Surface gravity water waves 161
PROBLEM 6.4
Make the suggested changes in the computer code while keeping the rest of
the data constant:
1. Change the reflection coefficient to zero (absorption) and one (full
reflection). Conduct the simulations, and then compare and comment
on the results.
2. Change the eddy viscosity parameter from 0.8 to 0.2 and 1.2. In
addition, change the right and left boundary conditions to reflection
instead of free radiation. Conduct the simulations, and then compare
and comment on the results.
3. Remove a 30 m central section of the breakwater leaving two sections
of 30 m each. Conduct the simulation and comment on the changes
of the wave and current pattern.
4. Make the water depth constant and equal to 6 metres. Run the simulation for three different breakwater reflection scenarios (rf = 0, 0.5
and 1) and comment on the results.
5. Run the simulation by changing the direction of wave incidence to
30°. Then change the lateral size of the solution domain from 180 m
to 1440 m and run the simulation again. Compare and comment on
the results obtained from the two simulations.
6.4 HARBOUR BASIN RESONANCE
An important operational problem pertaining to certain scale-size water
basins is the investigation of the eigen periods and eigenmodes of oscillation and the avoidance of resonance. Eigen periods are the natural periods
of oscillations of water bodies. The phenomenon of resonance refers to
a substantial increase of the amplitude of oscillation of the basin water
masses that have the tendency to oscillate according to natural periods of
oscillation, when they are triggered by an external periodic pulse having
the same period as one of the natural periods. The recognition of those
periods is important in the design of harbours in order to avoid the resonance phenomenon caused by long incident waves generating and propagating from the open sea to the harbour entrance. It is also important in the
analysis of storm surges, that is, the meteorologically induced long waves
on the water masses of coastal basins or lakes.
The system of equations that can be used to model the phenomenon of basin
resonance is the one developed for gravity long waves. This system comprises
of Equation 6.13 and Equation 5.24 re-written as
∂
∂
+
∂
∂
= −
∂
∂
−
u
t
u
u
x
g x
f
u u
h
b
ζ
(6.26)
PROBLEM 6.4
Make the suggested changes in the computer code while keeping the rest of
the data constant:
1. Change the reflection coefficient to zero (absorption) and one (full
reflection). Conduct the simulations, and then compare and comment
on the results.
2. Change the eddy viscosity parameter from 0.8 to 0.2 and 1.2. In
addition, change the right and left boundary conditions to reflection
instead of free radiation. Conduct the simulations, and then compare
and comment on the results.
3. Remove a 30 m central section of the breakwater leaving two sections
of 30 m each. Conduct the simulation and comment on the changes
of the wave and current pattern.
4. Make the water depth constant and equal to 6 metres. Run the simulation for three different breakwater reflection scenarios (rf = 0, 0.5
and 1) and comment on the results.
5. Run the simulation by changing the direction of wave incidence to
30°. Then change the lateral size of the solution domain from 180 m
to 1440 m and run the simulation again. Compare and comment on
the results obtained from the two simulations.
6.4 HARBOUR BASIN RESONANCE
An important operational problem pertaining to certain scale-size water
basins is the investigation of the eigen periods and eigenmodes of oscillation and the avoidance of resonance. Eigen periods are the natural periods
of oscillations of water bodies. The phenomenon of resonance refers to
a substantial increase of the amplitude of oscillation of the basin water
masses that have the tendency to oscillate according to natural periods of
oscillation, when they are triggered by an external periodic pulse having
the same period as one of the natural periods. The recognition of those
periods is important in the design of harbours in order to avoid the resonance phenomenon caused by long incident waves generating and propagating from the open sea to the harbour entrance. It is also important in the
analysis of storm surges, that is, the meteorologically induced long waves
on the water masses of coastal basins or lakes.
The system of equations that can be used to model the phenomenon of basin
resonance is the one developed for gravity long waves. This system comprises
of Equation 6.13 and Equation 5.24 re-written as
∂
∂
+
∂
∂
= −
∂
∂
−
u
t
u
u
x
g x
f
u u
h
b
ζ
(6.26)