• Title/Summary/Keyword: Shallow Cavity

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Effect of surface bolt on the collapse mechanism of a shallow rectangular cavity

  • Huang, Fu;Zhao, Lian-heng;Zhang, Sheng
    • Geomechanics and Engineering
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    • v.13 no.3
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    • pp.505-515
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    • 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.

3D stability of shallow cavity roof with arbitrary profile under influence of pore water pressure

  • Luo, W.J.;Yang, X.L.
    • Geomechanics and Engineering
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    • v.16 no.6
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    • pp.569-575
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    • 2018
  • The stability of shallow cavities with an arbitrary profile is a difficult issue in geotechnical engineering. This paper investigates this problem on the basis of the upper bound theorem of limit analysis and the Hoek-Brown failure criterion. The influence of pore pressure is taken into consideration by regarding it as an external force acting on rock skeleton. An objective function is constructed by equating the internal energy dissipation to the external force work. Then the Lagrange variation approach is used to solve this function. The validity of the proposed method is demonstrated by comparing the analytical solutions with the published research. The relations between shallow and deep cavity are revealed as well. The detaching curve of cavity roof with elliptical profile is obtained. In order to facilitate the application of engineering practice, the numerical results are tabulated, which play an important role in tunnel design and stability analysis of roof. The influential factors on potential collapse are taken into consideration. From the results, the impact of various factors on the extent of detaching is seen intuitively.

A Robust Design Study of Air Bearing Slider for HDD (HDD용 에어베어링 슬라이더의 강건설계에 관한 연구)

  • 전규찬;장동섭;좌성훈
    • Tribology and Lubricants
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    • v.16 no.4
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    • pp.247-252
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    • 2000
  • As the demand for higher areal recording densities requires a lower flying height of the slider, the variation of the flying height of the slider during drive operation becomes of great concern. The variation of the flying height is closely related with the slider design parameters such as air bearing shape, cavity depth, shallow step depth, crown, camber, pitch offset, roll offset, gram load, and so on. The objective of this work is to optimize the cavity depth and the shallow step depth, which are the control factors in air bearing design, using Robust Design method. It was found that the shallow step depth was statistically significant in affecting the variation of flying height, therefore the level of the shallow step depth should be chosen to minimize the variation of flying height.

Unsteady Flow in a Cavity Induced by An Oscillatory External Flow (외부유동에 의한 캐버티 내의 비정상 유동특성)

  • 서용권;박준관;문종춘
    • Journal of Ocean Engineering and Technology
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    • v.10 no.3
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    • pp.105-116
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    • 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.

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Natural Convection in Shallow Cavities

  • Bae, Dae-Seok
    • International Journal of Air-Conditioning and Refrigeration
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    • v.6
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    • pp.158-167
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    • 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.

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Effect of impingement edge geometry on the acoustic resonance excitation and Strouhal numbers in a ducted shallow cavity

  • Omer, Ahmed;Mohany, Atef;Hassan, Marwan
    • Wind and Structures
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    • v.23 no.2
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    • pp.91-107
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    • 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.

A Numerical Analysis of an Unsteady Flow in a Cavity Using an Ekman Pumping Model (에크만 분출 모델을 이용한 캐버티 내의 비정상 유동특성에 관한 수치해석)

  • 서용권;박춘근;최윤환;문종춘
    • Journal of Ocean Engineering and Technology
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    • v.11 no.4
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    • pp.102-110
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    • 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.

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High Performance $2{\times}4$ S-SEED Array with Extremely Shallow Quantum Well and Asymmetric Fabry-Peort Cavity Structure (저장벽 양자우물고조와 비대칠 패브리-페로 공명기 구조에 의한 고성능 $2{\times}4$ S-SEED Array 구현)

  • 권오균;최영완;김광준;이일항;이상훈;원용협;유형모
    • Korean Journal of Optics and Photonics
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    • v.5 no.1
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    • pp.144-151
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    • 1994
  • We designed and fabricated a $2{\times}4$ symmetric self electro-optic effect device array using GaAs/ AIo.04 G$\DeltaR$), and optical bistability loop width ($\Delta$). The average values of the elements of the $2{\times}4$ S-SEED array were CR~13.1, R~24%, and $\Delta$~91%. It was found that the AFP cavity structure enhances the self-biased optical bistability in ESQW-SEED under no external bias. That is due to the decreased intrisic region thickness in AFP-SEED structures, and which increases the built-in electric fields. The zero-biased S-SEED showed CR of ~4.7, R~9%, and $\Delta$~22%.X>~22%.

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Numerical Computation of Unsteady Flow in a Cavity Induced by an Oscillatory External Flow (외부유동에 의한 캐버티 내의 비정상 유동에 대한 수치계산)

  • Yong kweon Suh;Park, Yoon-Hwan;Park, Jun-Gwan;Moon, Jong-Ghoon
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.9 no.4
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    • pp.194-200
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    • 1997
  • A two-dimensional shallow-water flow around a cavity driven by a sinusoidally oscillating external flow was studied numerically. A container model of "T" shape was constructed in the numerical computation for comparison with the experimental observation. The numerical computation shows that the aspect ratio of the cavity is not much affecting the overall flow pattern, and for the aspect ratio 2, the deep region of the cavity has a stagnant flow motion. At larger Reynolds number, the flow field is characterized by many small vortices which are not present in the flow visualization. The flow pattern 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.particles.

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Analysis of Ground Subsidence on Gyochon Residential Region of Muan City (무안 교촌리주거지역 지반침하 안정성 분석)

  • Han, Kong-Chang;Cheon, Dae-Sung;Ryu, Dong-Woo;Park, Sam-Gyu
    • Tunnel and Underground Space
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    • v.17 no.1 s.66
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    • pp.66-74
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    • 2007
  • The analysis of ground subsidence stability was conducted for the residential area located on the limestone corrosion zone. For the investigation of the cavity distribution in limestone region, various geophysical investigations such as electroresistivity tomography, electromagnetic prospecting are carried out. Geotechnical field tests with drilling are also carried out for the evaluation of the ground characteristics. Based upon their results, numerical modeling is performed for the simulation and prediction of the ground subsidence with the conditions of cavity geometry and groundwater level. The main factor to cause the ground subsidence is estimated as the draw down of the groundwater level below soil overburden, which disturbs the mechanical equilibrium of ground and drives washing away the overburden soil through the cavity and solace subsidence. It seemed that it is essential to maintain the groundwater level continuously above the shallow cavity for the prevention of the ground subsidence on the limestone corrosion zone.