Experimental Study on Mooring Tension of Porous-Slope Type Floating Breakwater

Abstract

Floating breakwater is an alternative structure to fixed breakwater because of its effectiveness in coastal areas. Under certain conditions, floating breakwater is more flexible in design and more accessible in installation. The fundamental aspect of floating breakwater design is the mooring system to keep in position and determine the system's performance. This study uses physical modeling to determine the magnitude of maximum mooring stress on a mooring line. Moreover, several slope-porous floating breakwaters and pontoon types are examined. The floating breakwater model is constructed from polylactic acid, while the mooring line uses polyethylene. The physical experiment and testing are carried out in a wave flume with regular waves under several variations of wave height, wave period, slope angle, and porosity. It is cultivated that the mooring stress on the seaward position is always greater than on the leeward position since the seaward side will receive the first wave force, and the mooring line will dampen the wave force on the seaward side. However, the pontoon receives higher maximum mooring stress than the other models due to incoming wave forces that arrive on a vertical surface perpendicular to the direction of the waves. On the other hand, floating breakwaters with 5% porosity provide lower mooring stress than non-porous breakwaters. The greater the porosity is, the smaller the mooring forces are. The floating breakwater with 5% porosity can reduce the mooring stress by 16.5% (45 deg) and 13.5% (60 deg). At a slope of 45 deg, the maximum mooring stress received by the floating breakwater will increase by 8.5% and 5.3%, respectively, at 0% and 5% porosity.