Thrust control design for unmanned marine vehicles

Thesis (Master)--Izmir Institute of Technology, Mechanical Engineering, Izmir, 2012Includes bibliographical references (leaves: 65-70)Text in English; Abstract: Turkish and Englishxv, 74 leavesIn conventional electrically driven propulsion systems with fixed pitch propellers, thruster controllers are usually aimed at controlling propeller shaft speed only. Especially in unmanned marine vehicles which operate in dynamic flow conditions, these type thruster controllers provide unsatisfactory thrust responses. The reason for this is that the thrust force is simultaneously affected by dynamic effects like, variable ambient flow velocity and angle, thruster-thruster interaction and ventilation. It is aimed to achieve acceptable thrust tracking accuracy in all kind of dynamic flow conditions in this thesis work. A novel feed-back based thruster controller which includes the effect of incoming axial flow velocity, is designed for this purpose. In controller design, first, thruster propeller's open water characteristics in four-quadrant flow states are measured. Data collected from open water tests are then non-dimensionalized and embedded in the controller's thrust model code. Relation between ideal shaft speed and desired thrust is derived by using the four-quadrant propeller model. The proposed method is evaluated in the experimental test-setup designed for this study to simulate open water conditions. Results indicate that thrust tracking performance of novel controller is acceptable in all four-quadrant flow tests

Autonomous ROV inspections of aquaculture net pens using DVL

This article presents a method for guiding a remotely operated vehicle (ROV) to autonomously traverse an aquaculture net pen. The method is based on measurements from a Doppler velocity log (DVL) and uses the measured length of the DVL beam vectors to approximate the geometry of a local region of the net pen in front of the ROV. The ROV position and orientation relative to this net pen approximation are used as inputs to a nonlinear guidance law. The guidance law is based upon the line-of-sight (LOS) guidance law. By utilizing that an ROV is fully actuated in the horizontal plane, the crosstrack error is minimized independently of the ROV heading. A Lyapunov analysis of the closed-loop system with this guidance law shows that the ROV is able to follow a continuous path in the presence of a constant irrotational ocean current. Finally, results from simulations and experiments demonstrating the performance of the net pen approximation and control system are presented.acceptedVersio

USV based automatic deployment of booms along quayside mooring ships: scaled experiments and simulations

This article explores possible uses of marine Unmanned Surface Vehicles (USV) for the fully automatic deployment of containment booms along quayside mooring ships. The task of the USV is to tow the boom along adequate trajectories. The target is the prevention of contaminant spills in harbors or near the coast, for example during crude transfers. Surrounding ships with booms is becoming a common practice. This scenario belongs to the target of our research: to transfer robotic techniques to marine applications. The article experimentally shows that the USV based automatic deployment can be done, in accordance with a suitable planning in terms of waypoints. Actually, the article presents a successful automatic deployment, with a scale USV and a 50 m long experimental light boom. For the purposes of the research a set of models, of the boom, cables, and the USV dynamics, have been established. Based on these models, a simulation platform has been developed. The platform has been employed for analyzing and planning of experiments, and for the simulation of a real scale boom deployment scenario described in the article. Some recommendations are included in the final section

Development and testing of the propulsion system of MARTA AUV

This work deals with the design of the propulsion system of a modular AUV (Autonomous Underwater Vehicle). The authors describe the design methodologies and the testing devices used for the fast prototyping of MARTA (MARine Tool for Archaeology) AUV actuation system, including drivers, motors and propellers. In particular, the authors introduce the design criteria followed for the preliminary testing activities and the methodologies adopted for fast testing and prototyping of the proposed solutions. This is a quite important topic considering the high customization and the reliability required by this kind of applications