248
P. Liu
The total energy per wavelength is
e T =
E P + E K
λ
=
1
2
ρg A
2
If the potential flow of an ideal fluid is considered, then
u =
∂φ
∂ x
, v =
∂φ
∂ y
Kinetic energy is
E k =
1
2
ρ
λ
0
η
−H
∂φ
∂ x
2
+
∂φ
∂ y
2
dxdz
3.8.3 Types of Waves
Waves in the ocean are of various types, shapes, and names. The disturbing
forces of waves are: sun, moon, storm, earthquake, wind, etc.; the restoring
forces are: Coriolis force, gravity, surface tension, etc. Among the ocean
waves, the wind-induced gravity wave is the main one, also known as wind
wave.
(1) according to the cause of formation and frequency classification, there
are: surface tension wave with frequency less than 10 Hz; short period
gravity wave with frequency 1–10 Hz; gravity wave with frequency 1/30–
1 Hz; long period gravity wave with frequency 1/300–1/30 Hz; long
wave with frequency 1/8.64 × 10-4-1/300 Hz; inertial wave and Star
wave with frequency greater than 1/8.64 × 10-4 Hz.
(2) according to the interference force, there are wind waves, tide waves, ship
waves, etc.
(3) according to the excitation force, there are free wave and forced wave. For
example, the waves in still water caused by rocks are free waves. It refers
to the wave after the cancelation of the interference force. The propagation and evolution of the wave are only restricted by the nature of water.
The forced wave refers to the wave which is continuously acted by the
interference force. The operation of the forced wave is restricted by the
interference force and the nature of water. Tidal wave is a kind of forced
wave.