• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.575-583
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• 1991

The weld pool convection problem that occurs during the stationary GTA welding has been studied, considering the four driving forces for weld pool convection, i.e., the electromagnetic force, the buoyancy force, the aerodynamic drag force, and the surface tension force at the weld pool surface. In the numerical simulation, the difficulties associated with the irregular moving liquid-solid interface have been successfully overcome by adopting a Boundary-Fitted Coordinate system. In the experiments to show the validity of the numerical analysis, a deep periphery and shallow centerpentrated weld pool shape was observed from the etched specimen. It could be revealed that this type of weld pool shape could be simulated, only when some of aerodynamic drag force distributions are considered. Although slight disagreement arose, the calculated and the observed weld pool shapes were in a reasonable agreement.

• Fire Science and Engineering
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• v.14 no.2
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• pp.21-32
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• 2000

In this study, reduced-scale experiments as the alternative to a real-scale fire test were conducted to understand fire properties in tunnel, and their results were compared with those of numerical simulation. The 1/20 scale experiments were conducted under the Froude scaling since smoke movement in tunnel is governed by buoyancy farce. A numerical simulations were on performed 3D unstructured meshes with PISO algorithm and buoyant plume models. Results showed that data was in reasonable agreement with the numerical data of smoke velocity, temperature distribution, and clear height.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.540-545
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• 2008

An atrium has great potential in natural ventilation aided by buoyance effect. Architectural design of an atrium is very critical to maximize the effect. However, it is not easy of an atrium to have optimum shape for natural ventilation, from the aesthetic and economic point of view. Admitting this condition, we suggested a strategy to promote natural ventilation, which can be adopted only with small design change. At first, we installed BIPV on the top of an atrium to strengthen buoyancy effect, and combine forced ventilation by low pressure fan. To evaluate the performance of the measure, CFD simulation and Energy-Airflow analysis were achieved.

• Journal of the Korean Society of Safety
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• v.10 no.3
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• pp.68-80
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• 1995

A series of parametric calculations have been performed in order to investigate the short-term and short-range plume and puff behavior of toxic gaseous and solid pollutant dispersion in an open atmosphere. The simulation is made by the use of the computer program developed by this laboratory, in which a control-volume based finite-difference method is used together with the SIMPLEC algorithm for the resolution of the pressure-velocity coupling appeared In Wavier-Stokes equation. The Reynolds stresses are solved by the standard two-equation k-$\varepsilon$ model modified for buoyancy together with the RNG(Renormalization Group) k-$\varepsilon$ model. The major parameters considered in this calculation are pollutant gas density and temperature, the relative velocity of pollutants to that of the surrounding atmospheric air, and particulate size and density together with the height released. The flow field is typically characterized by the formation of a strong recirculation region for the case of the low density gases such as $CH_4$ and air due to the strong buoyancy, while the flow is simply declining pattern toward the downstream ground for the case of heavy molecule like the $CH_2C1_2$and $CCl_4$, even for the high temperature, $200^{\circ}C$. The effect of gas temperature and velocity on the flow field together with the particle trajectory are presented and discussed in detail. In general, the results are physically acceptable and consistent.

• Nuclear Engineering and Technology
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• v.56 no.2
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• pp.611-623
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• 2024

The ISP-47 TOSQAN experiment was analyzed with containmentFOAM which is an open-source CFD code based on OpenFOAM. The containment phenomena taking place during the experiment are gas mixing, stratification and wall condensation in a mixture composed of steam and non-condensable gas. The k-ω SST turbulence model was adopted with buoyancy turbulence models. The wall condensation model used is based on the diffusion layer approach. We have simulated the full TOSQAN experiment which had a duration 20000 s. Sensitivity studies were conducted for the buoyancy turbulence models with SGDH and GGDH and there were not significant differences. All the main features of the experiments namely pressure history, temperature, velocity and gas species evolution were well predicted by containemntFOAM. The simulation results confirmed the formation of two large flow stream circulations and a mixing zone resulting by the combined effects of the condensation flow and natural convection flow. It was found that the natural convection in lower region of the vessel devotes to maintain two large circulations and to be varied the height of the mixing zone as result of sensitivity analysis of non-condensing wall temperature. The computational results obtained with the 2D mesh grid approach were comparable to the experimental results.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.3
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• pp.441-450
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• 2022

The introduction of autonomous underwater gliders (AUGs) specifically addresses the reduction of operational costs that were previously prohibited with conventional autonomous underwater vehicles (AUVs) using a "scaling-down" design philosophy by utilizing the characteristics of autonomous drifters to far extend operation duration and coverage. Long-duration, wide-area missions raise the cost and complexity of in-water testing for novel approaches to autonomous mission planning. As a result, a simulator that supports the rapid design, development, and testing of autonomy solutions across a wide range using software-in-the-loop simulation at faster-than-real-time speeds becomes critical. This paper describes a faster-than-real-time AUG simulator that can support high-resolution bathymetry for a wide variety of ocean environments, including ocean currents, various sensors, and vehicle dynamics. On top of the de facto standard ROS-Gazebo framework and open-sourced underwater vehicle simulation packages, features specific to AUGs for ocean mapping are developed. For vehicle dynamics, the next-generation hybrid autonomous underwater gliders (Hybrid-AUGs) operate with both the buoyancy engine and the thrusters to improve navigation for bathymetry mappings, e.g., line trajectory, are is implemented since because it can also describe conventional AUGs without the thrusters. The simulation results are validated with experiments while operating at 120 times faster than the real-time.

• Journal of Navigation and Port Research
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• v.28 no.6
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• pp.565-572
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• 2004

Residual current plays more important role than the tidal current for long-term material transport in coastal areas. The main component of residual current is tide-induced residual current. Otherwise, wind driven current and buoyancy-driven current are important components which change the residual current. To clarify the characteristic of coastal current, application of a three -dimensional model is necessary. This study focuses on clarifying the stratified systems of coastal water affected by freshwater runoff from a river and analyzes the structure of current at Ulsan bay by applying a three-dimensional buoyancy-driven current model. According to the result of “Ulsan bay” study, it shows that the surface layer in semi-enclosed estuaries, which affected by freshwater runoff. has flows going out, and the bottom layer has flows coming in. Besides when the wind blows toward inside of the bay, the surface layer has flows coming in and the bottom layer has flows going out as compensation flows for the surface circulation. The results of simulation could be applicable to examine vertical upwelling, which might be caused by construction of artificial fishing reef to build aqua farm, submerged breakwater to control coastal sediment, and the formulation of oceanic ridge, or a basic study on application to the usage of deep water.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.7 s.250
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• pp.630-637
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• 2006

The flow regimes for a Taylor-Couette flow with a stable, axial stratification in density are investigated using numerical simulation. The flow configuration identical to that in the experiment of Boubnov, et al. (1995) is considered in the present research. The main objectives of this investigation are to verify the experimental and numerical results carried out by Boubnov, et al. and Hua et al. (1997), respectively, and to further study the detailed flow fields and flow bifurcations. With increasing buoyancy frequency of the fluid (N), the stratification-dominated flow regime, called the S-regime, is observed. It is also confirmed that the important effect of an axial density stratification is to stabilize the flow field. The present numerical results are in good agreement with Boubnov, et al. and Hua et al.'s observations.

• 한국연소학회:학술대회논문집
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• 2000.12a
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• pp.113-122
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• 2000

Dynamic structures of unsteady $CH_4$/Air jet diffusion flames with flame-vortex interaction were numerically investigated. A time-dependent, axisymmetric computational model was adopted for this calculation. Two step global reaction mechanism which considers 6 species, was used to calculate the reaction rates. The predicted results including gravitational effect show that the large outer vortices and the small inner vortex street can be well simulated without any additional disturbances in the downstream of nozzle tip. It was found that the temperature and species concentrations had various values for the same mixture fraction in flame-vortex interaction region. This unsteady jet flame configuration accompanying flame-vortex interaction is expected to give good implications for the structure of turbulent flames.

• Journal of Mechanical Science and Technology
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• v.16 no.2
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• pp.262-269
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• 2002

The effects of velocity boundary conditions on the structure of methane-air nonpremixed counterflow flames were investigated by two-dimensional numerical simulation. Two low global strain rates, 12 s$\^$-1/ and 20 s$\^$-1/, were considered for comparison with measurements. Buoyancy was conformed to have strong effects on the flame structure at a low global strain rate. It was shown that the location where a top hat velocity profile was imposed is sensitive to the flame structure, and that the computed temperature along the centerline agrees well with the measurements when plug flow was imposed at the inner surface of the screen nearest the duct exit.