• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.6
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• pp.989-1002
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• 2018

Grouting for the rock joint is to strengthen the rock strata by infiltrating cement grout materials into the rock joints. Grouting is one of a field of study which is difficult to develop deterministic and quantitative design approach because of multiphase behaviors of grout materials and 3 dimensional features of rock joints. Therefore, GIN (Grouting Intensity Number) can be a good index with appropriate monitoring of pressure and volume of grout. In this paper, we investigate the effects of joint roughness (JRC) and rheology of cement material during the infiltration of cement grout material into rock joint through CFD (computational fluid dynamics) analyses. With rough joint surface and increase of WC ratio, the frictional resistance during the grouting increases. The results have been summarized with polynomial correlations.

• Journal of ILASS-Korea
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• v.13 no.4
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• pp.200-205
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• 2008

Spray formation mechanism was controlled by a cavitation inside an injection nozzle. Nozzle geometry affects spray characteristics and formation behavior, which could determine engine performance and pollutant formation. A study was carried out on the influence of aspect ratio on cavitation inside a nozzle. The cavitation model available in Star-CD code was used to obtain cavitation behavior inside nozzle, which was compared with previous experimental results. In this paper, a CFD approach combining multiphase Volume-of-Fluid(VOF) and k-model was applied. The numerical results are similar with the experimental results.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.592-595
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• 2011

A numerical investigation on a suction vortices, free vortices and subsurface vortices behavior in the model sump system with multi-intakes is performed A test model sump and piping system were designed based on Froude similitude for the prototype of the recommended structure layout by HI-9.B Standard for Pump Intake Design of the Hydraulic Institute. A numerical analysis of three dimensional multiphase flows through the model sump is performed by using the finite volume method of the CFX code with multi-block structured grid systems. A ${\kappa}-{\omega]$ ShearStressTransportturbulencemodelandthe Rayleigh-Plesset cavitation model are used for solving turbulence cavitating flow. From the numerical analysis, several types of vortices are reproduced and their formation, growing shedding and detailed vortex structures are investigated. To reduce abnormal vortices, an anti-vortex device is considered and its effect is investigated and discussed.

• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.1152-1166
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• 2023

The bubbly flow of air or steam in subcooled water are investigated here in several test cases, characterized by different pipe sizes, bubble dimensions and flow rates, by means of CFD using a Eulerian-Eulerian approach. The performance of models that differ for the turbulence closure in the continuous phase, as well as for the description of the lift force on the dispersed phase, are compared in detail. When air is considered, the space of the experimental parameters leading to a reasonable performance for the selected models are identified and discussed, while the issues left in the modelling of the concurrent condensation are highlighted for the cases where steam is used.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.638-643
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• 2021

Oil is used in various industries, including the agricultural sector, food industry, and functional cosmetics. These oils are chemically unstable and prone to oxidation when exposed to oxygen, light, moisture, or high temperatures. Therefore, various attempts have been made to encapsulate them so that they are not exposed to such environments. When oil is injected into a refrigerant with greater density, the oil can be encapsulated as it rises due to buoyancy caused by the density difference. In this study, oil encapsulation was simulated to find the optimal conditions for operating equipment using computational fluid dynamics (CFD) for multiphase flows. Water or serum can be used as a refrigerant. The viscosity of water is relatively small, and if it is used as a refrigerant, oil droplets can be produced well even if oil and water are continuously injected in the equipment. However, the viscosity of serum is very high, and if it is used, the oil is stretched out and does not leave the nozzle. The results show that when using serum as a cooling medium, oil encapsulation is possible if the injection is stopped for some time after instantaneous injection at high speed.

• Journal of Ocean Engineering and Technology
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• v.35 no.1
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• pp.38-49
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• 2021

Slug flow is the most common multi-phase flow encountered in oil and gas industry. In this study, the hydrodynamic features of flow in pipes investigated numerically using computational fluid dynamic (CFD) simulations for the effect of slug flow on the vertical and bent pipeline. The compressible Reynold averaged Navier-Stokes (RANS) equation was used as the governing equation, with the volume of fluid (VOF) method to capture the outline of the bubble in a pipeline. The simulations were tested for the grid and time step convergence, and validated with the experimental and theoretical results for the main hydrodynamic characteristics of the Taylor bubble, i.e., bubble shape, terminal velocity of bubble, and the liquid film velocity. The slug flow was simulated with various air and water injection velocities in the pipeline. The simulations revealed the effect of slug flow as the pressure occurring in the wall of the pipeline. The peak pressure and pressure oscillations were observed, and those magnitudes and trends were compared with the change in air and water injection velocities. The mechanism of the peak pressures was studied in relation with the change in bubble length, and the maximum peak pressures were investigated for the different positions and velocities of the air and water in the pipeline. The pressure oscillations were investigated in comparison with the bubble length in the pipe and the oscillation was provided with the application of damping. The pressures were compared with the case of a bent pipe, and a 1.5 times higher pressures was observed due to the compression of the bubbles at the corner of the bent. These findings can be used as a basic data for further studies and designs on pipeline systems with multi-phase flow.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.4
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• pp.620-631
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• 2022

This paper shows the numerical prediction of the change in oil outflow rate according to the orifice shape of a damaged ship by using the computational fluid dynamics (CFD) analysis method. It also provides discharge coefficients for various orifice shapes to be used in theoretical prediction approaches. The oil outflow from the model ship was analyzed using a multiphase flow method under the condition that the Froude and Reynolds number similitudes were satisfied. The present numerical results were verified by comparing them with the available experimental data. Along with the aspect ratio of the orifice and the wall thickness of the cargo tank, the effects of the orifice shapes defined by mathematical figures on the oil outflow were investigated. To consider more realistic situations, the investigation of the ef ect of the crushed iron plate around the damaged part was also included. The numerical results confirmed the change in oil outflow time for various shapes of the damaged part of the oil tank, and discharge coefficients that quantify the viscous effects of those orifice shapes were extracted. To verify the predicted discharge coefficients, they were applied to an oil spill estimation equation. As a result, a good agreement between the CFD and theoretical results was obtained.

• Journal of computational fluids engineering
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• v.21 no.3
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• pp.55-63
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• 2016

Nowadays, large container ships are continually developed and that's why the bow and stern structural stability problems by slamming become a significant more and more. However, due to the complexity of slamming, it is difficult to consider those problems at the design stage. For this reason, we attempt numerical analysis through SNUFOAM by generating the bow and stern two-dimensional cross-sectional grid in WILS JIP experiment at KRISO. Unlike the conventional method for the computation time saving, by setting the inlet flow conditions referred to the model test, we analyzed the slamming without applying the grid deformation method. As a result, when the stern model, as in the previous studies, it was possible to obtain quantitatively the fluid impulse is close to the experimental results. When the bow model, we can found the change by the position of force sensors which are derived for the bulbous bow and obtained fluid impulse and flow shape at slamming similar to the model test.

• International Journal of Fluid Machinery and Systems
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• v.4 no.1
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• pp.76-83
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• 2011

This study highlights especially the mechanism of vortex cavitation occurrence from the end of the suction duct in a double-suction volute pump and pump oscillation which causes cavitation noise from the pump. In this study, full 3D numerical simulations have been performed using a commercial code inside the pump from the inlet of suction duct to the outlet of delivery duct. The numerical model is based on a combination of multiphase flow equations with the truncated version of the Rayleigh-Plesset model predicting the complicated growth and collapse process of cavity bubbles. The experimental investigations have also been performed on the cavitating flow with flow visualization to evaluate the numerical results.

• Transactions of the Korean hydrogen and new energy society
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• v.25 no.4
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• pp.443-448
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• 2014

This paper describes thermal flow characteristics in various pipelines: straight pipeline and curved pipeline. In the permafrost area, pipelines are exposed to an extremely low temperature ($-40^{\circ}C$). In this situation, three-dimensional flow analysis should be analyzed to investigate thermal effects such as pressure drop, temperature change, velocity deficit and distribution change of liquid droplet of internal fluid. In this paper, multi-phase and multi-species analysis was introduced to analyze the flow characteristics of permafrost pipelines on the vertical support members above ground.