Unsteady hydrodynamics and vibro-acoustic responses for a pump-jet propelled suboff under distributed pulsation force

This study presents the unsteady hydrodynamics of a pump-jet running in the wake of a suboff model and the resulting vibro-acoustic responses of a coupled pump-jet-shafting-suboff model. The unsteady hydrodynamics of the pump-jet are obtained using computational fluid dynamics (CFD) by simulating the pump-jet behind the suboff. The spectrum of pulsation forces in three directions of the pump-jet for a single blade is analyzed, which is dominated by shaft frequency and its harmonics. A mapping method based on radial basis function (RBF) is established between the CFD mesh and the structural mesh to obtain the distributed pulsation force on structural wet surface. The vibro-acoustic responses of the coupled pump-jetshafting- suboff model are predicted using a coupled finite element method (FEM) and the boundary element method (BEM) in the frequency domain. It is shown that except for the characteristic tonal spectrums, the vibro-acoustic responses exhibit peaks at characteristic structural modes, such as the 1st longitudinal mode in axial direction of the hull, the first and second longitudinal modes of the shafting system. Among three directions forces, the transverse distributed forces will dominate the responses in the low frequency range and the longitudinal distributed forces contribute most to the responses produced by the pump-jet over the 2nd harmonics of shaft frequency. The study will help to understand the characteristics of vibro-acoustic responses of the pump-jet-shafting-suboff model. Keywords: Pump-jet-shafting-hull, Vibro-acoustic response, Unsteady hydrodynamics, RBF