19 



The remarks previously made concerning the accuracy of measure- 

 ment are applicable also to these shallow-water wave tests. 



The measured values of wave velocity and wave length, for each 

 wave studied, are compared to the corresponding values computed from 

 theory in table 8. Columns 2 and 3 list the wave velocity and wave 

 length as computed by the Laplace-Airy (trochoidal) theory, where: 



^'""27 



^ u 27rc? 



tanh —J- 



(11) 



and: 



■L't — ^tJ-m 



Tot is the measured period which is assumed to have been correctly 

 determined. Columns 4 and 5 list the percentage differences between 

 measured and theoretical values. It will be noted that the agreement 

 between the measured values and the theoretical values derived from 

 the Laplace-Airy formulae is not as close as for the deep-water 

 waves, varying as much as about 6.5 percent. 



Table 8. — Shallow-water waves i j <C0.5 j — comparison of measured to theoretical 



velocity and length 



The theoretical values for wave velocity and wave length computed 

 by the formulae of the Stokes-Struik theory, where 



C/- 



.gTr 



27rd 



L '~ . 



2irdr~ 



27rd 



2ird 



e ^ ~^e ^ 



8ird _8ird / ijrd 4a-(/\ 



2ird 27rci\4 



) 



/ 27rd 



(12) 



and: 



L t — tT-n 



are given in columns 6 and 7. 



