height parameters with parameters from the other two classes depends on the 

 particular application. A rational approach for some applications is to 

 equate the average total wave energy in both monochromatic and irregular wave 

 trains. Thus, for sinusoidal, nonbreaking waves using relationships from 

 Chapter 3, Sections 11,2 and 11,3 



PgH^ = Pga^ (3-21) 



8 



fi? - PS ^ (3-22) 



m 

 h2 = — ^ (3-23) 



2 

 or 



H « H^ /VT (3-24) 



o 



Thus the height H , representing a monochromatic wave train with the same 

 energy as an irregular wave train with significant height H , is equal to 



0.71 H for deep water. A precise computation of the relationship in 



shallow water is much more difficult. Equation (3-24) is expected to be a 

 reasonable approximation for shallow water. 



*************** EXAMPLE PROBLEM 2*************** 



GIVEN : Based on wave hindcasts from a spectral model, the energy-based 

 wave height parameter H and the peak spectral period T were 



estimated to be 3.0 meters (10 feet) and 9 seconds in a water depth 

 of 6 meters (19.7 feet). 



FIND: 



(a) An approximate value of H . 



(b) An approximate value of H, . 



SOLUTION: 



(a) -4 = ^-^ „ = 0.00755 



gT 9.81(9) 



It is evident from Figure 2-7 in Chapter 2 that the relative depth d/gT^ 

 is sufficiently small that breaking is depth-limited. Thus ^ 



d-= 0.78 



R^ = 0.78 (6.0) = 4.7 m (15.4 ft) 



3-18 



