S. Esteban

Fast Ferry Vertical Accelerations Reduction with Active Flaps and T-Foil

Abstract The research deals with the design and use of actuators to improve the seakeeping performances of a fast ferry. The interest of the research is now restricted to heaving and pitching motions, with heading sea. The ship has active control surfaces (flaps and T-foil). The paper presents a control-oriented model of these actuators, in SIMULINK. This model can be easily coupled with a SIMULINK model of the ship, furnishing a simulation environment for control studies. Using this facility, a study of control alternatives (moving the actuators) has been started. We include in the paper first results with conventional PID control, which are useful as reference for comparison purposes.

Improving the comfort of a fast ferry

A study was conducted to determine the effectiveness of using controlled flaps and a T-foil to smoothen a ships vertical motion while navigating in head seas. The study comprised two steps: to develop a tool for control design in the form of a computer-based simulation and to use this tool to develop satisfactory controllers. The simulation was based on mathematical models of the ship, the actuators, the waves and the seasickness effect. Since the actuators have limited action, there is a limited margin for improvement based on more sophisticated control strategies. Possible improvements of motion sickness incidence (MSI) are linked to a control strategy that exploits better synchronization with incident waves.

Experimental Study of Controlled Flaps and T-Foil for Comfort Improvement of a Fast Ferry

Abstract Fast ships can suffer important negative effects from vertical accelerations. The sea-sickness of passengers is related, in a cumulative form, to these accelerations. Our research deals with the alleviation of vertical accelerations, using appendages that can move under control to counteract each incident wave: a T-foil near the bow and transom flaps. After a long modelling work, involving experiments in a towing tank institution, the conditions for the study of control design have been established. First experimental confirmations of the efficacy of controlled appendages have been achieved. A well tuned P.D. has been tested, with very promising results. The paper begins with a short recapitulation of the previous research. Next, the paper focus on the experiments with a replica with appendages.

Modelling of a High Speed Craft by a Non-Linear Least Squares Method with Constraints

Abstract A non linear least squares method with constraints have been tried. However, the extra complexity associated with non-linear systems, with constrains and no initial information of model structure, means that exhaustive search is not always feasible. In these cases genetic identification strategy can be used to obtain initial values. On the other hand, a trend in the area of system identification is to try to model the system uncertainties to fit the available analysis and design tools of robust control. The method described is applied to obtain the interval model of the vertical dynamic of a high speed craft for different speed, and comparative results obtained with the mathematical model and with a scaled model in a towing tank are showed.

A Simulation Tool for a Fast Ferry Control Design

Abstract The research considers a fast ferry with active appendages (actuators): a T-foil near the bow and transom flaps. The objective is to attenuate the ships vertical motions. There is a problem of control design, to move the actuators in the most effective way. For an easy and safe control study, a simulation tool has been developed using MATLAB and SIMULINK: a modular architecture results where it is easy to integrate control strategies to be analysed. Simulated experiments can be run with the tool, to see the behaviour of the important variables: vertical motions of the ship, motions of the actuators, sea-sickness incidence, etc. The paper describes the simulation tool from a functional point of view, and explains some details of the main parts of its internal structure.

Fast ships models for seakeeping improvement studies using flaps and T-foil

Fast ships are taking a relevant role with a clear interest for military purposes. Fast sea transportation encounters several problems to be solved. This article refers to the difficulties originated by brisk vertical motions. The waves encountered by fast ships induce such vertical motions, and this has negative effects: navigation risks, sea sickness, structural damages, and load displacement. It is also interesting for military uses to stabilize the ship when an aircraft is landing or when precision firing is required. By means of submerged actuators, it is possible to alleviate vertical motions. In this research, a pair of transom flaps and a T-foil near the bow are used to counteract the waves. These actuators must move with the maximum efficiency, taking into account the dynamical characteristics of the ship. As a consequence, there is a problem of automatic control design. To carry out this design, it is important to obtain mathematical models of all the aspects involved in the problem: the ship, the waves, the actuators, and the effect on crew and comfort. The aim of this paper is to present the development of these models and the use of them for problem analysis and control design.

The control of specific actuators for fast ferry vertical motion damping

The vertical motions of fast ships, which have a negative effect on comfort and safety, can be attenuated using moving actuators. There is the need of a control strategy to move the actuators in the most convenient way, considering several objectives. The paper considers this problem, studying a practical real example. Experiments with a scaled down replica of a fast ferry has been done, first for modeling purposes and second for control studies. Linear control shows serious application problems. Taking this into consideration, a nonlinear control approach is devised, with satisfactory results.

Control Code Generator Used for Control Experiments in Ship Scale Model

After a study of control design to get a good candidate for testing, it comes a step of experimental confirmation. The general objective of the research is to smooth the vertical motions of a fast ferry. A T-foil and transom flaps are added to a scaled-down replica of the fast ferry. These appendages can move under control. So there is a control system installed on the replica, that moves the appendages using motors, and measures the main variables of the ship and actuators motions. This control system is based on an industrial PC with electronic interfaces for motors and sensors. The control algorithm obtained by the design, must be implemented as real-time control software, to be executed on the industrial PC. For a fast and easy translation from design to real-time application, a new software tool has been developed. This tool generates directly C++ code, easy to compile, from a graphical description of the control. With this tool, the experiments have been achieved in short time. During experiments, several non expected circumstances appear, but this was not a problem: the tool allows for an easy improvement of the original design. The paper describes the tool and its use during experiments.

NEURO-FUZZY MODELLING OF A FAST FERRY VERTICAL MOTION

Abstract A neuro-fuzzy system has been developed to model the behaviour of a fast ferry. The sources of the available knowledge are the physical laws of the vertical dynamics of the craft, and some experimental and simulated data of the ship performance in regular waves. The non-linear model has been obtained by applying adaptive neurofuzzy inference. It is focus on the vertical motion of the craft, both heave and pitch. The modelling problem is complex and the results are original, and have been proved satisfactory for regular waves.

OVERVIEW OF A RESEARCH ON ACTUATORS CONTROL FOR BETTER SEAKEEPING IN FAST SHIPS

Abstract The paper is an overview of a research initiated seven years ago by three groups of three universities, under the auspices of a Spanish shipbuilder. The research aims to improve the seakeeping performances of fast ferries, by using moving appendages such transom flaps and T-foil. There is a problem of control design to move the actuators in adequate way, to counteract the effect of encountered waves. The research focuses on alleviation of seasickness. Several aspects have been covered along the research, motivating a long series of papers. The overview gives an ordered account of the main results, with the corresponding references. Main results concerning seasickness and navigation, prediction of seasickness during ship design, experimental modelling, control design and experimental verification, are presented.