• Journal of the Korean Society of Fisheries and Ocean Technology
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• 제36권1호
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• pp.60-65
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• 2000

The virtual mass of net is an important parameter in the analysis and control of net movement in the water. This experiment was performed with the purpose of getting a relation on the quantity of netting and virtual mass of trawl nets using the circulating water channel that can control flow speed. Twelve types of conical nets were examined. Resistance of the conical net at the steady and acceleration state was recorded as text on the personal computer through the tension meter and current meter. The results were obtained as follows ;1. Resistance(R) of the conical net is proportional to the degree of attack angle in the sam e amount of twine material.2. Coefficient of the resistance(Cd)could be defined by the following regression model as a function of Reynolds Number(Re). Cd=0.039Re-0.14743. Resistance(R) is proportional to TSA(Twine surface area) and defined as follows; R=21.398TSA-0.12194. Coefficient of virtual mass(CM) could be calculated by the following first order regression model. CM=37.557U-8.96845. Virtual mass is directly proportional to Volume of net(V) or d/l.

• Bulletin of the Korean Mathematical Society
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• 제51권1호
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• pp.55-66
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• 2014

In this paper, the authors establish the conditions for the extinction of solutions, in finite time, of the fast diffusive p-Laplace equation $u_t=div({\mid}{\nabla}u{\mid}^{p-2}{\nabla}u)+a{\int}_{\Omega}u^q(y,t)dy$, 1 < p < 2, in a bounded domain ${\Omega}{\subset}R^N$ with $N{\geq}1$. More precisely, it is shown that if q > p-1, any solution vanishes in finite time when the initial datum or the coefficient a or the Lebesgue measure of the domain is small, and if 0 < q < p-1, there exists a solution which is positive in ${\Omega}$ for all t > 0. For the critical case q = p-1, whether the solutions vanish in finite time or not depends crucially on the value of $a{\mu}$, where ${\mu}{\int}_{\Omega}{\phi}^{p-1}(x)dx$ and ${\phi}$ is the unique positive solution of the elliptic problem -div(${\mid}{\nabla}{\phi}{\mid}^{p-2}{\nabla}{\phi}$) = 1, $x{\in}{\Omega}$; ${\phi}(x)$=0, $x{\in}{\partial}{\Omega}$. This is a main difference between equations with local and nonlocal sources.

• Proceedings of the KSME Conference
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• 대한기계학회 2002년도 학술대회지
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• pp.479-482
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• 2002

Riblets with longitudinal grooves along the streamwise direction have been used as an effective flow control technique for drag reduction. A flexible micro-riblet with v-grooves of peak-to-peak spacing of $300{\mu}m$ was made using a MEMS fabrication process of PDMS replica. The flexible micro-riblet was attached on the whole surface of a NACA0012 airfoil with which grooves are aligned with the streamwise direction. The riblet surface reduces drag coefficient about $7.9{\%}\;at\;U_o=3.3m/s$, however, it increases drag about $8{\%}\;at\;U_o=7.0m/s$, compared with the smooth airfoil without riblets. The near wake has been investigated experimentally far the cases of drag reduction ($U_o\;=\;3.3 m/s$) and drag increase ($U_o\;=\;7 m/s$). Five hundred instantaneous velocity fields were measured for each experimental condition using the cross-correlation PIV velocity field measurement technique. The instantaneous velocity fields were ensemble averaged to get spatial distribution of turbulent statistics such as turbulent kinetic energy. The experimental results were compared with those of a smooth airfoil under the same flow condition. The micro-riblet surface influences the near wake flow structure largely, especially in the region near the body surface

• International Journal of Air-Conditioning and Refrigeration
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• 제9권2호
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• pp.85-93
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• 2001

The present study experimentally investigated the effect of refrigeration oil on the condensation heat transfer for R-22 and R-407C in a microfin tube with a U-bend. Mineral oil and POE oil were used for R-22 and R-407C respectively. Experimental parameters were an oil concentration from 0 to 5%, a mass flux from 100 to 400 $kg/m^2s$ and an inlet quality from 0.5 to 0.9. The enhancement factors for both R-22 and R-407C refrigerants at the first straight section decreased continuously as the oil concentration increased. The decreased rapidly as the mass flux decreased and the inlet quality increased. The heat transfer coefficients in the U-bend showed the maximum at the 90$^{\circ}$position. the heat transfer coefficients at the second straight section within the dimensionless length of 48 were larger by a maximum of 33% than the average heat transfer coefficient at the first straight section.

• Geomechanics and Engineering
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• 제21권6호
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• pp.503-511
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• 2020

This study evaluated the side resistance of drilled shafts socketed into rock sections. Commonly used analysis methods for side resistance of piles in rocks are examined by utilizing a large number of load test data. The analysis of the unit side resistance of pile foundations embedded into rock sections is based on an empirical coefficient (α) and the uniaxial compressive strength (q_u) or its root (${\sqrt{q_u}}$). The Davisson criterion was used to interpret the resistance capacity from the load test results to acquire the computed relationships. The α-${\sqrt{q_u}}$ relationship is proven to be reliable in the prediction of friction resistance. This study further analyzed the relationship by including the effect of rock quality designation (RQD) on the results. Analysis results showed that the analysis model of α-${\sqrt{q_u}}$-RQD provided better prediction and reliability considering the RQD classification. Based on these analyses, the side resistance of drilled shafts socked into rocks is provided with statistical data to support the analysis.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제12권6호
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• pp.541-549
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• 2000

The present study experimentally investigated the effect of refrigeration oil on the condensation heat transfer for R-407C and R-22 in a microfin tube with a U-bend. POE oil ($74.1\;\textrm{mm}^2/s,\;40^{\circ}C$,) and mineral oil $62.5\;\textrm{mm}^2/s,\;40^{\circ}C$,) were used for R-407C and R-22 respectively Experimental parameters were an oil concentration from 0 to 5%, a mass flux from 100 to $400kg/m^{2}s sand an inlet quality from 0.5 to 0.9. The enhancement factors for both R-22 and R-407C refrigerants at the first straight section decreased continuously as the oil concentration increased. They decreased rapidly as the mass flux decreased and the inlet quality increased. The heat transfer coefficients in the U-bend showed the maximum at the $90^{\circ}$/TEX> position. The heat transfer coefficients at the second straight section within the dimensionless length of 48 were larger by a maximum of 33% than the average heat transfer coefficient at the first straight section.

• Nuclear Engineering and Technology
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• 제53권2호
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• pp.611-617
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• 2021

The mechanical properties of α-Na₃(U_0.84(2),Na_0.16(2))O₄ have been researched using the first-principles calculations combined with the quasi-harmonic Debye model. The obtained lattice parameters agree well with the published experimental data. The results of elastic constants indicate that α-Na₃(U_0.84(2),Na_0.16(2))O₄ is mechanically stable. The polycrystalline moduli are predicted. The results show that the α-Na₃(U_0.84(2),Na_0.16(2))O₄ exhibits brittleness and possesses obvious elastic anisotropy. The hardness shows that it can be considered a "soft material". Furthermore, the Debye temperature θ_D and the minimum thermal conductivity k_min are also discussed, respectively. Finally, the thermal expansion coefficient α, isobaric heat capacity C_P and isochoric heat capacity C_V are evaluated through the quasi-harmonic Debye model.

• The Journal of Engineering Geology
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• 제21권3호
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• pp.259-269
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• 2011

Concentrations of uranium (U) and radon (Rn) were measured in groundwater from 74 wells in the Icheon area, with the aim of determining the range and distribution of concentrations in an area underlain by granite (in this case, the Icheon granite). U concentrations ranged from 0.02 to 1,640.0 ${\mu}g/L$ (median value, 2.03 ${\mu}g/L$) and Rn concentrations ranged from 40 to 23,400 pCi/L (median value, 4,649 pCi/L). U concentrations in 10.8% of the samples exceeded 30 ${\mu}g/L$, which is the maximum contaminant level (MCL) proposed by the US Environmental Protection agency (EPA), based on the chemical toxicity of U. In addition, U concentrations in 59.5% and 13.5% of the samples exceeded 4,000 pCi/L (the Alternative MCL (AMCL) of the US EPA) and 8,100 pCi/L (Finland’s guideline level), respectively. We found no significant correlations between U (Rn) and other constituents, except for U-$HCO_3$ (correlation coefficient of 0.71), U-Ca (0.69), U-Li (0.45), U-Sr (0.43), and U-F (0.42). U and Rn contents in the groundwater are low relative to those in areas in other countries with similar geological settings, possibly due to the inflow of shallow groundwater to the wells in the Icheon area.

• Journal of the Korean Society of Radiology
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• 제18권2호
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• pp.93-99
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• 2024

The digital medical imaging, especially, computed tomography (CT), should necessarily be considered in terms of noise distribution caused by converting to X-ray photon to digital imaging signal. Recently, the denoising technique based on deep learning architecture is increasingly used in the medical imaging field. Here, we evaluated noise reduction effect according to various noise types based on the U-net deep learning model in the lung CT images. The input data for deep learning was generated by applying Gaussian noise, Poisson noise, salt and pepper noise and speckle noise from the ground truth (GT) image. In particular, two types of Gaussian noise input data were applied with standard deviation values of 30 and 50. There are applied hyper-parameters, which were Adam as optimizer function, 100 as epochs, and 0.0001 as learning rate, respectively. To analyze the quantitative values, the mean square error (MSE), the peak signal to noise ratio (PSNR) and coefficient of variation (COV) were calculated. According to the results, it was confirmed that the U-net model was effective for noise reduction all of the set conditions in this study. Especially, it showed the best performance in Gaussian noise.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제30권3호
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• pp.278-286
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• 2006

Experiments were conducted to estimate the performance of drag force type vertical axis wind turbine with an opening-shutting rotor. It was operated by the difference in drag force generated on both sides of the blades. The rotational speed was measured by a tachometer in a wind tunnel and the tunnel wind speed was measured by using a pilot-static tube and a micro manometer. The performance test for a prototype was accomplished by calculating power, power coefficient, torque coefficient from the measurement of torque and rpm by a dynamometer controller. Various design parameters, such as the number of blades(B), blade aspect ratio(W/R), angle of blades$(\alpha)$ and drag coefficient acting on a blade, were considered for optimal conditions. At the experiment of miniature model, maximum efficiency was found at N=15, $\alpha=60^{\circ}$ and W/R=0.32. The measured test variables were power, torque, rotational speed, and wind speeds. The data presented are in the form of power and torque coefficients as a function of tip-speed ratio V/U. Maximum power was found in case of $\Omega=0.33$, when the power and torque coefficient were 0.14 and 0.37 respectively. Comparing model test with prototype test, similarity law by advance ratio for vertical axis wind turbine was confirmed.