• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.9
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• pp.821-826
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• 2016

The leak before break (LBB) concept is used in pipe line design for nuclear power plants. For application of the LBB concept, leak rates through cracks should be evaluated accurately. Usually leak late analyses are performed for through-thickness cracks with constant cross-sectional area. However, the cross-sectional area at the inner pipe surface of a crack can be different from that at the outer surface. In this paper, leak rate analyses are performed for the cracks with linearly-varying cross-sectional areas. The effect of varying the cross-sectional area on leak rates was examined. Leak rates were also evaluated for cracks in bi-material pipes. Finally, the effects of crack surface morphology parameters on leak rates were examined.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.2
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• pp.147-156
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• 2006

Statement of problem: The high melting temperature and chemical reactivity of titanium necessitates casting machines different from those used in conventional casting. Despite the new developments in Ti casting systems , inadequate mold filling and internal porosity are frequently observed casting defects. Therefore, the study on the fabrication technique including sprue design to solve these casting defects is still necessary. Purpose: The purpose of this study was to evaluate the effect of sprue design and cross sectional area of sprue on the internal porosity. Materials and methods: 30 simulated cast three units titanium crowns were prepared. 5 cast crowns for each with different sprue design(sinlge sprue, double sprue and plate sprue) of two cross sectional areas (small and large cross sectional areas) were fabricated. The sections of titanium castings were photographed in a microscope at ${\times}100$ magnification to record internal porosities. Results and Conclusion: Within the limits of this study, the following conclusions were drawn: 1. There was a significantly lower in internal porosity of titanium castings for large cross sectional area of sprue group than the small group (P<.05) 2. There was no significant difference in internal porosity among sprue designs in similar cross sectional area of sprue (P>.05).

• Journal of the Korean Society for Precision Engineering
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• v.17 no.9
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• pp.174-180
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• 2000

A reliable analytic model that determines the cross sectional shape of a workpiece(material) in round-oval(or oval-round) pass sequence has been developed. the cross sectional shape of an outgoing workpiece is predicted by using the linear interpolation of the radius of curvature of an incoming workpiece and that of roll groove to the roll axis direction. The requirements we placed on the choice of the weighting function were to ensure boundary conditions specified. The validity of the analytic model has been examined by hot rod rolling experiment with the roll gap and specimen size changed. The cross sectional shape and area of a workpiece predicted by the proposed analytic model were good agreement with those obtained experimentally. It was found that the analytic model has not only simplicity and accuracy for practical usage but also save a large amount of computational time compared with finite element method.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.12
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• pp.1056-1062
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• 2002

This paper reports the characteristics of the three dimensional turbulent flow in the 180 degree bends with decreasing cross-sectional area by numerical method. Calculated pressure and velocity, Reynolds stress distributions are compared to the experimental data. Turbulence model employed are low Reynolds number k-epsilon model and algebraic stress model. The results show that the main vortex generated from the inlet part of the bend maintained to outlet of the bend because of the contraction of cross-sectional area. The rate of increase of turbulent kinetic energy through the bend are lower than that of mean flow. Secondary flow strength of the flow is lower about 60% than that of square duct flow.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.9
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• pp.804-810
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• 2004

This paper reports the characteristics of the three dimensional turbulent flow by numerical method in the 180 degree bends with increasing cross-sectional area. Calculated pressure and velocity, Reynolds stress distributions are compared to the experimental data. Turbulence model employed are low Reynolds number $textsc{k}$-$\varepsilon$ model and algebraic stress model(ASM). The results show that the main vortex generated from the inlet part of the bend maintained to outlet of the bend and vortices are continually developed at the inner wall region. The distribution of turbulent kinetic energy along the bend are increase up to 120$^{\circ}$ because of increment of cross-sectional area. Secondary flow strength of the flow is lower about 60% than that of square duct flow.

• Magazine of the Korea Concrete Institute
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• v.2 no.3
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• pp.65-72
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• 1990

Theoretical expressions were dcrived for the numher of fibers per unit cross-sectional area in fiber reinforced concrete, with due consideration given to the effects of the surrounding boundaries. The number of fibers per unit cross-sectional area in steel fiber reinforced concrete was also measured experimentally for the specimens incorporating various volume fractions of fibers of different types. Statistical evaluation of the measured value was then performed in order to assess the differences in fiber concentration at different location on tbe cross section. Degree of reorientation of steel fibers in concrete occuring during vibration was examined by com¬paring the differences in the computed and measur'ed values of the number of fibers per unit cross-sectional area.

• Structural Engineering and Mechanics
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• v.37 no.3
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• pp.309-320
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• 2011

As a new type of large-span space structure, suspendome is composited of the upper single-layer reticulated shell and the lower cable-strut system. It has better mechanical properties compared to single-layer reticulated shell, and the overall stiffness of suspendome structure increases greatly due to the prestress of cable. Consequently, it can cross a larger span reasonably, economically and grandly with high rigidity, good stability and simple construction. For a better assessment of the advantages of mechanical characteristic of suspendome quantitatively, the static behavior of Kiewitt6 suspendome was studied by using finite element method, and ADINA was the software application to implement the analysis. By studying a certain suspendome, the internal forces, deformation and support constrained forces of the structure were obtained in this paper. Furthermore, the influences of parameters including prestress, stay bar length, cross-sectional area and rise-to-span ratio were also discussed. The results show that the increase of prestress and vertical stay bar length can improve the stiffness of suspendome; Cross-sectional area has nearly no impact on the static behavior, and the rise-to-span ratio is the most sensitive parameter.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.61-64
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• 2008

The present study of these experiments are close examination of spray characteristics that are continuous liquid jet and modulated pressure pulse liquid jet. The experiments were conducted using water, over a range of cross-flow velocities from 42${\sim}$136 m/s, with injection frequencies of 35.7${\sim}$166.2 Hz. Between continuous cross-flow jet and pressure pulsed cross-flow jet for characteristics of penetration, breakup point, spray angle and macro spray shape are investigated experimentally. In cross-flow field, main parameter of liquid jet for breakup was cross-flow stream rather than pressure pulse frequency. As oscillation of the periodic pressure that could make liquid jet moved up and down, the mixing efficiency was increased. Also, a bulk of liquid jet puff was detected at upper field of liquid surface. So, this phenomenon has a good advantage of mixing spray from concentration of center area to outer area. Because of pressure pulsation frequency, an inclination of SMD for the structured layer was evanescent. Cross-sectional characteristics of SMD at downstream area were non-structured distributions. Then cross-sectional characteristics of SMD size were about same tendency over a range that is effect of spray mixing. The tendency of volume flux value for various frequency of pressure pulse was same distribution. And volume flux was decreased when the frequency of pressure pulse increase.

• Journal of computational fluids engineering
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• v.20 no.3
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• pp.62-69
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• 2015

Pressure change inside cabin as well as in tunnel has been calculated to assess the passenger pressure comfort of high-speed train. $C-STA^{TM}$, a CFD program based on axi-symmetric Navier-Stokes equation and Roe's FDS has been used to simulate the pressure change in tunnel during a high-speed train passing through it. To present the relative motion between the train and the tunnel, a modified patched grid scheme based on the structured grid system has been employed. The simulation program has been validated by comparing the simulation results with field measurements. Extensive parametric study has been conducted for various train speed, tunnel cross-sectional area and tunnel length to the pressure change in cabin. KTX-Sancheon(KTX2) high-speed train has been chosen for simulation and the train speed have been varied from 200 km/h to 375 km/h. The tunnel length has been varied from 300 m to 7.5 km and tunnel area from $50m^2$ to $120m^2$. Total 504 simulations have been conducted varying the parameters. Based on the database produced from the parametric simulations, minimum tunnel cross-sectional area has been surveyed for various train speeds based on Korean regulation on pressure change in cabin.

• Journal of the Korean Society of Industry Convergence
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• v.24 no.6_1
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• pp.683-691
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• 2021

Bipolar plates with channel width of 0.5 mm, 0.4 mm, and 0.3 mm respectively were printed using a 3D printer. The shape of three b ipolar plates was rectangular, the channel depth was 0.5 mm, and the thickness of base was 0.5 mm. The bipolar plate with channel width of 0.5 mm had 45 channels, and their active area was 44.5 mm × 50 mm. The bipolar plate with channel width of 0.4 mm had 57 channels and its active area was 45.2 mm × 50 mm, and the bipolar plate with channel width of 0.3 mm had 75 channels and its active area was 44.7 mm × 50 mm. The bipolar plates were printed using PLA filament. The cross-sectional lengths of the bipolar plates with channel widths of 0.5 mm and 0.4 mm were identical by 96% of the designed cross-sectional length. Whereas the bipolar plate with a channel length of 0.3 mm had a large difference of 25% from the designed cross-sectional length.