APPENDIX B 
METHOD OF MEASURING WAVE REFLECTION COEFFICIENTS 
The method of Goda and Suzuki (1976) is used to determine laboratory reflec- 
tion coefficients for monochromatic and irregular conditions. Also used is the 
energy balance approach for both types of waves, so that wave energy transfer 
between frequencies and variable amounts of reflection over a range of fre- 
quencies can be considered. This approach gives a reflection coefficient that 
is formally defined as the square root of the ratio of the reflected wave energy 
to incident wave energy. For an idealized case where no energy transfers occur, 
the reflection coefficient is the ratio of reflected and incident wave heights. 
Reflection coefficients are determined by placing two or more gages several 
wavelengths seaward of the structure. Each pair of gages then gives an esti- 
mate of reflection coefficients. 
In these experiments wave records were sampled simultaneously at three wave 
gages (Fig. 2) at a rate of 16 times a second to obtain 4,096 data points for 
each run. An FFT was then performed cn each wave gage record to determine real 
and imaginary spectral coefficients, A and B, at each spectral line j. Let the 
subscripts } and » indicate the landward and seaward gages in a pair. The re- 
flected and incident wave amplitudes for each gage pair for each spectral line 
are then given by 
Eroes 1 Ka> - Ay cos kA2 - B, sin kA2)? + (By + Ay sin kAL - By cos kAL)? (B-1) 
1 2lsin kA 
Natkelss 1 KA> - A, cos kA& + By sin kAg)* + (Bp - Aj sin kAg - By cos kAL) 2 (B-2) 
r 2lsin kA 
A,B = spectral coefficients 
k = wave number = =" @=3)) 
AX = gage spacing 
Only gage pairs with 
0.05 < = < 0.45 (B-4) 
are used in the analysis, and wavelength, L, is determined from linear theory 
for irregular waves, 
2 
L= RE cearaln (24), (B-5) 
27 L 
and may be found using Dean's (1974) stream-function theory for steep monochro- 
matic waves (see App. C). 
All estimates of reflection coefficients found using the above procedure 
are averaged at each spectral line to give an incident wave amplitude and re- 
flection coefficient for line j: 
38 
