ANALYSIS OF LONG-CIRCUIT TYPE CAISSONS FOR ATTENUATION OF LONG-PERIOD WAVES

Abstract

Breakwaters provide convenient shelter for short-period waves, thus limiting the amount of energy entering the harbor. This wave energy in the port basins may be amplified, due to the wave reflection, disturbing port operations. Anti-reflective Jarlan-type (ARJ) structures (see Jarlan, 1961) have been proposed in the literature, along with other structures, to alleviate wave disturbance within port basins. ARJ anti-reflective mechanism is based on the destructive interference of waves. An anti-reflective zone width, B, must be almost a quarter of the wavelength for maximum efficiency. Longer waves easily enter the port-sheltered area where resonance phenomena could magnify its energy under certain conditions. This low-frequency energy is much more difficult to dissipate. Port resonance is the phenomenon of energy amplification that takes place in a harbor or port basin if the incident waves have frequencies close to those of the natural oscillation of the mass of water in the port basin. These infragravity long waves are frequently reported as causing trouble in cargo handling areas of many ports (see Rabinovich, 2009), even causing breakages of mooring lines and other relevant damage (see Thotagamuwage and Pattiaratchi, 2014).