• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.676-679
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• 2008

Numerical simulations of fluid injection into particulate materials were conducted to observe cavity initiation and propagation using distinct element method. After generation of initial particles and wall elements, confining stress was applied by servo-control method. The fluid scheme solves the continuity and Navior-Stokes equations numerically, then derives pressure and velocity vectors for fixed grid by considering the existence of particles within the fluid cell. Fluid was injected as 7-step into the assembly in the x-direction from the inlet located at the center of the left boundary under confining stress condition, 0.1MPa and 0.5MPa, respectively. For each simulation, movement of particles, flow rate, fluid velocity, pressure history, wall stress including cavity initiation and propagation by interaction of flulid-paricles were analyzed.

• Journal of the Korean Society of Combustion
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• v.12 no.1
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• pp.11-20
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• 2007

The supersonic combustion experiments are carried out using T3 free-piston shock tunnel. Different shock tube fill pressures have various inflow conditions. $15^{\circ}$ inclined hydrogen fuel injection is located before the cavity. Oblique shock is generated from the cavity and reflects off the top and bottom wall. For non-reacting flow, fuel makes the shear layer thicker above the cavity therefore, the shock is generated just before the trailing edge. This research has self-ignition in the combustor. For reacting flow, as the equivalence ratio increases, flame starts to generate near the injector or occur in the recirculation zone before the injector. High fuel injection sustains the jet shape in the cross flow and air can mix with fuel along the shear layer. Therefore, two flame layers find above the cavity for high equivalence ratio.

• Restorative Dentistry and Endodontics
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• v.11 no.1
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• pp.11-18
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• 1985

The purpose of this study was to observe the facial, lingual and gingival walls of the cavity walls with various kinds of cutting tools. Class II cavities were prepared in newly extracted sound humen mandibular 1st left premolars, and observed in Sanning electron microscope. Diamond point (#201) and Tungsten Carbide burs (#170L) were used in ultra high speed handpieces (rpm 200000), and Tungsten Carbide bur (#702) and Steel bur (#560) were used in conventional handpieces (rpm 6000). All cavities were prepared under water spray, except for some which were finished with a dry abrasive stone (#57). Some cavities were finished with chisels (#41, 42, 83). The following results were obtained. 1. The cavity walls prepared with Diamond point were rougher than the cavity walls with Carbide burs and Steel burs. 2. The chisels were produced the smoothest surface. 3. The cavity walls which were prepared with cutting blades rotated toward enamel surface from outside, were smoother than cavity walls which were prepared with cutting blades rotated toward outside from the enamel surface.

• Solar Energy
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• v.19 no.1
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• pp.77-86
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• 1999

The optimal thermal design of a single heat source on one wall of a vertical open top cavity was studied experimentally. The temperature and flow fields in the cavity were visualized. The objectives of this study is to obtain the best location of the single heat source and to examine the effects of heat source protrusion, substrate thermal conductivity and cavity aspect ratio on the natural convection cooling due to a single heat source. As the results, the cooling effect for the copper substrate is superior to that of the epoxy-resin substrate and is improved with increasing cavity width. For the epoxy-resin substrate of lower conductivity, the protrusion of the heaters plays a role in decreasing the cooling effect. The best location was the mid-height of the substrate.

• Restorative Dentistry and Endodontics
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• v.27 no.4
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• pp.389-393
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• 2002

The marginal integrity of the crown can be broken during endodontic access cavity preparation due to the vibration of burs. Therefore, the purpose of this study was to evaluate the effect of endodontic access cavity preparation on the marginal leakage of full veneer gold crowns. 24 intact molars were mounted in acrylic resin blocks and prepared for crowns by a restorative dentist and crowns were cast with gold alloy. 20 Crowns were cemented with glass ionomer cement and 2 crowns were not cemented for positive control. 200 thermo-cycles from 5$^{\circ}C$ to 5$0^{\circ}C$ with a travel time of 20s were completed. Then samples were randomly divided into 2 experimental groups of 9 each. Endodontic access preparation and zinc-oxide eugenol temporary fillings were done in Group 1. Teeth in Group 2 were not treated. Samples were coated with 2 layers of nail varnish and were immersed in 1% methylene blue dye for 20 hrs. Endodontic access was prepared in 2 samples, which were coated with nail varnish on all surfaces for negative control. After washing in running water gold crowns were cut with a #330 bur. Four buccolingual sections, 2 mm apart, were cut from the central section of each tooth and were examined and scored under the microscope for dye leakage. Score 1: leakage to the cervical 1/3 of the axial wall, Score 2: leakage to the middle 1/3 of the axial wall, Score 3: leakage to the coronal 1/3 of the axial wall, Score 4: leakage to the occlusal surface. The median value for Group 1 is 4 and for Group 2 is 2. The result of this study showed that samples in Group 1 leaked more than those in Group 2. This finding was significant(P<0.001).

• Development and Reproduction
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• v.15 no.4
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• pp.291-299
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• 2011

The membranous adhesions could induce implantation failure despite transplantation of high quality of embryo. Clinically, of the patients who have membranous filmy adhesions, endometrial polyps have been found in not infrequently. Thus this study was tried to evaluate the features of endometrial polyps and the effect of endometrial polyps on formation and extents of membranous adhesions in uterine cavity of infertile patients under hysteroscopy. A retrospective study was conducted on 34 infertile patients who were diagnosed as endometrial polyps with membranous adhesions during hysteroscopy from July 2008 to July 2011. Number, size, location and morophologic type of endometrial polyps were investigated. If needed, methylene blue solution was instillated to endometrial cavity to identify membranous adhesions. Then, associations between membranous adhesions with features of endometrial polyps were evaluated. Mean size of endometrial polyp was $1.6{\pm}0.6$ cm, the bigger of endometrial polyps was, the larger of extents of membranous adhesions. (p<0.05). Endometrial polyps were locate evenly in endometrial cavity as follows: anterior uterine wall, 39.1%; posterior uterine wall, 34.8%; lateral uterine wall, 26.1%; upper: 29.4%, middle: 32.4%, lower segment, 35.3%. Mean number of endometrial polyps was $2.26{\pm}1.3$. The pedunculated type was 37.7% and sessile type was 32.4%. There was no statistically significant association of location, number and morphologic type of endometrial polyps with membranous adhesions. In conclusion, hysteroscopy before in vitro fertilization on infertile patients was worthy because of removing of endometrial polyps and membranous adhesions.

• 한국전산유체공학회:학술대회논문집
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• 1999.11a
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• pp.127-138
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• 1999

In this study steady state solutions of cavity flows driven by two moving walls are studied. The north and east walls of the cavity are movable where as the remaining two walls are fixed in space. Numerical experiments for three different driving schemes for moving walls are done at two different Reynolds numbers of Re=40 and 400. The first scheme is to accelerate north and east walls simultaneously. In the second one, the north wall is started first and the east wall is accelerated later. In the third one the east wall starts first. It is usually expected that all these three cases yield the same steady state solution after sufficiently long time. However, present numerical experiments show that such a usual belief is valid only when the Reynolds number is low enough (Re=40). At higher Reynolds number (Re=400), the flow develops to three different steady states depending on the history of the boundary condition change.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.5
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• pp.41-47
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• 2009

Numerical computations were carried out to analyze the effect of a sub-cavity at several inlet Mach numbers on the control of cavity-induced pressure oscillations in two-dimensional supersonic flow. The present passive control method, the sub-cavity applied to the front wall of a square cavity, was studied for the inlet Mach numbers of 1.50, 1.83 and 2.50. The results show that the sub-cavity is effective in reducing the oscillations, and a resultant amount of the reduction depended on the inlet Mach number, the length of flat plate, and the depth of sub-cavity used as an oscillation suppressor.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.463-466
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• 2002

In order to examine the possibility of using a cavity as a passive device for reduction of skin friction and heat transfer, an intensive parametric study over a broad range of the cavity depth and length at different Reynolds numbers is performed for both laminar and turbulent boundary layers in the present study. Direct and large eddy simulation techniques are used for turbulent boundary layers at low and moderate Reynolds numbers, respectively. for both laminar and turbulent boundary layers over a cavity, a flow oscillation occurs due to the shear layer instability when the cavity depth and length are sufficiently large and it plays an important role in the determination of drag and heat-transfer increase or decrease. For a cavity sufficiently small to suppress the flow oscillation, both the total drag and heat transfer are reduced. Therefore, the applicability of a cavity as a passive device for reduction of drag and heat transfer is fully confirmed in the present study. Scaling based on the wall shear rate of the incoming boundary layer is also proposed and it is found to be valid in steady flow over a cavity.

• Journal of Mechanical Science and Technology
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• v.16 no.7
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• pp.966-974
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• 2002

An analytic approach has been employed to study condensate film thickness distribution inside cave-shaped cavity of a flat plate heat pipe. The results indicate that the condensate film thickness largely depends on mass flow rate and local velocity of condensate. The increasing rate of condensate film for circular region reveals about 50% higher value than that of vertical region. The physical properties of working fluid affect significantly the condensate film thickness, such as the condensate film thickness for the case of FC-40 are 5 times larger than that of water. In comparison with condensation on a vertical wall, the average heat transfer coefficient in the cave-shaped cavity presented 10∼15% lower values due to the fact that the average film thickness formed inside the cave-shaped cavity was larger than that of the vertical wall with an equivalent flow length. A correlation formula which is based on the condensate film analysis for the cave-shaped cavity to predict average heat transfer coefficient is presented. Also, the critical minimum fill charge ratio of working fluid based on condensate film analysis has been predicted, and the minimum fill charge ratios for FC-40 and water are about Ψ$\_$crit/=3∼7%, Ψ$\_$crit/=0.5∼1.3% respectively, in the range of heat flux q"=5∼90kW/㎡.