• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.17 no.4
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• pp.499-507
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• 1988

The pressure suppression pool of BWR(Boiling Water Reactor) is subjected to hydrodynamic impact in the event of a LOCA(Loss of Coolant Accident). The pressure increase in the reactor dry cell would force the existing water of a vent pipe into the suppression pool. When the water is ejected through the pipe opening into the suppression pool, an abrupt downward force is transmitted to the suppression pool floor. Consequently, many structures installed within the pool must be able to withstand these forces. In order to determine the optimum safe locations of the pool structures, numerical analysis have been carried out to investigate the hydrodynamic behavior of the water jet. In the present analysis, a two-dimensional numerical model is utilized to solve transient flow equations.

• Advances in aircraft and spacecraft science
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• v.4 no.2
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• pp.203-218
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• 2017

This paper focuses on the computational study of nonlinear effects of unsteady aerodynamics for non-classical aileron buzz. It aims at a comprehensive investigation of the aileron buzz phenomenon under varying flow parameters using the describing function technique with multiple inputs. The limit cycle oscillatory behavior of an asymmetrical airfoil is studied initially using a CFD-based numerical model and direct time marching. Sharp increases in limit cycle amplitude for varying Mach numbers and angles of attack are investigated. An aerodynamic describing function is developed in order to estimate the variation of limit cycle amplitude and frequency with Mach number and angle of attack directly, without time marching. The describing function results are compared to the amplitudes and frequencies predicted by the CFD calculations for validation purposes. Furthermore, a limited sensitivity analysis is presented to demonstrate the potential of the approach for aeroelastic design.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.22 no.4
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• pp.217-239
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• 2018

This paper examined the MHD and thermal behavior of unsteady mixed convection flow of a rotating fluid in a porous parallel plate channel in the presence of Hall current and heat source. The exact solutions of the concentration, energy and momentum equations are obtained. The influence of each governing parameter on non dimensional velocity, temperature, concentration, skin friction coefficient, rate of heat transfer and rate of mass transfer at the porous parallel plate channel surfaces is discussed. During the course of numerical computation, it is observed that as Hall current parameter and Soret number at the porous channel surfaces increases, the primary and secondary velocity profiles are increases while the primary and secondary skin friction coefficients are increases at the cold wall and decreases at the heated wall. In particular, it is noticed that a reverse trend in case of heat source parameter.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.10
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• pp.649-657
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• 2017

A rupture in a high-pressure pipe causes the fluid in the pipe to be discharged in the atmosphere at a high speed resulting in a supersonic jet that generates the compressible flow. This supersonic jet may display complicated and unsteady behavior in general. In this study, Computational Fluid Dynamics (CFD) analysis was performed to investigate the compressible flow generated by a supersonic jet ejected from a high-pressure pipe. A Shear Stress Transport (SST) turbulence model was selected to analyze the unsteady nature of the flow, which depends upon the various gases as well as the diameter of the pipe. In the CFD analysis, the basic boundary conditions were assumed to be as follows: pipe of diameter 10 cm, jet pressure ratio of 5, and an inlet gas temperature of 300 K. During the analysis, the behavior of the shockwave generated by a supersonic jet was observed and it was found that the blast wave was generated indirectly. The pressure wave characteristics of hydrogen gas, which possesses the smallest molecular mass, showed the shortest distance to the safety zone. There were no significant difference observed for nitrogen gas, air, and oxygen gas, which have similar molecular mass. In addition, an increase in the diameter of the pipe resulted in the ejected impact caused by the increased flow rate to become larger and the zone of jet influence to extend further.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.1
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• pp.9-18
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• 2016

The slender structures such as high rise building or marine riser are highly susceptible to dynamic force exerted by fluid-structure interactions among which vortex-induced vibration(VIV) is the main cause of dynamic unstability of the structural system. If VIV occurs in natural frequency regime of the structure, fatigue failure likely happens by so-called lock-in phenomenon. This study presents the numerical analysis of dynamic behavior of both structure and fluid in the lock-in regimes and investigates the subjacent phenomena to hold the resonance frequency in spite of the change of flow condition. Unsteady and laminar flow was considered for a two-dimensional circular cylinder which was assumed to move freely in 1 degree of freedom in the direction orthogonal to the uniform inflow. Fluid-structure interaction was implemented by solving both unsteady flow and dynamic motion of the structure sequentially in each time step where the fluid domain was remeshed considering the movement of the body. The results show reasonable agreements with previous studies and reveal characteristic features of the lock-in phenomena. Not only the lift force but also drag force are drastically increasing during the lock-in regime, the vertical displacement of the cylinder reaches up to 20% of the diameter of the cylinder. The correlation analysis between lift and vertical displacement clearly show the dramatic change of the phase difference from in-phase to out-of-phase when the cylinder experiences lock-in. From the results, it can be postulated that the change of phase difference and flow condition is responsible for the resonating behavior of the structure during lock-in.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.3
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• pp.210-219
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• 2014

The MPI dual injection engine can enhance the fuel efficiency and engine power. By using one injector per one intake port, MPI dual injection engine has an excellent fuel atomization and targeting injection. As the basic research for the MPI Dual injection engine design, this research was investigated in order to understand the characteristic of the in-cylinder flow and fuel behavior according to engine temperature condition and the fuel type in the MPI dual injection engines. The 3D unsteady CFD simulation for the MPI Dual injection engine was performed using STAR-CD. The engine operating condition was 2,000 rpm/WOT. The parameters for this study were fuel types, fuel temperatures and wall temperatures. As a result, the intake air amount, evaporated fuel in the cylinder and the fuel film on the wall were presented according to parameters that depend on the fuel properties and engine wall temperature. Also, the results were influenced by in-cylinder flow such as the intake flow, back flow and so on.

• Nuclear Engineering and Technology
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• v.44 no.3
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• pp.283-296
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• 2012

The natural convection in a horizontal enclosure heated from the bottom wall, cooled at the top wall, and having a square adiabatic body in the center is studied. Three different Prandtl numbers (0.01, 0.7 and 7) are considered for the investigation of the effect of the Prandtl number on natural convection. Adiabatic boundary conditions are employed for the side walls. A two-dimensional solution for unsteady natural convection is obtained, using an accurate and efficient Chebyshev spectral methodology for different Rayleigh numbers varying over the range of $10_3$ to $10_6$. It had been experimentally reported that the heat transfer mode becomes oscillatory when Pr is out of a specific Pr band beyond the critical Ra. In this study, we reproduced this phenomenon numerically. It was found that when Ra=$10_6$, only the case for intermediate Pr (=0.7) reached a non-changing steady state and the low and high Pr number cases (Pr=0.01 and 7) showed a periodically oscillatory fashion hydrodynamically and thermally. The variation of time- and surface-averaged Nusselt numbers on the hot and cold walls for different Rayleigh numbers and Prandtl numbers are presented to show the overall heat transfer characteristics in the system. Further, the isotherms and streamline distributions are presented in detail to compare the physics related to their thermal behavior.

• Journal of Korean Society of Water and Wastewater
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• v.13 no.4
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• pp.45-53
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• 1999

The microbial organisms named "Pseudomonas sp. LK-14" were isolated from farm land and shallow river sediment, activated, augmented and identified; which were using 2,4-D (2,4-Dichlorophenoxyacetic acid) as a sole carbon source and energy source. 2,4-D removal efficiency of LK-14 with 2,4-D sole carbon source (reactor S) were higher than that of Activated Sludge with 2,4-D sole carbon source (reactor A). Dynamic bioligical reaction kinetic parameters (sole carbon source was 2,4-D) obtained from batch reactor experiments were ${\mu}_{max}$ $0.105hr^{-1}$, $K_{s,24D}$ 15.64mg/L, $K_{i,24D}$ $1.94h^{r-1}$, $Y_{24D}$ 0.39 for LK-14 and ${\mu}_{max}$ $0.008hr^{-1}$, $K_{s,24D}$ 26.95mg/L, $K_{i,24D}$ $1.75hr^{-1}$, $Y_{24D}$ 0.10 for Activated Sludge. Using these parameters, we could predict the behaviors of 2,4-D substrate utilized by LK-14 and Activated Sludge in batch reactors. The kinetic parameters are enable to predict the 2,4-D substrate and microbial population behavior entering into wastewater treatment plants by using unsteady states dynamic simulation modeling technique.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.119-122
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• 2005

Ablation phenomena is very complicated because it includes momentum, energy and mass transfer, chemical reactions as well as phase change. In this paper, ablation at the rocket nozzle throat is modeled as unsteady one dimensional axi-symmetric with proper boundary conditions and field equation is solved numerically. Analytical results are compared with measured ablation data from firing experimental liquid rocket engine. Test variables are combustion pressure and mixture ratio. for low combustion pressure and low mixture ratio, the discrepancy between analysis and experiments are large but for the normal rocket operation range, two results show a simliar trend with maximum discrepancy of $100\%$.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.504-512
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• 2002

Bileaflet mechanical valves have the complications such as hemolytic and thromboembolic events, leaflet damage, and leaflet break. These complications are related with the fluid velocity and shear stress characteristics of mechanical heart valves. This fact makes clear the importance of determining the fluid velocity and shear stress characteristics of mechanical heart valves, and requires a detailed understanding of these system properties and further substantial research. The first aim of current study is to introduce fluid-structure interaction method for calculation of unsteady and three-dimensional blood flow through bileaflet valve and leaflet behavior interacted with its flow, and to overcome the shortness of previous studies, where the leaflet motion has been ignored or simplified, by using FSI method. To accomplish this goal, a finite volume computational fluid dynamics code and a finite element structure dynamics code have been used concurrently to solve the flow and structure equations, respectively, to investigate the interaction between the blood flow and leaflet. Physiologic ventricular and aortic pressure waveforms were prescribed as flow boundary conditions. The interaction of aortic flow and valve motion were computed.