A domain-based and reactive COLAV method with a partially COLREGs-compliant domain for ASVs operating in confined waters

Abstract

This article presents a collision avoidance (COLAV) method for autonomous surface vessels operating in confined waters with other vessels, using a novel target ship (TS) domain. The domain is implemented as part of a reactive COLAV method pipeline through the use of control barrier functions (CBFs) to avoid domain violation. A geometric interpretation of a vesselto-vessel encounter is used to classify the encounter type with respect to the COLREGs, and thereby which rules apply. Subsequently, a domain is assigned to the TS, where the domain parameters are rule-specific. In the domain design, the static environment is also considered, where an estimate for the available maneuverable space is calculated and applied when determining the size of each TS domain, in order to achieve a distance between vessels that is both safe and feasible for each encounter. Additionally, domains are assigned to static obstacles based on map data and lidar data. Once all domains for target ships and static obstacles are determined, CBFs are formulated based on the range to and velocity towards each domain. The set of CBFs are applied as inequality constraints in a quadratic program minimizing the vessel’s thrust allocation error. The efficiency and completeness of the novel TS domain are demonstrated through an extensive simulation study. The COLAV method as a whole is demonstrated through both complex simulations with multiple maneuvering vessels, and full-scale experiments with a radar- and lidar-based target tracking system. The proposed COLAV method shows compliance with COLREGs section II.