Ocean Engineering

Vortex-Induced Vibration and Coincident Current Velocity Profiles for a Deepwater Drilling Riser

[+] Author and Article Information
T. Srivilairit

 Bechtel Corporation, Houston, TX 77056tsrivila@bechtel.com

L. Manuel

Department of Civil, Architectural, and Environmental Engineering, University of Texas at Austin, Austin, TX 78712lmanuel@mail.utexas.edu

J. Offshore Mech. Arct. Eng 131(2), 021101 (Feb 26, 2009) (11 pages) doi:10.1115/1.3058684 History: Received June 27, 2007; Revised September 07, 2008; Published February 26, 2009

The objective of this study is to use full-scale field data on current velocities and riser motions to better understand the behavior of deepwater drilling risers. The data are comprised of riser accelerations and coincident current velocity profiles from the monitoring of vortex-induced vibration (VIV) of a drilling riser located at a 1000 m water depth site. Proper orthogonal decomposition (POD), an efficient numerical technique for characterizing the spatial coherence in a random field, is employed here to identify energetic current profiles. The accuracy resulting from the use of only a limited number of the most important POD modes is studied by comparing measured current velocity profiles with those reconstructed based on a reduced-order truncation. In addition to studying current velocity profiles, riser acceleration data from this deepwater drilling riser are also analyzed. In order to analyze the VIV response of this riser, in-line and cross-flow motions in different data segments are studied. Again, empirical POD procedures are employed—this time to derive energetic spatial vibration modes defining the riser motion. Importantly, these modes are identified without the need for either an analytical/computational model of the riser or any physical dimensions and material properties; instead, they are derived exclusively using the field data. Relationships between riser response and coincident current velocity profiles are investigated, especially for those data segments associated with observed lock-in response.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Locations of (a) current velocity measurement units and (b) riser acceleration loggers

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Figure 2

Histogram of current speed magnitudes at different measurement vertical levels along the depth

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Figure 3

Circular histograms of current directions in (a) the upper 500 m and (b) the lower 500 m

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Figure 4

First five POD modes of the current velocity for the entire data set

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Figure 5

Variance of the current field at different levels based on reconstruction using different numbers of POD modes

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Figure 6

Measured and reconstructed (using three POD modes) current velocity profiles over the 2 month monitoring period

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Figure 7

Actual and POD-based correlation coefficient estimates between current components at various depths

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Figure 8

Welch power spectra of rotated accelerations at nine loggers in the cross-flow (Y′) and in-line (X′) directions

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Figure 9

The first three POD mode shapes of cross-flow riser displacements

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Figure 10

Current profiles, riser and vessel rms displacements, and dominant current and riser response directions

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Figure 11

First three POD mode shapes of current velocity for (a) components in the 0 deg and 90 deg directions and (b) resultant and associated direction




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