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Yongun Jeon,박정선 한국항공우주학회 2024 International Journal of Aeronautical and Space Sc Vol.25 No.1
In structural health monitoring, the damage detection method using Lamb wave has been actively performed for composite laminates. It is hard to apply the Lamb wave to composite laminate because of its dispersion and multi-mode characteristics. This paper derived the dispersion equation for a single layer assuming monoclinic to calculate more accurate group velocity. Furthermore, the general solution for wave propagation is assumed that the wavenumber vector considers the displacements in three directions. Using the transfer matrix method with the slowness curve, the Lamb wave behavior for a single layer is extended to the composite laminate. By solving the matrix equation, the group velocity is theoretically calculated. For comparison with the theoretical results, an experimental test has been performed on the unidirectional composite plates with 12ply and 16ply. As a result, it has been confirmed that the theoretical and the experimental group velocities are well-matched except for the fiber direction (0°) because of the monoclinic and wavenumber assumption. An error analysis of the experimental and theoretical values has been performed for the fiber direction. It is concluded that a compensation method for group velocity in the fiber direction is needed for damage detection using the Lamb wave in unidirectional composite plate.
디젤 엔진 연소 해석을 위한 개선된 난류 분무 연소 모델의 연구
이용운(Yongun Lee),허강열(Kang Y. Huh),김현옥(Hyunok Kim),박경민(Kyungmin Park) 한국자동차공학회 2007 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
We present an improved model of turbulent spray combustion for a diesel engine in this study. The Conditional Moment Closure (CMC) routines are combined with KIVA to provide conditional flame structures to determine mean state variables, instead of mean reaction rates. An independent transport equation is solved for each flame group with equal mass of sequentially injected fuel group. Additional source terms due to evaporation are implemented in KIVA with scaled probability density function (PDF) and conditional scalar dissipation rates (CSDR). The expressions for vaporization source terms and scaling factors are based on recent direct numerical simulation (DNS) results. A heavy duty diesel engine is employed with early injection timings to test the improved CMC model. Soot modeling based on Lindstedt and Hiroyasu model is implemented in the KIVA code. Parametric investigation is performed with respect to EGR (Exhaust Gas Recirculation), injection timing and rpm. Measured pressure traces, NOx and soot emissions are reasonably reproduced in a wide range of engine operating conditions.
디젤 분무 연소에서 혼합 분율 스케일링의 영향에 대한 연구
이용운(Yongun LEE),허강열(Kangyoel Huh),박경민(Kyungmin Park),김현옥(Hyunok Kim) 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
In this study we present an improved model of turbulent spray combustion to improve accuracy of diesel combustion simulations. Additional source terms due to vaporization are implemented in KIVA with Conditional Moment Closure (CMC) model. Probability density function(PDF) and conditional scalar dissipation rate are scaled to consider limited ranges of mixture fraction by the saturation condition. The expression for the vaporization source term and scaling factors are based on recent direct numerical simulation (DNS) results on turbulent spary combustion. A heavy duty diesel engine is used with early injection timings to test the CMC model with scaled PDF and conditional scalar dissipation. Two and three times the mean mixture fraction are employed as the limiting range for scaling, while another suggestion is based on local PDF lower than an arbitrary small value. Parametric investigation is performed with respect to EGR (Exhaust Gas Recirculation) rate and injection timing. Measured pressure traces and NOx emissions are reasonably well reproduced in wide engine operating conditions.