On Model Predictive Control for Single-Strut Hydrofoil Vessel

Sammanfattning

This thesis investigates autonomous waypoint navigation for the single-strut electric hydrofoil vessel FoilCart II through the integration of modeling, planning, and control. A nonlinear six-degree-of-freedom first-principle model was derived to capture vessel dynamics and used as the baseline for controller design. A waypoint-based global planner was implemented using Bézier-spline trajectories with explicit acceleration minimization to satisfy seakeeping comfort limits. At the control level, a hierarchical architecture was developed, combining a nonlinear model predictive controller (MPC) at the coordination layer with the existing linear quadratic regulator (LQR) at the execution layer. The integrated MPC-LQR framework achieved substantial improvements in trajectory tracking compared to LQR alone. In the tested waypoint mission, position and heading root-mean-square errors were reduced by an order of magnitude, while accelerations remained within the ±0.25𝑔 comfort band. Real-time feasibility was demonstrated with an average MPC solution time of approximately 9.5ms at a 10Hz update rate. In parallel, this thesis also explored model augmentation from resid- ual dynamics using the Wide Array Nonlinear Dynamics Approximation (WyNDA) algorithm, which is a data-driven dynamics approach that augments a known baseline model by treating it as the fixed part of the dynamics and discovering the missing physics as residual terms. Although it did not succeed in identifying a usable discrepancy model under the available data, WyNDA exhibited accurate state estimation and demonstrated real-time computational performance, highlighting its potential for future augmentation with higher- frequency sensor data. The main limitations of the study include reliance on a non–real–time simulator, the assumption of fully observable states, and validation restricted to cruise speeds of around 8 m/s. Nevertheless, the results confirm that combining trajectory planning with a two-layer MPC–LQR structure provides a solid foundation for autonomous hydrofoil navigation and serves as a baseline for further model augmentation and real-world implementation.