Page 22 - 6634

As such, the metocean condition refers to a number of meteorological and

oceanographic conditions. These factors include:

local surface wind,

wind-generated local waves,

swell (long-period waves) generated by distant storms,

surface current also generated from the local storms,

energetic deep water currents associated with low frequency, large basin

circulation,

and

non-storm-related currents, which are site-specific, such as loop current in the

Gulf of Mexico or coastal current in the Norwegian northern North Sea.

Offshore structures, which are placed in the ocean for the exploration and

production of resources beneath the ocean floor, are at the mercy of the
environment they are subject to by nature. These environments that the structures

may face are the ocean waves, wind and current. Earthquakes and Tsunami waves
may also occur in the water in certain parts of the world. For the survival of these

structures, the effects of the environments on them must be known by the designer
of these structures. and considered in their design.

Additionally, the selection of rigs and handling equipment, and the design of

risers and mooring systems are also critically dependent on the predicted site-

specific metocean condition. This chapter describes the environment that may be

expected in various parts of the world, and their properties. Formulas in describing

their magnitudes are provided where appropriate so that the effect of these

environments on the structure may be evaluated.

Ocean waves are, generally, random in nature. However, larger waves in a

random wave series may be given the form of a regular wave that may be

described by a deterministic theory. Even though these wave theories are idealistic,

they are very useful in the design of an offshore structure and its structural

22