• Journal of Korean Society of Water and Wastewater
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• v.35 no.1
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• pp.93-100
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• 2021

Forward osmosis (FO) process is a chemical potential driven process, where highly concentrated draw solution (DS) is used to take water through semi-permeable membrane from feed solution (FS) with lower concentration. Recently, commercial FO membrane modules have been developed so that full-scale FO process can be applied to seawater desalination or water reuse. In order to design a real-scale FO plant, the performance prediction of FO membrane modules installed in the plant is essential. Especially, the flux prediction is the most important task because the amount of diluted draw solution and concentrate solution flowing out of FO modules can be expected from the flux. Through a previous study, a theoretical based FO module model to predict flux was developed. However it needs an intensive numerical calculation work and a fitting process to reflect a complex module geometry. The idea of this work is to introduce deep learning to predict flux of FO membrane modules using 116 experimental data set, which include six input variables (flow rate, pressure, and ion concentration of DS and FS) and one output variable (flux). The procedure of optimizing a deep learning model to minimize prediction error and overfitting problem was developed and tested. The optimized deep learning model (error of 3.87%) was found to predict flux better than the theoretical based FO module model (error of 10.13%) in the data set which were not used in machine learning.

• Journal of Korean Society on Water Environment
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• v.38 no.4
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• pp.177-189
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• 2022

Nature-based Solutions (NbS) are defined as practical and technical approaches to restoring functioning ecosystems and biodiversity as a means to address socio-environmental challenges and provide human-nature co-benefits. This study reviews NbS-related literature to identify its key characteristics, techniques, and challenges for its application in climate-adaptive water management. The review finds that NbS has been commonly used as an umbrella term incorporating a wide range of existing ecosystem-based approaches such as low-impact development (LID), best management practices (BMP), forest landscape restoration (FLR), and blue-green infrastructure (BGI), rather than being a uniquely-situated practice. Its technical form and operation can vary significantly depending on the spatial scale (small versus large), objective (mitigation, adaptation, naturalization), and problem (water supply, quality, flooding). Commonly cited techniques include green spaces, permeable surfaces, wetlands, infiltration ponds, and riparian buffers in urban sites, while afforestation, floodplain restoration, and reed beds appear common in non- and less-urban settings. There is a greater lack of operational clarity for large-scale NbS than for small-scale NbS in urban areas. NbS can be a powerful tool that enables an integrated and coordinated action embracing not only water management, but also microclimate moderation, ecosystem conservation, and emissions reduction. This study points out the importance of developing decision-making guidelines that can inform practitioners of the selection, operation, and evaluation of NbS for specific sites. The absence of this framework is one of the obstacles to mainstreaming NbS for water management. More case studies are needed for empirical assessment of NbS.

• Fashion & Textile Research Journal
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• v.25 no.1
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• pp.119-126
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• 2023

This study aimed to determine the effects of relative humidity and fiber properties on the moisture permeability of multilayer systems by measuring water vapor transmission in the overlapping condition of various fabrics. The results confirmed that the property of the fabric in contact with the humid environment affects the moisture permeability. If the layer facing the humid environment is hydrophobic and the layer facing the dry environment is superhydrophobic, water vapor transmission increases by up to 17.8% compared to the opposite conditions. Comparing the correction values of the water vapor transmission reflecting the thickness of the specimen under the multilayer condition showed that permeability was higher when the hydrophilic or hydrophobic layer was facing the humid environment. The opposite was true from the "push-pull" effect of absorption mechanism. In the case of moisture permeability, the more hydrophilic the surface facing the humid environment, the more permeable that water vapor diffuses and passes through. It was concluded that the "pull-push" effect, in which water vapor diffuses widely through the hydrophilic facing a humid environment and then passes through the hydrophobic layer, contributes to the improvement of permeability. Permeability differed according to the multilayer overlapping condition. When the relative humidity was high, the "pull-push" effect was insignificant. This is caused by water droplets absorption after the partial migration of water due to condensation. These results suggest that the overlapping conditions and properties of fabrics should vary depending on heavy sweating or not.

• Journal of Korean Ophthalmic Optics Society
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• v.15 no.4
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• pp.329-337
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• 2010

Purpose: The surfaces and compositions of rigid gas permeable (RGP) contact lenses were analyzed with the consistent methods, and the basic informations for the composition design of lens materials were suggested. Methods: The bulk structures were analyzed by using Fourier infrared spectroscopy (FTIR), the compositions of surface components were observed by using x-ray photoelectron spectroscopy (XPS), the surface morphology and roughness were observed using atomic force microscopy (AFM), and the wettabilities were estimated by the surface wetting angles. The relations and trends of those results were analyzed. Results: The high oxygen permeability RGP lenses showed the trend that the fluorine decreases and the silicon increases. As the silicon and fluorine contents increased, the carbon and oxygen contents of RGP lens materials decreased at a constant ratio. The decreasing ratio of the carbon contents was three times larger than the decreasing ratio of oxygen contents. The composition of the surface treated lens was far from these tendency line. When the silicon contents increased, the rough surface was formed with the cohered particles. When the fluorine contents increased, the rough surface was formed with the deep flaws. The surface roughness increased and then wettabilities decreased as the silicon and fluorine contents increased. For the surface roughness changes, the increasing ratio of the silicon contents was two times larger than the increasing ratio of fluorine contents. The surface of RGP lens materials appeared the hydrophobic character of which the wettabilities decreased when the roughnesses increased. Conclusions: The surfaces and compositions of RGP contact lenses were measured by the same methods. Those results and relationships were compared and analysed. It is considered that these research results will be applied with the basic data for the composition design of lens materials.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.303-311
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• 2009

In this study, weakly cemented sand was cured at air dry condition with different periods (3, 7, 14, 21, 28 days) and its unconfined compressive strength was evaluated. As a result, the strength of specimens with low cement ratios such as 4 and 8% increases until 7 days curing but, after 7 days, their strength continuously decreases. The strength of specimens with relatively high cement ratios such as 12 and 16% increases up to 7 days curing and then stays almost constant until 21 days. After 21 days curing, their strength suddenly dropped down, which is much lower than the strength of 3 days curing specimen. A cemented sand and gravel called CSG, which is highly permeable, could be exposed to repetitive drying and wetting conditions due to rainfall or groundwater table change during curing. In this study, the weakly cemented sand is exposed to repetitive drying and wetting and then its unconfined compressive strength was evaluated. As a result, the strength of a specimen with 27 days drying condition following 1 day wetting was at maximum 35% lower than the one cured under 28 days drying. The strength degradation due to wetting decreases as a cement ratio increases. However, the strength of a specimen with repetitive drying and wetting increases as the number of wetting increases until 3 cycles. After 3 cycles of drying and wetting, the rate of strength increase decreases due to an insufficient water for hydration or stays constant. If the sufficient water supply is provided to cemented sand during curing, the target or design strength increase can be achieved. Otherwise, the strength degradation due to wetting should be considered at the design stage.

• Journal of Korean Ophthalmic Optics Society
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• v.20 no.2
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• pp.141-150
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• 2015

Purpose: In the present study, a difference in tear volume between the cornea and the rigid gas permeable (RGP) lens relative to corneal shape and corneal astigmatism was investigated by the alignment fitting status of spherical and aspherical RGP lenses. Methods: Spherical and aspherical RGP lenses were fitted with alignment in 77 subjects (135 eyes) who were in their 20~30s. Tear volume stained with fluorescein was qualitatively analyzed by dividing cornea into center, mid-peripheral and peripheral parts. Results: For the spherical RGP lens fitting, tear volume differences were found in each part in all corneal types. For the aspherical RGP lens fitting, tear volume differences were in each corneal part in symmetric bow tie- and asymmetric bow tie-type corneas. However, the tear was equally distributed from the center to the peripheral part in round- and oval-type corneas. In the group with corneal astigmatism lower than 1.25 D, tear volume between center and peripheral parts, and mid-peripheral and peripheral parts, was different when a spherical RGP lens was fitted. However, tear volume in each part was not different in the group with corneal astigmatism over 1.50 D. Moreover, the tear volumes of the central and mid-peripheral parts were proportionally increased with increasing corneal astigmatism in both spherical and aspherical RGP lenses. Furthermore, aspherical RGP lenses showed greater increments than spherical RGP lenses. Conclusions: The results revealed that the difference in tear volume between aspherical RGP lens and cornea was less than spherical RGP lens, and the difference in tear volume varied according to corneal shape and astigmatism. In addition, the method of measuring relative tear volume between RGP lens and cornea that was established in the present study can be used to evaluate tear volume between contact lens and cornea.

• Magazine of the Korean Society of Agricultural Engineers
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• v.20 no.1
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• pp.4592-4598
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• 1978

The purpose of this research is to find out mathemetically an economical intake water depth in the design of head works through the derivation of some formulas. For the performance of the purpose the following formulas were found out for the design intake water depth in each flow type of intake sluice, such as overflow type and orifice type. (1) The conditional equations of !he economical intake water depth in .case that weir body is placed on permeable soil layer ; (a) in the overflow type of intake sluice, {{{{ { zp}_{1 } { Lh}_{1 }+ { 1} over {2 } { Cp}_{3 }L(0.67 SQRT { q} -0.61) { ( { d}_{0 }+ { h}_{1 }+ { h}_{0 } )}^{- { 1} over {2 } }- { { { 3Q}_{1 } { p}_{5 } { h}_{1 } }^{- { 5} over {2 } } } over { { 2m}_{1 }(1-s) SQRT { 2gs} }+[ LEFT { b+ { 4C TIMES { 0.61}^{2 } } over {3(r-1) }+z( { d}_{0 }+ { h}_{0 } ) RIGHT } { p}_{1 }L+(1+ SQRT { 1+ { z}^{2 } } ) { p}_{2 }L+ { dcp}_{3 }L+ { nkp}_{5 }+( { 2z}_{0 }+m )(1-s) { L}_{d } { p}_{7 } ] =0}}}} (b) in the orifice type of intake sluice, {{{{ { zp}_{1 } { Lh}_{1 }+ { 1} over {2 } C { p}_{3 }L(0.67 SQRT { q} -0.61)}}}} {{{{ { ({d }_{0 }+ { h}_{1 }+ { h}_{0 } )}^{ - { 1} over {2 } }- { { 3Q}_{1 } { p}_{ 6} { { h}_{1 } }^{- { 5} over {2 } } } over { { 2m}_{ 2}m' SQRT { 2gs} }+[ LEFT { b+ { 4C TIMES { 0.61}^{2 } } over {3(r-1) }+z( { d}_{0 }+ { h}_{0 } ) RIGHT } { p}_{1 }L }}}} {{{{+(1+ SQRT { 1+ { z}^{2 } } ) { p}_{2 } L+dC { p}_{4 }L+(2 { z}_{0 }+m )(1-s) { L}_{d } { p}_{7 }]=0 }}}} where, z=outer slope of weir body (value of cotangent), h1=intake water depth (m), L=total length of weir (m), C=Bligh's creep ratio, q=flood discharge overflowing weir crest per unit length of weir (m3/sec/m), d0=average height to intake sill elevation in weir (m), h0=freeboard of weir (m), Q1=design irrigation requirements (m3/sec), m1=coefficient of head loss (0.9∼0.95) s=(h1-h2)/h1, h2=flow water depth outside intake sluice gate (m), b=width of weir crest (m), r=specific weight of weir materials, d=depth of cutting along seepage length under the weir (m), n=number of side contraction, k=coefficient of side contraction loss (0.02∼0.04), m2=coefficient of discharge (0.7∼0.9) m'=h0/h1, h0=open height of gate (m), p1 and p4=unit price of weir body and of excavation of weir site, respectively (won/㎥), p2 and p3=unit price of construction form and of revetment for protection of downstream riverbed, respectively (won/㎡), p5 and p6=average cost per unit width of intake sluice including cost of intake canal having the same one as width of the sluice in case of overflow type and orifice type respectively (won/m), zo : inner slope of section area in intake canal from its beginning point to its changing point to ordinary flow section, m: coefficient concerning the mean width of intak canal site,a : freeboard of intake canal. (2) The conditional equations of the economical intake water depth in case that weir body is built on the foundation of rock bed ; (a) in the overflow type of intake sluice, {{{{ { zp}_{1 } { Lh}_{1 }- { { { 3Q}_{1 } { p}_{5 } { h}_{1 } }^{- {5 } over {2 } } } over { { 2m}_{1 }(1-s) SQRT { 2gs} }+[ LEFT { b+z( { d}_{0 }+ { h}_{0 } )RIGHT } { p}_{1 }L+(1+ SQRT { 1+ { z}^{2 } } ) { p}_{2 }L+ { nkp}_{5 }}}}} {{{{+( { 2z}_{0 }+m )(1-s) { L}_{d } { p}_{7 } ]=0 }}}} (b) in the orifice type of intake sluice, {{{{ { zp}_{1 } { Lh}_{1 }- { { { 3Q}_{1 } { p}_{6 } { h}_{1 } }^{- {5 } over {2 } } } over { { 2m}_{2 }m' SQRT { 2gs} }+[ LEFT { b+z( { d}_{0 }+ { h}_{0 } )RIGHT } { p}_{1 }L+(1+ SQRT { 1+ { z}^{2 } } ) { p}_{2 }L}}}} {{{{+( { 2z}_{0 }+m )(1-s) { L}_{d } { p}_{7 } ]=0}}}} The construction cost of weir cut-off and revetment on outside slope of leeve, and the damages suffered from inundation in upstream area were not included in the process of deriving the above conditional equations, but it is true that magnitude of intake water depth influences somewhat on the cost and damages. Therefore, in applying the above equations the fact that should not be over looked is that the design value of intake water depth to be adopted should not be more largely determined than the value of h1 satisfying the above formulas.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.3 no.2
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• pp.39-51
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• 2007

Unconsolidated and permeable alluvial deposit composed of sand and gravel is distributed along the fluvial plain at the Iryong study area. Previous studies on the area show that a single alluvial well can produce at least 1,650m3d-1 of bank infilterated shallow groundwater(BIGW) from the deposit. This study is aimed to evaluate and simulate the influence that seasonal variation of water levels and temperatures of the river have an effect on those of BIGW under the pumping condition and also to compare seasonal variation of COPs when indirectly pumped BIGW or directly pumped surface water are used for a water to water heat pump system as an heat source and sink using 3 D flow and heat transport model of Feflow. The result shows that the magnitude influenced to water level of BIGW by fluctuation of river water level in summer and winter is about 48% and 75% of Nakdong river water level separately. Seasonal change of river water temperature is about $23.7^{\circ}C$, on other hand that of BIGW is only $3.8^{\circ}C$. The seasonal temperatures of BIGW are ranged from minimum $14.5^{\circ}C$ in cold winter(January) and maximum $18.3^{\circ}C$ in hot summer(July). It stands for that BIGW is a good source of heat energy for heating and cooling system owing to maintaining quite similar temperature($16^{\circ}C$) of background shallow groundwater. Average COPh in winter time and COPc in summer time of BIGW and surface water are estimated about 3.95, 3.5, and about 6.16 and 4.81 respectively. It clearly indicates that coefficient of performance of heat pump system using BIGW are higher than 12.9% in winter time and 28.1% in summer time in comparision with those of surface water.

• Journal of the Korea Concrete Institute
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• v.22 no.6
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• pp.867-873
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• 2010

This study investigated the corrosion properties of reinforced concrete with the addition of steel fibers. The transport properties of steel fiber-reinforced concrete such as permeable void, absorption by capillary action, water permeability and chloride diffusion were first measured to evaluate the relationship with the corrosion of steel rebar. Test results showed a slight increase on the compressive strength with the addition of steel fibers as well as considerable improvement of penetration resistance to mass transport of harmful materials into concrete. The addition of steel fibers in reinforced concrete accelerated the initiation of steel corrosion contrary to the expected results based on the measured transport properties. The NaCl ponding surface showed the spalling failure due to the corrosion expansion of steel fibers and the cut-surface around the steel rebar showed the localized steel fiber's corrosion. The wet-dry cycling with high chloride ions as well as high temperature seems to induce the increase of salt crystallization on the pores continually and the increased pressure with the steel fiber's corrosion on the pores caused the spalling failure on the exposed surface. The microcracking on the surface therefore accelerated the movement of water, chloride ions and oxygen into the embedded steel rebar. The mechanism affecting corrosion of embedded steel reinforcement with steel fibers in this study are not yet fully understood and require further study comprising of accurate experimental design to isolate the effect of steel fiber's potential mechanism on the corrosion process.

• Geophysics and Geophysical Exploration
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• v.8 no.2
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• pp.156-162
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• 2005

Particularly in research related to seawater intrusion the change of fluid electrical conductivity is one of major concerns, and effective monitoring can help to optimize a water pumping performance in coastal areas. Special considerations should be given to the mounting of sensors at proper depth during the monitoring design since the vertical distribution of fluid electrical conductivity is sensitive to the characteristics of seawater intrusion zone. This tells us the multi-channel electrical conductivity monitoring is of paramount consequence. It, however, is a rare event when this approach becomes routinely available in that commonly used commercial stand-alone type sensors are very expensive and inadequate for a long term monitoring of electrical conductivity or water level due to their restricted storage and difficulty of real-time control. For this reason, we have developed a real-time monitoring system that could meet these requirements. This system is user friendly, cost-effective, and easy to control measurement parameters - sampling interval, acquisition range, and others. And this devised system has been utilized for the electrical conductivity monitoring in boreholes, Yeonggwang-gun, Korea. Monitoring has been consecutively executed for 24 hours, and the responses of electrical conductivity at some channels have been regularly increased or decreased while pumping up water. It, with well logging data implemented before/after pumping water, verifies that electrical conductivity changes in the specified depths originate from fluid movements through sand layer or permeable fractured rock. Eventually, the multi-channel electrical conductivity monitoring system makes an effective key to secure groundwater resources in coastal areas.