Structures in the
Offshore Environment
James F. Wilson
Offshore structures, constructed on or above the continental shelves and on
the adjacent continental slopes, take many forms and serve a multitude of purposes: towers for microwave transmission, installations for power génération,
portable pipeline Systems for mining the océan floor, and a few platforms and
floating islands that serve as resort hôtels. Most structures offshore, however.
hâve been built to support the activities of petroleum industries—activities
that include the exploration, drilling, production, storage, and transportation
of oil. Exploratory drilling is done from mobile platforms or carefully positioned
ships; production and storage operations involve more permanent structures;
and pipelines, buoys, and mooring Systems for floating structures and ships
support ail oil acquisition activities.
The design of marine structures compatible with the extreme offshore environmental conditions is a most challenging and créative task for the contemporary océan engineer. The engineer involved in designing these marine structures
must rely on the knowledge and expérience of meteorologists, oceanographers,
naval architects, geologists, and material scientists. The marine engineer's goal
is to conceive and design a lasting structure that can withstand the adverse
conditions of high winds and waves, earthquakes, and ice, remaining in harmony with its environment. Mulcahy (1979) expressed this design philosophy
as follows:
Offshore platforms are a bit like space capsules for each pound
of unnecessary deck space that can be trimmed from the structure,
the magnitude of the structure needed to support it can be reduced.
This is true for a guyed tower, a fixed platform, or a tension leg structure. Decreasing the wave load leads to lower overturning moments,
a lesser requirement for pilings, and a smaller number of strength
members in the structure. When this is accomplished, smaller launch
barges can transport the structure to the work site.
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