322
Coastal Engineering: Theory and Practice
executed for different combinations of wind and current fields as mentioned
below.
(1) Constant wind blowing over the entire région in the absence of current
field
(2) Constant wind in addition to in-line current field
(3) Constant wind over opposing current field
A 10 m/s constant northerly wind was assumed to blow over the région.
An initial wave was set up with the same wind condition and the simulation
carried out for forty-eight hours until the steady State was attained. In the
second case, with the above wind field, a constant in-line current of 5 m/s
was assumed to be présent. In the last case, a constant opposing current
field of 5 m/s was assumed. The current direction in the second condition
was the same as the wind direction while, in the last condition, it was 180°
out-of-phase with the wind direction.
The simulated wave field was analysed for estimated spectral parameters, significant wave height, Hs and peak wave period, Tp. The variation of
the said two wave characteristics which approaches asymptotic values are
projected in Fig. 10.2. A comparison of wave characteristics derived from
WAM with the wave spectral model and SMB prédiction curves [Sverdrup
and Munk (1947), Bretschneider (1952, 1958), US Army Coastal Engineering Research Centre (1977)] is presented in Table 10.1 for the constant wind
condition. Table 10.2 présents the variation in the wave parameters in the
presence of in-line and opposing current field are reported in Table 10.2,
whereas, the spectra for the three cases are shown in Fig. 10.3. It can be
seen that the in-line current field reduces the wave height and shifts the
peak frequency towards higher harmonies. The opposing current field however resulted in the steepening of the waves by focusing on the narrow
band of frequencies. The frequency components were shifted towards lower
harmonies.
Table 10.1. Variation of simulated wave estimâtes under the action of
constant wind and current fields.
S. No.
External forcing
WAM Wave spectral model SMB
1.
Significant Wave height
2.14
2.14
2.14
2.
Peak wave period
7.44
7.4
7.69
Coastal Engineering: Theory and Practice
executed for different combinations of wind and current fields as mentioned
below.
(1) Constant wind blowing over the entire région in the absence of current
field
(2) Constant wind in addition to in-line current field
(3) Constant wind over opposing current field
A 10 m/s constant northerly wind was assumed to blow over the région.
An initial wave was set up with the same wind condition and the simulation
carried out for forty-eight hours until the steady State was attained. In the
second case, with the above wind field, a constant in-line current of 5 m/s
was assumed to be présent. In the last case, a constant opposing current
field of 5 m/s was assumed. The current direction in the second condition
was the same as the wind direction while, in the last condition, it was 180°
out-of-phase with the wind direction.
The simulated wave field was analysed for estimated spectral parameters, significant wave height, Hs and peak wave period, Tp. The variation of
the said two wave characteristics which approaches asymptotic values are
projected in Fig. 10.2. A comparison of wave characteristics derived from
WAM with the wave spectral model and SMB prédiction curves [Sverdrup
and Munk (1947), Bretschneider (1952, 1958), US Army Coastal Engineering Research Centre (1977)] is presented in Table 10.1 for the constant wind
condition. Table 10.2 présents the variation in the wave parameters in the
presence of in-line and opposing current field are reported in Table 10.2,
whereas, the spectra for the three cases are shown in Fig. 10.3. It can be
seen that the in-line current field reduces the wave height and shifts the
peak frequency towards higher harmonies. The opposing current field however resulted in the steepening of the waves by focusing on the narrow
band of frequencies. The frequency components were shifted towards lower
harmonies.
Table 10.1. Variation of simulated wave estimâtes under the action of
constant wind and current fields.
S. No.
External forcing
WAM Wave spectral model SMB
1.
Significant Wave height
2.14
2.14
2.14
2.
Peak wave period
7.44
7.4
7.69