• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.3
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• pp.327-330
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• 2021

Though the stability review of buoyancy is generally done, the stability review of buoyancy moment, which is generated from the eccentricity between the center of fixed load and that of buoyancy, is not done in the water treatment concrete structure and the architectual structure. In this review, as the buoyancy force become larger, the action point of the fixed load (ΣW) and buoyancy (B), and the reaction distribution were considered to confirm the formation of the buoyancy moment rotational point and obtained the rotational uplift stability review formula for buoyancy moment in the water treatment concrete structure and the architechual structure, and put forward the stability review method for buoyancy moment.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.5
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• pp.375-393
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• 2022

This study was deal with blow-out and buoyancy stability evaluation method for slurry shield TBM. When applying a slurry shield TBM for the construction of a shallow tunnel under river or sea, the stability of slurry blow-out and segment lining buoyancy should be evaluated. However, there is a problem in that the currently applied theoretical formula is somewhat complicated, making it inconvenient to calculate in practice. In this study, some simple charts were proposed to easily evaluate the stability of slurry blow-out and segment lining buoyancy. In addition, the buoyancy safety factor of segment lining using the strength reduction method was evaluated and compared with the buoyancy safety factor based on the theoretical formula. The buoyancy safety factor by the theoretical formula was evaluated to be rather small, and it was confirmed that it was on the safe side. The simplified charts for the evaluation of slurry blow-out and buoyancy stability presented in this study are expected to be usefully utilized in the planning and design of undersea tunnels.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2019.11a
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• pp.130-133
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• 2019

수중(submerged)에 부유(floating)식으로 계류되는 거주목적의 구조체 설계(design basis) 관련 연구로서 계류안정성 모델(수중가옥)을 만들고 거동을 정수압적 유체역학적으로 수치분석한다. 임의 가정한 수중가옥의 1)배수량 규모 2) 함체형상에 따른 환경압 하에서의 계류안정성을 a)부력중심, b)무게중심과 가변하중의 변위에 따른 c)함체 기울기를 MATLAB프로그램을 이용하여 산정한다. 나아가 수중가옥의 동적(hydrodynamic) 계류안정성을 임의 시공 장소인 독도의 기상청 울릉도-독도 부이 최근 관측치를 근거로 OrcaFlex프로그램을 이용하여 분석하므로써 수중가옥의 수중건축 시공간상 계류안정성 설계요건(design basis)을 구체화 한다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2019.05a
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• pp.164-166
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• 2019

수중에 부유식으로 계류하는 규모와 생활지원 하중요건을 임의 가정한 수중가옥(함체)의 정수압적(hydrostatic) 계류안정성과 시공성 고찰을 목적으로 한다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.6
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• pp.623-635
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• 2015

Double-deck tunnels beneath the groundwater table have relatively large volume and commonly constructed as watertight tunnels. In this case, it requires to secure stability of the tunnels for buoyant force. Generally the contact force between lining and ground is sufficient to resist the buoyant force. However in the long-term the contact force could be reduced because of structural deterioration. In this study the effect of long-term buoyant force acting on the double-deck tunnel is investigated. The results has shown that the buoyant force has increased invert deformation and stress. It is indicated that the contact resilience between lining and ground needs to be kept during tunnel operation.

• Journal of Energy Engineering
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• v.10 no.3
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• pp.266-271
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• 2001

Buoyancy-driven natural convection is analysed by employing a linear stability theory in hori-zontal porous media with net through flow. Darcy's law is used to model the flow characteristics in porous media. Bated on the results of linear stability analysis, a heat transfer correlation was obtained by employing weakly nonlinear analysis. As the net through flow increases, the system becomes more stable and the effect of the Darcy-Rayleigh number on the Nusselt number decreases.

• Journal of Korea Water Resources Association
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• v.57 no.8
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• pp.493-507
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• 2024

RANS-based CFD analysis is widely applied in various engineering fields, including practical hydraulic engineering, due to its high computational efficiency. However, problems of non-physical behavior in the analysis of two phase flow, such as free surfaces, have long been raised. The two-equation turbulence models used in general RANS-based analysis were developed for single phase flow and simulate unrealistically high turbulence energy at the interface where there are abrupt changes in fluid density. To solve this issue, one of the methods recently developed is the buoyancy-modified turbulence model, which has been partially validated in coastal engineering, but has not been applied to open channel flows. In this study, the applicability of the buoyancy-modified turbulence model is evaluated using the VOF method in the open-source program OpenFoam. The results of the uniform flow showed that both the buoyancy-modified k-𝜖 model and the buoyancy-modified k-ω SST model effectively simulated the reduction of turbulence energy near the free surface. Specifically, the buoyancy-modified k-ω SST model accurately simulated the vertical velocity distribution. Additionally, the model is applied to dam-break flows to examine cases with significant surface variation and cavity formation. The simulation results show that the buoyancy-modified turbulence models produce varying results depending on the VOF method and shows non-physical behavior different from experimental results. While the buoyancy-modified turbulence model is applicable in cases with stable surface shapes, it still has limitations in general application when there are rapid changes in the free surface. It is concluded that appropriate adjustments to the turbulence model are necessary for flows with rapid surface changes or cavity formation.

• Defense and Technology
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• no.3 s.289
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• pp.58-65
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• 2003

접이식 방호부양장치체계 설계안은 전투장갑차의 부양장치로서 요구되는 부력, 방호성, 독자적 수상운행성을 위한 탑재운용성, 수상운행 준비시간을 최소화하는 구동장치의 최적화 및 수상안정성 극대화 등을 충족시키면서도 중량 증가 요인은 최소화하는 것이 가능할 것으로 검토된 바, 기존 방법으로는 기대할 수 없는 높은 수준의 수상운행성능 구현이 가능할 것으로 기대된다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.309-314
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• 2012

Flame flickering occurs mainly because of the buoyancy force for pool fires under ambient air. The cup-burner flame was used for experimental investigation of the effect of the oxidizer velocity on the gravitational instability. The results showed that the flickering frequency decreased with increasing oxidizer velocity. The frequency-buoyancy relation with nondimensional variables coincided with that of the buoyant flume and pool fires when the characteristic velocity was defined as the difference between the fuel and oxidizer velocities, which implies that the origin of the gravitational instability is the Kelvin-Helmholtz instability in the shear layer. The effect of the oxidizer composition on the instability was also examined through nitrogen dilution in the oxidizer stream. As the concentration of inert gas increased, the length of the blue flame increased and lift-off behavior was observed. The oscillation frequency was independent of the dilution ratio, but was related to the local flame structure.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2016.05a
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• pp.135-136
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• 2016

SUPER concrete poontoon is developed to overcome shortcomings about corrosion problem of steel pontoon and the insufficient freeboard line of concrete pontoon. Top slab of Pontoon resists truck load or sidewalk live load. The soffit slab and outer wall of Pontoon resist the horizontal and vertical components of wave pressure, and those were loaded along X and Y-axis of Pontoon. Global analysis for the Pontoon is carried out to design its cross-sections economically using a geometric non-linear time history analysis method by Strand7 and buoyance-stability calculated automatically on non-vertical boundary conditions. And the load-capacity of Pontoon is confirmed through mock-up tests.