• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.6
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• pp.421-428
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• 2008

In this paper, we investigated the flow of an incompressible viscous fluid past a sphere which is oscillated one-dimensionally over flow regimes including laminar flow at Reynolds number of 100, 200 and Strouhal number of up to 5000. In order to analyze flow and estimate critical Strouhal number, we introduce three-dimensional vortex element method. With this method, separation only appears in decreasing velocity region during the high Strouhal numbers. We find out that vorticity distribution around sphere is proportionl to the Strouhal number. And we can decide that low Strouhal number is below 100, high Strouhal number is above 500 from many results. Thus the critical Strouhal number(St) effected to the flow field is expected to be 100

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.3
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• pp.529-561
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• 2014

The two-phase turbulent flow past an interface-piercing circular cylinder is studied using a high-fidelity orthogonal curvilinear grid solver with a Lagrangian dynamic subgrid-scale model for large-eddy simulation and a coupled level set and volume of fluid method for air-water interface tracking. The simulations cover the sub-critical and critical and post critical regimes of the Reynolds and sub and super-critical Froude numbers in order to investigate the effect of both dimensionless parameters on the flow. Significant changes in flow features near the air-water interface were observed as the Reynolds number was increased from the sub-critical to the critical regime. The interface makes the separation point near the interface much delayed for all Reynolds numbers. The separation region at intermediate depths is remarkably reduced for the critical Reynolds number regime. The deep flow resembles the single-phase turbulent flow past a circular cylinder, but includes the effect of the free-surface and the limited span length for sub-critical Reynolds numbers. At different Froude numbers, the air-water interface exhibits significantly changed structures, including breaking bow waves with splashes and bubbles at high Froude numbers. Instantaneous and mean flow features such as interface structures, vortex shedding, Reynolds stresses, and vorticity transport are also analyzed. The results are compared with reference experimental data available in the literature. The deep flow is also compared with the single-phase turbulent flow past a circular cylinder in the similar ranges of Reynolds numbers. Discussion is provided concerning the limitations of the current simulations and available experimental data along with future research.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.7
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• pp.948-955
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• 2003

Pressure coefficient in rotating discharge hole was measured to gain insight into the influence of rotation to the discharge characteristics of rotating discharge hole. Pressure measurements were done by the telemetry system that had been developed by the authors. The telemetry system measures static pressure using piezoresistive pressure sensors. Pressure coefficients in rotating discharge hole were measured in longitudinal direction and circumferential direction with various rotating speed and 3 pressure ratios. From the results, the pressure coefficient, and therefore the discharge coefficient, is known to decrease with the increase of Ro number owing to the increase of flow approaching angle to the discharge hole inlet. However, there exists critical Ro number where the decrease rate of discharge coefficient with the increase of Ro number changes abruptly; flow separation occurs from the discharge hole exit at this critical Ro number. Critical Ro number increases with the increase of length-to-diameter ratio, but the increase is small where the length-to-diameter ratio is higher than 3. The decrease rate of discharge coefficient with the increase of Ro number depends on the pressure recovery at the discharge hole, and the rate is different from each length-to-diameter ratio; it has tendency that the short discharge hole shows higher decrease rate of discharge coefficient.

• Women's Health Nursing
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• v.17 no.3
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• pp.265-274
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• 2011

Purpose: This study determined the correlation between nurses' critical thinking disposition; problem solving process; and nursing performance. It also examined the impact of critical thinking disposition and problem solving process on nursing performance. Methods: The data was collected from 419 nurses. Descriptive statistics, t-test, ANOVA, scheffe test, pearson correlation analysis and multiple regression analysis were performed. Results: Nursing performance showed that there were differences according to age, marital status, educational level, total number of years in the career and the length of employment in the present department. The problem solving process showed differences in the educational level. Critical thinking disposition showed differences according to age, educational level and total number of years in the career. Problem solving process and nursing performance showed a positive relationship whereas critical thinking disposition and nurses' performance showed a positive relationship. Factors affecting nursing performance, were nurses' age, duration of employment in the present department, problem solving process and critical thinking disposition. This model was statistically significant and showed 22.1% of the total variance. Conclusion: The attention of nursing administrators should be drawn to the consideration that a certain amount of experience in the current department is positively related to nursing performance. Furthermore, in order to provide a improvement in professional nursing performance, educational programs towards nurses' critical thinking disposition and problem solving process should be provided.

• Acute and Critical Care
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• v.33 no.4
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• pp.197-205
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• 2018

Lung transplantation is widely accepted as the only viable treatment option for patients with end-stage lung disease. However, the imbalance between the number of suitable donor lungs available and the number of possible candidates often results in intensive care unit (ICU) admission for the latter. In the ICU setting, critical care is essential to keep these patients alive and to successfully bridge to lung transplantation. Proper management in the ICU is also one of the key factors supporting long-term success following transplantation. Critical care includes the provision of respiratory support such as mechanical ventilation (MV) and extracorporeal life support (ECLS). Accordingly, a working knowledge of the common critical care issues related to these unique patients and the early recognition and management of problems that arise before and after transplantation in the ICU setting are crucial for long-term success. In this review, we discuss the management and selection of candidates for lung transplantation as well as existing respiratory support strategies that involve MV and ECLS in the ICU setting.

• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.4
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• pp.269-278
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• 2004

Recently, critical velocity has become a topic to attract most interests from the researchers in the field of tunnel safety. As the minimum velocity to prevent smoke backlayering during a fire, many equations have been proposed so far, and the following three equations are being considered as a standard method in Korea to calculate the capacity of smoke extraction fans. Equation by Kennedy based on Froude number, Tetzner' s equation with additional variable, ${\beta}$ to modify the Kennedy's equation, and the equation with the concept of super critical velocity by Wu are studied in this paper for the comparative purpose. A contour map describing the relationship between the critical velocity and the capacity of smoke extraction fans is proposed as a tool to calculate the number of jet fans for smoke control during a fire in the local tunnels.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.9
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• pp.2981-2990
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• 1996

Dual solutions for steady natural convection of air between two horizontal concentric cylinders are numerically investigated in the range of $D_i$/TEX>/L(=diameter of inner cylinder/gap width)$\leq$10. It is found that, when the Rayleigh number based on the gap width exceeds a certain critical value, a new flow pattern forming two counter-rotating eddies in the half of the annulus can be realized, which is different from the crescent-shaped flow commonly observed. In the new flow pattern, the fluid near the top of the hot inner cylinder moves downward. This solution is found for D$_{i}$/L.geq.0.3, but not for$D_i$/TEX>/L$\leq$0.2. As $D_i$/TEX>/L increase, the critical Rayleigh number is decreased, and tends to a finite limit.t.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.783-788
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• 2000

Flow fields in two-dimensional plane channels with thin obstacles("baffles and blocks") mounted symmetrically in the vertical direction and periodically in the streamwise direction are studied numerically to understand how various geometric conditions influence the critical Reynolds number and pressure drop. Changing BR(the ratio of channel to baffle interval) from 1:1 to 1.5, we computed the critical Reynolds number and pressure drop. Especially when BR is 1:3, at which the critical Reynolds number turned out to be minimal, we added blocks in the geometry in order to study their destabiliting effects on the flows.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.10C
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• pp.937-945
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• 2009

In this paper, we investigate into the existence and various properties of absorbing sets in regular LDPC codes with variable node degree three. Also, we figure out the critical number of some absorbing sets that are believed to be the major cause of error floor in (3,5) Tanner LDPC codes.

• Journal of computational fluids engineering
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• v.9 no.4
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• pp.1-6
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• 2004

This study investigates the transition of flows in a natural convection problem with periodic wall temperatures of the form, T/sub L/=T₁＋δ Tsinκχ and T/sub L/=T₂＋δ Tsinκχ .The fluid considered is air with P/sub γ/=0.7. In the conduction-dominated regime with a small Rayleigh number, two large cells are formed over one wave length, for all wave numbers. When k≤1.8, the flow becomes unstable with increase of the Rayleigh number, and multicellular convection occurs above a critical Rayleigh number. The flow patterns are classified by the number of eddies over one wave length, and several kinds of transition phenomena, such as 2→3→4, 4→3→2, and 2→4 eddy flow, occur with increase( or decrease) of the Rayleigh number. Dual solutions are found above a critical Rayleigh number, and an anomalous bifurcation is observed.