Page 69 - Fundamentals of Ocean Renewable Energy Generating Electricity From The Sea

Tidal Energy Chapter | 3 61

(A)

(B)
FIG. 3.13 Relative positions of the Sun, Moon, and Earth corresponding to (A) spring and
(B) neap tides.

FIG. 3.14 Tidal datums.
a spring tide (highlighted) at day = 2, and a neap tide 7 days later (day = 9).
Associated with spring and neap tides are the strongest and weakest peak tidal
currents, respectively.
The type of tide varies considerably around the world. When the two high
waters and two low waters of each tidal day are approximately equal in height,
the tide is semidiurnal [5]. When there is a relatively large diurnal inequality in
the high or low waters (or both), the tide is mixed. If only one high water and one
low water occurs each tidal day, the tide is diurnal. Examples of tidal elevation
time series for two contrasting locations (Boston: semidiurnal, and Mississippi
Sound: diurnal) are given in Fig. 3.15. The form factor F can be used to classify
tides [4]