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김동건(D. G. Kim),윤소남(S. N. Yun),함영복(Y. B. Ham),박중호(J. H. Park) 한국동력기계공학회 2009 한국동력기계공학회 학술대회 논문집 Vol.2009 No.11
In this study, the characteristics of the energy harvesting equipment which consists of the aluminum cantilever with a bimorph type piezoelectric actuator, a vibrator and data measurement system were discussed. This study demonstrates a technique how to harvest the vibration energy and wind energy using the piezoelectric actuator. Also, this study suggests that the stored energy to the capacitor or small battery can be used to the wireless sensor network system.
모델 단순화에 의한 CFRP 복합 구조물의 유효 열전도율 추출 방법 연구
김동건(D.G. Kim),한국일(K.I. Han),최준혁(J.H. Choi),이장준(J.J. Lee),김태국(T.K. Kim) 한국전산유체공학회 2015 한국전산유체공학회지 Vol.20 No.4
The thermal balance test in vacuum chamber for satellite structures is an essential step in the process of satellite development. However, it is technically and economically difficult to fully replicate the space environment by using the vacuum chamber. To overcome these limitations, the thermal analysis through a computer simulation technique has been conducted. The CFRP composite material has attracted attention as satellite structures since it has advantages of excellent mechanical properties and light weight. However, the nonuniform nature of the thermal conductivity of the CFRP structure should be noted at the step of thermal analysis of the satellite. Two different approaches are studied for the thermal analyses; a detailed numerical modeling and a simplified model expressed by an effective thermal conductivity. In this paper, the effective thermal conductivities of the CFRP composite structures are extracted from the detailed numerical results to provide a practical thermal design data for the satellite fabricated with the CFRP composite structure. Calculation results of the surface temperature and the thermal conductivities along x, y, z directions show fairly good agreements between the detailed modeling and the simplified model for all the cases studied here.
김동건(D. G. Kim),박평원(P. W. Park),윤소남(S. N. Yun) 한국동력기계공학회 2009 한국동력기계공학회 학술대회 논문집 Vol.2009 No.6
This paper presents an energy harvester using piezoelectric elements that is a kind of generator which converts the mechanical power to the electric one using windmill system with many piezoelectric elements. In this study, low frequency characteristics of the cantilever-type piezoelectric element were experimentally investigated. Advantages of the cantilever use are to take a very large displacement and to improve the endurance of the piezoelectric element. The piezoelectric element of size of 45L×11W×0.6H and piezoelectric constant(rf<sub>31</sub>) of -180×10<sup>-12</sup>C/N was used. The material of cantilever is an aluminum and four kinds of cantilever of which sizes are (150, 170, 190, 210)[mm]×13[mm]× 1.5[mm] were experimented, respectively. The cantilever was fixed on the vibrator. The characteristics of frequency and mass variation of cantilever end part such as 0[g], 2.22[g], 4.34[g], 5.87[g], 8.66[g], 11.01[g] were investigated. The maximum voltage was generated at the cantilever size of 210[mm]×13[min]×1.5[mm].To improve of the energy conversion efficiency, several bridge diodes and smoothing condensers were used respectively.
야외 환경에 노출된 입체 구조물에 대한 열적외선 신호 예측 소프트웨어 개발 및 실험적 검증 연구
김동건(D.G. Kim),권구용(K.Y. Kwon),장현성(H.S. Jang),연윤모(Y.M. Yeon),하남구(N.K. Ha) 한국전산유체공학회 2021 한국전산유체공학회지 Vol.26 No.3
This paper contains experimental validation of surface temperature and IR(infrared) signal prediction performance for a 3D object placed in an outdoor environment as part of a software development process to predict thermal infrared signals based on computational thermal analysis with considering 3D thermal conduction and unsteady state. For experimental validation, CUBI targets, which are introduced as major verification cases abroad, were produced and installed on the experimental site. Also, thermocouple wires, infrared cameras, a solar tracker and a weather station were installed on the experimental site. Performance validation was carried out step by step, and as the first step, the suitability of the algorithm applied to the developed software was determined through comparison and analysis of prediction results for surface temperature. As a second step, the self-emitted radiance calculation result and the solar and sky reflected radiance calculation algorithm were validated through the analysis of the prediction result for infrared signals. In addition, by assigning the same input conditions to the other commercial software with similar concepts and comparing the calculated results together, the limitations of modeling inevitably appear in the comparison between modeling and measurement were considered. As a result of the validation, it is judged that the thermal infrared signal prediction performance of the software developed through this study is applicable to stereoscopic objects placed in an outdoor environment. In the future, it is necessary to prepare to become software with higher reliability through performance validation of 3D objects that have more complex forms or contain heat sources.
격자 세분화 방법을 고려한 복사열전달 형상계수 계산 기법 연구
김동건(D.G. Kim),한국일(K.I. Han),최준혁(J.H. Choi),이장준(J.J. Lee),김태국(T.K. Kim) 한국전산유체공학회 2014 한국전산유체공학회지 Vol.19 No.1
Since experiments on the actual operational status are said to be very impractical because of their economic and repeatability problems, it is difficult to understand the thermal profiles of aerospace or military equipments. Thus, the CFD codes with considering the radiation heat transfer are used to compensate the defect. In case, analyzing the radiation exchanges between the object surfaces are very important. Because the temperature and the IR signal distributions of the object surface are significantly affected by the radiative heat transfer. To achieve accurate thermal radiation exchange between surfaces, it is important to calculate the radiation view factor precisely. Finer subdivision of meshes can be used to increase the accuracy of radiation view factor, but if the mesh is subdivided infinitely, the time required for calculation increases significantly and thus decreasing the efficiency. If the subdivision is not sufficient, assurance of accuracy is not guaranteed. In this paper, optimal mesh subdivision method using the solid angle has been successfully tested and found to be useful in increasing the efficiency of calculating the shape factors.
윤소남 (S. N. Yun ),김동건 (D. G. Kim ),윤동원 (D. W. Yun ),신동우 (D. W. Shin ),김문곤 (M. G. Kim ) 한국동력기계공학회 2009 한국동력기계공학회 학술대회 논문집 Vol.2009 No.6
In this study, flow characteristics of the poppet valve for safety valve in electro-hydraulic proportional pressure control equipment were analyzed. A safety valve with a poppet which are applied in industrial field have some advantages like fast response and stable operation. But the displacement is very short and the flow path is very narrow because of above-mentioned roll. Tiny displacement affects the discharge coefficient and eddy flow directly. So, it is very important study to analyze the flow characteristics of the poppet valve in electro-hydraulic proportional pressure control equipment. In this study, flow field numerical analysis of the object poppet valve of which displacement is from 0.1 to 0.3mm was operated. And distribution characteristics of the flow pressure and velocity were analyzed.