• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.4
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• pp.283-289
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• 2008

An experimental investigation was conducted to investigate the heat/mass transfer for impingement/effusion cooling system with inclined jet. Jets with inclined angle of 60 are applied to impingement/effusion cooling. At the jet Reynolds number of 10,000, the experiments were carried out for blowing ratios ranging from 0.0 to 1.5. The local heat/mass transfer coefficients on the effusion plate are measured using a naphthalene sublimation method. The result indicates that the inclined jet causes the non-uniform and low heat/mass transfer compared to the vertical jet. At stagnation region, the peak position is shifted from the geometrical center of injection hole due to Coanda effect and its level is higher than that of vertical jet due to increase in turbulence intensity by steep velocity gradient near the stagnation region. Further, the secondary peak region disappears because the interaction between adjacent wall jets weakens. When the initial crossflow occurs, the distorted heat/mass transfer pattern appears. As the blowing ratio (crossflow rate) increases, the heat/mass transfer distributions become similar to those of the vertical jet. This is because the effect of crossflow is dominant compared to that of inclined jet under high blowing ratio $(M{\geq}1.0)$. At low blowing ratio $(M{\leq}0.5)$, averaged Sh value is 10% lower than that of vertical jet, whereas its value at high blowing ratio $(M{\geq}1.0)$ is similar to that of vertical jet.

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
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• v.14 no.2
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• pp.60-67
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• 2008

Purpose : The purpose of this study is to investigate that the change of lower-limb muscle activity when normal gait and assistive gait of older. Methods : The selected subjects of this study were 11 older who be in good physical health and have not problem to gait and over 60 age to analyze the muscle activity. This study has been conducted to analyze the muscle activity of normal gait and assistive gait in unitary status without any contrast group. We have them gait condition of a gradient of 0% and velocity of 1km/h, 2km/h, 3km/h electrode were attached to the motor point of Rectus femoris, Hamstrings, Tibialis anterior, Calf muscle. When normal gait and assistive gait performs, there are meaningful differences that the muscle activity takes a small drop in Rectus femoris by 9.17% at 1km/h, 9.79% at 2km/h, 13.80% at 3km/h, hamstring by 14.78% at 1km/h, 17.82% at 2km/h, 17.26% at 3km/h, Tibialis anterior by 24.38% at 1km/h, 23.85% at 2km/h, 33.52% at 3km/h, Calf muscle by 13.68% at 1km/h, 16.70% at 2km/h, 18.37% at 3km/h(p<0.05). Results : They show the significant difference in statistical figure. We've received the significant through the comparison between normal gait and assistive gait. These results will be utilized for the preliminary date in the future.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.6
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• pp.29-34
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• 2006

This study experimentally investigates the characteristics of Lamb wave propagating in a composite plate of varied thickness. In practical aerospace structures, there are so many parts that have varied thickness. Therefore, in order to employ the Lamb wave in a structural health monitoring of those parts, it is necessary to understand correctly the characteristics of Lamb wave for the structure with thickness variation. Thin surface-bonded piezoelectric transducers, which have great potential in integrated monitoring systems for structural health, were used to generate and receive Lamb waves. The predicted propagation velocity under the assumptions of ideal mode conversions was compared with the experimentally measured one. The validity of the results was supported by the frequency analysis of the signals. Consequently, the results show that the transient region is occurred when Lamb waves propagate across the region that thickness variation over some gradient exists.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.11 s.242
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• pp.1265-1276
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• 2005

The elliptic conceptual second moment models for turbulent heat fluxes, which are proposed on the basis of elliptic-blending and elliptic-relaxation equations, are applied to calculate the combined forced and natural turbulent convection in a vertical plane channel. The models satisfy the near-wall balance between viscous diffusion, viscous dissipation and temperature-pressure gradient correlation, and also have the characteristics of approaching its respective conventional high Reynolds number model far away from the wall. Also the models are closely linked to the elliptic blending model which is used for the prediction of Reynolds stress. In order to calibrate the heat flux models, firstly, the distributions of mean temperature and scala flux in fully developed channel flow with constant wall difference temperature are solved by the present models. The buoyancy effect on the turbulent characteristics including the mean velocity and temperature, the Reynolds stress tensor, and the turbulent heat flux vector are examined. In the opposing flow, the turbulent transport is greatly enhanced with both the Reynolds stresses and the turbulent heat fluxes being remarkably increased; whereas, in the aiding flow, the opposite change is observed. The results of prediction are directly compared to the DNS to assess the performance of the model predictions and show that the behaviors of the turbulent heat transfer in the whole flow region are well captured by the present models.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.5
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• pp.505-513
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• 2010

The tribrachial flame has attracted interest as a basic structure of the flame edge. This flame structure helps understand stabilization of laminar flames and re-ignition of turbulent flames. A number of analytical and experimental studies have been carried out on the tribrachial flame. However, the effect of the variation of the flammability limits on the structure of the tribrachial flame has not been studied in detail. In this study, the effect of non-symmetric flammability limits on the flame structure was investigated by adopting a simple numerical scheme based on several laminar flame theories. A fixed velocity field was considered and boundary matching algorithm was used on the premixed branch. The variation of the diffusion branches under the non-symmetric flammability limits and heat loss was investigated. The formation and extinction of the diffusion branch behind the premixed branch were successfully described. This basic study can help understand the fundamental structure of the flame and can form the basis of subsequent detailed studies.

• Journal of Wetlands Research
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• v.13 no.2
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• pp.363-375
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• 2011

Recently, Water quiality of urban river largely have gotten better by virtue of sewer pipe laying and sewage treatment plants construction. or the various contaminants which is flowed in into river have generated underwater ecosystem disturbance and red tide by lack of sewage and waste water disposal facilities. With tidal river, taehwa river of ulsan metropolitan city has large river width and gradual stream bed gradient at the dry and storage period. Moreover, the flow is paralyzed due to the bridge pier protection work, consist of the mat foundation which is about 1.2km from two bridge and the contaminant is accumulated. it is caused by of the red tide generated from the several years or it activates. In this study, When flow area is largest by changing independent footing of bridge pier of two bridges and using RMA2 model, we hydraulically analyzed a variable breadth of velocity and discharge. Consequently, flow rate increased the maximum 103%, discharge was exposed to increase the maximum 61%. Directly this cannot extinguish the red tide but suppresses the red tide occurrence or can reduce. And it is determined to prevent the depositioning of the contaminant and can control fundamentally the red tide occurrence cause.

• Journal of Biomedical Engineering Research
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• v.23 no.4
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• pp.281-286
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• 2002

In this study, blood flow in a carotid artery supplying blood to the human's brain has been numerically simulated to find out how the blood flow affects the genesis and the growth of atherosclerosis and arterial thrombosis. Velocity Profiles and hemodynamic parameters have been investigated for the carotid arteries with three different stenoses under physiological flow condition. Blood has been treated as Newtonian and non-Newtonian fluid. To model the shear thinning properties of blood for non-Newtonian fluid, the Carreau-Yasuda model has been employed. The result shows that the wall shear stress(WSS) increases with the development of stenosis and that the wall shear stress in Newtonian fluid is highly evaluated compared with that in non-Newtonian Fluid. Oscillatory shear index has been employed to identify the time-averaged reattachment point and this point is located farther from the stenosis for Newtonian fluid than for non-Newtonian fluid The wall shear stress gradient(WSSG) along the wall has been estimated to be very high around the stenosis region when stenosis is developed much and the WSSG peak value of Newtonian fluid is higher than that of non-Newtonian fluid.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.2
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• pp.101-109
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• 2005

The purpose of this study is to investigate the performance of outdoor heat exchanger for heat pump using carbon dioxide. Two types of fin and tube heat exchangers (2 rows for type A and 3 rows for B) are tested. Both heat exchangers have counter-cross flow and 1-circuit arrangement. Test results such as heat transfer rate, pressure drop characteristics and temperature distribution in the heat exchanger are shown with respect to mass flow rate of refrigerant and frontal air velocity For cooling mode, the minimum temperature difference between air and refrigerant of type B is smaller than that of type A by $1^{circ}C$, but the pressure loss of air side is much higher for type B by $29\%$. It is found that a large temperature gradient of carbon dioxide during gas cooling Process Promotes thermal conduction through tube wall and fins which results in degradation of heat transfer performance. For heating mode operation, type B heat exchanger shows higher heat transfer performance compared to type A. However, because pressure loss of refrigerant side of type B is much greater than that of type A, the refrigerant outlet pressure of type B becomes lower than that of type A.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.5
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• pp.419-428
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• 2014

This paper presents a numerical simulation method for the flow around advancing ships in regular waves by using a rectilinear grid system. Because the grid lines do not consist with body surface in the rectilinear grid system, the body geometries are defined by the interaction points of those grid lines and the body surface. For the satisfaction of body boundary conditions, no-slip and divergence free conditions are imposed on the body surface and body boundary cells, respectively. Meanwhile, free surface is defined with the modified marker density method. The pressure on the free surface is determined to make the pressure gradient terms of the governing equations continuous, and the velocity around the free surface is calculated with the pressure on the free surface. To validate the present numerical method, a vortex induced vibration (VIV) phenomenon and flows around an advancing Wigley III ship model in various regular waves are simulated, and the results are compared with existing and corresponding research data. Also, to check the applicability to practical ship model, flows around KRISO Container Ship (KCS) model advancing in calm water are numerically simulated. On the simulations, the trim and the sinkage are set free to compare the running attitude with some other experimental data. Moreover, flows around the KCS model in regular waves are also simulated.

• Journal of the Korean Wood Science and Technology
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• v.15 no.2
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• pp.53-66
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• 1987

Korean red pine (Pinus densiflora S. et. Z.) and pitch pine(Pinus rigida Mill) $5{\times}10cm$ dimension lumber were dried in a kiln providing a cross-circulation velocity of 5 m/sec at dry-and wet-bulb temperatures of 116 and $71^{\circ}C$, followed by 3 hours at 91 and $85^{\circ}C$. Compared to dimension lumber dried lumber were as follows. 1. To dry to 10 percent moisture content, the high-temperatures schedule of Korean red pine and pitch pine lumber took less than one seventh the time required by the conventional kiln drying schedule. 2. High-temperature drying rate and conventional drying rate to 10 percent moisture content of Korean red pine lumber were 2.75 and 0.35%/hr, and those of pitch pine lumber were 3.38 and 0.46%/hr respectively. 3. Compared to lumber of both species on conventional schedule, moisture gradient of high-temperature lumber was greater. 4. Compared to lumber on conventional schedule, maximum surface checking of high-temperature lumber of both species was severer, and maximum end checking of high-temperature lumber of both species was similar to that of lumber on conventional schedule. 5. Compard to lumber on conventional schedule, Korean red pine lumber dried at high temperature showed more honeycombing, but pitch pine lumber dried at high-temperature showed significantly slighter honeycombing. 6. Compared to lumber on conventional schedule, the high-temperature lumber showed less warping lumber of both species. 7. Collapse and casehardening of Korean red pine and pitch pine lumber on both scheules were slight.