• Journal of the Korean Geotechnical Society
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• v.33 no.2
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• pp.35-47
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• 2017

Thermal behavior of soils is mainly focused on thermal conduction, and the study of natural convection is very limited. Increase of soil temperature causes natural convection due to buoyancy from density change of pore water. The limitations of the analysis using fluid dynamics for natural convection in the porous media is discussed and a new numerical analysis is presented for natural convection in porous media using THM governing equations fully coupled in the macroscopic view. Numerical experiments for thermal probe show increase in the uncertainty of thermal conductivity estimated without considering natural convection, and suggest appropriate experimental procedures to minimize errors between analytical model and numerical results. Burial of submarine power cable should not exceed the temperature changes of $2^{\circ}C$ at the depth of 0.2 m under the seabed, but numerical analysis for high permeable ground exceeds this criterion. Temperature and THM properties of the seafloor are important design factors for the burial of power cable, and in this case effects of natural convection should be considered. Especially, in the presence of heat sources in soils with high permeability, natural convection due to the variation of density of pore water should be considered as an important heat transfer mechanism.

• Journal of Korea Society of Industrial Information Systems
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• v.29 no.1
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• pp.117-123
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• 2024

Bubbles generated in water receive an upward buoyant force due to the density and pressure difference of the surrounding fluid. Additionally, the behavior, shape, and heat exchange process of bubbles vary depending on the viscosity, surface tension, rising speed, and size difference with the surrounding fluid. In this study, we modeled speed, and heat transfer of a high-temperature single bubble rising in a cylindrical water tank. For this purpose, velocity, and temperature of the bubbles were calculated using theoretical equations, to be compared with numerical simulation results. The numerical analysis was performed using a commercial software, and the stability of the numerical analysis with mesh size was confirmed through calculation of the grid convergence index. The numerical analysis of the rising speed and temperature of a single bubble showed the values to converge when the minimum cell size was 1/160 of the bubble diameter, and the temperature decrease was confirmed to be the same as that of the surrounding fluid within 0.05 seconds.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.2
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• pp.208-215
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• 2017

When persistent oil, such as crude oil or Bunker C oil, is spilled at sea, viscosity increases through the weathering process. Equipment that can collect this oil when mixed with floating marine debris is very limited. In this study, devices that can be attached to the outside of existing oil skimmers have been applied to the inside of the main body, to develop an unmanned conveyor belt type floating marine debris and high viscosity oil recovery skimmer, which is composed of a conveyor belt, a sweeper with a forced inflow device, and a collection tank equipped with a buoyant body. The resulting skimmer was operated at a speed of 1.2 knots at a distance of 30 m in a sea area test. It was stable when moving laterally in any direction. An oil recovery performance test was conducted using a portable storage tank, and oil was recovered from a minimum of $7.8k{\ell}/h$ to a maximum of $23.3k{\ell}/h$. Moreover, recovery of $7.7k{\ell}/h$ was obtained in a wave water tank test with floating marine debris such as PET bottles and oil mixed. If the equipment developed in this study was used in the field for oil pollution accidents, it could be expected to contribute to improved response capability. We believe our equipment could be used in further studies to improvement the performance of existing portable oil skimmers.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.25 no.2
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• pp.75-81
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• 1989

In this paper, the authors describe on the field experiment of the newly designed actual stow net, standing on the result of the model experiment to examine the performance of the conventional net and the newly designed net, presented in two previous reports of this series. Concurrently the additional experiment to find out the possibility of changing of operating system from the side to the stern was carried out. 1. Fundamental shape of the experimented net was 20 times aslarge asthe newly designed model net. Performance of the net was detected by using two ultrasonic echo sounders: one was set downward at the top-most spreader of the shearing device to detect the opening height of the device from the sea bed, and the other sidewise at the starboard top-most spreader to detect the top-most opening width of the devices. Opening height of the newly designed net showed about 3m smaller than the conventional net at slow current of 0.6m/sec and less but it overcome 1m at speedy current of 0.8m/sec and more. Opening width of the newly designed net was 1.4 times as large as that of the conventional net, ant the front projection area of the newly designed net mouth was estimated as 1.3~1.6 times as large as that of the conventional net. 2. The experiment on the stern operating system was tightly limited by the structure of the ship employed in the experiment, which was a stern trawler of 2275 GT. The ship confronted by the wind with main anchor, while the net was put over the stern slipway and the hauling line of shearing device was operated through the top rollers of gallows. The experiment was very suggestive in the view point to mechanize the operating system, and so to decrease the man power except the following question. The of bow-stern line of ship, and that of net is much different.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.1
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• pp.77-89
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• 2020

Submerged floating tunnel (SFT) is a type of tunnel that allows tunnel segments to float underwater by buoyancy, and is being actively studied in recent years. When the submerged floating tunnel is connected to the ground, the tunnel and the bored tunnel inside the ground must be connected. There is risk that the stress will be concentrated at the connection between the two tunnels due to the different constraints and behavior of the two tunnels. Therefore, special design and construction methods should be applied to ensure the stability around the connection. However, previous studies on the stability at the connection site have not been sufficiently carried out, so study on the basic stage of the stability at connection site are necessary. In this study, numerical analysis simulating the connection between submerged floating tunnel and the bored tunnel confirmed that the shear strain concentration occurred in the ground around the connection, and it was analyzed that the structural factors can be handled during construction to have effects on the stability of the ground around the connection. Numerical results show that the risks from disproportionate displacements in the two tunnels can be mitigated through the construction of grouting material and joint design. Although the results from this study are qualitative results, it is expected that it will contribute to the determination of structural factors and risk areas that should be considered in the design of connections between the submerged floating tunnel and bored tunnel in the future studies.

• Tunnel and Underground Space
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• v.16 no.6 s.65
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• pp.526-535
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• 2006

An experimental study was carried out on a reduced scale tunnel model to grasp the behavioral feature of fire-induced smoke in the long tunnels. Based on Froude modeling, the 1/50 scaled tunnel model (20 m long) was constructed by acrylic tubes and paraffin gas was released inside the tunnel to simulate the 20 MW fire-induced smoke. me test results show, that after approximately 2 minutes of fire generation, was descended from the tunnel ceiling through the decrease of buoyancy, then it was symmetrically propagated about 90 meters for 4 minutes before jet fans were operated. The smoke was effectively controlled when the jet fans were operated and an air stream velocity was getting closed to reach a critical velocity (the minimum air velocity that requires to suppress the smoke spreading against the longitudinal ventilation flow during the tunnel fire situations). It was also found out that a range of smoke was spreaded about 3 meters from the origin of fire but the range was not propagated to the escape direction anymore. The early stage of the In operation, however, showed that the smoke was hardly controlled. It means that the operation of emergency ventilation system has many dangerous factors such as an intercepting breathing zone.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.4
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• pp.1215-1225
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• 2014

Volcanic rocks formed from magma near the earth surface commonly show vesicular structures due to exsolution of gaseous phases in magma. The distinction and the amount of vesicles are greatly various, but there are few researches on the effect of volume percentage of vesicles on the mechanical properties. In this study, mechanical characteristics of volcanic rocks in relation to the porosity are investigated through experimental tests with Jeju basalt. Two methods (the buoyancy method and the caliper method) are adopted for measuring porosity. And unconfined compressive strength, elastic modulus, tensile strength, and elastic wave velocity are plotted against porosity in order to propose the empirical relations after the regression analysis. Also, unconfined compressive strength and the elastic modulus in relation to the elastic wave velocity are proposed with the analysis. In the case of vesicular rocks with more than 5% porosity, it is found that the buoyancy method provides more accurate estimation of porosity than the caliper method. The unconfined compressive strength, the elastic modulus, and the elastic wave velocity decrease curvilinearly with increasing in porosity. Also, the unconfined compressive strength and the elastic modulus increase linearly with increasing in elastic wave velocity.

• Journal of the Korea Concrete Institute
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• v.27 no.6
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• pp.651-659
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• 2015

Currently, social demands for long span building structures are increasing due to architectural planning purposes and economic efficiency. As a result, lighter board-type voiding materials were suggested. With the use of board-type voiding materials, a slab is able to become light weight and convenient. This process efficiently eliminates concrete where it is not required; considerably diminishing dead weight while maintaining the flexural strength of the slab. The reduction in concrete also allows for overall cost reductions and design flexibility. Also it can be ease with fixing the voided material that is composed of one body form. Although board-type voiding materials are ideal, the top and bottom concrete plates lack integrity. Because of this, test results show horizontal cracking towards the tops and bottoms of the concrete columns, or webs, connecting the slabs. The key to correcting this problem is to increase the shear strength. In order to increase the shear strength of the structure, horizontal shear area must increase. R70(100)-D-F has the largest horizontal shear area as it also shows stronger strength. As a result, shear strength ($V_{nh}$) is dependent on the horizontal shear area (N). $V_{nh}={\alpha}{\times}0.16{\sqrt{f_{ck}}}{\frac{{\pi}D^2}{4}}{\times}N({\alpha}=1.8125)$. The web columns have a shear span to depth ratio (a/d) that is less than 2; which classifies it as a deep beam. In this case, however, the shear strength of the deep beams may be as much as 2 to 3 times greater than that predicated conventional equations developed for members of normal proportions. As a result, ${\alpha}$ is suggested as an extra coefficient in the equation for shear strength ($V_{nh}$).

• Journal of Korea Water Resources Association
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• v.51 no.7
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• pp.543-554
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• 2018

A methodology has been presented for evaluating the partial safety factors on the sliding failure mode of vertical caissons of composite breakwaters and for determining the cross sections of those by Level I reliability-based design method. Especially, a mathematical model has been suggested for the sake of a consistency of code format as well as convenience of application in practical design, for which the uncertainties associated with buoyancy and its own weight can be taken into account straightforwardly. Furthermore, design criteria equation has been derived by considering accurately the effect of uplift pressure, so that the cross sections of caissons can be assessed which must be safe against the sliding failure. It has been found that cross sections estimated from partial safety factors proposed in this paper are in very good agreement with the results of Level II AFDA and Level III MCS under the same target probability of failure. However, partial safety factors of the Technical Standards and Commentaries for Port and Harbour Facilities in Japan and Coastal Engineering Manual in USA tend to estimate much bigger or smaller cross sections in comparison to the present results. Finally, many reliability re-analyses have been performed in order to conform whether the stability level of cross section estimated by Level I reliability-based design method is satisfied with the target probability of failure of partial safety factors or not.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.50-50
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• 2022

한국농어촌공사 산하의 농업용저수지 중 3786개소에 대한 수질조사를 '19년도에 실시한 결과, TOC 기준 4등급 초과 저수지 비율은 약 20%로써, 도심 근교 저수지에서 녹조현상 빈발로 인해 수질, 악취, 미관 등의 환경문제 개선 민원이 다수 발생하고 있다. 현재 녹조 발생 사후관리를 위해 주로 사용되고 있는 대형 조류제거선은 저수심 수변부에서의 적용성에 한계가 있고, Al 기반의 응집제를 사용하여 조류를 수거해서 폐기하고 있는 실정이다. (주)이엔이티는 농어촌연구원, (주)코레드, (주)삼호인넷과 함께 호소나 정체하천의 수변지역에 적용될 수 있는 저에너지형 유해조류 포집시스템 개발과, 수거된 조류부산물을 무독화하여 농업재료로 재활용하는 방안을 연구하고 있다. 저수지나 정체수역의 녹조는 바람, 수면유동 등에 의해 수변에 집적되는 특성이 있어, 인공지능 기술로 녹조현상을 감시하여 조류 밀집구간에 접근할 수 있는 자율이동식 수상이동장치를 개발 중이다. 수상이동장치는 조류포집장치를 탑재하기 위한 부력체, 원격 운전이 가능한 무인항법장치, 수변식생대 및 저수심지역 이동을 고려한 수차방식 추진체, 전체 장치의 전원 공급을 위한 고성능 배터리 등으로 구성하여 상세 도면 설계를 진행하고 있다. 조류포집장치에는 표층에 주로 분포하는 남조류를 선택 흡입하는 포집 부표를 적용하였고, Al계 응집제 사용을 배제한 분리막 실험을 통해 침지형 막분리조 및 가압형 농축조를 설계하였다. 유해조류 포집 및 농축은 수상에서 이동체에 탑재하여 이뤄지고, 육상에서는 자원 회수가 가능하도록 회분식 응집공정으로 구분하였다. 조류 밀집지역에서 수거된 조류의 무독화 및 농업재료 자원화 타당성 평가를 위해 특용 버섯균주를 활용한 시료별 분석항목을 선정하고 실험 매트릭스에 따라 실증실험을 수행하였다. 수거조류를 전처리하여 성분 및 발열량을 분석하고 버섯재배 전후의 마이크로시스틴 독소(LR, RR, LR)를 포함한 성분 분석을 수행하여, 고체연료, 비료 및 사료로 활용방안을 검토하였다. 무인자율이동 조류포집장치는 실증화 규모로 제작하여 기선정된 테스트베드에서 현장적용성 평가를 수행할 예정이다. 본 연구를 통해 개발된 유해조류 포집 시스템은 기존의 녹조제거 방안을 보완하여 정체수역의 생태계 복원 및 친수공간의 환경개선 등에 적용되며, 무독화가 입증된 유해조류의 농업재료 자원화 기술은 고부가 상품 개발 및 환경폐기물 감축에 활용될 것이다.