• Restorative Dentistry and Endodontics
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• v.31 no.1
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• pp.20-29
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• 2006

The purpose of this study was to analyze the stress distribution aspect of unrestored and restored combined shape (wedge shape occulusally and saucer shape gingivally) class V cavity, which found frequently in clinical cases. A maxillary second permolar restored with a combined shape class V composite restorations were modeled using the three dimensional finite element method. Static occlusal load of 170 N was applied on lingual incline of buccal cusp at the angle of $45^{\circ}$ with the longitudinal axis of the tooth. And three dimensional finite element analysis was taken by ANSYS (Version 6.0, Swanson Analysis System Co., Houston, U.S.A) program which represent the stress distribution on unrestored and restored cavity wall and margin. The conclusions were as follows. 1. Compared to the unrestored cavity, Von Mises stress at the cementoenamel junction and line angle of the cavity base were reduced and in restored cavity. 2. Von Mises stress at the occlusal and cervical cavity margin and wall were increased in restored cavity in comparison with the unrestored cavity. 3. In the hybrid and hybrid/flowable composite resin restoration, Von Mises stress at the cementoenamel junction and line angle of the cavity base were reduced more than in the flowable restoration. 4. In the hybrid and hybrid/flowable composite resin restoration, Von Mises stress at the occlusal and cervical cavity margin and wall were increased more than in the flowable restoration.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.743-746
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• 2002

Experimental investigation of the flow field of supersonic cavity is described. In this research, supersonic cavity is used in chemical laser system. For efficient laser, downstream flow after cavity need to be uniform and clear for pressure recovery system. In previous research, it's known that there's oscillation In cavity and is due to Mach number and L/D ratio. A strong recompression occurs at the after wall and the flow is visibly unsteady. Cavity flow in this research is of the open type, that is, length-to-depth ratio $L/D<10\;at\;M\;=\;3$. Experiment is done with pressure measurement by piezo-type sensor and visualization by Schlirern method. The time-dependent experimental result is compared with computation.

• Geomechanics and Engineering
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• v.20 no.5
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• pp.399-410
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• 2020

Cavities often develop behind the vault during the construction of double-arch tunnels, generally in the form of various defects. The study evaluates the impact of cavities behind the vault on the mechanical and failure behaviors of double-arch tunnels. Cavities of the same sizes are introduced at the vault and the shoulder close to the central wall of double-arch tunnels. Physical model tests are performed to investigate the liner stress variation, the earth pressure distribution and the process of progressive failure. Results reveal that the presence of cavities behind the liner causes the re-distribution of the earth pressure and induces stress concentration near the boundaries of cavities, which results in the bending moments in the liner inside the cavity to reverse sign from compression to tension. The liner near the invert becomes the weak region and stress concentration points are created in the outer fiber of the liner at the bottom of the sidewall and central wall. It is suggested that grouting into the foundation soils and backfilling injection should be carried out to ensure the tunnel safety. Changes in the location of cavities significantly impact the failure pattern of the liner close to the vault, e.g., cracks appear in the outer fiber of the liner inside the cavity when a cavity is located at the shoulder close to the central wall, which is different from the case that the cavity locates at the vault, whereas changes in the location of cavities have a little influence on the liner at the bottom of the double-arch tunnels.

• Journal of Practical Engineering Education
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• v.8 no.2
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• pp.121-128
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• 2016

In injection molding process, the appearance quality issue occurs in most injection molded article. One of thermal designs for the mold was performed by increasing the cavity wall temperature with being as uniform as possible in any position. On the basis of the practical evaluation, the cavity wall temperature and finishing machined cavity surface under the optimum processing conditions are the most significant factors to avoid the appearance issue on the plastic part for a good cosmetic quality. Also, the wrong choice of gate type and location can have a considerable effect on the quality of a molded part and it's so important to keep the correct runner balance from each cavity. We've proposed the education training model of the practical tool technology course for the field oriented education to improve practical tool technology ability and optimized tooling design for injection molding quality which can be performed at the workplace substantially.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.1
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• pp.19-27
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• 2015

In the present study, an effort was made to numerically investigate rectangular cavity aeroacoustics with and without doors. The simulation was performed on an open cavity with an aspect ratio of 5:1:1 at Mach 0.85 using the delayed detached eddy simulation (DDES) approach based on the Spalart-Allmaras model. Two cavity configurations, a clean cavity and a cavity with doors, were modeled. The results obtained from the clean cavity were compared with the experimental sound pressure levels (SPL) and the root mean square for the pressures applied. Furthermore, comparisons of frequencies were made using a modified semi-empirical Rossiter formula. The simulation using DDES precisely predicted the pressure fluctuation and the results matched the experiment quite well. The SPLs at the rear of the cavity were much higher than those in the front due to the instability of the shear layer impinging on the rear wall. Comparisons of DDES for the clean cavity and the doors-on cavity revealed that the SPLs inside the cavity as well as the magnitude of tones are amplified by the side doors. The main focus of this investigation was to obtain a better understanding of the open cavity acoustic resonance phenomenon and investigate the effects of cavity doors on the SPL.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.458-466
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• 1993

Natural convection in trapezoidal sections of cavity was numerically investigated using a Finite Volume Method. Temperatures of the upper inclined and lower horizontal walls are constant, with vertical side walls being insulated. When the top wall is hotter than the bottom one, a single cell of stratified flow field is obtained and heat transfer occurs only by conduction. For the colder top wall, bifurcation solutions are obtained for the higher Rayleigh numbers, while unique solutions for lower values. Flow structure is strongly dependent on the configuration and the Rayleigh number.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.241-246
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• 1996

An analytical model to calculate rate of vapor generation due to heterogeneous wall nucleation in flashing flow is developed. In the present model, an important parameter of the vapor generation term, i.e. nucleation site density is calculated by integrating its probability distribution function with respect to active cavity radius. The limits of integration are minimum and maximum active cavity radii, and these are formulated using an active cavity model for nucleate boiling. This formulation, therefore. can statistically account for the effect of surface specific thermo-physical and geometric conditions on the vapor generation rate and flashing inception. For verifying the adequacy of the present model, steady state two-fluid and the bubble transport equations are solved with applicable constitutive equations. The applicable region of the bubble transport equation is also extended to churn-turbulent flow regime to predict interfacial area concentration at high void fraction. Predicted results in terms of axial pressure and void fraction profiles along the channels are compared with experimental data of Super Moby Dick and BNL Reasonable agreements have been achieved and this shows the applicability of the present model to flashing flow analysis.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.11 s.242
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• pp.1209-1219
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• 2005

In a closed square cavity filled with a liquid, a cooling horizontal upper wall and a heating lower wall, the flow isn't generated under the ground-based condition when Rayleigh number is lower than 1700. In this mechanism, Ra=1534, Temperature and velocity fields near an air-bubble in silicon-oil under a cooled upper wall were investigated. Temperature and velocity fields is visualized using the thermo-sensitive liquid-crystal and light sheet visualization technique. The quantitative analysis fer the temperature and the flow fields were carried out by applying the image processing technique to the original data. The symmetry shape of two vortexes near an air bubble was observed. As the bubble size increased, the size of vortex and the magnitude of velocity increased. In spite of elapsed time, a pair of vortexes was the unique and steady-state flow in a square cavity and wasn't induced to the other flow in the surround region.

• Journal of the Korean Society of Combustion
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• v.12 no.2
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• pp.20-25
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• 2007

The supersonic combustion experiments are carried out using T3 free-piston shock tunnel. Hydrogen Fuel is injected in the cavity parallel with air(or nitrogen) flow. The equivalence ratios in this study are 0.132 and 0.447. Experimental measurements use OH-PLIF near the cavity and pressures in the combustor. For parallel fuel injection case, direct fuel add into cavity leads to increase of cavity pressure. And Flame exists just near the bottom wall for low equivalent ratio. There is no flame in the cavity because of no mixing in it. Compared to the inclined fuel injection, ignition delay length is longer for low equivalence ratio in both case. OH distribution is not a single line but a repeatable fluctuation flame structure by turbulence. Pressure distributions have nothing to do with the fuel injection position.

• 한국연소학회:학술대회논문집
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• 2007.05a
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• pp.31-36
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• 2007

The supersonic combustion experiments are carried out using T3 free-piston shock tunnel. Hydrogen Fuel is injected in the cavity parallel with air(or nitrogen fuel) flow. The equivalence ratios in this study are 0.132 and 0.447. Experimental measurements use OH-PLIF near the cavity and pressures in the combustor. For parallel fuel injection case, direct fuel add into cavity leads to increase of cavity pressure. And Flame exists just near the bottom wall for low equivalent ratio. There is no flame in the cavity because of no mixing in it. Compared to the inclined fuel injection, ignition delay length is longer for low equivalence ratio in both case. OH distribution is not a single line but a repeatable fluctuation flame structure by turbulence. Pressure distributions have nothing to do with the fuel injection position.