Baoheng Yao

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.

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.

Research on marine riser in different installations stages of subsea production tree

The marine environment, such as wind, wave and current, can have a significant effect in subsea production tree installation process and has brought difficulties and challenges. In this paper, in order to analyze riser stress and displacement in tis installation with different marine environments, the loads and boundary conditions at different installation stages are elected, and the installation stage 3 and 4 are mainly studied. Then, an analysis model and equation have been established. In this model, the riser is regarded as a beam suspended in the floating platform and subjected to both axial and lateral forces. Because, the riser would be away from subsea wellhead in installation due to its displacement and the material of riser maybe be yielding due to the huge stress, the variation of stress and displacement of riser with drag coefficient, sea surface wind velocity, sea surface current velocity and SPT weight are discussed. Results show that the stress and the displacement increase with the increase of all factors mentioned above. The effect of drag coefficient weakens as the value of Cd increases and the effect of wind velocity is greater than that of current velocity. However, the effect of SPT weight is unremarkable.