3.3 WAVE FIELD
3.31 DEVELOPMENT OF A WAVE FIELD
Varions descriptions of the mechanism of wave génération by wind hâve
been given, and significant progress in explaining the mechanism was-^reported by Miles (1957) and Phillips (1957). Integraged discussions of the
results of many of the more prominent descriptions of wave génération by
wind are given by Kinsman (1965), Phillips (1966), and Ewing (1971).
Laboratory studies, (Hidy and Plate, 1966) and (Shemdin and Hsu,
1966), carefully designed to match the assumptions made by Miles and by
Phillips show reasonably good agreement with the theoretical prédictions.
Summaries of varions filed studies, (Inoue, 1966, 1967) démonstrate that
theory provides a reasonable framework for the analysis of observations.
The Miles-Phillips theory as extended and corrected by experimental
data permits the formulation of a differential équation goveming the
growth of wave energy. This équation can be written in a variety of ways.
(Inoue, 1966, 1967) and Barnett, 1968). This approach will not be discussed
in detail because it requires a large capacity computer and more meteorological data than is likely to be found except in a major forecast center.
A brief discussion of the physical concepts employed in the computer
wave forecast, however, is presented to show the shortcomings and merits
of simpler procedures that can be used in wave forecasting.
Growth and dissipation of wave energy are very sensitive to wave
frequency and wave direction relative to the wind direction. Thus it is
désirable to consider each narrow band of directions and frequencies
separately. A change in wave energy dépends on the advection of energy
into and out of a région; transformation of the wind’s kinetic energy
into the energy of water waves; dissipation of wave energy into turbulence
and by friction, viscosity and breaking; and transformation of wave energy
at one frequency into wave energy at other frequencies.
Wave energy is discussed in Section 2.238, Wave Energy and Power.
Although it is known that energy transfers from one band of wave frequencies to another do take place, this process is secondary to the transfer
of energy from the atmosphère to the sea, and is not yet well enough understood to justify its considération in a practical wave prédiction scheme.
Phillips (1957) showed that the turbulence associated with the flow
of wind near the water would create traveling pressure puises. These
puises generate waves traveling at a speed appropriate to the dimensions
of the pressure puise. Wave growth by this process is most rapid when
the waves are short and when their speed is identical with the component
of the wind velocity in the direction of wave travel. The empirical data
analyzed by Inoue (1966, 1967) indicates that the effect of turbulent
pressure puises is real, but is only about one-twentieth as large as the
original theory indicated.
3-15
3.31 DEVELOPMENT OF A WAVE FIELD
Varions descriptions of the mechanism of wave génération by wind hâve
been given, and significant progress in explaining the mechanism was-^reported by Miles (1957) and Phillips (1957). Integraged discussions of the
results of many of the more prominent descriptions of wave génération by
wind are given by Kinsman (1965), Phillips (1966), and Ewing (1971).
Laboratory studies, (Hidy and Plate, 1966) and (Shemdin and Hsu,
1966), carefully designed to match the assumptions made by Miles and by
Phillips show reasonably good agreement with the theoretical prédictions.
Summaries of varions filed studies, (Inoue, 1966, 1967) démonstrate that
theory provides a reasonable framework for the analysis of observations.
The Miles-Phillips theory as extended and corrected by experimental
data permits the formulation of a differential équation goveming the
growth of wave energy. This équation can be written in a variety of ways.
(Inoue, 1966, 1967) and Barnett, 1968). This approach will not be discussed
in detail because it requires a large capacity computer and more meteorological data than is likely to be found except in a major forecast center.
A brief discussion of the physical concepts employed in the computer
wave forecast, however, is presented to show the shortcomings and merits
of simpler procedures that can be used in wave forecasting.
Growth and dissipation of wave energy are very sensitive to wave
frequency and wave direction relative to the wind direction. Thus it is
désirable to consider each narrow band of directions and frequencies
separately. A change in wave energy dépends on the advection of energy
into and out of a région; transformation of the wind’s kinetic energy
into the energy of water waves; dissipation of wave energy into turbulence
and by friction, viscosity and breaking; and transformation of wave energy
at one frequency into wave energy at other frequencies.
Wave energy is discussed in Section 2.238, Wave Energy and Power.
Although it is known that energy transfers from one band of wave frequencies to another do take place, this process is secondary to the transfer
of energy from the atmosphère to the sea, and is not yet well enough understood to justify its considération in a practical wave prédiction scheme.
Phillips (1957) showed that the turbulence associated with the flow
of wind near the water would create traveling pressure puises. These
puises generate waves traveling at a speed appropriate to the dimensions
of the pressure puise. Wave growth by this process is most rapid when
the waves are short and when their speed is identical with the component
of the wind velocity in the direction of wave travel. The empirical data
analyzed by Inoue (1966, 1967) indicates that the effect of turbulent
pressure puises is real, but is only about one-twentieth as large as the
original theory indicated.
3-15