• Journal of Korean Association for Spatial Structures
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• v.19 no.1
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• pp.75-82
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• 2019

In the precedent study, the retractable-roof spatial structure was selected as the analytical model and a tuned mass damper (TMD) was installed to control the dynamic response for the earthquake loads. Also, it is analyzed that the installation location of TMD in the analytical model and the optimal number of installations. A single TMD mass installed in the analytical model was set up 1% of the mass of the whole structure, and the optimum installation location was derived according to the number of change. As a result, it was verified that most effective to install eight TMDs regardless of opening or closing. Thus, in this study, eight TMDs were installed in the retractable-roof spatial structure and the optimum mass ratio was inquired while reducing a single TMD. In addition, the optimum mass distribution ratio was identified by redistributing the TMD masses differently depending on the installation position, using the mass ratio of vibration control being the most effective for seismic load. From the analysis results, as it is possible to confirm the optimum mass distribution ratio according to the optimum mass ratio and installation location of the TMD in the the retractable-roof spatial structure, it can be used as a reference in the TMD design for large space structure.

• Tribology and Lubricants
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• v.37 no.2
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• pp.71-76
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• 2021

As opposed to using fossil fuels, we need to use eco-friendly resources such as sunlight, raindrops and wind to produce electricity and combat environmental pollution. A triboelectric nanogenerator (TENG) is a device that converts mechanical energy into electricity by inducing repetitive contact and separation of two dissimilar materials. During the contact and separation processes, electron flow occurs owing to a change in electric potential of the contacting surface caused by contact electrification and electrostatic induction mechanisms. A solid-solid contact TENG is widely known, but it is possible to generate electricity via liquid-solid contact. Therefore, by designing a hydrophobic TENG, we can gather electricity from raindrop energy in a feasible manner. To fabricate the superhydrophobic surface of TENGs, we employ a dip coating technique to synthesize an octadecylamine (ODA)- and polydimethylsiloxane (PDMS)-based coating on polyethylene terephthalate (PET). The synthesized coating exhibits superhydrophobicity with a contact angle greater than 150° and generates a current of 2.2 ㎂/L while water droplets fall onto it continuously. Hence, we prepare a box-type TENG, with the ODA/PDMS coating deposited on the inside, and place a 1.5 mL water droplet into it. Resultantly, we confirm that the induced vibration causes continuous impacts between the ODA/PDMS coating and the water, generating approximately 100 pA for each impact.

• Journal of Environmental Science International
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• v.31 no.10
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• pp.869-881
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• 2022

In this study, a field study was conducted to investigate the relationship between high-resolution remote images and the volumetric moisture, and the number of compaction. Changes in the shape of the surface and soil moisture content were observed and correlated with the number of compactions using roller equipment. As the compaction is repeated, the surface is flattened and the terrain curvature decreases and converges to zero. In particular, the tangential curvature changes as the number of compactions increase. Due to soil compaction, the vegetation index changed from a positive to a negative value, and most of the test site area was homogenized with a negative index. This suggests a decrease in porosity and an increase in volumetric water content associated with increasing soil compaction. Soil moisture, measured using a frequency domain reflectometry(FDR) sensor, tends to increase proportionately with the number of vibration compactions, but the correlation between the number of compactions and soil moisture is unclear. This study suggests that while it is necessary to consider the reproducibility of the experiments performed, the compaction quality of the soil can be evaluated using high-resolution terrain factors and soil moisture.

• Journal of Auto-vehicle Safety Association
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• v.14 no.2
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• pp.57-69
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• 2022

Recently, as interest in self-driving cars has increased worldwide, research and development on the Advanced Driver Assist System is actively underway. Among them, the purpose of Adaptive Cruise Control (ACC) is to minimize the driver's driving fatigue through the control of the vehicle's longitudinal speed and relative distance. In this study, for the research of the ACC test in the real environment, the real-road test was conducted based on domestic-road test scenario proposed in preceding study, considering ISO 15622 test method. In this case, the distance measurement method using the dual camera was verified by comparing and analyzing the result of using the dual camera and the result of using the measurement equipment. As a result of the comparison, two results could be derived. First, the relative distance after stabilizing the ACC was compared. As a result of the comparison, it was found that the minimum error rate was 0.251% in the first test of scenario 8 and the maximum error rate was 4.202% in the third test of scenario 9. Second, the result of the same time was compared. As a result of the comparison, it was found that the minimum error rate was 0.000% in the second test of scenario 10 and the maximum error rate was 9.945% in the second test of scenario 1. However, the average error rate for all scenarios was within 3%. It was determined that the representative cause of the maximum error occurred in the dual camera installed in the test vehicle. There were problems such as shaking caused by road surface vibration and air resistance during driving, changes in ambient brightness, and the process of focusing the video. Accordingly, it was determined that the result of calculating the distance to the preceding vehicle in the image where the problem occurred was incorrect. In the development stage of ADAS such as ACC, it is judged that only dual cameras can reduce the cost burden according to the above derivation of test results.

• Journal of Conservation Science
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• v.38 no.4
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• pp.277-288
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• 2022

'Eve 58-1', the subject of this study is a statue made of plaster and its structural stability was evaluated by utilizing the CAE program in order to prevent the risk of damage arising from impact and vibration that are generated during the packaging and transportation process given its material characteristics. CAE is an abbreviation for Computer Applied Engineering for realization by predicting changes at the time of application of virtual physical energy. It is applied by reflecting the physical property conditions and each boundary condition of plaster, and the digital images of the internal and external structure of the work were acquired through 3D scanning and CT analysis for interpretation by executing finite element modeling. When acceleration is applied to the work in the direction of its own weight, the left-right side and the front-rear side, it was possible to confirm a maximum displacement value of 15.24 mm in the head section of the front-rear side direction that has been tilted by approximately 27° from the Y-axis and the largest stress value of 12.46 MPa was at the left ankle section. The corresponding results confirmed that the left ankle section is the most vulnerable area and the section for which precautions need to be exercised and supplemented at the time of transporting the work by means of objective values.

• Journal of Korean Tunnelling and Underground Space Association
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• v.25 no.3
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• pp.221-243
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• 2023

The use of roadheaders has been increasing to mitigate the problems of noise and vibration during tunneling operations in urban area. Since lack of experience of roadheader for hard rock, the selection of appropriate machines and the evaluation of cutting rates have been challenging. Currently, empirical models developed overseas are commonly used to evaluate cutting rates, but their effectiveness has not been verified for domestic rocks. In this paper, a comprehensive literature review was conducted to assess the rock cutting force, cutterhead capacity, and cutting rate to select the appropriate machine and evaluate its performance. The cutterhead capacity was reviewed based on the literature results for the site. Furthermore, a new empirical model and simplified method for predicting cutting rates were proposed through data analysis in relation to operation time and rock strength, and compared with those of the conventional model from the manufacturer. The results show good agreement for high strength range upper 80 MPa of uniaxial compressive strength.

• Journal of the Korean GEO-environmental Society
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• v.24 no.5
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• pp.5-12
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• 2023

Recently, due to urban development and expansion, construction plans have been increasing adjacent to existing tunnel structures such as subways, roads, and large pipelines. Structural plans adjacent to existing tunnels have different effects on tunnel stability depending on the construction method, degree of proximity, and location of new structures. In particular, the pressure water tunnel shows a very large difference from other road tunnels and railway tunnels in geotechnical characteristics and operation characteristics. Therefore, it is necessary to review the safety zone due to adjacent construction in consideration of the geotechnical characteristics of the water tunnel and the new sturure construction method. In this study, the existing tunnel safety zone standards were investigated. A stability evaluation performed numerical analysis considering the deterioration of concrete lining in operation and the characteristics of water tunnel. In addition, the impact of vibration caused by pile construction and blasting excavation of new structures was reviewed. Based on this, a pressure water tunnel safety zone was proposed in consideration of adjacent construction.

• Composites Research
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• v.22 no.1
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• pp.22-31
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• 2009

Recently the wind energy has been alternatively used as a renewable energy resource instead of the mostly used fossil fuel due to its lack and environmental issues. This work is to propose a structural design and analysis procedure for development of the 500W class small wind turbine system which will be applicable to relatively low speed region like Korea and for the domestic use. The wind turbine blade was performed structural analysis including stress, deformation, buckling, vibration and fatigue. In addition, the blade should be safe from the impact damage due to FOD(Foreign Object Damage) including the bird strike. MSC.Dytran was used in order to analyze the bird strike penomena on the blade, and the applied method Arbitrary Lagrangian-Eulerian was evaluated by comparison with the previous study results. Finally, the structural test was carried out and its test results were compared with the estimated results for evaluation of the designed structure.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.11
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• pp.1697-1705
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• 2022

The safety of marine construction workers and marine pollution problems are occurring due to large-scale offshore construction. In particular, underwater construction work in the sea has a higher risk than other work, so it is necessary to apply an unmanned alternative system that considers the safety of the workers. In this paper, the ROV system for offshore construction has been developed for underwater unmanned work. A monitoring system was developed for position control through the control of underwater propellants, pneumatic gripper, and monitoring of underwater work. As a result of the performance evaluation, the underwater movement speed of the ROV was evaluated to be 0.89 m/s, and it was confirmed that the maximum load of the pneumatic gripper was 80 kg. In addition, the network bandwidth required for underwater ROV control and underwater video streaming was evaluated to be more than 300Mbps, wired communication at 92.7 ~ 95.0Mbit/s at 205m, and wireless communication at 78.3 ~ 84.8Mbit/s.

• Journal of dental hygiene science
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• v.23 no.2
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• pp.176-184
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• 2023

Background: Recently, a piezoelectric ultrasonic scaler based on a feedback control mechanism was introduced for pain relief. This study aimed to investigate the effects of a new ultrasonic scaler in reducing pain and discomfort in adults. Methods: A newly introduced ultrasonic scaler (Master 700^®) was used as the test device and a conventional ultrasonic scaler device (PIEZON^®) was used as the control device. Forty-one healthy adults visited the dental clinic for dental scaling but did not undergo scaling or periodontal treatment within 6 months. Intraoral examinations were performed before scaling and 3 months later; before scaling, both devices were randomly assigned on the left or right side of each dentition (split-mouth model) and scaling was performed by a registered dental hygienist. The levels of pain and discomfort during scaling were evaluated subjectively and objectively using the visual analog scale (VAS) and physiological monitoring of the heart rate (HR), respectively. Time was measured for each device. Results: All clinical indicators, except bleeding on probing, significantly improved with both devices. The treatment times were 7 minutes, 13 minutes (control) and 6 minutes, 59 minutes (test). VAS scores for pain were 4.89±2.12 (control) and 4.58±2.77 (test) points out of 10; for noise, these were 4.68±2.33 (control) and 4.55±2.55 (test), and for vibration, the values were 4.26±2.0 (control) and 4.18±2.48 (test). HR averages were 72.34±3.39 (control) and 75.97±9.78 (test) beats/min. No statistically significant differences were observed between the devices. Conclusion:The pain, discomfort levels, and scaling time of the new piezoelectric ultrasonic scaler did not differ from those of the conventional device. Further research and development are necessary for more prominent pain-relief effects of scaling devices.