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General
Testing Information
The wind tunnel is currently equipped to test
for both wind and underwater loads for two different types
of offshore structures:
semisubmersibles and
jack-up drilling rigs.
The wind tunnel testing procedures are the standard
procedures used for all off-shore platform tests at the
facility. The procedures meet as a minimum the “Guidelines
for Wind Tunnel Testing of Mobile Offshore Drilling Units”,
Technical & Research Bulletin 5-4, August 1988. Some of the
research used to develop these guidelines was performed at
the Oran W. Nicks Low Speed Wind Tunnel using the SEDCO 700
as a baseline. An example of graphed results from an
offshore structure test is available
here.
In addition to testing offshore structures,
the wind tunnel is fully equipped to fabricate models in our
machine shop with both full-time model engineers and student
technicians. The pictures on this page give examples
of some of the model fabrication work at the wind tunnel.
Contact the wind tunnel directly at
information@wind.tamu.edu for more information.
Model technicians installing a semisubmersible model for
testing.
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Semisubmersible Rigs
Testing for semisubmersible consists of two
separate parts: wind and underwater load testing.
Tests are conducted at a dynamic pressure of 65 psf that
corresponds to a Reynolds number of 1.487x106 per
foot. To help achieve this Reynolds number, 60 grit
sand grains are applied to all surfaces of the model.
Click on Picture to Enlarge.
Diagram of test set-up for a semisubmersible offshore
structure.
The mounting set-up uses a separate sub-floor
to reduce the floor boundary layer thickness. Without
the model present, this thickness was measured to be 0.25"
at the center the model.
Sub-floor with model legs mounted in place.
Also, a boundary layer fence is used to
achieve the desired boundary layer profile (wind gradient).
A boundary layer fence setup is placed upstream of the
model.
The model scale for the tests is 1:192, or
1/16" per foot. Once force and moment data for the
model is obtained from tests, the force and moment data per
square foot can be found by dividing the data by the dynamic
pressure. Next, full scale data per square foot can be
calculated by multiplying the model force per square foot by
the square of the scale and by multiplying the moments per
square foot by the cube of the scale. Additionally,
underwater loads can be found using the kips per square knot
data obtained in the tests and the water density.
These should enable a company to evaluate the results at any
current.
Example of testing underwater loads.
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Jack-Up
Drilling Rigs
Three models are tested to obtain the
information required for jack-up rigs. The first model, that of the hull, including
some small parts of the leg sections, is tested through a
rotation of 360 degrees. The hull is tested with the
cantilever beam in the stowed position, the fully extended
position and a position in the middle. The drill floor move
from side to side can also be tested. All of these tests are
run at a constant dynamic pressure and level to the floor.
The results include force and moment coefficients, which can
be used to obtain full scale forces and moments given the
hull height and velocity described by the atmospheric
velocity profile.
Testing the first model, the hull.
The second model, the leg section, is used to
obtain 2-dimensional section coefficients for use in the
studies of the leg contribution. These section coefficients
can be used with both air and water to obtain full scale
loads of the entire leg. The leg sections are tested through
a range of Reynolds Numbers to define its reactions and
changes. Using 60 grit sand grains, roughness is also added
to a second configuration of this model to study the effects
of Reynolds number as well as those of build-up underwater.
Testing the second model, the leg section.
The third model, one of the leg chord by
itself, is used to obtain additional 2-dimensional section
coefficients. Different Reynolds numbers and effects of
roughness are also studied with this model. These
coefficients are used to understand the effects of the
leg chord relative to the leg
section. By selecting the appropriate Reynolds number, these
coefficients can also be used in both air and water.
Testing the third model, the leg chord.
Currently, testing of a complete model is not
recommended. In order to obtain the structural
integrity of the test model, the leg scaling will have to be
modified, nullifying the advantages. Further research and
development of testing procedures is required in order for
the information obtained to be sufficiently reliable.
For more information, feel free to contact the Wind Tunnel.
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