The 21st century is a century of ocean. Ocean contains rich resources such as biology, oil and gas, mineral products, and etc., and it becomes the strategic space and resource base for the survival and sustainable development of human.

Due to the increasing complexity of ocean environment, diversity of tasks, and limited ability of single USV, current research on USV has shifted to cooperative control of multiple USVs. Coordinated USV systems can significantly reduce the operational burden, and enable large-scale, sustained, and intelligent marine operations.

In military field, coordinated USV systems have been playing an increasingly important role in many applications such as collective demining, collaborative escort, cooperative situational awareness, swarm tracking, and coordinated enclosing of the enemy ships. In civilian field, coordinated USV systems can greatly extend the range of marine operations, and execute more challenging missions which cannot be practiced or efficiently done by a single one.

To achieve the coordination of multiple USVs, coordinated path following is one of the most efficient methods. Coordinated path following of USVs has been studied by many researchers. Most studies focus on coordinated path following of multiple USVs over multiple parameterized paths, where a parallel formation is achieved by using a path variable synchronization method.

Later, a path variable containment approach is proposed for coordinated path following of USVs along one curve, and a queue formation is achieved. However, these studies are dedicated to formation control schemes over open curves.

In many circumstances, closed paths are preferable by oceanographers, since the sensor measurements collected along repeated orbits can be interpreted without using a complex ocean model. However, little attention has been paid to coordinated path following of USVs on a closed curve.

A new research paper named "Saturated Coordinated Control of Multiple Underactuated Unmanned Surface Vehicles Over a Closed Curve" is published in SCIENCE CHINA Information Sciences by PhD candidate Lu Liu? Professor Dan Wang, Associate Professor Zhouhua Peng from Dalian Maritime University, along with Professor H.T. LIU from University of Toronto.

A saturated coordinated path following control method is presented for multiple underactuated USVs on a closed curve, holding a symmetric formation pattern. Each vehicle is subject to unknown sideslip, uncertain vehicle kinetics, and limited control torques.

Robust adaptive coordinated controllers are developed by combing a parameter cyclic pursuit approach, a line-of-sight guidance principle, a reduced-order extended state observer neural networks and a dynamic surface design method. The key features of the proposed coordinated path following control method are as follows.

First, a parameter cyclic pursuit approach is proposed to guarantee that the vehicles are evenly distributed over the closed curve for achieving a symmetric formation. Second, the communication data is minimum, and each USV only receives the information from the one previous to it. Third, the control inputs of the coordinated controllers are bounded with the bounds known as a priori.

Research Report: "Saturated Coordinated Control of Multiple Underactuated Unmanned Surface Vehicles Over a Closed Curve "

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