• Proceedings of the Korean Society of Precision Engineering Conference
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.66-69
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• 2003

This paper presents the procedures for the evaluation of the maximum surface roughness and the shapes of the cut remainder employing the ridge method. The shapes and the heights of the cut remainder are estimated by overlapping adjacent ridges in consideration of the various machining parameters: the feedrate. the path interval. The maximum surface roughness in plane cutting modes are derived as a function of the maximum effective cutter radius, R$\_$eff,max/. and the path interval ratio, $\tau$$\_$fp/, The predicted results are compared with the values estimated by the conventional roughness model.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제4권3호
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• pp.155-162
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• 1992

Theoritical Study is performed on heat transfer and fluid flow induced by square-ribbed roughness elements in a concentric annulus. The fluid properties were assumed to be constant, and the radius($r_m$) of the maximum speed point was found by using the principle of equation of Leung and Labib. The Nusselt number and friction factor as a function of the Reynolds number($R_e=10^4$, $5{\times}10^4$, $7{\times}10^4$, $10^5$) in artifical roughness $S/{\epsilon}=5,10,20,30$, $P/{\epsilon}=2,5,8$ and prandtl number = 0.72 have been discussed. In this study, it has been found that the Nusselt number and friction factor of rough wall are larger than those of smooth ones.

• Journal of electromagnetic engineering and science
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• 제18권2호
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• pp.136-140
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• 2018

We propose an improved semi-empirical scattering model for X-band radar backscattering from rough sea surfaces. This new model has a wider validity range of wind speeds than does the existing semi-empirical sea spectrum (SESS) model. First, we retrieved the small-roughness parameters from the sea surfaces, which were numerically generated using the Pierson-Moskowitz spectrum and measurement datasets for various wind speeds. Then, we computed the backscattering coefficients of the small-roughness surfaces for various wind speeds using the integral equation method model. Finally, the large-roughness characteristics were taken into account by integrating the small-roughness backscattering coefficients multiplying them with the surface slope probability density function for all possible surface slopes. The new model includes a wind speed range below 3.46 m/s, which was not covered by the existing SESS model. The accuracy of the new model was verified with two measurement datasets for various wind speeds from 0.5 m/s to 14 m/s.

• Geomechanics and Engineering
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• 제18권4호
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• pp.391-406
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• 2019

The aim of this paper was to study the influence of the footing shape and the effect of the roughness of the foundation base on the bearing capacity of shallow foundations on rock masses. For this purpose the finite difference method was used to analyze the bearing capacity of various types and states of rock masses under the assumption of Hoek-Brown failure criterion, for both plane strain and axisymmetric model, and considering smooth and rough interface. The results were analyzed based on a sensitivity study of four varying parameters: foundation width, rock material constant (mo), uniaxial compressive strength and geological strength index. Knowing how each parameter influences the bearing capacity depending on the footing shape (circular vs strip footing) and the footing base interface roughness (smooth vs rough), two correlation factors were developed to estimate the percentage increase of the ultimate bearing capacity as a function of the footing shape and the roughness of the footing base interface.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제24권11호
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• pp.1478-1485
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• 2000

An experimental study has been performed to investigated the forced convection heat transfer characteristics of 6 circular cylinders in staggered arrangement in a cross flow of air. The water scale deposited on condenser wall of power plant was used to investigate the effect of roughness of scaled surfaces. The relative roughness*average diameter of scale/cylinder diameter) was in a range of k/d=0.0066, 0.0111, 0.0167, 0.0222 and 0.0278. The cylinder spacings(L/d) varies from 1.5 to 4.0 where L denote the cylinder spacings along and normal to the upstream uniform flow direction. The Reynolds number was varied in a range of 10, 000$\leq$ Re $\leq$ 50,000. The local and mean Nusselt numbers were investigated as a function of scale roughness, the cylinder spacing and Reynolds number. The results are compared with those of clean cylinder and inline tube bank, subsequently the mean fouling resistance over the entire circumference was estimated from those results as a function of scale roughness, the cylinder spacing and Reynolds number.

• Journal of Mechanical Science and Technology
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• 제20권7호
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• pp.1077-1088
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• 2006

This paper describes a numerical investigation on the performance deteriorations of a low speed, single-stage axial turbine due to use of rough blades. Numerical calculations have been carried out with a commercial CFD code, CFX-Tascflow, by using a modified wall function to implement rough surfaces on the stator vane and rotor blade. To assess the stage performance variations corresponding to 5 equivalent sand-grain roughness heights from a transition ally rough regime to a fully rough regime, stage work coefficient and total to static efficiency were chosen. Numerical results showed that both work coefficient and stage efficiency reduced as roughness height increased. Higher surface roughness induced higher blade loading both on the stator and rotor which in turn resulted in higher deviation angles and corresponding work coefficient reductions. Although, deviation angle changes were small, a simple sensitivity analysis suggested that their contributions on work coefficient reductions were substantial. Higher profile loss coefficients were predicted by higher roughness heights, especially on the suction surface of the stator and rotor. Furthermore sensitivity analysis similar to the above, suggested that additional profile loss generations due to roughness were accountable for efficiency reductions.

• Journal of Dental Rehabilitation and Applied Science
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• 제22권3호
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• pp.261-270
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• 2006

The success of an implant is determined by its integration into the tissue surrounding the biomaterial. Surface roughness is considered to influence the behavior of adherent cells. The aim of this in vitro study was to determine the effect of surface roughness on Saos-2 osteoblast-like cells. Titanium disks, blasted with $75{\mu}m$ aluminum oxide particles and anodic oxidized and machined titanium disks were prepared. Saos-2 were plated on the disks at a density of 50,000 cells per well in 48-well dishes. After 1 hour, 1 day, 6 days cell numbers were counted. One day, 6 days after plating, alkaline phosphatase(ALPase) activity was determined. Compared to experimental groups, the number of cells was significantly higher on control group. The stimulatory effect of surface roughness on ALPase was more pronounced on the experimental groups than on control group. These results demonstrate that surface roughness alters proliferation and differentiation of osteoblasts. The results also suggest that implant surface roughness may play a role in determining phenotypic expression of cells.

• Journal of Ocean Engineering and Technology
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• 제10권4호
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• pp.84-91
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• 1996

A fractal analysis on fracture surface of aluminium-particulate SiC composites was attempted. As the volume fraction of SiC in composites increases, the fractal dimension tends to increase. However, no correlation between the fractal dimension and the fracture toughness in terms of critical energy release rate was observed. Since the fractal dimension represents the roughness of fracture surface, the fracture toughness would be a function of not only fracture surface roughness but also additional parameters. Thus the applicability of fractal analysis to the estimation of fracture toughness must depend on the proper choice and interpretation of additioal paramerters. In this paper, the size of characteristic strctural unit for fracture was considered as an additional parameter. As a result, the size appeared to be a function of only volume fraction of SiC. Finally, a master curve for fracture toughness of aluminium-particulate SiC composites was proposed as a function of fractal dimension and volume fraction of SiC.

• KSCE Journal of Civil and Environmental Engineering Research
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• 제30권6B호
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• pp.571-578
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• 2010

Manning's roughness coefficients were reevaluated for the computation of river flow of the Han River, the Nakdong River and the Geum River. The roughness coefficients were estimated by two methods. One is based on the assumption that roughness is primarily a function of grain diameter and the other is based on the findings that roughness may vary significantly with the flow discharge. The roughness coefficients adopted in each river improvement master plan have been compared with those obtained using the FLDWAV in this study, and their applicabilities have been reviewed, using the FLDWAV and HEC-RAS models. The design flood water levels computed by the abovementioned models with the roughness coefficients proposed in this study have shown good agreement with the measurements of time variation. The roughness coefficients computed using the FLDWAV model showed nearly no close correlation with the various hydraulic characteristic factors, such as grain size and river depth, etc.. Finally the design flood water levels and levee safety about the downstream part from the Paldang Dam of the Han River has been reviewed using HEC-2 model with roughness coefficients of this study and the results indicated that some parts of the existing levees were short of safety.

• Corrosion Science and Technology
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• 제6권4호
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• pp.154-158
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• 2007

For the application of flexible printed circuit board (FPCB), electroplated copper is required to have low surface roughness and residual stress. In the paper, the effects of surface roughness and residual stress of electroplated copper as thick as $8{\mu}m$ were studied on organic additives such as inhibitor, leveler and accelerator. Polyimide film coated with sputtered copper was used as a substrate. Surface roughness and surface morphology were measured by 3D-laser surface analysis and FESEM, respectively. Residual stress was calculated by Stoney's equation after measuring radius curvature of specimen. The addition of additives except high concentration of accelerator in the electrolyte decreased surface roughness of electroplated copper film. Such a tendency was explained by the function of additives among which the inhibitor and the leveler inhibit electroplating on a whole surface and prolusions, respectively. The accelerator plays a role in accelerating the electroplating in valley parts. The inhibitors and the leveler increased residual stress, whereas the accelerator decreased it. It was thought to be related with entrapped additives on electroplated copper film rather than the preferred orientation of electroplated copper film. The reason why additives lead to residual stress remains for the future work.