Estimate the energy in peak 1 using equation (3a), the tabulated energy den- 
sity (Table), and the above value of E to convert the sum of energy density 
from percent to foot squared. 
5 
So1 = (Af) Es 
P dn 3 
(0.01074 Hz) (FsG- FEE) co £t2/Hz) 
Splice 
Similarly estimate the energy in peak 2 using equation (7a) 
100 
S Q & (Af) ) Ej 
, j=12 
36.4 pet 2 
(0.01074 Hz) ( 100 pet (192 £t“/Hz) 
On7S se" 
Estimate significant height for peak 1 using equation (4). 
Hy1 = 45,1 
ayf1.31 ft? = 4.6 ft 
Note that H,, is 1.1 feet lower than H, based on the full spectrum. Simi- 
larly, significant height for peak 2 is estimated from equation (8) 
Hao = 3.5 ft 
Hs, Hs1 and Hg2 are related in this example by 
Hg =f Hg1 ae H30 
V. INTERPRETATION OF SPECTRA FOR APPLICATIONS 
SENSITIVE TO SPECIFIC FREQUENCIES 
The interpretation of spectra in terms of wave trains is appropriate for 
most coastal engineering work. However, certain engineering applications, es- 
pecially applications in which resonance can occur, are highly sensitive to one 
frequency or a small range of frequencies. Estimates of how much energy can be 
expected at that frequency or range of frequencies are required. The estimates 
are obtained directly from the spectrum. Since the estimates are sensitive to 
data collection and analysis procedures, it is especially important that the 
procedures be optimum when such applications are intended cr anticipated. 
For frequency-sensitive applications, it is generally assumed that each 
frequency with nonzero energy represents an independent wave component, regard- 
less of whether it is a spectral peak. Thus, in a resonance problem sensitive 
to frequency fp, spectral energy at fp is treated as an independent wave. 
If fp corresponds to a major spectral peak, it would be appropriate (and 
conservative) to estimate the energy from equation (7). Ina floating break- 
water problem where energy at frequencies lower than some cutoff frequency, 
19 
