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Modeling and control for the reduction of wave induced motion of ramp-connected ships


The focus of the research in this thesis is the control of a unique vehicle in development called the T-Craft. The T- Craft is a surface effect ship (SES) capable of functioning like a catamaran or an air cushion vehicle (ACV). The goal is to ultimately stabilize a ramp connecting a large medium speed roll on/roll off (LMSR) vehicle, such as an aircraft carrier, to the T-Craft. The combination of the T-Craft connected to the LMSR is called the sea base. The system was first modeled by treating each vessel as semi-cylinder mono-hulls and simulated using SimMechanics, a rigid body mechanical toolbox available in Matlab. The ships were connected in a bow-to- stern orientation. In this setup, extremum seeking (ES) was used to tune the ramp length and wave heading to minimize the oscillations. Significant reduction of ramp oscillation was observed. Following tests on the SimMechanics model, a more accurate system model was produced that utilized a wave seakeeping program called AEGIR. This program produces hydrodynamic forces based upon the hull geometry and wave information inputs. In this setup, the T-Craft was modeled as a dual hull catamaran with air cushion effects added separately and the LMSR was modeled as a large mono-hull. Passive control was tested on this new system in the form of a spring damper connection between the ramp and each vessel. Additionally, backstepping was used to control the air cushion pressure in order to reduce the heave of the T- Craft in a side by side connected system. In both cases, ramp angle oscillation reduction is observed

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