• Journal of Aerospace System Engineering
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• v.17 no.2
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• pp.62-70
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• 2023

We proposed a technique for predicting Stress-Life (S-N) curve or fatigue life using geometric features of a ply-overlap joint structure in which plies of two composite materials are partially or wholly laminated and bonded. Geometric features that could affect fatigue properties of a structure were selected as variables. By analyzing relationships between geometric variables and material constants of the Epaarachchi-Clausen model, a fatigue model for composites, relational expressions of these two factors were proposed. To verify the prediction accuracy of the proposed method, fatigue life of a CFRP/GFRP ply-overlap joint was predicted. Predicted life and life obtained by test data-based model were compared to actual life. High prediction accuracy was confirmed by calculating the coefficient of determination of the predicted S-N curve.

• Economic and Environmental Geology
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• v.56 no.5
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• pp.501-514
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• 2023

Forest fires can generate numerous pollutants through the combustion of vegetation and cause serious environmental problems. The global warming and climate change will increase the frequency and scale of forest fires across the world. In Korea, many nuclear power plants (NPPs) are located in the East Coast where large-scale forest fires frequently occur. Therefore, understanding the sorption and transport characteristics of radionuclides in the forest fire areas is required against the severe accidents in NPPs. This article reviewed the physiochemical changes and contamination of groundwater and soil environments after forest fires, and discussed sorption and transport of radionuclides in the subsurface environment of burned forest area. We considered the geochemical factors of subsurface environment changed by forest fire. Moreover, we highlighted the need for studies on changes and contamination of subsurface environments caused by forest fires to understand more specific mechanisms.

• Journal of Aerospace System Engineering
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• v.18 no.3
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• pp.17-26
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• 2024

Aircraft engines are exposed to high temperatures, high pressures, and stress caused by the rotation of the turbine shaft during flight. These loads can result in microcracks both on the inside and outside surfaces of the structure. Consequently, this can lead to structural defects and negatively impact the lifespan of the parts. To proactively prevent these defects, a finite element analysis is carried out to identify cracks. However, this process is time-consuming and requires significant effort due to the repetitive nature of crack modeling. This study aims to develop a crack modeling method based on the finite element model. To achieve this, the Constrained Delaunay Triangulation (CDT) technique is employed to triangulate the space while considering limitations on point connections. The effectiveness of this method is validated by comparing stress intensity factors for semi-elliptical cracks in plates and cylindrical vessels. This approach proves to be a valuable tool for crack analysis studies.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.10 no.1
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• pp.93-103
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• 2000

The purpose of this case study is to report a case of lung cancer with exposure to welding fumes of welders in Korea and to demonstrate the causal relationship with exposure to welding fumes, especially with nickel and hexavalent chromium. The case is 47 years old, and had been engaged in welding, gas cutting, grinding and gousing on mild, stainless steel and nickel steel for 11 years from 1982 to 1993, and have been engaged in cleaning steel rollers with a cleaning oil in the same work shop since 1993. The level of welding fume exceeded the occupational exposure limit of $5mg/m^3$ established by the Korean Ministry of Labor and American Conference of Government Industrial Hygienists (ACGIH). Especially, detectable hexavalent chromium and nickel was generated during welding, gousing on stainless and nickel steel. However, there was no ventilation systems(local and dilution) and no personal protection. There is several evidence that the past (1983-1993) exposure would be higher than the present. In conclusion, the lung case could be associated with his task including welding, gousing, and this association could be attributed to carcinogenic potential of the nickel and chromium in the fume.

• Journal of Wetlands Research
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• v.17 no.3
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• pp.221-227
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• 2015

Urbanization increases the impervious cover, which affects the discharge of stormwater runoff and non-point source pollutants to the waterbodies. In order to improve the water quality and restore the aqua-ecosystem, the Ministry of Environment (MOE), Korea MOE introduced the Low Impact Development(LID) techniques on development projects. Therefore, research was performed to develop the bioretention technology for managing the stormwater runoff from urban areas. The test-bed was established on 2013 up to evaluate the performance of pollutant and runoff reduction. A total of 11 storm events have been monitored from November 2013 to present. Even though the SA/CA (surface area of bioretention/catchment area) is approximately 2.2%, the facility shows high pollutant and runoff reduction during storm events by increasing retention and infiltration capacities. The bioretention shows a 100% total runoff reduction at 0mm < R < 10mm rainfall range and more than 90% of runoff reduction at a rainfall range of 10mm < R < 20mm. Due to runoff volume reduction, more than 90% of nonpoint source pollutant were also removed by the bioretention.

• Journal of Environmental Health Sciences
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• v.42 no.2
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• pp.85-91
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• 2016

Objectives: The objective of this study was to assess heat stress, compare heat stress indices, and evaluate the usefulness of wet bulb globe temperature (WBGT) among outdoor workers exposed to heat during the summer season. Methods: WBGT, dry temperature, and heat index were measured using WBGT measurers (QUESTemp 32 model and QUESTemp 34 model, QUEST, WI, USA) by industrial hygienists from August 27 to September 16, 2015. Heat stress indices were measured at the workplaces of a shipbuilder in Ulsan and a construction site in Daegu. The dry temperature observed by the Automated Synoptic Observing System (ASOS) of the Korea Meteorological Administration was also compared. Results: Dry temperature measured by WBGT is different from that by ASOS. The temperature obtained from ASOS was less than $33^{\circ}C$, above which point a heat wave is forecast by the Korea Meteorological Administration. A heat index above $32.8^{\circ}C$ as a moderate risk was not observed during measurement. WBGT was consistently higher than $22^{\circ}C$, above which the risk of heat-related illness is increased in unacclimated workers involved in work with a high metabolic rate. WBGT was sometimes higher than $28^{\circ}C$, above which the risk of heat-related illness is increased in acclimated workers involved in work with a moderate metabolic rate in September. Conclusion: According to the measurement of heat stress indices, WBGT was more sensitive than heat index and temperature. Thus, general measures to prevent heat-related diseases should be implemented in workplaces during the summer season according to WBGT.

• Journal of Wetlands Research
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• v.18 no.2
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• pp.201-207
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• 2016

In LID facilities treating stormwater runoff, various kinds of plants are applied for water circulation recovery and pollutant reduction. However, rapid changes of soil moisture due to the use of porous media and spread of deicing material during winter season cause slow plant growth that detrimentally leads to many problems including death of plants. Therefore, this study was performed to evaluate the salt resistance of plants, its effects on pollutants removal, and water circulation recovery. Eight different kinds of plants applicable to an LID facility were selected for the experiment, which were Bridal wreath (Spiraea japonica, S.J), Azalea (Rhododendron indicum, R.I), Dawn Redwood (Metasequoia glyptostroboides, M.G), Sweet flag (Acorus calamus A.C), Dwarf fan-shape columbine(Aquilegia flabellata, A.F), Pink (Dianthus chinensis, D.C), Pratia pedunculata (Pratia pedunculata, P.B) and Marigold (Tagetes patula, T.P). Woody plants such as S.P, R.I, and M.G appear to have less salt resistance compared to the other herbaceous plants. Specifically, M.G achieved the highest salt resistance among the other woody plants being followed by S.P, and R.I, respectively. For herbaceous plants, T.L and D.C have the higher salt resistances than that of A.C, P.B, and A.F, respectively. Regardless of the influence of salt to most of the plants, TN and TP were reduced more than 60% and the study suggests the M.G showed high pollutant removal efficiency and provided better water circulation by means of active photosynthesis and respiration due to higher growth.

• Journal of Wetlands Research
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• v.18 no.2
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• pp.194-200
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• 2016

The impervious surface rate increased by urbanization causes various problems on the environment such as water cycle distortion, heat island effect, and non-point pollutant discharges. The Low Impact Development (LID) techniques are significantly considered as an important tool for stormwater management in urban areas and development projects. The main mechanisms of LID technologies are hydrological and environmental pollution reduction among soils, media, microorganisms, and plants. Especially, the media provides important functions on permeability and retention rate of stormwater runoff in LID facilities. Therefore, this research was performed to assess the pollutant removal efficiency for different types of media such as zeolite, wood chip, bottom ash, and bio-ceramic. All media show high pollutant removal efficiency of more than 60% for particulate materials and heavy metals. Double layered media is more effective in reducing heavy metals by providing diverse sizes of micro-pores and macro-pores compared to the single layered media. The results recommend the use of different sizes of media application is more cost-effective in LID than a single size of media. Furthermore, soluble proportion of total heavy metal in the stormwater is an important component in proper media selection and arrangement.

• Journal of Korean Society on Water Environment
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• v.33 no.1
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• pp.1-7
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• 2017

Bioretention systems, an advance low impact development and green infrastructure approach were currently utilized in different parts of the world because it promotes biodiversity thereby mimicking and preserving the pre-developed state of an area. This study investigated and compared the capability of four bioretention systems to identify factors affecting the hydraulic capabilities and pollutant removal efficiencies of each system. The two bioretention type A referred as Type A-C and Type A-FC were planted with perennials such as Chrysanthemum and Fan columbine, respectively. On the other hand, the two type B bioretention systems referred as Type B-A and Type B-JM were planted with shrub plant species such as Azalea and Japanese Meadowsweet, respectively. Based on the results, TV, infiltration mechanism, filter media depth and plant species were identified as the factors affecting the difference in flow attenuation, retained volume and pollutant removal efficiency of Type A-C, Type A-FC, Type B-A and Type B-JM bioretention systems. The design of bioretention Type B-A and Type B-JM were advantageous considering greater volume retention, groundwater recharge, longer HRT and peak flow attenuation and greater pollutant removal efficiency. On the other hand, the design of bioretention Type A-C and Type A-FC was more appropriate for design considering reduced groundwater contamination.

• Journal of Korean Society on Water Environment
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• v.33 no.6
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• pp.715-721
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• 2017

Tree box filters, an example of bioretention systems, were compacted and versatile urban stormwater low impact development technique which allowed volume and water quality treatment performance to be adjusted based on the hydrologic, runoff quality and catchment characteristics. In this study, the overall performance of a 6 year-old tree box filter receiving parking lot stormwater runoff was evaluated. Hydrologic and hydraulic factors affecting the treatment performance of the tree box filter were also identified and investigated. Based on the results, the increase in rainfall depth caused a decrease in hydrologic and hydraulic performance of the tree box filter including volume, average flow, and peak flow reduction (r = -0.53 to -0.59; p<0.01). TSS, organics, nutrients, and total and soluble heavy metals constituents were significantly reduced by the system through media filtration, adsorption, infiltration, and evapotranspiration mechanisms employed in the tree box filter (p<0.001). This significant pollutant reduction by the tree box filter was also found to have been caused by hydrologic and hydraulic factors including volume, average flow, peak flow, hydraulic retention time (HRT) and runoff duration. These findings were especially useful in applying similarly designed tree box filter by considering tree box filter surface area to catchment area of less than 1 %.