Rocío Muñoz-Mansilla

The problem of the coupling of the vertical movement control with roll movement in fast ferries

Abstract Previous researches have studied the attenuation of heaving and pitching motion in fast ferries. One observed problem that appears in these cases is the fact that actuators action (for instance, asymmetries T-foil), waves incidence with angle, and the control action itself cause a coupling with roll movement, and therefore an increasing in the rolling vertical component. Roll motion can be less relevant than the damped longitudinal movement, but it is significant and, in fact, it can result in unpleasant effects to passengers. In this work an analysis and design of a roll control have been carried out.

Nonlinear Control for Trajectory Tracking of a Nonholonomic RC-Hovercraft with Discrete Inputs

This work studies the problem of trajectory tracking for an underactuated RC-hovercraft, the control of which must be done by means of discrete inputs. Thus, the aim is to control a vehicle with very simple propellers that produce only a discrete set of control commands, and with minimal information about the dynamics of the actuators. The control problem is approached as a cascade control problem, where the outer loop stabilizes the position error, and the inner loop stabilizes the orientation of the vehicle. Stability of the controller is theoretically demonstrated and the robustness of the control law against disturbances and noise is established. Simulation examples and experiments on a real setup validate the control law showing the real system to be robust against disturbances, noise, and outdated dynamics.

Temporal Characterization of the Requests to Wikipedia

This chapter presents an empirical study about the temporal patterns characterizing the requests submitted by users to Wikipedia. The study is based on the analysis of the log lines registered by the Wikimedia Foundation Squid servers after having sent the appropriate content in response to users’ requests. The analysis has been conducted regarding the ten most visited editions of Wikipedia and has involved more than 14,000 million log lines corresponding to the traffic of the entire year 2009. The conducted methodology has mainly consisted in the parsing and filtering of users’ requests according to the study directives. As a result, relevant information fields have been finally stored in a database for persistence and further characterization. In this way, we, first, assessed, whether the traffic to Wikipedia could serve as a reliable estimator of the overall traffic to all the Wikimedia Foundation projects. Our subsequent analysis of the temporal evolutions corresponding to the different types of requests to Wikipedia revealed interesting differences and similarities among them that can be related to the users’ attention to the Encyclopedia. In addition, we have performed separated characterizations of each Wikipedia edition to compare their respective evolutions over time.

ROBUST CONTROL FOR THE COUPLING OF LATERAL AND LONGITUDINAL DYNAMICS IN HIGH-SPEED CRAFTS

Abstract In this work, the QFT technique was used to control a system with three degrees of freedom of coupled movement. The example is the coupling between the vertical and the horizontal dynamics of a high-speed craft. Since the angle between the heading and the seaway is different from 180 degrees, the action of the actuators for controlling each dynamic produces a coupling in the other dynamic. Firstly, controllers for the two dynamics were designed separately. Then, the actuator coupling was considered, and finally, it was shown how the controllers reduce the three coupled modes in the whole system.

Identification of longitudinal and transversal dynamics of a fast ferry

Abstract An analysis of the system identification methods have been carried out and a new alternative approach is proposed in order to estimate models for heave, pitch and roll dynamics of a high speed craft. As starting point, a first approach resolves the identification subject as an optimization problem to fit the best model, and uses genetic algorithms and nonlinear least squares with constraints methods applied in the frequency domain. The second and definitive one suggests a new parameterization which facilitates obtaining high quality starting values and avoids non-quadratic functions in the cost function. At last it is shown an example in which the two approximations are applied and compared.

Design of a stabilization control system for high-speed crafts based on robust techniques. Two different approaches

This work handles the design of a stabilization control for a high-speed craft in order to improve comfort and security in maritime transport. The goal is to damp the coupled dynamics of heave, pitch and roll by using active stabilization surfaces such as flaps, T-foil and fins. The methodology used is based on the Quantitative Feedback Theory (QFT) robust technique. Two approaches depending on the degree of coupling are presented. In the first approach, controllers for the longitudinal and transversal dynamics are designed separately and afterwards the actuator coupling is considered. The second approach provides a solution in cases where the effect of the actuator coupling is large. Hence, a combination of QFT and Eigenstructure Assignment (EA) methods is used. For both methods, time-domain simulations analyses for different conditions of sea state and angles of incidence provide satisfactory results and achieve damped responses. It is shown that robust techniques based on QFT methodology result feasible and very suitable since the problem can be applied to any angle of incidence and only one controller is required for any speed or sea state. Therefore they constitute attractive alternatives in the application of a stabilization control of an advanced marine system.

Design of a dynamic positioning system for a moored floating platform using QFT robust control

This paper describes the design of a dynamic positioning system for a moored floating platform by using robust control techniques, particularly Quantitative Feedback Theory (QFT). The goal is to minimize the drift resulting from the wave action by appropriate thrusters control. The model of the platform is a SIMO (single-input multiple-output) system, therefore an interesting question is that the plant has less degree of freedom for actuation and is difficult to control. The control problem of the underactuated system is solved by an iterative multi-stage sequential procedure. Simulation results are presented to demonstrate that the control achieves efficiently the dynamic positioning system. Therefore robust techniques based on QFT methodology constitute attractive alternatives in the application of positioning control of an underactuated marine system.

Applications of QFT robust control techniques to marine systems

In this work an overview of the application of the Quantitative Feedback Theory (QFT) technique to different marine systems is presented. Namely the problems of the stabilization of a high-speed craft, the dynamic positioning of a moored platform and the tracking control of a hovercraft are studied. An interesting question is that the plants have less degree of freedom for actuation and is more difficult to control. The three multivariable nonlinear problems are tackled by different procedures. Performance evaluation analyses and simulations in different conditions are carried out. It is shown that robust techniques based on QFT methodology result feasible and very suitable; and therefore they constitute attractive alternatives in the application of stabilization, dynamic positioning and tracking control of advanced marine systems.

A ROBUST QFT-EIGENSTRUCTURE ASSIGNMENT CONTROL METHOD FOR THE COUPLED DYNAMICS IN HIGH-SPEED CRAFTS

Abstract In this work, a combined QFT/EA approach is used to control a coupled system on a high speed-craft. Since the angle between the heading and the seaway is different from 180 degrees, the action of the actuators for controlling the longitudinal dynamic (heaving and pitching) produces a coupling in the lateral (rolling) dynamic, and vice- versa. The MIMO problem is firstly handled with EA technique in order to decouple the dynamics, which results in three SISO systems to solve with QFT design. It is shown that the combined EA/QFT technique is a robust method that accomplishes decoupling between the three dynamics and damped responses.