• Clean Technology
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• v.26 no.4
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• pp.263-269
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• 2020

Zeolite was synthesized hydrothermally using the water-treatment sludge, and the effects of various synthesis parameters like reaction temperature, reaction time, and Na2O/SiO2 molar ratio on the crystallization of zeolite were investigated. Crystal structure, physical property, and thermal stability of zeolite crystals were characterized by X-ray powder diffraction, FTIR spectroscopy, BET nitrogen adsorption, and TGA measurements. The removal efficiencies of nitrogen in ammonia, heavy metal ions, and TOC were calculated to evaluate zeolite's adsorption capacity. The primary chemical composition of water-treatment sludge was 28.79% Al2O3 and 27.06% SiO2. The zeolites were synthesized by merely employing the water-treatment sludge as silica and alumina sources without additional chemicals. Zeolite crystals synthesized through the water-treatment sludge were confirmed as an A-type zeolite structure. Zeolite A had the highest crystallinity obtained from a gel with the molar composition 2.1Na2O-Al2O3-1.6SiO2-65H2O after 5 h at a temperature of 90 ℃. The specific surface area of zeolite obtained was 55 ㎡ g-1, which was higher than commercial zeolite A. The removal efficiency of nitrogen in ammonia was 68% after 3 h of reaction time, while the removal efficiencies of Pb2+ and Cd2+ ions were 99.1% and 99.3%, respectively. These results indicate active ion exchange between Pb2+ or Cd2+ ion and Na+ ion in the zeolite framework. The adsorption experiments on the different zeolite addition conditions were performed for 3 h with 300 ppm humic acid. Based on the results, TOC's highest efficiency was 83% when 5 g of zeolite was added.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.2
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• pp.394-401
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• 2021

The construction of new renewable energy facilities is steadily increasing every year. In particular, the offshore wind farm market, which has abundant development scalability and a high production coefficient, is growing rapidly. The southwest sea has the highest possible offshore wind power potential, and related projects are to be promoted. This study presents a basic design procedure by the EUROCODE and considers structural safety in the development of an effective of shore wind foundation in the clay layer. In a previous study, the wind power generator of 5MW class was the main target, but the 8MW of wind turbine generator, which meets the technical trend of the wind turbine market in the Southwest sea, was selected as the standard model. Furthermore, a foundation that fulfills the geological conditions of the Southwest sea was developed. The structural safety of this foundation was verified using finite element method. Moreover, structural safety was secured by proper reinforcement from the initial design. Based on the results of this study, structural safety check for various types of foundations is possible in the future. Additionally, specialized structural design and evaluation guidance were also established.

• Clean Technology
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• v.28 no.4
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• pp.323-330
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• 2022

Microfluidic paper-based analytical devices (μPADs) have recently been in the spotlight for their applicability in point-of-care diagnostics and environmental material detection. This study presents a double-sided printing method for fabricating 3D-μPADs, providing simple and cost effective metal ion detection. The design of the 3D-μPAD was made into an acryl stamp by laser cutting and then coating it with a thin layer of PDMS using the spin-coating method. This fabricated stamp was used to form the 3D structure of the hydrophobic barrier through a double-sided contact printing method. The fabrication of the 3D hydrophobic barrier within a single sheet was optimized by controlling the spin-coating rate, reagent ratio and contacting time. The optimal conditions were found by analyzing the area change of the PDMS hydrophobic barrier and hydrophilic channel using ink with chromatography paper. Using the fabricated 3D-μPAD under optimized conditions, Ni²⁺, Cu²⁺, Hg²⁺, and pH were detected at different concentrations and displayed with color intensity in grayscale for quantitative analysis using ImageJ. This study demonstrated that a 3D-μPAD biosensor can be applied to detect metal ions without special analysis equipment. This 3D-μPAD provides a highly portable and rapid on-site monitoring platform for detecting multiple heavy metal ions with extremely high repeatability, which is useful for resource-limited areas and developing countries.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.7
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• pp.1259-1266
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• 2022

Recently, due to the specialization of structural design standards and evaluation methods, the classification rules are being integrated. A good example is the common international rules (CSR). However, detailed regulations are presented only for the cargo hold area where the longitudinal load is greatly applied, and no specific evaluation guidelines exist for the bow and stern structures. Structural design of the mentioned area is carried out depending on the design experience of the shipbuilder, and because no clear standard exists even in the classification, determining the root cause is difficult even if a structural damage problem occurs. In this study, an engineering-based solution was presented to identify the root cause of representative cases of buckling damage that occurs mainly in the stern. Buckling may occur at the panel wall owing to hull girder bending moment acting on the stern structure, and the plate thickness must be increased or vertical stiffeners must be added to increase the buckling rigidity. For structural strength verification based on finite element analysis modeling, reasonable solutions for load conditions, boundary conditions, modeling methods, and evaluation criteria were presented. This result is expected to be helpful in examining the structural strength of the stern part of similar carriers in the future.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.5
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• pp.488-496
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• 2023

Ship and bridge structures are a type of long box-shaped structure, and resistance to vertical bending moment is a key factor in their structural design. In particular, because box girders are repeatedly exposed to irregular wave loads for a long time, the continuous collapse behavior of structural members must be accurately predicted. In this study, plastic collapse behavior, including buckling according to load changes of the box girder receiving pure bending moments, was analyzed using a numerical analysis method. The analysis targets were selected as three box girders used in the Gordo experiment. The cause of the difference was considered by comparing the results of the structural strength experiment with those of non-linear finite element analysis. This study proposed a combination of the entire and local sagging shape to reflect the effect of the initial sagging caused by welding heat that is inevitably used to manufacture carbon steel materials. The procedures reviewed in the study and the contents of the initial sagging configuration can be used as a good guide for analyzing the final strength of similar structures in the future.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.2
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• pp.230-237
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• 2023

Due to the COVID-19 pandemic and climate change, shortages of essential commodities and resources continue to occur globally. To address this problem, trade volume demand suddenly increased, driving up the freight rate of container ships sharply. The size of container vessels progressively increased from 1,500 TEU (twenty-foot equivalent unit) in the 1960s to 24,400 TEU in 2021. As the improvement of container loading capacity is closely related to the enlargement of the lashing bridge structure, it is necessary to design a structure effective for good container securing and safe under the various external loads that occur during voyage. Major classification societies have recently issued structural-analysis-based guidelines to evaluate the structural safety of lashing bridges, but their acceptance criteria and evaluation methods are different, causing confusion among engineers during design. In this study, the strength change characteristics are summarized by variations in the main variables (modeling range, opening consideration, mesh size) likely to affect the results. Based on this result, the authors propose a reasonable structural-analysis-based evaluation that is expected to serve as a reference in the next revision of classification standards.

• Korean Journal of Ecology and Environment
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• v.35 no.2 s.98
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• pp.63-70
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• 2002

Long-term changes of the fish fauna and its community structure from the Jungrang Creek of the Han River system in Seoul were investigeted from 1990 to 2000. Total species occurred during the survey period were 14 species in 6 families, and total individual number was 108,366. Fishes at the Jungrang Creek had not been distributed in the 1980s and 1990 because of heavy water pollution as well as environmental damage in the riparian areas. However, Cyprinus carpio and Carassius auratus in cyprinidae were rehabitated since the early 1990s when the water quality was improved because of foundation of sewage division pipe. Species nombers gradually increased to 6 species in 1996, 9 species in 1998, and 11 species in 2000. Individual numbers rapidly increased to 164 individuals in 1996, 146 individuals in 1998, and 108,094 individuals in 2000. A large number of Cyprinus carpio and Carassius auratus, which are abundantly distributed in the main course of the Han River, were found when they migrate to the upper reaches of the Jungrang Creek for spawning. Mass fish floatings were occurred on the 21st of April and the 11th of June in 2000 due to DO depletion at the lower site (Site 4) of discharging point of Jungrang sewage treatment plant and stagnant spot(Site 3) of dammed pool. Major dominant species were Cyprinus carpio and Carassius auratus (Cyprinidae). Others dominant species were Pseudorasbora lab대 (Cyprinidae) and Silurus asotus (Siluridae). Dominance indices were relatively high (0.79 to 1.00). Species diversity andrichness indices were relatively low (0 to 1.66and 0 to 1.41, respectively). Species diversity and richness indices were slightly higher at the middle reaches (Site 2 and Site 3) than the upper reaches and the mouth of the Jungrang Creek. However, the fish fauna of the Jungrang Creek was very poor and its community structure was very simple.

• Journal of Ecology and Environment
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• v.29 no.6
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• pp.551-558
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• 2006

Effects of Pb and $CO_2$ on soil microbial community associated with Pinus densiflora were investigated using community level physiological profiles (CLPP) and 16S rDNA PCR-denaturing gradient gel electrophoresis (DGGE) methods. Two-years pine trees were planted in Pb-contaminated soils and uncontaminated soils, and cultivated for 3 months in the growth chamber where $CO_2$ concentration was controlled at 380 or 760 ppmv. The structure of microbial community was analyzed in 6 kinds of soil samples (CA-0M : $CO_2$ 380 ppmv + Pb 0 mg/kg + initial, CB-0M : $CO_2$ 380 ppmv + Pb 500 mg/kg + initial, CA-3M : $CO_2$ 380 ppmv + Pb 0 mg/kg + after 3 months, CB-3M : $CO_2$ 380 ppmv + Pb 500 mglkg + after 3 months, EA-3M : $CO_2$ 760 ppmv + Pb 0 mg/kg + after 3 months, EB-3M : $CO_2$ 760 ppmv + Pb 500 mg/kg + after 3 months). After 3 months, the substrate utilization in the uncontaminated soil samples (CA-3M vs EA-3M) was not significantly influenced by $CO_2$ concentrations. However, the substrate utilization in the Pb-contaminated soil samples (CB-3M vs EB-3M) was enhanced by the elevated $CO_2$ concentrations. The results of principal component analysis based on substrate utilization activities showed that the structure of microbial community structure in each soil sample was grouped by Pb-contamination. The similarities of DGGE fingerprints were 56.3 % between the uncontaminated soil samples (CA-3M vs EA-3M), and 71.4% between the Pb-contaminated soil samples (CB-3M vs. EB-3M). The similarities between the soil samples under $CO_2$ 380 ppmv (CA-3M vs CB-3M) and $CO_2$, 760 ppmv (EA-3M vs EB-3M) were 53.3% and 35.8%, respectively. These results suggested that the structure of microbial community associated with Pinus densiflora were sensitively specialized by Pb-contamination rather than $CO_2$ concentration.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.5
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• pp.335-347
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• 2013

In February 2008, high storm waves due to a developed atmospheric low pressure system propagating from the west off Hokkaido, Japan, to the south and southwest throughout the East Sea (ES) caused extensive damages along the central coast of Japan and along the east coast of Korea. This study consists of two parts. In the first part, we estimate extreme storm wave characteristics in the Toyama Bay where heavy coastal damages occurred, using a non-hydrostatic meteorological model and a spectral wave model by considering the extreme conditions for two factors for wind wave growth, such as wind intensity and duration. The estimated extreme significant wave height and corresponding wave period were 6.78 m and 18.28 sec, respectively, at the Fushiki Toyama. In the second part, we perform numerical experiments on wave-structure interaction in the Fushiki Port, Toyama Bay, where the long North-Breakwater was heavily damaged by the storm waves in February 2008. The experiments are conducted using a non-linear shallow-water equation model with adaptive mesh refinement (AMR) and wet-dry scheme. The estimated extreme storm waves of 6.78 m and 18.28 sec are used for incident wave profile. The results show that the Fushiki Port would be overtopped and flooded by extreme storm waves if the North-Breakwater does not function properly after being damaged. Also the storm waves would overtop seawalls and sidewalls of the Manyou Pier behind the North-Breakwater. The results also depict that refined meshes by AMR method with wet-dry scheme applied capture the coastline and coastal structure well while keeping the computational load efficiently.

• Journal of the Korean association of regional geographers
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• v.6 no.3
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• pp.1-36
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• 2000

Periodic markets of the later Choson dynasty had undergone fundamental changes during the late Chosun dynasty and Japanese colony period. This paper aims to analyse the spatial distributions and changes of the periodic markets in the middle stream of Han-River in this era in the use of the survey of documentary records and fieldwork. Before the early 1910s, long distance transportation was made by riverboats, short distance transportation was done by porters and pack animals. Because goods such as rice, soybean and salt were very heavy and needed long distance transport, they were mainly transported by riverboats. Accordingly, riverports on the shore of river played important roles in exporting and importing goods as nodes of long distance transportation. The opening of railroad Seoul-Busan, the construction of new roads(Sinjakno) of 1910s and the use of oxcarts produced striking changes in the spatial distribution and hierarchy structure of periodic markets. These changes also had influence on the outflow and inflow of goods in the middle stream of Han-River. In the parr of outflow of goods, it seems that the line linking Icheon city-Yongin city-Anseong city played a role in making the boundaries of the marketing areas between goods trams ported by the rail road Seoul-Busan and goods done by Han River river boats. Anseong, Osan and Suwon periodic markets located around railroad stations occupied the higher positions than those of other regions in the hierarchial structure of periodic markets. Their marketing areas could nearly overwhelm those of riverports located in the middle stream region of Han River and extend to the middle stream region of Han River as a result of decrease of transport cost through using of oxcarts and railroads. the opening of railroad Suwon-Yeoju(Suryoson) and railroad Cheonan-Janghawon(Cheonjangson) brought about changes of the structure of long distance trade again. In a part of outflow of goods, it seems that as a result of the new opening of their railroads periodic markets around railroads seized a large portion of the marketing area of the southern part of Yoju and Ichon area and therefore made extreme change in rivershipping of Han River. In the inflow part of goods, goods transported by riverboats from the downstream of Han River before the opening of railroad were imported directly from railroad stations. Accordingly, rivershipping and riverports declined. And because goods were imported by way of great periodic markets and supplied to small periodic markets and consumers before the opening of railroad, but supplied from railroad stations to small periodic markets and consumers after the opening of railroad. The volume of turnover of such great periodic markets as Anseong, Osan and Suwon periodic markets therefore declined. On the other hand, because Yangpyong area had not been yet included within the sphere of influence of railroad until 1930s, it heavily depended on rivershipping of Han River as before. But the opening of railroad Seoul-Wonju(jungangson) brought about decline of rivershipping in Yangpyong and Wonju area.