EXAMPLE PROBLEM II-7-5

FIND:

The period of the *diverging *waves generated by the vessel.

GIVEN:

A vessel is moving at a speed of 10 knots (5.157 m/sec) over water 5 m deep.

SOLUTION:

The vessel Froude number is

5.157

' 0.73

9.81 (5)

so Equation II-7-23 gives a direction of propagation

θ ' 35.27 [1 & *e * 12 (0.73&1)] ' 33.88E

and Equation II-7-21 gives a wave celerity

The linear wave dispersion equation can be written

2π *d*

tanh

2π

Inserting known values for *C*, *g*, and *d *into the dispersion equation leads to a trial solution for *T *of 2.8

sec. This is a typical period for vessel-generated waves and demonstrates why floating breakwaters are

usually effective in protecting against vessel waves.

II-7-56

Harbor Hydrodynamics

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