SOLUTION: Calculate, 



d 



2 

 gT 



= 0.0046 



From Figure 7-68: 



/=0.41 

 o 



Then, 



o 



Therefore, the inequality is satisfied and the steady-state Cq can be 

 used. 



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



Thirriot, et al. (1971) found that the satisfaction of equation (7-51) was 

 necessary only when Rg < 4 x 10 . For larger Reynolds numbers, they found 

 C approximately equal to the steady flow C , regardless of the value of 

 A/D . It is therefore unlikely that the condition imposed by equation (7-51) 

 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 *^n's obtained by Keulegan and 

 Carpenter (1956) is (C ) = 1.52 . The results plotted in Figure 7-85 

 (Thirriot et al., 1971) thatr 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. 



To obtain experimental values for C for large Reynolds numbers , field 

 experiments are necessary. Such experiments require simultaneous measurement 

 of the surface profile at or near the test pile and the forces acting on the 

 pile. Values of C (and C ) obtained from prototype-scale experiments 

 depend critically on the wave theory used to estimate fluid flow fields from 

 measured surface profiles. 



*************** EXAMPLE PROBLEM 24************** 



GIVEN ; When the crest of a wave, with H = 3.0 m (9.8 ft) and T = 10 s , 

 passes a pile of D = 0.3 m (0.9 ft) in 4.5 m (14.8 ft) of water, a force 



F = F^ = 7000 N (1,573 lb) is measured. 



Dm 



FIND ; The appropriate value of C^ . 



SOLUTION ; From Figure 7-72 as in the problem of the preceding section, K^, = 

 0.71 when H = 0.87 H, . The measured force corresponds to F^, ; 

 therefore, rearranging equation (7-38), 



F 



Dm 

 C = 



D , 2 



(l/2)pg DH K 



7-141 



