• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.11
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• pp.1440-1448
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• 2004

Multiple solutions in natural convection of air (Pr=0.7) between two horizontal walls with mean temperature difference and the same periodic nob-uniformities are investigated. An analytical solution is found for small Rayleigh number, and the general solution is investigated by using a numerical method. In the conduction-dominated regime, two upright cells are formed between two walls over one wave length. When the wave number is small, the flow becomes unstable with increase of the Rayleigh number, and multicellular convection occurs above a critical Rayleigh number. The multicellular flows at high Rayleigh numbers consist of approximately square-shape cells. And several kinds of multiple flows classified by the number of cells are found.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2248-2253
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• 2008

A numerical study on oscillatory thermocapillary flow in half-zone has performed to understand the effect of axial rotation. 2d unsteady code is developed to observe the onset of oscillation. 2cs Silicone oil with Prandtl number of 26.5 is used as a working fluid. The critical temperature difference at onset of oscillation is investigated under the different aspect ratios and rotation modes. It is shown that the onset of oscillation is delayed when aspect ratio reduces and rotating speed increases. The oscillatory flow is strongly reduced under top rotation and co-rotation modes, while it is augmented under bottom rotation and counter-rotation modes. It is thought that interaction between return flow and bottom wall is important to explain the oscillatory flow.

• Coupled systems mechanics
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• v.12 no.1
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• pp.21-40
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• 2023

In thisstudy, the vibration problem ofthermo elastic carbon nanotubes conveying pulsating viscous nano fluid subjected to a longitudinal magnetic field is investigated via Euler-Bernoulli beam model. The controlling partial differential equation of motion is arrived by adopting Eringen's non local theory. The instability domain and pulsation frequency of the CNT is obtained through the Galerkin's method. The numerical evaluation of thisstudy is devised by Haar wavelet method (HWM). Then, the proposed model is validated by analyzing the critical buckling load computed in presentstudy with the literature. Finally, the numerical calculation ofsystem parameters are shown as dispersion graphs and tables over non local parameter, magnetic flux, temperature difference, Knudsen number and viscous parameter.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.05a
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• pp.1-2
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• 2009

The high critical current ($I_c$, A) of SmBCO coated conductor in a magnetic field, the high production rate and the high material yield are promising for applications. The inhomogeneity of Ie at the long length coated conduct is very important problem for electric application. So we researched the reason of inhomogeneity of $I_c$ at long length tape prepared by batch type co-evaporation system called by EDDC. The long length SmBCO coated conductors were developed on $LaMnO_3/IBAD-MgO/Y_2O_3/Al_2O_3$/Hastelloy C276 template. The distribution of $I_c$ are from 0 to 397 A/cm at 77 K and self field. We have studied the microstructures of these films by using SEM, EDS and X-ray diffraction. The XRD and composition by EDS results of SmBCO film reveals subtle difference. But, the microscopic observation by SEM show the microcrack at the sample with low $I_c$.

• Atmosphere
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• v.30 no.3
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• pp.221-236
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• 2020

The Gangneung region has the complicated geographical characteristics being adjacent to East Sea and Taeback mountains, and thus sea breeze could play an important role in local weather in various aspects. This study aims to understand overall characteristics of sea breeze largely based on long-term (2009~2018) ground-based observation data. We also propose a selection criteria of sea breeze occurrence day; 1) daily precipitation is less than 10 mm, 2) surface wind direction is 0~110° (northerly to easterly) for more than 3 hours during the daytime, 3) wind direction is 110~360° for more than 3 hours during the nighttime, and 4) land and sea temperature difference is positive during the daytime, 5) sea and land sea-level pressure difference is more than 0.5 hPa. As a result, a total of 595 days was selected for the past 10 years. The occurrence of sea breeze is the highest in late Spring to early Summer (May to June). The passage time of sea breeze at the inland station (1.6 km farther inland) is one hour later than the coastal station. On the typical sea breeze event of April 12, 2019, the passage speed and duration of sea breeze was 15 km hr^-1 and about 9 hours, respectively, with its depth of about 500 m and its head swelling. The current results emphasize the critical role of sea breeze in forecasting surface temperature and wind, and contribute to relieve heat wave especially in summer in the Yeongdong region.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2743-2759
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• 2020

A detailed computational fluid dynamics (CFD) simulation analysis model was developed using ANSYS CFX 16.1 and analyzed to simulate the basic design and internal flow characteristics of a 180 MW small modular reactor (SMR) with a natural circulation flow system. To analyze the natural circulation phenomena without a pump for the initial flow generation inside the reactor, the flow characteristics were evaluated for each output assuming various initial powers relative to the critical condition. The eddy phenomenon and the flow imbalance phenomenon at each output were confirmed, and a flow leveling structure under the core was proposed for an optimization of the internal natural circulation flow. In the steady-state analysis, the temperature distribution and heat transfer speed at each position considering an increase in the output power of the core were calculated, and the conceptual design of the SMR had a sufficient thermal margin (31.4 K). A transient model with the output ranging from 0% to 100% was analyzed, and the obtained values were close to the T_hot and T_cold temperature difference value estimated in the conceptual design of the SMR. The K-factor was calculated from the flow analysis data of the CFX model and applied to an analysis model in RELAP5/MOD3.3, the optimal analysis system code for nuclear power plants. The CFX analysis results and RELAP analysis results were evaluated in terms of the internal flow characteristics per core output. The two codes, which model the same nuclear power plant, have different flow analysis schemes but can be used complementarily. In particular, it will be useful to carry out detailed studies of the timing of the steam generator intervention when an SMR is activated. The thermal and hydraulic characteristics of the models that applied porous media to the core & steam generators and the models that embodied the entire detail shape were compared and analyzed. Although there were differences in the ability to analyze detailed flow characteristics at some low powers, it was confirmed that there was no significant difference in the thermal hydraulic characteristics' analysis of the SMR system's conceptual design.

• Water for future
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• v.5 no.2
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• pp.17-29
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• 1972

The persent study aims at finding out a means of prevention cool spell damages on the hilly areas. The irrigation plots of 24 hour stored water warm water way and warm water plots, cool water way are respectively established to find out water temperature and influnce on the growing rice plants. The results obtained are summed up as follows. 1. Warm water areas consisted of $5 m^2 Q=0.93 1{\ell}/sec$, V=31 cm/sec, S=1/1, 000, L=81.6m, B=5cm, h=6cm, t=4min 33sec, drops=9 areas, are constructed to help the water temperature of $14.5^{\circ}C$ rise to that of $21.6^{\circ}C$. This indicates lower temperature than $23^{\circ}C$ of critical water temperature in irrigation facilities by $1.45^{\circ}C$ and than $26.2^{\circ}C$ of balanced water temperature of Seoul arears by $4.6^{\circ}C$. But this does not give much influance on rice plant cultivation. 2. The rising of water temperature is influened according to the temperature, solar radiation but the water temperature changes according to the heat absorption of organized materials, weather and terraces. The difference of water temperature could be found in the first growing stage. 3. Through the warm water way of water rises to the temperature of $21.6^{\circ}C$ which also rises to the temperature of around $30^{\circ}C$ in the paddy field of submerged irrigation. The rice plants are comparatively free from prolonged cool damage, reproduction abstructive damage. 4. The water temperature in rice field in proportion to temperature influence of weather condition but the water temperature approaches to that of weather in the days of later growing stage and water temperature become lower than the air temperature in the fruit stage. 5. The water in the submreged field is $10^{\circ}C$ warmer than in the warm water way during the first growing stage period but the water temperature in the warm water way is warmer in the later growing stage period. The cool water of $14.5^{\circ}C$ is warmed to $30.1^{\circ}C$ and rice plants cultivation is free from other damages. 6. The 12% increased production or 570.98kg/10a is made cool water plot by rising the temperature of water from $14.5^{\circ}C$ to $21.6^{\circ}C$ making the water run through warm water way. 7. The damage inflicted by the cool water irrigation during the first growing stage period is the obstruction of peak tillering stage and the obstruction of heading the later growing stage period and the obstruction of fruiting and number of panides per fill.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.2
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• pp.272-277
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• 1998

Filtering rates of two farming ascidians Styela clava and S. plicata, and of a farming mussel Mytilus edulis were experimentally investigated with reference to effects of water temperature and size. Absorptiometric determinations of filtering rates were carried out in a closed system with experimental animals being decreased indicate dyes neutral red. Optical density (OD) of 440 nm in path length 22 mm cell used as the indication of food particles absorption was appeared directly in proportion with the concentration of neutral red dyes. The filtering rate F is calculated by Kim's equation $F\;=\;V(1-e^{-z})$, where V is the water volume ($\ell$) in the experimental jar, and Z is the decreasing coefficient of OD as meaning of instantaneous removal speed as In $C_t\;=\;In\;C_{o}-Z{\cdot}t$, in this formula $C_t$ is OD at the time t. Filtering rate of S. clava increased as exponential function with increasing temperature while not over critical limit, and the critical temperature for filtering rate was assumed to be between $28^{\circ}C$ and $29^{\circ}C$. In case of S. plicata, the critical temperature was to be below $13^{\circ}C$, and through the temperature range $15\~25^{\circ}C$ appeared a little difference in level even though with significant. M. edulis was not appear any significant effects by water temperature less than $29^{\circ}C$. The model formula derived from the results is as below, where F is filtering rate (${\ell}/hr/animal$), T is water temperature ($^{\circ}C$), and DW is dry meat weight (g) of experimental animal. $$S.\;Clava;\;F\;=\;e xp\;(0.119\;T-4.540)\;(DW)^{0.6745},\;T<29^{\circ}C$$) $$S.\;plicata;\;F\;=\;e xp\;(A_t)\;(DW)^{0.5675},\;(13^{\circ}C $$[A_t =-8.56+0.6805\;T-0.0153\;T^2]$$ $$M.\;edulis;\;F\;=\;0.3844\;(DW)^{0.4952},\;<29^{\circ}C$$)

• Korean Journal of Agricultural and Forest Meteorology
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• v.20 no.1
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• pp.135-143
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• 2018

The effect of elevated temperature on temperate paddy rice will be significant for dependable food supply in East Asia. Using temperature gradient field chamber (TGFC), which was designed to make the horizontal air temperature gradient by $0^{\circ}C$ to $3^{\circ}C$ higher than outside, we examined the measurement to understand the effects of extremely high temperature on paddy rice. In particular, the data of the year 2016, the worst heat wave in over 22 years, was analyzed in this study. The rice height in the relatively warmed condition was rapidly increased during early growth stage. However, the average grain weight and number of spikelet per panicle in the warmed chamber condition were gradually declined with increasing air temperature averaged for 40 days after first heading in each chamber. In particular, the grain yield was more dramatically decreased by the raising temperature because the percent ripened grain was quickly dropped as getting over the threshold temperature for pollination. Therefore, the surplus photosynthetic product by such lower grain filling rate may disturbed the decreases of the NDVI (Normalized Difference Vegetation Index) and SPAD chlorophyll values after first (normal) heading. In addition, the late-emerging head grain were appeared. However, this yield was too small to recover the normal yields decreased by extremely high temperature condition. Our result represented that the warmed condition in 2016 would be the critical limit for the stable yield of temperate paddy rice.

• Korean Journal of Agricultural and Forest Meteorology
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• v.10 no.1
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• pp.25-31
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• 2008

Information on daily maximum air temperature is important in predicting the status of plants and insects, but the uneven and sparse distribution of weather stations prohibits timely access to the data in regions with complex topography. Since cumulative solar irradiance plays a critical role in determining daily maximum temperature on any sloping surfaces, derivation of a quantitative relationship between cumulative solar irradiance and the resultant daily maximum temperature is a prerequisite to development of such estimation models. Air temperatures at 8 sideslope locations with similar elevation and slope angle but aspect, circumventing a cone-shaped, grass-covered parasitic volcano (c.a., 570 m diameter for the bottom circle and 90m bottom-to-top height), were measured from June to December in 2007. Daily maximum temperatures from each location were compared with the average of 8 locations (assumed to be the temperature measured at a "horizontal reference" position). The temperature deviation at all locations increased with the day of year (or sun elevation) from summer solstice to winter solstice. Averaged over the entire period, the south facing location was warmer by $1^{\circ}C$ in daily maximum temperature than "horizontal reference" and the north facing location was cooler by $0.8^{\circ}C$ than the reference, resulting in the year round average south-north temperature difference of $1.8^{\circ}C$. In November, both south and north facing slopes showed the greatest deviation of $+2.0^{\circ}C$ and $-1.3^{\circ}C$, respectively in daily maximum temperature at monthly scale. On a daily scale, the greatest deviation was +3.8 and $2.7^{\circ}C$ at the south and north slope, respectively. The cumulative solar irradiance (on the slope for 4 hours from 11:00 to 15:00 TST) explained >60% of the variance in daily maximum temperature deviations among 8 locations, suggesting a feasibility of developing an estimation model for daily maximum temperature over complex topography at landscape scales.