• Wind and Structures
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• v.38 no.1
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• pp.59-74
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• 2024

Large Eddy Simulation (LES) is used to explore the influence of vibration frequency and amplitude on the aerodynamic performance of a rectangular cylinder with an aspect ratio of B/D=5 (B: breadth; D: depth of cylinder) at a Reynolds number of 22,000 near resonance frequency. In smooth flow conditions, the research employs a sequence of three-dimensional simulations under forced vibration with diverse frequency ratios f_e / f_o = 0.8-1.2 (f_e : oscillation frequency; f_o : Strouhal frequency when the rectangular cylinder is stationary ) and oscillation amplitudes A_h/D = 0.05 - 0.3. The individual influences of f_e / f_o and A_h/D on the characteristics of integrated and distributed aerodynamic forces are the focal points of discussion. For the integrated aerodynamic force, particular emphasis is placed on the analysis of the dependence of velocity-proportional component C₁ and displacement-proportional component C₂ of unsteady aerodynamic force on amplitude and frequency ratio. Near the resonance frequency, the dependencies of C₁ and C₂ on amplitude are stronger than that of frequency ratio. For the distributed aerodynamic force, the increase in frequency and amplitude promotes the position of the main vortex core and reattachment to the leading edge in the streamwise direction. In the spanwise direction, vibration enhances the spanwise correlation of aerodynamic force to weaken the three-dimensional effect of the flow field, and a lower frequency ratio and larger amplitude amplify this effect.

• Structural Engineering and Mechanics
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• v.53 no.4
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• pp.703-723
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• 2015

In this paper optimization of volume fraction distribution in a thick hollow cylinder with finite length made of two-dimensional functionally graded material (2D-FGM) and subjected to steady state thermal and mechanical loadings is considered. The finite element method with graded material properties within each element (graded finite elements) is used to model the structure. Volume fractions of constituent materials on a finite number of design points are taken as design variables and the volume fractions at any arbitrary point in the cylinder are obtained via cubic spline interpolation functions. The objective function selected as having the normalized effective stress equal to one at all points that leads to a uniform stress distribution in the structure. Genetic Algorithm jointed with interior penalty-function method for implementing constraints is effectively employed to find the global solution of the optimization problem. Obtained results indicates that by using the uniform distribution of normalized effective stress as objective function, considerably more efficient usage of materials can be achieved compared with the power law volume fraction distribution. Also considering uniform distribution of safety factor as design criteria instead of minimizing peak effective stress affects remarkably the optimum volume fractions.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.3
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• pp.210-219
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• 2014

The MPI dual injection engine can enhance the fuel efficiency and engine power. By using one injector per one intake port, MPI dual injection engine has an excellent fuel atomization and targeting injection. As the basic research for the MPI Dual injection engine design, this research was investigated in order to understand the characteristic of the in-cylinder flow and fuel behavior according to engine temperature condition and the fuel type in the MPI dual injection engines. The 3D unsteady CFD simulation for the MPI Dual injection engine was performed using STAR-CD. The engine operating condition was 2,000 rpm/WOT. The parameters for this study were fuel types, fuel temperatures and wall temperatures. As a result, the intake air amount, evaporated fuel in the cylinder and the fuel film on the wall were presented according to parameters that depend on the fuel properties and engine wall temperature. Also, the results were influenced by in-cylinder flow such as the intake flow, back flow and so on.

• International Journal of Automotive Technology
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• v.1 no.2
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• pp.79-87
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• 2000

Analytical approach was followed in this work under both the steady state and transient operating conditions to find optimum boundary conditions, where the optically accessible quartz engine can run safely without breaking. Temperature and stress distribution was predicted by FEM analysis. In order to validate thermal boundary condition, model reliability and constraint, outside cylinder temperature was measured and previous study was also followed up numerically. To reduce thermal stress level, three types of outside cooling (natural, moderate forced and intensive forced convection) were considered. Effects of clamping force and combustion pressure were conducted to investigate mechanical stress level. Cylinder thickness, was changed to fine the optimum cylinder thickness. The versatile results achieved from this work can be basic indication, which is capable of causing a sudden quartz cylinder breaking during fired operation.

• Journal of computational fluids engineering
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• v.20 no.4
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• pp.51-57
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• 2015

In the present study, two-dimensional numerical investigation of flow past a square cylinder beneath the free surface has been performed to identify the effects of presence of the free surface. An immersed boundary method was adopted for implementation of the cylinder cross-section in a Cartesian grid system. Also, a level-set method was used to capture the interface of two fluids. To prevent transition to three-dimensional flow, Reynolds number chosen for this simulation was 150. The cases for Froude number 0.2 and gap ratio(h/D) between 0.25 and 5.00 were examined. At the specific Reynolds number, we study the effects of gap ratio on flow characteristics around a square cylinder by computing flow fields, force coefficients and Strouhal number.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.4
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• pp.417-425
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• 2005

An experimental study is performed on the turbulent swirling flow behind a crcular cylinder using 2-D PIV technique. The Reynolds numbers investigated are 10.000, 15,000. 20.000 and 25.000. The mean velocity vector, time mean axial velocity, turbulence intensity, kinetic energy and Reynolds shear stress behind the cylinder are measured before and behind the cylinder along the test tube. A comparison is included without swirling flow behind a circular and square cylinder. The recirculation zones are shown unsymmetric profiles.

• Journal of Energy Engineering
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• v.24 no.1
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• pp.97-103
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• 2015

Natural convection heat transfer rates in vertical pipes were measured varying the diameter, length, and roughness of vertical cylinder. To achieve high Rayleigh number with relatively small test rig, mass transfer experiments instead of heat transfer were performed based on the analogy. Prandtl number was 2,014. The length of vertical cylinder was 0.1m, 0.3m, and 0.5m, which correspond to GrL $4.2{\times}10^7$, $1.1{\times}10^9$, and $5.5{\times}10^9$. To each length of vertical cylinder, the heat transfer rates were measured varying the iameter 0.005m, 0.01m, and 0.03m. The heat transfer rate for a short length pipe(0.1m) agreed with the prediction from Le Fevre correlation developed for a vertical plate for all diameter. The heat transfer rate decreases as the diameter and the length of the pipe increases. The heat transfer rate inside of vertical cylinder is affected by roughness only for a laminar flow regime.

• Journal of Korea Multimedia Society
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• v.20 no.2
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• pp.225-233
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• 2017

Line-laser beams are used for accurate measurement of 3D shape, which is robust to external illumination. For depth measurement, we project a line-laser beam across an object from the face and take an image of the beam on the object surface using a CCD camera at some angle with respect to the face. For shape measurement, we project parallel line-laser beams with narrow line to line distance. When a layer of thin materials attached to a cylinder is long narrow along its circumference, we can measure the shape of the layer with a small number of parallel line beams if we project line beams along the circumference of the cylinder. Measurement of the depth of the attached materials on a line-laser beam is based on the number of pixels between an imaginary line along the imaginary cylinder without the attached materials and the beam line along the materials attached to the cylinder. For this we need to localize the imaginary line in the captured image. In this paper, we model the shape of the line as an ellipse and localize the line with least square estimate. The proposed method results in smaller error (maximum 0.24mm) than a popular 3D depth camera (maximum 1mm).

• Journal of Korean Ophthalmic Optics Society
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• v.12 no.3
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• pp.105-110
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• 2007

To investigate the ametropia and refractive error of 222 ametropic eyes of the 111 high school students in Gwangju Metropolitan City, the visual acuity test was performed by the object and subject method. 85% of the eye types were positive for myopia, 14% for emmetropia, and 1% for hyperopia, respectively. 38% of the abnormal refraction eyes were positive for simple myopia, 4% for myopia simple astigmatism, 56% for myopia compound astigmatism, and 0% for simple hyperopia, 0% for hyperopia simple astigmatism, 2% for hyperopia compound astigmatism, 0% for mixed astigmatism, respectively. 92% of the axes fo astigmatism were for astigmatism with-the-rule, 6% for astigmatism against-the rule, 2% for astigmatism oblique, respectively. As for the astigmatic power, 0.50 < cylinder < 1.00D was 68%, 1.00 < cylinder < 2.00D was 25%, and anything over the 2.00 cylinder D was 7%. As for the equivalent spheric power of myopic abnormal refraction eyes, -0.50 < spheric equivalent < -2.00D was 26%, -2.00D < spheric equivalent < -6.00D was 55% and anything over the -6.00D was 19%. The rate of wearing glasses was 74%. It increases compared to 20 years ago. 91% of the eye test place was the optical shop, 9% the eye doctor hospital. 80% of the students need to change their optical lenses because spherical equivalent power was over 0.50D.

• The Journal of the Korea Contents Association
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• v.10 no.11
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• pp.446-451
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• 2010

To investigate the vortex induced vibrations the 2-d.o.f. spring mounted circular cylinder was tested in the wind tunnel. The circular cylinder was designed to have the translational and the rotational mode uncoupled to each other. During the wind tunnel tests the resonance behaviors of the translational and the rotational modes by the locking-on phenomena were observed. From the locking-on phenomena observed it is shown that the vortex shedding is correlated with the responses of the structures. And the forces generated by the vortex shedding are influenced by the amplitudes and the frequencies of the cylinders.