J.M. Riola

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.

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.

Ships confining an oil spill over: a scenario for automatized cooperation

Cooperation between robots is an important contemporary issue. This can be translated to the marine environment, either using marine robots or introducing automatics in the operations of ships. A general research on this kind of problems has started in our group, after several years of developing autonomous robotized ships. Several scenarios have been proposed for the study of cooperation details. This paper focus in a very interesting case, which is representative of other cases: several ships towing booms for oil spill over confinement. It turns out that the cooperation problem is not trivial. Along the operation several phases can be distinguished, and several coordination problems and needs appear. A computer simulation has been developed, after physics based analysis, and some initial coordinated control strategies have been proposed and tested. These strategies are supposed to be applied through verbal orders to captains. Along the operation phases the role of captains change, for an adaptive coordination. The paper introduces the research topic, then describes the scenario and its simulation, then focus on the cooperation problems emerging from the operation phases and the control and coordination solutions that have been proposed, and finally draws some conclusions.

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.

A cooperation scenario in the marine environment: First outlook

Abstract Marine environments offer suggestive scenarios for Automatic control and Cooperation strategies to be applied. The present paper focus on a particular one: Two ships towing together an off-shore oil retaining boom. Basic dynamical equations are presented for the combined displacement of both ships plus the boom. Computer simulation of basic manoeuvres works out the basic control implications of the problem and suggests cooperation among the ships as a more reliable technique to fulfil ships goals and minimize boom strain.

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.

Genetic planning of control actions for a high manoeuvrability AUV

For certain operations the control of AUV motions is subject to difficulties, due to motion coupling. In this paper a high manoeuvrability AUV is considered, with only thrusters for motion control. A Genetic planning of the control actions has been devised, considering a multiobjective optimisation problem, which includes energy and time saving, and smooth operation with realistic control actions. Since the inertia of the submergible filters out control brisk changes, it turns out that there are many almost equivalent control strategies obtaining similar trajectories. This is why the characteristics of the control actions have been included as part of the multiobjective optimisation. Several diving scenarios have been specified, including obstacles. The paper begins with a description of the AUV and the control problem, then it focus on the multiobjective optimisation problem and the genetic planning to solve the problem, then it considers several scenarios and present optimal results; finally, the paper comes to conclusions and future research, which will be experimental.