Experimental Comparisons to Assure the Similarity Between VIM (Vortex-Induced Motion) and VIV (Vortex-Induced Vibration) Phenomena

Vortex-Induced Motion (VIM) is another way to denominate the Vortex-Induced Vibration (VIV) in floating units. The main characteristics of VIM in such structures are the low aspect ratio (L/D < 4.0) and the unity mass ratio (m* = 1.0, i.e. structural mass equal water displacement). The VIM can occur in MPSO (Monocolumn Production, Storage and Offloading System) and spar platforms. These platforms can experience motion amplitudes of around their characteristic diameters. In such cases, the fatigue life of mooring and riser systems can be greatly reduced. Typically, the VIM model testing campaigns are carried out in the Reynolds range between 200,000 and 400,000. VIV model tests with low aspect ratio cylinders (L/D = 1.0, 1.7 and 2.0) and unity mass ratio (m* = 1.0) have been carried out at the Circulating Water Channel facility available at NDF/EPUSP. The Reynolds number range covered in the experiments was between 10,000 and 50,000. The characteristic motions (in the transverse and in-line direction) were obtained using the Hilbert-Huang Transform method (HHT) and then compared with results obtained in experiments found in the literature. The aim of this investigation is to definitely establish the similarity between the VIM and VIV phenomena, making possible to increase the understanding of both and, at same time, allowing some analytical models developed for VIV to be applied to the VIM scenario on spar and monocolumn platforms, logically under some adaption.

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Experimental Comparison of Two Degrees-of-Freedom Vortex-Induced Vibration on High and Low Aspect Ratio Cylinders with Small Mass Ratio

Journal of Vibration and Acoustics ◽

10.1115/1.4006755 ◽

2012 ◽

Vol 134 (6) ◽

Cited By ~ 13

Author(s):

Rodolfo T. Gonçalves ◽

Guilherme F. Rosetti ◽

André L. C. Fujarra ◽

Guilherme R. Franzini ◽

César M. Freire ◽

...

Keyword(s):

Aspect Ratio ◽

Degrees Of Freedom ◽

Small Mass ◽

Experimental Comparison ◽

Small Scale ◽

Mass Ratio ◽

Vortex Induced Vibration ◽

Two Degrees Of Freedom ◽

Low Aspect Ratio ◽

Aspect Ratios

Vortex-induced motion (VIM) is a specific way for naming the vortex-induced vibration (VIV) acting on floating units. The VIM phenomenon can occur in monocolumn production, storage and offloading system (MPSO) and spar platforms, structures presenting aspect ratio lower than 4 and unity mass ratio, i.e., structural mass equal to the displaced fluid mass. These platforms can experience motion amplitudes of approximately their characteristic diameters, and therefore, the fatigue life of mooring lines and risers can be greatly affected. Two degrees-of-freedom VIV model tests based on cylinders with low aspect ratio and small mass ratio have been carried out at the recirculating water channel facility available at NDF-EPUSP in order to better understand this hydro-elastic phenomenon. The tests have considered three circular cylinders of mass ratio equal to one and different aspect ratios, respectively L/D = 1.0, 1.7, and 2.0, as well as a fourth cylinder of mass ratio equal to 2.62 and aspect ratio of 2.0. The Reynolds number covered the range from 10 000 to 50 000, corresponding to reduced velocities from 1 to approximately 12. The results of amplitude and frequency in the transverse and in-line directions were analyzed by means of the Hilbert-Huang transform method (HHT) and then compared to those obtained from works found in the literature. The comparisons have shown similar maxima amplitudes for all aspect ratios and small mass ratio, featuring a decrease as the aspect ratio decreases. Moreover, some changes in the Strouhal number have been indirectly observed as a consequence of the decrease in the aspect ratio. In conclusion, it is shown that comparing results of small-scale platforms with those from bare cylinders, all of them presenting low aspect ratio and small mass ratio, the laboratory experiments may well be used in practical investigation, including those concerning the VIM phenomenon acting on platforms.

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Experimental Study on Vortex-Induced Vibration of Floating Circular Cylinders With Low Aspect Ratio

Volume 2: CFD and VIV ◽

10.1115/omae2014-23383 ◽

2014 ◽

Cited By ~ 1

Author(s):

Rodolfo T. Gonçalves ◽

André L. C. Fujarra

Keyword(s):

Experimental Study ◽

Aspect Ratio ◽

Water Channel ◽

Circular Cylinders ◽

Structural Damping ◽

End Effects ◽

Vortex Induced Vibration ◽

Low Aspect Ratio ◽

Aspect Ratios ◽

Ratio Range

Experiments regarding vortex-induced vibration on floating circular cylinders with low aspect ratio were carried out in a recirculation water channel. The floating circular cylinders were elastic supported by a set of linear springs to provide low structural damping on the system. Eight different aspect ratios were tested, namely L/D = 0.2, 0.3, 0.4, 0.5, 0.75, 1.0, 1.5 and 2.0. These aspect ratios were selected to cover the aspect ratio range of the main offshore circular platforms, such as spar and monocolumn. The aims were understanding the VIM of such platforms; due to this, the cylinders were floating, or m* = 1. The range of Reynolds number covered 2,800 < Re < 55,400. The amplitude results showed a decrease in amplitude with decreasing aspect ratio in both directions. The frequency results confirm a different behavior for cylinders with L/D ≤ 0.5; in these cases, the cylinder free-end effects were predominant. The resonant behaviour was no longer observed for L/D ≤ 0.2. The decrease in Strouhal number with decreasing aspect ratio is also verified. All the results presented here complement the work presented previously for stationary circular cylinder with low aspect ratio presented by Gonçalves et al. (2013), Experimental Study on Flow around Circular Cylinders with Low Aspect Ratio, OMAE2013-10454.

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Experimental Study on Vortex-Induced Vibration of Floating Circular Cylinders With Low Aspect Ratio and Different Free-End Corner Shapes

Volume 2: CFD and FSI ◽

10.1115/omae2018-77218 ◽

2018 ◽

Author(s):

Rodolfo T. Gonçalves ◽

Keigo Sakata ◽

Dennis M. Gambarine ◽

Murilo M. Cicolin ◽

Shinichiro Hirabayashi ◽

...

Keyword(s):

Experimental Study ◽

Aspect Ratio ◽

Water Channel ◽

Circular Cylinders ◽

Structural Damping ◽

End Effects ◽

Vortex Induced Vibration ◽

Low Aspect Ratio ◽

End Conditions ◽

Elastically Supported

Experiments regarding vortex-induced vibration (VIV) on floating circular cylinders with low aspect ratio, L/D = 0.5, and different free-end conditions were carried out in a recirculation water channel. The floating circular cylinders were elastically supported by a set of linear springs to provide low structural damping on the system. Four different free-end corner shape conditions were tested, namely r/R = 0.0, 0.25, 0.5 and 1.0; where r/R is the relation between chamfer rounding radius, r, and the radius of cylinder, R. These different free-end conditions were selected to promote changes in the structures shedding around the free end of the cylinder. The aims were to understand the free-end effects on the VIV of floating circular cylinders with very low aspect ratio. The range of Reynolds number covered 2,800 < Re < 55,400. All the results presented here complement the work presented previously for a floating circular cylinder with L/D = 2.0 by Gambarine et al. (2016) [6] - Experimental study of the influence of the free end effects on vortex-induced vibration of floating cylinder with low aspect of ratio, OMAE2016-54623. The present results showed that the amplitudes in both directions were the highest for the semi-sphere case, r/R = 1.0. The amplitudes were almost the same for the other radius values, 0.0 < r/R ≤ 0.5; in which the maximum amplitudes decreased with increasing the corner radius. A critical value, L/Dcrit = 0.5, in which only the free-end structures affect the VIV behavior of the cylinder piercing the free-surface could be stated. The conclusion was that the cylinder free-end affects the VIV behavior for cylinders with very low-aspect ratio.

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Two-degree-of-freedom vortex-induced vibration of circular cylinders with very low aspect ratio and small mass ratio

Journal of Fluids and Structures ◽

10.1016/j.jfluidstructs.2013.02.004 ◽

2013 ◽

Vol 39 ◽

pp. 237-257 ◽

Cited By ~ 15

Author(s):

R.T. Gonçalves ◽

G.F. Rosetti ◽

G.R. Franzini ◽

J.R. Meneghini ◽

A.L.C. Fujarra

Keyword(s):

Aspect Ratio ◽

Small Mass ◽

Degree Of Freedom ◽

Circular Cylinders ◽

Mass Ratio ◽

Vortex Induced Vibration ◽

Low Aspect Ratio ◽

Two Degree Of Freedom

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Heat Transfer From Low Aspect Ratio Pin Fins

Volume 4: Turbo Expo 2007, Parts A and B ◽

10.1115/gt2007-27431 ◽

2007 ◽

Cited By ~ 12

Author(s):

Michael E. Lyall ◽

Alan A. Thrift ◽

Atul Kohli ◽

Karen A. Thole

Keyword(s):

Heat Transfer ◽

Aspect Ratio ◽

Gas Turbines ◽

Channel Height ◽

Internal Cooling ◽

Number Range ◽

Pin Fin ◽

Heat Transfer Augmentation ◽

Low Aspect Ratio ◽

Pin Fins

The performance of many engineering devices from power electronics to gas turbines is limited by thermal management. Heat transfer augmentation in internal flows is commonly achieved through the use of pin fins, which increase both surface area and turbulence. The present research is focused on internal cooling of turbine airfoils using a single row of circular pin fins that is oriented perpendicular to the flow. Low aspect ratio pin fins were studied whereby the channel height to pin diameter was unity. A number of spanwise spacings were investigated for a Reynolds number range between 5000 to 30,000. Both pressure drop and spatially-resolved heat transfer measurements were taken. The heat transfer measurements were made on the endwall of the pin fin array using infrared thermography and on the pin surface using discrete thermocouples. The results show that the heat transfer augmentation relative to open channel flow is the highest for smallest spanwise spacings and lowest Reynolds numbers. The results also indicate that the pin fin heat transfer is higher than the endwall heat transfer.

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Experimental Study of Very Low Aspect Ratio Wings in Slender Bodies

Volume 2: Applied Fluid Mechanics; Electromechanical Systems and Mechatronics; Advanced Energy Systems; Thermal Engineering; Human Factors and Cognitive Engineering ◽

10.1115/esda2012-82332 ◽

2012 ◽

Cited By ~ 1

Author(s):

M. A. Arevalo-Campillos ◽

S. Tuling ◽

L. Parras ◽

C. del Pino ◽

L. Dala

Keyword(s):

Experimental Study ◽

Aspect Ratio ◽

Numerical Simulations ◽

Water Channel ◽

Vortex Sheet ◽

The Body ◽

Low Aspect Ratio ◽

Moderate Reynolds Number ◽

Slender Bodies ◽

Low Aspect Ratio Wings

The dynamics of very low aspect ratio wings (or strakes) vortices in slender bodies are complex due to the interaction of the shed vortex sheet and the body vortex. For missiles at supersonic speeds these interactions are not easily predicted using engineering level tools. To shed some new light onto this problem, an experimental study in a water channel for moderate Reynolds number (Re = 1000) was performed for a 19D body and strake configuration with strakes having a span to body diameter ratio of 1.25. Comparisons to numerical simulations in supersonic flow are also performed. Flow visualisation has been carried out to characterize the vortex dynamics at different angles of attack; these being 11°, 16°, 22° and 27°. The comparison between a slender body without strakes and the body-strake configuration has given some key indicators in relation to the vortex position of the core. Furthermore, unsteady wing-body interference has been observed at angles of attack above 20° for both experimental and numerical simulations. Consequently, the average position of the vortex core is located at larger distances from the missile in comparison to the body without strakes. The numerical simulations show good correlation with the experimental tests even though the dynamic convective interactions between the body vortex and strake vortex sheet are not predicted.

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High Speed Microactuators for Low Aspect Ratio High Speed Micro Aircraft Surfaces

Actuators ◽

10.3390/act10100265 ◽

2021 ◽

Vol 10 (10) ◽

pp. 265

Author(s):

Ronald Barrett-Gonzalez ◽

Nathan Wolf

Keyword(s):

Aspect Ratio ◽

Flight Control ◽

High Speed ◽

High Performance ◽

Dynamic Range ◽

Feedback System ◽

Analytical Models ◽

Control Surface ◽

Operational Environment ◽

Low Aspect Ratio

This paper covers a class of actuators for modern high speed, high performance subscale aircraft. The paper starts with an explanation of the challenges faced by micro aircraft, including low power, extremely tight volume constraints, and high actuator bandwidth requirements. A survey of suitable actuators and actuator materials demonstrates that several classes of piezoceramic actuators are ideally matched to the operational environment. While conventional, linear actuation of piezoelectric actuators can achieve some results, dramatic improvements via reverse-biased spring mechanisms can boost performance and actuator envelopes by nearly an order of magnitude. Among the highest performance, low weight configurations are post-buckled precompressed (PBP) actuator arrangements. Analytical models display large deflections at bandwidths compatible with micro aircraft flight control speed requirements. Bench testing of an example PBP micro actuator powered low aspect ratio flight control surface displays +/−11° deflections through 40 Hz, with no occupation of volume within the aircraft fuselage and good correlation between theory and experiment. A wind tunnel model of an example high speed micro aircraft was fabricated along with low aspect ratio PBP flight control surfaces, demonstrating stable deflection characteristics with increasing speed and actuator bandwidths so high that all major aeromechanical modes could be easily controlled. A new way to control such a PBP stabilator with a Limit Dynamic Driver is found to greatly expand the dynamic range of the stabilator, boosting the dynamic response of the stabilator by more than a factor of four with position feedback system engaged.

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Influence of Stiffness Ratio on Vortex-Induced Vibration of Cylinder With Low Aspect Ratio

Volume 2: CFD and FSI ◽

10.1115/omae2018-77665 ◽

2018 ◽

Author(s):

Dennis M. Gambarine ◽

Luiz E. B. Minioli ◽

Rodolfo T. Gonçalves ◽

André M. Kogishi ◽

André L. C. Fujarra

Keyword(s):

Aspect Ratio ◽

Degrees Of Freedom ◽

Offshore Structures ◽

Elastic Base ◽

The Other ◽

Special Focus ◽

Stiffness Ratio ◽

Force Coefficient ◽

Vortex Induced Vibration ◽

Low Aspect Ratio

Concern over the Vortex-induced Motions (VIM) acting on offshore structures, with special focus on monocolumn and spar platforms, mooring systems have crucial importance on system movements; the system has thus been transformed into a concept study herein. A floating and rigid circular cylinder with low aspect ratio (L/D = 2) was used in the experiments carried out to investigate the influence of stiffness ratio (kx/ky) on Vortex-Induced Vibration (VIV). The cylinder was mounted in an elastic base composed of four springs with differences in in-line and transverse stiffness, defining: kx/ky ≅ 0.3, 0.5, 1.0, 2.0 and 3.0. The Reynolds number analysed belongs to a range between 0.2 · 104 and 2 · 104. Some good qualitative and quantitative agreements are found for in-line amplitudes, and higher kx/ky systems demonstrate significant oscillation for low relative velocities. This variation can be seen and justified when the XY-plane trajectories were plotted. When kx/ky is defined as 2 and 3, the traditional VIV 8-shape is illustrated for reduced velocities between 3 and 6. In contrast, the other stiffness systems do not show significant movements and, consequently, a negligible XY shape. Roll and pitch degrees of freedom have shown the motions coupled with the transverse and the in-line motions respectively. Moreover, the yaw motion did not present considerable angles. kx/ky = 2 has presented the highest lift force coefficients, without a great difference from the other aspects ratios, though. The drag force coefficient showed constant values for kx/ky = 2 and 3, the smallest results were observed for the system kx/ky = 3.

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