• 한국신재생에너지학회:학술대회논문집
• /
• 2006.06a
• /
• pp.269-272
• /
• 2006

Numerical analysis of wind turbine scale effect was performed by using computational fluid dynamics. For the numerical analysis of wind turbine. Three dimensional Navier-Stokes solver with various turbulence models was tested and realizable k-e turbulence model was selected for the simulation of wind turbines. To validate the present method, performance of NREL (National Renewable Energy Laboratory) Phase VI wind turbine model was analyzed and compared with experiment and blind test data. Using the present method, numerical simulations for various size of wind tunnel model were carried out and characteristics were observed in detail. The power loss due to the interference between wind turbine and nacelle was also computed for relatively larger nacelle installation in wind tunnel test. The present results showed good correlations with experimental data and reasonable trends of scale effect of wind turbine.

• Proceedings of the KIPE Conference
• /
• 2019.07a
• /
• pp.380-381
• /
• 2019

This paper presents a grid voltage-sensorless current control design for an LCL-filtered grid-connected inverter with the purpose of enhancing the reliability and reducing the total cost of system. A disturbance observer based on the gradient steepest descent method is adopted to estimate the grid voltages with high accuracy and light computational burden even under distorted grid conditions. The grid fundamental components are effectively extracted from the estimated gird voltages by means of a least-squares algorithm to facilitate the synchronization process without using the conventional phase-locked loop. Finally, the estimated states of inverter system obtained by a discrete current-type full state observer are utilized in the state feedback current controller to realize a stable voltage-sensorless current control scheme. The effectiveness of the proposed scheme is validated through the simulation results.

• Journal of Wind Energy
• /
• v.2 no.1
• /
• pp.61-67
• /
• 2011

In the present study, numerical unsteady simulations of the NREL Phase VI wind turbine in downwind operation conditions were conducted to investigate rotor-tower interaction. The calculations were performed using an unstructured mesh, incompressible Reynolds-averaged Navier-Stokes flow solver. To capture the unsteady effects associated with the tower shadow between the rotor blades and the tower, the wind turbine was modelled including the rotor, tower, hub, and nacelle. The present results generally showed good agreements with available experimental data. At the lowest wind speed, the pressure distribution was characterized by a complete collapse of the suction peak on the blade when the blade passes through the tower wake. It was found that unsteady effects play a significant role in the response of the blades.

• Journal of information and communication convergence engineering
• /
• v.22 no.3
• /
• pp.231-236
• /
• 2024

This paper presents a method used to identify partial discharge defects in cast-resin power transformers using a back-propagation algorithm. The Rogowski-type partial discharge (PD) sensor was designed with a planar and thin structure based on a printed circuit board to detect PD signals. PD electrode systems, such as metal protrusions, particle-on-insulators, delamination, and void defects, were fabricated to simulate the PD defects that occur in service. PD characteristics, such as rising time, falling time, pulse width, skewness, and kurtosis without phase-resolved partial discharge patterns, were extracted to intuitively analyze each PD pulse according to the type of PD defect. A backpropagation algorithm was designed to identify PD defects using a virtual instrument (VI) based on the LabVIEW program. The results show that the accuracy rate of back-propagation (BP) algorithm reaches over 92.75% in identifying four types of PD defects.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.8
• /
• pp.1038-1045
• /
• 2000

An experimental study was carried out to delineate the flow characteristics in a closed countescurrent two-phase thermo syphon with concentric tubes. This is to be installed in the HANARO research reactor as a part of a Cold Neutron Source(CNS). In the present investigation, experiments ata room temperature with Freon-II3 as a moderator were performed. Results show that, based on the magnitude of pressure fluctuation, the flow regimes could be divided into 4 distinct ones in the ($V_f,\;Q_i$) plane, where $V_f$ represents the volume of the charged liquid and $Q_i$ the heat load: a stable flow regime, an oscillatory flow regime, a restablized flow regime and a dryout flow regime. For $V_f$>2.5l, the flow is stable at low $Q_i$. However, as $Q_i$ increases, the flow becomes oscillatory and finally restablizes As $V_f$ increases, the oscillation amplitude decreases, reaching to the restablized flow region at low $Q_i$, and the liquid level in the moderator cell remains high. In the oscillatory flow regimes, for a fixed VI; the oscillating period of time varies with $Q_i$, having a minimum value at a certain value of $Q_i$. The heat load, where the oscillating period of time is minimum, decreases as $V_f$ increases.

• Korean Journal of Veterinary Research
• /
• v.31 no.4
• /
• pp.355-365
• /
• 1991

This study was conducted in order to observe the changes in cellular association of seminiferous tubules from 16 to 24 weeks of age and to obtain the cycle and relative duration of the seminiferous epithelia from 28 to 44 weeks of age in Korean native dogs. The results were summarized as follows; 1. Gonocytes were seen at 16 weeks of age, however they were not observed as from 20 weeks of age. Both type A and type B-spermatogonia occurred from 20 weeks, while primary spermatocytes were found from 20 weeks. Secondary spermatocytes and spermatids appeared from 28 weeks. Spermatozoa were observed at first at 28 weeks of age. 2. Type A-spermatogonia appeared approximately 1.6 times as many at stage II compared to stage I, while the same numbers of cells were seen in both stage I and VII, showing the least number among VIII stages of the cycle of the seminiferous epithelia. The type B-spermatogonia were found from stage VI to VIII, Leptotene phase of the primary spermatocyte divided from type B-spermatogonia in stage VII observed at the stage VIII. Pachytene phase of the primary spermatocytes were shown the least in number at stage IV. The secondary spermatocyte could be seen only at stage IV. 3. The relative frequency of each stage from stage I to VIII of the cycle of the seminiferous epithelia was 30.3, 12.0, 9.8, 4.2, 8.5, 10.5, 11.4 and 13.4% respectively. Thus the establishment of spermatogenesis in Korean native dog was completed from 28 weeks of age.

• Journal of Korean Society of Forest Science
• /
• v.97 no.6
• /
• pp.561-564
• /
• 2008

Pinus densiflora(red pine) stands in Korea have been faced with the serious threat by pine wilt disease caused by Bursaphelenchus xylophilus (nematodes). It is not easy to early detect and prevent the infected trees because those cannot be visually identified during the initial phase of infection. Red pine is usually infected by B. xylophilus from May to July and can be just visually detected in October or November. While the infected trees are wilted, the spectral value of Near Infrared (NIR) is supposed to be decreased. Based on this phenomena, in this paper, the vegetation vitality change of infected trees was analyzed using vegetation indices. Spectral values of Red, Green and NIR had been acquired monthly by a portable NIR camera in the same place of red pine stands infected by pine wilt disease. It could be proven that the vegetation index, or vegetation vitality of damaged trees starts to decrease from June, in the early infecting phase.

• Journal of Physiology & Pathology in Korean Medicine
• /
• v.25 no.4
• /
• pp.674-682
• /
• 2011

The present study was undertaken to investigate the effect of acupuncture & moxibustion therapy on the hair follicle growth of skin 5 days and 10 days by macroscopic, microscopic and immunohistochemical methods. The results were as follows : Macroscopic hair follicle growth of plum-blossom needle treated group and strong moxibustion treated group was more increase than that of control group. Microscopic hair follicle growth of plum-blossom needle treated group and strong moxibustion treated group was hair growing cycle, anagen phase VI and that of control group and weak moxibustion treated group was hair growing cycle, anagen phase IV. Immunohistochemical observations on the expression of various growth factors, enzyme and receptor in hair follicle cycle after local treatment of acupuncture & moxibustion therapy are as follows: Expression of fibroblast growth factor was more intense in epidermis in plum-blossom needle treated group, epidermis and secondary hair germ cells in strong moxibustion treated group than control group. Expression of epidermal growth factor was more intense in epidermis in all experimental groups, and secondary hair germ cells in moxibustion treated group than control group. Expression of c-kit receptor was more intense in epidermis, secondary hair germ cells, outer root sheath in all experimental groups than control group. Expression of protein kinase C-${\alpha}$ was more intense in epidermis, secondary hair germ cells, outer root sheath in all experimental groups than control group. Expression of vascular endothelial growth factor was more intense in epidermis, bulge, secondary hair germ cells, outer root sheath in plum-blossom needle treated group and strong moxibustion treated group than control group. We concluded that acupuncture & moxibustion therapy related to the expression of various growth factors, enzymes and receptor on the hair growth cycle for hair growth.

• Journal of the Architectural Institute of Korea Planning & Design
• /
• v.35 no.3
• /
• pp.91-102
• /
• 2019

This study explores the causes and processes of morphological transformation of apartment complexes in Busan. All apartment complexes built until the year 2016 were selected for statistical analysis, drawing/map examination, field observation, selected expert interviews based on 6 periodical groups: Period I(~1990), Period II(1991~1995), Period III(1996~2000), Period IV(2001~2005), Period V(2006~2010), and Period VI(2011~2016). The research argues for three 'arrangement' types, P1U, L1U and P2U, which have dominated the whole periods occupying 88% of the total 260 complexes. The switch of the leading type represents for morphological transformation of apartment complexes. Four aspects, density(F.A.R.), height(maximum number of floors), deformed-building-type ratio, and building-orientation, have affected the change of 'arrangement' types. Density was the major cause of the arrangement-type switch, from P1U to L1U, on Period II(1991~1995). The morphological change, from type L1U to P2U, on Period V(2006~2010) was caused by height and orientation, and is correlated with the increased number of deformed-type buildings. The first phase morphological change on Period II(1991~1995) was resulted by the supply side of apartment. However, the second phase transformation on Period V(2006~2010) had gone through the complex process including reflection of consumers' demands. The significance of research is to reveal the morphological transformation process of apartment complexes through analytical investigation of the entire apartment data in Busan. The result shows that the major change of urban paysage started to occur from Period V(2006~2010), and the superficial evaluation on apartment 'being monotonous and repetitive' may not be proper at least from the perspective of town plan.

• Journal of computational fluids engineering
• /
• v.13 no.2
• /
• pp.55-61
• /
• 2008

The Reynolds-Averaged Navier-Stokes(RANS) analysis of the 3-D steady flow around the NREL Phase VI horizontal axis wind turbine(HAWT) rotor was performed. The CFD analysis results were compared with experimental data at several different wind speeds. The present CFD model shows good agreements with the experiments both at low wind speed which formed well-attache flow mostly on the upper surface of the blade, and at high wind speed which blade surface flow completely separated. However, some discrepancy occurs at the relatively high wind speeds where mixed attached and separated flow formed on the suction surface of the blade. It seems that the discrepancy is related to the onset of stall phenomena and consequently separation prediction capability of the current turbulence model. It is also found that strong span-wise flow occurs in stalled area due to the centrifugal force generated by rotation of the turbine rotor and it prevents abrupt reduction of normal force for higher wind speed than the designed value.