• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.189-192
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• 2008

Turbulent coherent structure near rod-roughened wall are investigated by analyzing the database of direct numerical simulation of turbulent boundary layer. The roughness sublayer id defined as two-point correlations are not independent of streamwise locations around roughness. The roughness sublayer based on the two-point spatial correlation is different from that given by one-point statistics. Quadrant analysis and probability-weighted Reynolds shear stress indicate that turbulent structures are not affected by surface roughness above the roughness sublayer defined by the spatial correlations. The conditionally-averaged flow fields associated with Reynolds shear stress producing Q2/Q4 events show that though turbulent vortices are affected in the roughness sublayer, these are very similar at different streamwise locations above the roughness sublayer. The Reynolds stress producing turbulent vortices in the log layer have almost the same geometrical shape as those in the smooth wall-bounded turbulent flows. This suggests that the mechanism by which the Reynolds stress is produced in the log layer has not been significantly affected by the present surface roughness.

• The Journal of Korean Academy of Prosthodontics
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• v.52 no.3
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• pp.177-185
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• 2014

Purpose: This study is designed to investigate the various impacts of different types of scaler tips such as cooper alloy base tip and the others on the surface roughness of teeth and implant by the method which is currently in clinical use. Materials and methods: Four different types of disc shaped porcelain, titanium, zirconia, and Type III gold alloy dental materials sized 15 mm diameter, 1.5 mm thickness were used for the experiment. Plastic hand curette (Group PS), cooper alloy new tip (Group IS), and stainless steel tip (Group SS) were used as testing appliances. A total of 64 specimens were used for this study; Four specimens for each material and appliance group. Surface roughness was formed with 15 degree angle in ultrasonic scaler tip and with 45 degree angle in hand curette of instrument tip and the specimen surface with 5 mm long, one horizontal-reciprocating motion per second for 30 seconds by 40 g force. To survey the surface roughness of each specimen, a field emission scanning electron microscope, an atomic force microscope, and a surface profiler were used. (Ra, ${\mu}m$). Results: According to SEM, most increased surface roughness was observed in SS group while IS groups had minimal roughness change. Measurement by atomic force microscope presented that the surface roughness of SS group was significantly greater than those of PS, IS and control groups in the type III gold alloy group (P<.05). IS group showed lesser surface roughness changes compared to SS group in porcelain and gold alloy group (P<.05). According to surface profiler, surface roughness of SS group showed greater than those of PS, IS and control groups and IS group showed lesser than those of SS group in all specimen groups. Type III gold alloy group had large changes on surface roughness than those of porcelain, titanium, zirconia (P<.05). Conclusion: The result of this study showed that newly developed copper alloy scaler tip can cause minimal roughness impacts on the surface of implant and dental materials; therefore this may be a useful alternative for prophylaxis of implant and restored teeth.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.1
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• pp.73-79
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• 2013

In this study, NIMAX material has been processed using the three-dimensional measuring instrument and white light interferometer. they were tested to roundness and surface roughness and results are as follows: As for a cutting characteristic, it indicated that F4 showed a lower result than 2F showed due to the high hardness of the material and showed a good result when spindle rotation speed and tool feed were low. As for the measurement of roundness through 3-Dimensional measuring machine, it indicated that 4F showed a good result like the condition of cutting component and that roundness showed a good result when spindle rotation speed of 1,700 rpm and tool feed speed of 85 mm/min were applied. As for the surface roughness of processing surface, Surface roughness showed better 4F than 2F and conditions of spindle rotation speed 1,700 rpm, tool feed rate 55 mm/min showed good results in the Ra $0.4025{\mu}m$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.7
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• pp.596-604
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• 2011

To improve the total efficiency of centrifugal compressor, it is necessary to reduce the disk friction loss, which is defined as the power loss. In this study, the disk friction loss due to the axial clearance and the surface roughness effect is analyzed and proposed the new empirical equation for the reduction of the disk friction loss. The rotating reference frame technique and the 2-equation k-${\omega}$ SST model using commercial CFD code FLUENT is used for the steady-state analysis of the centrifugal compressor impeller. According to CFD results, the disk friction loss of the impeller is more affected by the surface roughness than the change of the axial clearance. For the minimization of the disk friction loss on the centrifugal compressor impeller, the magnitude of the axial clearance should be designed to the same size compare with theoretical boundary layer thickness and the surface roughness should be minimized.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.856-865
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• 1994

Cylindrical fine-ceramics, $Al_{2}O_{3}$, was lapped on its outer surface by vibrational lapping unit manufactured in the laboratory. Cylindrical lapping of fine-ceramics is necessarily be characterized and optimized because its process as other finishing methods is time-spending and, so, inefficient one, and because it is very complicated and random process affected by numerous factors in itself and in its environment. In this study, an efficient experimental approach, experimental design method, was used to analyze characteristics of the cylindrical lapping of fine-ceramics, $Al_{2}O_{3}$, and response surface methodology(RSM) to find out the optimal variables combination for the maximum improvement of surface roughness($R_a$). From the final surface roughness point of view in the given lapping conditions, a stationary point or optimal lapping conditions as well as the possible maximum improvement of surface roughness($R_a$) was predicted.

• Restorative Dentistry and Endodontics
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• v.13 no.2
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• pp.207-220
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• 1988

The purpose of this study was to measure roughness on the polished surfaces of composite resin, and was to observe the polished surfaces under Scanning Electron Microscope. The surface roughness tester (Surfcom 700A Semitsu Profilometer Tokyo. Japan) was used to measure roughness of polished surfaces. In this study, 4 brands of composite resin were examined, Pyrofil bond anterior Bell-Feel anterior Clearfil F II and Microrest A.P. White point, Silicone point, Super snap, and Sof-Lex medium disc as cutting instrument, and celluloid matrix were used. The results obtained were as follows. 1) The celluloid matrix produced the smoothest surfaces. 2) Microrest composite resin had smoother surface than any other composite resins after polishing. 3) The values of surface roughness made by White point, Silicon point and Super snap were similar. 4) The surfaces made by Sof-Lex medium disc was smoother than the surfaces made by any other polishing instruments.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.6 no.3
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• pp.261-264
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• 2005

The 90 nm gate pattern technology have been virtualized by employing the hard mask and the planarization of fate poly silicon. We fabricated 70nm poly-Si on $200 nm-SiO_2/p-Si(100)$ substrates using low pressure chemical vapor deposition (LPCVD) to investigate roughness evolution by varying rapid annealing temperatures. The samples were annealed at the temperatures of $700^{\circ}C\~1100^{\circ}C$ for 40 seconds with a rapid thermal annealer. The surface image and the surface roughness were measured by a field emission scanning electron microscopy (FESEM) and an atomic force microscopy (AFM), respectively. The poly silicon surface became more rough as temperature increased due to surface agglomeration. The optimum conditions of poly silicon planarization were achieved by annealed at $700^{\circ}C$ for 40 seconds.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.4
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• pp.179-185
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• 2004

Surface finish technology is highly demanded in the wide field of industry applications from ultra-precision parts to rough casting parts. Therefore, many kinds of surface finish technologies have been developed for each purpose. Because surface of a car's wheel cast is very rough it becomes the reason of the corrosion. This surface is coated to complement such problem but because surface is rough, the result of coating is not good and the coated metal peels off well. Therefore before the wheel is coated, it is necessary to grind the surface. In this study, we devised the plant to apply a barrel machining to improve the surface roughness and enhance the productivity. Also we could obtain the optimum barrel machining conditions for the proper surface roughness.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1294-1303
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• 1993

The fully developed turbulent momentum and heat transfer induced by the square-ribed roughness elements on the inner wall surface in concentric annuli is studied analytically based on a modified turbulence model. The analytical results of the fluid flow is verified by experiment. The resulting momentum and heat transfer are discussed in terms of various parameters, such as the radius ratio, the relative roughness, the roughness density, fluid Reynolds number and for heat transfer, fluid Prandtl number. The study demonstrates that certain artificial roughness elements may be used to enhance heat transfer rates with advantages from the overall efficiency point of view.

• Journal of the korean academy of Pediatric Dentistry
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• v.23 no.4
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• pp.915-924
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• 1996

The purpose of this paper is to investigate the surface roughness of glass ionomer cement during initial setting time followed by applying surface coating agent. No other finishing or polishing procedure is done and each surface coating agents (varnish, adhesive, gloss, sealant) are used after filling of glass ionomer cement. Surface roughness indices(Ra) are measured and surface contours are obtained electronically by Surfcorder SEF-30D(Kosaka laboratory Ltd., Japan). The results are as follows: 1. During initial setting time, surface roughness increases slightly regardless of surface coating agents. But it is statistically insignificant. (p>0.05) 2. Among surface coating agents used, Ra indices of group using varnish are high significantly compared to other groups regardless of elapsed time.(p<0.05) Among the groups which has used other surface coating agents except for the varnish group, similar Ra index all over the experiment is obtained, when compared to control group (no agent). 3. If no surface treatment is performed, tri-cure glass ionomer cement (Vitremer) has higher Ra Index than light cure glass ionomer cement (Fuji II LC) (t<0.05). But there is no difference between two groups in Ra index if any kinds of agents are applied except for sealant. (t>0.05)