m No. 377 



cuiar f v produced by the rectilinear flow at a velocity V_ making an angle 

 with the u meter axis. The relationship in (ll-l6) can then be evaluated 

 by defining the function given by: 



RC 0) = $££■ . - (n-17) 



Ur <os<¥ 



Thus, for an ideal response to the cosine lav, R (0) = constant = 1.0. This 

 can be used to examine the calibration data given in appendix C. Values of 

 R (+0) and R(-0) were calculated, and these values are plotted as a function 

 of the towing speed V. in figure 11-12. Due to the closeness of the points 

 in the lower plot, lines were not connected between data values. 



There is a gross asymmetry of the response with respect to the sign 

 of 0. For values below k-0° both coefficients, B'(~0) and R(0), are similar 

 in their behavior. However, for values above 40° the R(=0) deviates sub- 

 stantially from 1.0. 



The flow at angles near 90 apparently tends to be unstable, resulting 

 in a gross deviation from the cosine relation. At these high angles the 

 tendency toward instability is understandably great because of the likelihood 

 of vortex shedding at a leading edge of the cylinder. In general^ the cosine 

 relation seems to hold well for all values of except for large angles, as 

 shown by the point at +80°. Both sets of values show that R(+0) and R(-0) 

 are essentially independent of the absolute towing velocity. There is a 

 slight tendency to attain a maximum value of R(0) between 40 and 60 cm sec™ ; 

 otherwise, the values of R(0) appear independent _ of V. . 



During all runs of the series, there was no visible response (i.e., no 

 rotation) of the vertical w meter. Hence, any vortex shedding or other 

 turbulent disturbance was not intense enough to affect the equilibrium, of 

 the perpendicular impeller. 



The asymmetry of function R(0) appears to be associated with the geometric 

 asymmetry of the coupled cylinders, with respect to the rotation in the plane 

 of 0. Fig. 11-11 indicates that flow with a positive angle of attack (+0) 

 would encounter a somewhat different shade configuration than flow at a nega~ 

 tive angle (-0). This could give rise to the asymmetric calibration with 

 respect to the 4^ values. The exact interpretation of this dynamic asymmetry 

 is obscure, and no effort was made to further examine this problem. 



It was planned to calibrate the OMDUM II system in terms of its response 

 to flow in the vertical or XZ plane. Unfortunately, this calibration could 

 not be performed with the rotating boom system because of scheduling problems. 

 Since work was proceeding on a new wave meter system ( OMDUM III),? no further 

 calibrations were performed on OMDUM II. 



The first series of wave measurements in the open ocean was made in 

 May 1963 using OMDUM II suspended from the Buzzards Bay Entrance Light 

 Station (BBELS). These preliminary observations (reported in detail as 



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