Study On The Hydrodynamic Performance Of Hinged Multi-Floating Structures

With the explore to the depth of the ocean,offshore floating structures are getting more and more complex and need to cooperate with each other.Besides the coupling between the floating structures and the mooring system,the mechanical coupling cause by mechanical components between floating structures is another important problem.The problem of solving hinged multi-floating structures need to consider the problems including the description of topologic structure,the fluid-structure coupling between structure and fluid,motion and dynamic coupling cause by hinge joint and the coupling between the floating structures and the mooring system.Therefore,solving the dynamic response of the hinged floating structures is complicate and necessary to research.In order to intensive study the mechanism of hinged multi-floating structures in waves,indirect time domain method based on three dimensional potential flow theory and the constraint matrix method of rigid multi-body dynamics are combined here to explore the characteristics.Compared with the existing method,the algorithm can significant improve the computational efficiency and saving time for numerical modeling.Through the theoretical derivation of constraint matrix method,the library of constraint matrix is established.A method is proposed which combined the constraint matrix method and the indirect time domain method based on three dimensional potential flow theory,then it is used to solve the dynamic response of hinged floating structures.Nonlinearity factors can be considered here including nonlinear wind force,nonlinear current force and nonlinear viscous force etc.And also the lumped mass method which is used to solve dynamic response of mooring system can be combined to make a full couple analysis.The method is achieved by FORTRAN to solve the three-dimensional nonlinear dynamic response of hinged multi-floating bodies.By comparing with the results of the tank test and the classical literature to prove the method is accurate and reliable in solving dynamic motion of the single floating structure and the hinged multi-floating structures,respectively.Then,the sensitivity of parameters for the hinged semi-submerge transverse floating structures is analyzed.The critical parameter of system including the characteristic length,diameter,hinge rotation stiffness,hinge rotation damping,draft and the numbers of hinged structures isconsidered.The effect of critical parameters on peak period of swing motion,peak period of heave motion and the amplitude of hinge rotation are discussed.In this paper,hinge multi-floating structures model is used to simulate the Pelamis wave energy converter.The hinged rotation stiffness and the damping is introduced to simulate the coupling between hydraulic cylinder and the floating structures,and also the coupling between floating structures and mooring system is considered here.Through coupled analysis of floating bodies with the hydraulic cylinder and mooring system,the effect of the random wave to the dynamic response of Pelamis is discussed.The spectrum analysis of motion is discussed to study the response characteristic of Pelamis.Using the effect of parameters of random wave to the motion of Pelamis wave energy converter as a reference for the safety assessment of extreme environmental conditions.The study of power generation efficiency can be reference for optimal design of Pelamis.The response mechanism is studied through the motion spectrum analysis.Because of the lack of research related to the catamaran floating crane,hydrodynamic performance is studied according to related articles.The catamaran floating crane is modeled by constraint matrix method which is combined by four separate rigid body hinged with each other.By calling the constraint matrix library,the constraint matrix is used in equation of motion to get the response of the catamaran floating crane.In this paper,hydrodynamic performance of free floating catamaran floating crane without hinge connection is analysis in frequency domain analysis firstly.Comparing results with the crane with hinge connection found that the catamaran floating crane has more stability than the floating crane with slewing arm.In order to prove the hinge joint can significantly reduce the gantry crane's motion,the connection force of free motion joint is contrast with the force of fix joint.The calculated results show that free motion hinge can significantly reduce the joint force.