• Transactions of Materials Processing
• /
• v.13 no.2
• /
• pp.122-128
• /
• 2004

In order to make a doubly-curved sheet metal effectively, a sheet metal forming process has been developed by adopting the flexibility of the incremental forming process and the principle of bending deformation which causes slight deformation in thickness. The developed process is an unconstrained forming process with no holder. For this study, the experimental equipment is set up with the roll set which consists of two pairs of support rolls and one center roll. In the experiments using aluminum sheets, it is found that the curvature of the formed sheet metal is determined by controlling the distance between supporting rolls in pairs and the forming depth of the center roll and it also depends on the thickness of the sheet metal. In order to check the effect of process parameters on the generation of sheet metal curvatures in this process, the orthogonal array is adopted. From the experimental results, among the process parameters, the distance between supporting rolls in pairs along the direction of one principal radius of curvature as well as the forming depth and the thickness of the material is shown to influence the generation of curvature in the same direction significantly. That is, the other distance between supporting rolls in pairs which are not located in the same direction of one principal radius of curvature, does not have an significant effect on the generation of the curvature in that direction. It mainly affects the generation of curvature in its own direction with the forming depth and the thickness of the material.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2003.08a
• /
• pp.53-57
• /
• 2003

In order to make a doubly curved sheet metal effectively, a sheet metal farming process has been developed by adopting the flexibility of the incremental forming process and the principle of bending deformation which causes slight deformation to thickness. The developed process is an unconstrained forming process with no holder. For this study, the experimental equipment is set up with the roll set which consists of two pairs of support rolls and one center roll. In the experiments using aluminum sheets, it is found that the curvature of the formed sheet metal is determined by controlling the distance between supporting rolls in pairs and the forming depth of the center roll and it also depends on the thickness of the sheet metal. In order to check the effect of process parameters on the generation of sheet metal curvatures in this process, the orthogonal array is adopted. From the experimental results, among the process parameters, the distance between supporting rolls in pairs along the same direction of one principle radius of curvature as well as the forming depth and the thickness of the material is shown to influence the generation of curvature in the same direction significantly. That is, the other distance between supporting rolls in pairs which are not located in the same direction of one principle radius of curvature, does not have an significant effect on the generation of the curvature in that direction. It just affects the generation of curvature in its own direction mainly with the forming depth and the thickness of the material.

• Journal of Energy Engineering
• /
• v.1 no.1
• /
• pp.66-75
• /
• 1992

The performance of heat transfer through double pane window has been investigated using experimental and numerical methods. The range of the gap distance between glasses are 0.5-10 cm. The convection heat transfer plays the dominant role for the case of the wide gap distance together with the large Rayleigh number and thereby, reduces the enhanced thermal resistance due to the increased air gap, while the conduction heat transfer does the major role for the case of small gap distance. In order to enhance the thermal insulation of the double pane window, the heat transfer of triple pane window, which is constructed to put one more glass at the middle of the double pane, is investigated to check the reduction of the convection heat transfer together with the effect of the radiation shield due to the presence of the additional glass. Further, a spacer is installed at the middle height of the double pane, and the effect of which on the suppression of the convective heat transfer is analyzed carefully, using experimental and numerical methods. For the case of the spacer-installation, the amount of energy saving is considered about 10%, but the energy saving increases a lot to 30-50% for the case of triple pane window, due to the substantial radiation shield effect of the presence of the additional glass.

• The Mathematical Education
• /
• v.62 no.4
• /
• pp.473-490
• /
• 2023

Previous studies from domestic and abroad are accumulating information on how to reason students' continuous changes through teaching experiments. These studies deal with scenes in which students who make 'smooth reasoning' and 'chunky reasoning' construct mathematical results together in teaching experiments. However, in order to analyze their results in more detail, it is necessary to check what kind of results a student reasoning in a specific way constructs for the tasks of previous studies. According to the need for these studies, the researcher conducted a total of 14 teaching experiments on one first-year high school student who was found to make 'chunky reasoning'. In this study, it was possible to observe a scene in which a student who makes 'chunky reasoning' constructs an output similar to 'a mathematical result constructed by students with various reasoning methods(smooth reasnoning or chunky reasoning) in previous studies.' In particular, the student who participated in this study observed a consistent construction method of constructing the function of 'time-speed' from the function of 'time-distance'. The researcher expected that information on this student's distinctive construction methods would be helpful for subsequent studies.

• KDI Journal of Economic Policy
• /
• v.36 no.1
• /
• pp.43-80
• /
• 2014

This study suggests a model for calculating total benefit rigorously to use the contingent valuation method (CVM) in cost-benefit analysis (CBA). Estimating households' willingness to pay through survey method, the study attempts to demonstrate if a respondent's income and the distance between a respondent's residence and the location of a target facility affect her willingness to pay. The estimation results from a structural model show that income and distance-decay effects exist and that the calculated total benefit varies largely when these effects are ignored. The study emphasizes the effects of income and distance-decay on the total benefit must be carefully considered in using CVM for CBA. Even though the total project cost is precisely estimated, the benefit/cost (B/C) ratio may differ largely when the total benefit is not correctly calculated. Also, an ad hoc model generates significantly different estimates from the utility difference model this study adopted. The difference in estimates suggests that the total benefit has to be estimated by a structural model. Finally, simulations are performed to check the validity of the model as well as to predict consequences when income and distance-decay effects are not properly treated. The results from simulations reveal it is not desirable to ignore those effects considering the perspectives of balanced regional development.

• Korean Journal of Optics and Photonics
• /
• v.29 no.1
• /
• pp.19-27
• /
• 2018

A change in object distance would generally change the magnification of an optical system. In this paper, we have proposed and designed a double-Gauss optical system with a fixed magnification and image surface regardless of any change in object distance, according to moving the lens groups a little bit to the front and rear of the stop, independently parallel to the direction of the optical axis. By maintaining a constant size of image formation in spite of various object-distance changes in a projection system such as a head-up display (HUD) or head-mounted display (HMD), we can prevent the field of view from changing while focusing in an HUD or HMD. Also, to check precisely the state of the wiring that connects semiconductor chips and IC circuit boards, we can keep the magnification of the optical system constant, even when the object distance changes due to vertical movement along the optical axis of a testing device. Additionally, if we use this double-Gauss optical system as a vision system in the testing process of lots of electronic boards in a manufacturing system, since we can systematically eliminate additional image processing for visual enhancement of image quality, we can dramatically reduce the testing time for a fast test process. Also, the Gaussian bracket method was used to find the moving distance of each group, to achieve the desired specifications and fix magnification and image surface simultaneously. After the initial design, the optimization of the optical system was performed using the Synopsys optical design software.

• Journal of the Korean Society of Environmental Restoration Technology
• /
• v.3 no.2
• /
• pp.47-52
• /
• 2000

This study was carried out to analyze the effects of elapsed years and physical properties on fill-slope alignment of forest road. For the study, 21 forest roads in Puy$\check{o}$-gun and Asan-shi of Chungchungnam-do were selected and fifteen factors that might influence on fill-slope alignment were analyzed. The major forms of alignment of the fill-slope in the time of construction were concave and compound. But, with the elapsed years, the concave and compound forms have decreased and linear and convex forms have increased. And fill-slope alignment was strongly related with fill-slope distance, fill-slope gradient and ground gradient among the physical properties.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.56 no.6
• /
• pp.1122-1129
• /
• 2007

For a system with multiple real-time tasks of different deadlines, it is very difficult to find the optimal checkpoint interval because of the complexity in considering the scheduling of tasks. In this paper, we determine the optimal checkpoint interval for multiple real-time tasks that are scheduled by RM(Rate Monotonic) algorithm. Faults are assumed to occur with Poisson distribution. Checkpoints are inserted in the execution of task with equal distance in the same task, but different distances in other tasks. When faults occur, rollback to the latest checkpoint and re-execute task after the checkpoint. We derive the equation of maximum slack time for each task, and determine the number of re-executable checkpoint intervals for fault recovery. The equation to check the schedulibility of tasks is also derived. Based on these equations, we find the probability of all tasks executed within their deadlines successfully. Checkpoint intervals which make the probability maximum is the optimal.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.18 no.1
• /
• pp.8-13
• /
• 2010

Many vehicles have significantly under-inflated tires, primarily because drivers infrequently check their vehicles' tire pressure. When a tire is used while significantly under-inflated, its sidewalls flex more and the tire temperature increases, increasing stress and the risk of failure. In this study we evaluated tire safety and economical efficiency at various inflation pressure. For tire safety we performed FMVSS indoor durability test, measurement of rolling tire temperature, braking performance at dry/wet road condition, and rolling resistance test for economical efficiency. Results show that low pressure decreases tire durability of both speed-increase condition and load-increase condition. Heat temperature of rolling tire increases as pressure decreases and significantly under-inflated tires cause increase of vehicle's stopping distance at wet road condition. Also Under-inflation increases the rolling resistance of a tire and, correspondingly, decreases vehicle's fuel economy.

• The Journal of Information Technology
• /
• v.4 no.4
• /
• pp.25-35
• /
• 2001

This paper presents a digital signature scheme for document image which directly embeds a signature onto the document. The time to take in signature is reduced by spreading of signature. Non-repudiation in origin, the 3rd condition of digital signature is realized by proposed digital signature scheme. The transmitter embeds the signature secretly and transfers it and the receiver makes a check of any forgery on the signature and the document, This scheme is compatible with the ITU-T.4(CCITT G3 or G4 facsimile standards).