• Tribology and Lubricants
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• 제30권6호
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• pp.350-355
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• 2014

This study proposes a sustainable bearing remanufacturing process using the ultrasonic nanocrystal surface modification (UNSM) technique. The UNSM technique is a newly developed and sophisticated surface modification technique that can increase the mechanical properties and improve the friction and wear performance of materials. Taking advantage of the bearing manufacturing process is the most significant way of optimizing the life of a bearing. The proper maintenance and usage of repaired bearings can increase their life to be equal to or greater than that of new bearings. This paper discusses the restoration of certain mechanical properties of worn, damaged, and discarded bearings, and suggests a remanufacturing process for used bearings, which can impart them with a lifespan equivalent to that of new bearings. The most damaged part of the discarded bearings is the raceway, which is the site of accumulated fatigue. The existing polishing or barrel finishing processes can recover the accumulated fatigue only partially. Rolling contact fatigue tests performed on UNSM-treated new and used specimens polished after $4{\times}10^6$ cycles reveal that UNSM-treated new specimens exhibit the longest fatigue life compared to other specimens. This study verifies the proposed complete fatigue recovery process, which can increase the fatigue life of used bearings to a level greater than that of new bearings.

• Korean Journal of Chemical Engineering
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• 제35권12호
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• pp.2384-2393
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• 2018

Porous alginate-based hydrogel beads (porous ABH) have been prepared through a facile and sustainable template-assisted method using nano-calcium carbonate and nano-$CaCO_3$ as pore-directing agent for the efficient capture of methylene blue (MB). The materials were characterized by various techniques. The sorption capacities of ABH towards MB were compared with pure sodium alginate (ABH-1:0) in batch and fixed-bed column adsorption studies. The obtained adsorbent (ABH-1:3) has a higher BET surface area and a smaller average pore diameter. The maximum adsorption capacity of ABH-1:3 obtained from Langmuir model was as high as $1,426.0mg\;g^{-1}$. The kinetics strictly followed pseudo-second order rate equation and the adsorption reaction was effectively facilitated, approximately 50 minutes to achieve adsorption equilibrium, which was significantly shorter than that of ABH-1:0. The thermodynamic parameters revealed that the adsorption was spontaneous and exothermic. Thomas model fitted well with the breakthrough curves and could describe the dynamic behavior of the column. More significantly, the uptake capacity of ABH-1:3 was still higher than 75% of the maximum adsorption capacity even after ten cycles, indicating that this novel adsorbent can be a promising adsorptive material for removal of MB from aqueous solution under batch and continuous systems.

• Proceedings of the Korea Water Resources Association Conference
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• 한국수자원학회 2015년도 학술발표회
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• pp.244-244
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• 2015

Managed Aquifer Recharge (MAR) in the form of Aquifer Storage and Recovery (ASR) systems are being applied for numerous water augmentation projects both in developed and developing countries. Given the onset of Climate Change and its influence on weather patterns and land use, it has been acknowledged the utilization of this technology will be ever increasing. This technique like all others does have its drawbacks or disadvantages, whereby to overcome these drawbacks or disadvantages it is recommended that logical planning process be followed. In this study, we developed a decision framework known as "Decision framework for the planning, designing, construction/testing and implementation of subsurface water storage system" to further standardize the planning and design process of subsurface water storage system to increase the probability of having a successful ASR/ASTR project. The formulation of this framework was based on earlier frameworks, guidelines, published papers and technical reports which were compiled into a data collection database. The database of which consider both qualitative and quantitative aspect for example recharge objectives, site location, water chemistry of the native, source and recovered water, aquifer characteristics(hydraulic conductivity, transmissivity, porosity), injection/pumping rate, ecological constraints, societal restrictions, regulatory restrictions etc. The assimilation of these factors into a singular framework will benefit the broad spectrum of stakeholder as it maps the chronological order under which ASR project should be undertaken highlighting at each stage the feasibility of the project. The final stage of which should result in fully operational ASR system. The framework was applied to two case studies and through the application of a modified ASR site selection suitability index (Brown et al., 2005) a score was derived to identify the performance of each site. A high score of which meant a maximize chance of success given the reduce presence of project constraints.

• Journal of Korea Port Economic Association
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• 제34권4호
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• pp.105-124
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• 2018

The purpose of this study is to identify human factors that directly or indirectly cause ship accidents and to suggest implications based on the derived human factors. In particular, we conducted a survey on the basis of the human factors derived from the literature survey and interviews, and applied the revised importance-performance analysis (IPA) to develop implications from a comparison of two groups: seafarers and shipping operations managers. Data were collected from 159 practitioners in the Korean shipping industry. The analysis structure consisted of five major factors with 20 components, including unique factors related to ship and shipping management companies, personal competence, in-vessel organization, and personnel's health, as well as social factors. The result of the IPA analysis indicates that in-vessel organization is the most urgent and major factor for improvement. Some differences exist in the components that should be improved between the two groups. For the seafarer group, an increase in unskilled onboard crew affected sustainable safety activities, thus implying an area of preferential improvement regarding the in-vessel organization factor. However, for the shipping operations managers group, the difference in recognizing safety standards among the crew members on board and the ability to communicate with other crew members should be improved first relative to in-vessel organization factors. The personnel's health factor was identified to be of low importance in both groups. Finally, the importance of improving the safety consciousness level according to the safety education and training implementation for seafarers on board was different for the two groups.

• Journal of Digital Convergence
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• 제19권10호
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• pp.15-20
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• 2021

The crisis of university must be overcome by emphasizing the acquisition and use of knowledge for students to participate in and solve contemporary and diverse social/regional problems through educational method innovation. University classes should be a way of contributing to solving human problems, the UN's Sustainable Development Goals(SDGs) and various issues in the community. This study focused on project-based learning to cultivate socially engaged and problem-solving talents. In addition, a problem definition toolkit model was produced and tested to improve problem solving ability. Through follow-up research, I plan to develop a performance measurement model corresponding to the field application-improvement-feedback of Living Lab project classes, and suggest a method that universities can easily apply to the existing curriculum.

• Journal of the Society of Naval Architects of Korea
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• 제58권5호
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• pp.294-302
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• 2021

In this study, the 3D printing technique called design for additive manufacturing (DfAM) that is widely used in various industries was applied to marine leisure ships of equipment. The DfAM for the stanchion for crew safety was applied to the equipment used in an actual recreational craft. As design constraints, the design alternatives were not to exceed the safety and weight of the existing stainless steel material, which were reviewed, and the production of a low-cost FFF-type 3D printing method that can be used even in small shipyards was considered. Until now, additive manufacturing has been used for manufacturing only prototypes owing to its limitations of high manufacturing cost and low strength; however, in this study, it was applied to the mass production process to replace existing products. Thus, a design was developed with low manufacturing cost, adequate performance maintenance, and increased design freedom, and the optimal design was derived via structural analysis comparisons for each design alternative. In addition, a life-cycle assessment based on the ISO 1404X was conducted to develop sustainable products. Through this study, the effectiveness of additive manufacturing was examined for future applications in the shipbuilding industry.

• Geomechanics and Engineering
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• 제25권1호
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• pp.41-48
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• 2021

In cold regions, the integrity of the infrastructures built on weak soils can be extensively damaged by weathering actions due to the cyclic freezing and thawing. This damage can be mitigated by exploiting soil stabilization techniques. Generally, ordinary Portland cement (OPC) is the most commonly used binding material for investigating the chemo-hydromechanical behavior. However, due to the environmental issue of OPC producing a significant amount of carbon dioxide emission, calcium sulfoaluminate (CSA) cement can be used as one of the eco-sustainable alternatives. Although recently several studies have examined the strength development of CSA treated sand, no research has been concerned about CSA cement-stabilized sand affected by cyclic freeze and thaw. This study aims to conduct a comprehensive laboratory work to assess the effect of the cyclic freeze-thaw action on strength and durability of CSA cement-treated sand. For this purpose, unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) tests were performed on the stabilized soil specimens cured for 7 and 14 days which are subjected to 0, 1, 3, 5, and 7 freeze-thaw cycles. The test results show that the strength and durability index of the samples decrease with the increase of the freeze-thaw cycles. The loss of the strength and durability considerably decreases for all soil samples subjected to the freeze-thaw cycles. Overall, the use of CSA as a stabilizer for sandy soils would be an eco-friendly option to achieve sufficient strength and durability against the freeze-thaw action in cold regions.

• Korean Journal of Organic Agriculture
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• 제29권1호
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• pp.137-148
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• 2021

The present study investigated the effect of average daily gain (ADG) on carcass traits of Hanwoo steers. A total of 233 heads of Hanwoo steer slaughtered from 2017 to 2020 were employed in the analysis. Their body weight profiles during feedlot and carcass traits were used. The entire feedlot period is split into two periods. ADG during the first period (ADG1) was then defined as an independent variable in statistical analysis. In the meantime, it was examined that how the cutoff month for the period split altered the significance of the effect of ADG1 on carcass traits. Subsequently, steers were assigned to two groups (High vs. Low) based on the median of total ADG1, and we compared the carcass traits of each group using a linear mixed model. ADG1 during 10 to 23 months showed a significant effect on all carcass traits except the marbling score. ADG1 significantly influenced carcass weight and eye muscle area of Hanwoo steers. And it was found that greater ADG1 could get greater carcass weight and eye muscle area (p<0.001). The result of this study provides preliminary information for the target month in the calculation of ADG1 mostly influencing carcass performance, and feeding strategy of Hanwoo steer in terms of sustainability.

• Journal of The Korean Society of Agricultural Engineers
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• 제61권4호
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• pp.63-73
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• 2019

Coastal and fishing facilities are gradually deteriorating in function due to the continual accumulation of soil sediments, which has affected local economic activities. Currently, there are many methods to remove soil sediments, but these methods are either a temporary solution or require a repetitive removal of the soil sediments, which is a huge financial burden for the maintenance of the facilities. To solve these problems, this study proposed a non-power soil cleaning system and evaluated field applicability by carrying out field model tests. The conditions for the evaluation focused on the drainage-elapsed time and drainage-outflow velocity according to the water level change in the water tank. In the field test, silty clay and sand were separately installed, and sedimentation soil removal test was practiced. As a result, the system was verified to have a sufficient outflow velocity for the removal of soil sediments. In addition, a generalization equation that can be used in different regions of the tide was suggested in this study. These results will greatly contribute to removing soil sediments in ports and dike gate facilities on the southwest coast. Since the system is an eco-friendly technology that does not require additional energy, thus it is expected to contribute to maintenance of sustainable facility performance as well as economic effect in the future.

• Korean Journal of Agricultural Science
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• 제46권1호
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• pp.137-149
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• 2019

Accurate estimation of reference evapotranspiration (RET) is important to quantify crop evapotranspiration for sustainable water resource management in hydrological, agricultural, and environmental fields. It is estimated by different methods from direct measurements with lysimeters, or by many empirical equations suggested by numerous modeling using local climatic variables. The potential to use some such equations depends on the availability of the necessary meteorological parameters for calculating the RET in specific climatic conditions. The objective of this study was to determine the proper RET equations using limited climatic data and to analyze the temporal and spatial trends of the RET in South Korea. We evaluated the FAO-56 Penman-Monteith equation (FAO-56 PM) by comparing several simple RET equations and observed small fan evaporation. In this study, the modified Penman equation, Hargreaves equation, and FAO Penman-Monteith equation with missing solar radiation (PM-Rs) data were tested to estimate the RET. Nine weather stations were considered with limited climatic data across South Korea from 1973 - 2017, and the RET equations were calculated for each weather station as well as the analysis of the mean error (ME), mean absolute error (MAE), and root mean square error (RMSE). The FAO-56 PM recommended by the Food Agriculture Organization (FAO) showed good performance even though missing solar radiation, relative humidity, and wind speed data and could still be adapted to the limited data conditions. As a result, the RET was increased, and the evapotranspiration rate was increased more in coastal areas than inland.