Adaptive nonlinear control of propeller-induced vibration

[Truncated abstract] Effective control of propeller-induced vibration (PIV) is crucial not only in reducing underwater sound radiation from submarine hull structures, but also in noise analysis and control of unmanned underwater vehicles. PIV is generated by hydrodynamic interactions between the running propeller and the non-homogeneous wake field. It propagates along the propeller shafting and transmits into hull structures, which are subsequently excited thereby radiating sound into the surrounding field. Traditionally, control of PIV is challenging not only because the thrust-delivery shafting does not allow insertion of elastic components to dissipate dynamic energy but also because a practical propeller-shafting system is normally characterised by nonlinearities, uncertain parameters and unknown disturbances, all of which require more advanced control structures. This thesis aims to develop an adaptive nonlinear controller to actively regulate the PIV energy transmitted into hull structures by systematically addressing the issues of system dynamics, controllability, actuating, uncertainties and nonlinearities.

PIV control directly contributes to the attenuation of sound radiation from the ship hull. To support current theoretical understanding of the links between sound radiation and PIV excitation, experimental studies were conducted on a torpedoshaped structure. Trends linking sound radiation patterns to corresponding structural vibration modes were observed; however, these do not totally agree with existing theoretical analysis because of the unique boundary conditions imposed by the special geometries of the torpedo ends.