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 



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



GIVEN ; UTien the crest of a wave, with H = 10 ft. and T = 10 sec, passes 

 a pile of D = 1 ft., in 15 ft. of water, a force F = F^)^ = 1,500 lbs. 

 is measured. 



FIND : The appropriate value of C^j. 



SOLUTION : From Figure 7-44 as in the problem of the preceding section, 

 ^Dm =0*7 when H = 0.87 H^,. The measured force corresponds to F^j^, 

 therefore, rearranging Equation 7-31, 



F 



Cr. = 



l/2)pgDH^K^^ 

 1500 



"^^ (1/2) (2) (32.2) (1) (10)2 (0.7) 



- 0.66 



If Airy theory had been used (H = 0) , Figure 7-44 with d/gT^ = 0.0047 

 would give K^ = 0.235 and therefore 



V^lAiry 



T^)h. 



■0.87 H, 



^'^)h=0.87H. 7 



= 0.66 '— = 1.96 



i^Dm].. .„^.^ ■ 0.235 



/^(V>'(H«0) 

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



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



GIVEN: Same conditions as preceding example, but with a wave height, 

 H = 50 ft., a depth, d = 100 ft., and F = F^^^ = 30,000 lbs. 



FIND : The appropriate value of C^). 



SOLUTION : From Figure 7-47 H^ = 66 ft; then H/H^ = 50/66 = 0.76. 

 Entering Figure 7-44 with d/gT^ = 0.031, K^^ = 0.38 is found. 

 Therefore, from Equation 7-31, 



F 



^ l/2PgDH2Ko^ 



30,000 



Cn ^ — : r = 0.98 . 



^ 1/2 (2) (32.2) (1) (50)2 (Q38) 



7-106 



