• Korean Chemical Engineering Research
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• v.55 no.2
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• pp.201-213
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• 2017

Water is removed from crude oil containing water by using oil separator. This study aims to develop a three-dimensional (3D) Eulerian computational fluid dynamics (CFD) model to predict the separation efficiency of air-water-oil separator. In the incompressible, isothermal and unsteady-state CFD model, air is defined as continuous phase, and water and oil are given as dispersed phase. The momentum equation includes the drag force, lift force and resistance force of porous media. The standard k-${\varepsilon}$ model is used for turbulence flow. The exit pressures of water and oil play an important role in determining the liquid level of the oil separator. The exit pressures were identified to be 6.3 kPa and 5.1 kPa for water and oil, respectively, to keep a liquid level of 25 cm at a normal operating condition. The time evolution of volume fractions of air, water and oil was investigated. The settling velocities of water and oil along the longitudinal separator distance were analyzed, when the oil separator reached a steady-state. The oil separation efficiency obtained from the CFD model was 99.85%, which agreed well with experimental data. The relatively simple CFD model can be used for the modification of oil separator structure and finding optimal operating conditions.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.6
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• pp.64-72
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• 2017

The longitudinal dynamic instability which can occur in the fueling process of a space launch vehicle is called pogo. It is caused by coupling between the fuselage and propulsion system and they would be formed as a closed-loop system. so that the amplitude of the response may increase or decrease. In this paper, a mathematical model which is applicable to the systematic pogo analysis of a general launch vehicle is developed for an example of space shuttle. The formulations are composed of the linearized second-order differential equation for the propulsion system, and of the pressure, weight displacement, and generalized displacement. Those are important parameters for pogo analysis, are derived through eigenvalue analysis. By the formulation suggested in this paper, it is expected that mathematical modeling method of the pogo system can be obtained and systematic pogo stability analysis for any launch vehicle will be enabled.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.2
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• pp.159-173
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• 1991

This paper describes a potential-based panel method formulated for the analysis of a super-cavitating two-dimensional hydrofoil. The method employs normal dipoles and sources distributed on the foil and cavity surfaces to represent the potential flow around the cavitating hydrofoil. The kinematic boundary condition on the wetted portion of the foil surface is satisfied by requiring that the total potential vanish in the fictitious inner flow region of the foil, and the dynamic boundary condition on the cavity surface is satisfied by requiring thats the potential vary linearly, i.e., the tangential velocity be constant. Green's theorem then results in a potential-based integral equation rather than the usual velocity-based formulation of Hess & Smith type. With the singularities distributed on the exact hydrofoil surface, the pressure distributions are predicted with improved accuracy compared to those of the linearized lilting surface theory, especially near the leading edge. The theory then predicts the cavity shape and cavitation number for an assumed cavity length. To improve the accuracy, the sources and dipoles on the cavity surface are moved to the newly computed cavity surface, where the boundary conditions are satisfied again. This iteration process is repeated until the results are converged. Characteristics of iteration and discretization of the present numerical method are much faster and more stable than the existing nonlinear theories. The theory shows good correlations with the existing theories and experimental results for the super-cavitating flow. In the region of small angles of attack, the present prediction shows and excellent comparison with the Geurst's linear theory. For the long cavity, the method recovers the trends of the Wu's nonlinear theory. In the intermediate regions of the short super-cavitation, the method compares very well with the experimental results of Parkin and also those of Silberman.

• Journal of Digital Convergence
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• v.15 no.7
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• pp.329-342
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• 2017

This study investigates convergent influence on Self Factors(SF), Stress Factors(STF), Resilience & Control Factors(RCF), Test Anxiety(TA), Learning Flow(LF) and academic burnout among Health College Students in TOEIC class(HCST). The survey was administered to 291 HCST from 1 college located in J area during the period from April 3, 2017 to April 14, 2017. The structured self-administered questionaries were used. With the analysis of covariance structure, we could confirm relationship among the six factors such as SF, STF, RCF, TA, LF and academic burnout. The results of the study indicate that the efforts, to manage these factors, are required to decrease the academic burnout of HCST. Squared multiple correlations, which explain the academic burnout related with the stress from economic pressure and job seeking, test anxiety, learning flow and self factors, were 98.8%. The results are expected to be useful for the development of TOEIC learning curriculum and course to decrease the academic burnout of HCST. In the following study, the analysis about additional factors of influence on academic burnout will be needed.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.1
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• pp.1-10
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• 1997

Viscous flow around actual ship is calculated by an use of RANS equations. The propriety of this computing method, usefulness to hull form design and the scale effect which is the effect of viscous flow depending on the scale of ship model are investigated. Reynolds stress is modelled by using k-${\varepsilon}$ turbulence model and the law of wall is applied near the body. Body fitted coordinates are introduced for the treatment of the arbitrary 3-dimensional shape of the ship hull form. The transformed equations in the computational domain are numerically solved by an employment of FVM. In the calculation of pressure, SIMPLE method is adopted and the solution of the discretized equation is obtained by the line-by-line method with the use of TDMA The calculations of two ships, 4410 TEU container carrier and 50,000 DWT class bulk carrier, are performed at model and actual ship scale. The results are compared and discussed with the model test results which are viscous resistance, nominal wake distribution at propeller plane and limiting streamline on the hull surface. They describe the effect of stem form and the scale effect very well. In particular, the calculated nominal wake distribution and limiting streamline are agreed qualitatively with the experiments and the viscous resistance values are estimated within ${\pm}5%$ difference from the resistance tests.

• Journal of the Korean Institute of Gas
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• v.16 no.3
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• pp.35-41
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• 2012

Manifold researches for carbon capture and storage (CCS) have been developed and large scale-carbon capture system can be performed recently. Hence, the technologies for $CO_2$ sequestration or storage become necessary to handle the captured $CO_2$. Among them, enhanced oil recovery using $CO_2$ can be a solution since it guarantees both oil recovery and $CO_2$ sequestration. In this study, the miscible flow of oil and $CO_2$ in porous media is modeled to analyze the effect of enhanced oil recovery and $CO_2$ sequestration. Based on Darcy-Muskat law, the equation is modified to consider miscibility of oil and $CO_2$ and the change of viscosity. Finite volume method is used for numerical modeling. As results, the pressure and oil saturation changes with time can be predicted when oil, water, and $CO_2$ are injected, respectively, and $CO_2$ injection is more efficient than water injection for oil recovery.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.12 no.2
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• pp.70-80
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• 2000

Princeton Ocean Model (POM) is modified to construct a three-dimensional, semi-implicit hydro¬dynamic model with a wetting-and-drying scheme. The model employs semi-implicit treatment of the barotropic pressure gradient terms and the vertical mixing terms in the momentum equations, and the velocity divergence term in the vertically-integrated continuity equation. Such treatment removes the external mode and thus the mode splitting scheme in POM, allowing the semi-implicit model to use a larger time step. Applied to hypothetical systems, both the semi-implicit model and POM give nearly the same results. The semi-implicit model, however, runs approximately 4.4 times faster than POM showing its improved computational efficiency. Applied to a hypothetical system with intertidal flats, POM employing the mode splitting scheme produces noises at the intertidal flats, that propagate into the main channel resulting in unstable current velocities. Despite its larger time step, the semi-implicit model gives stable current velocities both at the intertidal flats and main channel. The semi-implicit model when applied to Kyeonggi Bay gives a good reproduction of the observed tides and tidal currents throughout the modeling domain, demonstrating its prototype applicability.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.346-353
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• 2016

In the design conditions of some research reactors, the siphon phenomenon can cause continuous efflux of water during pipe rupture. A siphon breaker is a safety device that can prevent water efflux effectively. However, the analysis of the siphon breaking is complicated because many variables must be included in the calculation process. For this reason, a simulation program was developed with a user-friendly GUI to analyze the siphon breaking easily. The program was developed by MFC programming using Visual Studio 2012 in Windows 8. After saving the input parameters from a user, the program proceeds with three steps of calculation using fluid mechanics formulas. Bernoulli's equation is used to calculate the velocity, quantity, water level, undershooting, pressure, loss coefficient, and factors related to the two-phase flow. The Chisholm model is used to predict the results from a real-scale experiment. The simulation results are shown in a graph, through which a user can examine the total breaking situation. It is also possible to save all of the resulting data. The program allows a user to easily confirm the status of the siphon breaking and would be helpful in the design of siphon breakers.

• Resources Recycling
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• v.7 no.4
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• pp.27-34
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• 1998

In this research, the processing control of NiCuZn Ferrite (NCZF) had been studied. NiCuZn Ferrite, which calcined at $700^{\circ}C$ for 3 bours, was ball milled for about 60 hours to ill김ke a size of $0.5\mu\;extrm{m}$ followed by granulation using spray dryer Apparent densincatioo rate and initial permeability of NiCuZn Ferrite with an initial packing density had been investigated as f follows. 1.The relative packing density of NCZF green body increas$\xi$d in the range of 48.6-56.8% with an increased forming pressure of 20-170 MPa. 2. The higher the relative pac퍼ng density of NCZF and the sintering temperature are, the higher the initial densification rate. The increased bulk rlcnsity of NCZF was attributed to the densification rate with decreased open pore and increased closed pore as the relative packing density, sintering temperature, and sinteriog tim$\xi$ increased. 3. The initial P permeability of NCZF with constant composition is logarithmically proportional to the bulk density of NCZF sintered at $875~925^{\circ}C$ for 0-5h, and strongly depended on the relative packing density of NCZF green body. The empirical equation is as f follows; log $\mu$i=$G1{\times}BD$+$G2{\times}RPD$+b(0);where, G1, G2; gradient, B.D: bulk density, RPD; relative packing density, b(0); intercept.

• Journal of Korea Water Resources Association
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• v.51 no.7
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• pp.543-554
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• 2018

A methodology has been presented for evaluating the partial safety factors on the sliding failure mode of vertical caissons of composite breakwaters and for determining the cross sections of those by Level I reliability-based design method. Especially, a mathematical model has been suggested for the sake of a consistency of code format as well as convenience of application in practical design, for which the uncertainties associated with buoyancy and its own weight can be taken into account straightforwardly. Furthermore, design criteria equation has been derived by considering accurately the effect of uplift pressure, so that the cross sections of caissons can be assessed which must be safe against the sliding failure. It has been found that cross sections estimated from partial safety factors proposed in this paper are in very good agreement with the results of Level II AFDA and Level III MCS under the same target probability of failure. However, partial safety factors of the Technical Standards and Commentaries for Port and Harbour Facilities in Japan and Coastal Engineering Manual in USA tend to estimate much bigger or smaller cross sections in comparison to the present results. Finally, many reliability re-analyses have been performed in order to conform whether the stability level of cross section estimated by Level I reliability-based design method is satisfied with the target probability of failure of partial safety factors or not.