• Nuclear Engineering and Technology
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• v.42 no.4
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• pp.382-393
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• 2010

Thermal mixing by steam jets in a pool is dominantly influenced by a turbulent water jet generated by the condensing steam jets, and the proper prediction of this turbulent jet behavior is critical for the pool mixing analysis. A turbulent jet flow induced by a steam jet discharged through a vertical upward single hole into a subcooled water pool was subjected to computational fluid dynamics (CFD) analysis. Based on the small-scale test data derived under a horizontal steam discharging condition, this analysis was performed to validate a CFD method of analysis previously developed for condensing jet-induced pool mixing phenomena. In previous validation work, the CFD results and the test data for a limited range of radial and axial directions were compared in terms of profiles of the turbulent jet velocity and temperature. Furthermore, the behavior of the turbulent jet induced by the steam jet through a horizontal single hole in a subcooled water pool failed to show the exact axisymmetric flow pattern with regards to an overall pool mixing, whereas the CFD analysis was done with an axisymmetric grid model. Therefore, another new small-scale test was conducted under a vertical upward steam discharging condition. The purpose of this test was to generate the velocity and temperature profiles of the turbulent jet by expanding the measurement ranges from the jet center to a location at about 5% of $U_m$ and 10 cm to 30 cm from the exit of the discharge nozzle. The results of the new CFD analysis show that the recommended CFD model of the high turbulent intensity of 40% for the turbulent jet and the fine mesh grid model can accurately predict the test results within an error rate of about 10%. In this work, the turbulent jet model, which is used to simply predict the temperature and velocity profiles along the axial and radial directions by means of the empirical correlations and Tollmien's theory was improved on the basis of the new test data. The results validate the CFD model of analysis. Furthermore, the turbulent jet model developed in this study can be used to analyze pool thermal mixing when an ellipsoidal steam jet is discharged under a high steam mass flux in a subcooled water pool.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.8-14
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• 2019

A drop structure, one of the representative river-crossing structures, is constructed to stabilize a riverbed. On the other hand, the structure interrupts the continuity of the river and causes the destruction of the hydro-ecological environment. Therefore, laboratory experiments of a natural type of drop structure with low differences were performed, and the empirical formula of a local scour hole is proposed. Four experimental flow rates were tested for various types of the drop structure models with 28 test cases. Based on the scour test, it was confirmed that the maximum scour depth occurs rather than the result of applying the previously proposed scour depth formulae. Correlation analysis of the major factors of scour hole at the downstream of the drop structure revealed a strong correlation between the upstream flow characteristics, drop structure height, and total crossing length of the drop model. In addition, the depth and length estimation formula of the maximum scour hole were proposed using the dimensionless variables and validated. In the future, it is also expected that more accurate scour prediction and calculation can be derived by conducting experimental studies and numerical analysis considering the various bed materials and flow conditions.

• Steel and Composite Structures
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• v.18 no.4
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• pp.811-831
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• 2015

This paper focuses on the strengthening methods used for improving the compression behaviors of perforated box-section walls as provided in the anchorage zones of steel pylons. Rectangular plates containing double-row continuous elliptical holes are investigated by employing the boundary condition of simple supporting on four edges in the out-of-plane direction of plate. Two types of strengthening stiffeners, named flat stiffener (FS) and longitudinal stiffener (LS), are considered. Uniaxial compression tests are first conducted for 18 specimens, of which 5 are unstrengthened plates and 13 are strengthened plates. The mechanical behaviors such as stress concentration, out-of-plane deformation, failure pattern, and elasto-plastic ultimate strength are experimentally investigated. Finite element (FE) models are also developed to predict the ultimate strengths of plates with various dimensions. The results of FE analysis are validated by test data. The influences of non-dimensional parameters including plate aspect ratio, hole spacing, hole width, stiffener slenderness ratio, as well as stiffener thickness on the ultimate strengths are illustrated on the basis of numerous parametric studies. Comparison of strengthening efficiency shows that the continuous longitudinal stiffener is the best strengthening method for such perforated plates. The simplified formulas used for estimating the compression strengths of strengthened plates are finally proposed.

• Journal of the Korean Wood Science and Technology
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• v.44 no.5
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• pp.736-742
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• 2016

Wooden dowels are commonly used to join the wooden members together in many types of structures, But little information is available concerning their holding properties in domestic wood. This study was performed to determine the withdrawal loads and strengths on the effect of diameter of dowel and hole clearance. The test block was manufactured from 15 mm thick korean red pine and korean pine. The dowel was manufactured 6, 8 and 10 mm diameters from korean castanea, korean pine and tuliptree. Research reported here indicates that withdrawal loads increase, but withdrawal strengths decrease, in a linear fashion as the dowel diameter increases. This study also indicates that dowel withholding load and strength increase in a linear fashion as a hole clearance decreases.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.796-801
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• 2001

During cold operation period, fuel injection system directly contributes the unburned hydrocarbon formation in spark ignition engines. The relationship between injection parameters and HC emission behavior was investigated through a series of experiments. Spray behavior of port fuel injectors was characterized through a quantitative evaluation of mass concentration of liquid fuel by a patternator and PDA. 6-hole injector was found to produce finer spray than single hole one. Using a purpose-built test rig, the wall wetting fuel was measured, which was mostly affected by wall temperature. Varying coolant temperature($20{\sim}80^{\circ}C$), HC emissions were measured in a production engine. With respect to the different types of injectors, HC emission was also measured. In the 6-hole injector application, the engine produced less HC emission in low coolant temperature region. Though it produces much more amount of wetting fuel, it has the advantages of finer atomization quality. In high coolant temperature region, there was little effect between different types of injectors. The control schemes to reduce HC emissions during cold start could be suggested from the findings that the amount of fuel supply and HC emission could be reduced by utilizing fine spray and high intake wall temperature.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.11
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• pp.17-23
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• 2010

Titanium alloy is one of the hard processing materials made by the traditional manufacturing method because of the excellent mechanical strength. Ablation of titanium alloy is investigated by using a femtosecond laser which is a regenerative amplified Ti:sapphire laser with 1kHz repetition rate, 184fs pulse duration time and 785nm wavelength. Experiments are carried out under various ablation conditions with different pulse overlap ratios for the rectangular shape and micro hole. Test results show that the ablation characteristic according to pulse overlap ratio of titanium alloy seems to be as non-linear type at the different zone of energy fluence. The optimal condition of rectangular shape processing is obtained at the laser peak power 1.3mW, pulse overlap ratio of 90%, beam gap of $1\;{\mu}m$. The micro hole has a good quality from the pulse overlap ratio of 99% at the same laser peak power. With the optimal processing condition, the fine rectangular shape and micro hole without burr and thermal damage are achieved.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.6
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• pp.562-568
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• 2008

In this paper, the hole injection layer(HIL) materials have been synthesized and analyzed. Their HOMO levels are $4.93{\sim}5.22\;eV$, and their energy band gaps are $2.74{\sim}3.19\;eV$. Their glass transition temperatures($T_g$) are all above $114^{\circ}C$, which implies that they are highly thermal-stable. The green OLED devices with a structure of ITO(150 nm)/NEW_HIL(50 nm)/NPB(30 nm)/$Alq_3$(50 nm)/Al:Li(100 nm) were fabricated and tested, incorporating these newly synthesized HIL materials. According to the test results of OLED devices, the I-V-L performances of these devices increase in the following sequence: ELM307 > ELM200 > ELM321 > ELM327 > ELM325. In addition, the OLED device with ELM307 as a HIL has the highest brightness and efficiency at the same driving voltage. These experimental results have shown that ELM307 can be used as one of the most promising candidates for HIL materials.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.11
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• pp.1965-1971
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• 1997

The relaxation of stress concentration in notched members can be very significant in the improvement of notched strength and fatigue life. This paper investigated the relationship of stress concentration factor, and notched strength and fatigue life. The stress concentration factors were analyzed by FEM. Uniaxial tensile and fatigue tests were carried on plain woven composite specimens which have a main hole and two defence holes. From experimental results, the notched strength and the fatigue limit increased up to about 50% and 30% respectively due to the reduction in stress concentration. The fatigue lives predicted by Juvinall's approach were underestimated than test results and this trends were remarkable as nothed strength increased. This is because of the underestimation of a coefficient. A in S-N curve (.sigma.$_{ar}$ =A $N_{f}$ $^{B}$). Therefore, considering notched strength the coefficient A was modified. The fatigue lives by this process were agreed well with the experimental results.sults.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.6
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• pp.15-23
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• 2004

In order to investigate efficiency and flowfield charateristics of the intake-diffuser for the ship waterjet propulsion, new experimental verification technology was set up in the cavitation tunnel. 1-hole and 5-hole pilot tubes were designed and manufactured to measure the pressure and velocity distributions at intake-diffuser entrance and impeller inlet. The calibration of the 5-hole pilot tubes is conducted at the cavitation tunnel The cavitation inception occurs at the intake lip, and the occurrence position depends on IVR (Inlet Velocity Ratio) condition. The present experimental device will be applied sufficiently for the development of the design and performance improvement technologies.

• Korean Journal of Agricultural Science
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• v.42 no.4
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• pp.439-446
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• 2015

Kimbugak is one of Korea's traditional snacks made of laver. This study was conducted to investigate the physical drying and frying characteristics of kimbugaks made by a pasting & garnishing machine. The drying and frying characteristics should be analyzed to develop a continuous operation system for manufacturing kimbugak because kimbugak has a high moisture content after pasting process. Materials for pasting and garnishing on laver were rice gruel and sesame. The aluminum shelf with square hole was selected as a drying shelf. The recommended size of the square hole type was $1.5mm{\times}1.5mm$ because characteristics of deformation and easy separation from the shelf were excellent at the hole size. The drying time of 2 hours was also recommended with the drying temperature of $70^{\circ}C$ based on the test results such as dried condition (good), moisture conten t (3.7%), deformation (12.1 mm), and shrinkage rate (19.8%). As the frying conditions for dried kimbugaks, recommended oil temperature and frying time were $170^{\circ}C$, 15 seconds, respectively when corn oil was used. In the case of frying for undried kimbugaks, recommended oil temperature and frying time were $210^{\circ}C$, 2 - 3 minutes, respectively for improvement of work efficiency.