Hydrodynamic analysis of marine multibody systems by a nonlinear coupled model

This study investigates the hydrodynamic performance of two freely floating or interconnected barges. A nonlinear decomposition model in the framework of potential flow is employed to simulate the wave-body interactions in the time domain. This piece of work focuses on the accurate calculation of hydrodynamic forces and motions of a multibody floating system. The hydrodynamic forces are indirectly calculated through an auxiliary function approach, which is extended to application of two floating bodies in the present study. The resultant coupled motion equations for two bodies clearly demonstrate the influence of one body on the other. To incorporate an interconnection between two floating bodies, a constraint matrix method is developed where the connection constraints are mathematically represented by a constraint matrix. The constraint forces in the connection are solved in the modified motion equations. The newly formulated coupled auxiliary function and constraint matrix approaches for two bodies with and without interconnections are validated by comparisons of first-order response against linear frequency-domain models. Two types of interconnections, namely, the rigid connection and the middle-hinge connection, are examined in both beam sea and head sea to demonstrate the effectiveness of the proposed method. Coupling effects of different connection scenarios on body motions as well as the influence on constraint forces are discussed. Furthermore, simulations using relatively steeper waves are performed and compared with mild wave cases. The nonlinear effect is highlighted by decomposing the higher harmonic components of nonlinear responses.