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.