Research On Simulation Of Ship Towing System With Six Degrees Of Freedom

In recent years,with the development of marine shipping industry as well as increasing traffic density and towage business,more and more attention has been attracted to the towing system.The towing operation,however,has long been instructed by the experience of captain and pilot,which implies some risks and uncertainty on maneuverability.Using simulative method does make sense to simulate towing motion,forecast influence of environmental factors and further guarantee the safer towing.On above opinion,the following works in this paper have been completed.Based on Maneuvering Model Group(hereafter called as MMG)manipulation equations,summing up the mathematical model of hydrodynamic force,propeller thrust,rudder force and their appropriate correction,considering the influence of environment,the mathematical model of ship maneuvering motion with six degrees of freedom can be built according to maneuverability theory.By verifying the feasibility of this mathematical model with real ship sea trial results,the mathematical model of tug and barge with six degrees of freedom can be built and further the tug's maneuvering motion both in still water and in wind,wave,current can be simulated in real time.Combined with towing cable force which is calculated by means of catenary theory,the maneuvering model of towing system with six degrees of freedom,consisting of tug,towing cable and barge,can be built,with consideration of wind,wave as well as current.By employing fourth-order Runge-Kutta method,a computer program was made to give the solution to towing system motion equations based on which the maneuvering motion of towing system can be simulated in real time.Additionally the effects of towing speed and the length of towline on the sea-keeping capability can be analyzed;the maneuverability of towing system in wind,wave and current can be calculated.