Study On Hydrodynamic Response Of A Floating Crane Vessel Based On Multi-systems Coupling Model

Floating cranes play an important role in the installation of offshore engineering.The motion of crane vessel not only affects the comfort of ship’s crew,but also directly affects the efficiency and safety of the lifting operation.Therefore,it is necessary to analyze the hydrodynamic response of a floating crane vessel based on multi-systems coupling model and apply it to the design and operation of floating crane.In this paper,we take the model of revolving crane vessel “LANJING” as the model,the floating crane vessel,the load-lifting system and the mooring system are treated as a whole.This model can be used as the basic theory for predicting the behaviors of floating crane vessel,we can avoid some dangerous situations to protect the safety of crane operations.Based on seakeeping theory,the dynamic model of revolving crane vessel is derived.WAMIT software is applied to carry on frequency-domain analysis of the crane vessel.Addedmass,damping coefficients,1st-order Motion RAOs and 2nd-order Force RAOs are calculated.Using the classical theory of Rod,the mooring cable is assumed as a structure without bending stiffness,the nonlinear finite element method is used to transform the structure into a series of algebraic equations through an integral statement and the static equation and momentum equation is set up.The analysis program of the mooring system is established using nonlinear finite element method to analyse the shape and mooring force of the mooring cable with the coupling effect between vessel and mooring cable under three-class sea conditions.As for the load-lifting system,the Lagrange equations are established with proper general coordinates and general forces,considering the wind load and the six degrees of freedom motion of the lifted load.Then Runge-Kutta method is used to solve ordinary differential equations.The motion response of the lifting load system is analyzed under different sling lengths,lifting speed and excitation frequencies.Based on dynamics principle,the coupling effect between vessel and lifting rope,the coupling effect between vessel and cable and environmental forces play an important role.MATLAB/Simulink software is used to simulate and do some numerical analysis of the floating crane vessel under the coupling influence of multi-systems.Respectively,under different wave headings angles,different sea conditions and different elevation angles of crane arm,the displacement of the vessel on each degree of freedom and oscillation angle of lifting load system are compared,and influence law is presented.