Experimental study on the mooring forces and motions of a fish cage under regular waves.

Experiments are conducted in a flume to study the mooring forces and motions of a gravity cage in regular waves. Cage models are built with hollow pipes and nets. Mooring forces and cage motions including surge, heave and pitch are measured. With the increase of the wavelength, the mooring force, surge and heave increase while the rate of increase gradually slows down until stops. On the other hand, under short waves, the pitch increases with the decrease of the wavelength. In addition, the cage does not finish a cycle of motion before the next peak arrives, which leads to a reduction in mooring forces and motion in all directions. With the observation of overtopping, it can be concluded that the motion of the cage goes through three phases with the growth of the wavelength. Under short waves, the cage does not have enough time to complete a cycle of motion and overtopping occurs. With the increase of the wavelength, the motion of the cage starts to follow the waves and overtopping disappears. When the wave is long enough, the cage is pulled into the water by the mooring line and overtopping occurs again. • Experiments are conducted in a flume to study the mooring force and motion of a gravity cage subjected to regular waves. • A light and strong frame is designed to fix a motion sensor above the collar. Mooring forces and cage motions are measured. • Under short waves, the cage does not have enough time to complete a cycle of motion and overtopping occurs. • With the increase of the wavelength, the motion of the cage starts to follow the waves and overtopping disappears. • When the wave is long enough, the cage is pulled into the water by the mooring line and overtopping occurs again. [ABSTRACT FROM AUTHOR]