• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.8 s.227
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• pp.895-901
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• 2004

Single-phase convection and nucleate boiling heat transfer were locally investigated for confined planar water jets. The detailed distributions of the wall temperature and the convection coefficient as well as the typical boiling curves were discussed. The curve for the single-phase convection indicated the developing laminar boundary layer, accompanied by monotonic increase of the wall temperature in the stream direction. Boiling was initiated from the furthest downstream as heat flux increased. Heat transfer variation according to the streamwise location was reduced as heat flux increased enough to create the vigorous nucleate boiling. Velocity effects were considered for the confined free-surface jet. Higher velocity of the jet caused the boiling incipient to be delayed more. The transition to turbulence precipitated by the bubble-induced disturbance was obvious only for the highest velocity, which enabled the boiling incipient to start in the middle of the heated surface, rather than the furthest downstream as was the case of the moderate and low velocities. The temperature at offset line were somewhat tower than those at the centerline for single-phase convection and partial boiling, and these differences were reduced as the nucleate boiling developed. For the region prior to transition, the convection coefficient distributions were similar in both cases while the temperatures were somewhat lower in the submerged jet. For single-phase convection, transition was initiated at $x/W{\cong}2.5$ and completed soon for the submerged jet, but the onset of transition was retarded to the distance at $x/W{\cong}6$ for the fee-surface jet.

• Physical Therapy Rehabilitation Science
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• v.5 no.3
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• pp.149-154
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• 2016

Objective: The arm swing is associated with gait ability in healthy young adults. The purpose of this study was to examine the effects of arm swing during gait in healthy young adults. Design: Cross-sectional study. Methods: Forty-five subjects without any orthopedic or neurological injuries participated in this study. All subjects performed all three conditions according to the arm swing type as follows: first procedure (condition 1), walking as usual without arm swing constraint; second procedure (condition 2), constraint of dominant arm swing walking as usual; third procedure (condition 3), constraint of both arm swing walking as usual. Gait parameters such as gait velocity, stride length, cadence, step time, single limb support, and double limb support were measured in all arm swing conditions performed randomly, with the mean value obtained from three measurements. A rest period of 5 minutes was given to prevent repetition of each condition and learning effect. All data was analyzed using repeated measures ANOVA to notice the changes between arm swing conditions. Results: Within walking conditions, significant difference of gait velocity, stride length, cadence, and double limb support was noticed (p<0.05), except step time and single limb support. Gait velocity and stride length were significant reduced, and in cadence and double limb support were increased (p<0.05). Condition 3 had the most significant decrease of gait ability compared with condition 1 (p<0.05). Conclusions: These finding suggested that constraint arm swing conditions reduced gait ability in healthy young adults. Also, these findings can be utilized as a reference to future studies that not only pelvic, knee and ankle, but also upper limb affect to gait ability.

• Smart Structures and Systems
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• v.26 no.5
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• pp.619-629
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• 2020

Solar towers, which often has a large aspect ratio and low fundamental natural frequency, were extremely prone to large amplitude of wind-induced vibrations, especially Vortex-Induced Vibration (VIV). A tiny Tuned Mass Damper (TMD) with conveniently adjustable eddy current damping was specially designed and manufactured for elastic wind tunnel tests of a solar tower. A series of numerical simulations by using the COMSOL software were conducted to determine three key parameters, including the thickness of the back iron plate and the conductive plate (T_b and T_c), the distance between the magnet and the conductive plate (T_d). Based on the results of numerical simulations, a tiny TMD was manufactured and its structural parameters were experimentally identified. The optimized values of the tiny TMD can be conveniently realized. The tiny TMD was installed at the top of the elastic test model of a 243-meter-high solar tower, and a series of wind tunnel tests were carried out to examine the effectiveness of the TMD in suppressing wind-induced responses of the test model. The results showed that the wind-induced responses could be obviously reduced by the TMD, especially in the cross-wind direction. The cross-wind RMS and peak responses at the critical wind velocity can be reduced by about 86% and 75%, respectively. However, the maximum reduction of the responses at the design wind velocity is about 45%, obviously less than that at the critical wind velocity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.7 s.238
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• pp.878-885
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• 2005

The water jet impingement cooling is one of the techniques to remove the heat from high heat flux equipments. Local heat transfer of the confined water impinging jet and the effect of nozzle collar to enhance the heat transfer are investigated in the fee surface jet and submerged jet. Boiling is initiated from the farthest downstream and increase of the wall temperature is reduced with developing boiling, forming the flat temperature distributions. The reduction in the nozzle-to-surface distance fur H/W$\le$1 causes significant increases and distribution changes of heat transfer. Developed boiling reduces the differences of heat transfer for various conditions. The nozzle collar is employed at the nozzle exit. The distances from heated surface to nozzle collar, Hc are 0.25W, 0.5W and 1.0W. The liquid film thickness is reduced and the velocity of wall jet increases as decreased spacing of collar to heated surface. Heat transfer is enhanced fur region from the stagnation to x/W$\~$8 in the free surface jet and to x/W$\~$5 in the submerged jet. For nucleate boiling region of further downstream, the heat transfer by the nozzle collar is decreased in submerged jet comparing with higher velocity condition. It is because the increased velocity by collar is de-accelerated downstream.

• Fire Science and Engineering
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• v.30 no.1
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• pp.63-73
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• 2016

This study examined the effects of the wind conditions, such as wind velocity and wind directions, on the performance of the mechanical smoke exhaust systems for high-rise building fires. A scaled model design and CFD simulations were used to verify the effects both quantitatively and qualitatively. The results showed that the smoke exhaust velocity of the mechanical exhaust system can be reduced by up to 17% at a wind velocity of 5 m/s (equivalent to an outdoor wind speed of 16 m/s) and a wind direction of ${\theta}=5^{\circ}$. In addition, the angle of the outdoor wind direction below ${\theta}=25^{\circ}$ had a significantly influence on the smoke exhaust flow rate and reduced exhaust performance of the smoke exhaust system in a fire.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1452-1457
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• 2004

The water jet impingement cooling is one of the techniques to remove heat from high heat flux equipments. We investigate the local heat transfer of the confined water impinging jet and the effect of nozzle collar to enhance the heat transfer in the free surface jet and submerged jet. Boiling is initiated from the furthest downstream and the wall temperature increase is reduced with developing boiling, forming the flat temperature distributions. The reduction in the nozzle-to-surface distance for $H/W{\leq}1$ causes the significant increases and distribution changes in heat transfer. Developed boiling reduces the differences in heat transfer for various conditions. The nozzle collar is employed at the nozzle exit. The distances from heated surface to guide plate, $H_c$ are 0.25W, 0.5W and 1.0W. The liquid film thickness is reduced and the velocity of wall jet increase as decreased spacing of collar to heated surface. Heat transfer is enhanced for region from the stagnation to $x/W{\sim}8$ in the free surface jet and to $x/W{\sim}5$ in the submerged jet. For nucleate boiling region of further downstream, the heat transfer by the nozzle collar is decreased in submerged jet compare with higher velocity condition. It is because the increased velocity by collar is de-accelerated at downstream.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.2
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• pp.37-44
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• 2002

A theoretical study of spray and combustion characteristics due to coaxial twin-fluid injection is conducted to investigate the effects of liquid jet property, droplet size, contact length and liquid jet velocity. Model is properly validated with measurements and shows good agreement. Prediction of jet contact length, droplet size, liquid jet velocity reflects genuine features of coaxial injection in physical and practical aspects. Both the jet contact length and tile droplet size are reduced in a linear manner with an increase of injector diameter. Cross sectional area of liquid intact core is reduced with augmented jet splitting rate, thus the jet is accelerated to maintain the mass continuity and with an assistant of momentum diffusion by burnt gas.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.924-932
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• 1992

This paper presents the results of an experimental study on the characteristics of the vortex- induced vibration of an elastically supported circular cylinder in the cross air flow. For a range of velocities, power spectral densities of the signals from a hot-wire anemometer placed in the wake of an oscillating circular cylinder and gap sensors placed in the both ends of a circular cylinder were obtained to determine vortex-shedding frequencies, natural frequencies and vibrating frequencies of a cylinder. The effects of slots in the test section on vortex shedding and cylinder oscillation were investigated. The present study covered the reduced velocity range 1.0 .leg. Ur .leg. 64.6. The response characteristics of the cylinder has been shown to vary extensively, depending on the slots in the test section as well as on the reduced velocity. For an elastically supported cylinder, a purely translation mode oscillation was observed at a low velocity, however a rotation mode oscillation was often superposed for higher velocities. These two oscillating frequencies were equal to their natural frequencies irrespective of the changes of free stream velocities.

• Nutrition Research and Practice
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• v.11 no.4
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• pp.327-333
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• 2017

BACKGROUND/OBJECTIVES: Complications of diabetes, such as cardiovascular disease, are associated with increased mortality among type 2 diabetes mellitus patients. Homocysteine has been recently identified as a predictor of cardiovascular disease-related complications in diabetes. We investigated whether or not supplementation with folic acid tablets can lower homocysteine levels and improve parameters related with vascular complications. SUBJECTS/METHODS: We conducted a non-randomized 8-week trial involving postmenopausal diabetic women (n = 25) supplemented with $800{\mu}g$ of folic acid ($400{\mu}g$ twice a day) daily. Subjects' serum levels of folate, homocysteine, and vitamin $B_{12}$ were measured, along with vascular function and brachial-ankle pulse wave velocity. RESULTS: Folic acid supplementation significantly increased serum folate levels (P < 0.0001), reduced homocysteine levels (P < 0.0001), and increased vitamin $B_{12}$ levels (P = 0.0063). There were significant decreases in low-density lipoprotein cholesterol levels as well as the ratios of low-density lipoprotein cholesterol to high-density lipoprotein cholesterol and total cholesterol to high-density lipoprotein cholesterol. Brachial-ankle pulse wave velocities were not altered by supplementation. Changes in serum vitamin $B_{12}$ after folic acid supplementation were negatively correlated with changes in brachial-ankle pulse wave velocity. CONCLUSIONS: In this study on postmenopausal Korean women with type 2 diabetes mellitus, folic acid supplementation reduced serum homocysteine levels, increased serum folate and vitamin $B_{12}$ levels, and lowered lipid parameters.

• Journal of the Korean Institute of Gas
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• v.7 no.4 s.21
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• pp.24-29
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• 2003

Numerical analysis was conducted to predict the damage of indoor gas explosion for the propagation of explosion flame. Indoor gas diffusion distribution due to gas leakage was obtained by diffusion equation that adopted initial conditions from reference. Enthalpy of each gas-mixture ratio and reduced mechanism was applied to calculate flame temperature, and laminar combustion velocities with the variant of each gas concentration from reference were applied to the gas mixture. Turbulent combustion velocity was modeled by coupling of turbulent energy and laminar combustion velocity in k-$\epsilon$ model. For the analysis of flame propagation cartesian and cylindrical coordinate were used to indoor position and flame propagation respectively. The study analyzes the cause of pressure rising with the variation of flame propagation by glass damage, and the result shows that indoor pressure rising with ignition position varies window dimension.