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                       OCEAN ENERGY TECHNOLOGIES















                       This chapter addresses a number of technologies that are used to harvest oceanic
                       power, which is manifested in many different forms, including waves, tides, and ocean
                       and undercurrents.



                       Tidal Power


                       Tidal movement occurs as a result of the twice-daily variations in sea level caused
                       primarily by the moon and, to some extent, the sun. Tidal power has been in use in
                       milling grain since the eleventh century in Britain and France.



                       Tidal Physics: Effects of the Terrestrial

                       Centrifugal Force


                       The interaction of the moon and the earth results in bulging of the oceans facing the
                       moon. In the mean time, on the opposite side of the globe, this gravitational effect is
                       partly shielded by earth, which owing to the effect of the centrifugal force of earth’s
                       rotation, causes a small bulging out away from the moon. This is known as the lunar
                       tide. This process is further complicated by the gravitational effects of the sun, which
                       causes a similar bulging of waters on the facing and opposing sides of the earth. This
                       is known as the solar tide.
                         Since the sun and moon are not in fixed positions in the celestial sphere but rather
                       change positions with respect to each other, their influence on the tidal range, which is
                       the difference between low and high tide, is also affected. For example, when the moon
                       and the sun are in the same plane as the earth, the tidal range results from the superim-
                       position of the ranges owing to the lunar and solar tides. This results in the maximum
                       tidal range (also known as the spring tides). On the other hand, when the moon and the

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