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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?

c1?gTgT1gT?31.2m/s,c2?2?15.6m/s,c3?3?23.4m/s2?2?2?

LLLL?t1???64103s?17.81h,?t2???21368s?5.93hc2c1c3c1The 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：

gT2T?15s,H?2m,h?8m,L?2?k?4?2dtanh(2)?132.82mTg2?L1?2kh??0.0473m?1,c??8.855m/s,n??1??0.955LT2?sinh2kh??

deep water： gTc0?0?23.41m/s

2?sin?0sin?c0cos?0?,??10.9?,Hi?H0?2.21m c0c2cncos?