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( See Jo Kim ) 한국고무학회 2018 엘라스토머 및 콤포지트 Vol.53 No.4
Taylor rod impact tests have been the subject of many theoretical and experimental investigations. This paper discusses the numerical methods for simulating the Taylor impact test, which is widely used to obtain constitutive equations and failure conditions under high-velocity collisions of materials. With this in mind, a particle-based MPM (material point method) for linear viscoelastic solid materials was implemented, and MPM simulations for viscoelastic deformation behavior were numerically verified and confirmed by comparing the MPM and FEM results. In addition, this modeling and numerical approach could be extended to more complex viscoelastic models for basic understanding and to analyze the deformation and fracture behavior of more complicated viscoelastic material systems.
당뇨병성 신증의 조기예측지표로서 저항계수 및 박동계수의 의의
김상훈,김시영,이화영,이영래,김향,이상종,김병익,최윤상,이규백,조윤경,김유리,조용욱 대한신장학회 2000 Kidney Research and Clinical Practice Vol.19 No.5
Background: Diabetic nephropathy has long been known as most common culprit of ESRD. In NIDDM. histopathologically intrarenal hemodynamic changes are nonspecific, frequently with global glomerulosclerosis, interstitial fibrosis, tubular atrophy and severe arterosderosis. Duplex renal Doppler sonography is useful in the noninvasive assessment of intrarenal hemodynamic change and Doppler indices reflect increased renal vascular resistance. So we compared the values of R.I. and P.I., in NIDDM patients, with several clinical parameters to identify that R.I. and P.I. values can reflect increased renal vascular resistance and predict diabetic nephropathy as early markers. Methods: Renal Doppler US scan was performed on 40 patients with NIDDM to obtain Doppler signals from arcuate artery or interlobar artery and thereby calculate the R.I. and P.I. From every each individual, clinical and laboratory data including age, sex, morbidity period, BMW, mean blood pressure, total cholesterol, serum creatinine, BUN, HbA1c, 24 hr urine protein and creatinine clearance were analyzed. We analyzed the correlation between values of R.I. and P.I. with clinical parameters by using univariate and multiple linear regression analysis. The patients were classified as three groups on the basis of the amount of 24 hour urirne protein and value of serum creatinine: Group l(n=15) was defined as patients with 24 hr urine protein lees than 150mg/day and serum creatinine less than 1.5mg/dL, group 2(n=12) as between 150mg/day and 500mg/day and serum creatinine less than 1.5mg/dL and group 3(n=13) as more than 500mg/day or serum creatinine above 1.5mg/dL. Results: 1) R.I. values showed correlation with age, morbidity period, mean blood pressure, HbA1c, serum creatinine, BUN, creatinine clearance and 24 hour urine total protein. P.I. values showed correlation with age, morbidity period, mean blood pressure, serum creatinine, BUN, creatinine clearance and 24 hour urine total protein. 2) R.I. and P.I. values were significantly affected by creatinine clearance and age in multiple regression analysis. 3) There were statistically positive correlation between 24 hour urine protein and R.I. and P.I.. But when we divided into three groups based on their amount of 24 hour urine protein. R.I. didn't show statistical correlation but P.I, showed significant correlation in the group of patients with proteinuria over 500mg/day(p$lt;0.05). Conclusion: Renal doppler indices reflect increased renal vascular resistance in NIDDM patients and correlate with clinical parameters of diabetic nephropathy. We suggest that the R.I. and P.I. are useful marker for indicating diabetic vascular complication in NIDDM patients. However, further conative studies should be carried out to elucidate the usefulness of R.I. and P.I. as early markers or advantaging parameters in predicting diabetic nephropathy.
Kim See-Jo,Lim Kyung-Hun,Kim Chong-Youp The Korean Society of Rheology 2006 Korea-Australia rheology journal Vol.18 No.2
A finite-element method was employed to analyze axisymmetric unsteady motion of a deformable bubble near the wall. In the present study a deformable bubble in a Newtonian medium near the wall was considered. In solving the governing equations a structured mesh generator was used to describe the collapse of highly deformed bubbles with the Arbitrary Lagrangian Eulerian (ALE) method being employed in order to capture the transient bubble boundary effectively. In order to check the accuracy of the present FE analysis we compared the results of our FE solutions with the result of the collapse of spherical bubbles in a large body of fluid in which solutions can be obtained using a 1D FE analysis. It has been found that 1D and 2D bubble deformations are in good agreement for spherically symmetric problems confirming the validity of the numerical code. Non-spherically symmetric problems were also solved for the collapse of bubble located near a plane solid wall. We have shown that a microjet develops at the bubble boundary away from the wall as already observed experimentally. We have discussed the effect of Reynolds number and distance of the bubble center from the wall on the transient collapse pattern of bubble.
Manufacturing and Evaluating for the Two Layer/Explosive Materials and their Numerical Simulations
Kim, See Jo,Mun, Sang Ho,Lee, Kee Ahn,Lee, Chang Hee,Lee, Seong Trans Tech Publications, Ltd. 2014 Materials science forum Vol.767 No.-
<P>Combination of different materials used in the liner of the shaped charge is of great importance in designing for maximization of energy transfer. In general, a Cu liner is widely used for the special purpose in military as well as in industry. The reactive Cu liners require excellent mechanical properties and reactivity of the energetic materials. Pure Al powders are widely known as energetic materials. In this regard, the integrated work was done based on the three procedures. First, the kinetic-sprayed Al coating was fabricated on Cu substrate to generate a reactive Cu liner. And the reactivity, bonding and mechanical properties of kinetic-sprayed Al coatings were investigated. Second, the experimental evaluation of kinetic-sprayed Al coatings in terms of the strain rate. Finally numerical modeling and simulation were carried outand discussed for visibility validation.</P>
Kim, See-Jo,Hwang, Wook-Ryo 한국유변학회 2011 Korea-Australia rheology journal Vol.23 No.3
We investigated numerically effects of the capillary number, the droplet size and the viscosity ratio on the transient stress responses of a Newtonian droplet suspended in a Newtonian liquid in a sliding bi-periodic frame that represents a flow of two dimensional droplet emulsions in simple shear flow. Understanding the relationship between the droplet deformation and the transient stress responses such as the bulk shear stress and the first normal stress is particularly emphasized, using this computational model problem, where the rheological properties of medium and droplet fluids and flow conditions can be accurately controlled.
김시조(See Jo Kim),황욱렬(Wook Ryol Hwang),임경훈(Kyung Hun Lim) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.10
Screw extrusion processings are being used in many cases for blending or compounding in order to produce uniform mixtures of more than two different materials. As far as mixing in a single-phase flow is concerned in the single-screw extrusion process a striation thickness can be considered as a mixing measure. In the two-phase immiscible mixing system, however, due to combination of shear rate and interfacial tension on the drop interface, drops easily tend to be in the status of large elongation and eventually breakup under the repetition of the flow with high shear near the barrel surface and low shear near the screw walls. Recently, deformation and breakup mechanism of an immiscible drop were investigated experimentally in a screw channel flow, which mimics the flow in the metering section of section of the single-screw extruder. They presented the flow visualization results of drop deformation patterns and observed the peculiar thread deformation of drop as the comet-like thread. In our research, the numerical simulations by using the commercial software were carried out to understand the drop deformation and breakup mechanism and compared with the experimental results.
Yujin Seong,Youngkyu Kim,Im Doo Jung,Sungho Kim,See Jo Kim,Seong-gon Kim,Hak Jun Kim,Seong Jin Park 대한금속ㆍ재료학회 2017 대한금속·재료학회지 Vol.55 No.11
The material characterization of single crystalline Cu columns was numerically carried out at the submicroscopic level. A molecular dynamics (MD) simulation was employed using the embedded-atom method (EAM) interatomic potential between a pair of Cu atoms to describe the interactions among Cu atoms. First, the relationship between mechanical properties and factors affecting their behavior were numerically investigated using a crystal structure including several defects. The factors were specimen size, strain rate, and temperature. As the specimen size increased the normalized yield stress decreased, which was similar to results obtained at other length-scale. The yield stress tended to lead to exponential strain rate-hardening and a linear temperature-softening. Next, material characterization was conducted based on these results. These computational results can lead to the development of an in silico platform to characterize material properties and MD simulation can lay the groundwork for multi-scale modeling and simulation. (Received June 16, 2017; Accepted June 29, 2017)
Atomistic Simulation of Sintering Mechanism for Copper Nano-Powders
Seong, Yujin,Hwang, Sungwon,Kim, See Jo,Kim, Sungho,Kim, Seong-Gon,Kim, Hak Jun,Park, Seong Jin The Korean Powder Metallurgy Institute 2015 한국분말재료학회지 (KPMI) Vol.22 No.4
The sintering mechanisms of nanoscale copper powders have been investigated. A molecular dynamics (MD) simulation with the embedded-atom method (EAM) was employed for these simulations. The dimensional changes for initial-stage sintering such as characteristic lengths, neck growth, and neck angle were calculated to understand the densification behavior of copper nano-powders. Factors affecting sintering such as the temperature, powder size, and crystalline misalignment between adjacent powders have also been studied. These results could provide information of setting the processing cycles and material designs applicable to nano-powders. In addition, it is expected that MD simulation will be a foundation for the multi-scale modeling in sintering process.