4 How to Determine Wave Parameters
4.1 Introduction
In Chap. 3 various types of surface waves were described. Each of them possess
their own properties, and different techniques should be used for prediction of
these properties. However, some characteristics of all waves are common and
can be used to distinguish between various wave types. The most important
characteristics are relative wavelength (L / h), relative wave height (H / h) and
wave steepness (H / L ).
Depending on relative wavelength, waves can be classified as short, long or
intermediate:
long waves (shallow water waves)
when
waves on intermediate water depth when
short waves (deep water waves)
when
L
h> 10 (or 20)
L
2 < h < 10 (or 20)
L
- < 2
h
(4.1)
In shallow water areas, the wavelength is much larger than water depth and
therefore long waves are sometimes known as shallow water waves.
The relative wave height (H / h) and wave steepness (H / L) provide some
guide as to what kind of method should be used to calculate various wave
parameters. The complexity of prediction methods strongly depends on the
boundary conditions which should be satisfied in the calculations. Boundary
conditions usually describe the continuity (or lack of such continuity) of physical
quantities such as pressure or velocity, when crossing the boundary between
different media, e.g. when going from air into water or from water on the sea
bottom.
When the surface upon which the boundary conditions have to be imposed
is simple, the calculations simplify considerably. In wave analysis, the most
difficult boundary conditions are those at the sea surface. This results from
the fact that the displacement of the sea surface, (, is unknown a priori and
has to be found in the calculations. However, when relative wave height (H /h)
and wave steepness (H / L) are small, we can assume that the sea surface does
S. R. Massel, Fluid Mechanics for Marine Ecologists
© Springer-Verlag Berlin Heidelberg 1999
4.1 Introduction
In Chap. 3 various types of surface waves were described. Each of them possess
their own properties, and different techniques should be used for prediction of
these properties. However, some characteristics of all waves are common and
can be used to distinguish between various wave types. The most important
characteristics are relative wavelength (L / h), relative wave height (H / h) and
wave steepness (H / L ).
Depending on relative wavelength, waves can be classified as short, long or
intermediate:
long waves (shallow water waves)
when
waves on intermediate water depth when
short waves (deep water waves)
when
L
h> 10 (or 20)
L
2 < h < 10 (or 20)
L
- < 2
h
(4.1)
In shallow water areas, the wavelength is much larger than water depth and
therefore long waves are sometimes known as shallow water waves.
The relative wave height (H / h) and wave steepness (H / L) provide some
guide as to what kind of method should be used to calculate various wave
parameters. The complexity of prediction methods strongly depends on the
boundary conditions which should be satisfied in the calculations. Boundary
conditions usually describe the continuity (or lack of such continuity) of physical
quantities such as pressure or velocity, when crossing the boundary between
different media, e.g. when going from air into water or from water on the sea
bottom.
When the surface upon which the boundary conditions have to be imposed
is simple, the calculations simplify considerably. In wave analysis, the most
difficult boundary conditions are those at the sea surface. This results from
the fact that the displacement of the sea surface, (, is unknown a priori and
has to be found in the calculations. However, when relative wave height (H /h)
and wave steepness (H / L) are small, we can assume that the sea surface does
S. R. Massel, Fluid Mechanics for Marine Ecologists
© Springer-Verlag Berlin Heidelberg 1999