Research Papers: CFD and VIV

Drag Reduction and Vortex-Induced Vibration Suppression Behavior of Longitudinally Grooved Suppression Technology Integral to Drilling Riser Buoyancy Units

[+] Author and Article Information
H. Marcollo, A. E. Potts, D. R. Johnstone, P. Kurts

AMOG Consulting,
Melbourne 3168, Australia

P. Pezet

Matrix Engineering & Composites,
Perth 6166, Australia

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received August 15, 2016; final manuscript received November 22, 2017; published online June 28, 2018. Assoc. Editor: David R. Fuhrman.

J. Offshore Mech. Arct. Eng 140(6), 061802 (Jun 28, 2018) (11 pages) Paper No: OMAE-16-1095; doi: 10.1115/1.4038933 History: Received August 15, 2016; Revised November 22, 2017

Drilling risers are regularly deployed in deep water (over 1500 m) with large sections covered in buoyancy modules. The smooth cylindrical shape of these modules can result in significant vortex-induced vibration (VIV) response, causing an overall amplification of drag experienced by the riser. Operations can be suspended due to the total drag adversely affecting top and bottom angles. Although suppression technologies exist to reduce VIV (such as helical strakes or fairings), and therefore reduce VIV-induced amplification of drag, only fairings are able to be installed onto buoyancy modules for practical reasons, and fairings themselves have significant penalties related to installation, removal, and reliability. An innovative solution has been developed to address this gap: longitudinally grooved suppression (LGS). Two model testing campaigns were undertaken: small scale (subcritical Reynolds number flow), and large scale (postcritical Reynolds number flow) to test and confirm the performance benefits of LGS. The testing campaigns found substantial benefits measured in hydrodynamic performance that will be realized when LGS modules are deployed by operators for deepwater drilling operations.

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Fig. 3

(a) Flow pattern around a bare cylinder. Flow is from left to right: (b) the “R-Series” LGS profile changes the flow pattern around the structure, stretching and splitting the vortices, causing less disturbed wake. Flow is from left to right.

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Fig. 4

Drag coefficient versus reduced velocity (from subcritical free vibration model testing)

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Fig. 5

A/D verses reduced velocity (from subcritical free vibration model testing)

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Fig. 6

Maximum A/D versus number of rounded grooves (from subcritical model testing) note that “bare cylinder” is represented at 0

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Fig. 7

Comparison of various numbers of longitudinal grooves. Note that eight or nine grooves showed the best performance.

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Fig. 2

(a) Cross section of saguaro cacti and (b) cross section of a “T-series” LGS

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Fig. 1

(a) Inspiration for LGS—the saguaro cacti and (b) A rendered image of the LGS design

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Fig. 10

A variety of cacti-like cross sections were model tested

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Fig. 8

Drag coefficient versus number of rounded grooves (from subcritical model testing) note that “bare cylinder” is represented at 0

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Fig. 9

Picture/diagram of test setup (subcritical Reynolds)

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Fig. 11

Reynolds number versus flow velocity for DRBMs

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Fig. 14

Fixed drag coefficients—LGS compared to fairings, and an ideal bare smooth cylinder

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Fig. 12

Drag force on a DRBM per unit length versus flow velocity

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Fig. 15

The R8 LGS large-scale model

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Fig. 16

Large-scale R8 model being prepared for loading into the tow tank

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Fig. 13

Hoerner [8] cylinder drag data with projected postcritical data

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Fig. 17

Carriage loaded with large scale model and preparing to perform a test

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Fig. 19

Bare cylinder results: drag amplification from VIV

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Fig. 20

Longitudinally grooved suppression R8 results: drag amplification from VIV

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Fig. 18

Maximum peak A/D values were recorded during high Reynolds testing of R8 LGS and compare favourably against subcritical testing of R8 LGS (middle line with 0.7 maximum A/D) and subcritical conventional round modules (top line with 1.0 maximum A/D)



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