Simulation environment for the investigation of automatized cooperation of marine crafts
Introduction
There are marine operations, such as spill-over confinement, towing, rescue, etc., which involve the cooperation of several ships. In particular, the recent sinking of the “Prestige” oil tanker near the Spanish coast has shown some issues requiring further analysis. For instance, it was noticed that the usual operation for oil spill-over confinement consists in two ships towing a boom. Running some simulations in the environment described in this paper, put into light several coordination difficulties arising with just two ships towing the boom. More than two ships for this task cause still more difficulties. In such a case, the help of automatized real-time coordination procedures would be useful. This can be made with computers on board the ships, bringing advice to the ship captains. The purpose of our research is to add automatization to marine operations. The on-board computer interacts with the ship captain in a verbal form. All computers communicate and think about the operation evolution, to help captains to take optimal decisions for a good achievement of the general operation.
An important step for the research is to establish a simulation environment for the analysis of operations with several cooperating ships. The paper describes a first version of the environment. Some experiments about formations of ships have been already done, offering an interesting basis to analyse cooperation difficulties and possible solutions.
As reflected by the scientific literature, the research on ships working together has started recently. Several different scenarios have been considered. For instance about towing [5], about ship formation control [10], or about synchronization of two ships [6]. The general approach is to extend to the marine context a main stream of contemporary research about multirobot systems [9]. Given a mobile robot, its behaviour may be governed by a reactive [2] or by a deliberative [3] approach, or any combination of both. The term agent is used as an important metaphor, being applied in different areas with a variety of specific meanings. Robots taking own decisions can be considered as agents [7]. Several robots can work as a team, with proper strategies [1], [4], [8]. There are several issues to be considered to constitute a robotic team:
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The existence or not of communication means between agents. In case of having communications, they can be more or less error free.
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The type of coordination strategy. For instance, there is a central coordinator, or not. Decisions can be delegated in more or less extent. The coordination policy may change along an operation.
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Team members can have different capabilities or dynamic characteristics: the team can be homogeneous or heterogeneous (perhaps with hierarchies).
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The external conditions, which can change along an operation in the sea for instance.
The main approach of the simulation environment is that each ship is an agent. Each agent obeys to behaviour rules that are specified using the simulation facilities. The simulation environment is made with MATLAB–SIMULINK. The paper, after a description of the simulation environment, presents two simulation experiments about formation control, highlighting interesting phenomena.
Section snippets
Simulation environment design
According to [4] the cooperation of robots involves three main aspects. One is knowledge of one agent about other agents. Another is coordination between robots, which can be strong, light, or none. The last is organization, which can be strongly centralized, lightly centralized, or completely distributed. In this paper the following specifications have been considered:
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The agents have knowledge about each other.
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The agents are strongly coordinated. Each ship takes decisions taking into account
Details of the simulation environment
In the beginning of the research, it was decided to develop a flexible simulation platform, open to changes in several aspects of the simulation. Consequently, the simulation implementation is modular and prepared for incremental functional enrichment and improvement. The simulation environment has been developed with MATLAB and SIMULINK. The behaviour of the ships has been described with several local automata. The toolbox STATEFLOW has been used, and the results obtained have been
Examples of simulation studies
In the following two sections, two examples of simulation studies will be presented. Both examples have some specifications in common. Let us inform about it.
From years ago we conduct experiments in a towing tank facility near our University, in Madrid. The name of the facility is “Canal de Experiencias Hidrodinamicas de El Pardo (CEHIPAR)”. In particular, we use a 150 m × 30 m basin with a wavemaker. Five scaled down ships have been built for the research on cooperative marine operations. This is
Conclusions
In this paper a simulation environment has been introduced for the study of automatized cooperation in marine crafts operations. It is a modular and flexible environment where different cooperation protocols can be studied, and many types of operational scenarios can be defined. It is open for improvements and functional empowering. It can also be used for other robotic contexts, such aerial vehicles.
The simulation environment is being used to establish good cooperation protocol candidates, to
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