• 전력전자학회논문지
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• 제20권5호
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• pp.464-470
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• 2015

In this paper, a non-isolated three-level high step-up boost converter with output voltage balancing is proposed. By adding one extra inductor to the conventional three-level boost converter, the proposed converter is derived. Compared with the traditional boost converter and the three-level boost converter, the proposed converter can obtain very high voltage conversion ratio, and the voltage and current stress of switching devices and diodes are reduced. A 2.7 kW prototype converter is built and tested to verify performances of the proposed converter.

• Computers and Concrete
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• 제33권5호
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• pp.497-507
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• 2024

In squat reinforced concrete walls, the displacement capacity for lateral deformation is low and the ability to resist the axial load can quickly be lost, generating collapse. This work consists of testing two squat reinforced concrete walls. One of the specimens is built with conventional detailing of reinforced concrete walls, while the second specimen is built applying an alternative design, including stirrups along the diagonal of the wall to improve its ductility. This solution differs from the detailing of beams or coupling elements that suggest building elements equivalent to columns located diagonally in the element. The dimensions of both specimens correspond to a wall with a low aspect ratio (1:1), where the height and length of the specimen are 1.4 m, with a thickness of 120 mm. The alternative wall included stirrups placed diagonally covering approximately 25% of the diagonal strut of the wall with alternative detailing. The walls were tested under a constant axial load of 0.1f'cAg and a cyclic lateral displacement was applied in the upper part of the wall. The results indicate that the lateral strength is almost identical between both specimens. On the other hand, the lateral displacement capacity increased by 25% with the alternative detailing, but it was also able to maintain the 3 complete hysteretic cycles up to a drift of 2.5%, reaching longitudinal reinforcement fracture, while the base specimen only reached the first cycle of 2% with rapid degradation due to failure of the diagonal compression strut. The alternative design also allows 46% more energy dissipation than the conventional design. A model was used to capture the global response, correctly representing the observed behavior. A parametric study with the model, varying the reinforcement amount and aspect ratio, was performed, indicating that the effectiveness of the alternative detailing can double de drift capacity for the case with a low aspect ratio (1.1) and a large longitudinal steel amount (1% in the web, 5% in the boundary), which decreases with lower amounts of longitudinal reinforcement and with the increment of aspect ratio, indicating that the alternative detailing approach is reasonable for walls with an aspect ratio up to 2, especially if the amount of longitudinal reinforcement is high.

• 한국신뢰성학회지:신뢰성응용연구
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• 제15권4호
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• pp.262-269
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• 2015

Accelerated degradation mechanism of the heat-resistant steel for high temperature plant was analysed in terms of microstructure and hardness. In order to simulate the microstructure of the steel actually used at $540^{\circ}C$ in the field, isothermal exposure was carried out at $630^{\circ}C$ up to 4,800 hours. The artificial degradation mechanism was comparatively verified to successfully simulate degradation of the long-time used field material. For the artificially degraded specimens, databases including size and aspect ratio of carbide, chemical composition (i.e., Cr/Mo ratio) of grain boundary carbide were built up. These degradation parameters were suggested as fingerprints for PHM (i.e., prognostics health management) of power plants.

• International Journal of Aeronautical and Space Sciences
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• 제4권2호
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• pp.51-60
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• 2003

An experimental research program is being undertaken to develop a regeneratively-cooled experimental thrust chamber of liquid rocket engine using liquefied natural gas and liquid oxygen as propellants. Prior to firing test using a regenerative cooling with liquefied natural gas in this program, several firing tests were conducted with water as a coolant. Experimental thrust chambers with a thrust of about 10tf were developed and their firing test facility was built up. Injector used in the thrust chamber was of shear-coaxial type appropriate for propellants of gas and liquid phase and cooling channels are of milled rectangular configuration. Periodical variation of the soot deposition and discoloration was observed through an eyes' inspection on the inner wall of a combustion chamber and a nozzle after each firing test, and an intuitive concept of the periodical variation of mixture ratio near the inner wall of a combustion chamber and a nozzle at once was brought about and analyzed quantitatively. Thermal heat flux to the coolant was calculated and modified with the periodical variation model of mixture ratio, and the increment of coolant temperature at cooling channels was compared with measured one.

• Journal of Power Electronics
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• 제16권2호
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• pp.436-446
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• 2016

A novel step-up DC-DC converter with a switched-coupled-inductor-capacitor (SCIC) which successfully integrates three-winding coupled inductors and switched-capacitor techniques is proposed in this paper. The primary side of the coupled inductors for the SCIC is charged by the input source, and the capacitors are charged in parallel and discharged in series by the secondary windings of the coupled inductor to achieve a high step-up voltage gain with an appropriate duty ratio. In addition, the passive lossless clamped circuits recycle the leakage energy and reduce the voltage stress on the main switch effectively, and the reverse-recovery problem of the diodes is alleviated by the leakage inductor. Thus, the efficiency can be improved. The operating principle and steady-state analyses of the converter are discussed in detail. Finally, a prototype circuit at a 50 kHz switching frequency with a 20-V input voltage, a 200-V output voltage, and a 200-W output power is built in the laboratory to verify the performance of the proposed converter.

• 한국추진공학회지
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• 제3권4호
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• pp.38-43
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• 1999

본 연구는 액체 추진제 로켓 엔진의 연소성능을 평가할 수 있는 절차를 확립하고, 운동량비와 혼합비가 연소성능에 미치는 영향을 고찰하여 안정된 연소를 보장하면서 최대의 효율을 제공하는 설계조건을 결정하고자 수행되었다. 연구를 위해 질산/Kerosene을 추진제로 사용하고 추력 24 $\iota{b}_f$, 연소실 압력 200 psia, uni-element impinging streams doublet injector를 사용하는 엔진을 설계 및 제작하여 연소시험을 수행하였다. 연구로부터 점화시 발생하는 hard start 현상은 연소실 압력을 설계치의 25 % 정도가 되도록 한 후, 설계 압력으로 상승시키는 2단계 점화방법을 채택함으로서 최소화 할 수 있었다. 그리고 최대의 연소성능은 혼합비 3.6에 존재하였고, 연소성능은 운동량비 증가에 따라서 감소하였다.

• 경영과학
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• 제32권1호
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• pp.15-33
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• 2015

Under complete information, introducing additional constraints to a portfolio will have a negative impact on performance. However, real-life investments inevitably involve use of error-prone estimations, such as expected stock returns. In addition to the reality of incomplete data, investments of most Korean domestic equity funds are regulated externally by the government, as well as internally, resulting in limited maximum investment allocation to single stocks and risk free assets. This paper presents an investment framework, which takes such real-life situations into account, based on a newly developed portfolio selection model considering realistic constraints under incomplete information. Additionally, we examined the effects of additional constraints on portfolio's performance under incomplete information, taking the well-known Samsung and SK group stocks as performance benchmarks during the period beginning from the launch of each commercial fund, 2005 and 2007 respectively, up to 2013. The empirical study shows that an investment model, built under incomplete information with additional constraints, outperformed a model built without any constraints, and benchmarks, in terms of rate of return, standard deviation of returns, and Sharpe ratio.

• Journal of Mechanical Science and Technology
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• 제19권7호
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• pp.1393-1404
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• 2005

Fatigue crack growth and life have been estimated based on established empirical equations. In this paper, an alternative method using artificial neural network (ANN) -based model developed to predict fatigue damages simultaneously. To learn and generalize the ANN, fatigue crack growth rate and life data were built up using in-plane bending fatigue test results. Single fracture mechanical parameter or nondestructive parameter can't predict fatigue damage accurately but multiple fracture mechanical parameters or nondestructive parameters can. Existing fatigue damage modeling used this merit but limited real-time damage monitoring. Therefore, this study shows fatigue damage model using backpropagation neural networks on the basis of X -ray half breadth ratio B / $B_o$, fractal dimension $D_f$ and fracture mechanical parameters can estimate fatigue crack growth rate da/ dN and cycle ratio N / $N_f$ at the same time within engineering limit error ($5\%$).

• 건축역사연구
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• 제26권3호
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• pp.39-49
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• 2017

It is difficult to build a hipped and gable roof in slender rectangular type due to restraint in variation of lateral length caused by gongpo arranged on the side, purlin space and the form of gable part and aesthetical effect of chunyeo maru. Against this backdrop and with the assumption that this phenomenon is more apparent in roofs of three-bay-kan Buddhist temples with the hipped and gable roof among national treasure Buddhist temples, this study has aimed to prove that a roof can be built in a less slender rectangular type than that of flat form and to present the building methodology and found the following findings. First, The ratio of lateral to longitudinal length of the roof has been adjusted by protruding the chunyeo and the method of adjusting the ratio of lateral to longitudinal length of the roof is considered to be determined depending on the availability of woods to be used in chunyeo. Second, in order to symmetrically arrange the edge of the roof, which is critical from the perspective of construction morphology, the chunyeo angle has been intentionally adjusted to reduce the gap of length between the front roof and the lateral roof. To sum up, the characteristic of the hipped and gable roof, which is difficult to be built in slender rectangular type, is more clearly shown in the roof and it is identified that the length of the front roof and the lateral roof has been intentionally adjusted to achieve the symmetrical arrangement of roofline of the roof edge.

• 환경영향평가
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• 제7권1호
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• pp.11-22
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• 1998

In Korea, the Demilitarized Zone(Hereafter DMZ) and the vicinity have special importance for a natural ecosystem research. However, We have difficulty in studying this region due to the access control. The purpose of this study is to analyze the landcover and the vegetation status of DMZ and the vicinity using remote sensing and GIS techniques. The site was divided into two regions; less than 2km from DMZ and less than 10 km from DMZ. The analyzed results of this study are as follow. First, the result of vegetation analysis is that the region of South and North Korea are similar in the area less than 2km from DMZ. However, the region of South Korea have good vegetation status than the region of South Korea in the area less than 10km from DMZ. Second, the result of landcover analysis is that the ratio of the landcover of South and North Korea decreased forest, agricultural and grass, built-up, barren area by turns in the area less than 2km from DMZ. However, the built-up area of South Korea increased as much as the forest area decreased and the other areas of North Korea increased as much as the forest area decreased in the area less than 10 km from DMZ. There are some differences in landcover between analyzed result and an existing statistical data. The causes are using one season setellite images, and an existing statistical data with landuse types. The analysis using remote sensing and GIS techniques is the most suitable method to understand the landcover and vegetation status of DMZ and the vicinity. Further studies are expected to overcome the limitation of this study.