Design and Validation of a Course Control System for a Wave-Propelled Unmanned Surface Vehicle

Abstract

Unlike common marine vessels, wave-propelled vehicles cannot directly control their speed, but rely instead on the forces exerted by the environment to navigate as intended. The unique navigation capabilities of such vehicles motivate the study of control solutions that adapt the vehicle heading to the prevailing environmental conditions and ensure robust course-keeping performances across different sea states, winds, and currents over extended periods of time. This article presents the design and experimental validation of a path following and course control system for an underactuated, wave-propelled unmanned surface vehicle (USV). The major focus and novelty of this work stands in the analysis of the model nonlinearities that appear when the vehicle propulsion force does not prevail on the wind and sea current forces generated by the environment. In these situations, low maneuverability is experienced depending on the magnitude of counteracting forces and, in some cases, loss of controllability is a risk. Initial investigation of the vehicle’s nonlinear dynamics is followed by derivation of a simplified quasilinear mathematical model that isolates the major source of nonlinearity. This provides a basis for the control design, the theory of which is supported and validated by extensive field experiments. In particular, when the USV’s ground speed is close to zero, the theory shows singularities in the model that lead to instabilities and loss of controllability of the course over ground that is experienced in the field. Our test results verify that an effective solution is to switch to heading control when the ground speed is small.

ENC-based Anti-Grounding and Anti-Collision System for a Wave-Propelled USV

“…Furthermore, the full system functionalities should be further tested in the field in order to assess the validity of the theoretical assumptions. A future work is to include the nonlinear dynamic model of the USV and use that to update the vehicle's state when winds and currents affect its navigation [18].…”

“…This model is however very simplistic, since it assumes no drift due to winds and currents (i.e., χ = ψ, where ψ is the heading angle). As discussed in [18], steering of the USV is very much affected by the environmental forces, making this model not suited to represent the true dynamics of the USV in some cases. Nevertheless, the applicability of this model is confirmed by [19], in which both the kinematic equation and the full 3-DOF model were tested and produced only minor differences in the simulation results.…”

Monitoring the Growth of Coastal Algae Blooms in Harsh Weather Conditions Using a Wave-Propelled ASV: Challenges and Lessons Learned

“…The safe operation of ASVs powered by the environment, over longer periods of time, put demands on the guidance, navigation, and control capabilities. Several solutions to guidance, navigation, and control problems have been developed and tested for different environmentally powered ASVs (Liao et al, 2016;Dallolio et al, 2019;Niu et al, 2016;Wang et al, 2019;Dallolio et al, 2021). The long endurance capabilities of ASVs powered by the environment have already been demonstrated.…”

Assimilation of heterogeneous measurements at different spatial scales in the Arctic ocean and Norwegian sea

“…The AutoNaut USV carries an innovative propulsion system that relies on sea surface waves to produce forward thrust, making it suitable for sustained operations at sea without human assistance. The ground speed of the vehicle is mainly determined by waves and normally reaches 0.5 to 3 knots, although drifting forces generated by winds and sea currents may under certain circumstances degrade speed and impact navigation performance [33]. The USV's heading is governed by an electric stern rudder powered by an onboard battery bank.…”