The Use of Differential Evolution Algorithms to Determine Ship Roll Damping Coefficients from Decay Tests

Radoslav Nabergoj
NASDIS PDS, Izola, Slovenia


The execution of the extinction tests represent the classical experimental method used to estimate the damping of an oscillatory system. For the specific case of ship roll motion, the roll decay tests are carried out at model scale in a hydrodynamic basin. When the damping is far below the critical one, the transient decay is oscillatory. Here, a novel procedure is presented to evaluate the damping coefficients by directly fitting the roll decay curves, using a differential evolution algorithm (DEA) of global optimisation. The results obtained with this methodology are compared with the predictions from standard methods. This kind of approach is very promising when the motion model of the system under investigation is established with any level of non-linearities included. The usage of the fitting procedure on the numerical solution and the approximate analytic solution of the differential equation of motion demonstrates the flexibility of the method. Two experimentally measured roll extinction curves have been considered and suitably fitted as a benchmark example. Compared with the ones obtained from standard roll decay analysis, the newly predicted results show that the algorithm can perform a good regression on the measured data.