• Journal of the Korean Society for Precision Engineering
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• v.23 no.9 s.186
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• pp.156-163
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• 2006

The purpose of this study is to improve the machining of free-formed NURBS surfaces using newly defined G-codes which can directly deal with shapes defined from CAD/CAM programs on a surface basis and specialize in rough and finish cut. To this purpose, a NURBS surface interpolation system is proposed in this paper. The proposed interpolation system includes online tool-path planning, real-time interpolation and feedrate regulation considering an effective machining method and minimum machining time all suitable for unit NURBS surface machining. The corresponding algorithms are simultaneously executed in an online manner. The proposed NURBS surface interpolation system is integrated and implemented with a PC-based 3-axis CNC milling system. A graphic user interface (GUI) and a 3D tool-path viewer which interprets the G-codes for NURBS surfaces and displays whole tool-paths are also developed and included in our real-time control system. The proposed system is evaluated through actual machining in terms of size of NC data, machining time, regulation of feedrate and cutting force focused on finish cut in comparison with the existing method.

• KIPS Transactions on Software and Data Engineering
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• v.9 no.1
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• pp.11-16
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• 2020

3D printing is one of the emerging technologies and getting a lot of attention. To do 3D printing, 3D model is first generated, and then converted to G-code which is 3D printer's operations. Facet, which is a small triangle, represents a small surface of 3D model. Depending on the height or precision of the 3D model, the number of facets becomes very large and so the conversion time from 3D model to G-code takes longer. Apach Hadoop is a software framework to support distributed processing for large data set and its application range gets widening. In this paper, Hadoop is used to do the conversion works time-efficient way. 2-phase distributed algorithm is developed first. In the algorithm, all facets are sorted according to its lowest Z-value, divided into N parts, and converted on several nodes independently. The algorithm is implemented in four steps; preprocessing - Map - Shuffling - Reduce of Hadoop. Finally, to show the performance evaluation, Hadoop systems are set up and converts testing 3D model while changing the height or precision.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.1
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• pp.23-33
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• 2020

In this study, the effect of surface roughness distribution and its influence on the inflight icing code was investigated. Previous numerical studies focused on the magnitude of surface roughness, and the effects were only addressed in terms of changes in thermal boundary layers with fully turbulent assumption. In addition, the empirical formula was used to take account the turbulent transition due to surface roughness, which was regarded as reducing the accuracy of ice shape prediction. Therefore, in this study, the turbulent transition model based on the two-equation turbulence model was applied to consider the effects of surface roughness. In order to consider the effect of surface roughness, the transport equation for roughness amplification parameter was applied, and the surface roughness distribution model was implemented to consider the physical properties. For validation, the surface roughness, convective heat transfer coefficient, and ice shape were compared with experimental results and other numerical methodology. As a result, it was confirmed that the excessive prediction of the heat transfer coefficient at the leading edge and the ice horn shape at the bottom of the airfoil were improved accordingly.

• Nuclear Engineering and Technology
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• v.52 no.9
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• pp.1974-1982
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• 2020

Numerical prediction of fission product plateout and circulating coolant activities under normal operating conditions is crucial in the design of a high temperature gas-cooled reactor (HTGR). The results are used for the maintenance and repair of the components as well as the safety analysis regarding early source terms under loss of coolant accident scenarios. In this work, a new computer code named POSCA (Plate-Out Surface and Circulating Activities) was developed based on a one-dimensional model to evaluate fission product plateout and circulating coolant activities within the primary circuit of a HTGR. The verification and validation of study for the POSCA code was done using available analytical results and two in-pile experiments (i.e., OGL-1 and VAMPYR-1). The results of the POSCA calculations show that POSCA is able to simulate plateout and circulating coolant activities in a HTGR with fast computation and reasonable accuracy.

• Journal of computational fluids engineering
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• v.17 no.2
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• pp.21-27
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• 2012

Reynolds-averaged Navier-Stokes equations solver based on a pressure-based cell-centered finite volume method was developed using OpenFOAM libraries, which was an open source and providing computational continuum mechanics libraries. For the reasonable development of the turbulent boundary layer on the bow of the ship, specified library was developed. Grid sensitivities, such as skewness and aspect ratio of a cell, were tested for the solution convergence. Pressure, turbulent kinetic energy, turbulent dissipation rate contours on the ship surface computed by the developed CFD code were compared with those computed by the commercial CFD code, Fluent.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.5
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• pp.554-562
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• 2012

Processing of Scanning electron microscope imaging has been analyzed in both secondary electron (SE) imaging and backscattered electron (BSE) image. Because of unique characteristics of both secondary electron and backscattered electron image, mechanism of imaging process and image quality are quite different each other. For the sake of characterize imaging process, Monte Carlo simulation code have been developed. It simulates electron penetration and depth profile in certain material. In addition, secondary electron and backscattered electron generation process as well as their spatial distribution and energy characteristics can be simulated. Geometries that has fundamental feature have been imaged using the developed Monte Carlo code. Two, SE and BSE images generation process will be discussed. BSE imaging process can be readily used to discriminate in both material and geometry by simply changing position and direction of BSE detector. The developed MC code could be useful to design BSE detector and their position. Furthermore, surface reconstruction technique is possibly developed at the further research efforts. Basics of Monte Carlo simulation method will be discussed as well as characteristics of SE and BSE images.

• Solar Energy
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• v.4 no.2
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• pp.37-42
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• 1984

A computer code for an optimum design of solar space and domestic hot water heating system has been developed. The f-chart method developed by S.A. Klein et al. has been incorporated in the present computer code. The main conclusions obtained from the present work may be summarized as follows: (1) In Seoul area, about 46% of the total heating load can be obtained from the solar collectors whose total surface area is about one-third of the total heating floor area. (2) In Pusan area, total area of solar collectors should be about half of the total heating floor area in order to obtain an equivalent solar fraction of Seoul. (3) In cheju area, on the other hand, only about 42% of the total heating floor area of solar collectors is needed to get the same solar fraction as in Seoul and Pusan. (4) In order to get the first 50% solar fraction, only about 10-14 collectors ($4'{\times}8'$ collectors) are required, whereas about 48 collectors are needed to obtain the solar fraction of 100%. That is, roughly 3.5-4.5 times greater number of collectors are required to increase the solar fraction from 50% to 100%. Therefore, it can be concluded that it is relatively inefficient and less economical to build a solar system whose solar fraction exceeds more than 50%.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1431-1438
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• 2007

This paper presents a refined design model for current railroad design code on concrete structures exposed to marine environment. A time-varying diffusion coefficient(D) as well as surface chloride$(C_S)$ and chloride threshold level$(C_{lim})$ are studied. Averaging value of the D with time over exposed duration were used to refined durability design model to consider time dependent characteristic of D. The values for $C_S$ and $C_{lim}$ for the seashore in Korea revised for realistic durability design. The proposed model was verified by the so-called performance-based durability design, which is widely used in recent durability design code. Results show that the current standard specification underestimates durability performances of concrete structures exposed to marine environment, so that the cover depth design using current durability evaluation in the standard specifications is very much conservative. Thus, it is found that proposed durability design models for the railroad design code for railway concrete structures can be used effectively for service life design of concrete structures in marine environment.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.11 no.2
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• pp.68-74
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• 2015

Time domain response analysis for vibro-impact nonlinear behavior of multi-span tube with loose supports was performed using commercial FEA code and user subroutine. Support geometry of multi-span tube with a finite gap is realistically modeled by analytical rigid surface. Model of hydrodynamic force is based on the Qusai-steady model which accounts for the inclined angle of relative flow velocity and time delay between flow force and resulting tube motion. During tube vibration from flow loading, impact and friction at the support location is simulated using commercial FEA code with master slave contact algorithm. Analysis results has reasonable agreement with those of references and test experience. Plan of further refinement of analysis model and future test verification is briefly introduced.

• Nuclear Engineering and Technology
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• v.33 no.2
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• pp.241-253
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• 2001

Under severe accidents, the pressure and temperature response has an important role for the integrity of a nuclear power plant containment. The history of the pressure and temperature is characterized by the amount and state of steam/air mixture in a containment. Recently, the heat transfer rate to the structure surface is supposed to be increased by the wavy interface formed on condensate film. However, in the calculation by using CONTAIN code, the condensation heat transfer on a containment wall is calculated by assuming the smooth interface and has a tendency to be underestimated for safety. In order to obtain the best- estimate heat transfer calculation, we investigated the condensation heat transfer model in CONTAIN 1.2 code and adopted the new forced convection correlation which is considering wavy interface. By using the film tracking model in CONTAIN 1.2 code, the condensate film is treated to consider the effect of wavy interface. And also, it was carried out to investigate the effect of the different cell modelings - 5-cell and 10-cell modeling - for KNGR(Korean Next Generation Reactor) containment phenomena during a severe accident. The effect of wavy interface on condensate film appears to cause the decrease of peak temperature and pressure response . In order to obtain more adequate results, the proper cell modeling was required to consider the proper flow of steam/air mixture.