Podded propulsion systems offer greater maneuvering possibilities for marine vehicles than conventional shaft and rudder systems. As the propulsion unit rotates about its vertical axis to a specified azimuth angle, the entire thrust of the propeller contributes to the steering moment without relying on lift generation by a control surface such as a rudder. However, the larger sideforce and moment cause the ship to enter the nonlinear realm sooner than a ruddered vessel. Furthermore if the rudder or azimuthing propulsor is aft of the vessel's center of gravity then the system is non-minimum phase; during a turn the ship center initially moves in the direction opposite the turn. For these reasons it is necessary to design a robust maneuvering control system to set the azimuth angle of the propulsor in an intelligent and stable manner. This thesis focuses on the path following performance of a vessel with podded propulsion. The enhanced maneuvering abilities of such vessels allow the time constant of cross-track error response to be greatly reduced. Additionally these vessels can follow course changes and waypoints more precisely than ruddered vessels.

    (cont.) A simple path following algorithm was developed to achieve this performance; the algorithm uses simulation-based feedforward terms to anticipate the sliding motion of the vessel during a turn. The stability and performance analysis was performed in three domains: linear theory, a nonlinear simulation, and experiments with a 12-foot autonomous surface vessel. Experiments confirmed that path following performance was vastly improved using the feedforward algorithm for waypoints at which the course change angle was large.


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    Title :

    High performance path following for marine vehicles using azimuthing podded propulsion



    Publication date :

    2006


    Size :

    102 pages , 4301922 byte , 4306128 byte


    Remarks:

    Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.
    Includes bibliographical references (p. 101-102).


    Type of media :

    Theses


    Type of material :

    Electronic Resource


    Language :

    English