• Wind and Structures
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• v.23 no.5
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• pp.465-483
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• 2016

This study aims to enhance the understanding of the surface pressure distribution around rectangular bodies, by considering aspects such as the suction pressure at the leading edge on the top and side faces when the body aspect ratio and wind direction are changed. We carried out wind tunnel measurements and numerical simulations of flow around a series of rectangular bodies (a cube and two rectangular bodies) that were placed in a deep turbulent boundary layer. Based on a modern numerical platform, the Navier-Stokes equations with the typical two-equation model (i.e., the standard $k-{\varepsilon}$ model) were solved, and the results were compared with the wind tunnel measurement data. Regarding the turbulence model, the results of the $k-{\varepsilon}$ model are in overall agreement with the experimental results, including the existing data. However, because of the blockage effects in the computational domain, the pressure recovery region is underpredicted compared to the experimental data. In addition, the $k-{\varepsilon}$ model sometimes will fail to capture the exact flow features. The primary emphasis in this study is on the flow characteristics around rectangular bodies with various aspect ratios and approaching wind directions. The aspect ratio and wind direction influence the type of wake that is generated and ultimately the structural loading and pressure, and in particular, the structural excitation. The results show that the surface pressure variation is highly dependent upon the approaching wind direction, especially on the top and side faces of the cube. In addition, the transverse width has a substantial effect on the variations in surface pressure around the bodies, while the longitudinal length has less influence compared to the transverse width.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.115-120
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• 2003

In this study, smoke movement in tunnel fires was investigated with various aspect ratio(0.5, 0.667, 1.0, 1.5, 2.0) of tunnel cross section. Reduced-scale experiments were carried out under the Froude scaling using 8.27 kW ethanol pool fire. Temperatures were measured under the ceiling and vertical direction along the center of the tunnel. Smoke front velocity and temperature decrease rate were reduced as higher aspect ratio of the tunnel cross-section. Smoke movement was evaluated by analysis of vertical temperature distribution 3 m downstream from the fire source. Elevation of smoke interface according to N percent rule was under about 60% of tunnel height.

• Steel and Composite Structures
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• v.28 no.5
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• pp.541-557
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• 2018

This paper presents the influence of carbon nanotubes (CNTs) waviness and aspect ratio on the vibrational behavior of functionally graded nanocomposite sandwich annular sector plates resting on two-parameter elastic foundations. The carbon nanotube-reinforced (CNTR) sandwich plate has smooth variation of CNT fraction along the thickness direction. The distributions of CNTs are considered functionally graded (FG) or uniform along the thickness and their mechanical properties are estimated by an extended rule of mixture. In this study, the classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler content increases. Effects of CNT distribution, volume fraction, aspect ratio and waviness, and also effects of Pasternak's elastic foundation coefficients, sandwich plate thickness, face sheets thickness and plate aspect ratio are investigated on the free vibration of the sandwich plates with wavy CNT-reinforced face sheets. The study is carried out based on three-dimensional theory of elasticity and in contrary to two-dimensional theories, such as classical, the first- and the higher-order shear deformation plate theories, this approach does not neglect transverse normal deformations. The sandwich annular sector plate is assumed to be simply supported in the radial edges while any arbitrary boundary conditions are applied to the other two circular edges including simply supported, clamped and free.

• Transactions of Materials Processing
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• v.16 no.1 s.91
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• pp.48-53
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• 2007

LCD-BLU(Liquid Crystal Display - Back Light Unit) consists of several optical sheets: LGP(Light Guiding Plate), light source and mold frame. The LGP of LCD-BLU is usually manufactured by etching process and forming numerous dots with $50{\mu}m$ in diameter on the surface. But the surface roughness of LGP with etched dots is very high, so there is much loss of light. In order to overcome the limit of current etched dot patterned LGP, optical pattern design with microlens of $50{\mu}m$ diameter was applied in the present study. The microlens pattern fabricated by modified LiGA with thermal reflow process was applied to the optical design of LGP and optical simulation was carried out to know tendency of microlens patterned LGP simultaneously. The attention was paid to the effects of different aspect ratio(i.e. $0.2\sim0.5$) of optical pattern conditions to the brightness distribution of BLU with microlens patterned LGP. Finally, high aspect ratio microlens patterned LGP showed superior results to the one made by low aspect ratio in average luminance.

• Fire Science and Engineering
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• v.18 no.2
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• pp.1-6
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• 2004

In this study, numerical simulations were conducted to analyze an effect of the aspect ratio on smoke movement in tunnel fires using FDS 3.0. It was confirmed an application for tunnel fires in comparison with experimental results. The results showed relatively good agreement with experimental data within 1$0^{\circ}C$. Clear height of CFD by velocity distribution was about 3% higher than that of experiment. Smoke movement was confirmed by the analysis of temperature and velocity field. Results from variation of the aspect ratio showed good agreement with experimental data. The temperature at the vicinity of the fire source became lowly with the increase of the aspect ratio. But, decrease rate of the temperature was reduced by the decrease of the heat loss to the width direction.

• Steel and Composite Structures
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• v.25 no.6
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• pp.649-661
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• 2017

This paper is motivated by the lack of studies in the technical literature concerning to the influence of carbon nanotubes (CNTs) waviness and aspect ratio on the vibrational behavior of functionally graded nanocomposite annular sector plates resting on two-parameter elastic foundations. The carbon nanotube-reinforced (CNTR) plate has smooth variation of CNT fraction based on the power-law distribution in the thickness direction, and the material properties are also estimated by the extended rule of mixture. In this study, the classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler content increases. Parametric studies are carried out to highlight the influence of CNTs volume fraction, waviness and aspect ratio, boundary conditions and elastic foundation on vibrational behavior of FG-CNT thick sectorial plates. The study is carried out based on three-dimensional theory of elasticity and in contrary to two-dimensional theories, such as classical, the first- and the higher-order shear deformation plate theories, this approach does not neglect transverse normal deformations. The annular sector plate is assumed to be simply supported in the radial edges while any arbitrary boundary conditions are applied to the other two circular edges including simply supported, clamped and free. For an overall comprehension on 3-D vibration of annular sector plates, some mode shape contour plots are reported in this research work.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.297-301
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• 2008

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's $\kappa$-$\omega$ turbulence model. The flow field is observed to oscillate in the shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.297-301
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• 2008

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's ${\kappa}-{\varepsilon}$ turbulence model. The flow field is observed to oscillate in the "shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.6
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• pp.1156-1162
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• 1992

The effect of aspect ratio on the flow characteristics of elliptic jets was experimentally investigated. The flow characteristics of sharp-edged elliptic nozzles with aspect ratio of 1 (round nozzle), 2 and 4 were measured by using a 3-D LDV system along the major and minor axis at X/De = 2, 3, 5, 7 and along the centerline up to X/De = 14. At each measurement point mean velocites, turbulent intensities, skewness of three orthogonal velocity components, and Reynolds shear stress were obtained. The Reynolds number based on the nozzle exit velocity and nozzle equivalent diameter(De) was about 4 * 10$^{4}$. Difference in the spreading rate along the major and minor axis was remarkable. The jet half width along the major axis decreased at first and then increased again with going downstream. But the jet width along the minor axis increased steadly. The elliptic jet of AR = 2 had two switching points within the measurement range, while that of AR = 4 had only one. (AAA) : The elliptic jet of AR = 2 showed larger velocity decay rate than that of AR = 1 and AR = 4. The effect of aspect ratio on the flow characteristics of elliptic jets was dominant in the near jet regions of X/De < 7, and the skewness and Reynolds shear stress had quite different distribution depending on the aspect ratio of the elliptic nozzle.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.12
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• pp.1014-1022
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• 2002

This paper analyzed the characteristics of heat transfer in quadangle duct with absorber plate by solar radiation. Effects o( Reynolds number on increasing temperature at outlet for variation of absorber plate temperature were analyzed by using numerical analysis technique. And also the effects of turbulent intensity of inlet flow on increasing temperature at outlet for various duct height and effects of inlet aspect ratio of quadrangle duct and position of heating surface on the outlet temperature were analysed. As the results, Outlet temperature was greatly influenced in low Reynolds number. And the highest outlet temperature distribution appeared on the inlet aspect ratio 2 because of the buoyancy effect.