Co-Design of Planing Craft and Active Control Systems.

Abstract

The available planing craft design tools and guidelines were not envisioned to be used with vessels that have Active Control Systems (ACS). Consequently, vessels with ACS are conventionally designed in a sequential manner: first, the geometry of the vessel is designed using traditional guidelines, and then the ACS is implemented. However, sequential design is not always optimal for systems whose dynamics are coupled. This work establishes a co-design framework for a planing craft and its ACS, combines tools in the disciplines of naval architecture, control systems, and optimization in a novel way to perform co-design studies, and compares them with the sequential design. The study was limited to numerical studies based on reduced order models and the strip-theory time-domain planing craft simulation program POWERSEA. The planing crafts studied are prismatic and have a 12 m length and 10.2 tonne displacement. The ACS is modeled as body forces and the controller investigated is a linear-quadratic regulator (LQR); this work did not look into the design or optimization of the ACS's hardware. The calm-water performance was measured with a semi-empirical reduced order model and with POWERSEA. The seakeeping and seaway drag were estimated in sea states (SS) 2 and 3 and the Pareto front was estimated from an exhaustive search that varied the vessel's longitudinal center of gravity (lcg), deadrise and pitch velocity gain for the LQR estimation. Afterwards the Pareto estimation technique Adaptive Weighted Sum (AWS) was modified to better suit the Pareto estimation performed in this study, resulting in the Modified Adaptive Weighted Sum (MAWS). MAWS was applied to the case where the vessel's beam, lcg, deadrise and the LQR's pitch and heave velocity gains are optimized for SS 3. Finally, the real-world feasibility of designing the sequential and co-design vessels, obtained from the MAWS, was investigated with a case-study. Co-designing shows potential to significantly reduce calm-water and seaway drag (10% in some cases), and improve seakeeping (20% in some cases). Thus, the co-design framework offers an opportunity for designing planing craft that are more efficient and have better seakeeping than any planing craft ever built before.