Figure 2.8. Vertical variation of vertical velocity under a steep wave front across the 

 armor layer as a function of wave steepness 



The drag and inertia coefficients can be more accurately defined if we 

 assume spherical armor. Based on previous studies of forces on armor by Mizutani et 

 al. (1992) and Torum (1994), reasonable estimates for drag and inertia coefficients are 

 Co = 0.8 and C„ = 0.4 yielding 



C'z,= 



KXr 



= 0.5 {K, = 1.21) 



(2.13) 



C'=KC^ = 0.36 {K^ = 0.90) 



mem ^ c ^ 



(2.14) 



where ^^ = 1.21 corresponds to a sphere. The critical vertical velocity, v^., for the 

 incipient vertical armor movement reduces to 



27 



