SELECTION OF DESIGN WAVE SPECTRA
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height, although the frequency corresponding to each peak is different. This
characteristic, which is partly reflected by a shape parameter 7, must also be
considered in specifying design wave spectra. A shape parameter of 7 = 7 gives
a very sharply peaked JONSWAP spectrum, whereas by comparison, 7 = 3 produces a lower peak and wider band about the peak. For a Pierson-Moskowitz
spectrum, some investigators suggest that 7 = 1. For further details, see Rye
and Svee (1976) and Young (1999).
Figure 6.5 Illustration of a spectral family (Ochi, 1981).
The sélection of wave spectra used to evaluate the design of a particular
structure dépends on several factors, including the risk criteria adopted by the
owner of the structure. That is, the owner of the structure must décidé what
risk can be economically justified for a particular structure located at a given
site. This présumés that ail other design criteria are satisfied. In one case, for
instance, the most economical overall design may be based on a storm occurring
on the average once in 20 years, and in another case, once in 100 years. A
comprehensive discussion of risk criteria was presented by Borgman (1963).
From another perspective, FYeudenthal and Gaither (1969) suggested that
the wave spectra eventually selected for design pur poses should be based on the
157
height, although the frequency corresponding to each peak is different. This
characteristic, which is partly reflected by a shape parameter 7, must also be
considered in specifying design wave spectra. A shape parameter of 7 = 7 gives
a very sharply peaked JONSWAP spectrum, whereas by comparison, 7 = 3 produces a lower peak and wider band about the peak. For a Pierson-Moskowitz
spectrum, some investigators suggest that 7 = 1. For further details, see Rye
and Svee (1976) and Young (1999).
Figure 6.5 Illustration of a spectral family (Ochi, 1981).
The sélection of wave spectra used to evaluate the design of a particular
structure dépends on several factors, including the risk criteria adopted by the
owner of the structure. That is, the owner of the structure must décidé what
risk can be economically justified for a particular structure located at a given
site. This présumés that ail other design criteria are satisfied. In one case, for
instance, the most economical overall design may be based on a storm occurring
on the average once in 20 years, and in another case, once in 100 years. A
comprehensive discussion of risk criteria was presented by Borgman (1963).
From another perspective, FYeudenthal and Gaither (1969) suggested that
the wave spectra eventually selected for design pur poses should be based on the