Numerical simulation of forces and motion deformation of deep-water net cages in waves and currents

Abstract

This study is aimed to discuss the effects of waves combined with currents on forces and motion deformation of deep-water net cages,and provides a strong reference to risk assessment for net-cage aquaculture with severe marine conditions.The set value of wave and current elements were as follows:wave heights H=4-6 m,wave periods T=6.0-8.6s,current velocities U=0.3-0.9 m/s.With a numerical model previously validated by physical model tests,the mooring line forces,the wave-current forces,the volume reduction rate and the floating-collar pitches of the deep-water net cage were calculated.The simulated results indicated that the mooring line force,the wave-current force and the volume reduction rate were all in direct proportion to wave height as well as current velocity,but less related to wave period.Furthermore,the wave-current force on the cage was approximately equal to the sum of force on each mooring line on wave-side.The volume reduction rate reached 47%-56% for the cage caused by the conditions of wave height of 4 6 m and current velocity of 0.75m/s,which showed serious cage deformation.Therefore,we concluded that farming sites should not be placed in sea areas where current speed exceeded 0.75 m/s.The calculated results also showed that the influence of wave period on volume reduction rate was slight,while significant on the floating-collar pitch.The floating-collar pitch would decrease as wave period increasing at constant wave height and current velocity.