• Nuclear Engineering and Technology
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• v.29 no.4
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• pp.291-298
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• 1997

In advanced nuclear reactors, the passive containment cooling has been suggested to enhance the safety. The passive cooling has two mechanisms, air natural convection and oater cooling with evaporation. To confirm the coolability of PCCS, many works have been performed experimentally and numerically. In this study, the water cooling test was performed to obtain the evaporative heat transfer coefficients in a scaled don segment type PCCS facility which have same configuration with AP600 prototype containment. Air-steam mixture temperature and velocity, relative humidity and well heat flux are measured. The local steam mass flow rates through the vertical plate part of the facility are calculated from the measured data to obtain evaporative heat transfer coefficients. The measured evaporative heat transfer coefficients are compared with an analytical model which use a mass transfer coefficients. From the comparison, the predicted coefficients show good agreement with experimental data however, some discrepancies exist when the effect of wave motion is not considered. Finally, a new correlation on evaporative heat transfer coefficients are developed using the experimental values.

• Ocean and Polar Research
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• v.21 no.2
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• pp.87-97
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• 1999

To estimate absolute transports by advection in the southwestern East Sea (Japan Sea), an inverse method was applied to CTD data obtained in July 1993. The relative velocities are calculated using the thermal wind equation. The inverse model was formulated to obtain a reference velocity based on the mass conservation in each of four vertical layers within a region enclosed by hydrographic sections and the coastal boundary. The flow patterns in the surface layer are clockwise and anti-clockwise in the regions south and northwest of Ulleung Island, respectively, and a strong northward flow appears in between them. In the second layer, the flow fields are generally weak. The inverse calculation yields the southward flow along the coast, and this suggests that the subsurface low salinity water in the Ulleung Basin is supplied by the southward transport along the east coast of Korea.

• Bulletin of the Society of Naval Architects of Korea
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• v.12 no.1
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• pp.37-40
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• 1975

Heave and pitch amplitude and phase lag, relative vertical displacement, velocity and acceralation at bow as bow motion and wave exciting force and moment of a DWT 260,000 ton class tanker in the regular head wave have been calculated. All the calculations have been made by the computer program SD08 of Seoul National University. As the results it is cleared heave amplitude and acceralation have large value in the ballast condition and low Froude-number than full load condition and higher Froude numer as for as the $\frac{\lambda}{L}$ is lower than near around 1.0, however they have quite large values as $\frac{\lambda}{L}$ goes up.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.1
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• pp.34-44
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• 2000

In this paper, a modified skyhook control for the semi-active Macpherson suspension system is investigated. A new model for the semi-active type suspension, which incorporates the rotational motion of the unsprung mass, is introduced and an output feedback control law using the skyhook control method is derived. The gains in the skyhook controller are adaptively adjusted by estimating the road conditions. Because two vertical acceleration sensors, one for the sprung mass and another for the unsprung mass, are used rather than using the angle sensor for the rotational motion of the control arm, the relative velocity of the rattle space is filtered using the acceleration signals. For testing the control performance, the actual damping force has been incorporated via the hardware-in-the-loop simulations. The performances of a passive damper and a semi-active damper are compared. Simulation results are provided.

• International Journal of Internet, Broadcasting and Communication
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• v.13 no.1
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• pp.47-53
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• 2021

Gait kinematics and kinetics have a similar tendency between men and women, yet it remains unclear how walking while carrying a load affects the gait mechanism. Twenty adults walked with preferred velocity on level ground of 20 m relative to change of a load carriage (no load, 15%, 30% of the body weights) aimed to observe gait mechanism. We measured gait posture using the three-dimensional image analysis and ground reaction force system during stance phase on left foot. In main effect of gender difference, men showed increased displacement of center of gravity (COG) compared to women, and it showed more extended joint angle of hip and knee in sagittal plane. In main effect of a load difference, knee joint showed more flexed postuel relative to increase of load carriage. In main effect of load difference on the kinetic variables, medial-lateral force, anterior-posterior force (1st breaking, 2nd propulsive), vertical force, center of pressure (COP) area, leg stiffness, and whole body stiffness showed more increased values relative to increase of load carriage. Also, men showed more increased COP area compared to women. Interaction showed in the 1st anterior-posterior force, and as a result of one-way variance analysis, it was found that a load main effect had a greater influence on the increase in the magnitude of the braking force than the gender. The data in this study explains that women require little kinematic alteration compared to men, while men in more stiff posture accommodate an added load compared to women during gait. Additionally, it suggests that dynamic stability is maintained by adopting different gait strategies relative to gender and load difference.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.5
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• pp.399-406
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• 2016

The large scale wind turbine blades usually experience periodic change of inflow speed due to blade rotation inside the ground shear flow region. Because of the vertical wind shear, the inflow velocity in the boundary layer region is maximum at uppermost position and minimum at lowermost position. These spatial distribution of wind speeds can lead to the periodic oscillation of the 6-component loads at hub and low speed shaft of the wind turbine rotor. In this study we compare the aerodynamic loads between two inflow conditions, i.e, uniform flow (no vertical wind shear effect) and normal wind profile. From the computed results all of the relative errors for oscillating amplitudes increased due to the ground shear flow effect. Especially bending moment and thrust at hub, and bending moments at LSS increased enormously. It turns out that the aerodynamic analysis including the ground shear flow effect must be considered for fatigue analysis.

• Journal of the Korean Geotechnical Society
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• v.28 no.9
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• pp.5-15
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• 2012

Field monitoring data for embankments in thirteen road construction sites at coastal area of the Korean Peninsula were analyzed to investigate the characteristics of lateral flow in soft grounds, to which vertical drain methods were applied. First of all, the effect of the embankment scale on the lateral flow was investigated. Thicker soft soils and lager relative embankment scale produced more horizontal displacements in soft grounds. Especially, if thick soft grounds were placed, the relative embankment scale, which was given by the ratio of thickness of soft ground to the bottom width of embankments, became larger and in turn large horizontal displacement was produced. And also higher filling velocity of embankments induced more horizontal displacements in soft grounds. The other major factors affecting the lateral flow in soft ground were the thickness and undrained shear strength of soft grounds, the soil modulus and the stability number. Maximum horizontal displacement was induced by less undrained shear strength and soil modulus of soft grounds. Also more stability numbers produced more maximum horizontal displacements. When the shear deformation does not develop, the stability number was less than 3.0 and the safety factor of bearing was more than 1.7. However, if the stability number was more than 5.14 and the safety factor of bearing was less than 1.0, the unstable shear failure developed in soft ground. 50mm can be recommended as a criterion of the allowable maximum horizontal displacement to prevent the shear deformation in soft ground, while 100mm can be recommended as a criterion of the allowable maximum horizontal displacement to prevent the shear failure in soft ground.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.4
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• pp.683-690
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• 2012

In this work, the semi-active control of a large-sized bus suspension system with an MR damper was studied. An MR damper model that can aptly describe the hysteretic characteristics of an MR damper was adopted. Parameter values of the MR damper model were suitably modified by considering the maximum damping force of a passive damper used in the suspension system of a real large-sized bus. In addition, a fuzzy logic controller was developed for semi-active control of a suspension system with an MR damper. The vertical acceleration at the attachment point of the MR damper and the relative velocity between sprung and unsprung masses were used as input variables, while voltage was used as the output variable. Straight-ahead driving simulations were performed on a road with a random road profile and on a flat road with a bump. In straight-ahead driving simulations, the vertical acceleration and pitch angle were measured to compare the riding performance of a suspension system with a passive damper with that of a suspension with an MR damper. In addition, a single lane change simulation was performed. In the simulation, the lateral acceleration and roll angle were measured in order to compare the handling performance of a suspension system using a passive damper with that of a suspension system using an MR damper.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.21 no.1
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• pp.11-15
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• 1988

Square slices of sea tangle was dried in constant condition of thickness (1.54mm), air temperature $(50^{\circ}C)$, relative humidity $(30\%)$ and air velocity (0.4m/s). The shrunk surface area and the shrinking rate were investigated. The results obtained are summarized as follows : 1) Comparing the shrinking of transverse section with that of vertical section, the transverse section was proceeded more double shrinkage than vertical section. 2) The shrunk surface area curve showed nearly a linear shrinkage up to 90min of drying time. 3) The shrinking rate was rapidly increased in first falling rate period, and was largest in the early period of second falling rate period.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.1
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• pp.16-22
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• 2012

Experimental investigations were carried out to examine the heat and mass transfer characteristics of LiCl aqueous solution for a plate heat exchanger type dehumidifier. Cooling dehumidification was adopted vertical type heat exchanger. Also non woven fabric is attached surface of the heat exchanger for spreadability of LiCl aqueous solution. Mass flow-rate of LiCl aqueous solution and concentration were selected as experimental conditions. Also, In this study, the effects of relative humidity of process air and velocity were investigated experimentally. As a result of heat transfer coefficient and mass transfer coefficient of were increased film reynolds number increased. heat transfer coefficient and mass transfer coefficient of LiCl aqueous solution were 0.14~0.24 kW/$m2^{\circ}C$ and $1.3{\times}10-63{\sim}6.2{\times}10-6$ m/s respectively.