Study On The Algorithm For Realtime Calculation Of Ship Hydrodynamic Interaction Force And Trajectory Control In Restricted Waters

Due to the advances in shipbuilding technology and the needs for development of shipping industry,ships are gradually developing in the direction of large dimensions.As upgrading of hardware and software of the supporting facilities in restricted waters such as ports,waterways,and quays is very much lagging behind,the problem of navigation safety of ships in restricted waters has attracted extensive attention of scholars at home and abroad.Compared with open waters,the hydrological information of restricted waters is complicated and the effective width of the channel is very small,while the traffic is extremely heavy.Ships are easily affected by the shallow water effect,the bank effect and the ship-to-ship interaction effect,which threaten the safety of ship navigation.In the existing ship collision avoidance control methods,the attention is focused on withstanding the disturbance of wind,wave and current during the navigation of the ship,and there are few researches on the hydrodynamic interaction of ships in restricted waters that often cause navigation safety accidents.In this thesis,the real-time calculation method of ship hydrodynamic interaction in restricted waters and the method for ship trajectory control are studied,and the following research work has been carried out:Firstly,the potential flow based method for the calculation of ship hydrodynamic interaction is studied.Based on the boundary element method,a numerical method suitable for real-time calculation of multi-ship hydrodynamic interaction in restricted waters is proposed.The algorithm is verified against analytical solutions such as the flow field about the sphere and the added masses of ellipsoids.On this basis,the boundary conditions of free surface,horizontal and non-horizontal water bottoms are dealt with by low Froude number assumption,mirror image method and the paneled moving patch method,and a calculation method of hydrodynamic interaction in restricted waters is established.Based on the research on the influence law of calculation accuracy and calculation efficiency,a method for determining the parameters for real-time calculation of ship hydrodynamic interaction in restricted waters is proposed.After that,numerical simulations of the typical scenarios of ship hydrodynamic interaction in restricted waters are carried out,and the results of the model test and RANSE numerical simulation are compared,and the influences of free surface and viscous effect on the numerical results are analyzed,and the accuracy and applicable range of this algorithm are obtained.Secondly,separate and response kinematics models of ship maneuvering accounting for hydrodynamic interation are studied.The hydrodynamic interaction force obtained based on the potential flow theory is added into the MMG maneuvering motion equation,and a multi-ship maneuvering motion model in restricted waters is constructed.Numerical simulations are carried out for the typical scenarios of ship hydrodynamic interaction in restricted waters and the ship motion trajectory characteristics accounting for hydrodynamic interaction are studied.Through a linear simplification and the Laplace transformation,the ship response maneuvering model in restricted waters is obtained,that is,the Nomoto equation with variable parameters.Finally,the control method of ship collision avoidance in restricted waters is studied.The hydrodynamic interaction is used as a known quantity to design the controller,and the PID+feedforward control method and adaptive compensation PD control method are proposed for the real-time collision avoidance scenarios of multi-ship in restricted waters.The hydrodynamic interaction forces are added to the controller as a feedforward term,and a PID+feedforward ship trajectory controller is designed to eliminate the steady-state error caused by the hydrodynamic interaction.Based on the PID+feedforward controller,the ship trajectory simulation is carried out for the typical restricted water ship hydrodynamic interaction conditions,and the ship trajectory control performance with various parameters is analyzed,and the applicability of the PID+feedforward controller for moderate hydrodynamic interaction cases is verified.Because the feedforward term cannot fully include in the hydrodynamic interaction term,the PID+feedforward controller is not suitable for the trajectory control of two ships interacting in very shallow water depth and in close proximity.To solve this problem,an adaptive approximation function is constructed.Based on the unmodeled dynamics of the KT equation with varying parameters,an adaptive compensation PD trajectory controller is designed,and the stability of the control system is analyzed using the Lyapunov method.Numerical simulations of the ship trajectory control under hydrodynamic interaction are also carried out to verify the adaptive compensation PD trajectory controller.The adaptive approximation problem of complex unmodeled dynamics of ships under hydrodynamic interaction is solved.In this thesis,the method for real-time calculation of ship hydrodynamic interaction in restricted waters is studied,as well as the method of solution to the ship trajectory under the effect of hydrodynamic interaction and the trajectory control.Through theoretical analysis and simulation experiments,the accuracy of the real-time solution method of hydrodynamic interaction and the control effect of the ship trajectory control method are verified.This proposed method is also applicable to the real-time calculation of hydrodynamic interaction and ship trajectory control in the presence of banks,irregular water bottoms or other structures.The methods and results proposed in this thesis can provide theoretical basis and reference for ship trajectory control in restricted waters.