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송정훈,박종진,Song, Jung-Hoon,Park, Jong-Jin 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.11
Compared to a full three dimensional FEM, the Slab-FEM hybrid method reduces the required computation time distinctly and it can be applied to the analysis of a shape rolling process. However, the method is somewhat approximate and predictions by the method contain certain inaccuracies. In the present investigation a parameter called T-factor was introduced to compensate the inaccuracies of the method and proper values of the parameter were estimated for different widths of bars and reduction ratios. Then, the method was applied to analyze cold and hot rollings of rectangular bars and predicted results were compared to those of experiments. Nonuniform distributions of temperature in the bars were predicted by utilizing the temperature equation obtained for a semi-infinite solid under radiation and convection boundary conditions. It was found out that accuracies of spread and roll separating force predictions could be enhanced by using proper values of the T-factor.
SI 기관에서 초기 화염의 생성 및 성장에 대한 모델링
송정훈,선우명호,Song, Jeonghoon,Sunwoo, Myoungho 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.2
In spark ignited engines, the electrical spark not only sets the time for the onset of combustion but also is able to greatly influence the character of the initial flame growth and the subsequent combustion, and thereby can influence engine performance. The relative importance of the ignition energy is particularly high under lean or high residual gas or exhaust gas recirculation (EGR). In this study, a modeling of flame Initiation and its development is proposed. Submodels consist in representing of cylinder pressure and temperature, heat transfer to cylinder wall, and flame kernel heat transfer to ambient air and to spark plug electrodes. The breakdown process and the subsequent electrical power input initially control the kernel growth while intermediate growth is mainly dominated by diffusion or conduction. Then, the flame propagates by the chemical energy, and laminar and turbulent flame velocity.
가시화를 이용한 정적연소기에서 점화장치가 화염전파에 미치는 영향에 관한 연구
송정훈,선우명호,Song, Jeong-Hun 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.12
A visualization study using the schlieren method is adopted in an optically-accessible, cylindrical constant volume combustion chamber to identify the mechanism of ignition energy and ignition system interaction in spark ignited, lean gasoline-air mixture. In order to research the effects of ignition system on flame propagation, two kinds of ignition system are designed, and several kinds of spark plugs are tested and evaluated. To control the discharge energy, the dwell time is varied. The initial flame development is quantified in terms of 2-D images which provides information about the projected flame area and development velocity as a function of ignition system and discharge energy. The results show that high ignition energy and extended spark plug gap can shorten the combustion duration in lean mixtures. The material, diameter and configuration of electrodes the flame development by changing the transfer efficiency from electrical energy to chemical energy and discharge energy. However these factors do not affect of flame development as much a ignition energy or extended gap does.
Observation of Plasmon Hybridization in Gold Nanoparticle Pairs
송정훈,Arto V. Nurmikko,이기원,Sa-Yong Hong,Tolga Atay,Yong-Gi Kim,Young-You Kim 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.3
The hybridization of an individual plasmon in gold nanoparticle dimers was observed. By varying the interparticle separation within the metallic nanoparticle on a nanometer scale, we observed a renormalization, as well as a splitting, of the surface plasmon energy. The distinct hybridization and splitting of the individual plasmon mode were detectable in dimer plasmons when the edge-to-edge separation was smaller than $\sim$13 nm in gold particle pairs with a diameter of 160 nm, and a height of 40 nm for each particle. The range of the interparticle separation where the hybridization was detectable was sensitive to each particle's aspect ratio and size. An initial study of the ultrafast nonlinear optical response of exciton-plasmon coupled system is also reported. We observed an enhancement of the transient nonlinear transmission of Frenkel excitons in an organic semiconductor, cyanine J-aggregate, resonantly coupled with surface plasmons in gold metallic particle arrays.