• Journal of Advanced Marine Engineering and Technology
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• v.33 no.1
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• pp.62-70
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• 2009

In this paper, the fluid flow behavior past a pair of rectangular cylinders placed in a two dimensional horizontal channel has been investigated using Lattice-Boltzmann Method(LBM). The LBM has built up on the D2Q9 model and the single relaxation time method called the Lattice-BGK(Bhatnagar-Gross-Krook)model. Streamlines, velocity, vorticity and pressure contours are provided to analyze the important characteristics of the flow field for a wide range of non dimensional parameters that present in our simulation. Special attention is paid to the effect of spacing(d) between two cylinders and the blockage ratio A(=h/H), where H is the channel height and h is the rectangular cylinder height. for different Reynolds numbers. The first cylinder is called upstream cylinder and the second one as downstream cylinder. The downstream fluid flow fields have been more influenced by its blockage ratios(A) and Reynolds numbers(Re) whereas the upstream flow patterns(in front of downstream cylinder) by the gap length(d) between two cylinders. Moreover, it is observed that after a certain gap, both upstream and downstream flow patterns are almost similar size and shape. The simulation result has been compared with analytical solution and it is found to be in excellent agreement.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.2
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• pp.159-165
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• 2007

The Characteristics of the flowfield around two circular cylinders in tandem arrangement was investigated by PIV. Strouhal numbers. velocity vectors and velocity profiles were observed at centre-to-centre space ratios of P/D= 1.5. 2.0 and 2.5, and Reynolds number of $Re=3.0{\times}10^3{\sim}5.0{\times}10^3$. As the results the Strouhal numbers measured in the rear region of the cylinder of wake side were decreased with the space ratios. The flow between two cylinders was almost stagnated and the size of the stagnated region was larger in the close side than in the far side of the front cylinder. The direction of vortex between two cylinders was opposed each other with the small difference(${\alpha}\;{\pm}1.0^{\circ}$) of the attack angle ${\alpha}$.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.1
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• pp.1-7
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• 2013

Pneumatic cylinders are widely used to actuators in automatic equipments because they are relatively inexpensive, simple to install and maintain, offer robust design and operation, are available in a wide range of standard sizes and design alternatives. This paper presents a comparative study among the dynamic characteristics of meter-out and meter-in speed control of pneumatic cushion cylinders with a relief valve type cushion mechanism. Because of the nonlinear differential equations and a requirement for simultaneous iterative solution in a mathematical model of a double acting pneumatic cushion cylinder, a computer simulation is carried out to investigate pressure, temperature, mass flow rate in cushion chamber and displacement and velocity time histories of piston under various operating conditions. It is found that the piston velocity and pressure response in meter-in speed control are more oscillatory than with meter-out those when pneumatic cushion cylinders are driven at a high-speed. In meter-out speed control, the effective area of the flow control valve is larger than that of meter-in, and the supply pressure has to be much higher than the pressure required to move the load because it has also to overcome the back pressure in cushion chamber.

• International Journal of Automotive Technology
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• v.6 no.6
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• pp.579-584
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• 2005

Unsteady state free natural gas jets injected from several types of injectors were numerically simulated. Simulations showed good agreements with the schlieren experimental results. Moreover, injections of natural gas in intake manifolds of a single-valve engine and a double-valve engine were predicted as well. Predictions revealed that large volumetric injections of natural gas in intake manifolds led to strong impingement of natural gas with the intake valves, which as a result, gave rise to pronounced backward reflection of natural gas towards the inlets of intake manifolds, together with significant increase in pressure in intake manifold. Based on our simulations, we speculated that for engines with short intake manifolds, reflections of the mixture of natural gas and air were likely to approach the inlets of intake manifolds and subsequently be inbreathed into other cylinders, resulting in non-uniform mixture distributions between the cylinders. For engines with long intake manifolds, inasmuch as the degrees of intake interferences between the cylinders were not identical in light of the ignition sequences, non-uniform intake charge distributions between the cylinders would occur.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.4
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• pp.11-22
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• 1992

It this study, the aerodynamic responses of circular cylinder behind a pair of circular cylinders arranged side by side in a uniform flow were investigated. We confirmed that four types of oscillation are occured on downstream cylinder in such an arrangement. Influenced by upstream cylinders, the amplitude of vortex induced oscillation is increased and wake buffeting occured when S/D(S: distance between the centers of upstream cylinders, D: diameter of cylinder) is smaller than 1.2. When S/D is larger than 1.2, gap flow introduces to oscillation which maintains a uniform amplitude in spite of increasing wind speed. This oscillation is reduced to "wake galloping" if its amplitude exceeds the limit point.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.7 no.3
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• pp.117-120
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• 2014

In general a main technology of control a sluice gate is accurate synchronous position control for the two cylinders when they are moving with the sluice gate together over 10[m]. Because the nonlinear friction and the unconstant supply flow. Cylinders' displacement will be different. In this case the sluice gate may be deformed and abraded, and even the sluice gate may unable to work. In order to design the controller for this system, we designed two kinds of Fuzzy PI controllers. Fuzzy PI position controller and Fuzzy PI synchronous controller have been designed. We show some simulation results for its availability.

• Journal of KSNVE
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• v.5 no.3
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• pp.303-311
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• 1995

Tests on flow-induced vibration of inclined cylinders in uniform flow were performed in the cavitation tunnel at the Korea Instituteof Machinery and Metals. The test program was intended to investigate flow-induced vibration characteristic of the cylinders with three different inclined angles of 10$^\circ$, 20$^\circ$ and 30$^\circ$ and to estimate the fluid force coefficients acting on the cylinders. Important observations are as follows: 1) Numal drag is dominant compared with viscous drag for the inclined angle over 20.deg. and it has the value from 1.7 to 2.0 as was observed by other researchers. 2) Lift force coefficient has large value at the lock-in range determined by 4$\Theta/f_nD$<8. Measured maximum lift force coefficients at the inclined angle of 30.$^\circ$ and 20$^\circ$ were 0.9 and 0.4 respectively.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.9
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• pp.2933-2943
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• 1996

A grating composed of elliptical cylinders (GEC), specially designed, is applicable to control of radiation heat transfer from a heated surface, as reported in our previous work. In this study, an analysis of radiation heat transfer is performed for a physical model in which the GEC is placed in front of a heated black-base surface and the major axes of the elliptical cylinders are inclined as a certain angle from the normal to the row of elliptical cylinders. Numerical solutions are obtained. Variations of the direction and the radiative energy concentration with slant angle of the major axis are shown for some parameters. It is verified that the GEC is able to widely change the direction of radiation heat transfer from the heated surface.

• 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.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.5
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• pp.691-697
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• 2008

Heat exchangers are commonly used in practice in a wide range of application, from heat and air-conditioning system in a household, to chemical processing and power production in large plant. An Experimental study was conducted to investigated the fluid flow and heat transfer around four circular cylinders of in-line in a cross flow of air. The local and average heat transfer characteristics for tube banks are investigated in the present study. Heat transfer in a heat exchanger usually involves convection in each fluid and conduction through the wall separating the two fluid. The in-line pitch ratio was in the range $1.5{\leq}L/d{\leq}4.0$, where L is the center distance and d the cylinder diameter, and in the Reynolds number $8,000{\leq}Re{\leq}50,000$. The local and mean Nusselt numbers were estimated. Subsequently, the heat transfer characteristics of four circular cylinders are found to exhibit a strong dependency upon the separation point of their upstream cylinders.