changing wave conditions. This conclusion is supported by the consideration 

 that wave reflection and dissipation are associated with various complex flow 

 processes, and that the number of parameters chosen to correlate the data is 

 inadequate to account for all these physical factors. 



The effect of relative open-tube breakwater width, L T /L- , on reflection 

 coefficient, C , is shown in Figure 131 for an arrangement with various 

 numbers of open tubes. Here L™ is the average tube length, defined as the 

 total length of tubes in the system divided by the number of tubes, and L- 

 is the incident wavelength. Generally, all values are contained between a 

 maximum of C = 0.35 and a minimum of C = 0.10, allowing for experimental 

 scatter. This indicates that the number of tubes is not too critical, since 

 for the short and intermediate waves the wave energy is concentrated in the 

 upper parts of the water column. Hence, the reflection coefficient is reduced 

 by a relatively small number of tubes to a value corresponding to that of 

 beaches of relatively small slope. When the effect of wave steepness, Hr/L^, 

 is isolated (Fig. 132), it is apparent that the reflection coefficient, C , 

 decreases sharply with increasing values of wave steepness (for low values of 

 wave steepness), and approaches a minimum value for higher wave steepness at 

 all relative breakwater widths, L T /L^. For all types of arrays, the reflec- 

 tion coefficient was found to decrease at constant wave steepness as relative 

 breakwater width decreased. 



Transmission coefficients, CL, versus relative breakwater widths, 

 Lip/L^, are presented in Figure 133 for a constant value of wave steepness, 

 H^/L^ = 0.02. Generally, the transmission coefficients decrease materially 

 with increasing values of L^./Lj (with decreasing wavelength). Hence, the 

 effectiveness of the open-tube concept as an energy dissipator increases as 

 the wavelength decreases (conversely, as the breakwater width increases). 

 When the steepness is incorporated as a parameter, the transmission coeffi- 

 cient was found to decrease with increasing wave steepness for all tube arrays 

 (Fig. 134). It was also found that the transmission coefficients approached a 

 constant value for large wave steepness, H. /L • . 



b. Variation of Power Loss with Wave Steepness . Power losses, computed 

 by equation (74) for the experimental tests of Ippen and Bourodimos (1964), 

 are presented in Figure 135 as a function of incident wave steepness, H-/L-, 

 and relative breakwater width, L T /L.. Power losses, P D , increased with the 

 number of rows in the array, but the change above three rows was not very 

 significant. Hence, additional rows do not seem justified for the range of 

 wave conditions tested. Power losses decrease sharply with a decrease in the 

 relative breakwater width, L T /L-. For low wave steepness and longer wave- 

 lengths, there is littl-e variation in the relatively small power loss for the 

 different arrangement of open-tube system. However, the power losses were 

 distinctly higher for the random-type structure as wavelengths became shorter 

 and wave steepness increased, indicating the favorable aspects of the irreg- 

 ularity of tube arrangements. 



Ippen and Bourodimos (1964) made several general conclusions as a result 

 of this experimental investigation into the effectiveness of an open-tube 

 system application for floating breakwater utilization. Depending on the 

 particular type array, reflection coefficients, C , ranged from a minimum 

 of 0.05 to a maximum of 0.53. Transmission coefficients, C t , showed cor- 

 responding values from 0.40 to 0.96. Energy dissipation was accomplished 



194 



