No description available.

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.

Recent developments in autonomous underwater vehicles (AUV) have created the need for a low cost AUV that is comparable in class and payload capabilities to existing, commercially available, expensive and sub-optimal crafts. The Navy is active in research of autonomous, unmanned, highly efficient, high speed underwater craft. Small, low cost AUVs capable of swarm control are of special interest for military mine applications. No matter the nature of the application or class of craft, a common challenge is the accuracy of maneuvering predic- tions. Maneuvering predictions not only affect design, but also the real time understanding of mission capabilities and endurance. Thus the proliferation of AUVs in recent times for commercial and defense applications have led to the need of higher fidelity of physics based lumped parameter models. The sensor data, along with maneuvering model data can tie into a more accurate trajectory. Multiple such incremental advances in the literature for prediction of maneuvering shall lead to a more accuracy. This work hopes to bridge some important gaps that ensure the creation of such a non-linear LPM to predict the maneuver- ing characteristics of an AUV using non linear hydrodynamic derivatives obtained through static and dynamic CFD. This model shall be implemented for the craft designed for DIVE technologies, our industrial sponsor and an in-house craft, the 690. This model shall also be made generalized for most submerged craft with a torpedo or slender hull form, with cruciform or X configuration of fins. This dissertation looks to provide the framework to identify CFD informed high fidelity dynamic model for AUVs. The model thus created shall be spe- cialized to account for specific important effects such as flow interaction among appendages, effect of using steady and unsteady maneuvers as CFD information and kinematic charac- teristics of captive maneuvers. The specific, innovative contributions in this dissertation are listed below: 1. Definition of a new stability index to incorporate effects of gravity at low-moderate speeds 2. Novel method for identification of hydrodynamic derivatives 3. Systematic and comprehensive study on the parameters affecting VPMM / Doctor of Philosophy / The maneuvering model for an AUV is an indispensable tool that makes the autonomy part of AUVs possible and efficient. The maneuvering model that exists today is mostly linearized and of lower fidelity to increase efficiency. The use of a non linear, higher order hydrodynamic model facilitates better accuracy of maneuvering predictions, essential to mission completion of AUVs applied in research and defense sectors. This higher fidelity can be achieved through informing the model using CFD that is reasonably efficient in computation. This dissertation presents a non-linear, higher order hydrodynamic maneuvering model for the 690 and DIVE crafts, informed with steady and unsteady CFD.