Page 133 - Fundamentals of Ocean Renewable Energy Generating Electricity From The Sea

124 Fundamentals of Ocean Renewable Energy

FIG. 5.8 Wave refraction along an irregular coastline. Dashed lines represent depth contours, and
solid lines that propagate towards the coast are the wave orthogonals.

general case, this flux towards the coast is a constant per unit distance parallel
to the shoreline
EC g cos ψ = constant (5.48)

Therefore, the variation in wave amplitude may be expressed in terms of deep
water reference values as follows
1/2 1/2

C g0 cos ψ 0
a = a 0 (5.49)
C g cos ψ
This result shows that, since ψ 0 >ψ in general, waves approaching a coast
obliquely are amplified less than those approaching a coast normally (where
ψ = ψ 0 = 0).

5.3 DIFFRACTION

Diffraction is the process by which wave energy may be transferred laterally
along a wave crest, or may be reflected (or scattered). These possibilities are
not allowed in refraction. Diffraction occurs in cases in which the assumption
of small bottom slope breaks down or in which obstacles or steep-walled
boundaries are present.
Consider a wave travelling in water of constant depth, around a headland or
breakwater (Fig. 5.9A). In the absence of refraction (since the bed is flat), the