Data collection in the ocean is a challenging sparse-sampling problem; the range of spatial scales virtually guarantees that any phenomena of interest will be undersampled. Phenomena with fast temporal dynamics, such as harmful algal blooms are especially difficult to measure, as the measurement of interest can vary faster than our ability to deploy sensors.
However, aerial imaging techniques have had tremendous success in finding and measuring algal blooms. The fluid physics simply favor fast travel in air, yet imagery cannot be a replacement for direct measurements. The ideal algal bloom sampling platform would be able to use aerial imagery to find and characterize the bloom, while still retaining the ability to collect water samples - a single aerial/aquatic vehicle platform.
In this research, we target two biomimetic designs for aerial/aquatic vehicles: energy capture from the air/water interface using a fixed-wing aircraft to improve the endurance of sampling vehicles, and a study of flapping actuators capable of both aerial and aquatic locomotion.
Figure 1. In-line Motion Examples: In-line motion is defined as a flapping trajectory where the foil is moved upstream or downstream in addition to across the flow.
Guillemots, puffins, and other auks both swim and fly using the same propulsor, providing an existence proof that aerial/aquatic vehicles are indeed possible. Specifically, in- line motion(1) on a flapping foil could provide the necessary force envelope to enable the both modes of flight.
In-line motion trajectories can be chosen to either create large thrust without an oscillating lifting force, analogous to the flapping performance of sea turtles(2), or create large lifting forces analogous to birds flying at slow speeds(3). Changing the degree of in-line motion could greatly expand the performance of flapping wings. Rather than relying on the static parameters of the airfoil to perform adequately in both air and water, the flapping trajectory could instead be modified.
Figure 2. PIV Wake Measurements on Optimized Flapping Motions: Thrust is created through the production of a pulsed-jet wakes, consistent with the lack of transverse force. Alternatively, the lift coefficient can be boosted to as high as CL=4, at the cost of expended power by the flapping actuator. Experiments performed on a long-aspect ratio wing with simultaneous force measurements.
Figure 3. Preliminary Vehicle Design (left): Diagram of flapping vehicle design. Inner span of the wing would be used for weight support during aerial flight, and deactivated underwater (A). Flapping trajectories for aerial (B) and underwater (C) modes of travel would use in-line motion to boost the lift or thrust respectively.