and 



FIND ; The height of the wave H assuming that linear theory applies and the 

 average frequency corresponds to the average wave amplitude. 



SOLUTION ; 



1 1 



T = - = ^ 15 s 



f (0.0666) 



L = 1.56t2 = 1.56(15)2 = 351 m (1152 ft) 

 o 



d 12 



— = * 0.0342 



L 351 

 o 



From Table C-1 of Appendix C, entering with d/L , 



d 



- = 0.07651 

 L 



hence , 



12 



L = = 156.8 m (515 ft) 



(0.07651) 



/2iTd\ 

 cosh = 1.1178 



Therefore, from equation (2-29) 



^ cosh[2Tr(z + d)/L] _ cosh[2Tr[-ll .4 + 12)/156.8] _ 1.0003 _ 

 z~ cosh(2Trd/L) ~ 1.1178 1.1178 ~ * 



Since n = a = H/2 when the pressure is maximum (under the wave crest), 

 and N = 1.0 since linear theory is assumed valid, 



H _ N(p + pgz) _ 1.0 [124 + (10.06) (-11.4)] _ , nA ,. r-^ A^ ft^ 



2 ^iK (10.06) (0.8949) ^'^"^ "^ ^^-"^"^ ^""^ 



z 



Therefore, 



H = 2(1.04) = 2.08 m (6.3 ft) 



Note that the tabulated value of K in Appendix C, Table C-1, could not be 

 used since the pressure was not measured at the bottom. 



*************************************** 



g. Velocity of a Wave Group . The speed with which a group of waves or a 

 wave train travels is generally not identical to the speed with which individ- 

 ual waves within the group travel. The group speed is termed the group veloc- 

 ity C ; the individual wave speed is the phase velocity or wave celerity 



2-23 



