• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.7 s.124
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• pp.624-631
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• 2007

PFA (power flow analysis) has been recognized as a useful method in vibration analysis of medium-to-high frequency ranges. Until now, PFA method has been developed for steady-state vibration problems. In this paper, PFA method has been expanded to transient problem. New energy governing equations are derived considering time dependent terms in beam and plate. Analytic solutions of those equations are found in simple beam and plate, and are verified by comparing with modal solutions.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.715-720
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• 2000

Stratified flow past a three-dimensional obstacle such as a sphere has been a long-lasting subject of geophysical, environmental and engineering fluid dynamics. In order to investigate the effect of the stratification on the near wake, in particular, the unsteady vortex formation behind a sphere, numerical simulations of stratified flows past a sphere are conducted. The time-dependent Navier-Stokes equations are solved using a three-dimensional finite element method and a modified explicit time integration scheme. Laminar flow regime is considered and linear stratification of density is assumed under Boussinesq approximation. The computed results include the characteristics of the near wake and the unsteady vortex shedding. With a strong stratification, the separation on the sphere is suppressed and the wake structure behind the sphere becomes planar, resembling that behind a vertical cylinder.

• Journal of Korean Society for Atmospheric Environment
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• v.12 no.4
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• pp.479-485
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• 1996

Volatile organic compounds are air pollutants exhausting from industrial process, evaporation of solvent, and so on. Most of VOCs are the combustible gas of low calorific value as it is diluted by air. The systems burning such a hazardous gas need to increase enthalpy in order to increase flame stability. In this study an incinerator with reciprocating flow in the honeycomb ceramic has been used for the experiment of VOCs control. By the reciprocating flow system, the enthalpy of combustion gas is effectively regenerated into the enthalpy increases of the combustible gas through the honeycomb ceramic, which provides a heat storage. The position of the reaction zone is strongly dependent on the parameters of mixture velocity and time frequency. Flame front is changed to the point where burning velocity is coincided with burning velocity in the honeycomb ceramic. In this system it is important that flame front should be located symmetrically at the center of honeycomb ceramic for the purpose of increasing the reaction rate at one point. Peak temperature becomes higher with decreasing time frequency, at which the flow direction is regularly reversed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.347-352
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• 2004

The unsteady aerodynamic characteristics of an aerofoil gradually accelerating or decelerating at subsonic speeds are investigated through two-dimensional, unsteady, compressible Navier-Stokes simulations. An acceleration factor is defined to provide various acceleration or deceleration characters of the time-dependent flow over the aerofoil. The results show that an increase in the absolute value of the non-dimensional acceleration factor leads to a lesser change in the location and range of flow featues such as shockwave and boundary layer separation in a specific time range. Generally, the gradual speed-up and speed-down of the subsonic aerofoil results in different aerodynamic characteristics whose changes are more significant at angles of attack.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.05a
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• pp.52-57
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• 2001

Laminar two-dimensional time-dependent flow past a circular cylinder is numerically investigated using direct numerical simulation for the low Reynolds number (Re=164∼280). The higher-order finite difference scheme is employed for the spatial distributions along with the second order Adams-Bashforth and the first order backward-Euler time integration. The convection term is applied by the 7th order up wind scheme and the pressure and viscosity terms are applied by the 4th order central difference. The grid system makes use of the regular grid system and it is generated by an equation. The calculated results of drag coefficients, lift coefficients, pressure distributions, and vorticity contours and other information are compared with experimental and numerical ones. These results obtained by the present DNS show good agreement with the previous studies.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.17 no.31
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• pp.115-123
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• 1994

Group scheduling, which is a kind of operations scheduling based on the GT concept is analyzed in a multi-stage manufacturing system. The purpose of this research is to develop and evaluate a heuristic algorithm for determining gro up sequence and job sequence within each group to minimize a complex cost function, i.e. the sum of the total pe-nalty cost for tardiness and the total holding cost for flow time, in a multi-stage manufacturing system with group setup time dependent upon group sequence. A heuristic algorithm for group sc heduling is developed, and a numerical example is illustrated. For the evaluation of the pro-posed heuristic algorithm, the heuristic solution of each of 63 problems is compared with that of random scheduling. The result shows that the proposed heuristic algorithm provides better solution in light of the proposed cost function.

• Journal of Korean Institute of Industrial Engineers
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• v.11 no.2
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• pp.75-85
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• 1985

The application of GT results in the mass production effect to multi-product, small lot-sized production. Group scheduling, which is operations scheduling based on the GT concept, is analyzed in a multistage manufacturing system. But the research has been limited in independent setup time models. A heuristic algorithm has been developed to minimize the mean flow time when setup times are dependent to sequence of group in multistage. For evaluation of the heuristic algorithm, the solution of heuristic algorithm is compared with that of random scheduling. The result of comparison indicates that the proposed heuristic algorithm provides good solutions with relatively fewer computational effort.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.19 no.2
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• pp.103-121
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• 2015

In this paper, we briefly review and describe a projection algorithm for numerically computing the two-dimensional time-dependent incompressible Navier-Stokes equation. The projection method, which was originally introduced by Alexandre Chorin [A.J. Chorin, Numerical solution of the Navier-Stokes equations, Math. Comput., 22 (1968), pp. 745-762], is an effective numerical method for solving time-dependent incompressible fluid flow problems. The key advantage of the projection method is that we do not compute the momentum and the continuity equations at the same time, which is computationally difficult and costly. In the projection method, we compute an intermediate velocity vector field that is then projected onto divergence-free fields to recover the divergence-free velocity. Numerical solutions for flows inside a driven cavity are presented. We also provide the source code for the programs so that interested readers can modify the programs and adapt them for their own purposes.

• Journal of Advanced Marine Engineering and Technology
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• v.21 no.4
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• pp.430-436
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• 1997

Time-dependent Flow characteristics of a two-dimensional lid-driven square cavity flow of six high Reynolds numbers, $10^4 2{\times}lO^4., 3{\times}l0^4, 5{\times}lO^4, 7.5{\times}lO^4$ and $10^5$ were investigated. A convection conservative difference scheme based upon SOLA to maintain the nearly 2nd-order spatial accuracy was adopted on irregular grid formation. Irregular grid number is $80{\times}80$ and its minimum size is about 1/400 of the cavity height(H) and its maximum is about 1/53 H. The result shows that at Re= $10^4$, periodic migration of small eddies appearing in corner separation region and its temporal sinusoidal fluctuation are represented. And another critical Reynolds number which shows the commencement of flow randomness emerging from the periodic fluctuation is assumed to be around Re= $1.5{\times}10$. At five higher Reynolds numbers ($2{\times}lO^4., 3{\times}l0^4, 5{\times}lO^4, 7.5{\times}lO^4$ and $10^5$), an organizing structure of four consecutive vortices similar to a Moffat vortex at two lower corners is revealed from time-mean flow patterns.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.863-868
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• 2003

Mixers are used in various industrial fields where it is necessary to intimately mix two reactants in a short period of time. However, despite their widespread use, complex unsteady flow characteristics of industrial mixers are not systematic investigated. The present study aimed to clarify unsteady flow characteristics induced by various impellers in a tank. Impellers arc hydrofoil turbine and neo-hydrofoil turbine types. A high speed CCD camera and an Ar-Ion laser for illumination were adopted to clarify the time-dependent flow characteristics of the mixers. The rotating speed of impellers increased from 6Hz to 60Hz by 6Hz, The maximum velocity around neo-hydrofoil impeller is higher than the hydrofoil type impeller. These two types of turbine shows that typical flow characteristics of axial turbine and suitable for mixing high-viscosity materials.