Xt/Ho 



0.0 0.5 



3.0 3.5 



Figure 53. X t /H as a function of £ c 



Breaker Vortex 



151. The breaker vortex is formed when air becomes entrapped by the 

 overturning crest at the plunge point. As the vortex penetrates the water 

 column, the angular velocity of the vortex decreases and the cross -sectional 

 area A„ of the vortex becomes greater, until the energy is dissipated. 

 Because the vortex area increases as the vortex moves into the water column, 

 measurements of A^ were made at a distinct location. The plunge point is 

 unique to all breaking waves and is also the location of vortex formation; 

 therefore, A^ was measured at this point. The shape of the vortex was 

 elliptical in most cases (Figure 7); the major and minor axes of the vortex 

 were measured, and the equation for an ellipse was used to estimate vortex 

 area. 



152. Vortex area was estimated for 34 tests with seaward angles less 

 than 10 deg. Vortex area normalized by deepwater wave height was plotted as a 

 function of £ in Figure 54, which shows A^/H^ is small for spilling 

 breakers and larger for plunging and collapsing breakers. Although only three 

 cases in the collapsing range were available for analysis, the data show the 

 trend represented by the visually fit equation 



106 



