Abstract
Biomimetic propulsion is an active area of research in the field of robotics. This work presents advancements to help improve the performance of vehicles employing oscillating foil propulsion. For vehicles operating near the sea floor, ground effect on rolling and pitching foils was investigated in Manuscript 1. The ‘ground effect’ was found to be present and to cause a repulsion force on the foil as well as an increased thrust force. It was also shown that ground effect can be activated by biasing the foil into the ground effect zone while the vehicle maintains a greater distance from the boundary. The effects on the foil due to `ground effect' were compared to previous work done with heaving and pitching foils showing that `ground effect' is an inherently 3 dimensional phenomena and studies using 2 dimensional constrained flow cannot be extrapolated into rolling and pitching foils. The second manuscript expands on this work, investigating the effect that free surface has on the oscillating foil. Similar to `ground effect' it was found that the presence of the boundary creates a repulsive force pushing the foil away from the boundary. However, instead of increased thrust, the free surface causes a decrease in thrust forces on the foil. The third manuscript uses an analytical model to design a control system that uses force feedback from the foil in order to compensate and estimate a constant disturbance such as crossflow. The control system was able to compensate for a constant crossflow and was able to estimate the angle of the crossflow based on the force feedback to within 0.5 degrees. These advancements will help improve vehicles with oscillating foil propulsion that will open up new opportunities for investigation and exploration of complex oceanic environments.
Highlights
Introduction and BackgroundThe complexity of operating efficiently and effectively underwater has driven researchers and engineers to search for biological examples to improve propulsion mechanisms in underwater vehicles
Computational fluid dynamics (CFD) techniques are only beginning to approach the practical capability to model unsteady, 3-D fluid-structure interaction at Reynolds numbers approaching those of practical unmanned underwater vehicles
The repulsion force is present in similar magnitudes, the change in mean thrust is negative as opposed to the increase in thrust seen by a foil operating in ground effect
Summary
Introduction and BackgroundThe complexity of operating efficiently and effectively underwater has driven researchers and engineers to search for biological examples to improve propulsion mechanisms in underwater vehicles. This paper is a first experimental study of three dimensional high aspect ratio thrust producing foils in ground effect. This paper focuses on three dimensional (3-D) rolling and pitching oscillating foils and is the first experimental study of 3-D high aspect ratio thrust producing foils near a free surface. New vehicles are being designed that have biomimetic propulsion to improve the maneuverability and agility of these platforms With these new types of propulsion, the vehicles will need new control systems to allow for accurate thrust and lift production while operating. Foils Self-propelled underwater vehicles using oscillating foils can be seen in [1] and [2] These vehicles use coupled rolling and pitching motions to induce a flow across a foil providing lift which can be vectored to produce thrust on a vehicle. More in depth descriptions of different oscillating foil configurations can be found in [3]
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