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members. The wave theories that are normally applied to offshore structures are

described in this section.

There are several wave theories that are useful in the design of offshore

structures. These theories, by necessity, are regular. Regular waves have the

characteristics of having a period such that each cycle has exactly the same form.

Thus the theory describes the properties of one cycle of the regular waves and

these properties are invariant from cycle to cycle. There are three parameters that

are needed in describing any wave theory (fig. 2.3).

Period ( T ) , which is the time taken for two successive crests to pass a

stationary point,

Height ( H ) , which is the vertical distance between the crest and the following

trough. For a linear wave, the crest amplitude is equal to the trough amplitude,

while they are unequal for a non-linear wave.
Water depth (d), which represents the vertical distance from the mean water

level to the mean ocean floor. For wave theories, the floor is assumed horizontal
and flat.

Figure 2.3 – Wave theory parameters

Several other quantities that are important in the water wave theory may be

computed from these parameters. They are:

wavelength (L), which is the horizontal distance between successive crests,

wave celerity or phase speed (c), which represents the propagation speed of the

wave crest,
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