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김동일(Dong-il Kim),복기소(Ki-So Bok),이승규(Seung-Gyu Lee) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
To seek the fan operating point on a cooling system with fans, it is very important to determine the system impedance and it has been usually examined with the fan tester(wind tunnel) based on ASHRAE standard and AMCA standard. This leads to a large investment in time and cost, because it could not be executed until the system is made actually. Therefore it is necessary to predict the system impedance curve through numerical analysis so that we could reduce the measurement effort. This paper presents how the system impedance curve (pressure drop curve) is computed by CFD in substitute for experiment. In reverse order to the experimental principle of the fan tester, pressure difference was adopted first as inlet and outlet boundary conditions of the system and then flow rate was calculated.
렌즈의 온도 구배를 고려한 결상광학계의 초점 열화 영향 분석
안재훈(Jaehoon Ahn),김은진(Eunjin Kim),차종환(Jonghwan Cha),복기소(Kiso Bok) 대한기계학회 2023 대한기계학회 춘추학술대회 Vol.2023 No.11
In order to address the issue of thermal drift, which causes the focus of the imaging optical system to blur due to temperature changes, an athermal design was conducted. In this process, the influence of temperature gradients distributed across each lens on changes in back focal length (△BFL) was analyzed. As an athermal design approach, the Imaging optical system was functionally divided into a projection system and an image system. The projection system used an optical passive athermalization method, while the image system utilized a mechanical passive athermalization method. Functionally, the projection and image systems were designed so that the movement direction of their respective focal lengths changed in opposite directions, and they were designed to move only a certain distance to ensure that the combined effect after temperature changes would cancel each other out. Additionally, finite element analysis results from multiple physics fields such as optics, optomechanics and cooling field were utilized for a more precise analysis. The proposed athermal design enables the core component, the projection lens, to act as a temperature compensator across the entire system, while reducing tolerance sensitivity, contributing to improvements in optical performance and competitive pricing.