This paper addresses two interrelated problems concerning the planar three degree-of-freedom motion of a vehicle, namely, the path planning problem and the guidance problem. The monotone cubic Hermite spline interpolation (CHSI) technique by Fritsch and Carlson is employed to design paths that provide the user with better shape control and avoid wiggles and zigzags between the two successive waypoints. The conventional line-of-sight (LOS) guidance law is modified by proposing a time-varying equation for the lookahead distance, which is a function of the cross-track error. This results in a more flexible maneuvering behavior that can contribute to reaching the desired path faster as well as obtaining a diminished oscillatory behavior around the desired path. The guidance system along with a heading controller form a cascaded structure, which is shown to be $\kappa$ -exponentially stable when the control task is to converge to the path produced by the aforementioned CHSI method. In addition, the issue of compensating for the sideslip angle $\beta$ is discussed and a new $\kappa$ -exponentially stable integral LOS guidance law, capable of eliminating the effect of constant external disturbances for straight-line path following, is derived.

Integral LOS Path Following for Curved Paths Based on a Monotone Cubic Hermite Spline Parametrization

On uniform semiglobal exponential stability (USGES) of proportional line-of-sight guidance laws

The path-following (PF) problem of an autonomous underwater vehicle (AUV) is studied, in which the path convergence is viewed as the main task while the speed profile is also taken into consideration as a secondary task. To accommodate the prioritized PF tasks, a novel multiobjective model predictive control (MPC) (MOMPC) framework is developed. Two methods, namely, weighted sum (WS) and lexicographic ordering, are investigated for solving the MOMPC PF problem. A logistic function is proposed for the WS method in an attempt to automatically select the appropriate weights. The Pontryagin minimum principle is subsequently applied for the WS-MOMPC implementation. The implicit relation between the two methods is shown, and the convergence of the solution with the MOMPC PF control algorithms is analyzed. Simulation studies on the Saab SeaEye Falcon AUV demonstrate the effectiveness of the proposed MOMPC PF control.

Path-Following Control of an AUV: A Multiobjective Model Predictive Control Approach

A mix between a monograph and an article collection, this PhD thesis considers the concept of guided motion control for marine vehicles, in particular focusing on underactuated marine surface vehic ...

Topics in Guided Motion Control of Marine Vehicles

https://www.fossen.biz/home/papers/LekkasFossen%20MCMC%202012.pdf

A Time-Varying Lookahead Distance Guidance Law for Path Following

MPC-based optimal path following for underactuated vessels

Autonomous ships are creating significant interest in the maritime world and the need for a more consistent definition framework is very apparent. This paper suggests building a framework based on the SAE J3016 standard for autonomous cars, but to extend it where necessary. One main difference is that ships are larger, slower and fewer than cars, but that consequences of accidents may be more severe. This is a typical characteristic of industrial autonomous systems. For ships one also must consider a more complex functional system (duration of voyage, energy, steering, hull integrity and stability etc.) as well as a very likely possibility that autonomous ships will be supervised form shore. This points to a constrained autonomy, where the system has programmable limits to the actions it may take. This creates a more complex taxonomy, in terms of the operational scenario possibilities, in how the control problem is solved and how responsibilities are divided between humans and computer systems.

/pdf/characterization-of-autonomy-in-merchant-ships-qbtakiwaxt.pdf

Characterization of Autonomy in Merchant Ships

Current guidelines for approval of autonomous ship systems are focused on the ships’ concrete operations and their geographic area. This is a natural consequence of the link between geography and the navigational complexity, but moving the ship to a new area or changing owners may require a costly re-approval. The automotive industry has introduced the Operational Design Domain (ODD) that can be used as a basis for approval. However, the ODD does not include the human control responsibilities, while most autonomous ship systems are expected to be dependent on sharing control responsibilities between humans and automation. We propose the definition of an operational envelope for autonomous ship systems that include the sharing of responsibilities between human and automation, and that is general enough to allow approval of autonomous ship systems in all geographic areas and operations that falls within the envelope. We also show how the operational envelope can be defined using a system modelling language, such as the unified modelling language (UML).

/pdf/towards-approval-of-autonomous-ship-systems-by-their-49lp0fxcr2.pdf

Towards approval of autonomous ship systems by their operational envelope.

New developments in maritime industry include the design and operation of autonomous ships. The AUTOSHIP project is one initiative promoting the use of autonomous ships in European waters focusing on two specific use cases, a Short Sea Shipping (SSS) cargo vessel and an Inland Waterways (IWW) barge. The AUTOSHIP objectives include thorough regulatory, societal, financial, safety and security analyses for the two investigated use cases as well as the development of a novel framework and methods for the design of autonomous vessels. This objective is achieved with the support of a number of activities, including supply chain, regulatory, risk and gaps analyses. Some results and findings from these activities are presented in this paper. The results demonstrate that the supply chain analysis is important to understand the complex relationships between different partners and phases for the effective design of maritime autonomous systems. Furthermore, a number of regulatory gaps needs to be addressed for the wider adoption of the AUTOSHIP use cases. There is a number of essential hazards associated with each of the two use cases; measures to mitigate these hazards are presented.

Paving the way toward autonomous shipping development for European Waters – The AUTOSHIP project

The Concept of Operations, or ConOps, has become a central document for the specification, design and approval of autonomous ship systems and operations in the absence of prescriptive rules and regulations. The flexible structure of the ConOps and the fact that it is written in prose text makes it very accessible for all involved stakeholders, but also prone to discrepancies between the descriptions and the actual design. This paper proposes a description framework, for autonomous ship systems and operations, that covers the information items requested through the ConOps. The proposed framework has the potential to facilitate development of a formalized ConOps, which in turn could lead to a standardization of the current approval procedures for autonomous ship systems and operations.

Håvard Nordahl

Papers

MPC-based optimal path following for underactuated vessels

Characterization of Autonomy in Merchant Ships

Towards approval of autonomous ship systems by their operational envelope.

Paving the way toward autonomous shipping development for European Waters – The AUTOSHIP project

A framework for description of autonomous ship systems and operations