• Tribology and Lubricants
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• v.31 no.6
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• pp.245-250
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• 2015

This study investigates the lubrication characteristics of fuel injection pumps with reference to different fuel oils. Medium-speed diesel engines use fuel oils with various viscosities, such as heavy fuel oil (HFO, which is a high-viscosity fuel oil) and light diesel oil (LDO, which is a low-viscosity fuel oil). When fuel oil with a low viscosity is used, both fuel oil and lubricating oil lubricate the system. Thus, the lubrication of the fuel injection pump is in a multi-viscosity condition when the fuel oil in use changes. We suggest three cases of multi-viscosity models, and divide the fuel injection pump into three lubrication sections: a, the new oil section; b, the mixed oil section; and c, the used oil section. This study compares the lubrication characteristics with variation of the multi-viscosity model, clearance. The volume of Section b does not affect the lubrication characteristics. The lubrication characteristics of the fuel injection pump are poor when high-viscosity fuel oil transfers to low-viscosity fuel oil. This occurs because the viscosity in the new oil section (i.e., Section a) dominates the lubrication characteristics of the fuel injection pump. However, the lubricant oil supply in the used oil section (i.e., Section c) can improve the lubrication characteristics in this condition. Moreover, the clearances of the stem and head significantly influence the lubrication characteristics when the fuel oil changes.

• Journal of computational fluids engineering
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• v.18 no.2
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• pp.56-65
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• 2013

Two compression ramp problems and an impinging shock problem are computed to investigate influence of turbulence models and eddy viscosity on the shock-wave / boundary layer interaction. A Navier-Stokes boundary layer generation code was applied to the generation of inflow boundary conditions. Computational results are validated well with the experimental data and effects of turbulence models are investigated. It is shown that the behavior of turbulence (eddy) viscosity directly affects both the extent of the separation and shock-wave positions over the separation.

• Journal of the Korean Society of Safety
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• v.32 no.2
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• pp.112-116
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• 2017

Present study investigated the influence of time step size, turbulent eddy viscosity, and the number of layer on rapid and unsteady propagation of dam break flow. When the time step size had a value such that it resulted in Cr of 0.89, a significant numerical oscillation was observed in the vicinity of the wave front. Higher turbulent viscosity ensured smooth and mild slope of velocity and water stage compared with the flow behavior by no viscosity. The vertical velocity at the lower layer positioned near the bottom showed lower velocity compared with other layers.

• Korea-Australia Rheology Journal
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• v.15 no.1
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• pp.35-41
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• 2003

It is expected that particle size distribution of any portion obtained through screening, is of more uniform than that of the original mixture, typically following such as log-normal, Rosin-Rammler distributions and so on. In this study, therefore, a new relation between parameters of the uniform distribution and flow characteristics of the coarse particle suspensions is derived based on the continuous polydisperse model (Ookawara and Ogawa, 2002b), which is derived from the discrete polydisperse model (Ookawara and Ogawa,2002a). The derived model equation predicts a linear increase of viscosity with shear rate, viz., dilutant flow characteristics. Further, the increase of viscosity is expected to be proportional to the square of volume fraction of particles, and to show the linear dependency on density and average diameter of particles. It is also shown that the uniform distribution model includes additional term that expresses the effect of distribution width. For verification of the model, the experimental results of Clarke (1967) are cited as well as in our previous work for the monodisperse model (Ookawara and Ogawa,2000) since most parameters were varied independently in his work. It is suggested that the newly introduced term expands the applicable range compared with the monodisperse model.

• 한국해양학회지
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• v.29 no.2
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• pp.119-131
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• 1994

Vertical structures of wind-driven and tidal currents in a rectangular shaped uniform-depth basin of homogeneous water have been investigated using a mode-splitted, multi-level grid-box, hydrodynamic numerical model. The model was verified using analytical solutions for various vertical eddy viscosity profiles such as: a constant eddy viscosity, a linearly decreasing or increasing variation with depth, a quadratic variation with depth and an exponential variation with depth. Particular attention has been paid on the effects of "near-surface wall layer" on vertical shear of velocity. In numerical calculations, the whole water depth was divided into 13 levels with an unequal grid spacing. the model satisfactorily reproduces the velocity profile, but in case the eddy viscosity decreases rapidly with depth as in quadratical or exponential variation with depth, the vertical gradient of velocity near the bottom became very steep, and analytical solutions and numerical results showed some discrepancy. The vertical structures of horizontal velocity vary with both the depth-averaged value of eddy viscosity and its profiles. the velocity near the sea surface and near the bottom responded sensitively to the eddy viscosity of wall layer. For wind-driven current, the strong velocity shear was generated near the sea surface as eddy viscosity near the surface became small. For tidal current, the velocity above the sea bottom layer was almost constant regardless of the profiles of vertical eddy viscosity, but velocity in the sea bottom layer showed strong shear as eddy viscosity became small.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.2
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• pp.103-114
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• 2001

During a compression molding process of Unidirectional Fiber Reinforced Plastic Composites, control of filling patterns in mold and distribution of fiber is needed to predict the effects of molding parameters on the flow characteristics. To obtain an excellent product and decide optimum molding conditions, it is important to know the relationship between molding conditions and viscosity. In this study, the anisotropic viscosity of the Unidirectional Fiber Reinforced Plastic Composites is measured by using the parallel plastometer. The model for flow state has been simulated by using the viscosity. The composites is treated as an incompressible New-tonian fluid. The effects of longitudinal/transverse viscosity ration A and slip parameter $\alpha$ on buldging phenomenon and mold filling patterns, are also discussed.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.4
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• pp.670-690
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• 2015

In this paper, numerical investigations for tank sloshing, based on commercial CFD package FLUENT, are performed to study effects of boundary layer grid, liquid viscosity and compressible air on sloshing pressure, wave height and rising time of impact pressure. Also, sloshing experiments for liquids of different viscosity are carried out to validate the numerical results. Through comparison of numerical and experimental results, a computational model including boundary layer grid can predict the sloshing pressure more accurately. Energy dissipation due to viscous friction leads to reduction of sloshing pressure and wave elevation. Sloshing pressure is also reduced because of cushion effect of compressible air. Due to high viscosity damping effect and compressible air effect, the rising time of impact pressure becomes longer. It is also found that liquid viscosity and compressible air influence distribution of dynamic pressure along the vertical tank wall.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.7
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• pp.20-27
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• 2002

An analysis model for an elliptical fluid film bearing is described. The principles of hydrodynamic lubrication are outlined together with an expanded version of the governing pressure field equation as related to elliptical journal bearing. Finite element method approximations are given for the pressure field equation and a temperature model, both related to the fluid film thickness. The thermal effects in the lubricant viscosity, lubricant film thickness, variation of the journal rotating speed and influence of turbulence are investigated in this paper A finite element model and an iterative computational process are described, whereby full simultaneously converged field solutions for fluid film thickness, temperature, viscosity, pressure, stiffness and damping coefficient are obtained.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.539-545
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• 2005

In this paper, the thermal characteristics of natural convection in a rectangular cavity with nanofluids such as water-based nanofluids containing alumina are theoretically investigated with a new model of the thermal conductivity for nanofluids presented by Jang and Choi and various models for effective viscosity. In addition, based on theoretical results, the effects of various parameters such as the volume fraction, the temperature, and the size of nanoparticles on free convective instability and heat transfer characteristics in a rectangular cavity with nanofluids are suggested.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.7
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• pp.820-830
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• 1999

The coupled turbulent flow and solidification is considered in a typical slab continuous easting process using commercial program FIDAP. Standard $k-{\varepsilon}$ turbulence model is modified to decay turbulent viscosity in the mushy zone and laminar viscosity is set to a sufficiently large value at the solid region. This coupled turbulent flow and solidification model also contains thermal contact resistance due to the mold powder and air gap between the strand and mold using an effective thermal conductivity. From the computed flow pattern, the trajectory of inclusion particles was calculated. The comparison between the predicted and experimental solidified shell thickness shows a good agreement.