Wave Refraction and Energy Attenuation Properties of Underwater Curved Breakwaters and Their Potential Application for Coastal Defence

An investigation was carried out to determine
the energy-dissipating effects of submerged curved
planform breakwaters on water waves. The submerged
breakwaters are of the shape of planoconvex and
planoconcave optical lenses in planform. Physical
modeling involving small-scale structures in a wave tank
was done.
The general concept is to make use of the refractive
effects of the contours of these shapes to refract and
cause converging or diverging of water waves so that
they undergo superposition after passing over the
shapes. When the waves superpose constructively their
heights will increase according to the principle of
superposition and, if the wave-breaking criteria for deep
to shallow water are reached, breaking will occur and
the wave energy will be dissipated in the lee of the
submerged breakwaters. This will help to reduce wave
impacts on coastal structures and on vulnerable
shorelines by using an unobtrusive and aesthetic means
of coastal protection.
The research involved measuring the wave heights
of incident waves in front of the submerged structures
and the wave heights of transmitted waves in the lee. In
this way, the incident and transmitted wave energy
density can be obtained to determine the wave
transformations that may have been caused by the
breakwaters. Energy loss coefficients were also
computed. Comparisons were done with the wave energy
transformations produced by rectangular planform
submerged breakwaters of comparable size.
Generally, it was found that all three types of
breakwaters dissipated wave energy, with the
planoconcave ones performing the least and the
rectangular ones the best. The planoconvex breakwaters
performed comparably to the rectangular ones, showing
only slightly smaller energy density dissipations and loss
coefficients.
So, it is possible for planoconvex breakwaters to
replace rectangular ones and give comparable energy
attenuation performance for a lower cost and fewer
building materials.