Wave Filtering and Dynamic Positioning of Marine Vessels Using a Linear Design Model: Theory and Experiments

Abstract

This chapter describes a procedure to obtain an improved design model of ships subjected to the influence of currents and sea waves. The model structure is at the heart of the application of new techniques in control and estimation theory to the problem of Dynamic Positioning (DP) and wave filtering of marine vessels. The model proposed captures the physics of the problem at hand in an effective manner and includes the sea state as an uncertain parameter. This allows for the design of advanced control and estimation algorithms to solve the DP and wave filtering problems under different sea conditions. Numerical simulations, carried out using a high fidelity nonlinear DP system simulator, illustrate the performance improvement in wave filtering as a result of the use of the proposed model. Furthermore, using Monte-Carlo simulations the performance of three DP controllers, designed based on the plant model developed, is evaluated for different sea conditions. The first controller is a nonlinear multivariable PID controller with a passive observer. The second controller is of the Linear Quadratic Gaussian type and the third controller builds on $$\mathcal{H}_{\infty }$$ control techniques using the mixed-μ synthesis methodology. The theoretical results are experimentally verified and the performance of wave filtering in DP systems operated with the controllers designed for different sea conditions are further examined by model testing a DP operated ship, the Cybership III, in a towing tank equipped with a hydraulic wavemaker.