Vibration (Marine engineering)

Towing tank/water flume experiments are conducted to characterize the dynamics
of a Remotely-Piloted Unmanned Underwater Vehicle (RPUUV) propelled by a
vectored-thruster system. Force and torque measurements are used to determine the
coefficients of drag, lift, yaw-moment and thrust of the vehicle as a function of the
vehicle yaw angle and the vectored-thruster rudder angle. Simultaneously, particle Image
Velocimetry (PIV) measurements of the propeller inlet flow are also performed to
examine the variation of flow conditions at the propeller inlet with rudder angle. The tests
are conducted at 0.150 rnls, 0.300 rnls, 0.515 rnls and 0.773 rnls. While the measured
drag coefficient is slightly higher than predicted by theory at low Reynolds number (1.44
x10^5 and 2.88 x10^5), the hydrodynamic coefficients data are expected to be useful in
predicting the response of vehicles in the field. Additionally, the magnitude of the thrust
vector varies nonlinearly with rudder angle and for nonzero rudder angles the thrust
vector does not point in the same direction as the thruster axis.

In the present dissertation, the hydrodynamic and hydro-elastic characteristics of ship hull and plate vibrations are analyzed using theoretical and numerical methods. The wave forces are determined using a suite of methods which include the Froude-Krylov method for incident wave forces, Wagner's method and ABS rules for the slamming wave force, and numerical methods for nonlinear wave radiation forces. Finite difference methods are developed to determine the wave forced vibrations of ship hull plates which are modeled using a range of plate theories including nonlinear plate theory with and without material damping and orthotropic plate theory for stiffened hull plates. For small amplitude deformation of thin plates, a semi-theoretical superposition method is used to determine the free and forced vibrations. The transient ship hull vibration due to whipping is also analyzed using the finite difference method. Results, in the form of deformations and stress distributions, are obtained for a range of scantling and wave parameters to identify key parameters to consider in ship structural design.