| The structural dimensions of the net cage are constantly increasing,and the workplace is gradually shifting towards deep and distant seas.The hydrodynamic calculation methods have many limitations when facing increasingly complex and intense environmental loads.In order to meet the needs of current engineering development,a hydrodynamic calculation model for cage floating collar based on strip theory has been developed,which can calculate nonlinear hydrodynamic forces.The purpose is to adapt to different calculation conditions,reduce the dependence on empirical coefficients and model tests,and consider the nonlinear components in the hydrodynamic forces while quickly and accurately calculating the hydrodynamic forces of floating collar.A program for calculating the hydroelastic response of a net cage has been developed based on the mature computing model.In order to accurately calculate the impact of the load instantaneity,the impulse response function is introduced.The impulse response function is used to transform the motion equation of the floating collar in the frequency domain into the motion equation in the time domain,and the memory effect of the hydrodynamic force is considered,so that the calculation results of the transient response of the structure under load are more accurate.Based on this point,this program can be used to calculate and evaluate the transient response of net cage under instantaneous and strong nonlinear loads,as well as their impact on net cage.The calculation model and program developed above were gradually and hierarchically verified through a series of numerical examples.Firstly,an example of a nearly rigid floating collar is used to verify the hydrodynamic calculation model of the floating collar;Secondly,an example of a flexible floating collar was used to further validate the hydrodynamic calculation model of the floating collar,while also verifying the program’s floating collar hydroelastic response calculation module;Finally,an example of the coupled calculation of the floating collar and net clothing verifies the hydrodynamic and hydroelastic response calculation modules of the program.The verification results show that the calculation model is accurate and effective,and the calculation program is stable and fast.Although there may be some errors in the calculation when the three-dimensional hydrodynamic effect generated by the structure is strong,it can meet the requirements of engineering applications.Based on the validated program,the nonlinear hydroelastic response of the cage was studied.In the current calculation example,the nonlinear characteristics of the floating collar hydrodynamic force are not obvious.However,by comparing the steady-state solutions obtained by the program through the frequency domain motion equation and the time domain motion equation,the correctness of the pulse response function based motion equation frequency conversion solution method adopted by the program is theoretically verified.The slap load phenomenon caused by the cage structure is worth paying attention to,as it can cause the tension of the mesh to increase several times in an instant.According to the analysis of the calculation results,although the impact of slap load on the response of the floating collar structure is limited,it has potential destructive effects on the mesh,and is worthy of attention and further research in engineering. |
