of nitrate, and chloride in groundwater samples was $5.0mg\;L^{-1}$, $16.6mg\;L^{-1}$ for low livestock density, $6.9mg\;L^{-1}$, $17.7mg\;L^{-1}$ for medium livestock density and $7.6mg\;L^{-1}$, $22.7mg\;L^{-1}$ for high livestock density and total nitrogen (T-N) was $7.7mg\;L^{-1}$ for low livestock density, $9.4mg\;L^{-1}$ for medium livestock density, $10.7mg\;L^{-1}$ for high livestock density. In conclusion, based on this research, for managing groundwater quality near livestock farming regions, $Ca-(Cl+NO_3)$ group from the Piper diagram is more efficient than using 19 factors for water quality standard.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.8
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• pp.530-537
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• 2010

With the advancement of technology, the density of IT equipment, heat load and power consumption continue to increase in high density internal-load dominated buildings as datacenters. To improve the HVAC system's energy performance and efficiency, there is a need to find methods of using outside air. Through cooling tower control that is based on outside wet-bulb temperature, the water-side economizer made it possible to achieve a maximum energy performance improvement of about 16.6% over the basic chilled water system, whereas the air-side economizer, through control based on outdoor air enthalpy, made it possible to achieve about 42.4% improvement.

• Journal of Magnetics
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• v.21 no.4
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• pp.570-576
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• 2016

The shape optimization of the stator and the rotor is important for electrical motor design. Among many motor design parameters, the stator tooth and yoke width are a few of the determinants of noload back-EMF and load torque. In this study, we proposed an equivalent magnetic circuit of motor stator for efficient stator tooth and yoke width shape optimization. Using the proposed equivalent magnetic circuit, we found the optimal tooth and yoke width for minimal magnetic resistance. To verify if load torque is truly maximized for the optimal tooth and yoke width indicated by the proposed method, we performed finite element analysis (FEA) to calculate load torque for different tooth and yoke widths. From the study, we confirmed reliability and usability of the proposed equivalent magnetic circuit.