Oceanographic submersibles--Mathematical models

The development of an unmanned underwater vehicle at Florida Atlantic
University with onboard optical sensors has prompted the temporal and spatial optical
characterization of Port Everglades, with in-situ measurements of the turbidity,
conductivity, and temperature. Water samples were collected for laboratory analysis
where attenuation and absorption were measured with a bench top spectrometer. All of
the measurements showed a high degree of variability within the port on a temporal and
spatial basis. Correlations were researched between the measured properties as well as
tide and current. Temporal variations showed a high correlation to tidal height but no
relation was found between turbidity and current, or salinity. Spatial variations were
primarily determined by proximity to the port inlet. Proportionality constants were
discovered to relate turbidity to scattering and absorption coefficients. These constants
along with future turbidity measurements will allow the optimization of any underwater
camera system working within these waters.

In this study, a laminar flow hull shape is implemented on an Autonomous Underwater Vehicle (AUV), with boundary layer suction at the aft end of the hull to prevent separation. The hull shape has the largest diameter of the vehicle near the aft end of the hull resulting in an accelerating flow over the majority of the hull's surface. The problem of axially symmetrical flow around the AUV is solved using a potential flow analysis. A finite difference algorithm evaluates the stream function, leading to the computation of fluid velocity and pressure fields. The boundary layer characteristics are analyzed to predict the risk of separation. The numerical results are compared with laboratory measurements of the flow using a Particle Image Velocimetry system. Fuzzy Logic Sliding Mode Controllers are implemented to control the vectored thruster vehicle, and are simulated using a six-degree of freedom dynamic model of the vehicle.

This thesis describes the determination of linear and nonlinear coefficients for the Morpheus vehicle. Added mass and nonlinear damping terms were obtained by strip-theory. These added mass coefficients were compared to the ones previously computed by boundary-integral method. Open-loop simulations were conducted using both sets of added-mass coefficients along with the damping terms, which were adjusted to fit at-sea data. A previously estimation technique for hydrodynamic coefficients has been applied to the Morpheus AUV using a Kalman filter. This technique based on linearized equations of motion was tested with linear and nonlinear data generated by simulation. Steering and diving motions were considered resulting in the estimation of different sets of coefficients. Results showed that the estimated values were able to reproduce accurately the vehicle motion in the linear as well as in the nonlinear case.