• Geomechanics and Engineering
• /
• 제13권3호
• /
• pp.505-515
• /
• 2017

Based on the collapse characteristics of a shallow rectangular cavity, a three-dimensional failure mechanism which can be used to study the collapsing region of the rock mass above a shallow cavity roof is constructed. Considering the effects of surcharge pressure and surface bolt on the collapsing block, the external rate of works produced by surcharge pressure and surface bolt are included in the energy dissipation calculation. Using variational approach, an analytic expression of surface equation for the collapsing block, which can be used to study the collapsing region of the rock mass above a shallow cavity roof, is derived in the framework of upper bound theorem. Based on the analytic expression of surface equation, the shape of the collapsing block for shallow cavity is drawn. Moreover, the changing law of the collapsing region for different parameters indicates that the collapsing region of rock mass decreases with the increase of the density of surface bolt. This conclusion can provide reference for practicing geotechnical engineers to achieve an optimal design of supporting structure for a shallow cavity.

• 한국해양공학회지
• /
• 제10권3호
• /
• pp.105-116
• /
• 1996

In this paper, we report the experimental results for the flow pattern and the material transport around a cavity subject to a sinusoidal external flow at the far region to ward the open side of the cavity. A tilting mechanism is used to generate a oscillatory flow inside a shallow rectangular container having a cavity at one side. The surface flow visualization is performed to obtain the unsteady behavior of vortices generated at two edges situated at the entrance of the cavity. It was found that at the period 4.5 sec., the behavior of the vortices is asymmetric, and there exists a steady residual flow in the cavity. The bottom flow patterns are also visualized. There are two regions outside of the cavity where the bottom fluid particles concentrate. The material transport in this flow model is very peculiar; fluid particles in the cavity flows outward through the passage along the walls starting from the edges, and particles in the outer region approach the cavity from the central region.

• International Journal of Air-Conditioning and Refrigeration
• /
• 제6권
• /
• pp.158-167
• /
• 1998

Natural convection heat transfer in a rectangular enclosure is investigated numerically for low aspect ratio(height/width) cavities. Numerical results are obtained for aspect ratios between ${10}^{-2}$ and ${10}^0$, Rayleight numbers from ${10}^3$ to ${10}^7$ and Prandtl numbers from 10$^{-2}$ to 10$^3$. Results are compared with existing analytical and experimental results. A heat transfer correlation is developed to predict the mean Nusselt number as a function of the three governing dimensionless parameters: Rayleigh number, aspect ratio and Prandtl number.

• 한국해양공학회지
• /
• 제11권4호
• /
• pp.102-110
• /
• 1997

A two dimensional shallow-water flow around a cavity driven by a sinusoidally oscillating external flow was studied numerically with an Ekman pumping model. A container model of "T" shape was constructed in the numerical computation for comparison with the experimental observation. The material transport in the external region is in good agreement with the experimentally recorded particle trajectories. It turns out that two large coherent vortices situated in the exterior region of the cavity are responsible for clockwise and counterclockwise drift motions, in large scale, of particles. The Ekman pumping model suggested in this study was found to be satisfactory.isfactory.

• Wind and Structures
• /
• 제23권2호
• /
• pp.91-107
• /
• 2016

Flow-excited acoustic resonance in ducted cavities can produce high levels of acoustic pressure that may lead to severe damage. This occurs when the flow instability over the cavity mouth, which is created by the free shear layer separation at the upstream edge, is coupled with one of the acoustic modes in the accommodating enclosure. Acoustic resonance can cause high amplitude fluctuating acoustic loads in and near the cavity. Such acoustic loads could cause damage in sensitive applications such as aircraft weapon bays. Therefore, the suppression and mitigation of these resonances are very important. Much of the work done in the past focused on the fluid-dynamic oscillation mechanism or suppressing the resonance by altering the edge condition at the shear layer separation. However, the effect of the downstream edge has received much less attention. This paper considers the effect of the impingement edge geometry on the acoustic resonance excitation and Strouhal number values of the flow instabilities in a ducted shallow cavity with an aspect ratio of 1.0. Several edges, including chamfered edges with different angles and round edges with different radii, were investigated. In addition, some downstream edges that have never been studied before, such as saw-tooth edges, spanwise cylinders, higher and lower steps, and straight and delta spoilers, are investigated. The experiments are conducted in an open-loop wind tunnel that can generate flows with a Mach number up to 0.45. The study shows that when some edge geometries, such as lower steps, chamfered, round, and saw-tooth edges, are installed downstream, they demonstrate a promising reduction in the acoustic resonance. On the other hand, higher steps and straight spoilers resulted in intensifying the acoustic resonance. In addition, the effect of edge geometry on the Strouhal number is presented.