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표면 결함이 있는 모재에 대한 용사 공정에서 용응 금속 액적의 충돌현상과 응고 과정 해석
하응지,김우승,Ha, Eung-Ji,Kim, Woo-Seung 대한기계학회 2002 大韓機械學會論文集B Vol.26 No.11
In this study, numerical investigation has been performed on the impingement, spreading and solidification of a coating material droplet impacting onto a solid substrate in the thermal spray process. The numerical model is validated through the comparison of the present numerical result with experimental data fer the flat substrate without surface defects. An analysis of deposition formation on the non-polished substrate with surface defects is also performed. The parametric study is conducted with various surface defect sizes and shapes to examine the effect of surface defects on the impact and solidification of the liquid droplet on the substrate.
표면장력과 후압을 고려한 고에너지밀도 레이저 용접공정 해석
하응지(Eung-Ji Ha),김우승(Woo-Seung Kim) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
In this study, numerical investigation has been performed on the evolution of key-hole geometry during high-energy density laser welding process. Unsteady phase-change heat transfer and fluid flow with the surface tension and recoil pressure are simulated. To model the overheated surface temperature and recoil pressure considering subsonic/sonic vapor flow, the one-dimensional vaporization models proposed by Ganesh and Knight are coupled over liquid-vapor interface. It is shown that the present model predicts well both the vaporization physics and the fluid flow in the thin liquid layer over the other model.
오일갤러리 유동을 고려한 디젤 엔진 피스톤 온도분포 예측
하응지(Eung-Ji Ha),문길민(Kilmin Moon),박재인(Jaein Park) 한국자동차공학회 2007 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Control of piston temperature has become one of the important factor for a recent high power and high speed diesel engines. The temperature control for diesel engine piston is commonly achieved by piston cooling jet system with oil gallery flow. However, the oil flow and piston cooling characteristics in the oil gallery have not been understood accurately. Therefore, a numerical procedure has been developed to simulate unsteady oil flow in the piston oil gallery and to predict the piston temperature distribution with oil gallery flow. The predicted piston temperature distribution showed good agreement with measured data Parametric studies were performed to evaluate the influence of oil jet velocity, oil jet nozzle area and oil gallery exit area on the piston temperature. It is found that the average heat transfer coefficient of the oil gallery increased proportional to the amount of oil jet flow. The filling ratio of oil flow and the average piston temperature are converged as the oil flow rate increased.
자유표면변형을 고려한 저에너지밀도 레이저 용접공정 해석
하응지(Eung-Ji Ha),김우승(Woo-Seung Kim) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11
In this study, numerical investigation has been performed on the evolution of weld pool geometry with<br/> moving free surface during low-energy density laser welding process. The free surface elevates near the weld<br/> pool edge if ∂σ /dT is dominantly negative. On the contrary, the free surface rise at the center of weld pool<br/> in case of mainly positive ∂σ /dT . The predicted weld pool width and depth with moving free surface are<br/> 5∼15% greater than those with flat weld pool surface. It is considered that weld pool surface oscillation<br/> during melting process augments convective heat transfer rate in the weld pool.