• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2009.10a
• /
• pp.124-127
• /
• 2009

In this paper, a longitudinal die insert fracture which occurred during cold forging of a high strength ball-stud with a sound die design nearly optimized empirically for relatively low strength material of SCM435 is introduced and the reason is revealed. A comparative study between SCM435 and ESW105 is quantitatively made using a thermoelastic finite element method for die structural analysis coupled with a forging simulator theoretically based on a rigid-plastic finite element method. It has been shown that the longitudinal die insert fracture caused from non-optimized value of shrink fit, emphasizing that the die optimal design is inevitable for cold forging of high strength materials.

• Proceedings of the KSR Conference
• /
• 2003.10b
• /
• pp.170-175
• /
• 2003

The ASCE formula of pipeline' soil interaction force is the basis of semi-analytical relationship for buried pipelines subjected to longitudinal permanent ground deformation due to seismic induced liquefaction. However, since the ASCE formula has been developed based on the stiffness of non-liquefied region, it is needed to modify for the varied stiffness of liquefied region. With this object, the consideration of decreasing effect of soil stiffness in liquefied region is made: i.e. the spatial distributions of pipeline. soil interaction force in liquefied region. It means that the improved formula can reflect various patterns of permanent ground deformation more realistically. Through the comparative analyses using both the improved and ASCE formula, the applicability of the improved, the limitation of the existing formula and semi-analytical relationship are discussed.

• Structural Engineering and Mechanics
• /
• v.76 no.3
• /
• pp.355-365
• /
• 2020

In this study, considering the hydroelastic response represented by the springing and whipping phenomena, we propose a method of estimating the fatigue damage in the longitudinal connections of ships. First, we screened the design sea states using a load transfer function based on the frequency domain. We then conducted a time domain fluid-structure interaction (FSI) analysis using WISH-FLEX, an in-house code based on the weakly nonlinear approach. To obtain an effective and robust analytical result of the hydroelastic response, we also conducted an experimental model test with a 1/50-scale backbone-based model of a ship, and compared the experimental results with those obtained from the FSI analysis. Then, by combining the results obtained from the hydroelastic response with those obtained from the numerical fatigue analysis, we developed a fatigue damage estimation method. Finally, to demonstrate the effectiveness of the developed method, we evaluated the fatigue strength for the longitudinal connections of the real ship and compared it with the results obtained from the model tests.

• Journal of Ocean Engineering and Technology
• /
• v.21 no.3 s.76
• /
• pp.16-25
• /
• 2007

A comparative study on the turbulent flaw simulation and the potential flaw analysis has been performed. A law Mach number preconditioned Navier-Stokes solver, using the multi-block grid method and a panel method based on the velocity potential, have been developed and validated by comparison to the experimental data. The present numerical analysis methods are applied to the ground effect problem around the NACA 4412 airfoil. It has been confirmed that the potential flaw analysis on the ground effect, using the image method, is consistent, to some degree, with the viscous calculations for high Reynolds number flows.

• Journal of Korean Elementary Science Education
• /
• v.27 no.4
• /
• pp.356-370
• /
• 2008

The study aims to explore sequence of earth science content in elementary school science curriculum in Korea and the U.S.. The analysis is focused on a) general content structure of earth science part; b) concept relationship between grades in the specific field of 'geology'; c) longitudinal connection of concepts and content in 'geology.' The findings are as follows. First, earth science curriculum content in Korea is structured according to sub-scientific disciplines centering on not science concepts but topics or inquiry activities whereas the U.S. curricular content is organized through integrative earth science topics with basic concepts and sub-concepts. Second, it is a common feature that basic concepts are interrelated to sub-concepts in all grades in both countries. However, basic concepts are scattered all over the grades, presented in a linear pattern in Korea while those are provided together in 3rd grade and repeated with extended concepts in a spiral structure in the U.S.. Last, it is not clear how concepts and content are longitudinally connected between grades in Korean curriculum. On the contrary, concepts and content in the U.S. curriculum have a strong longitudinal connection between grades with conceptual hierarchy. Such results indicate that Korean elementary school science curriculum would limit students' comprehensive understanding of science concepts through grades. The study suggests Korean science content should strengthen interrelationship among concepts as well as longitudinal connection between grades, in order to achieve the ultimate goal of science education, 'scientific literacy'.

• Korean Journal of Culture and Social Issue
• /
• v.27 no.4
• /
• pp.629-659
• /
• 2021

This study compared the influences of Korean psycho-social experiences on emotional-distress(stress, depression, anxiety, anger) of Koreans between two-periods during COVID-19. First, an online survey was conducted among 600 participants between April 13, 2020 and 21, while WHO had declared the pandemic, and Daegu-Gyungbuk were declared as a special-disaster area. Second, an online survey was conducted among 482 participants out of 600 study participants from the first study during August 21 to September 2, while COVID-19 re-spreaded around the world, and total confirmed cases were over 1,000 for a week in Seoul-Gyeonggi province. Hierarchical-regression analysis was used to determine the influence of personal characteristics, fear and social constraints, relationship conflict and income-decreasing factors on stress, depression, anxiety, anger in the two-time points. Results suggest that gender, quality-of-life, 'frequent information-checking about COVID-19', 'fear of unpredictability' and 'difficulties on hospital treatment access' predicted distress(stress, depression, anxiety, anger) at both Time1 and 2. 'Difficulties with official schedule' predicted distress at Time 1, and age, vulnerability to infection and difficulties with personal schedules predicted distress(stress, depression, anxiety, anger) at Time 2. Based on the reseults, implications and recommendations were presented.

• Transactions of Materials Processing
• /
• v.29 no.2
• /
• pp.76-88
• /
• 2020

The need for advanced high strength steel (AHSS) forming technology is increasing as interest in light weight and safe automobiles increases. Multipoint dieless forming (MDF) is a novel sheet metal forming technology that can create any desired longitudinal and transverse curvature in sheet metal. However, since the springback phenomenon becomes larger with high strength metal such as AHSS, predicting the required MDF to produce the exact desired curvature in two directions is more difficult. In this study, a prediction model using artificial neural network (ANN) was developed to predict the springback that occurs during AHSS forming through MDF. In order to verify the validity of model, a fit test was performed and the results were compared with the conventional regression model. The data required for training was obtained through simulation, then further random sample data was created to verify the prediction performance. The predicted results were compared with the simulation results. As a result of this comparison, it was found that the prediction of our ANN based model was more accurate than regression analysis. If a sufficient amount of data is used in training, the ANN model can play a major role in reducing the forming cost of high-strength steels.

• Steel and Composite Structures
• /
• v.34 no.1
• /
• pp.35-51
• /
• 2020

Integral abutment bridges (IABs) are those bridges without expansion joints. A single row of steel H-piles (SHPs) is commonly used at the thin and stub abutments of IABs to form a flexible support system at the bridge ends to accommodate thermal-induced displacement of the bridge. Consequently, as the IAB expands and contracts due to temperature variations, the SHPs supporting the abutments are subjected to cyclic lateral (longitudinal) displacements, which may eventually lead to low-cycle fatigue (LCF) failure of the piles. In this paper, the potential of using finite element (FE) modeling techniques to estimate the LCF life of SHPs commonly used in IABs is investigated. For this purpose, first, experimental tests are conducted on several SHP specimens to determine their LCF life under thermal-induced cyclic flexural strains. In the experimental tests, the specimens are subjected to longitudinal displacements (or flexural strain cycles) with various amplitudes in the absence and presence of a typical axial load. Next, nonlinear FE models of the tested SHP specimens are developed using the computer program ANSYS to investigate the possibility of using such numerical models to predict the LCF life of SHPs commonly used in IABs. The comparison of FE analysis results with the experimental test results revealed that the FE analysis results are in close agreement with the experimental test results. Thus, FE modeling techniques similar to that used in this research study may be used to predict the LCF life of SHP commonly used in IABs.

• Korean Journal of Radiology
• /
• v.23 no.1
• /
• pp.42-51
• /
• 2022

Objective: This study aimed to investigate the direction of tissue contraction after microwave ablation in ex vivo bovine liver models. Materials and Methods: Ablation procedures were conducted in a total of 90 sites in ex vivo bovine liver models, including the surface (n = 60) and parenchyma (n = 30), to examine the direction of contraction of the tissue in the peripheral and central regions from the microwave antenna. Three commercially available 2.45-GHz microwave systems (Emprint, Neuwave, and Surblate) were used. For surface ablation, the lengths of two overlapped square markers were measured after 2.5- and 5-minutes ablations (n = 10 ablations for each system for each ablation time). For parenchyma ablation, seven predetermined distances between the markers were measured on the cutting plane after 5- and 10-minutes ablations (n = 5 ablations for each system for each ablation time). The contraction in the radial and longitudinal directions and the sphericity index (SI) of the ablation zones were compared between the three systems using analysis of variance. Results: In the surface ablation experiment, the mean longitudinal contraction ratio and SI from a 5-minutes ablation using the Emprint, Neuwave, and Surblate systems were 28.92% and 1.04, 20.10% and 0.53, and 24.90% and 0.45, respectively (p < 0.001). A positive correlation between longitudinal contraction and SI was noted, and a similar radial contraction was observed. In the parenchyma ablation experiment, the mean longitudinal contraction ratio and SI from a 10-minutes ablation using the three pieces of equipment were 38.60% and 1.06, 32.45% and 0.61, and 28.50% and 0.50, respectively (p < 0.001). There was a significant difference in the longitudinal contraction properties, whereas there was no significant difference in the radial contraction properties. Conclusion: The degree of longitudinal contraction showed significant differences depending on the microwave ablation equipment, which may affect the SI of the ablation zone.

• Journal of Educational Research in Mathematics
• /
• v.19 no.2
• /
• pp.207-231
• /
• 2009

The purpose of this study is to examine the state of problem solving in Korean elementary mathematics. To do this, we considered the meaning of problem and problem solving in mathematics education, and analyzed the mathematics curricula in the longitudinal-latitudinal dimensions respectively. The longitudinal one consists in examining and comparing the all-time Korean elementary mathematics curricula. Meanwhile the latitudinal one consists in examining and comparing the elementary mathematics curricula of Singapore, the United Kingdom, Japan, and France. As a result of analysis, we selected ten sieves for analysing Korean elementary mathematics textbooks according to the 7th mathematics curriculum. By the analysis, we conclude that we teach problem solving quite positively in school mathematics relative to another countries, in particular we have to reconsider some issues including dealing problem solving as a independent content not a process integrated in other contents.