• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2489-2494
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• 2008

The two-dimensional circular cylinder freely falling in a channel has been simulated by using Immersed boundary - lattice Boltzmann method in order to analyze the characteristics of motion originated by the interaction between the fluid and the solid. The wide range of the solid/fluid density ratio has been considered to identify the effect of the solid/fluid density ratio on the motion characteristics such as the falling time, the terminal velocity and the trajectory in the vertical and horizontal directions. In addition, the effect of the gap between the cylinder and the wall on the motion of two-dimensional circular cylinder freely falling has been revealed by taking into account a various range of the gap size. The Reynolds number in terms of the terminal velocity is diminished as the cylinder becomes close to the wall at the initial dropping position, since the repulsive force induced between the cylinder and wall constrains the vertical motion. Quantitative information about the flow variables such as the pressure coefficient and vorticity on the cylinders is highlighted.

• International Journal of Concrete Structures and Materials
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• v.5 no.1
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• pp.49-55
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• 2011

The main objective of this investigation is to study size effect on compressive strength of CFRP confined concrete cylinders subjected to axial compressive loading. In total 24 concrete cylinders with different sizes were tested, small specimens with a diameter of 100 mm and a height of 200 mm, medium specimens with a diameter of 200 mm and a height of 400 mm, and big specimens with a diameter of 300 mm and a height of 600 mm. The lateral confining pressure of each specimen is the same and from that hypothesis the small specimens were confined with one layer of CFRP, medium and big specimens were performed by two and three layers of CFRP respectively. Test results indicate a significant enhancement in compressive strength for all confined specimens, and moreover, the compressive strengths of small and medium specimens are almost the same while a bit lower for big specimens. These results permit to conclude that there is no size effect on compressive strength of confined specimens regardless of cylinder dimension.

• Journal of the korean Society of Automotive Engineers
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• v.14 no.3
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• pp.80-89
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• 1992

An experimental study of in-cylinder of flow and combustion characteristics in two gasoline engines of different intake ports which are denoted as original port and masked shroud head (MSH) ports is presented. The flows generated by the MSH and the original port are invest- igated by laser Doppler velocimeter(LDV) under steady flow and motoring (non-firing) condit -ions. Combustion characteristics with different swirl levels produced by two intake ports are analyzed by combustion pressure measurement and statistical calculation. The swirl inside the cylinder of the MSH port engine is found to be much higher than the original port, and the MSH has a large eddy motion of cylinder diameter size. Using ensemble average method to valuate engine turbulence under motoring condition, the MSH port engine is shown to have h -igher turbulence intensity than the original port, so that the effect of the MSH port on fast burn is shown. Also the cyclic variations of peak pressure and the reaching time in the MSH port are apparently reduced.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.1
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• pp.32-41
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• 2003

For the countermeasure of expected higher thermal load in miller cycle engine, coolant flows in the cylinder head of base engine with several coolant flow methods and drilled hole passages were measured by using PIV technique. And the cooling effect was evaluated by measurements of wall temperatures according to each coolant flow method. It was found that the series flow system was most suitable among the discussed 3 types of coolant flow methods since it had the best cooling effect in cylinder head by the fastest coolant flow velocity It was also found that for drilled water passage to decrease the large thermal load in exhaust valve bridge, nozzle type is more effective compared with round type of water passage, and its size has to be determined according to the coolant flow pattern and velocity in each cylinder.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.6
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• pp.51-59
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• 2000

In-cylinder spray flow motion plays an important in the adjustment of mixture preparation with a fundamental spray characteristics and in-cylinder flow field well in direct-injection gasoline engine. In this study, the fundamental spray characteristics such as mean drop size, velocity distribution, spray angle were measured and in-cylinder spray flow motion was visualized in order to optimize intake port, piston top land and combustion chamber shapes in the development stage of mass-produced G야 engine. For these experiments, the PDPA measurements and Mie scattering technique were used for detailed spray characteristics and in-cylinder spray motions were obtained by use of ICCD camera through the single-cylinder optical engine. From the experimental results, the test injector shows a good low-end linearity between the dynamic flow and fuel injection pulse width and the fuel spray of 20mm or less in SMD with good spray symmetry. In addition, the in-cylinder tumble flow has more effect on the homogeneous mixture formation than that of in-cylinder swirl flow at early injection mode and the in-cylinder swirl flow plays a better role of stratified mixture preparation than tumble flow at late injection mode.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.2089-2094
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• 2003

The flow around a circular cylinder was controlled by attaching O-rings to reduce drag force acting on the cylinder. Four experimental models were tested in this study; one smooth cylinder of diameter D (D=60mm) and three cylinders fitted with O-rings of diameters d=0.0167D, 0.05D and 0.067D with pitches of PPD=1D, 0.5D and 0.25D. The drag force, mean velocity and turbulent intensity profiles in the near wake behind the cylinders were measured for Reynolds numbers based on the cylinder diameter in the range of $Re_D=7.8{\times}10^3{\sim}1.2{\times}10^5$. At $Re_D=1.2{\times}10^5$, the cylinder fitted with O-rings of d=0.0167D in a pitch interval of 0.25D shows the maximum drag reduction of about 5.4%, compared with the smooth cylinder. The drag reduction effect of O-rings of d=0.067D is not so high. For O-ring circulars, as the Reynolds number increases, the peak location of turbulence intensity shifts downstream and the peak magnitude is decreased. Flow field around the cylinders was visualized using a smoke-wire technique to see the flow structure qualitatively. The size of vortices and vortex formation region formed behind the O-ring cylinders are smaller, compared with the smooth cylinder.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.5
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• pp.349-357
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• 2009

Effect of computational domain size in simulating of periodic obstacle flow has been investigated for the flow past tube banks. Reynolds number, defined by freestream velocity ($U_{\infty}$) and cylinder diameter (d), was fixed as 200, and center-to-center distance (P) as 1.5d. In-line square array and staggered square array were considered. Drag coefficient, lift coefficient and Strouhal number were calculated depending on domain size. Circular cylinders were implemented on a Cartesian grid system by using an immersed boundary method. Boundary condition is periodic in both streamwise and lateral directions. Previous studies in literature often use a square domain with a side length of P, which contains only one cylinder. However, this study reveals that the domain size is improper. Especially, RMS values of flow-induced forces are most sensitive to the domain size.

• Journal of ILASS-Korea
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• v.7 no.1
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• pp.14-20
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• 2002

It is well known that the flow and spray characteristics is critical factor on the performance and emission of a direct injection diesel engine. So this study aims to investigate the interaction of flow and spray characteristics. At first, in cylinder flow distributions in swirl adaptor for 4-valve cylinder head of DI Diesel engine were investigated under steady conditions for different SCV angles mounted on the cylinder head with steady rig test and 2-D LDV. And the in-cylinder flow was quantified in terms of mean flow coefficient and swirl ratio/tumble ratio. It was found that the swirl ratio is controlled between 2.3 and 3.8. Then spray characteristics of the intermittent injection were investigated. PDA system was utilized for measurement of a droplet size and velocity. The analyses of the PDA results are carried out with Time Dividing Method. It was found that there is a correlation between the swirl flow and SMD. The droplet size and the velocity were nearly constant value with each SCV angle. And the swirl ratio is higher, SMD smaller. The swirl ratio was helpful factor to the atomization of droplet.

• Journal of Magnetics
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• v.19 no.4
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• pp.349-352
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• 2014

The system for producing magnetic field constitutes an important component of magnetic refrigerator. Many researchers have directed significant effort to increase the magnetic field intensity, because the magnetocaloric effect at the Curie temperature increases with the power of 2/3 of the magnetic field. In this study, we report the simulation of the magnetic field intensity at polar axis of a Halbach cylinder (HC) by i) changing the length and thickness of the HC, ii) having with or without gap of the HC, and iii) surrounding the HC with a soft magnet shell, acting as a shielding. We simulated the field distribution of a HC with a finite size. Furthermore, the detailed numerical results of the magnetic field distribution and its dependence on shielding are presented in this study.

• Journal of Energy Engineering
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• v.11 no.1
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• pp.74-80
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• 2002

In this study, a numerical method for fuel droplet evaporation in cylinder of S.I. engine is presented. This study was newly defined non-dimensional critical droplet lifetime and modeled heating and evaporation processes of fuel droplet during intake and compression stroke of gasoline engine. The simulation results show that simultaneous increase of gas temperature and pressure in compression stroke seems to have compensative effect on droplet gasification rate. The environment variations in cylinder have little effect on the fuel droplet gasification process. The droplet size for full evaporation at the end of compression stroke can be estimated using this program.