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배열회수보일러 케이싱 파손방지를 위한 열응력 저감 Heat Sink 설치 효과
최석민(Seok Min Choi),김선호(Seon Ho Kim),김풍일(Poongil Kim),고석재(Seok Jae Ko),정희봉(Hee Bong Chung),한봉기(Bong Gi Han),조형희(Hyung Hee Cho) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
This study investigate thermal stress on the HRSG casing adopting heat sink by experimental data and numerical simulation. Heat sink is adopted on the HRSG casing to reduce the thermal stress. Thermocouples are installed on the operating HRSG casing to measure the temperature. Measured data shows that temperature gradient is rapid on the middle section of the HRSG casing. On the middle section, the temperature gradient is average 100℃ and it will cause extreme thermal stress. By numerical simulation we found out the local temperature data and measeared the thermal stress on the HRSG casing. Thermal stress on the middle section of HRSG casing is the highest and we can easily assume that the breakages are frequently happens on that position. So, we installed the heat sink on the vulnerable position on the HRSG casing to reduce the thermal stress. By installing the heat sink, we can reduce the peak thermal stress by 10% on the vulnerable position. As a result, heat sink can reduce the thermal stress on the HRSG casing.
Cascaded 멀티레벨 인버터의 고장 허용 제어를 위한 Level-Shifted PWM 기반의 새로운 변조 기법
김석민(Seok-Min Kim),이준석(June-Seok Lee),이교범(Kyo-Beum Lee) 대한전기학회 2015 전기학회논문지 Vol.64 No.5
This paper proposes a novel level-shifted PWM (LS-PWM) strategy for fault tolerant cascaded multilevel inverter. Most proposed fault-tolerant operation methods in many of studies are based on a phase-shifted PWM (PS-PWM) method. To apply these methods to multilevel inverter systems using LS-PWM, two additional steps will be implemented. During the occurrence of a single-inverter-cell fault, the carrier bands scheme is reconfigured and modulation levels of inverter cells are reassigned in this proposed fault-tolerant operation. The proposed strategy performs balanced three-phase line-to-line voltages and line currents when a switching device fault occurs in a cascaded multilevel inverter using LS-PWM. Simulation and experimental results are included in the paper to verify the proposed method.
김석민(Seok Min Kim),박동성(Dong Sung Park) 대한치과의사협회 2007 대한치과의사협회지 Vol.45 No.6
The aim of this study was to investigate the effect of the hybrid instrumentation method with ProTaper and ProFile on the change of root canal area and distance from the canal to the root surface after canal shaping. The mesial canals of twenty extracted mandibular first molars having 10-20°? curvature were scanned using X-ray micro-computed tomography (XMCT)-scanner before root canals were instrumented. They were divided into four groups (n=10 canals per group). In Group 1, root canals were instrumented by the step-back technique with stainless steel K-Flexofile after coronal flaring. The remainders were instrumented by the crown-down technique with, ProTaper system (Group 2), ProFile (Group 3) or ProTaper and ProFile (Group 4). All canals were prepared up to size 25 at the end-point of preparation and scanned again. Pre-and post-operative cross-sectional images of 1, 3, 5, and 7㎜ from the apical foramen were compared. For each level, change of cross-sectional canal area and distance to the nearest external root surface was calculated using Adobe Photoshop 6.0 and image software program. In the change of cross-sectional area, Group 4 was less than Group 2 at 3 ㎜ and 5 ㎜ level (p<0.05). In the difference of the distance from the canal to the root surface after canal shaping, Group 4 was least among the other groups at 7 ㎜ level (p<0.05). According to the results, the methods using ProFile or K file only and the hybrid instrumentation technique using ProTaper and ProFile are more appropriate methods of canal preparation than ProTaper system for narrow or curved canals.