TT H O 



The ratio L«/L^ can be obtained from Figure 7-68. 



An additional parameter, the importance of which was cited by Keulegan and 

 Carpenter (1956), is the ratio of the amplitude of particle motion to pile 

 diameter. Using Airy theory, this ratio A/D can be related to a period 

 parameter equal to ^^rnax ^^/^ (introduced by Keulegan and Carpenter) thus: 



A 1 u T 



A _ J_ mix 



D 211 D 

 When z = equation (7-48) gives 



(7-48) 



L 

 H 1 Ho 

 A= ^ = (7-49) 



2 



tanh 



2Trd 

 L 



2 L 



A 



The ratio L^/L^ is from Figure 7-68. 



In a recent laboratory study by Thirriot et al. (1971), it was 

 found that for 



^ > 10 , C^ « C^ (steady flow) 



1 < ^ < 10 , C^ > C^ (steady flow) 



Combining this with equation (7-49), the steady-state value of Cj^ should 

 apply to oscillatory motion, provided 



t = 1^ ^ > 10 (7-50) 



or equivalently, 



^ > 20 -^ (7-51) 



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



*************** EXAMPLE PROBLEM 23************** 



GIVEN : A design wave with height of H = 3.0 m (9.8 ft) and period T = 10 

 s in a depth d = 4.5 m (14.8 ft) acts on a pile of diameter D = 0.3 m 

 (0.9 ft) . 



J|IND: Is the condition expressed by the inequality of equation (7-51) 

 satisfied? 



7-140 



