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Experimental and modeling investigation on machined surfaces of HDPE-MWCNT polymer nanocomposite
Gong, Y.,Baik, Y. J.,Li, C. P.,Byon, C.,Park, J. M.,Ko, T. J. Springer Science + Business Media 2017 INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TE Vol.88 No.1
<P>This study investigates end-milled surfaces of HDPE-MWCNT polymer nanocomposite. The feed rate and the cutting speed are varied and their effects on the surface roughness are investigated in detail. The relationship between the surface roughness and the processing parameters are investigated by using a response table and a response function. In addition, the relationship is also discussed in terms of the Deborah number which characterizes viscoelastic behavior of polymeric materials.</P>
Strain gradient plasticity based finite element analysis of ultra-fine wire drawing process
S. M. Byon,C. H. Moon,Y. Lee 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.12
Steady-state rigid-plastic finite element analysis coupled with strain gradient plasticity theory has been performed to examine the size effect of material on its plastic deformation behavior and find an optimal semi-cone angle of die which minimizes the drawing energy in the ultra-fine wire drawing process. A stream-line tracing method was adopted to calculate strain component at each element and a strain surface function was introduced to compute the equivalent strain gradient of each element. Introduction of this function enables us to use an established FE code without renewal of its main structure. Hence, the constitutive equation in FE formulation is changed to couple the strain gradient plasticity. A series of FE simulation reveals that significant differences in drawing stress are observed when material size approaches its intrinsic material length. When the strain gradient plasticity theory is reflected on the steady-state FE analysis, the optimal semi-cone angle of the die is reduced by 30%. The variation of optimal semi-cone angle is attributable to considerable increment of homogeneous deformation when the material size reaches its intrinsic material length.
Thermal performance of heterogeneous PCHE for supercritical CO<sub>2</sub> energy cycle
Jeon, S.,Baik, Y.J.,Byon, C.,Kim, W. Pergamon Press ; Elsevier Science Ltd 2016 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.102 No.-
The supercritical CO<SUB>2</SUB> (S-CO<SUB>2</SUB>) energy cycles are gaining increasing attention due to its high efficiency in a compact footprint and ability to utilizing various heat sources. The printed circuit heat exchanger (PCHE) is regarded an essential component in the S-CO<SUB>2</SUB> cycle due to its high compactness and structural rigidity. In this study, an innovative type of PCHE, the heterogeneous type PCHE is proposed and its thermal performance is investigated numerically. The effect of channel sizes of heat source fluid and heat sink fluid, the spacing between the channels, and the channel cross-sectional shape on the thermal performance is analyzed. The results indicate that the thermal performance of the PCHE decreases monotonically as the either of channel size increases, because the flow velocity decreases subject to fixed mass flow rate condition. The spacing between the channels is shown to hardly affect the thermal performance of the PCHE. However, the spacing significantly affects the structural reliability of the PCHE. The channel cross-sectional shape also does not have significant effect on the thermal performance, provided that the hydraulic diameter of the channel remains constant.
마라톤선수의 연속적 고지훈련 후 심폐기능, 혈액세포, EPO 및 사이토카인농도의 변화
김기진 ( K. J. Kim ),김상현 ( S. H. Kim ),변자영 ( J. Y. Byon ),홍창배 ( C. B. Hong ),안나영 ( N. Y. Ahn ),김재훈 ( J. H. Kim ),김홍화 ( H. H. Kim ) 한국운동생리학회(구 한국운동과학회) 2011 운동과학 Vol.20 No.2
본 연구는 중국 쿤밍 (1,950m)에서의 4주간과 케냐 엘도렛 (2,200m)에서 8주간의 고지훈련을 연속적으로 실시하는 과정에서 마라톤선수들의 심폐기능 및 혈액세포, EPO 및 사이토카인농도의 변화를 분석하였다. 연구대상자는 20대 우수한 마라톤선수로서 고지훈련그룹 5명과 평지훈련의 통제그룹 4명으로 구성하였다. 고지훈련 전과 쿤밍에서의 4주간 고지훈련 후, 엘도렛 현지, 엘도렛훈련 후 평지로 되돌아온 1주, 2주 및 3주경과 후에 각각 신체구성, 최대하 및 최대운동검사, 혈액세포, 혈중 EPO 및 사이토카인농도 등을 각각 측정하였다. 고지훈련 후 심폐기능이 향상된 것으로 나타났으며, 고지훈련을 마친 후 평지로 되돌아 온 2주경과시부터 개선되어 3주까지 지속되는 것으로 생각된다. 2주경과시가 가장 우수한 심폐기능을 나타냈다. 엘도렛 체류시 생리적 기능은 제한되는 양상을 나타냈다. 적혈구수 및 헤모글로빈농도는 고지훈련 후 긍정적인 효과를 나타내며, 아울러 혈중 EPO농도도 현저하게 증가되는 것으로 나타났다. 그러나 혈액세포변인의 변화는 고지훈련의 기간이 계속적으로 연장될 경우 지속되지 않는 것으로 나타났다. 쿤밍훈련 4주와 엘도렛훈련 8주의 연속적인 고지훈련은 선수들의 피로현상을 초래할 가능성이 있기 때문에 지나친 장기간의 고지훈련은 신중하게 검토해야 할 것으로 생각된다. This study analyzed the changes of cardiopulmonary function, blood cell parameters, erythropoietin (EPO), and cytokines after a successive altitude training of 4 week-Kunming (1,950m) and 8 week-Eldoret (2,200m) in marathoners. Subjects were 20-aged elite marathoners, and were divided into two groups as altitude training group (N=5) and control group (N=4). We measured the cardiopulmonary function of submaximal and graded treadmill testing, blood cell parameter, body composition, blood concentration of EPO and cytokines before and after altitude training. After altitude training, altitude training group showed a significant increase of cardiopulmonary function as maximal oxygen uptake and exercise duration to all-out in graded treadmill testing. This improvement of cardiopulmonary function can extend to 2 weeks after altitude training. And the subjects showed the limitation of physiological function during Eldoret. After altitude training, altitude training group showed a significant positive changes of erythrocyte number, hemoglobin and EPO concentration. Because a successive altitude training of 4 week-Kunming and 8 week-Eldoret is apt to develop a fatigue in marathoners, we should check the detailed changes of phyiological function in long duration of altitude training.