During the last decade there has been considerable interest in the design and development of uninhabited underwater vehicles (UUVs). Many advancements have been realized in this area, however, the need for advanced navigation, guidance and control (NGC) systems for UUVs continues to grow as the demands increase for such craft to undertake more complex missions. Within the context of this special issue, UUV is taken as being a generic term to describe both autonomous underwater vehicles (AUVs) and remotely operated vehicles (ROVs). Also classed in the AUV category are underwater gliders.
The dynamic characteristics of an UUV present a control system design problem which classical linear methodologies cannot easily or effectively accommodate. In addition, given the environment in which such vehicles operate, sophisticated NGC systems are essential particularly where the onboard sensor suites are low cost. Further complications also arise in the design of a NGC system for a vehicle where it is required to function and co-operate with others in a group to fulfil the objectives of a given task.
To complete a task successfully requires a meticulous mission planning strategy to be evolved prior to and during its execution. In the case where an UUV is employed to fulfil the requirements of a mission objective there is no exception. Hence the first paper in this special issue by Carreras et al. is concerned with the design and implementation of a mission control system for an AUV based upon the implementation of a Petri net in real time in a behavioural control architecture.
Whilst a mission is underway it is extremely important for an UUV to know its orientation and position as accurately as possible. Indeed, many in this research area consider the providing a solution to the problem of navigation of such vehicles as being the one of the greatest challenges. Thus the next four papers relate to various aspects of navigation. The paper by Oliveira proposes a multi-model adaptive estimator as a terrain reference system for UUVs. Whereas Wang et al. develop the concept of a variable buoyancy AUV with the capability landing and remaining on the seabed for long periods gathering data. An important aspect of UUV navigation is collision avoidance. This is considered by Tan et al. who report a novel obstacle avoidance system based on a unique amalgamation of the manoeuvre automaton and rapidly-exploring random tree algorithms with a state-dependent Riccati equation controller. In addition, Molnar et al. discuss the design of a highly manoeuvrable UUV platform for undertaking high resolution seabed surveys in both shallow and deep water.
Closely allied to the navigation problem of a UUV is the difficulty associated with vessel guidance. Guidance being linked to the generation and detection of a path trajectory for a given craft. Whilst heading control is instigated via a suitably designed autopilot. Of course, other degrees of freedom may also be controlled such as roll and pitch for example in order to ensure a stabilized and steady platform for the vehicle's sensor suite and/or payload. In the past, many guidance and control subsystems for vehicles have been developed separately adopting the philosophy that the latter can be designed with a sufficiently large bandwidth to track the command signal from the former thereby leading to a suboptimal performance in many cases. Here several facets of guidance and control are reported in a further five papers. In Cavalletti et al. a switching control scheme is proposed to allow a ROV to cope with different load configurations. The stability of the control scheme being analysed using Lyapunov theory. Aquiar and Pascoal address the problem of dynamic positioning and waypoint tracking of an underactuated AUV with a nonlinear adaptive controller. This is followed by the paper by Caccia and Bruzzone who describe the design of an execution controller for a ROV NGC system. The NGC tasks being represented on a Petri net as a discrete event system. Nasuno et al. report the development of a small AUV that employs a control system design based on linear matrix inequalities in order to cope with the speed dependent dynamic behaviour of the vehicle. Furthermore, Refsnes et al. present an output feedback controller for an underwater vehicle which is used to reduce the destabilizing effect of dynamic forces and moments that act upon it whilst in operation.
Notwithstanding the intellectual and technical demands of designing and developing a NGC system for an individual UUV, matters are exacerbated when a mission scenario requires the use of a number of underwater vehicles working in concert. The four remaining papers are concerned with multiple UUV control. In the work by Caiti et al., two algorithms are introduced for adaptive online planning of oceanographic missions that are to be performed in cooperation by a team of AUVs. Whilst Giovanni et al. propose an algorithm for autonomous strategic mission planning to allow multiple UUVs to cooperate in order to perform a variety of tasks. The question of mission planning is considered as a receding horizon mixed integer constrained quadratic optimal control problem. Additionally, Wu et al. use a genetic algorithm based path planning algorithm that allows a swarm of AUVs to perform a surveying mission in the presence of known obstacles. Likewise, Zhang et al. model a class of underwater gliders as Newtonian particles for navigation and control purposes.
Finally, the guest editors would like to thank the editor-in-chief of the International Journal of Control, Professor Eric Rogers, for his assistance and guidance with the preparation of this special issue. Also the friendly assistance in the preparation of the issue by the authors is gratefully acknowledged. In addition, they are to be congratulated on producing papers of such excellent quality. Furthermore, due recognition must be given to the referees for their support in this endeavour and the unselfish manner in which they reviewed and commented on the papers that have been presented. Through their academic prowess and enthusiasm, it has been possible to ensure and maintain the high quality publication output that is the hallmark of this journal. It is sincerely hoped that readers from all disciplines will find this special issue interesting, stimulating and useful in whatever aspect of UUV design they are involved, and that it will also provide the genesis for the importation of ideas into other fields of study.