Junliang Cao

Toward Optimal Rendezvous of Multiple Underwater Gliders: 3D Path Planning with Combined Sawtooth and Spiral Motion

In this paper, a path planning system is proposed for optimal rendezvous of multiple underwater gliders in three-dimensional (3D) space. Inspired by the Dubins Paths consisting of straight lines and circular arcs, this paper presents the first attempt to extend the 3D Dubins curve to accommodate the characteristic glider motions include upwards and downwards straight glides in a sawtooth pattern and gliding in a vertical spiral. This modified 3D Dubins scheme is combined with genetic algorithm (GA), together with a rendezvous position selection scheme to find rendezvous trajectories for multiple gliders with minimal energy consumption over all participating vehicles. The properties and capabilities of the proposed path planning methodology are illustrated for several rendezvous mission scenarios. First, a simple application was performed for a single glider to rendezvous with a fix dock. Simulation results show the proposed planner is able to obtain more optimized trajectories when compared with the typical Dubins trajectory with nominal velocity. Additional representative simulations were run to analyse the performance of this path planner for multiple gliders rendezvous. The results demonstrate that the proposed path planner identifies the optimal rendezvous location and generates the corresponding rendezvous trajectories for multiple gliders that ensures they reach their destination with optimized energy consumption.

Seagull — Designed for oceanographic research

Seagull is a small fully functional underwater glider designed for oceanographic research with 1 knot operating speed and six months duration. In this paper, we present the design of this glider and analyze its performance. The Seagull glider uses a piston-based buoyancy engine system with an inexpensive gear pump as the main system actuator. The Seagulls emergency release system is characterized for low power consumption. Towing experiments are performed to measure the accurate hydrodynamic coefficients of the glider. The operation of Seagull and the results of field trials in Qiandao Lake are reported.

Optimal path planning of underwater glider in 3D dubins motion with minimal energy consumption

In this paper, a path planning system is proposed for optimal motions of underwater glider in three-dimensional (3D) space. Inspired by the Dubins Paths consisting of straight lines and circular arcs, this paper presents the 3D Dubins curve to accommodate the characteristic glider motions, including sawtooth motion and spiral motion. This modified 3D Dubins scheme is combined with genetic algorithm (GA), to find the trajectory with minimal energy consumption of the vehicle. The properties and capabilities of the proposed path planning methodology are illustrated through simulating comparisons with conventional method which has maximal translational velocity. The results demonstrate that the proposed path planner identifies the optimal trajectories for gliders that ensures they reach their destination with optimized energy consumption.

A bio-inspired underwater glider with undulatory fin for long-duration, spatially explicit water column sampling

This paper presents the design and experimental evaluation of a bio-inspired underwater glider with undulatory fin, which is highly maneuverable and energy efficient and holds strong promise for long-duration monitoring of aquatic environments. A novel scheme is proposed for spatially explicit water column sampling using the bio-inspired underwater glider. The scheme using spiraling motion to sample each water column, followed by sawtooth motion toward the direction of the next water column. Once surfacing, the glider uses undulatory fin propulsion to reach the next column location. Comprehensive design for the bio-inspired underwater glider prototype, comprised of six individually-actuated fin, is provided. Experiments are performed in a test tank to investigate the performance and maneuverability of the bio-inspired underwater glider prototype via surface swimming.

Hydrodynamic and vertical motion analysis of an underwater glider

This paper presents a towing tank-based experiment study on hydrodynamic coefficients on the underwater glider - Seagull. The present measurements were carried out at typical speeds of glider (0.2-0.5m/s) with varying angle of attack and slide. The measurements were used to study variation of drag, lift and pitching moment coefficients and angle of attack. The measurements have also been used to validate results obtained from CFD software. In addition, the Hess-Smith method was applied for added mass calculation. These results provide a better basis of designing guidance and control system of the Seagull glider.

Nonlinear multiple-input-multiple-output adaptive backstepping control of underwater glider systems

In this article, an adaptive backstepping control is proposed for multi-input and multi-output nonlinear underwater glider systems. The developed method is established on the basis of the state-space equations, which are simplified from the full glider dynamics through reasonable assumptions. The roll angle, pitch angle, and velocity of the vehicle are considered as control objects, a Lyapunov function consisting of the tracking error of the state vectors is established. According to Lyapunov stability theory, the adaptive control laws are derived to ensure the tracking errors asymptotically converge to zero. The proposed nonlinear MIMO adaptive backstepping control (ABC) scheme is tested to control an underwater glider in saw-tooth motion, spiral motion, and multimode motion. The linear quadratic regular (LQR) control scheme is described and evaluated with the ABC for the motion control problems. The results demonstrate that both control strategies provide similar levels of robustness while using the proposed ABC scheme leads to the more smooth control efforts with less oscillatory behavior.