• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.6
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• pp.242-252
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• 2018

It is well known that an Oscillating Water Column Wave Energy Converter (OWC-WEC) is one of the most efficient wave absorber equipment. This device transforms the vertical motion of water column in the air chamber into the air flow velocity and produces electricity from the driving force of turbine as represented by the Wells turbine. Therefore, in order to obtain high electric energy, it is necessary to amplify the water surface vibration by inducing resonance of the piston mode in the water surface fluctuation in the air chamber. In this study, a new type of OWC-WEC with a seawater channel is used, and the wave deformation by the structure, water surface fluctuation in the air chamber, air outflow velocity from the nozzle and seawater flow velocity in the seawater channel are evaluated by numerical analysis in detail. The numerical analysis model uses open CFD code OLAFLOW model based on multi-phase analysis technique of Navier-Stokes solver. To validate model, numerical results and existing experimental results are compared and discussed. It is revealed within the scope of this study that the air flow velocity at nozzle increases as the Ursell number becomes larger, and the air velocity that flows out from the inside of the air chamber is larger than the velocity of incoming air into the air chamber.

• The Journal of Engineering Geology
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• v.30 no.4
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• pp.541-555
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• 2020

The grouting method is used for reinforcing and waterproofing the soft ground, increasing the bearing capacity of structures damaged by lowering or subsidence due to rise and vibration, and for ordering. This study attempted to develop a blast furnace slag-based cementless grout material to increase the strength and hardening time of the grout material using reinforcing fibers. In this regard, in this study, it was used in combination with calcium hydroxide, which is an alkali stimulant of the three fine powders of blast furnace slag, and the content of calcium hydroxide was used by substituting 10, 20, and 30% of the fine powder of blast furnace slag. In addition, in order to compare the strength according to the presence or absence of reinforcing fibers, an experiment was performed by adding 0.5% of each fiber. As the content of carbon fibers and aramid fibers increased, the uniaxial compressive strength increased, and it was confirmed that the crosslinking action of the fibers in the grout material increased the uniaxial compressive strength. In addition, it was confirmed that the gel time sharply decreased as the content of the alkali stimulate increased.

• Explosives and Blasting
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• v.39 no.4
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• pp.22-33
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• 2021

Recently, the frequent occurrence of ground subsidence in urban areas has caused increasing anxiety in residents and incurred significant social costs. Among the causes of ground subsidence, the rupture of old water and sewer pipes not only halts the operation of the buried pipes, but also leads to ground and water pollution problems. However, because most pipes are buried after construction and cannot be seen with the naked eye, the importance of maintenance has underestimated compared to other structures. In recent years, integrated physical exploration has been applied to the maintenance of underground pipes and structures. Currently, to investigate the internal conditions and vulnerable portions of the ground, consolidated physical surveys are executed. Consolidated physical surveys are analysis techniques that obtain various material data and add existing data using multiple physical surveys. Generally, in geotechnical engineering, consolidated physical surveys including electrical and surface wave surveys are adopted. However, it is difficult to investigate time-based changes in under ground using these surveys. In contrast, surveys using cosmic-ray muons have been used to scan the inner parts of nuclear reactors with penetration technology. Surveys using muons enable real-time observation without the influence of vibration or electricity. Such surveys have great potential for available technology because of their ability to investigate density distributions without requiring as much labor. In this paper, survey technologies using cosmic ray muons are introduced, and the possibilities of applying such technologies as new physical survey technologies for underground structures are suggested.

• Smart Media Journal
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• v.11 no.5
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• pp.75-81
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• 2022

In order to respond to carbon neutrality and climate change in agriculture, agricultural machinery, which has been developed centered on internal combustion engines, needs to be converted to an electric-based technology that does not emit greenhouse gases. In this study, simulations for electric UTV suspension design were performed to reduce vibration and shock of electric UTV for agricultural use and to improve driving stability and control performance of the vehicle. The simulation was performed by dividing the tolerance load of the vehicle body and the loaded load state. The range of motion of the suspension spring of UTV is within 30% of the range of motion under condition B under tolerance, the displacement of the UTV suspension with full load is reduced from 264mm to 121mm, and the damping speed is 260mm/s to 300mm/s that it can be seen that the range of motion is within 60%. Suspension design of electric UTV for multi-purpose agricultural work is a very important factor for maintaining agricultural work ability in towing work such as tillage as well as driving and terrain adaptation. The results of this study can be usefully used to determine the spring parameters with the appropriate damping range so that the electric UTV can be used for various agricultural tasks.

• Composites Research
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• v.35 no.4
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• pp.277-282
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• 2022

In this study, a smart material applicable to speed bumps was developed using low-cost starch and waterbased suspensions, and their properties were investigated. Viscosity and shear stress according to the shear rate was measured by a rheometer to observe shear thickening behavior according to starch concentration. The shear thickening phenomenon and applicability to speed bumps were identified macroscopically via drop weight test and bike driving test, measuring the vibration after impact with a driving speed of 5-25 km/h. As a result of the viscosity measurement, shear thickening occurred after the shear thinning region at the beginning, and the critical strain causing the shear thickening phenomenon decreased as the concentration of starch increased. Also, the viscosity and shear stress increased significantly with the increase of the starch concentration. As a result of the drop weight test and the bike driving test, the suspension was changed to a solid-like state in a short time, and the impact energy was absorbed in the fluid. The shear thickening phenomenon easily occurred as the concentration of the fluid and the applied impact (velocity) increased. Therefore, it can be proposed the development of a smart speed bump material that operates in the range of 5-25 km/h with a Non-Newtonian fluid based on water and starch.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.1
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• pp.79-94
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• 2022

The demand for tunnel construction is increasing as part of underground space development due to urban saturation. The shield TBM method minimizes vibration and noise and minimizes ground deformation that occurs simultaneously with excavation, and shield TBM is generally applied to tunnel construction in urban areas. The importance of urban ground settlement prediction is increasing day by day, and in the case of shield TBM construction, ground deformation is minimized, but ground settlement due to tunnel excavation inevitably occurs. Therefore, in this study, the correlation between shield TBM, which is highly applicable to urban areas, and ground settlement is analyzed to suggest the shield TBM construction factors that have a major effect on ground settlement. Correlation analysis was performed between the shield TBM construction data and ground settlement measurement data collected at the actual site, and the degree of correlation was expressed as a correlation coefficient "r". As a result, the main construction factors of shield TBM affecting ground settlement were thrust force, torque, chamber pressure, backfill pressure and muck discharge. Based on the results of this study, it is expected to contribute to the presentation of judgment criteria for major construction data so that the ground settlement can be predicted and controlled in advance when operating the shield TBM in the future.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.4
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• pp.20-29
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• 2022

The operational modal analysis (OMA) technique, which extracts the modal parameters of a structural system using ambient vibrations, has been actively developed as a field of structural health monitoring of cable-supported bridges. In this paper, the short and long-term modal parameters of a cable-stayed bridge were evaluated using the acceleration data obtained from the two ambient vibration tests (AVTs) and three years of continuous measurements. A total of 27 vertical modes and 1 lateral mode in the range 0.1 ~ 2.5 Hz were extracted from the high-resolution AVTs which were conducted in the 6th and 19th years after its completion. Existing OMA methods such as Peak-Picking (PP), Eigensystem Realization Algorithm with Data Correlation (ERADC), Frequency Domain Decomposition (FDD) and Time Domain Decomposition (TDD) were applied for modal parameters extraction, and it was confirmed that there was no significant difference between the applied methods. From the correlation analysis between long-term natural frequencies and environmental factors, it was confirmed that temperature change is the dominant factor influencing natural frequency fluctuations. It was revealed that the decreased natural frequencies of the bridge were not due to changes in structural performance and integrity, but to the environmental effects caused by the temperature difference between the two AVTs. In addition, when the TDD technique is applied, the accuracy of extracted mode shapes is improved by adding a proposed algorithm that normalizes the sequence so that the autocorrelations at zero lag equal 1.

• The Journal of Engineering Geology
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• v.31 no.1
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• pp.67-81
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• 2021

Grouting is used for reinforcement and waterproofing of soft ground to increase its bearing capacity, reduce the impacts of rising or lowering groundwater levels, and reduce subsidence due to vibration and general causes. This study investigated the enhancement of grout strength and hardening time by the addition of reinforcing fibers, and the development of non-cement grouting materials from blast furnace slag. An experiment was performed to measure the increase in grout strength resulting from the addition of 0.5% increments of aramid and carbon reinforcing fibers. The results show that the uniaxial compressive strength of grout increases with increasing content of reinforcing fiber. Comparison of three admixtures of finely powdered blast furnace slag and 10%, 20%, and 30% calcium hydroxide stimulating agent showed that the uniaxial compressive strength of the mixture increases with increasing content of alkaline stimulant; however, the strength was lower than for 100% pure cement. The reaction of calcium hydroxide with blast furnace slag powder, which increases the strength of the grout, is more effective if injected as a solution rather than a powder.

• Journal of Environmental Impact Assessment
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• v.31 no.6
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• pp.449-464
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• 2022

This study reviewed the development process of the consultation guideline for the environmental assessment of offshore wind power. Based on this, implications and improvement plans for a future revision of the guidelines. Domestic and foreign case studies reviewed the consulting cases on domestic offshore wind power development projects, environmental location consulting cases, and guidelines related to overseas offshore wind power and analyzed location characteristics and significant environmental issues by project. Major environmental issues related to offshore wind power include birds, noise and vibration, marine animals and plants, marine physics, marine water quality and sediments, marine landscapes, and other auxiliary facilities installed on land. Implications and improvements for revising the consultation guidelines for evaluating offshore wind environments require data and clear guidelines at the central government level to determine areas where offshore wind projects can be located. In a situation where the importance of cumulative impact assessment is emphasized, guidelines for cumulative impact assessment methodologies for each item that reflect the domestic situation should be prepared for a cumulative impact assessment on offshore wind power environmental issues. In addition, when revising the consultation guidelines, empirical research cases should be reflected through the accumulation of environmental surveys and monitoring data of offshore wind farms by sea area.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.2
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• pp.119-129
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• 2023

Sleep apnea causes various secondary disease such as hypertension, stroke, myocardial infarction, depression and cognitive impairment. Early detection and continuous management of sleep apnea are urgently needed since it causes cardio-cerebrovascular diseases. In this study, wearable device for monitoring respiration during sleep using PVDF film was developed to detect vibration through trachea caused by breathing, which determines normal breathing and sleep apnea. Variables such as respiration rate and apnea were extracted based on the detected breathing sound data, and a noise reduction algorithm was established to minimize the effect even when there is a noise signal. In addition, it was confirmed that irregular breathing patterns can be analyzed by establishing a moving threshold algorithm. The results show that the accuracy of the respiratory rate from the developed device was 98.7% comparing with the polysomnogrphy result. Accuracy of detection for sleep apnea event was 92.6% and that of the sleep apnea duration was 94.0%. The results of this study will be of great help to the management of sleep disorders and confirmation of treatment by commercialization of wearable devices that can monitor sleep information easily and accurately at home during daily life and confirm the progress of treatment.