• Tunnel and Underground Space
• /
• v.19 no.1
• /
• pp.31-42
• /
• 2009

One set of hardware system of guide point method (GP method), modified from the multistage convergent photographing technique, was developed to interpret the geometrical characteristics of Joints photogrammetrically on rock slope. Before the field application of the hardware system, the level of errors and constraints that ran be acceptable in the field measurement has been severely investigated in the laboratory and the optimum photographing scheme was analyzed. The range of the most suitable convergence angle between two cameras was $25^{\circ}{\sim}150^{\circ}$ and the photographing distance was about 5.5 m when using a 2 M pixel digital camera. An extended analyzing technique, which was newly developed in this study, was applied to the field measurement to magnify the benefits of GP method. This technique can be applied when survey for the wide range of rock surface is necessary. The global coordinates of ground control points for the neighbor photographing area ran be introduced without any preparation from the previous photographed area using this technique. It could reduce phographing time in the field.

• Transactions of Materials Processing
• /
• v.22 no.1
• /
• pp.23-29
• /
• 2013

In this study, a micro/nano-random-pattern-structure surface was machined by electric discharge machining (EDM) followed by replicating the EDM surface with a silicone elastomer having low energy and greater hydrophobicity. The variation of hydrophobicity was of prime interest and was examined as a function of the surface roughness of the replicated silicone elastomer. The hydrophobicity was evaluated by the water contact angle (WCA) measured on the relevant surface. For the experiments, the original surfaces were machined by die sinking electric discharge machining (DS-EDM) and wire cutting electric discharge machining (WC-EDM). The ranges of surface roughness were Ra $0.8{\sim}19{\mu}m$ for the DS-EDM and Ra $0.5{\sim}4.7{\mu}m$ for the WC-EDM. In order to fabricate a hydrophobic surface, the EDM surfaces were directly replicated using a liquid-state silicone elastomer, which was thermally cured. The measured WCA on the replicated surfaces for DS-EDM was in the range of $115{\sim}130^{\circ}$ and for WC-EDM the WCA was in the range of $123{\sim}150^{\circ}$. Additionally, the dynamic hydrophobicity was evaluated by measuring an advancing and a receding WCA on the replicated silicone elastomer surfaces.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.12
• /
• pp.1702-1710
• /
• 2001

Supersonic coaxial jets are investigated numerically by using the axisymmetric, Wavier-Stokes equations which are solved using a fully implicit finite volume method. Three different kinds of coaxial nozzles are employed to understand the flow physics involved in the supersonic coaxial jets. Two convergent-divergent supersonic nozzles are designed to have the same Mach number 2.0, and used to compare the coaxial jet flows with those discharging from one constant-area nozzle. The impingement angle of the annular jets are varied. The primary pressure ratio is changed in the range from 2.0 to 10.0 and the assistant jet ratio from 1.0 to 3.0. The results obtained show that the fluctuations of the total pressure and Mach number along the jet axis are much higher in the constant-area nozzle than those in the convergent-divergent nozzles, and the constant-area nozzle lead to higher total pressure losses, compared with the convergent-divergent nozzles. The assistant jets from the annular nozzle affect the coaxial jet flows within the distance less than about ten times the nozzle throat diameter, but beyond it the coaxial jet is conical with self-similar velocity profiles. Increasing both the primary jet pressure ratio and the assistant jet pressure ratio produces a longer coaxial jet core.

• Journal of Power System Engineering
• /
• v.20 no.5
• /
• pp.66-71
• /
• 2016

The measurements of heat transfer and total friction factors for turbulent flows in the convergent rectangular channels with two opposite in-line ribbed walls are reported. The study has covered three different angled ribs ($30^{\circ}$, $45^{\circ}$ and $60^{\circ}$) and Reynolds number in the range of 22,000 to 75,000. The channel, composing of ten isolated copper sections in the length of test section of 1 m, has the channel convergence ratio of $D_{ho}/D_{hi}=0.67$. The results show that the ribs pointing downstream (${\wedge}-shaped$) is somewhat greater than the ribs pointing upstream (V-shaped) in the dimensionless Nusselt number and total friction factors.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.17 no.2
• /
• pp.94-104
• /
• 2013

A numerical analysis has been conducted to determine the pitch thrust vectoring characteristics of a two-dimensional convergent divergent exhaust nozzle for supersonic aircraft application. The numerical analysis was done by using Fluent and verified by the experimental test results. Analysis was performed with pitch angle of $0^{\circ}$ and $20^{\circ}$ each at the ambient temperature condition. To see the effect of a ratio of pitch flap length and pitch flap height, the ratio was varied from 0.5 to 2.5. The numerical analysis shows that pitch thrust is changed greatly with pitch flap length. The big difference of the pitch thrust with pitch flap length is due to the shock interactions in the nozzle.

• The Journal of Korean Academy of Prosthodontics
• /
• v.38 no.6
• /
• pp.791-799
• /
• 2000

Statement of problem. Targis/Vectris restorations provide excellent esthetics. Marginal accuracy is significantly influenced by the preparation design. There were no studies to examine the effect of preparation design on the marginal discrepancy and fracture strength of Targis / Vectris crowns. Purpose. This study evaluated the marginal accuracy before and after cementation, and the fracture strength of FRC/Ceromer(Targis / Vectris) crowns according to different preparation design. Material and method. Three metal dies with different convergence angles($6^{\circ},\;10^{\circ},\;15^{\circ}$) were prepared. Total 30 (10 for each angle) Targis/Vectris crowns were made. The restorations were evaluated for adaptation of the margin before and after cementation, then were compressively loaded to failure. Fracture surfaces of the crowns were examined using a SEM. Results. The mean marginal gap was $49{\yen}m\;for6^{\circ},\;55{\S}>for\;10^{\circ}\;and\;70{\S}>for\;15^{\circ}$ and in clinically acceptable level. The mean marginal gap increased significantly after cementation. The increasing amount during cementation was the largest in the $6^{\circ}$ group. The crowns on 60 convergence angle had a significantly higher fracture strength than the crowns on $15^{\circ}$ angle. Mean fracture strength of total crowns regardless of convergence angle was 1390 N, which was higher than all-ceramic crowns. SEM observation showed two-mode fracture pattern. Conclusion. From the results of this study, all of the FRC/Ceromer crowns had clinically acceptable marginal accuracy and could withstand the bite force. Moreover, less convergent angle than all-ceramic crown might be recommended for preparation procedure.

• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
• /
• v.7 no.11
• /
• pp.447-455
• /
• 2017

At the modern industry, the composite material has been widely used. Particularly, the material of carbon fiber reinforced plastic hardened with resin on the basis of fiber is excellent. As the specific strength and rigidity are also superior, it receives attention as the light material. Among these materials, the carbon fiber reinforced plastic using carbon fiber has the superior mechanical property different from another fiber. So, it is utilized in vehicle and airplane at which high strength and light weight are needed at the same time. In this paper, the tensile property due to the fiber design is investigated through the analysis study with CT specimen composed of carbon plastic reinforced plastic. At the stress analysis of CFRP composite material with hole, the fracture trend at the tensile environment is examined. Also, it is shown that the lowest stress value happens and the deformation energy of the pre-crack becomes lowest at the analysis model composed of the stacking angle of 60° through the result due to the stacking angle. On the basis of this study result, it is thought to apply the foundation data to anticipate the fracture configuration at the structure applied with the practical experiment.

• Proceedings of the KSME Conference
• /
• 2001.06e
• /
• pp.323-328
• /
• 2001

Supersonic coaxial, axisymmetric, jets issuing from various kinds of dual coaxial nozzles were experimentally investigated. Four different kinds of coaxial, dual nozzles were employed to characterize the major features of the supersonic, coaxial, dual jets. Two convergent-divergent supersonic nozzles with an impinging angle in the jet axis of the annular jets were designed to have the Mach number 2.0 and used to compare the coaxial jet flows with those discharging from two sonic nozzles. The primary pressure ratio was changed in the range from 4.0 to 10.0 and the assistant jet ratio from 1.0 to 4.0. The results obtained show that the assistant jets from the annular nozzle affect the coaxial jet flows and an increase of both the primary jet pressure ratio and assistant jet pressure ratio produces longer supersonic length of the dual, coaxial jet.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.7 no.5
• /
• pp.440-446
• /
• 1996

The multiple-ridged circular waveguides is analyzed using Fourier series and the mode matching technique. The enforcement of the boundary conditions yields the simultaneous equations for the field coefficient inside the waveguides. The simultaneous equations are solved to represent a dispersion relation in an analytic series form. The numerical computation is performed to illustrate the behavior of the cutoff wavenumbers in terms of number, length and angle of ridges. The presented series solution is exact and rapidly-convergent so that it is efficient for numerical computation. A simple dispersion relation based on the dominant mode analysis is obtained and is shown to be very accurate for most practical applications.

• Proceedings of the KSME Conference
• /
• 2001.11b
• /
• pp.417-422
• /
• 2001

The shock structure of supersonic, dual, coaxial jet is experimentally investigated. Eight different kinds of coaxial, dual nozzles are employed to observe the major features of the near field shock structure of the supersonic, coaxial, dual jets. Four convergent-divergent supersonic nozzles having the Mach number of 2.0 and 3.0, and are used to compare the coaxial jet flows discharging from two sonic nozzles. The primary pressure ratio is changed in the range between 4.0 and 10.0 and the assistant jet pressure ratio from 1.0 to 4.0. The results obtained show that the impinging angle, nozzle geometry and pressure ratio significantly affect the near field shock structure, Mach disk location and Mach disk diameter. The annular shock system is found depending the assistant and primary jet pressure ratios.