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Search Results: 1 - 10 of 7321 matches for " Jeong-Kil Choi "
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Development of Ubiquitous Simulation Service Structure Based on High Performance Computing Technologies

Sang-Hyun CHO,Jeong-Kil CHOI,

材料科学技术学报 , 2008,
Abstract: The simulation field became essential in designing or developing new casting products and in improving manufacturing processes within limited time, because it can help us to simulate the nature of processing, so that developers can make ideal casting designs. To take the prior occupation at commercial simulation market, so many development groups in the world are doing their every effort. They already reported successful stories in manufacturing fields by developing and providing the high performance simulation technologies for multipurpose. But they all run at powerful desk-side computers by well-trained experts mainly, so that it is hard to diffuse the scientific designing concept to newcomers in casting field. To overcome upcoming problems in scientific casting designs, we utilized information technologies and full-matured hardware backbones to spread out the effective and scientific casting design mind, and they all were integrated into Simulation Portal on the web. It professes scientific casting design on the NET including ubiquitous access way represented by "Anyone, Anytime, Anywhere" concept for casting designs.
Impact analysis of casting parts considering shrinkage cavity defect
Si-Young Kwak,Jie Cheng,Jeong-Kil Choi
China Foundry , 2011,
Abstract: Shrinkage cavity may be detrimental to mechanical performances of casting parts. As a consequence, design engineers often use overly large safety factors in many designs due to insufficient understanding of quantitative effects of shrinkage cavity defects. In this paper, process of Al alloy wheel impact test was computationally analyzed for both the wheel models with and without shrinkage cavity defects. Based on shrinkage cavity data obtained from industrial CT (Computerized Tomography), the shrinkage cavity defects were modeled with SSM (Shape Simplification Method), which reconstructs shrinkage cavity defects to hollow spheroid primitives. After the impact simulation was conducted, the results show that under impact test condition, the wheel considering shrinkage cavity defects may fracture while the sound-assumed wheel may not.
Heat Transfer between Casting and Die during High Pressure Die Casting Process of AM50 Alloy-Modeling and Experimental Results

Zhipeng GUO,Shoumei XIONG,Sang-Hyun Cho,Jeong-Kil Choi,

材料科学技术学报 , 2008,
Abstract: A method based on die casting experiments and mathematic modeling is presented for the determination of the heat flow density (HFD) and interfacial heat transfer coefficient (IHTC) during the high pressure die casting (HPDC) process. Experiments were carried out using step shape casting and a commercial magnesium alloy, AM50. Temperature profiles were measured and recorded using thermocouples embedded inside the die.Based on these temperature readings, the HFD and IHTC were successfully determined and the calculation results show that the HFD and IHTC at the metal-die interface increases sharply right after the fast phase injection process until approaching their maximum values, after which their values decrease to a much lower level until the dies are opened. Different patterns of heat transler behavior were found between the die and the castingat different thicknesses. The thinner the casting was, the more quickly the HFD and IHTC reached their steady states. Also, the values for both the HFD and IHTC values were different between die and casting at different thicknesses.
Application of Integrated Database to the Casting Design

In-Sung Cho,Seung-Mok Yoo,Chae-Ho Lim,Jeong-Kil Choi,

材料科学技术学报 , 2008,
Abstract: Construction of integrated database including casting shapes with their casting design, technical knowledge, and thermophysical properties of the casting alloys were introduced in the present study. Recognition tech- nique for casting design by industrial computer tomography was used for the construction of shape database. Technical knowledge of the casting processes such as ferrous and non-ferrous alloys and their manufacturing process of the castings were accumulated and the search engine for the knowledge was developed. Database of thermophysical properties of the casting alloys were obtained via the experimental study, and the properties were used for .the in-house computer simulation of casting process. The databases were linked with intelligent casting expert system developed in center for e-design, KITECH. It is expected that the databases can help non casting experts to devise the casting and its process. Various examples of the application by using the databases were shown in the present study.
Virtual Mold Technique in Thermal Stress Analysis during Casting Process

Si-Young Kwak,Jae-Wook Baek,Jeong-Ho Nam,Jeong-Kil Choi,

材料科学技术学报 , 2008,
Abstract: It is important to analyse the casting product and the mold at the same time considering thermal contraction of the casting and thermal expansion of the mold. The analysis considering contact of the casting and the mold induces the precise prediction of stress distribution and the defect such as hot tearing. But it is difficult to generate FEM mesh for the interface of the casting and the mold. Moreover the mesh for the mold domain spends lots of computational time and memory for the analysis due to a number of meshes. Consequently we proposed the virtual mold technique which only uses mesh of the casting part for thermal stress analysis in casting process. The spring bar element in virtual mold technique is used to consider the contact of the casting and the mold. In general, a volume of the mold is much bigger than that of casting part, so the proposed technique decreases the number of mesh and saves the computational memory and time greatly. In this study, the proposed technique was verified by the comparison with the traditional contact technique on a specimen. And the proposed technique gave satisfactory results.

GUO Zhipeng,XIONG Shoumei,CHO Sang-Hyun,CHOI Jeong-Kil,

金属学报 , 2007,
Abstract: 通过采集高压铸造过程中铸型内部温度的变化曲线,采用热传导反算法,求解了以铝合金ADC12Z为铸件材料的铸件-铸型界面换热系数,分析了该界面换热系数随铸件厚度的变化规律.计算及分析结果表明:在压铸过程中,铸件-铸型界面换热系数迅速升至最大值,随后下降,凝固结束后趋于稳定.铸件厚度增大不仅提高了换热系数,而且对换热系数的变化趋势也有很大影响.同时,不同厚度的铸件,其固相率和冷却速率的变化规律也有较大区别.
Development of high performance casting analysis software by coupled parallel computation
Sang Hyun CHO,Jeong Kil CHOI
China Foundry , 2007,
Abstract: Up to now, so much casting analysis software has been continuing to develop the new access way to real casting processes. Those include the melt flow analysis, heat transfer analysis for solidification calculation, mechanical property predictions and microstructure predictions. These trials were successful to obtain the ideal results comparing with real situations, so that CAE technologies became inevitable to design or develop new casting processes. But for manufacturing fields, CAE technologies are not so frequently being used because of their difficulties in using the software or insufficient computing performances. To introduce CAE technologies to manufacturing field, the high performance analysis is essential to shorten the gap between product designing time and prototyping time. The software code optimization can be helpful, but it is not enough, because the codes developed by software experts are already optimized enough. As an alternative proposal for high performance computations, the parallel computation technologies are eagerly being applied to CAE technologies to make the analysis time shorter. In this research, SMP (Shared Memory Processing) and MPI (Message Passing Interface) (1) methods for parallelization were applied to commercial software "Z-Cast" to calculate the casting processes. In the code parallelizing processes, the network stabilization, core optimization were also carried out under Microsoft Windows platform and their performances and results were compared with those of normal linear analysis codes.
Genetic Effects of FTO and MC4R Polymorphisms on Body Mass in Constitutional Types
Seongwon Cha,Imhoi Koo,Byung L. Park,Sangkyun Jeong,Sun M. Choi,Kil S. Kim,Hyoung D. Shin,Jong Y. Kim
Evidence-Based Complementary and Alternative Medicine , 2011, DOI: 10.1093/ecam/nep162
Abstract: Sasang constitutional medicine (SCM), a Korean tailored medicine, categorizes human beings into four types through states of physiological imbalances and responsiveness to herbal medicine. One SCM type susceptible to obesity seems sensitive to energy intake due to an imbalance toward preserving energy. Common variants of fat mass and obesity associated (FTO) and melanocortin 4 receptor (MC4R) genes have been associated with increased body mass index (BMI) by affecting energy intake. Here, we statistically examined the association of FTO and MC4R polymorphisms with BMI in two populations with 1370 Koreans before and after SCM typing, and with the lowering of BMI in 538 individuals who underwent a 1-month lifestyle intervention. The increased BMI replicated the association with FTO haplotypes (effect size ? 1.1 kg/m2) and MC4R variants (effect size ? 0.64 kg/m2). After the lifestyle intervention, the carriers of the haplotype represented by the minor allele of rs1075440 had a tendency to lose more waist-to-hip ratio (0.76%) than non-carriers. The constitutional discrepancy for the accumulation of body mass by the effects of FTO and/or MC4R variants seemed to reflect the physique differences shown in each group of SCM constitutional types. In conclusion, FTO and MC4R polymorphisms appear to play an important role in weight gain, while only FTO variants play a role in weight loss after lifestyle intervention. Different trends were observed among individuals of SCM types, especially for weight gain. Therefore, classification of individuals based on physiological imbalance would offer a good genetic stratification system in assessing the effects of obesity genes.
Die Casting Mold Design of the Thin-walled Aluminum Case by Computational Solidification Simulation

Young-Chan Kim,Chang-Seog Kang,Jae-Ik Cho,Chang-Yeol Jeong,Se-Weon Choi,Sung-Kil Hong,

材料科学技术学报 , 2008,
Abstract: Recently, demand for the lightweight alloy in electric/electronic housings has been greatly increased. However, among the lightweight alloys, aluminum alloy thin-walled die casting is problematic because it is quite difficult to achieve sufficient fluidity and feedability to fill the thin cavity as the wall thickness becomes less than 1 mm. Therefore, in this study, thin-walled die casting of aluminum (Al-Si-Cu alloy: ALDC 12) in size of notebook computer housing and thickness of 0.8 mm was investigated by solidification simulation (MAGMA soft) and actual casting experiment (Buhler Evolution B 53D). Three different types of gating design, finger, tangential and split type with 6 vertical runners, were simulated and the results showed that sound thin-walled die casting was possible with tangential and split type gating design because those gates allowed aluminum melt to flow into the thin cavity uniformly and split type gating system was preferable gating design comparing to tangential type gating system at the point of view of soundness of casting and distortion generated after solidification. Also, the solidification simulation agreed well with the actual die-casting and the casting showed no casting defects and distortion.
Unitary Transformation of the Time-dependent Hamilton System for the Linear, the V-shape and the Triangular Well Potentials into the Quadratic Hamiltonian System
Jeong Ryeol Choi
Journal of Applied Sciences , 2004,
Abstract: In the present study, the unitary relation between time-dependent Hamiltonian system for the linear, the V-shape and the triangular well potentials and quadratic Hamiltonian system is obtained. Exact wave functions for the three types of time-dependent system by making use of the unitary transformation approach was derived. The results are complete so that they can be used to investigate various quantum-mechanical properties of the time-dependent systems.
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