• Computers and Concrete
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• v.21 no.5
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• pp.505-511
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• 2018

This paper investigates the potential of a hybrid model which combines the least squares support vector machine (LSSVM) and an improved particle swarm optimization (IMPSO) techniques for prediction of concrete compressive strength. A modified PSO algorithm is employed in determining the optimal values of LSSVM parameters to improve the forecasting accuracy. Experimental data on concrete compressive strength in the literature were used to validate and evaluate the performance of the proposed IMPSO-LSSVM model. Further, predictions from five models (the IMPSO-LSSVM, PSO-LSSVM, genetic algorithm (GA) based LSSVM, back propagation (BP) neural network, and a statistical model) were compared with the experimental data. The results show that the proposed IMPSO-LSSVM model is a feasible and efficient tool for predicting the concrete compressive strength with high accuracy.

• Bulletin of the Korea Photovoltaic Society
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• v.6 no.1
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• pp.8-20
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• 2020

Nepal has huge potential of hydro and other renewable energy resources including solar energy. However, only 70% of the total population have access to electricity despite the long history of hydropower development in the country. Still more than 37% population in rural areas and around 73% population in Karnali Province, one of the least developed provinces, are living without access to electricity despite taking several initiatives and implementing various policies by government supporting electrification in off-grid rural areas. Government together with donors and private sector has extensively been promoting the off-grid solar photovoltaic (PV) echnology in un-electrified areas to increase electricity access. So far, more than 900,000 households in rural areas of Nepal are getting electricity from stand-alone solar PV systems. However, there are many challenges including financial, technical, institutional, and governance barriers in Nepal. This study based on extensive review of literatures and author's own long working experiences in renewable energy sector in Nepal, shares the best practices and lessons of off-grid solar PV for increasing access to electricity in rural areas of Nepal. This study suggests that flexible financial instruments, financial innovations, bundling of PV systems for concentrating energy loads, adopting standards process, local capacity building, and combination of technology, financing and institutional aspects are a key for enhancing effectiveness of solar PV technology in rural areas of Nepal.

• The Journal of the Korea Contents Association
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• v.17 no.4
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• pp.1-11
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• 2017

Interest in all kinds of renewable energies has been highly increased while the micro-small-hydro power(MSHP) development has shown relatively slowly growth because of the negative public recognition about dam site development. It is, however, announced that the micro-SHP shows higher energy conversion efficiency compared to other renewable energies and does not emit any carbon dioxide. Thus, it is concerned about the development and application of micro-SHP as an alternative energy. In this study, the application for Android was exploited with Eclipse to visualize readily the potential realizable amount of hydropower by micro-SHP. With this application, we can select the region from the map, obtain the design discharge of the selected site was calculated with HEC-HMS, presented by U.S. Army of Corp. and perform the simply economic analysis in sequence. Yeongwol in Gangwon-do Province, Korea was chosen as the target area since historically abundant precipitation was found and it is possible to obtain fundamental data from WAMIS. Results from this study could be expanded the whole region of Korea. Also, the initial investment cost would be reduced if the location for micro-SHP would be determined properly, because this application can help us easily select and examine the potential micro-SHP sites without on-the-spot visit.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.61.2-61.2
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• 2015

In the past decades, green energy, such as solar energy, wind power, hydropower, biomass energy, geothermal energy, and so on, has been widely investigated and developed to solve energy shortage. Recently, organic solar cells have attracted much attention, because they have many advantages, including low-cost, flexibility, light weight, and easy fabrication [1-3]. Organic solar cells are as a potential candidate of the next generation solar cells. In this abstract, to improve the power conversion efficiency and the stability, the inverted polymer solar cells with various structures were developed [4-6]. The novel cell structures included the P3HT:PCBM inverted polymer solar cells with AZO nanorods array, with pentacene-doped active layer, and with extra P3HT interfacial layer and PCBM interfacial layer. These three difference structures could respectively improve the performance of the P3HT:PCBM inverted polymer solar cells. For the inverted polymer solar cells with AZO nanorods array as the electronic transportation layer, by using the nanorod structure, the improvement of carrier collection and carrier extraction capabilities could be expected due to an increase in contact area between the nanorod array and the active layer. For the inverted polymer solar cells with pentacene-doped active layer, the hole-electron mobility in the active layer could be balanced by doping pentacene contents. The active layer with the balanced hole-electron mobility could reduce the carrier recombination in the active layers to enhance the photocurrent of the resulting inverted polymer solar cells. For the inverted polymer solar cells with extra P3HT and PCBM interfacial layers, the extra PCBM and P3HT interfacial layers could respectively improve the electron transport and hole transport. The extra PCBM interfacial layer served another function was that led more P3HT moving to the top side of the absorption layer, which reduced the non-continuous pathways of P3HT. It indicated that the recombination centers could be further reduced in the absorption layer. The extra P3HT interfacial layer could let the hole be more easily transported to the MoO3 hole transport layer. The high performance of the novel P3HT:PCBM inverted polymer solar cells with various structures were obtained.

• Journal of Korea Water Resources Association
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• v.38 no.5 s.154
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• pp.365-377
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• 2005

This paper presents numerical works carried out for developing an advanced computational framework for understanding injury- and mortality-inducing flow phenomena in hydropower facilities. Large-eddy simulation (LES) of a circular jet flow is carried out to help interpret the results of recent experiments that exposed live fish to the shear zone of a turbulent jet. The instantaneous flow field of LES is characterized by intense velocity, pressure, and vorticity fluctuations, which could exert forces and moments on a fish considerably larger than those exerted by the same fish exposed to the corresponding steady, time-averaged flow. In this study, also, unsteady modeling of flow in a hydroturbine draft tubewas carried out using a hybrid unsteady RANS/LES, so-called detached-eddy simulation (DES). Results from DES show that the potential for disorientation and excessive residence times of fish within the draft tube is certainly considerable.

• The KSFM Journal of Fluid Machinery
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• v.18 no.6
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• pp.45-56
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• 2015

This paper aims to develop a submerged propeller turbine for micro hydropower plant which allows to sustain high values of efficiency in a broad range of hydrological conditions (H=2~6 m, $Q=0.15{\sim}0.39m^3/s$). The two aspects to be considered in this development are mechanical simplicity and high-efficiency operation. Unlike conventional turbines that have spiral casing and gear box, this is directing driving and no spiral casing. A 10 kW class turbine which has the most high potential of the power generation has been developed. The most important element in the design of turbine is the runner blade. The initial blade is designed using inverse design method and then the runner geometry is modified by classical hydraulic method. The design process is carried out in two steps. First, the blade shape is fix and then other components of submerged propeller turbine are designed. Computational fluid dynamics analyses based on the Navier-Stokes equations have been used to obtain overall performance data for the blade and the full turbine, respectively. The results generated by performance parameters(head, guide vane opening angle and rotational speed) variations are theoretically analysed. The evaluation criteria for the blade and the turbine performances are the pressure distribution and flow's behavior on the runner blades and turbine. The results of simulation reveals an efficiency of 91.5% and power generation of 10.5kW at the best efficiency point at the head of 4m and a discharge of $0.3m^3/s$.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.70-70
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• 2020

기후변화 대응을 위해 파리기후협약에서는 온실가스 배출량 감축을 위한 구체적인 목표를 제시하였다. 에너지 분야는 온실가스가 가장 많이 배출되는 분야 중 하나이며, 온실가스 감축 방안으로 신재생 에너지에 대한 관심이 증가하고 있다. 특히 수력에너지는 신재생 에너지 중 가장 현실적이고 많이 활용되는 에너지원으로 각광받고 있다. 아시아 지역은 개발도상국이 다수 위치하고 있고 미개발된 잠재 수력에너지가 풍부한 지역으로 국내 기업의 진출 가능성이 높은 지역이다. 수력에너지 개발을 위해서는 수력 발전 가능량 평가가 필수적이며, 수력 발전 가능량은 기후, 수문조건에 민감하게 반응하기 때문에 기후변화에 따른 수력 발전 가능량의 변동 가능성이 있다. 본 연구에서는 아시아 지역에 대한 AR5 기후변화 시나리오 기반 수력 발전 가능량을 전망하고 분석하고자 하였다. 수력 발전 가능량 산정을 위한 수문 자료 생성은 지표수문해석 모형 VIC (Variable Infiltration Capacity)를 이용하였으며, 모형 입력 자료로 APHRODITE (Asian Precipitation -Highly Resolved Observational Data Integration Towards Evaluation of water resources) 기상 자료, USGS (U.S. Geological Survey) 수치지형도, FAO (Food and Agriculture Organization) 토양도, NCC (Norwegian Climate Centre) NorESM 기후변화 시나리오를 활용하였다. 분석결과 수력 발전 가능량은 과거 및 미래 기간에 동남아시아, 남아시아 지역에 풍부한 것으로 나타났다. 동남아시아는 유출량이 풍부하며, 남아시아는 유역별 낙차가 크기 때문에 수력 발전 가능량이 풍부한 것으로 나타났다. 따라서 동남아시아 지역의 수력 발전 가능량이 남아시아에 비해 기후변화의 영향을 크게 받는 것으로 나타났다. 또한 미래 기후변화로 인해 유출량의 변동 폭이 더욱 넓어져 발전 효율이 감소하는 것으로 나타나 수력발전의 안정성이 감소하였다. 본 연구는 아시아 지역의 수력 발전 가능량을 산정하고 특징을 분석하였다는 점에서 의미가 있다.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.233-233
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• 2015

Vu Gia - Thu Bon basin is located in central Vietnam between Truong Son mountain range on the border with Lao in the west and the East Sea in the east. The basin occupies about 10,350 km2 or roughly 90% of the Quang Nam Province and includes Da Nang, a very large city with about 876,000 inhabitants. Total annual rainfall ranges from about 2,000 mm in central and downstream areas to more than 4,000 mm in southern mountainous areas. Rainfall during the monsoon season accounts for 65 to 80% of total annual rainfall. The highest amount of rainfall occurs in October and November which accounts for 40 to 50% of the annual rainfall. Rainfall in the dry season represents about 20 to 35% of the total annual rainfall. The low rainfall season usually occurs from February to April, accounting for only 3 to 5% of the total annual rainfall. The mean annual flow volume in the basin is $19.1{\times}109m 3$. Similar to the distribution of rainfall, annual flows are distinguished by two distinct seasons (the flood season and the low-flow season). The flood season commonly starts in the mid-September and ends in early January. Flows during the flood season account for 62 to 69% of the total annual water volume, while flows in the dry season comprise 22 to 38% of total annual run-off. The water volume gauged in November, the highest flow month, accounts for 26 to 31% of the total annual run-off while the driest period is April with flows of 2 to 3% of the total annual run-off. There are some hydropower projects in the Vu Gia - Thu Bon basin as the cascade of Song Bung 2, Song Bung 4, and Song Bung 5, the A Vuong project currently under construction, the Dak Mi 1 and Dak Mi 4 projects on the Khai tributary, and the Song Con project on the Con River. Both the Khai tributary and the Song Con join the Bung River downstream of SB5, although the Dak Mi 4 project involves an inter-basin diversion to Thu Bon. Much attention has recently been focused on the effects that climate variability and human activities have had on runoff. In this study, data from the Vu Gia - Thu Bon River Basin in the central of Viet Nam were analyzed to investigate changes in annual runoff during the period of 1977-2010. The nonparametric Mann-Kendall test and the Mann-Kendall-Sneyers test were used to identify trend and step change point in the annual runoff. It was found that the basin had a significant increasing trend in annual runoff. The hydrologic sensitivity analysis method was employed to evaluate the effects of climate variability and human activities on mean annual runoff for the human-induced period based on precipitation and potential evapotranspiration. This study quantitatively distinguishes the effects between climate variability and human activities on runoff, which can do duty for a reference for regional water resources assessment and management.