Ph.D. Thesis

In this page you find a summary of my Ph.D. thesis and a link to the final version of the thesis.


 

A brief summary of my Ph.D thesis

During my Ph.D. project I focused on the design of several control methods for autonomous marine vehicles. These kind of vehicles are used for a number of operations which may be dangerous or impossible to perform for a human operator. An example is the exploration and mapping of the sea bed in arctic environment. Therefore, it is important to develop control laws which allow unmanned vehicles to safely and robustly execute dangerous tasks in complete or partial autonomy.

Marine vehicles are under-actuated, that is, they have less degrees of actuation than degrees of freedom. In other words, the motion of an under-actuated vehicle is subjected to some constraints and there are some directions in space where the vehicle cannot directly move. For instance, a marine vehicle cannot directly move sideway while moving forward. This condition makes non-trivial the design of control laws for the motion of these kind of vehicles.

My Ph.D. thesis deals with a number of control problems for under-actuated vehicles:

  • Path following of marine vehicles: The path following task requires a vehicle to converge and move along a given path with constant forward velocity. For practical applications, this is a very important problem since when a vehicle is deployed for executing an exploration task, it is required to follow a desired path. The thesis deals with the path following control problem tackling it from different perspectives. In fact, strategies for straight-line and curved paths are presented. Furthermore, strategies considering parametrized and unparametrized paths are also given;
  • Trajectory tracking problem: The trajectory tracking task is similar to the path following one. The main difference stays in the fact that the trajectory tracing problem gives time constraints to the motion of the vehicle, that is, the vehicle is required to converge to a path and move along it but at a certain point in time the vehicle has to stay at a specific point of the path.
  • Synchronization of multi-vehicle systems: The use of marine vehicles is generally expensive and the cost generally depends on the time of deployment, especially if the mission has to be performed in harsh environments, for instance, arctic environments. Therefore, it is common to use several marine vehicles simultaneously in order to cover larger area during the exploration phase and consequently save time and money. At this point, it is clear that it is relevant to design control laws for the coordination or synchronization of the motion of the vehicles. In my Ph.D. thesis this problem is covered.
  • Source seeking control problem:  Marine vehicles are also used for surveillance and monitoring tasks. In particular, the vehicles may be used to monitor pipelines or other infrastructures and detect if and when maintenance is necessary. An example may be the surveillance of a pipeline in order to detect possible leaks. When a leaks occur the vehicles may send a message to a ground station in order to let operators intervene and fix the problem, or, in some cases, the vehicles may intervene if equipped with the right and appropriate tools. The thesis deals also with design of a coordination control law for multi-vehicle systems which may improve the effectiveness of surveillance tasks.

A copy of the thesis can be found here.