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Research Papers

VIV of a Composite Riser at Moderate Reynolds Number Using CFD

[+] Author and Article Information
T. Rakshit, S. Atluri1

Mechanical Engineering Department, University of Houston, Houston, TX 77204-4006

C. Dalton2

Mechanical Engineering Department, University of Houston, Houston, TX 77204-4006

1

Present address: Technip USA, Houston, TX.

2

Corresponding author.

J. Offshore Mech. Arct. Eng 130(1), 011009 (Feb 20, 2008) (10 pages) doi:10.1115/1.2783849 History: Received March 21, 2006; Revised September 29, 2006; Published February 20, 2008

The vibratory response of a long slender riser, made of composite materials and subject to an ocean current, is examined for a range of conditions. A major focus of this study is the performance of composite materials when used for risers. The influence of the number of modes of vibration is studied, as is the influence of the mass ratio and the value of the damping coefficient. The flow past the riser is represented by a shear flow, ranging from Re=8000 at the lower end of the riser to Re=10,000 at the upper end of the riser. The riser vibration is treated as a coupled fluid-flow/vibration problem. The fluid-flow equations are represented by a large eddy simulation model for the wake turbulence present in the flow. Strip theory is used to represent different forcing locations along the length of the riser. Since the composite riser has a material damping that is frequency dependent (it decreases with increasing frequency), its response is different from, say, a steel riser with a constant material damping. The composite riser, with variable damping, has a larger rms displacement than a riser with constant damping, primarily because of the smaller mass ratio. The vibration amplitude is found to increase with an increase in the number of modes.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Representation of the riser in strip-theory formulation

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Figure 2

Time average of wall vorticity for different grid sizes for a uniform 2D flow past a cylinder at Re=13, 000

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Figure 4

Relative contribution of different modes at plane 15

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Figure 5

Relative contribution of different modes at plane 30

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Figure 6

Relative contribution of different modes at plane 45

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Figure 8

Instantaneous displacements at different times over the period of simulation

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Figure 9

rms displacements for the reference case and with constant damping ratios of 0.011, 0.055, and 0.1

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Figure 10

Displacements for the reference case with a damping ratio=0.011 for plane 15

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Figure 11

Displacements for the reference case with a damping ratio=0.011 for plane 30

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Figure 12

Displacements for the reference case with a damping ratio=0.011 for plane 45

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Figure 15

Effect of the top tension on the maximum displacements

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Figure 16

Effect of the mass ratio on the rms displacement

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Figure 17

Displacements for m*=0.43 and m*=1.0 for plane 30

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Figure 18

Maximum displacements of the riser for different mass ratios

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Figure 19

Normal and reversed damping

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Figure 20

rms displacements with normal and reversed damping

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Figure 21

Maximum displacements with normal and reversed damping

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Figure 14

Effect of the top tension on displacement at plane 30

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Figure 13

Effect of the top tension on the rms displacement.

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Figure 7

rms displacements of modes 9 and 10

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Figure 3

rms displacement of the riser for 10 and 12 modes for 60 simulation planes

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