3.4 Basic Waves Characteristics
a
wave , crest
, x+L
A
-------- ----,- -:x- -still water :
level
- : - - - - - - - - -wave trough - - - - - - - - -:bottom
b
--~ -------------:t --"
still water
level
' .
wavelength L
.: h
, t + T
,
------Th
wave period T
83
---------~
time
Fig. 3.2: Vertical profile of idealized sinusoidal surface wave: a at a given instant of
time, b at a given location
The frequency, f, is measured in hertz, Hz, and 1 Hz = 1 cycle/so Apart from
frequency, the angular frequency, W, is used in this book. It is expressed as
the number of radians per second. We note that 1 radian = 360 0 /27r rv 57.30.
Therefore, the wave motion with frequency, f, has an angular frequency, w,
equal to:
27r
W = 27rf = - .
T
(3.3)
The profile of real wind induced waves is not necessary regular and periodic,
but is usually very irregular and random. We will discuss random, irregular
waves in Sect. 3.5 and 4.3.
In this book we will frequently distinguish between deep and shallow water
depths, in the context of surface waves. Water is considered 'deep' when water
depth is larger than half of the wavelength. Otherwise water is treated as
'shallow'. Thus, if the water basin is deeper than one half wavelength, the