3-D Hydroelasticity Analysis Method For Wave Loads Of Ship

In modern ship industry many new types of ships with large scale high speed and unconventional hull form are frequently put into operation. High strength steel and composite materials are widely used in ship construction. Therefore, some typical assumptions used for wave loads prediction gradually show their limitations. These assumptions include the 2-D hydrodynamic method based on planar flow assumption, rigid body model without including the effect of elastic deformation of hull and the linear potential flow theory suitable for low sea state and low forward speed.In order to develop a 3-D nonlinear hydroelasticity analysis method which is fit for motions and wave loads prediction of large ship, the present study is carried out based on 3-D free surface Green function and 3-D Rankine source method. The following problems are emphatically investigated.First, a comparison study between two modal analysis method namely the transfer matrix method and finite element method is carried out. Combined the vibration model of beam and the existing wet surface mesh generation method of rigid hull, the 2-D vibration mode is expanded to 3-D a convenient wet surface mesh generation method of elastic hull is presented. To meet the need of distribution singular points on free surface in Rankine source method, a method to generate the hydrodynamic mesh in the free surface is presented using the already established discretized waterline panel obtained by accumulative chord length cubic parameter spline function.Second, according to 3-D potential flow theory and considering the elastic deformation of hull, a hydroealsticity analysis model which is suitable for predicting the motions and wave loads of medium and low speed ship is established in frequency domain. Combined with the wet surface generation method, the velocity potential of flow field is solved by the source-sink distribution method. After all the wave forces acting on the hull are obtained, the forced vibration equation of hull structure is established. Then, the principal coordinates of each order vibration and the section loads of ship are got. Through the examples of large bulk carrier and large container ship, this method is verified. Furthermore, an analysis on the elastic effect of motions and wave loads of large ship is performed.Third, a kind of 3-D nonlinear time domain simulation hydroelasticity analysis method of ship motions and wave loads is presented with the nonlinear factors due to the instantaneous position variation of body surface and the slamming force being considered. For the purpose to solve the divergence problem of ship motion equation in obsque waves, according to the theory of ship maneuvering motion in waves, the PID (Proportional, Integral and Derivative) autopilot model is used. The rudder force and moment are included in the equilibrium relationship in the form of coefficient matrix. Therefore, the ship motion equation considering maneuverability is established. Taking the large bulk as example, the effect of the PID autopilot and the validity of the hydroelasticity analysis method is verified. Then, this method is applied to calculating the principal coordinates and wave loads of a lager container ship with slamming force acting.Finally, based on the Rankine source method, considering the elastic deformation of hull, a kind of 3-D time history simulation hydroelasticity analysis method is investigated. The artificial numerical beach is adopted to meet the radiation condition. The source distribution integral equation is transformed into second order differential equations using panel method and the source strength are solved by difference method. Then, ship motions and wave loads are obtained. Through an example of a 10000TEU container ship, the validity this method is verified and the analysis for the velocity effect of wave loads is made.