or equivalently. 



H H4 



- > 20 (7-44) 



D L„ 



************** EXAMPLE PROBLEM *************** 



GIVEN : A design wave with height, H = 10 ft., period, T = 10 sec. in a 

 depth, d = 15 ft. acts on a pile of diameter, D = 1 ft. 



FIND: Is the condition expressed by the inequality of Equation 7-44 

 satisfied? 



SOLUTION : Calculate, 



d 



From Figure 7-40: 



Then , 



gT^ 





0.00466 



= 0.41 



H 10 ^A 



- = — = 10 > 20 = 8.2 . 



D 1 L 



o 



Therefore, the inequality is satisfied and the steady state C^ can 

 be used. 



************************************* 



Thirriot, et al. (1971) found that the satisfaction of Equation 7-44 

 was necessary only when Rg < 4 x lO'*. For larger Reynolds numbers, they 

 found C^) approximately equal to the steady flow Cp, regardless of the 

 value of A/D. It is therefore unlikely that the condition imposed by 

 Equation 7-44 will be encountered in design. However, it is important 

 to realize the significance of this parameter when interpreting data of 

 small-scale experiments. The average value of all the C^'s obtained by 

 Keulegan and Carpenter (1956) is (.(^D^avq ~ 1'52. The results plotted in 

 Figure 7-58 (Thirriot, et al., 1971) that account for the influence of 

 A/D show that C^ «; 1.2 is a more representative value for the range of 

 Reynolds numbers covered by the experiments. 



7-105 



