Fully Nonlinear Numerical Simulation On A Moored Floating Body Undergoing Large-amplitude Motion In Waves

Marine structures are the tools that we used to exploite and utilize marine resources,and they are always accompanied by complex marine environment conditions during its services.It is easy to cause adverse loads and strenuous exercise of structures.Therefore,it is important to predict the maximum wave loads that the structures may suffered at the design stage.Based on the higher-order Rankine boundary element method,a fully nonlinear model for the interaction of water waves and three-dimensional structure in a open circular domain has been developed by using a open sea simulation technique together with a velocity potential separation technique.A simple Rankine source Green function is used to discretize the fluid domain;And a direct calculation method is established to deal with the problem of singular integrals in the Cauchy principal value;Take advantage of the space angle geometry relationship,the value of solid angle coefficient is solved directly.In this model,the incident wave is simulated by higher-order Stokes wave theory,and the reflected wave is eliminated by damping layer arrangement technique.The mixed Euler-Lagrangian method is adopted to track the free surface and a following updating method is utilized to rearrange the element nodes on the instantaneous free surface.Using the surface mesh reconstruction technique to capture and simulate the shape of the grid element on the wet surface of the instantaneous hull.The auxiliary function method is introdured for calculate nonlinear wave loads of structures indirectly.With the established nonlinear model,several numerical simulations are carried out for wave diffraction around a fixed vertical cylinder,the nonlinear wave response of a floating cylinder structure,the fully nonlinear hydrodynamic responses of Wigley ship hull and the influence of mooring system on the nonlinear response of the JIP Spar platform.The numerical results are in good agreement with physical experimental data and published simulation results.In this way,we can firmly make sure the ability to accurately capture the instantaneous free surface and the wet body surface shape of the developed nonlinear analytical model,as well as the ability to accurately simulate the fully nonlinear fluid force.By comparing simulations of fully nonlinear response of the JIP Spar platform in mooring and unconstrained condition,it is found that,the mooring system can also suppress the heave and pitch nonlinear response of the platform.