Page 70 - Fundamentals of Ocean Renewable Energy Generating Electricity From The Sea

62 Fundamentals of Ocean Renewable Energy

FIG. 3.15 Water surface elevation time series at two contrasting locations: Boston (semidiurnal)
and Mississippi Sound (diurnal). (Data from NOAA.)

H K1 + H O1
F = (3.20)
H M2 + H S2
where H M2 , etc. is the amplitude of the M2 tidal constituent, etc. F can be
used to quantify the type of tide, using the interpretation shown in Table 3.2.
Form factor is plotted globally from the FES2012 global tidal atlas in Fig. 3.16.
Although the majority of high tidal stream regions throughout the world are
semidiurnal (e.g. the northwest European shelf seas or the northeast of the
United States), many important regions are diurnal, such as the South China
Sea, East China Sea, New Guinea, and Northern Australia. It is therefore
important that semidiurnal and diurnal constituents be included in any resource
assessment.

3.10 OVERTIDES AND TIDAL ASYMMETRY
As described in previous sections, astronomical tides are generated by the
gravitational forces of the Sun and the Moon on the oceans; therefore, the
frequencies of tidal signals (water elevation and velocity) can be directly related
to lunar or solar days in the deep oceans. The propagation of barotropic tides
in the deep ocean can be assumed to be mainly governed by linear processes.
The interaction of tidal components in the deep ocean leads to subharmonic