Chemistry Reference
In-Depth Information
(a)
40
30
20
1
2
3
4
Wavenumber, rad/cm
(b)
1.00
0.10
0.01
1
2
3
4
Wavenumber, rad/cm
Fig. 2.
Phase velocities and relative amplitudes of harmonics of a short gravity
wave with a wavelength 7.5 cm.
Fig. 2a
: i- measured velocity, solid line -linear
theory.
Fig. 2b:
wave amplitude 0.6mm (Ÿ) and 3mm (Ŷ), solid lines - Stocks
theory
Obviously, the phase velocities of high-order harmonics with wave-
lengths
L/n
are equal to the phase velocity of the basic harmonic (
n=1
), so
that these harmonics can be considered as bound to the basic wave. The
measured harmonic amplitudes for the second and third harmonics are
found to be in good agreement with Stokes theory. The amplitude of the
4th harmonic
a
IV
is about 2 times larger than that in theory; this is, as we
assume, because the Stokes expansion is not valid for strong gravity waves
with asymmetric slopes and parasitic capillary ripples propagating along
the forward wave slopes.
3.1.2 Wind waves
The wave number-frequency spectrum of wind waves was measured at
low wind velocity, 2.5 m s
-1
, and at two different fetches. Dominant dm-
cm-scale wind waves are steep enough and are characterized by asymmet-
ric profile and parasitic ripples generation even at such a low wind veloc-
ity, so that we expect that nonlinear effects can be quite strong. Co-located
measurements of wave height were conducted using a wave gauge. The
