The work in this thesis is concerned with the generation of Lumped Parameter Models (LPM) for two, slender, torpedo shaped, X-fin craft. This process involves the use of CFD to simulate captive maneuvers that are normally performed using test equipment in the field. These captive maneuvers are refereed to as planar motion mechanisms (PMM), and when simulated through CFD are refereed to as virtual planar motion mechanisms (VPMM). The results from VPMM are used to determine the hydrodynamic derivatives that inform the LPM. There was some inconsistency in the VPMM data based on the frequency and amplitude that the VPMM was run. A brief study was run to look at this effect. Afterwards, Open and closed loop, autopilot assisted, maneuvers are implemented and performed using the LPM model through Simulink. Results of these maneuvers are analyzed for craft stability. Additionally, comparisons of LPM maneuvers to field data are performed. Critiques of the craft stability and effect of the autopilot are made. / Master of Science / The work carried out in this thesis involves the creation of a physics based model of an underwater craft. This physics based model is informed through characteristics determined by running computational fluid dynamics (CFD) simulations. The benefit of such a model, is the simplification from CFD to a 6 degree of freedom (6-DOF) lumped parameter model (LPM). These physics models, LPM, are generated for two particular craft of interest. One craft is an existing design used by NUWC (named Tonnetto), while the other design is one generated to be similar in shape and size to the NUWC craft (named Hokie). Computer simulated maneuvers are carried out using these models to asses craft stability and performance. An autopilot is implemented into the models for some of these simulations to see its affects on the crafts performance. Additionally, these simulated maneuvers are compared to field data collected by NUWC.

PMM testing is a method used to identify the added mass and damping coefficients used in the equations of motion of a vehicle by attempting to decouple the forces on a body due to velocity and acceleration as a result of creating "hydrodynamically pure" velocities and accelerations. This makes it possible to use quasi-steady state models with terms independent of both velocity and acceleration. This paper explores the ability of simple damping models (solely a function of velocity) with added mass terms (solely a function of acceleration) to simulate the heave force of an 8:1 ellipsoid undergoing PMM testing. In order to help explain the complexity of the flow during PMM tests, a flow analysis of the 8:1 spheroid is provided, which discusses the flow topology of spheroids at steady angle of attack, validity of quasi-steady models, and some other basic flow features seen in PMM testing. In this paper, a simple proportionality relationship between a linear and quadratic damping model is revealed. It is also shown that variations in the heave force response during PMM tests are most heavily influenced by viscous effects, especially cross flow separation. Finally, it is shown where these models break down, owing to the increasing nonlinearity of the flow induced by the harsher motions of large amplitude and/or large frequency tests. / Master of Science