• 드라이브 ㆍ 컨트롤
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• 제9권3호
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• pp.29-36
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• 2012

The hydraulic cylinder is used for actuating the roller-link type rotating floodgate which controls the volume of water in the reservoir. The locating points of hydraulic cylinder are restricted to the limited space and determined to minimize the cylinder force necessary for actuating the floodgate. Generally, the head end point of cylinder is fixed at underground and the rod end point of cylinder is connected to the support link. Therefore there exist three design variables to be determined to minimize the cylinder force within the rotating range of floodgate. First, the mathematical model of the roller-link type rotating floodgate is derived to find the cylinder force corresponding to the floodgate angle. Then, the optimal locating point of hydraulic cylinder is searched using the complex method that is one kind of constrained direct search method.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.629-634
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• 2004

Cavities are inevitable structures in automobile configuration. The flow-induced noise is generated from the wheel housing section by the interaction between a rotating wheel and the unsteady flows in the cavity. In this research the wheel housing was assumed by a rectangular cavity for simplification. We measured the radiated sound from the 2-D cavity without cylinder and from the rotating cylinder in the cavity by using the sound source localization method with an acoustic mirror system. In the 2-D cavity case of low Mach number(Ma=0.029), the sound sources were found to be located near the leading edge of cavity due to the shear layer instabilities. Comparing the cases of the rotating and the non-rotating cylinder, it is observed that the sound Pressure levels around the rotating cylinder in the cavity increased and the main acoustic sources were located at the rear section of the rotating wheel.

• 한국생산제조학회지
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• 제6권3호
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• pp.9-16
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• 1997

A numerical method based on the spectral collocation method is developed for the steady rotating flows in eccentric annulus. Steady flows between rotating cylinders are of interest on lubrication in large rotating machinery. Steady rotating flow is generated by the rotating inner cylinder with constant angular velocity. The governing equations for laminar flow are simplified from Navier-Stokes equations by neglecting the non-linear convection terms. Integrating the pressure round the rotating cylinder based on the half Sommerfeld method, the load on the cylinder is evaluated with eccentricity. The attitude angle and Sommerfeld variable are calculated from the load. It is found that those values are influenced by the eccentricity. The attitude and Sommerfeld reciprocal are decreased with eccentricity. As expected, the effect of the annular gap ratio on them is negligible.

• 대한기계학회논문집A
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• 제24권1호
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• pp.16-28
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• 2000

The steady rotating flows in eccentric annulus has been studied by a numerical method based on the spectral collocation method. The inner cylinder has a constant angular velocity while the outer on e is stationary. Flow between eccentric cylinders is of considerable technical importance as it occurs in journal bearings. In the present work, the governing equations for laminar flow are expressed as Navier-Stokes equations, including the non-linear convection terms. The solutions were utilized i, estimate the effects of the nonlinear terms on the load acting on the rotating cylinder. Based on the half and the full Sommerfeld methods, the load on the rotating cylinder is evaluated with eccentricity, by integrating the pressure and skin friction around the cylinder. The attitude angle and Sommerfeld reciprocal are calculated from the load. Also, the torque on the rotating inner cylinder was calculated. considering the skin friction. The attitude angle and Sommerfeld reciprocal are decreased with eccentricity. Viscous damping coefficient due to the skin friction becomes larger with decreasing the annular space. It is found the non-linear effects of the convection terms on the flow and the load are important. especially on the attitude angle, for relatively wide annular configurations however, the effects on those are minor for very narrow annular ones.

• Korea-Australia Rheology Journal
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• 제21권1호
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• pp.27-37
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• 2009

In this work, we numerically investigate the effect of viscoelasticity on 2D laminar vortex dynamics in flows past a single rotating cylinder for rotational rates $0{\leq}{\alpha}{\leq}5$ (the rotational rate ex is defined by the ratio of the circumferential rotating velocity to free stream velocity) at Re=100, in which the vortex shedding has been predicted to occur in literature for Newtonian fluids. The objective of the present research is to develop a promising technique to fully suppress the vortex shedding past a bluff body by rotating a cylinder and controlling fluid elasticity. The predicted vortex dynamics with the present method is consistent with the previous works for Newtonian flows past a rotating cylinder. We also verified our method by comparing our data with the literature in the case of viscoelastic flow past a non-rotating cylinder. For $0{\leq}{\alpha}{\leq}1.8$, the frequency of vortex shedding slightly decreases but the fluctuation of drag and lift coefficient significantly decreases with increasing fluid elasticity. We observe that the vortex shedding of viscoelastic flow disappears at lower ${\alpha}$ than the Newtonian case. At ${\alpha}$=5, the relationship between the frequency of vortex shedding and Weissenberg number (Wi) is predicted to be non-monotonic and have a minimum around Wi=0.25. The vortex shedding finally disappears over critical Wi number. The present results suggest that the vortex shedding in the flow around a rotating cylinder can be more effectively suppressed for viscoelastic fluids than Newtonian fluids.

• 소음진동
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• 제7권4호
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• pp.613-620
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• 1997

Steady and unsteady flows between rotating cylinders are of interest on lubrication, convective heat transfer and flow-induced vibration in large rotating machinery. Steady rotating flow is generated by rotating cylinder with constant velocity while the unsteady rotating flow by oscillating cylinder with homogeneoysly oscillating velocity. An analytical method is developed based on the simple radial coordinate transformation for the steady and unsteady rotating flows in concentric annulus. The governing equations are simplified from Navier-Stokes equatins. Considering the skin friction based on the radial variation of circumferential flow velocity, the torques acting on the fixed and the rotating cylinder are evaluated in terms of added-inertia and added-damping torque coefficients. The coefficients are found to be influenced by the oscillatory Reynolds number and the radius ratio of two cylinders; however, the effect of the oscillatory Reynolds number on the coefficients is minor in case of relatively low radius ratio.

• Coupled systems mechanics
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• 제2권2호
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• pp.191-214
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• 2013

The unsteady flow past a circular cylinder which starts rotating or rotary oscillating impulsively from rest in a viscous fluid is investigated for Reynolds numbers Re=200 and 1000, rectilinear speed ratios ${\alpha}$ between 0.5 and 5.0, and forced oscillating frequencies $f_s$ between 0.1 and 2.0. Numerical solutions of the Navier-Stokes equations are obtained by using a finite volume method on an unstructured colocated grid. The objective of the study is to examine the effect of the rotating and rotary oscillating circular cylinder on the flow patterns and dynamics loads. The numerical results reveal that the $K\acute{a}rm\acute{a}n$ vortex street vanishes entirely behind the rotating cylinder when the ratio ${\alpha}$ exceeds the critical value, and the vortex shedding behind the rotary oscillating cylinder undergoes mainly three modes named 'synchronization', 'competition' and 'natural shedding' with the increase of $f_s$. Based on the amplitude spectra analysis of the lift coefficients, the regions of the classification of flow structure modes are presented, which provide important references for the flow control in the ocean engineering.

• 소음진동
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• 제11권3호
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• pp.428-436
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• 2001

The rotating inner cylinder executes a periodic translational motion in concentric annulus while the outer one is stationary. In the study of flow-induced vibrations and relaxed instabilities, it is of interest to evaluate the fluid-dynamic forces acting on the rotating inner cylinder. In the present work, the governing equations for the confined flow are expressed as Navier-Stokes equations, including the steady and unsteady terms. The fluid parameters for steady flow generated by the rotating cylinder are determined analytically while the unsteady ones by the oscillatory motion are evaluates by a numerical method based on the spectral collocation method. In order to validate the numerical approach, the numerical results are compared wish the analytical ones given by existing theories, for simple cases where the both approaches are applicable. Good agreement was found between the results. It is found the effects of the Reynolds number, defined by rotating velocity, on the fluid-dynamic forces are important for the case of relatively low oscillatory Reynolds number, defined by oscillatory frequency : j.e., in case of $Re_\omega\gg Re_S$.

• 대한조선학회지
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• 제16권3호
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• pp.9-19
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• 1979

A method of improving rudder effectiveness by applying a rotating cylinder to a rudder(so called "rotating-cylinder rudder") has been experimentally studied. Also, the improvements in ship's maneuvering characteristics with its application has been analytically evaluated. It has been shown that this improvement is significant.

• 한국세라믹학회지
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• 제41권4호
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• pp.344-347
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• 2004

The influence of spindle immersion depth on the determination of glass melt viscosity was examined in rotating cylinder method. The exact adjustment of spindle immersion depth into soda lime silicate standard glass melts could be peformed by self-constructed electric system. The results showed a slight dependence of viscosity value on the immersion depth change of spindle shaft. The viscosity error per unit length of spindle was 0.4%/mm under the present cylinder dimension.