• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.4
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• pp.40-47
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• 2010

This study deals with the investigation about the effect of the pilot and split injection strategies on the spray-atomization characteristics of biodiesel fuel derived from a soybean oil. Experimental results were compared with the calculation results obtained from the numerical analysis. Fuel properties of biodiesel according to the variation of the fuel temperature were inserted to the fuel library in the KIVA code. The amount of fuel injection is divided into equal mass for each split and main injection. In this work, the pilot injection strategy can be achieved by the amount of fuel injection shortly before the start of the main injection. A spray tip penetration, radial distance and spray area were measured for the analysis of macroscopic spray characteristics. In addition, the local and overall droplet size distribution were calculated by using KIVA-3V code to study the effect of split and pilot injection on the atomization performance under high ambient pressure. From these studies, the experimental results showed the multiple injection induced the decrease of the spray tip penetration due to the reduction and division of the spray momentum compared to single injection. In the atomization performance, the droplet size increased in the case of the multiple injection a little. Moreover, the SMD slightly increased as the fuel droplets goes through the axial direction. The spray behavior of numerical results were well predicted the experimental multiple spray characteristics of biodiesel fuel.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1043-1058
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• 1990

The Strain rate effect in electro-magnetic forming, which is one of the high velocity forming methods, is studied by the finite element method in this paper. The forming process is simplified by neglecting the coupling between magnetic field and work-piece deformation, and the impulsive magnetic pressure is regarded as inner pressure load. A rate-dependent elasto-plastic material model, of which tangential modulus depends of effective strain rate, is proposed. The model is shown to well describe the transient increase of yield stresses, the decreases of the final displacement and yield stress, the decrease of the difference in the distribution of deformation along the axial direction, and the change of deformation mechanism due to strain rate effect. As a result, displacement, final deformed shape, radial velocity, deformation energy, and the changes of effective stress, effective strain and effective strain rate through plastic working are given. Based on the results, the effectiveness of this model and the strain rate effect of the deformation process of the work-piece are discussed.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.5 s.347
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• pp.11-16
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• 2006

This paper reports the correlation between dielectric constant and degree of amorphism of the hybrid type SiOC thin films. SiOC thin films were deposited by high density plasma chemical vapor deposition using bistrimethyl- silylmethane(BTMSM,$H_{9}C_{3}-Si-CH_{2}-Si-C_{3}H_{9}$) and oxygen precursors with various flow rate ratio. As-deposited film and annealed films at $400^{\circ}C$ were analyzed by XRD. The SiOC thin films were amorphous from XRD patterns. For quantitative analysis, the diffraction pattern of the samples was transformed to radial distribution function by Fourier analysis, and then compared with each other. The degree of amorphism of annealed films was higher than that of as-deposited ones. The dielectric constant varied in accordance with flow rate ratio of precursors. The lowest dielectric constant was obtained from the as-deposited film which has the highest degree of amorphism after annealing.

• The Journal of the Korea institute of electronic communication sciences
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• v.12 no.2
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• pp.315-324
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• 2017

The smart grid with distributed power supply introduces a number of problems including not only the problems of the existing power grid but also the problem of protection co-operation due to new electric phenomenon because it has a mixed operation structure combining the existing radial operation structure and the new loop operation structure. The EMTP based power system analysis method has flexibility and convenience from the view of system configuration but it requires another experimental verification because of uncertainty of design and analysis results. On the other hand, the real demonstration system has difficulties in observing accurate fault on large scale system due to considerable economical and spatial construction cost, system configuration constraint, and it is difficult to demonstrate the distributed, autonomous and adaptive control strategy of smart grid. In this paper, a basic theory for a micro smart grid simulator design using MEMS(Micro Electro-Mechanical Systems) miniaturization technology is studied which can safely and freely experiment and observe electrical phenomena, and distribution, autonomous adaptive control strategy for disturbances on 22.9kV smart grid under minimum economic and spatial cost.

• The KSFM Journal of Fluid Machinery
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• v.10 no.6
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• pp.32-37
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• 2007

Aerodynamic forces and moments have been used to control rocket propelled vehicles. If control is required at very low speed, Those systems only provide a limited capability because aerodynamic control force is proportional to the air density and low dynamic pressure. But thrust vector control(TVC) can overcome the disadvantages. TVC is the method which generates the side force and roll moment by controlling exhausted gas directly in a rocket nozzle. TVC is classified by mechanical and fluid dynamic methods. Mechanical methods can change the flow direction by several objects installed in a rocket nozzle exhaust such as tapered ramp tabs and jet vane. Fluid dynamic methods control the flight direction with the injection of secondary gaseous flows into the rocket nozzle. The tapered ramp tabs of mechanical methods are used in this paper. They installed at the rear in the rocket nozzle could be freely moved along axial and radial direction on the mounting ring to provide the mass flow rate which is injected from the rocket nozzle. In this paper, the conceptual design and the study on the tapered ramp tabs of the thurst vector control has been carried out using the supersonic cold flow system and schlieren system. This paper provides the thrust spoilage, three directional forces and moments and distribution of surface pressure on the region enclosed by the tapered ramp tabs.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.11
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• pp.1183-1189
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• 2015

This study focuses on the design of the tapered joints of a wind power turbine. The main variables of the tapered joint are the transmitted torque, shaft diameter, contact area of the tapered ring, and tightening torque of the bolts, which applies a compressive pressure from the hub to the shaft. The stress distribution of the taper fit was calculated under axisymmetric plane strain conditions because of the small taper angle. The axial displacement of the clamp can be calculated from the radial elastic deformation and the taper angle. The stress field of each ring is obtained from the cylinder stress equation. To verify the accuracy of the calculation, finite element (FE) analysis was performed, and the results of the calculation and FE analysis were compared. The hoop stress of the tapered surface showed a discrepancy of approximately 10, but the trends of the stress distributions of each component and the relative movement obtained by FE analysis were in good agreement with the analytical calculation results.

• Journal of The Korean Astronomical Society
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• v.28 no.2
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• pp.153-167
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• 1995

More than 22,300 stars in NGC 6752 were measured over the region of 5' < r < 23' in B and V AAT plates. The most of these are main sequence(MS) stars and about 130 blue horizontal branch(BHB) stars were detected. The C-M diagram of all measured stars shows gaps appearing at $V{\approx}15.^{m}2$ and $16.^{m}2$ along the red giant branch(RGB) and their appearance shown by Lee & Cannon(1980) is found to be independent of measured region. The bimodal distribution of BHB stars is confirmed again and a wide gap shown by Lee & Cannon(1980) at $V{\approx}16^m$ is clearly seen for stars in the outer part (8' < r < 13') in the cluster. It is noted, however, that this gap is occupied by about a dozen of BHB staIs located in the inner region (5' < r < 8'). The number ratio of bright BHB star (V < $15^m$) to faint BHB stars (V > $15^m$) decreases with increasing radial distance from the cluster center. Three faintest BHB stars were found, and two stars ($V{\approx}18.^{m}5$) of there are located in the inner region of $r{\approx}6'$ and the other faintest one ($V{\approx}19.^{m}3$) located in the outer part of $r{\approx}13'$. Also a bluest star of (B - V) $\approx$ -0.5 at $V{\approx}17.^{m}2$ is found but it is located at the outer part of $r{\approx}13'$ in NE region. Therefore, the membership of the faintest BHB star and bluest star is suspected. The luminosity function(LF) and mass function(MF) for NGC 6752 were derived for MS stars. The LF for stars of $M_v\;<\;6^m$ in the outer part of r > 8' shows a consistency with that derived by Penny & Dickens(1986).

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.397-399
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• 2015

Recently, cosmic voids have been recognized as a powerful cosmological probe. A number of studies have focused on the effects of the gravitational lensing by voids on the temperature (and in some cases polarization) anisotropy of the Cosmic Microwave Background (CMB) background at relatively large to medium scales, l ~ 1000. Many of these studies attempt to explain the unusually large cold spot in CMB temperature maps and dynamical evidence of dark energy via detections of late-time integrated Sachs Wolfe (ISW) effect. Here, the effects of lensing by voids on the CMB temperature anisotropy at small scales, up to l = 3000, will be investigated. This work is carried out in the light of the benefits of adding large catalogues of cosmic voids, to be identified by future large galaxy surveys such as EUCLID and LSST, to the analysis of CMB data such as those from Planck mission. Our numerical simulation utilizes two methods, namely, the small-de ectionangle approximation and full ray-tracing analysis. Using the fitted void density profiles and radius (RV ) distribution available in the literature from N-body simulations, we simulated the secondary temperature anisotropy (lensing) of CMB photons induced by voids along a line of sight from redshift 0 to 2. Each line of sight contains approximately 1000 voids of effective radius $RV_{,eff}=35h^{-1}Mpc$ with randomly distributed radial and projected positions. Both methods are used to generate temperature maps. The two methods will be compared for their accuracy and effciency in the implementation of theoretical modeling.

• Journal of The Korea Institute of Healthcare Architecture
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• v.22 no.1
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• pp.51-61
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• 2016

Purpose: To improve and establish functions for public health centers in rural public, an analysis will be done on arrangement plan and area by function for public health centers in farming and fishing villages. After finding out this relationship and architectural characteristics, spatial organization and area ratio for providing efficient medical service and the relationship between the two will be examined. Methods: 8 of them were selected and site visit and interview with the person in charge were conducted to investigate the current status. The drawings collected for analysis were input as CAD data and schematized. The relationship between the arrangement type and area for the public health centers in farming and fishing villages was analyzed and based on this, an analysis was done on agricultural scale and characteristics, and putting these analyzed results together, an appropriate method of improvement was proposed for spatial organization by function for public health centers in farming and fishing villages and to provide efficient service. Results: Firstly, the Plan types found in the public health centers in farming and fishing villages could be classified into three including single-type, multiple-type and radial-type. Secondly, according to an analysis of areas by function, in the case of treatment function, there was a difference in the area ration for selective treatment. This ratio is considered to be greatly influenced by the project each public health center focuses on. Thirdly, I could become aware of the relationship between spatial organization and area ratio based on the analysis of arrangement and area derived above. Implication: As the data to refer to in future research on spatial organization for public health centers, if the object of analysis becomes more expanded and investigated, it will be utilized in detail for spatial planning of public health centers, thereby being expected to contribute to more efficient and qualitatively enhanced medical service provided by public health centers.

• Nuclear Engineering and Technology
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• v.35 no.4
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• pp.356-368
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• 2003

Material properties such as coolant specific heat, film heat transfer coefficient, cladding thermal conductivity, surface diffusion coefficient of the multi-bubble are improved in MACSIS-Mod1. The axial power and flux profile module was also incorporated with irradiation history. The performance and feasibility of the updated driver fuel pin have been analyzed for nominal parameters based on the conceptual design for the KALIMER breakeven core by MACSIS-MOD1 code. The fuel slug centerline temperature takes the maximum at 700mm from the bottom of the slug in spite of the nearly symmetric axial power distribution. The cladding mid-wall and coolant temperatures take the maximum at the top of the pin. Temperature of the fuel slug surface over the entire irradiation life is much lower than the fuel-clad eutectic reaction temperature. The fission gas release of the driver fuel pin at the end of life is predicted to be $68.61\%$ and plenum pressure is too low to cause cladding yielding. The probability that the fuel pin would fail is estimated to be much less than that allowed in the design criteria. The maximum radial deformation of the fuel pin is $1.93\%$, satisfying the preliminary design criterion ($3\%$) for fuel pin deformation. Therefore the conceptual design parameters of the driver fuel pin for the KALIMER breakeven core are expected to satisfy the preliminary criteria on temperature, fluence limit, deformation limit etc.