DeepStar – High Reynolds Number Results
Background
DEEPSTAR (www.deepstar.org) have made available high Reynolds (Re) number data for Vortex-Induced Vibration (VIV) benchmarking purposes. DEEPSTAR is a JIP consisting of the following operator companies:
Anadarko
BP
Chevron Corporation
ENI/Agip
Kerr-McGee
Marathon
Petrobras
Statoil
Total
The high RE data comes from CTR 5402 and CTR 6402. The purpose of these CTRs was to assess the potential value of high RE data as a source of predicting the response of flexible marine risers. The work relating to CTR 5402 was conducted during 2001, and supplemental high RE data was acquired during 2003 and covered by CTR 6402.
Experimental Details
The high RE data was obtained by Oceanic Consulting Corporation at St. Johns, Newfoundland, Canada. The experiments were conducted in the IMD 200m wave/towing tank facility, and the specifications of which are provided below.
IMD Wave/Towing Tank Facility Specifications |
|
---|---|
Length |
200m |
Width |
12m |
Still Water Depth |
7m |
Tow Carriage Speed |
10m/s |
Max. Wave Height (regular waves) |
1m |
Max. Sig. Wave Height (irregular waves) |
0.5m |
Range of Wavelengths at 7m Depth |
0.5m – 40m |
Max. Wind Speed: 1m from fans |
11m/s |
Max. Wind Speed: 5m from fans |
5m/s |
RE Range |
2×105 – 1×106 |
The experimental setup for the high RE tests are summarised in the table below.
Test Cylinder Characteristics |
|
---|---|
Cylinder Length [L] |
6m |
Cylinder Diameter [D] |
0.325m |
Depth of Cylinder During Towing |
2m below surface |
Cylinder Surface: Rough |
Ks/D = 0.0025 |
Cylinder Surface: Intermediate Rough |
Ks/D = 0.0008 |
Cylinder Surface: Straked (Rough Jacket) |
Ks/D = 0.0025 |
Strake Height |
0.25 D |
Strake Pitch |
16 D |
Cylinder Vibrating Mass [MVibrating] |
817kg |
Cylinder Displaced Mass [MDisplaced] |
525kg |
Mass Ratio = MVibrating/MDisplaced |
1.56 |
Mass Ratio = (p/4) MVibrating/MDisplaced |
1.22 |
Two different modes of operations were tested:
Free vibration mode
Forced vibration mode
For the free vibration mode, the cylinder is mounted in between the ends of tow bars. The tow bars can be interchanged to allow the cylinder to oscillate in one or 2 degrees of freedom, namely the transverse and in-line directions. A schematic drawing of the towing frame and the cylinder (pipe dynamometer) is shown below.
In
the free vibration mode, turbulence screens were also used to assess
the effects of turbulence on a smooth cylinder. Two different screens
were used (fine and course). The position of the fine screen,
relative to the smooth cylinder, is shown below.
The
position of the course screen, relative to the smooth cylinder, is
shown below.
In
the forced vibration mode, the cylinder is placed directly between
supporting struts and the tow bars were removed. The supporting
struts are excited by an actuator, and mono-chromatic (single
frequency excitation) and bi-chromatic (double frequency excitation)
were applied to the cylinder. A schematic of the cylinder position
operating in this mode is shown below.
Experimental
Results
The data for high RE testing are divided into 2 key categories:
Detailed experimental results:
Clv against A/D: lift coefficient against vibration amplitude
Cm against A/D: added mass coefficient against vibration amplitude
Cd against A/D: drag coefficient against vibration amplitude
Summary experimental results:
A/D against Vrn: this data is based on Clv against A/D and taking Clv = 0.
Within each of the above categories, the following sub-categories are used:
Cylinder surface type: Smooth, Almost Smooth, Intermediate Rough, Rough, Straked
Vibration type: Free (1DOF and 2DOF), Forced (Monochromatic and Bi-chromatic)
Turbulence screen (Smooth, Almost Smooth cylinders only): Fine grid (0.05m), Course grid (0.40m)
Data is presented in graphical format as well as tabular form.