Vliegel and Delmonte 



ed by a number of persons (see, for example, Laird, 1971). It has 

 been found that the relationship among the frequency (cycles per se 

 cond) of the eddies, f e , the diameter of the cylinder D and the 

 flow velocity V is given by the Strouhal number N g , 



19 7 f e D 



where Nr> is the Reynolds number, VD/u ,in which i<is the kinema- 

 tic viscosity. Except in the range of laminar flow, the Reynolds num- 

 ber effect in this equation can be neglected. For flow in the sub-criti- 

 cal range (Nn less than about 2. x 10 ), there is a considerable 

 variation of N ; in fact, it is most likely that a spectrum of eddy 

 frequencies exists (see Wiegel, 1964, p. 268 for a discussion of this). 

 Extensive data on N g at very high Reynolds numbers, as well as 

 data on C^ (Figure 1) and the pressure distribution around a circular 

 cylinder with its axis oriented normal to a steady flow, has been 

 given by Roshko (1961) for steady flow. Few data are available on the 

 resulting oscillating transverse forces. Cq is the coefficient of 

 drag in the equation 



F D ' T ' °D AV2 < 2 > 



where F n is the drag force, p is the mass density of the fluid, 

 A is the projected area of the cylinder and V is the speed of flow 

 of fluid relative to the body. 



What is the significance of N for the type of oscillating flow 

 that exists in wave motion ? The horizontal component of water par- 

 ticle velocity is 



ttH cosh 2 tt (y + d) /L 2 tt t 



" t— - — cos 



T sinh 2 tt d/L T 



762 



(3) 



