Using Monte-Carlo simulations and experimental model tests, the performance of three controllers designed for dynamic positioning (DP) of marine vessels and offshore rigs subjected to the influence of sea waves, currents, and wind loads is compared for different sea conditions: calm, moderate, high, and extreme seas. The first controller is a nonlinear multivariable PID with a passive observer. The second controller is of the Linear Quadratic Gaussian (LQG) type and the third controller builds on H_∞ control techniques using the mixed-μ synthesis methodology. We further examine the performance of wave filtering of the controllers operating in different sea conditions. The Monte-Carlo simulations highlight the strength of each method as well as its shortcomings and drawbacks.
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