• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.3
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• pp.219-226
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• 2012

Columns are the key elements supporting load in structure. Column failure causes the structure to collapse. It is important to evaluate residual strength for damaged columns under blast load for preventing progressive collapse. In this paper, columns were investigated to compare the blast resistance on the change of the number of steel bars within the range of reinforcement ratio. And this study was carried out 4 different analytical models to evaluate effects of aspect ratio. The results indicate that the vertical strain was unaffected by the number of steel bars and aspect ratio. As the number of steel bars facing blast load increase, the blast resisting capacity of the columns was improved in the lateral strain. Also, the analysis results showed that a large moment of inertia of area, as compared to a small one would be superior in residual strength as well as force of restitution.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.2
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• pp.113-120
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• 2014

This paper showed the behavior of the material four members under blast load, and are trying to demonstrate the effectiveness of the prestress. The prestressed concrete structures are on the rise, but there is little research in this regard explosion. Concrete panels, Reinforced concrete panels, the prestressed concrete panels, and the prestressed reinforced concrete panels was set variables. TNT 500 kg was an explosion in the distance 3m. Analysis, concrete and reinforced concrete members after an explosion occurred continuously deformed, but the including prestressed panel deformation occurs only at the beginning of the explosion were able to see the results. That is, the including prestressed member is prestressed against blast load cracking and destruction can be seen that control.

• Journal of Computational Design and Engineering
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• v.1 no.3
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• pp.173-186
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• 2014

The failure of a subsea production plant could induce fatal hazards and enormous loss to human lives, environments, and properties. Thus, for securing integrated design safety, core source technologies include subsea system integration that has high safety and reliability and a technique for the subsea flow assurance of subsea production plant and subsea pipeline network fluids. The evaluation of subsea flow assurance needs to be performed considering the performance of a subsea production plant, reservoir production characteristics, and the flow characteristics of multiphase fluids. A subsea production plant is installed in the deep sea, and thus is exposed to a high-pressure/ low-temperature environment. Accordingly, hydrates could be formed inside a subsea production plant or within a subsea pipeline network. These hydrates could induce serious damages by blocking the flow of subsea fluids. In this study, a simulation technology, which can visualize the system configuration of subsea production processes and can simulate stable flow of fluids, was introduced. Most existing subsea simulations have performed the analysis of dynamic behaviors for the installation of subsea facilities or the flow analysis of multiphase flow within pipes. The above studies occupy extensive research areas of the subsea field. In this study, with the goal of simulating the configuration of an entire deep sea production system compared to existing studies, a DES-based simulation technology, which can logically simulate oil production processes in the deep sea, was analyzed, and an implementation example of a simplified case was introduced.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.12
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• pp.706-713
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• 2017

This study compared and analyzed the water treatment efficiency and the applicability of water treatment plant using the existing Mechanical Rapid-Mixer by introducing the Non-powered Vortex Mixer to the domestic water treatment plant. For this study, fluid flow characteristics and head loss of a Non-powered Vortex Mixer are calculated by Computational Fluid Dynamics (CFD)respectively. The head loss rate inside the mixer was 11.30% when the inflow velocity was 0.5 m/sec, 16.27% at 0.6 m/sec and 21.44% at 0.7 m/sec, the head loss rapidly increased at the optimal velocity of 0.5 m/sec. For the inflow velocity of 0.5 m/sec, the turbulent intensity at the inlet was 2.37% and at the outlet was 7.83%, so there was sufficient mixing strength for the particulate matter and the coagulant. The result of the water quality of the treatment plants with the inflow velocity of 0.38 m/sec that was operated in three years after replacing all 12 units of the existing Rapid-Mixer with the Non-powered Mixer met the standards. Hence, it is possible to reduce the energy consumption of 64,143 ~ 65,306 kWh/year since the Rapid-Mixer is replaced by the Non-powered Vortex Mixer.

• Corrosion Science and Technology
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• v.12 no.5
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• pp.227-232
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• 2013

A number of components installed in the secondary system of nuclear power plants are exposed to aging mechanisms such as FAC (Flow-Accelerated Corrosion), Cavitation, Flashing, and LDIE (Liquid Droplet Impingement Erosion). Those aging mechanisms can lead to thinning of the components. In April 2013, one (1) inch small bore piping branched from the main steam line experienced leakage resulting from wall thinning in a 1,000 MWe Korean PWR nuclear power plant. During the normal operation, extracted steam from the main steam line goes to condenser through the small bore piping. The leak occurred in the downstream of an orifice. A control valve with vertical flow path was placed on in front of the orifice. This paper deals with UT (Ultrasonic Test) thickness data, SEM images, and numerical simulation results in order to analyze the extent of damage and the cause of leakage in the small bore piping. As a result, it is concluded that the main cause of the small bore pipe wall thinning is liquid droplet impingement erosion. Moreover, it is observed that the leak occurred at the reattachment point of the vortex flow in the downstream side of the orifice.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.1 s.151
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• pp.8-15
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• 2007

In this paper, numerical calculations are performed to analyze the unsteady flow of NACA airfoil sections. In order to ease the flow computation for the fluid region changing in time, improve the quality of solution and simplify the grid generation for the oscillating foil flow, the computational method adopts a moving and deforming mesh with the multi-block grid topology. The multi-block, structured-unstructured hybrid grid is generated using the commercial meshing software Gridgen V15. The MDM (Moving & Deforming Mesh) and the UDF (User Define function) function of FLUENT 6 are adopted for computing turbulent flows of the foil in pitching motion. Computed unsteady lift and drag forces are compared with experimental data. in general, the characteristics of unsteady lift and drag of the experiments are reproduced well in the numerical analysis.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.1
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• pp.246-253
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• 2013

This paper addresses the technology of active flow control for stabilizing a flow field. In order for flow field modeling from the control point of view, the huge-data set from CFD(computational fluid dynamics) are reduced by using a POD(Proper Orthogonal Decomposition) method. And then the flow field is expressed with dynamic equation by low-order modelling approach based on the time and frequency domain analysis. A neural network flow estimator from the pressure information measured on the surface is designed for the estimation of the flow state in the space. The closed-loop system is constructed with feedback flow controller for stabilizing the vortices on the flow field.

• Journal of Navigation and Port Research
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• v.44 no.2
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• pp.53-64
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• 2020

This paper discusses the hydrodynamic characteristics of a catamaran at low speed. In this study, the Delft 372 catamaran model was selected as the target hull to analyze the hydrodynamic characteristics by using the RANS (Reynold-Averaged Navier-Stokes) numerical method. First, the turbulence study and mesh independent study were conducted to select the appropriate method for numerical calculation. The numerical method for the CFD (Computational Fluid Dynamic) calculation was verified by comparing the hydrodynamic force with that obtained experimentally at high speed condition and it rendered a good agreement. Second, the virtual captive model test for a catamaran at low speed was conducted using the verified method. The drift test with drift angle 0-180 degrees was performed and the resulting hydrodynamic forces were compared with the trends of other ship types. Also, the pure rotating test and yaw rotating test proposed by Takashina, (1986) were conducted. The Fourier coefficients obtained from the measured hydrodynamic force were compared with those of other ship types. Conversely, pure sway test and pure yaw test also were simulated to obtain added mass coefficients. By analyzing these results, the hydrodynamic coefficients of the catamaran at low speed were estimated. Finally, the maneuvering simulation in low speed conditions was performed by using the estimated hydrodynamic coefficients.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.425-431
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• 2013

Nowadays, high speed train has settled down as a fast and convenient environment-friendly transportation and it's need is gradually increasing. However increased train speed leads to increased aerodynamic noise, which causes critically affects comfortability of passengers. Especially, the pantograph of high speed train is protruded out of train body, which is the main factor for increased aerodynamic noise. Since aerodynamic noise caused pantograph should be measured in high speed, it is difficult to measure it and to analysis aerodynamic noise characteristics due to the various types of pantograph. In this research, aerodynamic noise of pantograph is predicted by CFD (Computational Fluid Dynamic) and FW-H (Ffowcs Williams-Hawkings) equation. Also, Wind tunnel test results and numerical simulation results were compared. As a result, Simulation results predicting sound pressure level is very similar with wind tunnel test result. To analyze contribution of the pantograph to the noise of high-speed train, simulation results compared with measurement results of exterior noise. The simulation reuslts found that pantograph is a dominant noise source of high-speed trains's exterior noise in low frequency section. This dominant noise was come out from vortex shedding of the panhead in the pantograph. This research will be utilized for reduce sound pressure level of pantograph.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.8
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• pp.532-538
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• 2015

In a reciprocating compressor, highly impulsive pressure fluctuations induced by a reciprocating piston give rise to serious noise and vibration problems. A muffler is frequently used to reduce this impulsive noise, but also has adverse effects on compressor performance due to additional pressure drop and heat transfer of refrigerants through it. Therefore, the flow and acoustic performances of mufflers used in a compressor should be considered simultaneously. In this study, both of flow and acoustic performances of mufflers are investigated using computational fluid dynamic techniques by solving full three-dimensional compressible Reynolds-Averaged Navier-Stokes equations. For validation purpose, the numerical method is initially applied to predict the transmission loss of a simple expansion muffler, and its predicted results show good agreements with theoretical and experimental results. Then, the flow and acoustic performances of an existing muffler is numerically investigated. On the basis of the analysis results, a new muffler is purposed and its performances are compared with the existing one. Improved performances of the new muffler are confirmed.