energy flux per unit wave crest width transmitted across a plane perpen- 

 dicular to wave advance is 



P = InC = EC . (2-40) 



g 



Energy flux F is frequently called wave power and 



47rd/L 

 1 + 



sink (47rd/L) 



If a plane is taken other than perpendicular to the direction of wave 

 advance F = F C sin (J), where (j) is the angle between the plane across 

 which the energy is being transmitted and the direction of wave advance. 



For deep and shallow water. Equation 2-40 becomes 



P^ = - E^C (deep water). (2-41) 



o 2 " " *^ 



P = EC^ = EC (shallow water) . (2-42) 



An energy balance for a region through which waves are passing will 

 reveal, that for steady state, the amount of energy entering the region 

 will equal the amount leaving the region provided no energy is added or 

 removed from the system. Therefore, when the waves are moving so that 

 their crests are parallel to the bottom contours. 



or, since 



1 C^ = EnC . (2-43) 



2 



o o 



When the wave crests are not parallel to the bottom contours, some parts 

 of the wave will be traveling at different speeds, the wave will be 

 refracted and Equation 2-43 does not apply. (See Section 2.3. WAVE 

 REFRACTION.) 



The following problem illustrates some basic principles of wave energy 

 and energy flux. 



2-28 



