Cargo Pendulation Mitigation Of Ship-mounted Cranes Using Eddy-current Nonlinear Energy Sinks

Ship-mounted cranes are important handling equipment and are widely used in materials handling,equipment installations and other engineering operations in the construction of cross-sea bridges.However,due to the effect of wave load and wind load under complex sea condition,the cargos of the ship-mounted cranes inevitably oscillate and easily collide with surrounding objects,which greatly affects the crane work efficiency and the safety of workers.The conventional method to reduce cargo pendulation mainly uses mechanical or mechanical-electronic cargo pendulation systems.This conventional method is complicated,and the overall modification of the cargo is large,so its applications are still limited.Based on the previous studies,this thesis combines the concept of eddy current with track nonlinear energy sink(NES)according to the theory of vibration mitigation.A new type of ETNES was proposed and applied to mitigate cargo pendulation.In this thesis,the performance of the proposed ETNES were investigated,via scale experiment,theoretical analysis and numerical simulation.The main work is as follows:(1)Based on the actual cargo hook parameters of a ship-mounted cranes in Maldives,using ANSYS to build a finite-element model and analyze its dynamic response under measured waves;a scale model with a length of 2m and a new ETNES device were designed and fabricated.A series of experiments on cargo hook-ETNES were carried out,using free vibration and harmonic excitation as the experimental conditions.By changing the weight plate and adjusting the magnetic field strength of the ETNES,the control performance of the ETNES with different mass ratios and damping parameters was tested,respectively.(2)The equation of motion of the cargo hook-ETNES system under various working conditions was derived using the Lagrangian equation method,and the equation was solved by the Runge-Kutta method.The cargo’s acceleration and inclination were calculated under various working conditions.The time-history response fully verified the cargo reduction performance of ETNES.Through a series of parameter analysis,the influence of the mass ratio,damping parameter and initial swing angle of the ETNES on the pendulation of the cargo is determined,which is compared with the experimental results.A parameter optimization method of the ETNES was proposed.In this thesis,the scale model experiment and numerical simulation were compared.The results showed that the pendulation reduction of the ETNES on the cargo can reach 30% or beyond.This study provides a new pendulation reduction method for the cargos of ship-mounted cranes.