A unified seakeeping and manoeuvring model with a PID controller for path following of a KVLCC2 tanker in regular waves
Heading control of ships in calm water has been investigated by several authors using different control techniques. However, the study on heading control of ships in actual sea conditions is very limited. This paper attempts to investigate the heading control in regular waves using a PID controller. A 6 DoF unified seakeeping and manoeuvring numerical model is integrated with a PID controller. A crude oil carrier (KVLCC2) prototype is used in the numerical study. The second order wave mean drift forces are calculated based on Salvesen's method and affect the horizontal motions. The wave exciting forces/moments and the restoring forces in the vertical planes are calculated for the exact wetted surface area. Empirical relations available in the existing literature are used to compute the propeller thrust, control forces/moments and hydrodynamic forces. PID controller gains Kp,Kd and Ki changes for different sea states depending on the external wave force. Hence these gains are pre-calculated for different sea states by trial and error. The performance of the controller under the wave action is then studied for path-following application.
Numerical investigation of the manoeuvring motions and trajectory tracking of a KVLCC2 tanker using PID controller in regular waves
An autopilot based on a PID control technique is incorporated in a 6DOF unified seakeeping and manoeuvring numerical model of a ship in a seaway. A crude oil carrier (KVLCC2) prototype is used in the study. The surge, sway and yaw are assumed to be slowly varying motions and the heave, roll and pitch respond to the rapidly varying wave forces. The second order wave mean drift forces act on the horizontal motions. For heave, roll and pitch, the Froude-Krylov forces and the restoring are calculated for the exact wetted surface area for each time step. The hull resistance and the control forces are calculated based on an empirical data available in the existing literature. The reference heading is obtained from Line Of Sight (LOS) algorithm using way-points. The effectiveness of autopilot developed based on PID controller is studied in regular waves.
A unified ship manoeuvring model with a nonlinear model predictive controller for path following in regular waves
In this paper, a nonlinear model predictive controller for path following of a surface vessel in the presence of regular waves is studied. A model predictive controller is developed for a 3DoF unified manoeuvring model of the KVLCC2 crude oil tanker. The surge, sway and yaw motions of the ship are influenced by the second order wave drift forces and moments calculated based on a potential flow solver. Propeller thrust, rudder and hydrodynamic forces and moments are computed using empirical formulas available in the literature. For path following purposes, waypoints are assigned in head and beam wave conditions and a line of sight algorithm computes the reference heading angle. The rudder control is exerted by a nonlinear model predictive controller and the effectiveness of the controller is studied. The performance of the nonlinear model predictive controller is compared against that of a basic PID controller.