• 전기의세계
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• v.26 no.6
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• pp.59-65
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• 1977

A study on the decreasing method of secondary arc current on single phase reclosing. One of the major problem in case of using the single phase reclosing scheme for long distance UHV transmission line is the time required to deionize secondary arc current. This paper descritbes the way of inducing the formular of secondary arc current originated at the times of opening and closing the ground interrupting switch. The result was investigated by the method of numerical analysis and proved that the secondary arc current was decreasing sufficiently. Application of this method proposed by the authod makes it possible to deduce the dead time and to improve success-rate of reclosing.

• Tunnel and Underground Space
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• v.24 no.6
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• pp.464-472
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• 2014

In large-opening room-and-pillar mining sites, particularly without the devices for the ventilation control, the airflow pattern created by the local fan operation is too complicated to quantify and also shows low ventilation efficiency. This study aims at performing a series of CFD analysis for the so-called venturi effects of the local fans; the effects of increasing airflow rate along the axis downstream of fan resulting from increased kinetic energy and subsequently decreased static pressure in the downstream. Effects of the fan type and installation height are compared. 1 vane-axial fan and 2 propeller fans are analyzed for their venturi effects, while the vane-axial fan was installed at the height of 1.0, 1.5 and 2.0m for comparison. The results can be applied to improve the economy and efficiency of local fans for securing better air quality and work environment management.

• International Journal of Fluid Machinery and Systems
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• v.5 no.3
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• pp.109-116
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• 2012

Water hammer pumps can effectively use the water hammer phenomenon for water pumping. They are capable of providing an effective fluid transport method in regions without a well-developed social infrastructure. The results of experiments examining the effect of the geometric form of water hammer pumps by considering their major dimensions have been reported. However, these conventional studies have not fully evaluated pump performance in terms of pump head and flow rate, common measures of pump performance. The authors have focused on the effects on the pump performance of various geometric form factors in water hammer pumps. The previous study examined how the hydrodynamic characteristics was affected by the inner diameter ratio of the drive and lift pipes and the angle of the drive pipe, basic form factors of water hammer pumps. The previous papers also showed that the behavior of water hammer pump operation could be divided into four characteristic phases. The behavior of temporal changes in valve chamber and air chamber pressures according to the air volume in the air chamber located downstream of the lift valve was also clarified in connection with changes in water hammer pump performance. In addition, the effects on water hammer pump performance of the length of the spring attached to the drain valve and the drain pipe angle, form factors around the drain valve, were examined experimentally. This study focuses on the form of the lift valve, a major component of water hammer pumps, and examines the effects of the size of the lift valve opening area on water hammer pump performance. It also clarifies the behavior of flow in the valve chamber during water hammer pump operation.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.5
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• pp.553-560
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• 2015

Fracture mechanics analysis for cracked pipes is essential for applying the leak-before-break (LBB) concept to nuclear piping design. For LBB assessment, crack instability and leak rate should be predicted accurately for through-wall cracked pipes. In a nuclear piping system, elbows are connected with straight pipes by circumferential welding; this weld region is often considered a critical location. Hence, accurate crack assessment is necessary for cracks in the interface between elbows and straight pipes. In this study, the stress intensity factor (SIF) and elastic crack opening displacement (COD) were estimated through detailed 3D elastic finite element (FE) analyses. Based on the results, closed-form solutions of shape factors for calculating the SIFs and elastic CODs were proposed for circumferential through-wall cracks in the abovementioned interfaces under internal pressure. In addition, the effect of the elbow on shape factors was investigated by comparing the results with the existing solutions for a straight pipe.

• Tunnel and Underground Space
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• v.27 no.1
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• pp.1-11
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• 2017

Most of the local limestone mines are developed as large-opening underground mines, while mine ventilation is heavily dependent on the natural ventilation and auxiliary systems, rather than the mechanical ventilation system using main fans. The current auxiliary ventilation system with fan and ducting requires optimization since enhanced deployment of diesel equipment demands higher airflow rate and the associated cost is expected to be too excessive for the local mine operators. This paper aims at optimizing the fan capacity for the working site ventilation through comparing the fan pressure in the mine airway and the ventilation efficiency of an axial-flow fan and a propeller fan developed in this study.

• Journal of Biosystems Engineering
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• v.31 no.5 s.118
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• pp.389-394
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• 2006

The characteristic of moisture absorption of granular fertilizer was measured at several different opening sizes on the top cover of a hopper in a humid weather. The size of the opening was to represent the degree of looseness of sealing of the top cover of the hopper. The application distribution was characterized by the scattering distance of granular fertilizer with different degree of moisture absorption in a pneumatic granular fertilizer applicator. The moisture absorption rates were 12.92 and 12.26 mg of moisture an hour for one gram of each granular fertilizers of NPK 22-12-12 and 21-17-17, respectively. The moisture absorption increased linearly as the opening size increased. The median value of the scattering distance distribution decreased with time of absorption, however, it decreased very slowly after three hours of absorption.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.3
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• pp.253-258
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• 2016

The effect of temperature on the fracture energy, crack propagation, and crack tip opening displacement (CTOD) was determined for particulate reinforced composites using the wedge splitting test. The materials that were used consisted of a polymer binder, an oxidizing agent, and aluminum particles. The test rate of the wedge splitting specimen was 50 mm/min, the temperature conditions were $50^{\circ}C$, room temperature, $-40^{\circ}C$, and $-60^{\circ}C$. The fracture energy, calculated from splitting load-crack mouth opening displacement(CMOD) curves, increased with decreasing temperature from $50^{\circ}C$ to $-40^{\circ}C$. In addition, the strength of the particulate reinforced composites increased sharply at $-60^{\circ}C$, and the composites evidenced brittle fracture due to the glass transition temperature. The strain fields near the crack tip were analyzed using digital image correlation.

• Journal of the Korean Geographical Society
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• v.45 no.4
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• pp.444-460
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• 2010

This study analyzed the changes in climate elements that affects the opening and closing dates of the ski resorts, and the snowmaking. Climatology data from the weather stations adjacent to the ski resorts in the central region of Korea were analysed to understand the snowmakig status. The fan type snowmaker has been used in the capital region (over 94% of the whole snowmaking), while the gun type snowmaker has been used in Yongpyong. There has been obviously an increased trend of the daily minimum temperature in November in Daegwallyeong and a little decreased trend in Icheon after 1980s. That caused the effect on the opening dates of the ski resort in the capital region of Korea during 2000s. Closing dates of ski resorts were earlier in the capital region (with $2{\sim}4^{\circ}C$ of daily maximum temperature in mid-February) than in Yongpyong. The obviously increasing rate of the snowmelting day in Icheon also hardened the management and maintenance of the ski resorts in the capital region of Korea.

• Journal of Internet of Things and Convergence
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• v.9 no.6
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• pp.125-134
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• 2023

The purpose of this paper is to propose a method to improve the performance of the previous research is characterized by recognizing facial gestures from the 3D coordinates of seven landmarks selected from the MediaPipe Face Mesh model, generating corresponding user events, and executing corresponding commands. The proposed method applied adaptive moving average processing to the cursor positions in the process to stabilize the cursor by alleviating microtremor, and improved performance by blocking temporary opening/closing discrepancies between both eyes when opening and closing both eyes simultaneously. As a result of the usability evaluation of the proposed facial gesture interface, it was confirmed that the average recognition rate of facial gestures was increased to 98.7% compared to 95.8% in the previous research.

• International Journal of Concrete Structures and Materials
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• v.18 no.3E
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• pp.213-219
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• 2006

Modified singular fracture process zone(S-FPZ) model is proposed in this paper to determine a fracture criterion for continuous crack propagation in concrete. The investigated fracture properties of the proposed fracture model are strain energy release rate at a micro-crack tip and the relationship between crack closure stress(CCS) and crack opening displacement(COD) in the FPZ. The proposed model can simulate the actual fracture energy of experimental results fairly well. The results of the experimental data analysis show that specimen geometry and loading condition did not affect the CCS-COD relation. However, the strain energy release rate is a function of not only specimen geometry but also crack extension. The strain energy release rate remained constantly at the minimum value up to the crack extension of 25 mm, and then it increased linearly to the maximum value. The maximum fracture criterion occurred at the peak load for specimens of large size. The fracture criterion remained at the maximum value after the peak load. The variation of the fracture criterion is caused by micro-cracking and micro-crack localization. The fracture criterion of strain energy release rate can simply be the size effect of concrete fracture, and it can be used to quantify the micro-cracking and micro-crack localizing behavior of concrete.