• Tribology and Lubricants
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• v.29 no.1
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• pp.27-32
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• 2013

This study examined the effects of surface roughness in the mixed lubrication regime of smooth and rough surfaces for roller bearings. The average flow model was adopted for interaction between the flow rheology of the lubricant and the surface roughness. The average Reynolds equation and related flow factor that describes the coupled effects of surface roughness and flow rheology, the viscosity-pressure and density-pressure equations, the elastic deformation equation, and the force balance equation were solved simultaneously. The results showed that the effects of surface roughness on the film thickness and pressure distribution should be considered, especially in elastohydrodynamic lubrication contact problems.

• Korean Chemical Engineering Research
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• v.53 no.1
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• pp.91-102
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• 2015

Analytical solutions for the forced convection heat transfer of viscoelastic fluids obeying the Giesekus model are obtained in a concentric annulus under laminar flow for both thermal and hydrodynamic fully developed conditions. Boundary conditions are assumed to be (a) constant fluxes at the walls and (b) constant temperature at the walls. Temperature profiles and Nusselt numbers are derived from dimensionless energy equation. Subsequently, effects of elasticity, mobility parameter and viscous dissipation are discussed. Results show that by increasing elasticity, Nusselt number increases. However, this trend is reversed for constant wall temperature when viscous dissipation is weak. By increasing viscous dissipation, the Nusselt number decreases for the constant flux and increases for the constant wall temperature. For the wall cooling case, when the viscous dissipation exceeds a critical value, the generated heat overcomes the heat which is removed at the walls, and fluid heats up longitudinally.

• Journal of Ocean Engineering and Technology
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• v.21 no.6
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• pp.120-124
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• 2007

The purpose of this study was to investigate the stability of the arched and fan types of artificial reefs, which provide habitats for shellfish and seaweed. According to the Froude similitude, parameters affecting the stability of the artificial reefs were analytically, experimentally studied. First, the design parameters of the artificial reefs in wave and current fields were presented. Then, using dimensionless parameters, such as the surf similarity parameter and water particle speed, the stability of the arched and fan types of artificial reefs was investigated. From the hydraulic experiments, it is shown that the stability heavily depends on the way the artificial reefs are installed. Therefore, the installation of the artificial reefs on the surf zone should be carefully executed.

• International Journal of Fluid Machinery and Systems
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• v.1 no.1
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• pp.109-120
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• 2008

An innovative method of changing a centrifugal low specific speed pump performance and pressure fluctuation by applying outlet flaps to impeller exit has been investigated. The outlet blade edge section corresponds to the trailing edge of wing on the circular-cascade, which dominates the pump performance and pressure fluctuation. Computational fluid dynamics (CFD) analysis of the entire impeller and volute casing and an experimental investigation are conducted. The pressure fluctuation and the vibration of the shaft are measured simultaneously. Kurtosis is applied as a dimensionless parameter with which the unevenness of velocity distribution at impeller outlet is indicated. The influence of the flaps on the pressure fluctuation is explained by the kurtosis. This paper presents a theoretical method of predicting the pump performance related to the attachment of a flap at impeller outlet.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.3 s.234
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• pp.411-417
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• 2005

Surface texturing of tribological application is another attractive technology of friction reducing. Also, reduction of friction is therefore considered to be a necessary requirement for improved efficiency of machine. In this paper attempts to investigate the effect of density for micro-scale dimple pattern using photolithography on bearing steel flat mated with pin-on-disk. We demonstrated the lubrication mechanism for a Stribeck curve, which has a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. It is found that friction coefficient is depended on the density of surface pattern. It was thus verified that micro-scale dimple could affect the friction reduction considerably under mixed and hydrodynamic lubrication conditions from based on friction map. Lubrication condition regime has an influence on the friction coefficient induced the density of micro dimple.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.887-892
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• 2003

A modeling method for the modal analysis of a rotating composite beam is presented in this paper. Linear differential equations of motion are derived by using the assumed mode method. For the modeling, hybrid deformation variables are employed and approximated to derive the equations of motion Symmetrical laminated layers are considered for the composite beam. The effects of the dimensionless angular velocity, the hub radius and the fiber orientation angle parameter on the variations of modal characteristics are investigated.

• Structural Engineering and Mechanics
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• v.57 no.4
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• pp.703-716
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• 2016

In this paper, we have investigated shear horizontal wave propagation in a layered structure, consisting of granular macromorphic rock (Dionysos Marble) substrate underlying a viscoelastic layer of finite thickness. SH waves characteristics are affected by the material properties of both substrate and the coating. The effects of microstructural parameter "characteristic length" of the substrate, along with heterogeneity, internal friction and thickness of viscoelastic layer are studied on the dispersion curves. Dispersion equation for SH wave is derived. Real and damping phase velocities of SH waves are studied against dimensionless wave number, for different combinations of various parameters involved in the problem.

• Journal of Ship and Ocean Technology
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• v.4 no.1
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• pp.21-27
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• 2000

The slamming force occurring in the free fall impact of cylindrical bodies on the water surface is analyzed in both compressible and incompressible stages. In the compressible phase the hydrodynamic analysis is carried on by the acoustic approximation, obtaining a closed form expression for the maximum impact force. The incompressible analysis is approached through and unsteady boundary element method to compute the free surface evolution and the slamming force on the body. A similar behavior seems to characterize the maximum slamming force versus a dimensionless mass parameter.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.6
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• pp.478-485
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• 2004

Vibration localization characteristics of mistuned repeated structures are investigated. The mistuning often creates significant response discrepancies among subcomponents of a repeated structure. As the result of the discrepancies, critical fatigue often occurs in a repeated structure. Therefore, it is of great importance to predict the vibration response of the mistuned repeated structures accurately. In this paper, a simplified model is employed and dimensionless parameters that influence the localization characteristics are identified. Through parameter study, two localization phenomena are investigated and compared.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.237-241
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• 1998

This study is concerned with the optimum blank design which is able to minimize earing phenomena. A new analytic method is proposed to determine the optimum blank shape only using the tension test and standard deep drawing tests. Introducing a dimensionless parameter related to the earing and using a Fourier analysis, the optimum blank shape can be obtained by R-value and the tested results. The theoretical results by the proposed method are good agreement with the experimental results through several deep drawing tests using steel as working materials.