o 

 o 



> 



J I I I I I L 



1.00 



Figure 22. Drag force current meter example. 



For values of period parameter near 15 (fig. 14), neither C,^,J nor Cq can 

 really be considered constant throughout the wave cycle, and equation (24) 

 cannot be used with constant coefficients. If data had period parameter values 

 near 15, additional experimental work would be necessary. 



An effort to recover any low-amplitude, low-frequency, or essentially dc 

 signals in the presence of these typical swell records places very severe require- 

 ments on a system. No dc velocity signals were ever detected visually on any 

 of the Tower records . 



ACCURACY 



Consider now the accuracy of finding the steady d-c velocity after 

 filtering out the ac terms. For the first case, assume that high-period parameter 

 values are used and therefore the drag coefficient will be constant throughout 

 the wave cycle. If the inertial term in equation (24) could be neglected, the 

 actual force per unit length on the cylinder, F, would be given by the second 

 term of equation (24), 



where 



F = K2 U\U\ 

 K2 = 1/2 (Cq d p) = constant. 



(26) 



34 



