4. CONCLUSIONS AND RECOMMENDATIONS
Two different procedure were applied in order to identify hydrodynamic coefficients from standard full scale manoeuvres. Both the procedures allow to obtain values of the coefficients which are in a reasonable agreement with experimental data derived from PMM tests (see table 2)
Table 2 Comparison between identified values and experimental values from PMM trials
By both the procedures, in general, the hydrodynamic coefficients were identified with an error lower than 15% and even if it is not still possible to identify a unique value for each of the coefficients, it can be already concluded that the procedure can be useful for tuning the mathematical model of the regression.
One of the reasons for the differences in the two sets of data identified can be the difference existing between the two mathematical models used.
It has to be noted moreover that the influence of experimental disturbances (such as wind and current) is probably not negligible, especially for the filtering technique where all the time history is processed and this could also explain the differences between the values obtained with the two procedures applied. It is considered therefore that the analysis of environmental effects remain an important object for future work.
For what regards the filtering technique, further work will be also dedicated to the analysis of the feasibility of considering contemporarily the two manoeuvres of ZigZag and Turning Circle; it is believed, in fact, that, even if the Turning Circle alone cannot be used to identify a complete set of coefficients, it could be useful for obtaining some data about the steady state of the manoeuwe and thus to improve the simulation results.
For what regards the optimization technique, the influence of the objective function chosen on the results will be analyzed, especially in order to give more importance to the second part of the Turning Circle manoeuvre, which is still not perfectly simulated.
Finally, in order to validate the procedures described, they will be applied to a series of similar vessels with the final aim of obtaining a general trend to adjust the existing regression formulae used by SIMSUP.
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Michele Viviani: graduated in Naval Architecture and Marine Engineering at the University of Genova where is working on a PhD project, works since 2001 in Fincantieri's Hydrodynamic and Acoustic Department, member of NATO ST/NSM, also involved in EC and MoD projects.
Roberta Depascale: graduated in Naval Architecture and Marine Engineering at the University of Genova, works since 2001 in CETENA's Hydrodynamic Department, member of CRS group and NATO ST/NSM, also involved in EC projects.
Luca Sebastiani: graduated in Physics at the University of Genoa. Since 1986 he is working in CETENA where actually is head of Hydrodynamic Department.
Carlo Podenzana-Bonvino: graduated in Naval Architecture and Marine Engineering at the University of Genova, full professor of Naval Architecture, head of the Department of Naval Architecture and Marine Technologies, Faculty of Engineering, University of Genova.
Roberto Dattola, Cdr: Italian Navy Officer, graduated in Naval Architecture and Marine Engineering at the University of Naples, works since 1998 in the Naval Surface Ship Design Office of Italian Navy General Staff as Hydrodynamics Specialist, representative member of WEAO projects and NATO ST/NSM.
Massimo Soave: graduated in Naval Architecture and Marine Engineering at the University of Genova in 1988 and Officer of the Italian Navy, since 2001 Director of the C.E.I.M.M. (Italian Navy Cavitation Tunnel) and involved in hydrodynamic and cavitation experiences.