J. Recas

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.

Model Based Analysis of Seasickness Effects in a Fast Ferry

Abstract In a experimental research about increasing the comfort of a fast ferry, using moving flaps and a T-foil, mathematical models of heave and pitch motions of the ship have been determined. Besides this, knowledge about seasickness and waves has been gathered. This is important to determine good control of the actuators, to avoid or alleviate seasickness of passengers. However this is not all: it is also important to extract some criteria for the captain (manoeuvring), for ship designers and for actuators engineering. Taking advantage of the models obtained, a study of seasickness prediction has been done, and some interesting results have been obtained. Part of these results is also valuable as orientation for the control design. The general perspective of the paper, to tackle the evaluation problem, is an analogy with filters.

Autonomous fast ship physical model with actuators for 6DOF motion smoothing experiments

Abstract This paper describes a new experimental system that has been recently developed for a research on vertical motion alleviation of fast ferries. The case of a fast ferry with a pair of transom flaps, lateral fins and a T-foil is considered. All these actuators should be moved in the most effective way, and an appropriate control strategy must be obtained and tested. A scaled physical model of the fast ferry has been built, with moving actuators and a distributed monitoring and control system. The research considers 6DOF motion attenuation, for any ships heading. For this scenario, an autonomous physical model, not to be towed, is required. The physical model includes two scaled waterjets, with the jet orientation under control. The ship has no rudder. Heading and motion alleviation control includes many sensors and actuators. As a good practical control solution, a distributed architecture based on the CANbus has been devised. There is a set of microcontrollers and an embedded PC as coordinator. The microcontrollers for the actuators simulate the time behaviour of hydraulic cylinders. The microcontrollers for sensors include signal conditioning functions. There is a digital radio communication with an off-shore monitoring system. The off-shore system can display the present and the recorded experiments with animated 3D graphics. The complete experimental platform can be used as an Internet laboratory. The system can be easily tailored for use in real ships.

New results about model based study of seasickness in fast ferries

Abstract As part of a research on increasing the passengers comfort in fast ferries by using moving actuators, some study was devoted to the application of control-oriented models to predict seasickness. The key idea is to apply an analogy of three filters. In a previous paper, some criteria were presented concerning the captain, on how to avoid navigation parameters inducing seasickness, and also criteria were given for the ship designer. In this paper new results are presented, linking two seasickness indexes, and offering a frequency domain method to estimate the comfort of a ship from the beginning of the ship design.

Distributed electronic system for monitoring and control of a fast ship physical model

This paper is related with a research on vertical motion alleviation of fast ferries. A scaled down replica of a fast ferry was built, for experimental studies in a towing tank facility. Some submerged moving actuators were added to the replica: a pair of transom flaps, lateral fins and a T-foil near the bow. Two series of experiments with waves generated in a large basin must be done. One of the series is devoted to modelling, and the second for model-based control studies. Due to the fast motions of the experimental ship, it is not possible to attach it to a computerized carriage with instrumentation (it is part of the towing tank facility). Instead, the experimental ship must be autonomous, with all monitoring and control systems on board. Since there are six motions of the ship to be considered, the number of on-board sensors and actuators, and the complexity of control, take us to decide the design of a distributed electronic system. It is based on a central embedded PC, several microcomputer nodes, and the CANbus. The on board system interacts, using a wireless data link, with an off-shore experiment control and data processing system, with an interesting visualization performance. The purpose of the paper is to introduce this system and the associated experimental framework.

First Principles Modelling Study for the Development of a 6 DOF Motions Model of a Fast Ferry

Abstract Proceeding along a research on the use of moving submerged appendages for motions smoothing of a fast ferry, now a 6 DOF motions model of the ship is needed for control studies, at least to be able to conduct experiments in a basin. During the first steps of the research, restricted to head seas, experience has been acquired about modelling heave and pitch motions. In addition, actuators such flaps and T-foil, have been modelled. Using the models of the ship motions and the actuators, a simulation environment has been developed for control design. After these results, the research faces now a more difficult challenge: to smooth the motions for every heading of the ship. The set of actuators increases with the addition of lateral fins. Experimental data are difficult to obtain: new experimental systems, involving the use of an autonomous scaled down replica of the ship, are under development. The source of data we have in this moment is a CFD program. The purpose of this paper is to combine physical reasoning and the CFD data, to develop the basis of a first 6 DOF motions model of the ship.

A fast autonomous scaled ship for experimental seakeeping control studies

A second part of our research on the seakeeping control in fast ferries, is devoted to general heading and sea state conditions. Although scaled ships are basis for experimental studies, it is not possible to keep using them in towing tanks. The main reason is that high speeds require large space for experiments, so towing tanks are not large enough. This has been noticed after the first part of our research, with head seas, in a 150 m /spl times/ 30 m towing tank with wave maker. Consequently, we are preparing for open air experiments. A new fast autonomous scaled ship has been developed. She is self-propelled, and is self-governed by an embedded PC on-board. The ship carries sensors for heading, speed and seakeeping control. Several scaled moving appendages have been added: two transom flaps, two lateral fins, and a T-foil. The ship uses two scaled waterjets, which also control the heading: the ship has no rudder. A distributed monitoring and control system has been designed and implemented for on-board operation. All equipment has to be very light, since the real fast ferry that we reproduce at 1/40 scale is aluminium made. A digital radio link has been provided for distant off-shore monitoring. The paper describes the autonomous ship, the on-board monitoring and control system, and shows several experimental results with quiet waters and with several types of waves.

Advances in the 6 DOF motions model of a fast ferry

Abstract In the present stage of our research on the use of moving submerged appendages for motions smoothing of a fast ferry, a 6 DOF motions mathematical model of the ship for control studies is under development. This model is needed from the very beginning of the next experimental research, because we are going to use an autonomous scaled physical model of the ship, and we need to design a basic course control. The actuators for motion smoothing of the fast ferry are two transom flaps, two lateral fins and a T-foil. These actuators must be considered by the 6DOF model. In a previous paper we discussed a first principles approach to build the mathematical control-oriented model, using data from a CFD program. On the basis of these principles, now we present new developments of the 6DOF model. In particular, we study the ship dynamic behaviour for heading angles of 180°, 150° and 90°. Some hints are obtained to predict how the model will change for other heading angles.

Actuator and control design for fast ferry using seasickness criteria

Abstract Along our research on increasing the passengers comfort in fast ferries by using moving actuators, frequency domain models to predict seasickness caused by ship motions in different seas states, have been established. Seasickness can be alleviated by a correct control of the moving actuators, in this case flaps, fins and T-foil. The capability of seasickness prediction based on models are useful for actuator and control design focusing on minimizing seasickness. In particular, there is a frequency band where the actuation should intervene; while there are other ship motion frequencies with much less impact on seasickness, so actuators work is not needed and can be saved. The paper is devoted to actuator and control design based on seasickness models. This study considers in particular the effect of actuator area and position on seasickness alleviation. The control design turns out to be nonlinear, due to saturations. A particular actuator and control design example is studied in detail.