Research on a novel robot mooring system based on dual-parallel elastic under-actuated mechanisms

Abstract

Parallel mechanisms have the advantages of a high carrying capacity, large stiffness and compact structure. To develop the theory and key technology of robot mooring systems, in this paper, focusing on a 266,000 m3 LNG ship model with a scale of 1:60, a novel robot mooring system based on dual-parallel elastic under-actuated mechanisms is proposed. The configuration, structure parameters and workspace of the system are determined by experiments and simulations of the ship model with conventional mooring arrangements. Based on the influence coefficient method, the global stiffness model of a parallel-robot mooring system (PRMS) is presented, yielding a stiffness matrix in tensor form. The boundary conditions for the PRMS-moored ship in an experimental basin are introduced and a dynamic equation is given considering the two work modes of the PRMS. Numerical simulations and experiments are carried out to obtain the motions of the PRMS-moored ship when encountering unidirectional irregular waves, and the results indicate that the system can reduce the frequency drift motions of ships in surge, sway and yaw induced by the second order wave drift force.