• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.6
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• pp.795-801
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• 2019

The aim of this study was to investigate the possibility of the skin-friction reduction by vortex control. A vortical system such as a horseshoe vortex, a hairpin vortex, and a wake region was induced around a hemisphere attached on a Perspex flat plate in the circulating water channel. Hairpin vortices were developed from the wake region and horseshoe vortices were formed by an adverse pressure gradient in front of the hemisphere. The horseshoe vortices located on the flank of the hemisphere induced a high momentum flow in the wake region by the direction of their vorticity. This process increased the frequency of the hairpin vortices as well as the frictional drag on the surface of the wake region. To reduce the skin-friction drag, suction control in front of the hemisphere was applied through a hole. Flow visualization was performed to optimize the free-stream velocity, size of the hemisphere, and size of the suction hole. Once the wall suction control mitigated the strength of the horseshoe vortex, the energy supplied to the wake region was reduced, causing the frequency of the hairpin vortex generation to decrease by 36.4 %. In addition, the change in the skin-friction drag, which was measured with a dynamometer connected to a plate in the wake region, also decreased by 2.3 %.

• Membrane Journal
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• v.25 no.4
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• pp.301-309
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• 2015

Importance of pretreatment for seawater desalination is growing rapidly. Proper selection of pretreatment is critical for the successful, long-term operation in the seawater desalination plant such as seawater reverse osmosis (SWRO). The purposes of seawater pretreatment are to remove particulate, colloidal materials, organic, inorganic materials, microorganisms and their by-products present in the seawater, and thus to improve the performance of seawater desalination systems. However, pretreatment is most challenging for designing and operating seawater desalination plants because of fluctuations of water qualities, site specifications and wide ranges of target materials present in the seawater to be treated. In addition, it is also becoming evident increasingly that microscopic algae are a major cause of operational problems, for example, membrane fouling which is long-standing problem in SWRO process. Pretreatment strategies prior to the operation of seawater desalination technologies should be even more complicated by algae blooms and release of their harmful by-products in marine environment. This paper reviews the roles of various pretreatment methods in seawater desalination process. Benefits and drawbacks are described, which should be taken into account in future studies on selecting pretreatment for seawater desalination process.

• Spatial Information Research
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• v.8 no.1
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• pp.85-99
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• 2000

Accurate information on habitat distribution of protected fauna is essential for the habitat management of Korea, a country with very high development pressure. The objectives of this study were to develop a habitat suitability model of wild boar based on GIS and logistic regression, and to create habitat distribution map, and to prepare the basis for habitat management of our country s endangered and protected species. The modeling process of this restudyarch had following three steps. First, GIS database of environmental factors related to use and availability of wild boar habitat were built. Wild boar locations were collected by Radio-Telemetry and GPS. Second, environmental factors affecting the habitat use and availability of wild boars were identified through chi-square test. Third, habitat suitability model based on logistic regression were developed, and the validity of the model was tested. Finally , habitat assessment map was created by utilizing a rule-based approach. The results of the study were as folos. First , distinct difference in wild boar habitat use by season and habitat types were found, however, no difference in wild boar habiat use by season and habitat types were found , however, ho difference by sex and activity types were found. Second, it was found, through habitat availability analysis, that elevation , aspect , forest type, and forest age were significant natural environmental factors affecting wild boar hatibate selection, but the effects of slope, ridge/valley, water, and solar radiation could not be identified, Finally, the habitat at cutoff value of 0.5. The model validation showed that inside validation site had the classification accuracy of 73.07% for total habitat and 80.00% for cover habitat , and outside validation site had the classification accuracy of 75.00% for total habitat.

• Nuclear Engineering and Technology
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• v.52 no.7
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• pp.1386-1395
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• 2020

High fidelity nuclear reactor fuel assembly simulation using CFD method is an effective way for the structure design and optimization. The validated models and user practice guidelines play critical roles in achieving reliable results in CFD simulations. In this paper, the international benchmark MATiS-H is studied carefully and the best user practice guideline is achieved for the rod bundles simulation. Then a 5 × 5 rod bundles model in the advanced pressurized water reactor (PWR) is established and the detailed three-dimensional thermal-hydraulic characteristics are investigated. The influence of spacer grids and mixing vanes on the flow and hear transfer in rod bundles is revealed. As the coolant flows through the spacer grids and mixing vanes in the rod bundles, the drastic lateral flow would be induced and the pressure drop increases significantly. In addition, the heat transfer is enhanced remarkably due to the strong mixing effects. The calculation results could provide meaningful guidelines for the design of advanced PWR fuel assembly.

• Korean Journal of Food Science and Technology
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• v.31 no.4
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• pp.1011-1016
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• 1999

This study was performed to search a physical method having high yield and quality and minimum environmental pollution for extraction of pectin from apple pomace. Based on the physical solubilization of plant cell wall under the condition of high temperature, pressure and shearing stress, apple pomace was treated by a corotating intermeshing type twin-screw extruder with the diameter-to-length ratio of 1/20. The specific mechanical energy of extruder was introduced as system parameter for extrusion process modeling and the shaft speed, feed rate and moisture content as process variables. The yield, average molecular weight and galacturonic acid content of water-soluble polysaccharides obtained by extrusion were, respectively, modeled with the linear functions of the system parameter which was of the form as a linear function of process variables. The specific mechanical energy increased with increase of shaft speed and with decrease of feed rate and moisture content. Out of process variables, moisture content had the greatest effect on specific mechanical energy. The yield increased with increase of specific mechanical energy while the average molecular weight and galacturonic acid content increased with its decrease. In aspects of yield and quality of pectin, the results from this study showed the possibility to replace a traditional acidic method with the extrusion treatment of this study.

• Geotechnical Engineering
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• v.1 no.1
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• pp.59-72
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• 1985

This paper deals with the numerical analysis by the (mite element method introducing Biot's theory of consolidation and the modified Cambridge model proposed by Roscoe school of Cambridge University as constitutive equation and using Christian-Boehner's technique. Especially, time interval and division of elements are investigated in vies of stability and economics. In order to check the validity of author's program, the program was tested with one-dimensional consolidation case followed by Terzaghi's exact solution and with the results of the Magnan's analysis for existing banking carried out for study at Cubzac-les-ports in France. The main conclusions obtained are summarized as follows: 1. In the case of one-dimensional consolidation, the more divided the elements are near the surface of the foundation, the higher the accuracy of the numerical analysis is. 2. For the time interval, it is stable to divide 20 times per 1-lg cycle. 3. At the element which has long drain distance, the Mandel-fryer effect appears due to time lag. 4. Lateral displacement at an initial loading stage predicted by author's program, in which the load was assumed as not concentrative. but rather in grid form, is well consistent with the value of observation. 5. The pore water pressure predicted by author's program has a better accordance with the value of observation compared with Magnan's results. 6. Optimum construction control by Matsuo-Kawamura's method is possible with the predicted lateral displacement and settlement by the program.

• Journal of Korean Society of Forest Science
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• v.103 no.4
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• pp.703-708
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• 2014

This study was conducted to investigate effects of soil amendments on survival rate and growth of seedlings in a semi-arid region, Mongolia. 2-year-old Populus sibirica and Ulmus pumila seedlings were planted in alkaline sandy soils and treated with 2 levels of nitrogen, elemental sulfur, artificial moisture retention and converted loess. After 4 months, the seedling survival rate of both species decreased as the amount of nitrogen increased. Nitrogen has been generally known to increase seedling survival rate and growth by supplying nutrients, however, reduced survival rate in this study might be affected by consequential increase in soil osmotic pressure, which was caused by excessive nitrogen fertilization. The root collar diameter (RCD) growth of both species increased significantly by the treatment of converted loess, and only RCD growth of P. sibirica increased by the artificial moisture retention treatment. Although P. sibirica is drought-tolerant, it is in the group of Populus spp. which requires a high capacity of available water. Conversely, the elemental sulfur treatment showed no effect on survival rate and RCD growth for both species due to the low oxidation of sulfur in arid soils. The extended monitoring of seedling growth and soil characteristics is required to elucidate the long-term effects of soil amendments in the semi-arid region, and the further studies are also needed to examine the appropriate amount of fertilizers for both species.

• Journal of the Korean Electrochemical Society
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• v.12 no.4
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• pp.329-334
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• 2009

This study is to develop a fuel cell system applicable to an in situ NMR (Nuclear magnetic resonance) diagnosis. The in situ NMR can be used in real time monitoring of various reactions occurring in the fuel cell, such as oxidation of fuel, reduction of oxygen, transport phenomena, and component degradation. The fuel cell for this purpose is, however, to be operated in a specifically designed tubular shape toroid cavity detector (TCD), which constrains the fuel cell to have a tubular shape. This may cause difficulties in effective mass transport of reactants/products and uniform distribution of assembly pressure. Therefore, a new flow field designed in a particular way is necessary to enhance the mass transport in the tubular fuel cell. In this study, a tubular-shaped close-type flow field made of non-magnetic material is developed. With this flow field, oxygen is effectively delivered to the cathode surface and the produced water is readily removed from the membrane-electrode assembly to prevent flooding. The resulting DMFC (direct methanol fuel cell) outperforms the open-type flow field and exhibits $36\;mW/cm^2$ even at room temperature.

• Journal of the Korean Ceramic Society
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• v.41 no.5
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• pp.370-374
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• 2004

Sr$_{l-x}$Ba$_{x}$Al$_2$O$_4$:Eu (x = 0, 0.1, 0.2, and 0.3 mol) phosphor was synthesized by the hydrothermal method and its properties of photoluminescence and long-afterglow were investigated. The mixtures of Sr(NO$_3$)$_2$, Al(NO$_3$)$_3$9$H_2O$, and Eu(NO$_3$)$_3$$.$6$H_2O$ salts dissolved in distilled water, after controlling their pH by NH$_4$OH solution, put into an Autoclave reactor with high temperature and pressure to react. Such synthesized SrAl$_2$O$_4$:Eu powders showed homogeneous and ultra-fine particles of sub-micron size. In order to have the photoluminescence characteristic, powders were heat treated at 1100 -140$0^{\circ}C$ for 2 h in Ar/H$_2$ reduction atmosphere. Photoluminescence spectra showed a excitation along the wide wavelength of 250 ∼ 450 nm, and broaden emission with maxima peak at 520 nm. Also, it showed a good long afterglow with decaying over 1000 sec after excitation illumination for 10 min. In addition, the microstructure and crystal structure of SrAl$_2$O$_4$:Eu powders were investigated by an SEM and XRD, respectively.

• Journal of Environmental Science International
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• v.26 no.5
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• pp.573-584
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• 2017

In order to simulate a typhoon precisely, the satellite observation data has been assimilated using WRF (Weather Research and Forecasting model) three-Dimensional Variational (3DVAR) data assimilation system. The observation data used in 3DVAR was GPS Radio Occultation (GPS-RO) data which is loaded on Low-Earth Orbit (LEO) satellite. The refractivity of Earth is deduced by temperature, pressure, and water vapor. GPS-RO data can be obtained with this refractivity when the satellite passes the limb position with respect to its original orbit. In this paper, two typhoon cases were simulated to examine the characteristics of data assimilation. One had been occurred in the Western Pacific from 16 to 25 October, 2015, and the other had affected Korean Peninsula from 22 to 29 August, 2012. In the simulation results, the typhoon track between background (BGR) and assimilation (3DV) run were significantly different when the track appeared to be rapidly change. The surface wind speed showed large difference for the long forecasting time because the GPS-RO data contained much information in the upper level, and it took a time to impact on the surface wind. Along with the modified typhoon track, the differences in the horizontal distribution of accumulated rain rate was remarkable with the range of -600~500 mm. During 7 days, we estimated the characteristics between daily assimilated simulation (3DV) and initial time assimilation (3DV_7). Because 3DV_7 demonstrated the accurate track of typhoon and its meteorological variables, the differences in two experiments have found to be insignificant. Using observed rain rate data at 79 surface observatories, the statistical analysis has been carried on for the evaluation of quantitative improvement. Although all experiments showed underestimated rain amount because of low model resolution (27 km), the reduced Mean Bias and Root-Mean-Square Error were found to be 2.92 mm and 4.53 mm, respectively.