Experimental Study on Flow-Induced Vibration of Floating Squared Section Cylinders With Low Aspect Ratio: Part I — Effects of Incidence Angle

2015 ◽  
Author(s):  
Rodolfo T. Gonçalves ◽  
Dênnis M. Gambarine ◽  
Felipe P. Figueiredo ◽  
Fábio V. Amorim ◽  
André L. C. Fujarra
Keyword(s):  
Aspect Ratio ◽  
Incidence Angle ◽  
Ocean Basin ◽  
Circular Cylinders ◽  
Structural Damping ◽  
Flow Induced Vibration ◽  
Double Frequency ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Elastically Supported

Experiments regarding flow-induced vibration on floating squared section cylinders with low aspect ratio were carried out in an ocean basin with rotating-arm apparatus. The floating squared section cylinders were elastically supported by a set of linear springs to provide low structural damping to the system. Three different aspect ratios were tested, namely L/D = 1.0, 2.0 and 3.0, and two different incidence angles, namely 0 and 45 degrees. The aims were to understanding the flow-induced vibration around single columns of multi-column platforms, such as semi-submersible and TLP. VIV on circular cylinders were also carried out to compare the results. The range of Reynolds number covered was 2,000 < Re < 27,000. The in-line and transverse amplitude results showed to be higher for 45-degree incidence compared with 0-degree, but the maximum amplitudes for squared section cylinders were lower compared with the circular ones. The double frequency in the in-line motion was not verified as in circular cylinders. The yaw amplitudes cannot be neglected for squared section cylinders, maximum yaw amplitudes around 10 degrees were observed for reduced velocities up to 15.

Experimental Study on Flow-Induced Vibration of Floating Squared Section Cylinders With Low Aspect Ratio: Part II — Effects of Rounded Edges

2016 ◽  
Author(s):  
Rodolfo T. Gonçalves ◽  
Dennis M. Gambarine ◽  
Aline M. Momenti ◽  
Felipe P. Figueiredo ◽  
André L. C. Fujarra
Keyword(s):  
Aspect Ratio ◽  
Reynolds Numbers ◽  
Ocean Basin ◽  
Separation Point ◽  
Flow Induced Vibration ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Significant Difference ◽  
Flow Induced Vibrations ◽  
Elastically Supported

Experiments regarding flow-induced vibration on floating rounded squared section cylinders with low aspect ratio were carried out in an ocean basin equipped with a rotating-arm apparatus. Floating squared section cylinders with rounded edges and aspect ratios of L/D = 2.0 were elastically supported by a set of linear springs in order to provide low structural damping to the system. Two different incidence angles were tested, namely 0 and 45 degrees. The Reynolds numbers covered the range from 2,000 to 30,000. The aim was to understand the flow-induced vibrations around single columns, gathering information for further understanding the causes for the Vortex-Induced Motions in semi-submersible and TLP platforms. Experiments on circular and squared sections cylinders (without rounded edges) were also carried out to compare the results with the rounded square section cylinders (with rounded edges). The amplitude results for in-line, transverse and yaw amplitude for 0-degree models showed to be higher for squared section cylinders compared to those for the rounded square section cylinders. No significant difference between the 45-degree models was observed. The results of ratio between frequency of motion in the transverse direction and natural frequency in still water confirmed the vortex-induced vibration behavior for the squared and rounded square section cylinders for 45-degree incidence; and also the galloping characteristics for 0-degree incidence cases. The rounded effect on the square section cylinders showed to be important only for reduced velocity larger than 8, which is probably related to the position of the separation point that changes around the rounded edge, behavior that did not occurr for the squared edge that fixed the separation point for any reduced velocity.

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

2014 ◽  
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.

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

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.

Experimental Study on Flow Around Circular Cylinders With Low Aspect Ratio

2013 ◽  
Author(s):  
Rodolfo T. Gonçalves ◽  
Guilherme F. Rosetti ◽  
Guilherme R. Franzini ◽  
André L. C. Fujarra
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Strouhal Number ◽  
Water Channel ◽  
Circular Cylinders ◽  
Piv Measurements ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Fluctuation Frequency ◽  
Six Degree Of Freedom

Experiments were carried out in a recirculating water channel regarding the flow around stationary circular cylinders with low aspect ratio piercing the water free surface. Eight different aspect ratios were tested, namely L/D = 0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 1.5 and 2.0; this range corresponds to aspect ratio related to circular offshore systems, such as spar and monocolumn platforms. Force was measured using a six degree-of-freedom load cell and Strouhal number is inferred through the transverse force fluctuation frequency. The range of Reynolds number covers 10,000 < Re < 50,000. PIV measurements were performed in some aspect ratio cases, namely 0.3, 0.5, 1.0 and 2.0 for Reynolds number equal to 43,000. The results showed a decrease in drag force coefficients with decreasing aspect ratio, as well as a decrease in Strouhal number with decreasing aspect ratio. The PIV showed the existence of an arch-type vortex originated in the cylinder free end.

Fabrication of Hybrid Micro-Nanofluidic Devices With Centimeter Long Ultra-Low Aspect Ratio Nanochannels

2013 ◽  
Author(s):  
Marie Pinti ◽  
Shaurya Prakash
Keyword(s):  
Aspect Ratio ◽  
Volumetric Flow Rate ◽  
Critical Dimension ◽  
Water Desalination ◽  
Adhesion Layer ◽  
Critical Dimensions ◽  
Lab On Chip ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Nanofluidic Devices

Hybrid microfluidic and nanofluidic devices have a variety of applications including water desalination, molecular gates and DNA sieving among several other lab-on-chip uses. Most microfluidic and nanofluidic devices currently are fabricated in glass, silicon, polydimethylsiloxane (PDMS), or with a combination of these materials. In order to impart functionality, metals, polymers or auxiliary components are often integrated with these devices. Ultra-low aspect ratio channels have several advantages including critical dimensions on the nanoscale but increased throughput compared to higher aspect ratio channels with the same critical dimension, which is important for applications where a higher volumetric flow rate is desired. Additionally, theoretical analysis is significantly easier as ultra-low aspect ratio channels can be modeled as 1-D systems. The fabrication methods for achieving low aspect ratios (< 0.005) usually require extensive facilities with several innovative fabrication and bonding schemes being previously reported. In this paper, we report on fabrication and bonding of ultra-low aspect ratio microfluidic and nanofluidic devices with aspect ratios at 0.0005 in glass/PDMS devices in contrast to the previous best reported result of 0.005 achieved in a silica device using stamp and stick PDMS bonding. The simplicity of our approach presents a new pathway to achieving the lowest aspect ratio nanochannels ever reported for channels fabricated using an interfacial layer for bonding. Centimeter long nanochannels on a borosilicate substrate were fabricated by standard UV photolithography followed by wet etching. Surface roughness of the fabricated channels is on the same order as the roughness of the initial substrate (2–3 nm) and therefore can enable fabrication of channels with critical dimensions approaching 15 nm or less. Devices were then bonded using a second borosilicate substrate with a thin PDMS adhesion layer (∼ 2 μm). The PDMS adhesion layer allows rapid, facile, and alignment-free bonding compared to traditional fusion or anodic bonds. Successful verification of device operation and functionality was determined by verifying flow in operational devices and with scanning electron microscopy to confirm bonding for the formation of nanochannels.

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

2012 ◽  
Vol 134 (6) ◽  
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.

Performance Prediction for High Turning Low Aspect Ratio Stator Cascades in the Transonic Regime

1970 ◽  
Vol 92 (4) ◽  
pp. 390-398
Author(s):  
H. F. L. Griepentrog
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Flow Field ◽  
Performance Prediction ◽  
Transonic Flow ◽  
Secondary Flows ◽  
Compressor Stage ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Boundary Layer Interaction

This paper describes a method for the prediction of the transonic flow field in a high solidity, high turning cascade, suitable for use as stator of a shock-in-rotor supersonic compressor stage. Effects of shock boundary layer interaction is taken into account by empirical correlation, valid for blade aspect ratios below unity. Use of partial slots for reduction of the secondary flows is briefly discussed and a correlation on slot efficiency is presented.

Coriolis effect on the vibration of flat rotating low aspect ratio cantilever plates

1981 ◽  
Vol 16 (2) ◽  
pp. 97-106 ◽  
Author(s):  
S Sreenivasamurthy ◽  
V Ramamurti
Keyword(s):  
Aspect Ratio ◽  
Degrees Of Freedom ◽  
Mode Frequency ◽  
Coriolis Effect ◽  
Skew Angle ◽  
Noticeable Effect ◽  
Torsional Mode ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Skew Angles

The Coriolis effect on the first bending and first torsional frequencies of flat rotating low aspect ratio cantilever plates has been investigated using finite element method. The cantilever plate has been modelled using plane triangular shell elements with three nodes and eighteen degrees of freedom. Three typical skew angles (0, 45, and 90 degrees) and two aspect ratios (1 and 2) are considered in the analysis. In addition to the Coriolis effect other effects, namely the geometric stiffness and the supplementary stiffness, have been considered. The mass and stiffness matrices have been derived using area coordinates. It has been found that the effect of including Coriolis effect is to lower the first two frequencies. This effect is negligible when the skew angle is 90 degrees. In the other two cases, skew of 0 and 45 degrees, there is a noticeable effect on the first torsional mode frequency when the aspect ratio is unity and on the first bending mode frequency when the aspect ratio is 2. An increase in the Coriolis effect is observed when the aspect ratio is increased from 1 to 2, with the skew angles of 0 and 45 degrees and a decrease when the skew angle is 90 degrees. The difference between the two frequencies (with and without Coriolis effect) becomes more and more noticeable as the rotational speed increases.

scholarly journals Vibrations of Slender Structures Caused by Vortices

2021 ◽  
Vol 1203 (2) ◽  
pp. 022025
Author(s):  
Irena Gołębiowska ◽  
Maciej Dutkiewicz ◽  
Tomasz Lamparski ◽  
Poorya Hajyalikhani
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Transmission Lines ◽  
Flow Direction ◽  
Vortex Wake ◽  
Small Aspect Ratio ◽  
Flow Induced Vibration ◽  
Cylindrical Structures ◽  
Overhead Transmission Lines ◽  
Elastically Supported

Abstract Slender cylindrical structures such as overhead transmission lines, skyscrapers, chimneys, risers, and pipelines can experience flow induced vibration (FIV). The vortex vibrations are a type of FIV; they arise because of oscillating forces caused by flow separation and the detachment of vortices. The paper presents a brief overview of experimental research on vortex induced vibration - VIV of short, rigid cylinders elastically supported (with a small aspect ratio). This overview summarizes the basic results of the vortex vibration (VIV) which have been performed in the last five decades. These studies were mainly related to determining the influence of selected parameters - mass, damping and Reynolds number on the cylinder response, either in one direction only or simultaneously in the flow direction and transverse to the flow direction, and with the search for a map of vortex images in the trace (vortex wake pattern map).

Wake Flow and Vortex Shedding Patterns Behind Rotating Finite Length Cylinders

2019 ◽  
Author(s):  
Amber Donaldson ◽  
John C. Vaccaro ◽  
David M. Rooney
Keyword(s):  
Aspect Ratio ◽  
Vortex Shedding ◽  
Rotational Speed ◽  
Maximum Velocity ◽  
Velocity Profiles ◽  
Wake Flow ◽  
Circular Cylinders ◽  
Mean Velocity ◽  
Constant Length ◽  
Aspect Ratios

Abstract An experimental wind tunnel study was performed to assess the effect of aspect ratio and rotational speed of circular cylinders of varying diameter on the flow patterns behind the cylinders in the presence of a uniform upstream crossflow. Six circular cylinders of constant length but different diameters, producing aspect ratios 6 ≤ AR ≤ 32 were examined at a single upstream velocity such that the Reynolds number varied between 1920 ≤ Re ≤ 10240. Rotational speeds from stationary up to 3600 rpm were applied to the cylinders, so that the maximum relative velocity α = πfD/U∞ = 0.80. Mean velocity profiles were measured three diameters downstream of the cylinder axis at 6 equidistant locations, and PSD power spectral density were generated for 26 equidistant locations along the cylinder, to create a comprehensive record of spanwise variations under all rotational conditions. For the highest aspect ratio tested, the wake velocity profiles were independent of rotational speed at all spanwise locations, whereas at lower aspect ratios, the maximum velocity defect diminished with increasing rotational speed along most of the span and became asymmetric near the free end. Two distinct shedding cells were found only for a cylinder with an aspect ratio of twelve at three relative spin rates of 0.067, 0.27, and 0.4. In cases where only a single cell existed, increased rotational speed produced a higher vortex shedding frequency on a given aspect ratio cylinder.

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