| Summary: | The flow field behavior in the vicinity of a perforated breakwater and the
efficiency of the breakwater under regular waves were studied.
To examine the efficiency of the structure thirteen types of regular wave
conditions with wave periods T = 1, 1.2, 1.6, 2, 2.5 sec and wave heights Hi = 2, 4, 6, 8,
10 cm in an intermediate water depth of 50 cm were tested. The incoming, reflected and
transmitted wave heights were measured using resistance type wave gauges positioned at
the required locations. The efficiency of the structure was calculated considering the
energy balance for the system. The efficiency of the structure for different wave
conditions and with different parameters are shown and compared.
Seven types of regular waves with wave periods T = 1, 1.6, 2, 2.5 sec and wave
heights Hi = 4, 6, 8, 10 cm in an intermediate water depth of 50 cm were tested for the
flow behavior study. In order to study the flow field variation with phase, ten phases
were considered per one wave. The Particle Image Velocimetry (PIV) technique was
employed to measure the two dimensional instantaneous velocity field distribution and
MPIV (Matlab toolbox for PIV) and DaVis (a commercial software) were used to calculate the velocity vectors. By repeating the experiments and taking an average, the
mean velocity field, mean vorticity field, mean turbulent intensity and mean turbulent
kinetic energy field were calculated for each phase and for each wave condition. The
phase average fields for each wave condition for each of the above mentioned
parameters were calculated taking the average of ten phases. The phase averaged
velocity, vorticity and turbulent kinetic energy fields are presented and compared. The
energy dissipation based on both elevation data and the velocity data are presented and
compared.
It was found that for more than 75% of the tested wave conditions, the energy
dissipation was above 69%. Thus the structure is very effective in energy dissipation.
Further it was found that for all the tested wave conditions most of the turbulent kinetic
energy form near the free surface and near the front wall, where as behind the back wall
of the structure the turbulent kinetic energy was very small.
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