Imaging through a homogeneous circular cylinder: the role of virtual caustics, rainbow glare points, and image fragmentation

2020 ◽  
Vol 59 (21) ◽  
pp. F53
Author(s):  
James A. Lock
Keyword(s):  
Circular Cylinder ◽  
Image Fragmentation

The role of separation on the forces acting on a circular cylinder with a control rod

2021 ◽  
Vol 915 ◽  
Author(s):  
M.M. Cicolin ◽  
O.R.H. Buxton ◽  
G.R.S. Assi ◽  
P.W. Bearman
Keyword(s):  
Circular Cylinder ◽  
Control Rod

Abstract

Flow-induced vibration control of a circular cylinder using rotational oscillation feedback

2018 ◽  
Vol 847 ◽  
pp. 93-118 ◽  
Author(s):  
D. Vicente-Ludlam ◽  
A. Barrero-Gil ◽  
A. Velazquez
Keyword(s):  
Circular Cylinder ◽  
Transverse Velocity ◽  
Water Channel ◽  
Transverse Displacement ◽  
Flow Induced Vibration ◽  
Rotational Oscillation ◽  
Image Velocimetry ◽  
Steady State Oscillation ◽  
Type Response

The effect of imposed rotation on a slender elastically mounted circular cylinder free to oscillate transversely to the incident flow has been studied experimentally in a free-surface water channel. Rotation rate and direction are imposed to be proportional to either the cylinder’s transverse displacement or the cylinder’s transverse velocity to determine the effectiveness of these rotation laws to control the dynamics of the cylinder, either to reduce or to enhance oscillations. The former can be of interest for energy harvesting purposes whereas the latter can be useful to avoid unwanted oscillations. In all cases, non-dimensional mass and damping are fixed ($m^{\ast }=11.7$, $\unicode[STIX]{x1D701}=0.0043$) so the analysis is focused on the role of the rotation law and the reduced velocity. The Reynolds number based on the diameter of the cylinder ranges from 1500 to 10 000. Results are presented in terms of steady-state oscillation characterization (say, amplitude and frequency) and wake-pattern topology, which was obtained through digital particle image velocimetry. Both laws are able to either reduce or enhance oscillations, but they do it in a different way. A rotation law proportional to the cylinder’s displacement is more effective to enhance oscillations. For high enough actuation, a galloping-type response has been found, with a persistent growth of the amplitude of oscillations with the reduced velocity that shows a new desynchronized mode of vortex shedding. On the other hand, a rotation law proportional to the cylinder’s transverse velocity is more efficient to reduce oscillations. In this case only vortex-induced-type responses have been found. A quasi-steady theoretical model has been developed, which helps to explain why a galloping-type response may appear when rotation is proportional to cylinder displacement and is able to predict reasonably the amplitude of oscillations in those cases. The model also explains why a galloping-type response is not expected to occur when rotation is proportional to the cylinder’s velocity.

Effect of confinement on three-dimensional stability in the wake of a circular cylinder

2009 ◽  
Vol 642 ◽  
pp. 477-487 ◽  
Author(s):  
SIMONE CAMARRI ◽  
FLAVIO GIANNETTI
Keyword(s):  
Stability Analysis ◽  
Circular Cylinder ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Dimensional Stability ◽  
Opposite Sign ◽  
Three Dimensional ◽  
The Body ◽  
Karman Street

This paper investigates the three-dimensional stability of the wake behind a symmetrically confined circular cylinder by a linear stability analysis. Emphasis has been placed on discussing analogies and differences with the unconfined case to highlight the role of the inversion of the von Kármán street in the nature of the three-dimensional transition. Indeed, in this flow, the vortices of opposite sign that are alternately shed from the body into the wake cross the symmetry line further downstream and they assume a final configuration which is inverted with respect to the unconfined case. It is shown that the transition to a three-dimensional state has the same space–time symmetries of the unconfined case, although the shape of the linearly unstable modes is affected by the inversion of the wake vortices. A possible interpretation of this result is given here.

Simulations of three-dimensional viscoelastic flows past a circular cylinder at moderate Reynolds numbers

2010 ◽  
Vol 651 ◽  
pp. 415-442 ◽  
Author(s):  
DAVID RICHTER ◽  
GIANLUCA IACCARINO ◽  
ERIC S. G. SHAQFEH
Keyword(s):  
Circular Cylinder ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Viscoelastic Flow ◽  
Dimensional Structure ◽  
Recirculation Region ◽  
Viscoelastic Flows ◽  
Cylinder Wake ◽  
Complex Flows

The results from a numerical investigation of inertial viscoelastic flow past a circular cylinder are presented which illustrate the significant effect that dilute concentrations of polymer additives have on complex flows. In particular, effects of polymer extensibility are studied as well as the role of viscoelasticity during three-dimensional cylinder wake transition. Simulations at two distinct Reynolds numbers (Re = 100 and Re = 300) revealed dramatic differences based on the choice of the polymer extensibility (L2 in the FENE-P model), as well as a stabilizing tendency of viscoelasticity. For the Re = 100 case, attention was focused on the effects of increasing polymer extensibility, which included a lengthening of the recirculation region immediately behind the cylinder and a sharp increase in average drag when compared to both the low extensibility and Newtonian cases. For Re = 300, a suppression of the three-dimensional Newtonian mode B instability was observed. This effect is more pronounced for higher polymer extensibilities where all three-dimensional structure is eliminated, and mechanisms for this stabilization are described in the context of roll-up instability inhibition in a viscoelastic shear layer.

Adhesive contact of a rigid circular cylinder to a soft elastic substrate – the role of surface tension

Soft Matter ◽  
2015 ◽  
Vol 11 (19) ◽  
pp. 3844-3851 ◽  
Author(s):  
Tianshu Liu ◽  
Anand Jagota ◽  
Chung-Yuen Hui
Keyword(s):  
Surface Tension ◽  
Circular Cylinder ◽  
Contact Mechanics ◽  
Half Space ◽  
Elastic Material ◽  
Adhesive Contact ◽  
Elastic Substrate ◽  
Rigid Cylinder

This article studies the effects of surface tension on the adhesive contact mechanics of a long rigid cylinder on an infinite half space comprising an incompressible elastic material.

The electrophoretic mobilities of a circular cylinder in close proximity to a dielectric wall

2016 ◽  
Vol 804 ◽  
Author(s):  
Ehud Yariv
Keyword(s):  
Circular Cylinder ◽  
Electric Field ◽  
Finite Limit ◽  
Shear Stresses ◽  
Cylinder Wall ◽  
Dielectric Wall ◽  
Electrophoretic Mobilities ◽  
Close Proximity ◽  
Uniform Current

In their bipolar-coordinate analysis of circular-cylinder electrophoresis near a dielectric wall, Keh et al. (J. Fluid Mech., vol. 231, 1991, pp. 211–228) found that, when an electric field is applied parallel to the wall, the translational and rotational electrophoretic mobilities increase monotonically as the ratio $\unicode[STIX]{x1D6FF}$ of the cylinder–wall separation to the cylinder radius decreases, eventually diverging as $\unicode[STIX]{x1D6FF}^{-1/2}$ when $\unicode[STIX]{x1D6FF}\rightarrow 0$. Considering the singular limit $\unicode[STIX]{x1D6FF}\ll 1$ from the outset, we conduct here an asymptotic analysis of that electrokinetic problem, providing insight to the manner by which the intense electric field in the narrow gap is transformed into $O(\unicode[STIX]{x1D6FF}^{-3/2})$ shear stresses; these stresses, in turn, overcome the large Stokes resistance so as to provide the large electrophoretic mobilities. In a companion problem, where the cylinder is exposed to a uniform current emanating from a nearby reactive electrode, the intense gap-scale electric field results in an $O(\unicode[STIX]{x1D6FF}^{-2})$ pressure, giving rise in turn to a large repulsive force. In that problem we find that the cylinder velocity perpendicular to the wall approaches a finite limit as $\unicode[STIX]{x1D6FF}\rightarrow 0$. We also discuss the role of ‘dielectrophoretic’ forces which are inevitable in the above semi-bounded configurations.

The role of information sources in image fragmentation

2016 ◽  
Vol 57 ◽  
pp. 242-245 ◽  
Author(s):  
Raquel Camprubí ◽  
Lluís Coromina
Keyword(s):  
Information Sources ◽  
Image Fragmentation ◽  
Role Of Information
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