Design and Control of the "TransBoat": A Transformable Unmanned Surface Vehicle for Overwater Construction

TL;DR

The paper presents the TransBoat, a transformable omnidirectional USV designed for overwater construction under wave disturbances, featuring four deployable outriggers and a switchable magnet docking system. It develops a gray-box, wave-aware dynamic model and an online nonlinear model predictive controller (NMPC) that applies across contracted and expanded hull forms, with parameter identification performed over multiple expansion lengths. Experimental results demonstrate improved docking performance and trajectory tracking, particularly in the expanded form, and showcase a rapid bridge-construction demonstration that integrates docking, transport, and assembly. The work demonstrates a viable path toward autonomous, module-based overwater construction, with the expanded hull form providing enhanced stability and docking reliability in rough water. Future work will explore independent, potentially asymmetric outrigger expansion and advanced planning/collision avoidance for more complex structures.

Abstract

This paper presents the TransBoat, a novel omnidirectional unmanned surface vehicle (USV) with a magnetbased docking system for overwater construction with wave disturbances. This is the first such USV that can build overwater structures by transporting modules. The TransBoat incorporates two features designed to reject wave disturbances. First, the TransBoat's expandable body structure can actively transform from a mono-hull into a multi-hull for stabilization in turbulent environments by extending its four outrigger hulls. Second, a real-time nonlinear model predictive control (NMPC) scheme is proposed for all shapes of the TransBoat to enhance its maneuverability and resist disturbance to its movement, based on a nonlinear dynamic model. An experimental approach is proposed to identify the parameters of the dynamic model, and a subsequent trajectory tracking test validates the dynamics, NMPC controller and system mobility. Further, docking experiments identify improved performance in the expanded form of the TransBoat compared with the contracted form, including an increased success rate (of ~ 10%) and reduced docking time (of ~ 40 s on average). Finally, a bridge construction test verifies our system design and the NMPC control method.

Figures (12)

• Figure 1: A fleet of TransBoats can build a temporary bridge using prefabricated building blocks.
• Figure 2: (a) System overview of the TransBoat, (b) front view, (c) contracted form, (d) expanded form, (e) deployable mechanism and design parameters.
• Figure 3: Architecture of the electronic system.
• Figure 4: (a) System overview of the docking system. (b) The docked state and (c) undocked state when the magnet is switched on and off.
• Figure 5: Block diagram of the gray-box parameter identification.