Average Momentum (Table XI, Item 7) 



^' =-7h^= °-'°' 



8 L| 

 M = 0.505(187) = 94.42 Ib-sec/ft^ 



Arxrage Momentum Flux in Wave Direction (Table XI, Item 8) 

 ¥ ' = T-sfr = 0.603 



X 



M 



F = 0.603(8080) = 4872 lb/ft 



X 



The average momentum flux has been recognized in recent years as an important dynamic 

 quantity and is related to wave setup within the surf zone and also is an important factor in 

 the longshore transport of littoral material. 



Average Momentum Flux Transverse to Wave Direction (Table XI, Item 9) 



F' = 7^= 0.156 



m 

 Y 



F^ = 0.156(8080) = 1260 



y 



From the momentum flux components presented, it is possible to obtain any component 

 of the radiation stress tensor (Bowen, 1969). 

 Example 5— Free Surface Breaking Parameters 



The free surface breaking parameters as defined by Equations (48) and (49) are based on 

 two stability considerations. The kinematic free surface breaking parameter is defined in 

 terms of the speed of a water particle on the surface at the crest relative to the wave form 

 speed. If this parameter should equal unity, then the wave is regarded as unstable due to 

 kinematic considerations. The dynamic free surface breaking parameter is defined as the 

 ratio of the vertical acceleration of a water particle on the surface at the wave crest relative 

 to the acceleration of gravity. The interpretation is that if this parameter should equal unity, 

 then the pressure immediately under the crest would be zero and if the parameter should 



83 



