Vortex Induced Vibration on Pipeline
Vortex-induced vibration is a major cause of fatigue failure in submarine oil and gas pipelines and steel catenary risers. One of the serious problems for the structural safety of pipelines is
uneven areas in the seafloor as they enhance the formation of free
spans. Route selection, therefore, plays an important part in design, Matteelli
(1982). However, due to many obstacles it is difficult to find a
totally obstruction free route. In such cases the pipeline may have free
spans when crossing depressions. Hence, if dynamic loads can occur, the
free span may oscillate and time varying stresses may give unacceptable
fatigue damage. A major source for dynamic stresses in free span
pipelines is vortex induced vibrations (VIV) caused by steady current. This effect is in fact dominating on deep water pipelines since wave
induced velocities and accelerations will decay with increasing water
depth. The challenge for the industry is then to verify that such spans
can sustain the influence from the environment throughout the lifetime
of the pipeline.
The aim of the present project is to improve the understanding of vortex
induced vibrations (VIV) of free span pipelines, and thereby improve
methods, existing computer programs and guidelines needed for design
verification. This will result in more cost effective and reliable
offshore pipelines when laid on a very rugged seafloor.To evaluate two different strategies for field development; one based on
offshore loading and the other on a pipeline to an onshore gas
terminal. A key problem for the last alternative is that the seafloor between
these fields and the coast is extremely rugged meaning that a pipeline
must have more and longer free spans than what is seen for conventional
pipelines.
Practical engineering is still based on empirical models, while use of
computational fluid dynamics (CFD) is considered immature mainly because
of the needed computing resources. CFD models may certainly be linked to a non-linear structural model, but
the needed computing time will become overwhelming. Then, one of the
main focuses of the present research is investigation about time domain
model for analysis of vortex induced vibrations for free span pipelines
and the other is about multi free span pipelines where neighbor spans
may interact dynamically. The interaction will depend on the length and
stiffness of the pipe resting on the sea floor between the spans, and
sea floor parameters such as stiffness, damping and friction. Each of
them has important issues to investigate for improvement of our VIV
knowledge.
Daftar Pustaka :
http://www.diva-portal.org/smash/get/diva2:217873/FULLTEXT01.pdf
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