• Journal of Soil and Groundwater Environment
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• v.18 no.5
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• pp.65-76
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• 2013

The water-table fluctuation (WTF) method has been often used for estimating groundwater recharge by analysis of waterlevel measurements in observation wells. An important assumption inherent in the method is that the water level rise is solely caused by precipitation recharge. For the observation wells located near a stream, however, the water-level can be highly affected by the stream level fluctuations as well as precipitation recharge. Therefore, in applying the WTF method, there should be consideration regarding the effect of stream-aquifer interactions. Analysis of water-level hydrographs from the National Groundwater Monitoring Wells of Korea showed that they could be classified into three different types depending on their responses to either precipitation recharge or stream level fluctuations. A simple groundwater flow model was used to analyze the errors of the WTF method, which were associated with stream-aquifer interactions. Not surprisingly, the model showed that the WTF method could greatly overestimate recharge, when it was used for the observation wells of which the water-level was affected by streams. Therefore, in Korea, where most groundwater hydrographs are acquired from wells nearby a stream, more caution is demanded in applying the WTF method.

• Journal of The Korea Institute of Healthcare Architecture
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• v.24 no.1
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• pp.51-58
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• 2018

Purpose: In this study, through the comparison of the pressure fluctuation and air exchange volume in negative isolation room according to the type of the door and door opening/closing speeds, which is one of the main factors causing the cross contamination of the negative pressure isolation room, establishes standard operating procedures to prevent cross contamination in high risk infectious diseases and isolation room design. Methods: In this study, the air flow each of the room is analyzed using ANASYS CFX CODE for flow analysis. In addition, the grid configuration of the door is constructed by applying Immersed Solid Methods. Results: The pressure fluctuation due to the opening and closing of the hinged door was very large when the moment of the hinged door opened and closed. Especially, at the moment when the door is closed, a pressure reversal phenomenon occurs in which the pressure in the isolation room is larger than the pressure in the anteroom. On the other hand, the pressure fluctuation due to the opening and closing of the sliding door appeared only when the door was closed, but the pressure reversal phenomenon not occurred at the moment when the sliding door was closed, unlike the hinged door. As the opening and closing speed of the hinged door increases, the air exchange volume is increased. However, as the opening and closing speed of the sliding door is decreased, the air exchange volume is increased. Implications: According to the results of this study, it can be concluded that the pressure fluctuation due to the opening and closing of the hinged door is greater than the pressure fluctuation due to the opening and closing of the sliding door. In addition, it can be confirmed that the pressure reversal phenomenon, which may cause to reduce the containment effect in negative pressure isolation room, is caused by the closing of the hinged door. Therefore, it is recommended to install a sliding door to maintain a stable differential pressure in the negative isolation room. Also, as the opening and closing speed of the hinged door is slower and the opening and closing speed of the sliding door is faster, the possibility of cross contamination of the room can be reduced. It is therefore necessary to establish standard operating procedures for negative isolation room for door opening and closing speeds.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.1
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• pp.615-621
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• 2018

To enhance the energy saving and comfort of indoors, this study performed a stimulation of sound fluctuation, color temperature, and aroma. The experiment with EEG, HRV, and Vibra images was conducted in an environmental test room with a temperature of $25[^{\circ}C]$, relative humidity of 50[RH%], air current speed of 0.002[m/s], and illuminance of 1000[lux]. The stimulation experiment set up different sensory stimulation conditions, such as before exposure, single-sensory stimulation of fluctuation a=1.106 jazz music, single-sensory stimulation of RED color lighting, single-sensory stimulation of scent aroma, and multi-sensory stimulation of fluctuation a=1.106 jazz music, RED color lighting, and scent aroma. After the multi-sensory stimulation of fluctuation a=1.106 jazz music, RED color lighting and scent aroma, the capacity for work and attention were increased, and the stress index and fatigue degree were decreased. In addition, multi-sensory stimulation of fluctuation a=1.106 jazz music, RED color lighting, and scent aroma were effective in maintaining a stable heart and health. In addition, the Vibra image appeared to decrease tension/anxiety and stress. The multi-sensory stimulation of fluctuation a=1.106 jazz music, RED color lighting, and scent aroma help increase the Neuro-energy more than that by no exposure and single-sensory stimulation.

• Wind and Structures
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• v.7 no.5
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• pp.317-332
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• 2004

Wind tunnel experiments were conducted under highly turbulent and disturbed flow conditions over a solid/perforated plate with a long splitter plate in its plane of symmetry. The effect of varied level of perforation of the normal plate on fluctuating velocities and fluctuating pressures measured across and along the separation bubble was studied. The different perforation levels of the normal plate; that is 0%, 10%, 20%, 30%, 40% and 50% are studied. The Reynolds number based on step height was varied from $4{\times}10^3$ to $1.2{\times}10^4$. The shape and size of the bubble vary with different perforation level of the normal plate that is to say the bubble is reduced both in height and length up to 30% perforation level. For higher perforation of the normal plate, bubble is completely swept out. The peak turbulence value occurs around 0.7 to 0.8 times the reattachment length. The turbulence intensity values are highest for the case of solid normal plate (bleed air is absent) and are lowest for the case of 50% perforation of the normal plate (bleed air is maximum in the present study). From the analysis of data it is observed that $\sqrt{\overline{u^{{\prime}2}}}/(\sqrt{\overline{u^{{\prime}2}}})_{max}$, (the ratio of RMS velocity fluctuation to maximum RMS velocity fluctuation), is uniquely related with dimensionless distance y/Y', (the ratio of distance normal to splitter plate to the distance where RMS velocity fluctuation is half its maximum value) for all the perforated normal plates. It is interesting to note that for 50% perforation of the normal plate, the RMS pressure fluctuation in the flow field gets reduced to around 60% as compared to that for solid normal plate. Analysis of the results show that the ratio [$C^{\prime}_p$ max/$-C_{pb}(1-{\eta})$], where $C^{\prime}_p$ max is the maximum coefficient of fluctuating pressure, $C_{pb}$ is the coefficient of base pressure and ${\eta}$ is the perforation level (ratio of open to total area), for surface RMS pressure fluctuation levels seems to be constant and has value of about 0.22. Similar analysis show that the ratio $[C^{\prime}_p$ max/$-C_{pb}(1-{\eta})]$ for flow field RMS pressure fluctuation levels seems to be constant and has a value of about 0.32.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2297-2302
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• 2007

Numerical simulations are conducted to analyze conjugate heat transfer characteristics in a ribbed channel. In this simulation, the effects of Reynolds number and heat capacity of the solid channel wall on convective heat transfer are observed in the turbulent flow regime. In the case of the conducting wall against isothermal wall, the relative ratio of the thermal resistance between the solid wall and the flow field varies with Reynolds number. Thus the characteristics of the conjugate heat transfer are changed with the Reynolds number. Heat capacity ratio affects the temperature fluctuation inside solid wall. The temperature fluctuation inside the solid wall decreases with increasing the heat capacity of the solid wall so that the convective heat transfer increases. When the thermal conductivity ratio is smaller than 10, the effects of flow characteristics on heat transfer are changed.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.3037-3045
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• 2011

The optimization of the overhead contact lines according to the increased train speed is to design the low-sag-wire so that the pantograph can follow the vertical fluctuation of the catenary. Main factors for the overhead contact lines design include the span, dropper interval, movable bracket, vertical fluctuation of the catenary, tension, and wave propagation speed. In this paper, a model is proposed to improve the electric railway speed, and the speed improvement analysis technology is examined to ensure the stable and reliable electric railway. In addition, the effect between pantograph and catenary according to the speed improvement is quantitatively analyzed by using simulation.

• Journal of Environmental Science International
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• v.3 no.4
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• pp.333-348
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• 1994

The groundwater levels at 11 sites and the vertical variations o( the water Quality at 1 site were measured to study the characteristic of the groundwater level fluctuation of Cheju Island. The results of the measurements for the groundwater levels were as follows; In the eastern part, inculding Kimnyong, Jongdal and Sungsan, a sinusoidal fluctuation of groundwater levels occurred in response to oceanic tides. The tidal effect on the groundwater level was reduced depending upon the distance from seashore. But time lag showed that the trend is reversed. However, in the Samyang, Kosan and Shinhyo areas show that the groundwater level was directly influenced by the amount of precipitation. Especially, Shinhyo area which southern part in Cheju was affected the most and show upper parabasal groundwater level. In Susan- I which eastern part in Cheju, well rovealed that water Quality changed with the period of a tide. Salinity at the lim, bellow the natural groundwater level, was approched to the brackish groundwater(1000ppm).

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.3
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• pp.328-336
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• 2002

decrease in efficiency due to cavity fluid fluctuation. The purpose of this study is to examine erosion aspect on the SS400 specimen by cavitation and the effect of impact pressure generated from the demolition of the cavity of ultrasonic vibrator horn in the marine sludge oil environment. The erosion damage of specimen was investigated mainly on weight loss, weight loss rate and maximum erosion rate with variation of the vibration amplitude of $50{\mu}m, 24{\mu}m$ as well as the change of space between transducer horn and specimen. The experimental results showed that as the space between ultrasonic vibrator horn and specimen disk increased, the weight loss and weight loss rate decreased and the values were larger in SFO than in SLO. These findings would help interpret the aspect of cavitation erosion damage in metallic materials of different operating environment and material characteristics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.04a
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• pp.229-232
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• 1997

A free space transmission method using standard gain horn antennas in the frequency range from 9.0 to 10.5GHz is applied to determine the dielectric properties of grain such as rough rice, brown rife and barley. The dielectric constant and loss factor, which depend on the moisture content of the wetted grain are obtained from the measured attenuation and phase shift by vector network analyzer. The effect of density fluctuation, which is an important parameter governing the dielectric properties of grain, on the dielectric constant and loss factor is presented. A new density-independent model in terms of measured attenuation and moisture density is proposed for reducing the effects of density fluctuation on the moisture content measurement.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1827-1832
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• 2003

In this research, the simulation method for acoustic sounds by a uniform flow around a two-dimensional circular cylinder by using the finite difference lattice Boltzmann model is explained. To begin with, we examine the boundary condition which determined with the distribution function $f_i^{(0)}$ concerning with density, velocity and internal energy at boundary node. Very small acoustic pressure fluctuation, with same frequency as that of Karman vortex street, is compared with the pressure fluctuation around a circular cylinder. The acoustic sound' propagation velocity shows that acoustic approa ching the upstream, due to the Doppler effect in the uniform flow, slowly propagated. For the do wnstream, on the other hand, it quickly propagates. It is also apparently the size of sound pressure was proportional to the central distance $r^{-1/2}$ of the circular cylinder. The lattice BGK model for compressible fluids is shown to be one of powerful tool for simulation of gas flows.