Modeling And Simulating Of Self-propulsion And Pushing Motion Of The Tugboat In Swell

Swell,as a form of waves,is a serious marine natural disaster with complex formation mechanisms,movement patterns and propagation processes.Swell has a serious impact on drilling platform operation,offshore buildings,navigation of ships at sea,port operation and so on.Tugboat is an important port equipment,which is highly susceptible to swell disturbance during harbor operations.In order to explore the influence of swell on efficiency of self-propelling and pushing motion of the tugboat and predict the motion state of tugboat in swell,and ensure the safety of port tugboat pushing operation,the geometric characteristics of swell are analyzed and modelled and the influence of swell on tugboat self-propelling and pushing operation is forecasted in this paper.Firstly,the basic geometric characteristics of swell are analyzed synthetically.And the advantages,disadvantages and applicable conditions of various methods of swell simulation and prediction are summarized.The inverse calculation of the swell spectrum of Wen shengchang by the Fourier Fast Transformation method is used to establish the sea surface height field,which realizes the real-time simulation of the near shore swell.Based on the idea of Separate Modeling Thought,the swell disturbance force and moment of tugboat during the self-propelling and pushing operation are calculated with the application of the obtained wave amplitude and wavelength.The Four-Degree-of-Freedom mathematical model of the tugboat pushing operation and the six-degree-of-freedom mathematical model of the tugboat self-propelled operation under swell disturbance are established by applying the non-linear model of the rubber fender feedback force and the collision detection algorithm of the axial enclosure box.In order to calculate the added resistance of the ship in wave and the stall condition of the pushing tugboat,the non-linear curve of tugboat stall is regressed via higher-order polynomials.The actual pushing efficiency of tugboat to the pushed boat is obtained by using empirical formula of ship’ added resistance proposed by He Huiming.Finally,the off-line test simulation platform of tugboat simulator is built via VS2013.The Four-Degree-of-Freedom mathematical model and six-degree-of-freedom mathematical model of tugboat pushing operation under swell disturbance are simulated and the actual operation efficiency of port tugboat under swell condition is analyzed.The simulation results show that the model built accords with the self-propelling motion and pushing operation law of the tugboat affected by the swell.This model can explain the correctness and rationality of the swell disturbance model and provide a theoretical basis for the rational allocation of the tugboat power,the optimization of tugboat dispatch and the rational utilization of the tugboat resources in the port.