Environmental Engineering Reference
In-Depth Information
FIGURE 7.4
Point absorber.
•
An
attenuator
is a long floating structure like the terminator, but it is ori-
entated parallel to the waves rather than normal to them (see
Fig u r e 7.6
)
.
It rides the waves like a ship, and movements of the device at its bow and
along its length can be restrained to extract energy. A theoretical advantage
of the attenuator over the terminator is that its area normal to the waves is
small so the forces it experiences are much lower.
TIDAL ENERGY
The tides rise and fall in eternal cycles. Tides are changes in the level of the oceans
caused by the gravitational pull of the moon and sun and the rotation of the Earth.
The relative motions of these cause several different tidal cycles, including a semidi-
urnal cycle (with a period of 12 hours and 25 minutes); a semimonthly cycle (spring
or neap tides corresponding with the position of the moon, with the highest tides
occurring in March and September); a semiannual cycle (with a period of about
178 days which is associated with the moon's orbit); and longer term cycles (e.g., a
