EM 1110-2-1100 (Part II)
30 Apr 02
Figure II-7-41. Typical vessel-generated wave record
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
F'
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
C ' 5.157 cos (33.88E) ' 4.28 m/s
The linear wave dispersion equation can be written
gT
2π d
C'
tanh
2π
CT
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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