U^T/d = 44.7 



C,,(Q} 2 =^8-8-^ 



1 r 



1 r 



-0-0-0-°-° o o S~~9-^o-.g_o-o-D''° o' 



J \ \ L 



J L 



T 



Cg(Qi 1-0—0—0-0 



0.4 ().(i 



t/T 



0.8 



T 8 o , ^ , , 8 



g— -0— 0— o — 0—0— 0—0'^ "-0— 0— o — o- 



J i I i 1 I I I 



1.0 



Figure 15. Example of variation of the inertia and drag coefficients of a cylinder 

 during a wave cycle.^^ 



3. The maximum force and phase were found as a function of period 

 parameters (fig. 16). 



The problem with using equation (24) for an actual current meter is that 



It is therefore highly desirable for the parameters to 



both U and -— are uiiknown. 



be chosen so that the acceleration term can be neglected. Furthermore the value 

 of Cg should be constant over the operating range of the instrument. Corrections 

 for variations of C^, would be unrepeatable since these variations are connected 

 with fluid acceleration and eddy formations, and varying coefficients complicate 

 data reduction. Steady-state data show that the range of Reynolds number for 

 constant Cq is between 1 x 10"* and 2 x 10'^. Figure 11 shows that the higher 



values of the period parameter I , J are desired because Cg and Cy are nearly 



constant in this range. In the shallow ocean, U^ and T are fixed by the amplitude 

 and period of the swell. The only variable over which there is control is the 

 diameter d of the cylinder, which must be small if period parameters are to be 

 large. The reduction of rf, however, reduces the di-ag force proportionately. These 

 smaller forces produce more demands on the electiical transducer. 



28 



