• Geotechnical Engineering
• /
• v.14 no.1
• /
• pp.93-108
• /
• 1998

In this study, the analytic solutions and numerical methods were used to estimate the shape and size effects on the stability of underground openings. The stability of underground openings was evaluated by scrutinizing the effects of the rock mass quality, the state of in-situ stresses and the lateral earth pressure coefficient on the displacement, the stress concentration and the plastic region developed in the vicinity of the openings. The analytic solutions have shown that the stress concentration factor is inversely proportional to the radius of curvature of openings. Through parametric study on the various shapes and sizes of underground openings the characteristics of the controlling factors concerned with the stability were analyzed. Then, the study was extended to the horseshoe-shaped openings commonly used for under ground storage. Through the extended study the effects of the stress ratio and the height-towidth ratio of openings on the maximum displacement and plastic region developed around the openings were estimated. The results have shorn that the height-to-width ratio of domestic storage caverns can be increased economically without stability problem, as far as the lateral earth pressure coefficient is appropriate.

• Journal of the Korean Institute of Gas
• /
• v.12 no.4
• /
• pp.63-68
• /
• 2008

This paper describes about the simulation and the experimental results of optical cavity with curved mirror surface and vertical mirror surface to improve the light intensity and efficiency of the optical sensors. When we use the vertical mirror surface, the distribution of light reached to the filter surface of detector shows an elliptical shape. Whereas, the curved mirror surface focuses the light into circular shape. Therefore, due to focusing effects in case of using curved mirror surface, the light intensity per unit area has been improved. Consequently, the output voltage of gas sensor has been expected to increase. Based upon the simulation, the experiment of gas sensor has been conducted with $CO_2$ gas from 0ppm to 2,500 ppm at 250 ppm step and $25^{\circ}C$, 45%R.H. ambient. The output voltage of gas sensor that has a curved mirror surface increases approximately 200 mV than that of vertical mirror surface.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2007.04a
• /
• pp.295-298
• /
• 2007

The effectiveness of passive control techniques for reducing the pressure oscillation generated in a supersonic cavity flow was investigated numerically and experimentally, respectively. The control device includes a sub-cavity installed in the upstream edge of a rectangular cavity. Time-dependent supersonic cavity flow characteristics with turbulent features were examined by using the three-dimensional, mass-averaged Navier-Stokes computation based on a finite volume scheme and large eddy simulation. The results show that the pressure oscillation near the trailing edge dominates overall time-dependent cavity pressure variations. Such an oscillation can be attenuated more significantly in the presence of the sub-cavity compared with the cavity without sub-cavity, and a larger sub-cavity leads to better control performance.

• Journal of the Society of Naval Architects of Korea
• /
• v.54 no.4
• /
• pp.321-328
• /
• 2017

In practice, cavitation phenomena occur in unbounded flows. However, the wall effect is unavoidable during experiments at a closed section such as a cavitation tunnel. Especially, supercavity generated behind a cavitator is relatively large and thick, so that geometric and dynamic characteristics of the cavity are affected by the tunnel wall. In order to apply experimental results into the unbounded flow field, physical correlations are necessary. In this paper, we proposed an image method based on a potential flow to simulate the wall effect. Considering two-dimensional wedge-shaped bodies, configurations and drag characteristics of the cavity were examined according to the distance ratio to the wall surface. The results were compared and verified with existing theoretical and experimental results.

• Proceedings of the Korean Institute of Landscape Architecture Conference
• /
• 2013.03a
• /
• pp.19-25
• /
• 2013

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2000.05a
• /
• pp.101-104
• /
• 2000

In this paper. the electric field intensity has been theoretically evaluated by the method of moments in a cavity by a external source. The numerical results show a good agreement with the results of other papers. It is found that the electromagnetic penetration through aperture in the cavity shows peak values at some frequencies dependent largely on the structure of the cavity and aperture.

• The Journal of Engineering Geology
• /
• v.5 no.1
• /
• pp.31-44
• /
• 1995

The puppose of this study is to propose the numerical modelling criteria for underground opening, rock mass continuum is regarded as homogeneous rock behaved linear elastic. The results of this study are summarized as follows: - Boundaries of the finite element mesh should be located at least 6 radii away from the center of the opening. - For circular openings, tension only developed when $K_0$ was less than one-fourAs the ratio of initial horiwntal to vertical stress increased, the inward springline movement increased and the inward crown movement decreased. - The displacement patterns developing for opening I shaped horse-shoe and opening II shaped powerstation are similar to those for circular openings. For both type opening I and opening II, stress concentrations develop at the intersection of the wall and floor. Greater stress concentrations are found for the type opening II.

• Explosives and Blasting
• /
• v.23 no.2
• /
• pp.23-35
• /
• 2005

Excavation of an opening in a saturated porous rock may lead to the development of pore pressure around the opening due to the redistribution of initial rock stresses. The built-up of pore pressure, in turn, may affect the mechanical behavior of rock mass and give the different pattern of stress distribution around the opening from that of the case where the coupling is neglected. In this study, the short time response of an opening excavated in saturated ground under anisotropic initial stress conditions was investigated numerically. Not on the wall of opening but at a short distance from the wall, the tangential stresses were peak during the short period after excavation when the hydro-mechanical coupling is considered.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 1999.11a
• /
• pp.106-109
• /
• 1999

The problem of electromagnetic field through apertures in cavity has been theoretically and experimentally investigated. The electric field intensity has been theoretically evaluated by the method of moments. Experiment results are some different from numerical simulation about the magnitude of electric field intensity, But The form of electric field intensity distributions In cavity is similar to numerical simulation. Reactance-loaded method for reducing electric field penetration In cavity by external sources is used In this paper.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.30 no.5
• /
• pp.101-108
• /
• 2002

A numerical simulation of an incompressible cavity flow is conducted. Two dimensional Navier-Stokes equations are integrated using staggered grid and a finite volume method with C-QUICK scheme for spatial derivatives and fully implicit scheme for the time derivatives. SIMPLE-C algorithm is employed to solve the pressure field. Computational results show that the third eddy is generated in the shear layer mode but not in the steady mode. This signifies that the third eddy plays an important role in cavity flow stability. As a means to control the flow, jet blowing is applied to a position below the cavity upstream edge. Effects of flow control parameters on the stability such as the frequency, the phase, and the velocity magnitude are reported.