Research On Rigid-flexible Coupling Model And Dynamic Characters Of Moored Crane Ship

Floating cranes play an important role in the operation of offshore engineering. During the operation or sail in the sea, wave-induced ship motions may cause the hoisted cargo to pendulate, so the crane payload pendulations became dangerous large and the operation had to be suspend. In order to avoid the loss during the operation, we should pay much attention to the dynamics of the floating crane. Although the issue of ship dynamics has been addressed extensively in a large number of recent researches, we still lack of full study on this problem because of the particularity of the floating crane.In order to save times during working in the sea, large ship-mounted crane appeared recently. The large crane ships are different from those small crane ships, the load is heavier and the operation speed is higher, so they have some new different features: (1) the flexibility of the boom can affect the dynamics of the crane-ship; (2) the dynamics of load and ship are coupled with each other. Aiming to the features in this dissertation, the whole crane-ship dynamics modeling theory and method are studied and the corresponding simulations are performed, and the main contributions of the research include:(1) The boom and rope are taken as elastic bodies, governing equations for the dynamic response of a crane-ship coupled with the pendulum motion of the payload are derived based on Lagrange's equations. The presented flexible dynamics model has good versatility. The planar pendulum and sphere pendulum models are used to model the load system, and the difference of these two models are studied. The coupling of the ship and load are also studied.(2) A nonlinear three-dimensional lifting load system dynamic model was set up based on the general form of Lagrange's equation, the dynamic response of the cargo was studied using numerical methods. The result demonstrates that the dynamic response of the cargo depends on the length of cable, reeling and unreeling speed and wave frequency, and the in-plane angle have coupling with the out-of-plane angle. Melnikov function are used to ascertain the key parameters that chaotic motions appeared in the system, and the chaotic vibration is studied using phase portraits, Poincare maps and maximum Lyapunov exponents. The method to avoid chaos is proposed.(3) Governing equations of mooring system are derived based on finite element method, the motion equation is solved by Wilson method to obtain the dynamic response of the mooring cable, the result demonstrate that the force of the mooring system can be approximated by a polynomial. A special mechanism has been developed to model the nonlinear behavior of real mooring systems, which can be used in experiment. The profile of the cam was defined and a solid model was designed in design software.(4) The boom is taken as flexible bodies and modeled based on finite element method, in order to avoid time consuming solution of equations in complex structures dynamics analysis, Dc gains of the individual modes of vibration were used as the criterion of modal truncation, the relative importance of the contributions of each of the individual modes was obtained and a small state space model was defined. The reduced model can accurately describe the pertinent dynamics of original system, and then the flexible model of the boom is established, which can be used for the rigid-flexible coupling model.5) A Virtual prototype model of the mooring crane-ship is established based on finite element method and flexible multi-body theory. Basic crane maneuvers, such as cable reeling and unreeling and load falling off, are taken into consideration, the analysis reveals how the dynamics of the crane-ship affected by those key parameters of the system. The influences of the flexibility of the boom are also taken into consideration.At last, we built an experimental setup, the platform used is capable of producting arbitrarily prescribed, independent surge and heave motions. The dynamic test of the load system is carried out. The comparison between test and simulation shows that the dynamics model presented in this dissertation is correct and feasible.