Numerical Study on Vortex Induced Motion of Circular Cylinder With Low Aspect Ratio in Currents

2019 ◽  
Author(s):  
Jiawei He ◽  
Decheng Wan
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Circular Cylinder ◽  
Numerical Study ◽  
Circular Cylinders ◽  
Natural Period ◽  
Low Aspect Ratio ◽  
Free Decay ◽  
Induced Motion ◽  
Decay Tests

Abstract This paper presents the investigation results of the VIM phenomenon, discloses the characteristics of the relative motions of a floating cylinder. Floating circular platforms present a large characteristic diameter associated with a large natural period of motions in the horizontal plane. In this paper, the VIM around floating circular cylinders, m* = 1.0, with very low aspect ratio, L/D = 2, as a motivation for better understanding the VIM of Spar platforms. In order to study vortex induced motions (VIM) response of a circular cylinder, numerical computations are carried out by our in-house VIM solver vim-FOAM-SJTU. In the CFD simulations the cylinder is moored with linear springs to provide a range of reduced velocities. The fluid domain is gridded by an unstructured grid. The boundary layer is modeled with a first boundary layer y+≈2. The focus is on the effect of reduced velocity on the VIM response. Free decay tests and vortex-induced motion (VIM) tests have been built numerically. The Fourier analysis of the motions have been performed in order to explain in figure-eight-type motion trajectory.

Fluctuating Forces on a Rectangular Prism and a Circular Cylinder Placed Vertically in a Turbulent Boundary Layer

1984 ◽  
Vol 106 (2) ◽  
pp. 160-166 ◽  
Author(s):  
H. Sakamoto ◽  
S. Oiwake
Keyword(s):  
Boundary Layer ◽  
Experimental Study ◽  
Aspect Ratio ◽  
Circular Cylinder ◽  
Turbulent Boundary Layer ◽  
Cross Section ◽  
Boundary Layer Thickness ◽  
Bluff Body ◽  
Three Dimensional ◽  
Circular Cylinders

An experimental study was conducted to investigate the fluctuating force generated by the shedding of vortices from a three-dimensional bluff body placed vertically in a turbulent boundary layer. A conventional strain-gauge balance was modified and used in the experiment. The balance used has a relatively high natural frequency and gives a linear relation between force and strain. Prisms with a square cross section and circular cylinders were selected as three-dimensional bodies varing in aspect ratio and height. The aspect ratio and the ratio of the height to the boundary layer thickness were varied in the measurement of the fluctuating force on a body.

A Model for High-Reynolds-Number Flow Past Rough-Walled Circular Cylinders

1977 ◽  
Vol 99 (3) ◽  
pp. 486-493 ◽  
Author(s):  
O. Gu¨ven ◽  
V. C. Patel ◽  
C. Farell
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Circular Cylinder ◽  
Turbulent Boundary Layer ◽  
Pressure Coefficient ◽  
Empirical Relation ◽  
Reynolds Numbers ◽  
Boundary Layer Separation ◽  
Circular Cylinders ◽  
Mean Flow

A simple analytical model for two-dimensional mean flow at very large Reynolds numbers around a circular cylinder with distributed roughness is presented and the results of the theory are compared with experiment. The theory uses the wake-source potential-flow model of Parkinson and Jandali together with an extension to the case of rough-walled circular cylinders of the Stratford-Townsend theory for turbulent boundary-layer separation. In addition, a semi-empirical relation between the base-pressure coefficient and the location of separation is used. Calculation of the boundary-layer development, needed as part of the theory, is accomplished using an integral method, taking into account the influence of surface roughness on the laminar boundary layer and transition as well as on the turbulent boundary layer. Good agreement with experiment is shown by the results of the theory. The significant effects of surface roughness on the mean-pressure distribution on a circular cylinder at large Reynolds numbers and the physical mechanisms giving rise to these effects are demonstrated by the model.

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

2011 ◽  
Author(s):  
Rodolfo T. Gonc¸alves ◽  
Ce´sar M. Freire ◽  
Guilherme F. Rosetti ◽  
Guilherme R. Franzini ◽  
Andre´ L. C. Fujarra ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Water Channel ◽  
Analytical Models ◽  
Mass Ratio ◽  
Water Displacement ◽  
Transform Method ◽  
Number Range ◽  
Vortex Induced Vibration ◽  
Low Aspect Ratio ◽  
Induced Motion

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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