Homework(6)
1.Make some calculations to evaluate the possibility that long-period but
low-amplitude forerunner (T=20sec) might be used to predict the imminent arrival of short-period (T=10 to 15sec) waves of large heights. For example, how much warning time will the forerunners give if the storm distance is 2000km?
c 1=gT gT 1gT =31.2m /s , c 2=2=15.6m /s , c 3=3=23.4m /s 2π2π2π L L L L ∆t 1=-=64103s =17.81h , ∆t 2=-=21368s =5.93h c 2c 1c 3c 1
The warning time is from 5.93h to 17.81h.
2.A wave of 2m height in deep water approaches shore with straight and parallel contours at a 30° angle and has a wave period of 15s. In water of 8m, what is the direction of the wave and what is its wave height?
In water of 8m：
T =15s , H =2m , h =8m , L ≈k ==132.82m 2πL 1⎡2kh ⎤=0.0473m -1, c ==8.855m /s , n =⎢1+=0.955L T 2⎣sinh 2kh ⎥⎦
deep water：
gT c 0=0=
23.41m /s 2π
sin α0sin α=, α=10.9︒, H i =H =2.21m c 0c