Modeling and Analysis of Offshore Crane Retrofitted With Cable-Driven Inverted Tetrahedron Mechanism

Crane operations might be very dangerous in rough sea conditions due to unexpected payload swing induced by ship excitations. In this paper, a novel Cable-Driven Inverted Tetrahedron Mechanism (CDITM) is presented to suppress the payload swing for sake of the workers' safety. The CDITM retrofitting on an offshore crane is simplified as a constrained pendulum with a moving base, and its equations of motion are obtained by Newton Euler Method. Next, three-dimensional dynamic analysis is performed using Matlab/Simulink, and the influence law of ship excitations, tagline tension, crane pose and CDITM configuration on the payload swing are investigated. Finally, through comparative experimental verification, it is found that the simulation tendencies of in-plane swing follows the experiment curves quite well, and the variations between the simulation and experiment results are acceptable. Thus the dynamic modeling and analysis of CDITM are verified. The theoretical and experimental results are fundamental and valuable for the engineering application of CDITM in the offshore industries.