Swimming tips from a jellyfish relative
Biomimetics, a fancy term for when inventions mimic processes from the natural world, play a key part in our day to day lives. We have designed snow tyres based on the texture of a polar bear’s foot, and swim suits that mimic shark skin. And now, researchers at the University of Oregon think that the future of marine vehicle propulsion could be greatly improved by taking inspiration from a close relative of the Jellyfish - Nanomia bijuga. Kelly Sutherland and Kevin Du Clos spoke to Will Tingle about what makes this animal’s method of movement so special, and what it hopes to inspire for the future of marine vessel movement.
Kelly - So we've been studying jellyfish for quite some time and we've been studying jellyfish that just have a single swimming unit that swims by jet propulsion. So they pull fluid into their body and then they squeeze their muscle bands and push the water out the back end. And they have this smoke ring like locomotion. It turns out that there are jellies that actually have many swimming units. It's kind of like a bunch of small jellyfish strung together. And so it was sort of an obvious next step to start looking at jellyfish that have multiple swimming units. And it kind of opens up a whole array of interesting questions about what happens when you have distributed swimming units, what kinds of swimming modes does that open up?
Will - And Kevin, what are some of the benefits of having multiple jets instead of just one?
Kevin - Having multiple jets rather than just one, makes them more maneuverable so they can actually pulse just one jet, which can cause them to do a very tight turn. It makes them more adaptable. So they have redundancy. If one of the jets is not functioning, they swim essentially as well as they could with all the jets. And then for the case of this study, what we're interested in is they can vary the timing of propulsion by all the different jets. And so that allows them to swim in different swimming modes. So they have a swimming mode that's good for escaping predators, for swimming away fast. And they have one that's better for more routine swimming that requires less energy.
Will - Purely in terms of underwater vehicular design, how is this locomotion better than what we already have?
Kevin - What we suggested in this paper is that by changing the timing of thrust production, you could actually produce a vehicle with swimming modes that were well suited to different tasks. So without changing anything about the hardware, with just an underwater vehicle that has multiple propellers for example, just by varying the timing of thrust production, with software changes, you could have a vehicle switch from a high speed mode to an energy efficient mode. And so that's sort of an advantage in making a vehicle adaptable to circumstances.
Kelly - So in addition to the high speed swimming and the more economical swimming for long distance swims. In earlier work, we also looked at the maneuverability, and also swimming reversals in these colonies. So they have a really diverse array of swimming maneuvers. And the key to that is really having multiple propulsive units that are identical.
Will - We talk about underwater vehicles, but that seems a bit broad. Would you mind shedding some light on which vehicles you think would benefit most from this particular design?
Kelly - Vehicles that are small and maybe surveying something like a coral reef where there's a lot of nooks and crannies. This is a long, narrow design together with the maneuvering and the capability of swimming long distance or long distances economically, as well as maneuvering quickly. With this work, we're really fundamentally interested in the organisms and how they make a living successfully. And a lot of times there's lessons to be learned that can be applied in a design sense. And a lot of times what we're learning are really fundamental principles. So it's not so much about designing a vehicle someday that looks like Nanomia. It's more about taking some of those principles that we've learned like, 'oh, what if we have distributed propulsions and have many of them? What about incorporating that design element into a vehicle?'
Will - Are there any other marine organisms that you're looking at to shape the future of marine propulsion?
Kelly - I love that question. Because it turns out that having distributed props is actually more common than people realize. So it's sort of hard for us to wrap our heads around. But out in the open ocean, the strategy of having multiple propulsions is not all that uncommon. So it only appears in a couple of animal lineages. So it appears in siphonophores, like Nanomia, it appears in another group called the Salps. But when we go out diving in the open ocean, a lot of times the water column is really dominated by these colonial organisms and it's likely important for migrating long distances. So a lot of these animals, siphonophores included, are making long migrations to the surface each night. So they undertake these what are called diel vertical migrations, where they migrate up to the surface to feed each night and then go back to depth during the day. So it's kind of the equivalent of us running a marathon each day in terms of putting on the scale of their body size. These colonial animals are of broad interest to our research and we are continuing to learn new things about the different arrangements of the swimming units, and how different arrangements underlie swimming performance.