Positioning Of Large Surface Vessels Using Multiple Tugboats PDF Download

The goal of this Trident project was to develop an independent control scheme to allow a team of autonomous tugboats to move a large disabled vessel, such as a barge, to a desired position and orientation. Independence refers to the extent to which each tugboat's actions were free from knowledge of the locations and actions of other tugboats. Performance of the team was quantified by measuring the positional error and time required to affect the motion, while respecting maximum power constraints on the thrust. Applications of the project include difficult or dangerous tasks such as moving disabled vessels or vessels "not under command" through hostile or dangerous areas, and transportation of large objects such as marine construction equipment, off-shore bases, drilling platforms, and sonar arrays. Although it would be ideal to increase both the independence and performance of the system, it must be realized that by increasing one of these, the other is typically degraded. In order to measure performance, a control strategy (the baseline) was designed that required the attachment points of all tugboats to be known. However, this architecture was not desirable, since it was less independent of system knowledge. In contrast, to allow for the elimination of known tugboat location, an adaptive control strategy was developed which resulted in degradation of performance. These two Scenarios were explored and in the course of solving them, the tradeoff between performance and independence was quantified. To the author's knowledge, this is the first study of its kind and complexity. Although previous work has studied adaptive control of a multi-input and multi-output system, its extent and focus was not close to this research. Each tugboat used on-line adaptive control methods to compensate for the unknown actions of other swarm members. The analysis was verified through simulation. In addition, an experimental proof-of-concept device was built and in-water experiments were used to validate the results. An incremental approach to experiment design was used to mitigate the challenges of in-water experimentation.