(n is the ratio of wave group celerity to phase celerity) , 6 is the local 

 wave direction (defined as shown in Figure 8) , and E is the wave energy 

 density. The values of H , k , and 6 are obtained from RCPWAVE. 



52. Lateral shear. In the numerical model, the coordinate scheme is 

 chosen such that x is positive in the offshore direction and y is approxi- 

 mately in the alongshore direction. An eddy viscosity formulation is chosen 

 for the lateral shear. The eddy viscosity is assumed to be anisotropic. 

 Denoting e and e as the eddy viscosities in x- and y-dlrections, respec- 

 tively, in general, e is assumed to be a function of x and y and e a 

 X y 



constant. Accordingly, 



xy 



\ y 3y X 8x/ 



For field applications, the eddy viscosity e is chosen according to the 

 following relation given by Jonsson, Skovgaard, and Jacobsen (1974): 



2 

 e = S_|I cos^ e (55) 



Air h 



This represents twice the value used by Thornton (1970). The value of e 

 was, in general, taken to be equal to the value of t at the deepest part 

 (usually near the offshore boundary) of the numerical grid. 

 Method of solution 



53. In view of the similarity among Equations 44-46 and the equations 

 for long waves (Equations 7-9) , CURRENT was developed by modifying WIFM. Thus 

 CURRENT also is an implicit finite difference model and uses the SC scheme 

 described previously. Details of the method of solution can be found in 

 Vemulakonda (1984). 



Initial and boundary conditions 



54. In order to solve the problem under consideration, appropriate 

 initial and boundary conditions must be specified. Usually an initial condi- 

 tion of rest is chosen so that ri , U , and V are zero at the start of the 

 calculations. To avoid shock, the radiation stress gradients are gradually 

 built up to their full values over a number of time-steps. The numerical 

 computation is stopped when a steady state is deemed to have been reached. 



34 



