• Wind and Structures
• /
• v.21 no.1
• /
• pp.25-40
• /
• 2015

Oscillating motions of flexible cylinders are associated to some extent with the aerodynamic response of plants. Tandem motions of reeds with flexible stems in a colony are experimentally investigated using an array of flexible cylinders made of polydimethylsiloxane (PDMS). Consecutive images of flexible cylinders subjected to oncoming wind are recorded with a high-speed camera. To quantify oscillating motions, the average bending angle and displacement of flexible cylinders are evaluated using point-tracking method and spectral analysis. The tandem motions of flexible cylinders are closely related to the flow characteristics around the cylinders. Thus, the dynamic motions of a tandem arrangement of flexible cylinders are investigated with varying numbers of cylinders arranged in-line, numbers of cylinders in a group (behaving like a single body), and Reynolds numbers (Re). When the number of cylinders in a group increases, the damping effect caused by the support of downstream cylinders is pronounced. These results would be provide useful information on the tandem-arranged design of complex structures and energy harvesting devices.

• Wind and Structures
• /
• v.9 no.1
• /
• pp.75-93
• /
• 2006

This paper presents a quasi-steady model of vibrations of two cylinders in a side-by-side arrangement. The cylinders have flexible support and equal diameters. The model assumes that both cylinders participate in the process of vibration, each of them having two degrees of freedom. The movement of cylinders is described by a set of four non-linear differential equations. These equations are evaluated on the basis of a numerical simulation and experimental data. Moreover many features of cylinder vibrations are found from numerical results and are described in this paper.

• Proceedings of the KSME Conference
• /
• 2007.05b
• /
• pp.2845-2850
• /
• 2007

Flow-induced forces on two identical nearby circular cylinders immersed in the cross flow at Re =100 were numerically studied. We consider all possible arrangements of the two circular cylinders in terms of the distance between the two cylinders and the inclination angle with respect to the direction of the main flow. It turns out that significant changes in the characteristics of flow-induced forces are noticed depending on how the two circular cylinders are positioned, resulting in quantitative changes of force coefficients on both cylinders. Collecting all the numerical results obtained, we propose a contour diagram for drag coefficient and lift coefficient for each of the two cylinders. The perfect geometrical symmetry implied in the flow configuration allows one to use those diagrams to estimate flow-induced forces on two identical circular cylinders arbitrarily positioned in physical space with respect to the main flow direction.

• Proceedings of the KSME Conference
• /
• 2007.05b
• /
• pp.2890-2895
• /
• 2007

Heat transfer on two identical nearby circular cylinders immersed in the uniform cross flow at Re = 100 and Pr = 7.0 was numerically studied. We consider all possible arrangements of the two circular cylinders in terms of the distance between the two cylinders and the inclination angle with respect to the direction of the main flow. It turns out that significant changes in the characteristics of heat transfer are noticed depending on how the two circular cylinders are positioned, resulting in quantitative changes of heat transfer coefficients on both cylinders. Collecting all the numerical results obtained, we propose a contour diagram for averaged Nusselt number for each of the two cylinders. The perfect geometrical symmetry implied in the flow configuration allows one to use those diagrams to estimate heat transfer rates on two identical circular cylinders arbitrarily positioned in physical space with respect to the main flow direction.

• Journal of computational fluids engineering
• /
• v.13 no.2
• /
• pp.42-47
• /
• 2008

Heat transfer on two identical nearby circular cylinders immersed in the uniform cross flow at Re=120 and Pr=0.7 was numerically studied. We consider all possible types of arrangements of the two circular cylinders in terms of the distance between the two cylinders and the inclination angle with respect to the direction of the main flow. It turns out that significant changes in the characteristics of heat transfer are noticed depending on how the two circular cylinders are positioned, resulting in quantitative changes of heat transfer coefficients on both cylinders. Collecting all the numerical results obtained, we propose a contour diagram for averaged Nusselt number for each of the two cylinders. The perfect geometrical symmetry implied in the flow configuration allows one to use those diagrams to estimate heat transfer rates on two identical circular cylinders arbitrarily positioned in physical space with respect to the main flow direction.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.31 no.9
• /
• pp.754-763
• /
• 2007

Flow-induced forces on two identical nearby circular cylinders immersed in the cross flow at Re=100 were numerically studied. We consider all possible arrangements of the two circular cylinders in terms of the distance between the two cylinders and the inclination angle with respect to the direction of the main flow. It turns out that significant changes in the characteristics of flow-induced forces are noticed depending on how the two circular cylinders are positioned, resulting in quantitative changes of force coefficients on both cylinders. Collecting all the numerical results obtained, we propose a contour diagram for drag coefficient and lift coefficient for each of the two cylinders. The perfect geometrical symmetry implied in the flow configuration allows one to use those diagrams to estimate flow-induced forces on two identical circular cylinders arbitrarily positioned in physical space with respect to the main flow direction.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2001.05a
• /
• pp.139-143
• /
• 2001

Ring-stiffened cylinders are widely used as the pressure hull of submarines and underwater vehicles. For large ring-stiffened cylinders cylindrical shells are fbricated by cold rolling of flat plates and then welding of curved shells. After forming cylinders ring-stiffeners are welded on th the cylinders. Due to these cold roiling and welding initial shape imperfections and residual stresses exists in fabricated ring-stiffened cylinders. It is well known that the initial shape and material imperfections affect the ultimate strength of ring-stiffened cylinders significantly. In this paper previous researches on the effects of initial shape imperfections and residual stresses are briefly reviewed Recently a numerical analysis computer program was developed to predict the ultimate strength of ring-stiffened cylinders subjected to hydrostatic pressure, which is based on the Dynamic Relaxation technique. This program was employed to numerically investigate those effects. The numerical predictions were substantiated with relevant experimental results.

• Wind and Structures
• /
• v.23 no.2
• /
• pp.109-125
• /
• 2016

Flow interference is investigated between two tripped cylinders of identical diameter D at stagger angle ${\alpha}=0^{\circ}{\sim}180^{\circ}$ and gap spacing ratio $P^*$ (= P/D) = 0.1 ~ 5, where ${\alpha}$ is the angle between the freestream velocity and the line connecting the cylinder centers, and P is the gap width between the cylinders. Two tripwires, each of diameter 0.1D, were attached on each cylinder at azimuthal angle ${\beta}={\pm}30^{\circ}$, respectively. Time-mean drag coefficient ($C_D$) and fluctuating drag ($C_{Df}$) and lift ($C_{Lf}$) coefficients on the two tripped cylinders were measured and compared with those on plain cylinders. We also conducted surface pressure measurements to assimilate the fluid dynamics around the cylinders. $C_D$, $C_{Df}$ and $C_{Lf}$ all for the plain cylinders are strong function of ${\alpha}$ and $P^*$ due to strong mutual interference between the cylinders, connected to six interactions (Alam and Meyer 2011), namely boundary layer and cylinder, shear-layer/wake and cylinder, shear layer and shear layer, vortex and cylinder, vortex and shear layer, and vortex and vortex interactions. $C_D$, $C_{Df}$ and $C_{Lf}$ are very large for vortex and cylinder, vortex and shear layer, and vortex and vortex interactions, i.e., the interactions where vortex is involved. On the other hand, the interference as well as the strong interactions involving vortices is suppressed for the tripped cylinders, resulting in insignificant variations in $C_D$, $C_{Df}$ and $C_{Lf}$ with ${\alpha}$ and $P^*$. In most of the (${\alpha}$, $P^*$ ) region, the suppressions in $C_D$, $C_{Df}$ and $C_{Lf}$ are about 58%, 65% and 85%, respectively, with maximum suppressions 60%, 80% and 90%.

• Tribology and Lubricants
• /
• v.17 no.5
• /
• pp.391-398
• /
• 2001

Two dimensional slow viscous flow around two counter-rotating equal cylinders is investigated based on Stokes'approximation. An exact formal expression of the stream function is obtained by using the bipolar cylinder coordinates and Fourier series expansion. From the stream function obtained, the streamline patterns around the cylinders are shown and the pressure distribution in the flow field is determined. By integrating the stress distributions on the cylinder, the force and the moment exerted on the cylinder are calculated. The flow rate through the gap between the two cylinders is also determined as the distance between two cylinders varies. Special attention is directed to the case of very small distance between two cylinders concerned with the lubrication theory and the minimum pressure is calculated to explain a possible cavitation.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2000.06a
• /
• pp.142-149
• /
• 2000

Two dimensional slow viscous flow around two counter-rotating equal cylinders is Investigated based on Stokes' approximation. An exact formal expression of the stream function is obtained by using the bipolar cylinder coordinates and Fourier series expansion. From the stream function obtained, the streamline patterns around the cylinders are shown and the pressure distribution In the flow field is determined. By Integrating the stress distribution on the cylinder, the force and the moment exerted on the cylinder are calculated. The flow rate through the gap between the two cylinders is determined as the distance between two cylinders vary. It Is also revealed that the velocity at the far field has finite non-zero value. Special attention is directed to the case of very small distances between two cylinders by way of the lubrication theory.