Dolphins have long been renowned for their ability to position themselves relative to another animal or to a hard surface such as the bow of a moving ship. Less commonly known is the ability of dolphins to surf on large waves, but this is another example of a complex underwater control task which is enabled by the dolphin’s mechanoreceptive abilities. The skin of the dolphin, which is covered with longitudinal dermal ridges and a patterned arrangement of collagen and elastic fibres and preterminal nerves in tunnels at the base of the ridges suggest that the skin is a specialized pressure-transducing mechanism, which is instrumental in enabling the dolphin to become aware of its body image in relation to the water around it.
Figure 1. Images of dolphins surfing in waves, and in front of larger cetaceans in the wild.
We are working to develop an underwater vehicle that emulates the ability of the real dolphin to stabilize in waves or other pressure fields through sensors. A surface array of pressure sensors provides the vehicle with the ability to sense its local flow, imparting critical information on its own velocity, body position and orientation relative to the flow. This flow-relative information in conjunction with the pressure which is measured by the array itself constitutes the feedback which is necessary to self-stabilize in dynamic and destabilizing environments, including the presence of waves or other bodies. Flow-relative control also yields the possibility of using local flows for efficient travel or fast maneuvers. Toward this goal, we have been developing fast algorithms which are capable of decoding information from local pressure fields to inform these control systems for improved stability or maneuverability, and building an experiment to investigate the ability of a pressure sensor array to provide the feedback necessary for robust control.
Figure 2. Dynamic 3D BEM simulation showing pressure field created by a large ship and smaller dolphin surfing on the pressure gradient created at its bow. The left image depicts the surface pressure felt by the dolphin.