• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.164-169
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• 2009

Study on swimming of microorganisms like, sperm motility, cilia beating, bacterial flagellar propulsion has found immense significance in the field of biological fluiddynamics. Because of the complexity involved, it is challenging for the researchers to model such problems. Immersed boundary method has proved its efficacy in the field of biological fluiddynamics, The present work aims at performing a numerical study on the microorganism locomotion using the immersed boundary method proposed by Peskin[1]. A two-dimensional model of the microorganism is modeled as thin elastic filament described as a sine wave. The neutrally buoyant organism undergoing deformations is immersed in a viscous and incompressible fluid. The fluid quantities are described using Eulerian coordinates and the immersed body is represented by Lagrangian coordinates. The Eulerian and Lagrangian variables are connected by the Dirac delta function. The Navier-Stokes equations governing the fluid flow are solved using the fractional step method on a staggered Cartesian grid system. The developed numerical code in FORTRAN will be validated by comparing the numerical results with the available results.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.2
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• pp.21-30
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• 1990

Theoretical and experimental techniques to analyze the two-dimensional liquid motion in a tank are discussed. A Lagrangian FEM with a velocity correction procedure is introduced to describe incompressible free surface fluid flow. A mesh rezoning technique is used to prevent strong distortion of finite elements in the Lagrangian description. Model test technique for sloshing tank is developed using a hydraulic type bench tester. The influence of the variation in the exciting frequency and amplitude are observed for various fill depths. The results of theoretical calculations are compared with those of experiments.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.10 s.241
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• pp.1163-1171
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• 2005

The shape optimization of an airfoil has been performed for an incompressible viscous flow. In this study, Pareto frontier sets, which are global and non-dominated solutions, can be obtained without various weighting factors by using the multi-objective genetic algorithm An NACA0012 airfoil is considered as a baseline model, and the profile of the airfoil is parameterized and rebuilt with four Bezier curves. Two curves, front leading to maximum thickness, are composed of five control points and the rest, from maximum thickness to tailing edge, are composed of four control points. There are eighteen design variables and two objective functions such as the lift and drag coefficients. A generation is made up of forty-five individuals. After fifteenth evolutions, the Pareto individuals of twenty can be achieved. One Pareto, which is the best of the . reduction of the drag furce, improves its drag to $13\%$ and lift-drag ratio to $2\%$. Another Pareto, however, which is focused on increasing the lift force, can improve its lift force to $61\%$, while sustaining its drag force, compared to those of the baseline model.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1335-1340
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• 2007

The media transport systems, such as printers, copy machines, facsimiles, ATMs, cameras, etc. have been widely used and being developed rapidly. In the development of those sheet-handling machineries, it is important to predict the static and dynamic behavior of the sheet with a high degree of reliability because the sheets are fed and stacked at such a high speed. Flexible media are very thin, light and flexible, so they behave in geometric nonlinearity with large displacement and large rotation but small strain. In the flexible media analysis, aerodynamic effect from the surrounding air must be included because any small force can make large deformation. In this paper, surrounding air was modeled by incompressible Navier-Stokes flow and an arbitrary Lagranigan-Eulerian(ALE) finite element method with automatic mesh-updating technique was formulated for large domain changes. In the numerical simulations, the results with consideration of the air fast decayed and converged into static results while the results without considering air oscillated continuously.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.9
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• pp.1018-1024
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• 2011

Liquid sloshing occurs when a partially filled liquid tank is subjected to undesirable external forces or acceleration/deceleration for positioning control. Installation of baffles is still the most popular way to suppress the sloshing, but recent successes of input shaping in reducing structural vibrations may give a possible alternative. We aim at investigating the applicability of input shaping to sloshing suppression by numerically solving fluid motions in a rectangular tank. The tank is partially filled with water and it is suddenly put into a sequence of horizontal motions of acceleration and constant speed. The flow is assumed to be two-dimensional, incompressible, and in viscid, and a VOF two-phase model is used to capture the free surface. Results show that the sloshing can be successfully suppressed by shaping the input, i.e., the velocity or acceleration profile of tank. Three different input shapers (ZII, ZVD, and two-mode convolved ZV shapers) are tested and compared in this study Among them, the convolved ZV shaper shows a best performance to eliminate the sloshing almost completely.

• Journal of computational fluids engineering
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• v.16 no.4
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• pp.7-13
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• 2011

A comparative analysis of thermal models in the lattice Boltzmann method(LBM) for the simulation of laminar natural convection in a square cavity is presented. A HYBRID method, in which the thermal equation is solved by the Navier-Stokes equation method while the mass and momentum conservation are resolved by the lattice Boltzmann method, is introduced and its merits are explained. All the governing equations are discretized on a cell-centered, non-uniform grid using the finite-volume method. The convection terms are treated by a second-order central-difference scheme with a deferred correction method to ensure stability of the solutions. The HYBRID method and the double-population method are applied to the simulation of natural convection in a square cavity and the predicted results are compared with the benchmark solutions given in the literatures. The predicted results are also compared with those by the conventional Navier-Stokes equation method. In general, the present HYBRID method is as accurate as the Navier-Stokes equation method and the double-population method. The HYBRID method shows better convergence and stability than the double-population method. These observations indicate that this HYBRID method is an efficient and economic method for the simulation of incompressible fluid flow and heat transfer problem with the LBM.

• Tribology and Lubricants
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• v.31 no.5
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• pp.205-212
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• 2015

In this research, effects of profile changes of stem section of the plunger on the lubrication characteristics of a fuel injection pump (FIP) were evaluated by hydrodynamic lubrication analysis. The clearance between plunger and barrel was divided into two regions, head and stem. The head was not involved in preventing a decrease of fuel oil pressure. So, research efforts were focused on both edges of the plunger’s stem. The two -dimensional Reynolds equation was used to evaluate lubrication characteristics with variations in viscosity, clearance and profile for a laminar, incompressible, unsteady-state flow. Moreover, the equilibrium equation of moment and forces in the vertical and horizontal directions were used to determine the motion of the plunger. The equations were discretized using the finite difference method. Lubrication characteristics of the FIP were investigated by comparing the dimensionless minimum film thickness, or film parameter, which is the ratio of minimum film thickness to surface roughness. Through numerical analyses, we showed that the profile of the lower edge of the stem had no effect on lubrication characteristics, but the profile of the upper edge had a significant influence on lubrication characteristics. In addition, changes in the profile were more effective in improving lubrication characteristics under low viscosity conditions.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.3
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• pp.115-123
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• 2003

With the advent of high performance computers and more efficient numerical algorithms, computational fluid dynamics(CFD) has come out as a modem alternative for reducing the use of wind tunnels test in automotive engineering. However, in spite of the fact that many competent researchers have made all their talents in developing turbulence model over since the past dozen or more years, it has been an important impediment in using the CFD effectively to design machinery and to diagnose or to improve engineering problems in the industry since the turbulence model has been acting as the Achilles' tendon in aspect of the reliability even to this time. In this study, Reynolds-averaged Wavier-Stokes equations were solved to simulate an incompressible turbulent flow around a bus-like bluff body near ground plane. In order to investigate the effect of the discretisation schemes and turbulence model on the aerodynamic forces several turbulence models with five convective difference schemes are adopted. From the results of this study, it is clear that choice of turbulence model and discretisation scheme profoundly affects the computational outcome. The results also show that the adoption of RNG $k-\varepsilon$ turbulence model and nonlinear quadratic turbulence model with the second order accurate discretisation scheme predicts fairly well the aerodynamic coefficients.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.1-7
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• 2005

Incompressible Reynolds-averaged Navier-Stokes equations with $\varepsilon{-SST}$ turbulence model are adopted for the investigation of the flow fields between the square cylinder and the ground. When the grounds moves, the diminish of the shear layer intensity on the ground promotes the interaction between the lower and the upper separated shear layer of the cylinder. Hence vortex shedding occurs at the lower gap height than stationary ground. In the moving ground, the secondary shedding frequency disappears due to the absence of the separation bubble on the ground which exists in the stationary ground. In addition, the shedding frequency and aerodynamic coefficients in the moving ground become higher than those of the stationary ground.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2002.04a
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• pp.35-40
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• 2002

A numerical analysis based on two-dimensional and three-dimensional incompressible Navier-Stokes equations has been carried out for double-circular-arc compressor cascades and the results are compared with available experimental data at various incidence angles. The 2-D and 3-D computational codes based on SIMPLE algorithm adopt pressure weighted interpolation method for non-staggered grid and hybrid scheme for the convertive terms. Turbulence modeling is very important for prediction of cascade flows, which are extremely complex with separation and reattachment by adverse pressure gradient. In this paper k-$\varepsilon$ turbulence model with wall function is used to increase efficiency of computation times.