*-x 



Fig. 10, Schematic wave profile with a rough surface (7), 

 and wind force components ( 'ZT^j Z.) of the 

 effective wind stress f . ( (3^ = velocity of 

 wave propagation in direction of the wind 

 velocity v. 



resistances" in the exact meaning of the definition, will be attri- 

 buted to an effective "frictional-resistance" with regard to the 

 general profile (L, Prandtl, [I6], p. 160). In this way, the wind 

 force acting on each surface element of the rough sea surface may 

 be divided into an effective pressure force and an effective friction* 

 al force, where the first one may be considered as a normal com- 

 ponent and the second one as an effective tangential component with 

 respect to the general profile. The work done by these single 

 components on the waves at present cannot be estimated with the 

 necessary degree of accuracy, if we consider their actions separ- 

 ately. It only seems possible to examine these effects in a merely 

 formal manner, if we consider a very simple main profile of waves, 

 as is shown, for example, in Fig. 11. We assume a simple sine 

 wave, for which the elevation relative to the undisturbed level 

 may be given by 



48 



