Passive Control of Viv With Drag Reduction

Owen, J. J. T.; Bearman, P. W.; Szewczyk, Albin A.

doi:10.1006/jfls.2000.0358

Cited by 205 publications

(82 citation statements)

References 6 publications

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“…Control of flow structure around a sphere for various active and passive methods was studied by Suryanarayana and Prabhu (2000), Suryanarayana and Meier (1995), Suryanarayana et al (1993), Ozgoren et al(2011bOzgoren et al( , 2011c, Kim and Durbin (1988), Kiya (1988), Owen and Bearman (1988), Mehta (1985) and further investigations cited therein [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36].…”

Section: Introductionmentioning

confidence: 99%

Comparison of Flow Characteristics of Different Sphere Geometries Under the Free Surface Effect

Özgören

Doğan

Okbaz

et al. 2013

EPJ Web of Conferences

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Abstract.Comparison of the experimental results of turbulent flow structures between a smooth sphere and a sphere with a vent hole, roughened, and o-ring is presented in the presence of a free-surface. Dye visualization and particle image velocimetry (PIV) techniques were performed to examine effects of passive control methods on the sphere wake for Reynolds number Re = 5000 based on the sphere diameter with a 42.5mm in an open water channel. Instantaneous and time-averaged flow patterns in the wake region of the sphere were examined from point of flow physics for the different sphere locations in the range of 0≤h/D ≤2.0 where h was the space between the top point of the sphere and the free surface. The ratio of ventilation hole to sphere diameter was 0.15, o-ring was located at 55 o with a 2 mm from front stagnation point of the sphere and roughened surface was formed by means of totally 410 circular holes with a 3 mm diameter and around 2 mm depth in an equilateral triangle arrangement. The flow characteristics of instantaneous velocity vectors, vorticity contours, time-averaged streamline patterns, Reynolds stress correlations and streamwise and cross-stream velocity fluctuations for both the smooth and passively controlled sphere were interpreted.

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Section: Introductionmentioning

confidence: 99%

Comparison of Flow Characteristics of Different Sphere Geometries Under the Free Surface Effect

Özgören

Doğan

Okbaz

et al. 2013

EPJ Web of Conferences

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“…Several passive/active flow control strategies have been developed and verified to justify their vibration control performances versus potential installation, operational and maintenance costs. In particular, passive flow control devices such as strakes and fairings have been widely used by the oil and gas industrialists for riser VIV control [9,29,31,40]. However, it is well known that the introduction of such devices along the long slender structure modifies the structural configuration and increases the drag forces, apart from their high costs in manufacturing, installation, and maintenance.…”

Section: Introductionmentioning

confidence: 99%

Two-dimensional vortex-induced vibration suppression through the cylinder transverse linear/nonlinear velocity feedback

Srinil

2017

Acta Mech

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Suppressing vortex-induced vibration (VIV) has recently attracted numerous researchers due to its practical significance in many engineering applications. Most of the previous studies have focused on a passive or active flow control. A structurally active control approach to mitigate a two-dimensional, nonlinear coupled, cross-flow/in-line VIV has not been well studied. This paper presents a reduced-order fluid-structure dynamic model and combined analytical-numerical solutions for the efficient suppression of two-dimensional VIV of a flexibly mounted circular cylinder in uniform flows. The theoretical model is based on the use of coupled Duffing-Rayleigh oscillators with three variables describing the cylinder cross-flow/in-line displacements and the strength of the fluid vortex circulation in the cylinder wake. These equations of fluid-structure motions contain geometric and hydrodynamic nonlinearities. Closed-loop linear and nonlinear velocity feedback controllers are implemented in the transverse direction governing the larger cross-flow response than the associated in-line counterpart. Approximated analytical expressions are derived by using the harmonic balance to explicitly capture the system nonlinear dynamic features and the effects of key dimensionless parameters. Parametric investigations are carried out to evaluate the linear versus nonlinear controller performance in terms of the maximum response suppression capability and the power requirement in a wide range of reduced flow velocities, mass ratios, and control gains. Over the main lock-in resonance region with coupled cross-flow/inline responses, the linear controller is found to be more efficient in suppressing the two-dimensional VIV by also modifying the system frequencies and phase relationships. Nevertheless, based on the power comparison, the nonlinear control is superior to the linear control for very small targeted controlled amplitudes of a very low-mass cylinder. These active control strategies may be further applied to the multimode VIV suppression of a long flexible cylinder with multi degrees of freedom.

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“…For example, a small secondary cylinder has been placed on the side of a cylinder to suppress vortex shedding at low Reynolds numbers (Strykowski & Sreenivasan 1990). Spanwise waviness has been adopted in rectangular cylinder (Bearman & Owen 1998), circular cylinder (Owen, Bearman & Szewczyk 2001) and square cylinder (Darekar & Sherwin 2001) wakes to successfully suppress vortex shedding in the wake. The mechanism of suppression was in each case attributed to three-dimensional distortion of the two-dimensional shear layers that otherwise roll up to form vortex streets.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear optimal suppression of vortex shedding from a circular cylinder

2015

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This study is focused on two-and three-dimensional incompressible flow past a circular cylinder for Re ≤ 1000. To gain insight into the mechanisms underlying the suppression of unsteadiness for this flow we determine the nonlinear optimal open-loop control driven by surface-normal wall transpiration. The spanwise-constant wall transpiration is allowed to oscillate in time although steady forcing is determined to be most effective. At low levels of control cost, defined as the square integration of the control, the sensitivity of unsteadiness with respect to wall transpiration is a good approximation of the optimal control. The distribution of this sensitivity suggests that the optimal control at small magnitude is achieved by applying suction upstream of the upper and lower separation points and blowing at the trailing edge. At high levels of wall transpiration the assumptions underlying the linearised sensitivity calculation become invalid since the base flow is eventually altered by the size of the control forcing. The large magnitude optimal control is observed to spread downstream of the separation point, draw the shear layer separation towards the rear of the cylinder through suction while blowing along the centreline eliminates the recirculation bubble in the wake. We further demonstrate that it is possible to completely suppress vortex shedding in two-and three-dimensional flow past a circular cylinder up to Re = 1000, accompanied by 70% drag reduction when a nonlinear optimal control of moderate magnitude (with root mean square value 8% of the free stream velocity) is applied. This is confirmed through linearised stability analysis about the steady state solution when the nonlinear optimal wall transpiration is applied. While continuously distributed wall transpiration is not physically realisable, the study highlights localised regions where discrete control strategies could be further developed. It also highlights the appropriate range of application for linear and nonlinear optimal control to this type of flow problem.

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Passive Control of Viv With Drag Reduction

Cited by 205 publications

References 6 publications

Comparison of Flow Characteristics of Different Sphere Geometries Under the Free Surface Effect

Comparison of Flow Characteristics of Different Sphere Geometries Under the Free Surface Effect

Two-dimensional vortex-induced vibration suppression through the cylinder transverse linear/nonlinear velocity feedback

Nonlinear optimal suppression of vortex shedding from a circular cylinder

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